The Function of the Fornix in Syrian Golden Hamsters:
A Lesion and Behavioral Study of Papez Circuit
by
Anthony 0. Okobi
B.S. Neurobiology and Behavior
Cornell University, 1999
SUBMITTED TO THE DEPARTMENT OF ELECTRICAL ENGINEERING AND
COMPUTER SCIENCE IN PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE DEGREE OF
MASTER OF SCIENCE IN BIOELECTRICAL ENGINEERING
AT THE
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
BARKER
MAHUSSITuTE
OF TECHNOLOGY
FEBRUARY 2002
JUL 3 1 2002
©2002 Anthony 0. Okobi, All rights reserved.
LIBRARIES
The author hereby grants to MIT permission to reproduce and to distribute publicly paper
and electronic copies of this thesis document in whole or in part.
Signature of Author:
SgtefA :
of Health Sciences and Technology
January 7, 2002
Certified by:
Gerald E. Schneider
'rofessor of Neuroscience
Thesis Co-Supervisor
Certified by:_
Louis D. Braida
Professor of Electrical Engineering
Thesis Co-Supervisor
Accepted by:
C
I'A
Professor of Electrical Engineering andCvo
De
u
cn
nXL
The Function of the Fomix in Syrian Golden Hamsters:
A Lesion and Behavioral Study of Papez Circuit
by
Anthony 0. Okobi
Submitted to the Department of Electrical Engineering and Computer Science
On January 7, 2002 in Partial Fulfillment of the
Requirement for the Degree of Master of Science in
Bioelectrical Engineering
ABSTRACT
Little is known about the function of the fornix in hamsters, as well as in other animals.
It is a part of the Papez circuit. Papez circuit is known to play an important role in the
emotional aspects of behavior. Normal, sham surgery and bilateral fornix lesion hamsters
were tested in a semi-natural habitat (SNH). The behavior of the dorsal fornix lesion,
pre-commissural and post-commissural fornix lesion hamsters were compared to the
behavior of the control animals, as well as to the their own behavior prior to surgery. All
the behaviors documented involved instinctual responses, not visuo-spatial task learning
responses. Statistical analysis was done on the behaviors to determine the deficits caused
by fomix lesions. Results support change in motivation state, rather than spatial memory
deficit, as the affect caused by lesions of the fornix.
Thesis Co-Supervisor: Gerald E. Schneider
Title: Professor of Neuroscience
Thesis Co-Supervisor: Louis D. Braida
Title: Professor of Electrical Engineering
2
Acknowledgements:
*
I would like to thank both of my thesis supervisors, Prof. Gerald E. Schneider and
Prof. Louis D. Braida. The former for teaching me everything I know about the
neuroanatomy and behavior of hamsters and the latter for teaching me everything
I know about circuits and bode plots.
*
Thanks to Rutledge Ellis-Behnke for his assistance in everything from capturing
images on the computer to coating subslides with gelatin.
*
Of course I have to thank my foster mother, Barbara Lewis, for repeatedly telling
me to worry about finishing my SM thesis and not kill myself with details.
* Finally, this thesis could not have been finished in time without the help of the
many lab busy or lazy bees, known as MIT UROP students.
3
Table of Content:
I
Specific Aim of Research
2
Introduction and Background
2.1
Papez Circuit......................................................................7
2.2
Lesion Studies of Components of Papez Circuit............................
2.3
3
2.2.1
Hippocampal Formation.............................................
2.2.2
Fornix Fibers.............................................................9
2.2.3
Septal Area............................................................
2.2.4
Hypothalamus and Mammillary Bodies...........................12
8
8
11
14
Syrian Golden Hamster.......................................................
2.3.1
Taxonomy and History..............................................14
2.3.2
Stereotyped Behaviors...............................................
2.3.3
Photoperiodicity and Rhythmicity of Behavior..................16
15
Materials and Experimental Design
3.1
Animal Subjects and Diet........................................................18
3.2
Surgical Procedure............................................................
3.3
Semi-Natural Habitat..........................................................21
3.3.1
Schneider Experimental Cage......................................21
3.3.2
Hamster Arena.........................................................23
3.4
Behavioral Testing Procedure...................................................27
3.5
Summary of Experiments....................................................
3.6
Histological Procedure........................................................33
3.7
4.
6
30
3.6.1
Perfusion and Tissue Sectioning.....................33
3.6.2
Staining Methods....................................................
33
Statistical Analysis...........................................................
35
Results
4.1
19
In-Cage Behavior..................................................................36
4.1.1
Hoarding Behavior.......................................................36
4
4.2
4.1.2
Nesting Behavior....................................................
37
4.1.3
In-Cage Activity......................................................
38
4.1.4
Before and After Surgery: In-Cage Behavior Comparisons........41
Arena Behavior....................................................................42
4.2.1 Activity Level........................................................
42
4.2.2 Grooming..............................................................44
4.2.3 Novelty Response....................................................45
4.2.4 Foraging Behavior...................................................
46
4.2.5 Before and After Surgery: Arena Behavior Comparison......49
4.3
Food Consumption and Weight.............................................
51
5
Conclusion
52
6
Discussion
54
7
Future Work
56
References
57
5
1
Specific Aims of Research
The purpose of this research is to determine the effect of a fornix lesion on the
behavior of the Syrian Golden hamster (Mesocricetusauratus). Little is known about the
function of the fornix in hamsters or in other animals. The fornix is a bundle of axons
that originates in the hippocampal formation, loops around the thalamus and terminates in
the hypothalamus. It is a part of Papez circuit. Papez circuit is known to play an
important role in the emotional aspects of behavior (Bear et al., 1996). Many
experiments have been done on the hippocampus, which deals with memory, and on the
hypothalamus, which deals with motivational states, including fear, appetite, etc. While
these experiments have increased our knowledge of these two structures, little light has
been shed on the functions of the fornix, which links them.
We hypothesize that a fornix lesion would be expected to cause some deficits in
the emotional or motivational aspects of Syrian hamster behavior, such as loss of
curiosity. Lesioning as a method of exploration was chosen because lesion studies have
allowed scientists to assign certain functions to specific anatomical regions of the brain,
as well as help to separate the roles of different regions of the brain. Such lesion studies
have revealed that some anatomical regions of the brain play different roles in different
species. For example, Schneider (1967, 1969) proposed that in mammals, cortical and
subcortical visual structures have distinctly different roles in mediation of rodent and
primate visual behavior.
Though lesion studies have been done on the fornix, most of them have
concentrated on the fornix's relationship with the hippocampus and the effects of a fornix
lesion on spatial memory and visuo-spatial encoding. The research discussed in this
thesis, on the other hand, was designed to focus on the fornix's relationship with the other
limbic structures, such as the septum and hypothalamus, and to determine the emotional
and motivational deficits in the natural behavior of Syrian hamsters that might be caused
by a fornix lesion. Thus, one of the big challenges in this experiment was the
construction of an environment that was natural enough to elicit normal behaviors from
hamsters, yet structured in such a way as to allow control of external parameters and easy
quantification of the behaviors.
6
2
Introduction and Background
2.1
Papez Circuit
The search for the connection between emotions and the physical brain has a long
history. But it was not until 1937, that James Papez first proposed the idea that specific
brain circuits were the link between the cerebral cortex and the effector systems devoted
to emotional experiences and expression (Purves et al., 1997). Recognizing the unique
neuroanatomical properties of the limbic system, Papez argued that the limbic system
was indeed this link. Papez based his argument on the works of Philip Bard of Johns
Hopkins University and Walter Hess, which demonstrated that the hypothalamus had
great influence on the expression of emotion. Furthermore, Papez realized that the cortex
and hypothalamus were interconnected through a pathway that included many other
nuclei in the brain. This pathway became known as Papez circuit (Figure 1). Although
there is still some controversy concerning the exact constitutes of the limbic system, the
major structures that make up Papez circuit include the cingulated gyrus, the
parahippocampal gyrus (paralimbic area), the hippocampal formation, the septal area, and
parts of the thalamus and hypothalamus. Today, Papez circuit is the simplest circuit of
the limbic system, which is composed of several other neurological structures
interconnected by myelinated fiber tracts to form other various circuits (Nauta and
Feirtag, 1986b). The most prominent fiber tract in the Papez circuit is the fornix. It is
generally accepted that the various circuits of the limbic system, centered around Papez
circuit, generate the experience of moods, emotions, and consolidation of short-term
memory into long-term memory.
Association area
)
(neocortex
Paralimbic
Anterior nucleicnuaecra
of thalamus
Entorhinal
Cinsaexres
fMammillarymbodes
areas,
area
Hippocampal forma
I
Hypothala us ISeptal
x (Ach)
IF
area
Figure 1. Papez circuit plus diagram adapted from figure by Gerald E.
Schneider: A brain circuit between the neocortex and the effector systems
devoted to emotional experiences and expression Fornix fibers, originating
from the hippocampal formation, has many targets.
7
2.2
Lesion Studies of Components of Papez Circuit
Papez circuit is composed of several neuroanatomical structures, but in this
research we are only concerned with the fornix fibers and the structures that are
immediately related to the fornix: the hippocampal formation, the septum, the
hypothalamus and the mammillary bodies. The latter two neuroanatomical structures
were not lesioned nor were they immediately adjacent to the site of the lesion, but they
are targeted by the fornix and thus are indirectly influenced. Information on the brain
mechanisms underlying hamster behavior regulation is limited, so many of the lesion
studies discussed in this section were done on mice, rats and humans, other than the
Syrian Golden hamster.
2.2.1
Hippocampal Formation
The hippocampus, also known as Ammon's horn, is an elongated bulge just
ventral to the cingulated gyrus that resembles the sea horse from which it received its
name. Unlike the other parts of the cerebral cortex, that have six cell laminae, the
hippocampus, known as the archicortex ("primitive cortex"), has neuronal cell bodies that
occupy only one layer (Nauta and Feirtag, 1986a). Archicortex, although regarded as
being a very primitive type of cortex, greatly misrepresents the hippocampus in terms of
its precisely organized and highly complex patterns of connections. According to Brodal
(1981 a), the most impressive cellular elements of the hippocampus are the large
pyramidal cells. The efferent fibers of the hippocampus come from these pyramidal cells
and leave the hippocampus via the fornix.
The hippocampus is a highly specialized cortical structure that plays a very
important role in learning and memory, especially in visuo-spatial tasks. Two aspects of
the connections of the hippocampus can be considered crucial to the understanding of its
function: First, the extensive two-way connections with various cortical association areas
and second, the direct connections with other limbic structures such as the cingulated
gyrus and the septal nuclei (Brodal, 1998). The surface of the hippocampus facing the
ventricle is the deepest layer, and consists of myelinated fibers, which collect on its
surface, giving rise to efferent fibers that unite to form the fornix (Brodal, 198 1a). While
anatomically, the delimitation of the hippocampus is fairly clear, its functional
relationship with neighboring regions is much more obscure. It is thus common to lump
the hippocampus with its surrounding region, including the dentate gyrus, subiculum and
entorhinal cortex, together and call them the "hippocampal formation" or "hippocampal
region" (Brodal, 1981 a).
It is quite widely accepted that the hippocampal formation plays a critical role in
learning and memory, but a precise characterization of the type of role and the means by
which it accomplishes this role still remains debatable. Spatial learning seems to be the
most disrupted in animals with hippocampal lesions, especially in the CAl area. Wilson
8
and Tonegawa (1997) found that CA1-knock out mice were severely deficient in the
acquisition of spatial memory (learning of the position of the hidden platform by using
the relationships among distal cues around the pool). Hippocampal-damaged animals can
still learn to respond to an individual stimulus, but they are notably impaired at many
tasks involving learning relationships between stimuli, especially in the absence of
explicit reinforcement (Gluck and Myers, 1996).
Animals with hippocampal damage have also been shown to have deficits in
foraging behavior (Osborne and Dodek, 1986). A lesion study conducted by Borer et al.
(1979a), using Syrian Golden hamsters, revealed that following hippocampal
transactions, food consumption increased 1.3-fold during the seven postoperative weeks.
They further concluded that hamsters with hippocampal lesions not only gained weight,
but became hypoactive due to reduced motivation to run and not to neurosurgically
induced motor impairment nor to a shortage in metabolic fuels available for exercise
(Borer et al., 1979a). Whishaw et al. (1994), on the other hand, found that rats with
damage to the hippocampal formation were hyperactive.
2.2.2
Fornix Fibers
The most prominent fiber tract in the Papez circuit is the fornix. The fornix is a
massive bundle of axons. In the human brain, it comprises a million fibers, which is
equal, in this respect, to the optic tract (Nauta and Feirtag, 1986a). Projections from the
superior anterior portion of the hippocampal formation come together to form the fornix
fiber. According to Per Brodal (1998), with the advent of axonal transport of
radioactively labeled amino acids, it has been shown that most of the fornix fibers
originate in the subiculurn (part of the hippocampal formation) and not from the
hippocampus proper. After culminating at the surface of the hippocampus, the fornix
then bifurcates and sends one set of fibers, known as the pre-commissural fibers of the
fornix, projecting into the septal area. The second set of fornix fibers, known as the postcommissural fibers of the fornix, loop around the thalamus and terminate in the
hypothalamus and mammillary bodies. These post-commissural fibers of the fornix are
also known as the fornix columns. Most of the afferent fibers to the mammillary nucleus
arrive through these fibers (Brodal, 1998).
Current evidence suggests that lesions of the fornix in rats lead to visuo-spatial
impairment, much like those experienced by rats with complete hippocampal removal
(Whishaw et al., 1997). Walker and Olton (1984) were able to show, in experiments
using series of maze tasks that varied in spatial working memory requirements, rats with
fimbria-fornix lesions performed at chance levels. They concluded that the performance
of these fimbria-fornix lesioned rats could have possibly been due to a temporary
retrograde amnesia. Experiments, using radial arm mazes, have also supported these
results that the poor performance of fimbria-fornix lesioned rats was due to a difficulty in
spatial memory and not from an insufficient time to process stimulus information
(Walker and Olton, 1979). Whishaw et al. (1997) notes that like hippocampal damaged
rats, rats with fornix lesions seem unable to learn any new spatial response in only a few
9
trials. They did however note that the results they obtained might have been task
dependent.
However, the results obtained from the fimbria-fornix lesions might not be
indicative of the function of the fornix because other experiments have indicated that the
fornix and the fimbria differ in their involvement in behavior. For example, using a Tmaze and a semi-circular multiple discrimination apparatus to test the effects of selective
partial lesions of the fimbria-fornix, M'Harzi et al. (1987) concluded that the fimbria
produced a significant deficit in reversal and place learning, whereas lesions of the fornix
only disturbed learning based on a reversal procedure. Combined funbria-fornix lesions
seemed to result in impairment of the retention of spatial discrimination, when tested in
the two mazes (M'Harzi et al., 1987).
Many other fornix lesion studies have concentrated on the relationship between
the fornix and the hippocampus and the effects of a fornix lesion on spatial memory and
visuo-spatial encoding. But very little research has been done on the motivational aspect
of animal behavior, such as in foraging. As was stated previously, animals with
hippocampal damage have also been shown to have deficits in behavior dealing with food
consumption. Many researchers however have argued that the deficits observed in
foraging behavior might be due to the fact that the behaviors observed were documented
during tasks that required spatial memory. Hippocampal damaged animals have been
known to have information processing deficits during foraging tasks (Osborne and
Flashman, 1986).
Evidence suggests that while visuo-spatial impairments are seen with fornix
lesioned animals, there seems to be no affect on the major homeostatic regulatory
mechanisms that might be associated with a damaged hypothalamus, although the fornix
projects to the hypothalamus (Osborne and Dodek, 1986). Instead what seems to be
influenced were the sequencing of behaviors involved in foraging, eating, drinking, etc.
However, alteration of the sequence of behaviors is environment dependent. Research by
Collier and Rovee-Collier (1981) has shown that the most important constraints on
feeding behavior, in a natural setting, is the availability of food and the animals ability to
alter their feeding behavior accordingly. Osborne and Flashman (1986) claim though that
when spatial components were removed that fornix lesioned rats adjusted just as well to
the different foraging situations as the control. Thus they concluded that hippocampal
damage, which they assume was the same as a fornix lesion, does not cause differences in
responses to the environment, but instead disturbs the micro-regulation of the sequence of
foraging behaviors. Osborne and Flashman (1986) do admit that there is a possibility that
fornix lesioned rats might be so sensitive to sensory distraction that even miniscule
amounts of sensory information were unable to be filtered out. Thus the disruption in the
sequence of foraging behavior shown by fornix lesioned rats might be due to some type
of attention disorder. The fornix and/or the hippocampus might then be viewed as a
structure embodying a brain mechanism which regulates what behavioral sequence is
appropriate for a given situation and the continuation of this sequence to its natural
termination.
10
2.2.3
Septal Area
According to Brodal (198 1a), the septal area develops from the telencephalon
and, in humans, consists of a sheet of gray matter, traversed by many fibers, arranged in
the vertical plane of the medial wall of the anterior horn of the lateral ventricle, chiefly in
front of the anterior commissure. However, there are slight variations among different
species of mammals. It seems that the lateral septal nucleus is the main part of the septal
area receiving afferents from the hippocampus, while the medial septal nucleus gives rise
to most of the septal efferents going to the hippocampal formation (Brodal, 198 1a). The
septal afferents from the hippocampus and the adjoining subiculum project through the
fimbria and the pre-commissural fornix to the lateral septal nucleus (Swanson, 1977).
The septal nuclei are particularly rich in cholinergic neurons and are in fact the
most well defined neuroanatomical structure containing these cells (Brodal, 1998). Thus
it is not surprising that acetylcholine is particularly prominent in the septal region.
Among the cholinergic cell groups, the septal nuclei was the first to attract interest
because early lesions and electrical, as well as chemical, stimulation of this region of the
basal forebrain demonstrated that they influenced not only autonomic functions, but also
emotions and behavioral reactions (Brodal, 1998). Septal lesions, in particular, seem to
alter sexual and foraging behaviors. According to Per Brodal (1998), the effects caused
by septal lesions can be in part explained by the connections between the septal nuclei
and the hypothalamus, as well as the amygdala, because lesions in these neuroanatomical
structures also induce similar effects.
According to Siegel (1985), Syrian Golden hamsters with septal lesion have
displayed increased levels of aggression, decreased hoarding and nest building. Both
antero-ventral and posterior septal-anterior thalamic lesioned groups showed deficits in
nesting, hoarding, as well as in sexual behavior (Potegal et aL., 198 1a). Such results were
also obtained by Shipley and Kolb (1977), when they demonstrated that septal-lesioned
hamsters not only displayed increased levels of shock-induced aggression, but also
displayed deficits in nest building and hoarding.
According to Borer et al. (1977, 1979b), following septal lesions there is a 1.2fold increase in food intake during ten postoperative days and following
septohypothalamic cuts, weight gain was five times faster and food intake was 1.1 to 1.2
times greater during the first postoperative month. Borer et al. (1983a) also states that
the hypoactivity that accompanies lesions of rostromedial septum, VMH (Borer, 1974),
hippocampal transactions (Borer et al., 1979a), and septohypothalamic cuts (Borer et al.,
1979b) is related to acceleration in the rate of weight gain rather than to neurosurgically
induced motor impairment or to shortages in metabolic fuels available for exercise. Thus
when compelled by electric shock, septal-lesioned hamsters will run as fast and as long as
neurologically intact hamsters. According to Borer (1985) what distinguished them from
neurologically intact hamsters was the reduced motivation to run or the reduced ability of
physical activity to mobilize metabolic fuels in a way that would sustain rapid and
prolonged bouts of running, which is characteristic of normal hamsters. Their conclusion
11
was that the limbic forebrain circuit that encompasses fibers interconnecting
hypothalamus, septum and hippocampus is responsible for linking spontaneous running
and weight regulation in a non-homeostatic fashion.
2.2.4
Hypothalamus and Mammillary Bodies
Although the research presented in this thesis is not strictly concerned with
functions of the hypothalamus or the mammillary bodies, these structures are the final
destination of the fornix and thus should be addressed. The hypothalamus is a
structurally small, but functionally very significant part of the brain. It is part of the
diencephalon, along with the thalamus, and is crucial for the control and regulation of
emotions, homeostatic and reproductive functions, as well as being influential in other
more primitive behaviors such as fear, appetite, etc (Purves et al., 1997). Structurally and
functionally related to the hypothalamus is the pituitary gland, also known as the
hypophysis, by means of the infundibulum (or infundibular stalk). The pituitary gland is
a critical endocrine organ capable of regulating the functions of other endocrine organs.
Posterior to the main area of the hypothalamus, the infundibulum is continuous
with a slight bulge in the floor of the third ventricle, the tuber cinereum. Further along
the floor of the third ventricle, a larger bulge occurs at the transition of the diencephalon
to the mesencephalon, giving rise to the mammillary bodies (Brodal, 198 1a). According
to Brodal (198 1a), the mammillary bodies can be found in the interpeduncular fossa, one
on each side of the median plane. The fornix leading to the mammillary bodies can be
found among the fiber bundles mingled with the gray matter that make up the lateral
walls and floor of the third ventricle (Brodal, 198 1a). Fornix fibers can easily be
distinguished as one of the larger fiber bundles leading to the mammillary bodies.
Very little is known about the function of mammillary bodies. One of the major
deficits associated with damaged mammillary bodies is memory loss and or formation.
Clinical observations have identified lesions of the mammillary bodies or their
connection to the thalamus (mammillothalamic tract) as being the cause of anterograde
amnesia, the inability to establish new memories, and retrograde amnesia, inability to
retrieve previously formed memories (Brodal, 1998). Furthermore, bilateral lesioning of
the fornix leading to the mammillary bodies in epiletic patients has also been reported to
cause the same sort of amnesia (Brodal, 1998).
It is generally accepted, after numerous experiments, that the function of the
hypothalamus serves not only in the regulation of motivational and emotional rewarding
system, but also to coordinate endocrine, autonomic, and somatic motor responses to
behavior needed to meet immediate goals and necessities of the body, such as feeding,
drinking and reproduction (Brodal, 1998). Furthermore, the suprachiasmatic nuclei
(SCN), which is believed to regulate the photoperiodicity and rhythmicity of many of the
behaviors exhibited by the Syrian Golden hamster, is a nucleus of the hypothalamus.
Hypothalamic nuclei have a rich network of mutual connections, so that a lesion of one
nucleus will interfere with the functioning of several others as well (Brodal, 1998). Thus
12
many of the behaviors exhibited by the hamster can be altered by changing the nature of
the signals received by the hypothalamus. Many of these signals received by the
hypothalamus come via the fornix. Lesioning of the fornix should inevitably alter the
output of the hypothalamus and thus the emotional state and behavior of the lesioned
animal.
13
2.3
Syrian Golden Hamster
2.3.1
Taxonomy and History
Syrian Golden hamsters are members of the rodent family and are one of many
species of hamsters. Originally the Syrian Golden hamster was named Cricetus auratus,
based on the skin and skull of one dead female specimen, by George Robert Waterhouse
in 1839 (Clark, 1987). Then in 1902 A. Nehring renamed the Syrian Golden hamster
Mesocricetus auratus. It carries this name to this day. Currently the taxonomic position
of the Syrian Golden hamster is as follows: order, Rodentia; family, Cricetidae;
subfamily, Cricetinae; genus, Mesocricetus; and species, auratus(Honacki et al., 1982).
Syrian Golden hamsters, also known as Syrian hamsters, Golden hamsters, or Golden
Syrian hamsters, are small furry animals, with short legs and a very short tail (Figure 2).
~A
Figure 2. Syrian Golden Hamster, Mesocricetus auratus.
In the wild, the Syrian Golden hamster is mainly prey to flying predators, such as
hawks and owls. So they must be constantly alert and vigilant while in open fields for
moving objects in the sky. Hamsters themselves are primarily granivores, eating mostly
domesticated grains and wild seeds, but they have been known to also eat the green parts
of plants, as well as the roots, fruits, and even insects. A normal hamster does not eat its
food out in the open field were it forages, but instead takes it back to the safety of its
home before commencing to eat (Schneider, unpublished). Having long sharp claws and
teeth, Syrian hamsters are adept diggers in the dry, rocky steppes and brushy slopes that
make up their natural habitat. They inhabit underground multi-chambered burrows, in
which they hoard the food they foraged from the fields during the twilight and night
(Billingham and Silvers, 1963). Each chamber of a multi-chambered burrow usually
serves a special function, such as for hoarding food, depositing fecal bulbous or sleeping.
In general, Syrian hamsters live alone and will readily fight off other hamsters who enter
their burrow (Nowak and Paradiso, 1983; Anderson and Jones, 1984).
14
It appears that most of the Syrian Golden hamsters used as laboratory animals or
pets are descended from three or four hamsters captured by Professor Isreal Aharoni of
the Department of Zoology of the Hebrew University in 1930 (Clark, 1987). Such a
homogenous population of animals might be considered good for research because little
variation would be expected to be found from one hamster to another, either behaviorally
or anatomically. A second population of Syrian Golden hamsters was introduced to the
United States, by Michael R. Murphy, in 1971. Murphy was a graduate student in
Department of Psychology (now the Department Brain and Cognitive Sciences) at the
Massachusetts Institute of Technology (MIT) when he made the second capture of live
Syrian Golden hamsters (Murphy, 1985). While at MIT, observations on the natural
history and comparisons of these hamsters with the original domesticated stock were
made. Descendents of the hamsters captured by Murphy are maintained at the National
Institute of Health, Bethesda, Maryland.
Syrian hamsters have become established, along with the mouse, rat, guinea pig,
rabbit, cat and dog, as a major asset among the important animals commonly used for
experimental work in biology and medicine, as well as in other fields. They have many
unique characteristics that make them exceptionally well suited as laboratory animals. A
unique trait possessed by the Syrian hamster is the paired eversible cheek pouches, which
hamsters use to carry food and other small objects, like pebbles. Another unique
characteristic of the Syrian hamster deals with its atypical immuno-genetic tolerance to
many diseases and trauma caused during surgery in lesion studies (Fulton, 1968).
2.3.2
Stereotyped Behaviors
Many of the behaviors displayed by Syrian hamsters are stereotyped and are quite
predictable. One such normal behavior exhibited by both male and female hamsters is
that of nest building. If given suitable materials, such as cotton, a Syrian hamster will
build a nest that is enclosed, much like the burrows they dig. Although the behaviors of
hamsters are rarely as stereotyped in the sense that many of the behaviors displayed by
birds or reptiles, which are nearly invariant in their form, timing, rhythm, or repetition
rate, Syrian hamsters do perform a few actions that can easily be distinguished and seem
to serve as communicative functions (Johnston, 1985). For instance hamsters can be
observed to groom right before executing a action, such as exiting cage or approaching
another hamster, or after being attacked by another hamster, scared, or encountering a
novel object. Thus grooming, other than serving its main function as a means of keeping
the animal clean, is also an indication of indecision and or disturbance (Schoenfeld and
Leonard, 1985). Syrian hamsters show rudimentary grooming-like movements very early
in life. Dieterlen (1959) called these early grooming-like actions "movements of
defense," because they are displayed in response to irritative stimulation about the snout,
as when a pup attempts to wipe its snout immediately before and after sneezing.
15
2.3.3
Photoperiodicity and Rhythmicity of Behavior
Syrian hamsters are primarily twilight animals, becoming active only when the
sun is setting. They then remain active throughout most of the night. During daylight
hours they can be found sleeping or organizing their nests, in the burrows they
constructed or stole from another hamster. They have a very precise internal biological
clock or circadian rhythm that has been extensively studied. This biological clock seems
to control many of the Syrian hamster's behavior, including activity level, food
consumption, etc. (Zucker and Stephen, 1973). A true "circadian rhythm" would be
expected to have a 24 hour period or cycle, that is maintained with no external inputs.
The hamster does not have a "true circadian rhythm", but instead has one that must be
kept in synchrony with the earth's 24 hour day. For hamsters, the only documented
external oscillator or Zeitgeber is the light-dark (LD) photoperiod (Morin, 1985).
Photoperiodic control of the Syrian hamster's circadian rhythm has been well
established in many experiments. Many of the research done in this area of hamster
nocturnal behavior have utilized specialized rotating wheels to monitor their activity
level. Syrian hamsters are sufficiently nocturnal animals that under a LD 12:12 cycle,
99% of all wheel revolutions occur in the dark phase (Zucker and Stephan, 1973).
Furthermore, Bruce (1960) demonstrated that a 24-hour light cycle can entrain the
hamster's locomotor rhythmicity. The cycle of the Syrian hamsters circadian rhythm
varies slightly with the earth's position in orbit around the sun, but on average it is
around 23 hours 56 minutes and 3.4 seconds (Morin, 1985). The anatomical relationship
of the suprachiasmatic nuclei (SCN) to the visual system has been demonstrated to play
an important role in the regulation of circadian rhythms, yet no neuroanatomical correlate
has been discovered that might actually generate the periodicity (Moore, 1983; Pickard
and Silverman, 1981).
Syrian hamster feeding also seems to have a component of rhythmicity to it.
Hamsters eat about 15 times spread over 24 hours (Borer et al., 1980; Rowland, 1982;
Morin, 1981). Individual meals do not entrain to the LD cycle, nor are they affected by
light. Furthermore, feeding does not free run in synchrony with the wheel-running
rhythm, but instead persists with a periodicity in the ultradian range. According to Borer
(1985), hamster feeding gives the appearance of a centrally programmed ultradian rhythm
of standard-sized meals, the spacing of which may be imposed in part by a strong
peripheral negative feedback. She believes that this negative feedback is composed of
mechanical, chemical, or hormonal signals associated with meal processing and that these
signals are dissipated more rapidly in circumstances where increased meal frequency and
food consumption are induced. Thus mechanisms controlling feeding behavior seem to
be integrated with mechanisms controlling energy storage. According to Granneman and
Wade (1982), changes in energy utilization may be more important than changes in
energy intake in the adaptation of Syrian hamsters to food restrictions.
16
Hamster feeding also seems to be coordinated by internal clocks that remain
unaffected during food deprivation and over-feeding (Morin, 1981b). After being starved
for 12 hours or longer, normal hamsters were unable to increase their food consumption,
given the same diet, and were unable to change their feeding patterns (Granneman and
Wade, 1982; Borer et al., 1979). According to Rowland (1982), measures of the gastric
fill and plasma metabolites indicate that filling and emptying of the fore-stomach may
occur with a periodicity similar to that of spontaneous meals. The feeding periodicity is
clearly distinguishable from the running, gnawing, and hoarding rhythms of hamsters.
For instance, hamsters will hoard 45 mg Noyes pellets in a LD rhythm, with
approximately ten times more being hoarded at night (Toates, 1978). According to
Zucker and Stephan (1973) the rhythmicity of feeding causes males to eat about 55% of
their food during the 12-hr dark phase. Thus a certain component of Syrian hamster
feeding pattern appears to be a circadian rhythm. According to Morin (1985), it is
possible that the circadian rhythm in the feeding pattern of Syrian hamsters is the result
of time competition between mutually exclusive behaviors, such as general locomotion or
drinking.
17
3
Materials and Experimental Design
3.1
Animal Subjects and Diet
We chose Syrian hamsters as subjects in this study because hamsters have some
advantages over other animals for use in surgical experiments. Hamsters exhibit many
fixed action patterns, known as instincts, that are constant from one animal to another.
These instincts are clear-cut and easily quantified. Lastly, Professor Gerald E. Schneider
and members of his laboratory have been doing research on Syrian Golden hamster
behavior for decades, and thus have a firm grasp of the behavioral patterns of Syrian
Golden hamsters. Sexual dimorphic differences between male and female Syrian Golden
hamsters in brain structure and behavior meant that we had to use one or the other, but
not both sexes. Because males tend to be single-minded in their pursuit of females and
were consistently trying to escape, we chose to use only female Syrian hamsters in this
research.
The food given to the subjects in this research was in the form of pellets that were
on average 1" x / 2" x %/".
Each pellet was composed of no less than 22% crude protein,
5% crude fat, 5% crude fiber, 6% ash, and no less than 2.5% added minerals. These food
pellets were produced by LabDiet@ under the title SP00 Prolab@ RMH3000. The
ingredients used to make the pellets are as follows: ground wheat, dehulled soybean
meal, wheat middlings, ground corn, fish meal, animal fat preserved with BHA,
dehydrated alfalfa meal, calcium carbonate, brewers dried yeast, soybean oil, salt,
dicalcium phosphate, DL-methionine, L-lysine, magnesium oxide, ferrous sulfate, zinc
oxide, manganous oxide, copper sulfate, calciumiodate, cobalt carbonate, vitamin A
acetate, cyanocobalamin, riboflavin, nicotinic acid, calcium pantothenate, menadione
dimethylpyrimidinal bisulfite (source of vitamin K), folic acid, pyridoxine hydrochloride,
thiamin mononitrate, biotin, and choline chloride.
18
3.2
Surgical Procedure
In this research several types of fornix lesion surgeries, as well as sham or
exposure control surgeries, were done on various subjects in order to determine the exact
function of the fornix. Each subject was anesthetized during the surgery using a
combination of valium and pentobarbital. The amount of anesthesia given was
determined by that subject's weight, at 0.08cc/IO0g for pentobarbital and 0.16cc/IOOg for
valium. After the injected anesthetic had taken hold, the skull of the animal was exposed
and an opening was made at the site of surgery using the lambda and bregma landmarks
on the skull. Gentle suction was used to remove the neocortical area and expose the
hippocampal formation and fornix. This was the point where the control exposure
surgeries ended. For fornix lesion surgeries, a stainless steel micro-surgical knife made
of tungsten wire was used to cut the designated fornix fibers. After successful surgery,
gel-foam soaked in saline was placed into the site of surgery and the skin above the site
of surgery was sutured closed using surgical staples. The subject was closely monitored
until she awakened and moved around adequately enough to obtain food and water.
Approximately two weeks of recuperation was allowed before initiation of the behavioral
tests.
All surgeries were bilateral (Figure 3). This was done so that the fornix bundle in
one hemisphere does not compensate for the loss of the other, which would result in
close-to-normal behavior. Although the fornix was cut in these surgeries, the location
along the bundle's trajectory from the hippocampus to the hypothalamus where the lesion
was administered differed for the different surgeries. Bilateral dorsal fornix lesions were
made to disrupt all fornix connections between the hippocampal formation and the
hypothalamus and the manmillary bodies, as well as bilateral lesions of the postcommissural fornix fibers (fornix-column lesions), which directly connected the
hippocampal formation with the other two structures. Since some of the axons from the
fornix fiber reached the hypothalamus via the septum, lesions were made of the precommissural fornix connection (fornix-septum lesions). These surgeries were done to
determine which of the trajectories of the fornix were most crucial in maintaining the
normal hamster behaviors observed.
19
---
P.ost-comme
sural rarnr
T
_j
tiernalIle
-u-
-
Pre-coanmssural rarnix
Hippocampal Formnillon
T-R
4-1
Figure 3. A visual table of the fornix surgeries performed. All original
sketches were done by Dr. Gerald E. Schneider. (1) A top view of the
hippocampal formation and the fornix fibers as they would be situated in a
hamster brain. (2) A side view of the hippocampal formation and the
fornix fibers, along with the location of the hypothalamus and mammillary
body. (3) A sketch of a dorsal fornix lesion. (4) A sketch of a fornixcolumn lesion. (5) A sketch of a fornix-septum lesion. (Note: the fact that
all surgeries were bilateral is not represented in this figure)
All surgeries in this research were done in accordance with the Massachusetts
Institute of Technology's Division of Comparative Medicine guideline for animal surgery
and the approved protocol for animal surgery, protocol number 97-043-3, in Gerald E.
Schneider's Laboratory.
20
3.3
Semi-Natural Habitat
3.3.1
Schneider Experimental Cage
The experimental cages, which served as the subjects' living facilities during the
experimental periods, were designed by Dr. Gerald E. Schneider. Each cage is 21" x
9.75" x 13.75", and is divided into a front-section and a back-section (Figure 4). The
walls of the experimental cage were made of transparent plexi-glass, except for the top
level of the front-section of the cage, which was made of chicken wire mesh. Covering
the top of the cage was a lid with chicken wire mesh on the interior and stainless steel
borders bent 90 degrees to make the lid. Located on the middle of the left, right, front
and back of the cage lid were hooks where latches on the experimental cages, located
across from the hooks, could be fastened. The back-section of the experimental cage was
composed of two levels, top and bottom. Situated on the top level of the back-section
were two quartz stones. These stones were placed there for the subjects to use to file
down their ever-growing teeth. Connecting the top level of the back-section with the
bottom level of the back-section was a tunnel made of smooth polished black plexi-glass.
The bottom back-section, which was separated from the bottom and middle levels of the
front-section by the same black plexi-glass, formed an enclosed compartment referred to
as the den. The den of each experimental cage was filled completely with a mixture of
the heat-treated pine shavings and 100% pure cotton balls. The mixture of pine shavings
and cotton formed a composite that could be burrowed through by the hamster and used
to build specialized compartments, referred to as nests, in the den.
21
Side
View
Back
Front
TopLll
View
Back
Front-
Figure 4. A transparent computerized model of a Schneider
Experimental Cage. The side view shows the front-section of the
cage, divided into the top, middle and bottom levels, as well as the
back-section with its top and bottom (den) levels. Subjects were
housed in these cages during the experimental period.
The front part of the cage had three levels instead of two: top, middle, and bottom.
The top and bottom levels of the front-section each had a door that lead into the habitat.
These two doors, like the walls making up the experimental cage, were made of seethrough plexi-glass. A 6" ramp connected the bottom level of the front-section to the
middle level, in of each cage. The middle level was in turn connected to the den by a
tunnel. Sticking into the bottom level of the front-section of the cage and opposite the
bottom level door was a metal tube, which was attached to a glass water bottle, that
served as the hamster's source of water. This water bottle sits outside of the experimental
cage on a clear plexi-glass platform attached to the front of the cage. The floor of each
cage was made up of rows of metal rods approximately (1 cm) in diameter and spaced so
that feces and urine can be collected in a 20" x 10" stainless steel tray, located below
each cage. Covering left, right and back walls of the den and the top level of the backsection of each experimental cage, are 10" x 9" sheets of black plexi-glass cover-doors
that can be opened. Each cover-door is fastened to the body of the cage by a latch that
could be un-hinged, allowing the cover-door to be opened and the investigator to view
the inside of the cage through the clear plexi-glass making up the walls of the den and
back-portion of the cage.
These cages were designed to mimic an underground dwelling, as well as the
immediate surroundings, a hamster might inhabit in the rocky hills of a Syrian landscape.
Thus Schneider Experimental Cages created a more natural habitat for the subjects
22
compared to the animal Division of Comparative Medicine's standard hamster cages,
while maintaining the sanitary, food and water dispensary requirements, as well as
ventilation needed to sustain a laboratory animal such as the Syrian Golden Hamster.
Furthermore, the transparent plexi-glass walls, as well as the sanitation tray of each cage,
provided ways for the investigator to monitor and track subjects inside their experimental
cages.
3.3.2
Hamster Arena
All behavioral tests were conducted in an apparatus known as the Semi-Natural
Habitat (Figure 5), which was composed of the Schneider Experimental Cages situated
on top of the Hamster Arena. The floor of the Hamster Arena was constructed out of four
rectangular 3/8" birch plywood. Each of these rectangular plywood pieces was
approximately 6' long and 2' wide. Long pieces of plywood, with front-end dimensions
of 2" x 4", were screwed to the bottom edges of the four Arena floor pieces, so that these
four rectangular pieces now stood approximately 4 and 3/8" high. Three holes were
drilled into the now 4 and 3/8" sides of the Arena floor pieces along the 6' length, except
on the sides that would form the ends of the Arena. Special 4" long pegs were
constructed to fit into these holes in such a way that they would rest in holes of one
Hamster Arena floor piece and insert into the holes of an opposing floor piece if the two
pieces were pushed together. Therefore, when all the Hamster Arena floor pieces were
placed together, width-wise so that the pegs on one plywood piece inserts into the
matching holes in the opposing piece, an Arena floor that was approximately 8' long, 6'
wide, and 4 and 3/8" high was created. All components of the Hamster Arena floor were
coated with water-based semi-gloss polyurethane to protect them from the rotting affects
of moisture.
23
Caige 1, Cage 2
Cage 5 I(aue 6
Cage 4
Cage 3
CB)
____
(
JCC)
F~N
/
C®
/
/1
/
/
~.1'~~
Figure 5. Semi-Natural Habitat (Hamster Arena and the Schneider
Experimental Cages). Six subjects, housed in the cages labeled Cage I
through Cage 6, could be tested during an experiment. The circles
around the letters A, B, C and P represent the foraging stations with the
visual cues Apple, Bell, Cone and Pumpkin, respectively. Represented
on the bottom left is the Lake Area. The Novelty Area is the triangular
area on the bottom right.
The six experimental cages (only four cages in the first experiment) rested side by
side along the length of one of the end rectangular Hamster Arena floor pieces. This end
of the Arena was designated as the top of the Arena. The other rectangular end floor
piece was designated the bottom of the Arena and was extensively modified. An
irregular hexagonal portion of the bottom left end of the Arena, which could be
approximated by an area 34" long and 30" wide, was lowered 2" below the rest of the
Arena. This left bottom region of the Hamster Arena is known as the Lake Area.
Additional modifications were made to the Lake Area. Two perpendicular 11" x 6.5"
areas were carved out of the Lake Area and two 2" tall clear plastic containers, of the
exact same area, were placed into these areas, so that they were flush with the surface of
the Lake Area. The left-most plastic container was lined with multi-colored pebbles and
filled with sterile autoclaved water. This was the lake. The right-most container was also
filled with multi-colored pebbles and was known as the rock bin. Located on the bottomright end of the Arena, was another region known as the Novelty Area. The Novelty
24
Area was designated by an isosceles triangular region made by a 38" long divider that sat
in slots on the right and bottom wall of the Arena. Thus the sides of the Novelty Area
were 38" x 27" x 27". The divider, which was supposed to characterize a hilly region in
a Syrian landscape, was 12" at its highest point and 5.5" at its lowest. A 3.5" x 3.33"
opening was carved out of the divider which allowed the subjects to enter and exit the
Novelty Area. A new novelty object was placed in the Novelty Area the next time the
same subject was behaviorally tested in the Semi-Natural Habitat (SNH). The reactions
of the subjects to the novel objects were observed and recorded.
Circular holes, slightly larger than 8.5" in diameter, were pseudo-randomly drilled
into the floor of the Hamster Arena. Positioned into these holes were four bowls,
specially designed by Gerald E. Schneider for food retrieval, known as foraging stations
(Figure 6). Each of these stations was a 2.5" deep bowl, with a diameter of 8.5". All the
bowls were made of black plexi-glass tubing and had smooth rounded rims. They sat
snuggly inside their holes and were held up by a support platform under the floor of the
Arena, such that the rims of the bowls were flush with the floor of the Hamster Arena.
Located at the center of each foraging station, and raised approximately 2.5" from the
bottom of the bowl, was 1/2" thick black plexi-glass circular platform with a diameter of
5". Holding up this platform at its center was a dowel, 8" long with a diameter of 3/8",
made of stainless steel and painted black to match the rest of the foraging station. Since
the diameter of the platform was smaller than that of the bowl, the subjects could climb
into the foraging stations. The purpose of the platform was to hide the food pellets,
foraged by the subjects, from view.
Dowel
8"5
2.52
F
Bow
2.75"
8.5"
Figure 6. A sketch of a foraging station. The foraging station was
designed to show that the subject could not see the food without either
entering the station or coming very near to it.
Four visual cues, made of cardboard and painted black, were mounted on top of
each dowel. The visual cues were a black Apple to designate foraging station A (also
known as Bin A), a black Bell designated station B (also known as Bin B), a black Cone
25
for station C (Bin C), and a black Pumpkin to designate foraging station P (Bin P). Since
the foraging station bowls were set into the Hamster Arena, such that they were almost
flush with the floor, only the dowels, the visual cues, and a small portion of each station's
platform were visible to the subjects. Thus the subjects could not see nor remove food
pellets from the foraging stations without crawling into them. The visual cues were used
by the investigator to distinguish the foraging stations for observational and data analysis
purposes. It was possible that the subjects also used them as landmarks.
Enclosing the Hamster Arena on the two sides and at the bottom were three
removable walls made of the 3/8" birch plywood. The two sidewalls were both
approximately 8' long and 16" tall, while the bottom end wall was approximately 6' long
and 16" tall. Insertion slots, 1" deep and 10" wide, were screwed to the left and right
sides, as well as the bottom side of the Arena floor, for the walls to be placed in and held
firmly. The left and right sides of the Arena had three insertion slots, while the bottom
side had two insertion slots. Two wedge-like slots were nailed to the right wall and the
bottom wall to hold the Novelty Area divider. Lastly, blockers and covers were
constructed to prevent the subjects from escaping during behavioral testing. The blockers
were made out of the same 3/8" birch plywood as most of the Arena and were
constructed to be inserted in between the experimental cages and between the end cages
and the sidewalls. Three covers were constructed out of transparent plexi-glass. Two
35" x 31" covers were used to cover the experimental cages with the front ends extended
over the Arena so that the subjects could not climb up the cages and escape during
behavioral testing. The third cover was triangular, 45" x 32" x 32", and was placed over
the Novelty Area to prevent escape from that avenue. All three walls and the blockers
were treated with water-based polyurethane to protect them from the moisture deposited
by subjects as they vaginal scent mark and urinate during their foraging of the Hamster
Arena.
In order to make the SNH resemble the Syrian Golden hamster's natural habitat,
mountainous ranges, distant trees, and bushes were painted on the walls of the Hamster
Arena. Natural objects that would be found in the Syrian landscape, such as wood, rocks,
etc., were placed in the Arena. For example, four polished sections of a birch branch,
approximately 1.5" in diameter and 6" long, were attached together using Velcro to
simulate a pile of wood debris. A miniature representation of a tree was constructed out
of a polished oak branch inserted into a pine log. Three red bricks were used to simulate
a rock formation that could provide temporary shelter and protection for the subjects
during foraging. It was the hope of the investigator that the more natural environment of
the SNH, would help trigger latent instincts and induce the subjects to behave in a
manner similar to that of a wild Syrian Golden hamster in the natural habitat of the Syrian
country-side.
26
3.4
Behavioral Testing Procedure
Although there were slight modifications in the behavioral testing procedure from
experiment to experiment, in general the same procedure was followed for all the
experiments conducted in this research. Subjects were generally tested over a course of
approximately one week to one month, depending on the experiment and survival of the
subject (See Summary of Experiments, p. 3 1). The order in which the subjects were
tested was pseudo-random, that is to say that all possible sequences were exhausted
before repeating the same order of testing. By dropping the food pellets, through the
front-section bottom level door of the experimental cage, onto the metal rods, an audible
clanking noise was made, that was used to condition the hamsters to come out of their
den. During actual behavioral testing, this noise was used to bring the subjects out of
their dens before starting the test. Though the subject was expected to forage in the
Hamster Arena during the behavioral tests, for additional food, each subject was supplied
with a constant source of water and two pellets a day.
All observations were done between 2:00PM and 7:00PM. This time was
important because hamsters are twilight animals. A behavioral testing period, also
known as an observational period, usually ranged between 10 to 30 minutes, depending
on the experiment and the subject's behavior. During this behavioral testing period, each
subject was allowed to exit her experimental cage and enter the open area of the SNH.
The behavior of the each subject was recorded using a Sony 72X Digital Zoom hand-held
video camera, during the first three experiments, and using a Sony DCR-TRV900 Digital
hand-held video camera, during the last two experiments. The difference between the
two cameras is that the latter allowed the digitally recorded video to be directly captured
and displayed on a personal microcomputer. The video camera used during the
observational period was mounted on a tripod and positioned approximately 7.5' above
the SNH (Figure 7). Not only was a camera useful in recording the behavior of the
subjects, but it was also useful because they displayed the time of day, and could be used
to calculate the length of an observation as well as the length of various behavioral
activities. Both types of digital video cameras used in this research had night vision
capability.
27
Camera Angle Diagram
Video camera
Tripod
Semi-Natural
Habitat
6'
Weght BaIance
UL
Figure 7. A diagram of the position of the video camera during
behavioral testing. The camera used during the observational period
was mounted on a tripod and positioned approximately 7.5' above the
Semi-natural habitat.
Before the start of each observation period, the water in the lake area was
replaced with freshly sterilized water and a new object placed within the novelty area.
Two food pellets, approximately 1" x 'A" x
" each, were placed into each foraging
stations, if no food pellets remained from the previous behavioral testing period. Care
was taken to make sure that each pellet was out of sight and the visual range of the
subject until she was within 6" from the edge of the foraging station. The video camera,
already mounted and positioned in place above the SNH, was then turned on using a
remote control. The bottom plexi-glass door to one of the subject's experimental cage
was opened and remained open for the entire duration of that subject's testing. Only the
door to the experimental cage of the subject who was being tested was open during that
observational period. During the observational period, auditory notes were made about
the subject's behavior and any other events occurring in or near the SNH. After the
allotted time had elapsed or when the subject had foraged all the foraging stations and
had extensively explored the Arena, she was then coaxed back into her experimental
cage. Food pellets removed from the foraging stations by the subject that was tested were
replaced with new pellets and the door to another subject's experimental cage was
opened. The number of subjects tested per day depended on the number of subjects, the
experiment, and the time of day the testing began.
In the first three experiments, the subjects were kept on a constant day/night cycle
of 16 hours light and 8 hours of darkness. Total darkness, the time when no lights were
28
on, occurred at 6:00PM. All observations of these female subjects were done between
3:30PM and 7:00PM, over the week-long period. The time between 3:30PM and 7:00PM
is divided into three periods. First of the time periods was between 3:30PM and 5:00PM
and was referred to as Day, because all the lights were on in the Behavioral Room, which
contained both the SNH and the Schneider laboratory hamster colony. The time period
between 5:00PM and 6:00PM was referred to as Twilight because the main light sources
were off, but a second smaller and much dimmer light source was still on. Two overhead
lights were the sources of the main light. These two overhead lights were on a timer
system and the source of the day/night cycle. The smaller light source, which was
suppose to represent the weak light from a sunset, was a regular desk lamp, with standard
60 watt Phillips@ incandescent light bulb. This desk lamp was on a different timer than
the main lights and was on for only one hour. Since the desk lamp went off at 6:00PM,
the period between 6:00PM and 7:00PM was referred to as the Night period. Only the
normal subjects of the first experiment were tested in all three Periods. All other subjects
used in this research were tested during the "Day" period. In the last two experiments of
this research, the subjects were kept under a constant day/night cycle of 14 hours and 10
hours. Total darkness occurred at 7:00PM.
A special data sheet was used to record the quantitative aspects, as well as the
qualitative aspects, of the target behaviors exhibited by the subjects (Figure 8). Regions
of the SNH where behaviors of interest were exhibited were then recorded onto the data
sheet, along with the time and length of the behaviors. At the completion of an
experiment the video-recorded behavior of each hamster was also reviewed using a VCR
and television. Furthermore, the stainless steel tray, underneath the individual
experimental cages, was used to determine the overall organization of the den, the bottom
level of the back-section of the cage. Because the nests built by the subjects were usually
located in the interior of the den, the number, organization, and functions of these nests
could not be determined directly. Since the Tray Analysis was done at the conclusion of
an experiment, the information extracted from them was the averaged sum of all the
events that occurred in the experimental cages, with the most recent events being
somewhat weighted greater.
29
3.5
Summary of Experiments
Normal control subjects, who never underwent surgery, were indicated by a
normal hamster (NH) number (i.e. NH-7). A hamster fornix experiment (Hfx) number
(i.e. Hfx-1) was used to identify any subject who had undergone surgery, including sham
(exposure) surgery. A "B" in front of the Hfx number (i.e. BHfx-1) was used to identify
subjects before they underwent surgery. At the completion of each of the following
experiments, all surviving subjects were sacrificed, perfused and their brains preserved in
2% paraformaldehyde.
In the first experiment, the control experiment, a group composed of four pseudorandomly selected female Syrian Golden hamsters (NH-1, NH-2, NH-3 and NH-4) were
used to determine and quantify normal hamster behavior in the newly designed seminatural habitat (SNH). All four subjects were approximately eight months old and were
bred in Gerald E. Schneider's hamster colony. Therefore their parentage and lineage
were known. The subjects were allowed 30 days to habituate to the novel environment of
the SNH. The behavioral testing transpired over a period of one week, during which time
each subject was tested six times.
A second experiment was done using six female Syrian Golden hamsters of
similar age, three of which were normal and three experimentals. All the experimentals
had undergone surgery. The subjects were then randomly placed in one of the six
Schneider experimental cages. All the subjects were approximately 8 months old. The
subjects were then allowed one week to habituate to the SNH. Both the hamster in the
third cage, Hfx-12, and the one in the fourth cage, Hfx- 11, died during this period and
could not be behaviorally tested. Behavioral testing transpired over a period of 9 days.
The subjects, NH-5 and NH-6, were tested 4 times. Hfx-10 and Hfx-16 were also
observed 4 times. NH-5 and NH-6 were normal controls and Hfx-10 was a bilateral
dorsal fornix exposure control. Hfx-16 had undergone a different type of surgery then
the ones presented in this thesis and thus will not be discussed or used in any of the
calculations or conclusions made.
In the third experiment, six normal female hamsters, approximately five months
old at the beginning of the experiment, were used to determine the effect of a bilateral
fornix lesion on Syrian Golden hamster behavior in the SNH. Thus behavioral
observations were made of these hamsters before and after they underwent surgery.
None of these subjects were closely related. Five of the six subjects were moved into the
experimental cages and allowed approximately three days to habituate to the SNH. The
sixth subject, who went into the fourth experimental cage, was introduced late into the
SNH and but also had three days to habituate to them before being tested. Pre-surgical
behavioral testing transpired over a four-week period. The subject in cage 1, BHfx-22,
was tested 12 times and the subject in cage 2, BHfx-23, was tested 10 times. BHfx-20, in
cage 3, was also tested 10 times, while NH-7a, in cage 4, was observed 9 times. The
subject in cage 5, BHfx-19, was observed 10 times and BHfx-18, in cage 6, was tested 12
times.
30
Surgery was done on all six subjects -after the pre-surgery behavioral testing.
They were then allowed a four-week recovery period before being placed back into the
SNH. It was during this period of time that NH-7a died and was replaced by a normal
hamster of comparable age and size, NH-7b. An additional five days were allowed for
the operated subjects and the new subject to re-habituate to the experimental cages and
the Arena, before commencement of the post-surgery behavioral testing. The postsurgery behavioral observations transpired over a period of three weeks. Hfx-22, in cage
1, was tested 11 times, while Hfx-20, the subject in cage 2, was only observed 4 times.
The subject in cage 3, Hfx-23, was observed 5 times and NH-7b, the subject in cage 4,
was tested 12 times. Lastly, the subject in cage 5, Hfx-19, was tested 10 times and cage 6
subject, Hfx-18, was tested 12 times. NH-7b was a normal control. Hfx-19 and Hfx-22
had undergone bilateral dorsal fornix exposure surgeries, while Hfx- 18 and Hfx-23 had
undergone bilateral dorsal fornix lesions. Hfx-20 will not be discussed or used in any of
the calculations or conclusions made, because she underwent a different type of surgery
then the ones covered by this thesis.
The fourth experiment, like the second, was composed of two groups of hamsters,
experimentals and controls. Six female hamsters of approximately eight months old
were used in this experiment. Two of them were controls, NH-8 and Hfx-28 (in cages 4
and 5, respectively), while the other four were experimentals. The subject in cage 3, Hfx24, and the one in experimental cage 6, Hfx-26, had undergone fornix-column lesion
surgeries, while Hfx-27 (in cage 1) and Hfx-25 (in cage 2) underwent fornix-septum fiber
lesions. All subjects were allowed approximately one week to habituate to the SNH
before behavioral testing began. During this period of habituation, Hfx-25 died and
therefore was not behaviorally tested. For the rest of the subjects, behavioral testing
transpired over a period of five weeks. Both Hfx-26 and Hfx-27 were tested 13 times.
NH-8 and Hfx-28 were both observed 12 times, while Hfx-26 was only tested 7 times
because she died prematurely.
The fifth experiment was composed of six female Golden Syrian hamsters, each
of which was approximately 4 months old. These hamsters were not bred in Gerald E.
Schneider's hamster colony, but were instead purchased from the Charles River
Laboratory and shipped in cardboard containers from the Charles River Laboratory to
MIT, where they were quarantined for approximately one week before being introduced
to the Schneider hamster colony. The subjects used in this experiment had exposure to
many more alien environments, than the subjects used in the previous experiments. After
approximately three days of habituation to the environment of the Schneider hamster
colony, these six subjects were placed in their individual experimental cages. They were
then allowed approximately one week to adapt to the SNIH. Pre-surgical testing began on
the sixth day after introduction to the experimental cages for subjects BHfx-36, BHfx-37
and NH-10 (in cages 1, 2 and 3, respectively), and on the seventh day for subjects BHfx35, NH-9 and BHfx-34 (in cages 4, 5 and 6, respectively). The pre-surgical behavioral
testing transpired over a period of two weeks. Three of the six subjects were tested each
day, giving a total of seven observations per subject over the two weeks.
31
At the end of the two-week observation period, the subjects were removed from
their experimental cages and surgery was done on them. NH-9 and NH- 10 did not
survive the surgical procedure and were replaced by Hfx-38 and Hfx-39. Hfx-34 and
Hfx-35 underwent bilateral dorsal fornix lesion surgeries. Hfx-36 and Hfx-38 had
undergone bilateral fornix-column lesions, while Hfx-37 and Hfx-39 underwent bilateral
fornix-septum lesion surgeries. All the subjects were allowed one full week of recovery
before they were re-introduced to the experimental cages. After allowing for another
week of full recovery and re-habituation to the experimental cages, the subjects
underwent post-surgical behavioral testing. The post-surgical testing also transpired over
a period of two weeks, during which time each subject was observed seven times.
32
3.6
Histological Procedure
3.6.1
Perfusion and Tissue Sectioning
At the completion of each experiment, the animals used in the experiment were
sacrificed. An overdose of pentobarbital was injected into the liver. After the animal
became deeply sedated, it was then perfused. First the thorax was opened, by removing
the rib cages, and the heart exposed. A perfusion needle, connected through a rubber
tube to a container of phosphate-buffered saline solution (PBS), was inserted into the left
ventricle of the heart. The superior vena cava was cut and a motorized pump was started
that pumped PBS through the circulatory system of the animal, flushing out all the blood.
After it was assured that the circulatory system was completely flushed, the PBS was
exchanged for 2% paraformaldehyde, which was pumped through the system using the
same apparatus. After the animal was properly perfused, the brain of that subject was
removed and placed in a container of 2% paraformaldehyde to be preserved. The brain
was labeled and left in the refrigerator for at least four days, before being transferred
from the paraformaldehyde into a container with 30% sucrose solution. At least three
days, or until the brain sank to the bottom of the sucrose solution, was allowed before
sectioning the brain. After removing the brains from the 30% sucrose solution, it was
placed on a water-resistant treated block of wood. The brain was blocked so that the area
of interest could be sectioned.
The brain sections were cut on a Bright Microtome Cryostat 5030, OTF Series.
First the brain was blocked (i.e. frozen) in an O.C.T. 4583 Compound (OCT), an
embedding medium for frozen tissue specimens made by Tissue-Tek@, and frozen at
approximately -30 degrees Fahrenheit in the Cryostat Quick Freezer. The brain was then
mounted onto a sectioning platform and sections 30 microns thick were cut. The sections
were place immediately from the microtome blade to the gelatin-coated subslide. Three
series of sections (A, B, and C) were made for each brain. The sectioned brain piece on a
subslide of the A series was 30 microns apart from the next sectioned brain piece on a
subslide of the B series, which was 30 microns apart from the following section on the
subslide of the C series and so on. The A series was used in cresyl violet staining and the
B series for myelin staining. The C series served as a spare for the A and B series.
3.6.2
Staining Methods
After sectioning the brain, the A series subslides containing the regions of interest
were stained using cresyl violet and Loyez stain to determine the exact location and
extent of lesion. A modified protocol, from Gerald Schneider, was used to stain for the
Nissl substance in the cell bodies of the neurons in the tissue of the mounted sections
using cresyl violet. Neurons contain Nissl substance, which is primarily composed of
rough endoplasmic reticulum, with the amount, form, and distribution varying in different
types of neurons. Because of the RNA content, Nissl substance is very basophilic and
will be very sharply stained with basic aniline (cationic) dyes, such as with cresyl violet.
33
Slides containing cresyl violet stained sections were used to identify areas with damaged
cell bodies, caused by the surgery.
The staining solution used to label the Nissl substances was composed of cresyl
violet, glacial acetic acid and distilled water. Before staining, the mounted brain sections
were first allowed to dry overnight and then allowed to sit for one more night in 70%
ethanol. The next day, these mounted sections were put through a series of distilled
water to hydrate them, and then stained with cresyl violet. Four changes of distilled
water were used to wash off the excess cresyl violet from the tissues. They were placed
momentarily into chloroform and then into the differentiator. The differentiator was
made of 95% ethanol and drops of glacial acidic acid. All the mounted sections were left
in the differentiator until the background tissue appeared almost white. They were then
put through a series of ethanol washes, meant to dehydrate the mounted tissue, and then
through a series of xylene solutions. Coverslips were adhered to the mounted sections on
the subslides, using Permount@.
The B series sections were stained for degenerated axons using Loyez staining
method for myelinated axons in frozen sections. Since the fornix fiber is a column
composed of myelinated axons, myelin stained sections allowed us to identify whether
the fornix, as well as the septum which also contains myelinated axons, was transected
by the lesion. Myelin stained section also allowed us to determine if the lesion was
complete or there was some sparing. The Loyez staining solution used to stain these
sections was composed of haematoxylin, dissolved in absolute ethanol, distilled water,
and saturated aqueous lithium carbonate. The protocol used for the Loyez staining was
modified from an older protocol used to Loyez stain unmounted floating sections. After
cutting, the mounted sections were washed first in 3 solutions of PBS and then again in
distilled water. The sections were then placed into a solution of ferric ammonium
sulphate for hours, while being gently rocked. They were then washed with distilled
water and then placed into the Loyez staining solution for about another hour or two on
the rocker. Afterwards, these mounted sections were washed again thoroughly in
distilled water. Next, they were placed into the differentiator, until the background tissue
appeared almost white. The sections were then washed several times with distilled water,
until the differentiator was completely washed off. They were then put through a series
of ethanol washes, meant to -dehydrate the mounted tissue, and then through a series of
xylene solutions. Coverslips were adhered to the mounted sections using Permount®.
34
3.7
Statistical Analysis
Statistical analysis was done on the behavioral testing results obtained from the
experiments. The quantitative data, obtained directly from the testing results or
calculated from them, were inputted into a statistics software package, STATA@, to
conduct all the statistical tests. All statistical results presented were from two-tailed t-test
analysis. The graphs were produced using Microsoft Excel@.
35
4
Results
4.1
In-Cage Behavior
After the completion of the behavioral tests for each Experiment, the subjects
were removed from their experimental cages. The experimental cages were then
meticulously examined. Sketch, notes, and videotapes were taken on the organization of
the subjects in den. Overall cleanliness of each cage, as well as the location of hoards,
was also noted. The sanitary tray underneath each experimental cage was also used to
verify the location, function, and organization of the nests, found in the den. However,
there were indications that the subjects occasionally reorganized their dens. Thus the
location and number of the nests and hoards recorded were the result of the cumulative
sum of the subject's activity while in their den.
4.1.1
Hoarding Behavior
All normal hamster subjects hoarded food pellets, whether they were given the
pellet (all subjects were given two pellets a day) or obtained it from foraging in the
Hamster Arena. The number of hoards maintained by normal hamsters ranged from 1 to
4 hoards. Individual number of hoards maintained by the bilateral dorsal fornix exposure
subjects also ranged from I to 4. Comparison of the number of hoards maintained by
normal hamsters and dorsal fornix exposure subjects revealed that the difference in
means was not significant (p= 0.4146). Although given two food pellets a day, none of
the bilateral dorsal fornix-lesion subjectss or the bilateral fornix-septum lesion subjects
established or maintained a food hoard. Both gave statistically significant differences of
p= 0.0027, when compared to the normal hamster subjects. One bilateral fornix-column
lesion subject, Hfx-24, maintained one food hoard. Comparison of the number of hoards
maintained by fornix-column lesion subjects and normal hamsters gave a statistically
significant difference of p= 0.0096.
36
Food Hoard
2.5
2
1.5
0
S1
0.5
0
NH
DF
DE
FC
FS
Subject Group
Figure 8. The mean number of food hoards maintained by the five
groups of subjects tested. Statistical difference from normal group: DE p=
0.4146; DF p= 0.0027; FC p= 0.0096; FS p= 0.0027. (NH=normal
hamster (n=20), DE=bilateral dorsal fornix exposure (n=4), DF=bilateral
dorsal fornix lesion (n=4), FC=bilateral fornix-column lesion (n=4),
FS=bilateral fornix-septum lesion (n=4)).
4.1.2
Nesting Behavior
When given suitable materials, such as the cotton and pine shaving bedding inside
the den of the Schneider experimental cages, normal hamsters would burrow into the
bedding and build a nest that was enclosed, much like the burrows they would dig
underground in nature. All normal hamster subjects tested built nests. The number of
nests built by normal hamsters and dorsal fornix exposure subjects varied from 3 to 5
nests. There was no difference in nesting between normal and dorsal exposure hamsters
(p> 0.9999). The mean number of nests built by the bilateral dorsal fornix-lesion subjects
also had a variance of 1 nest, but the difference between the normal hamsters and dorsal
fornix-lesion subjects in the number of nests built was statistically significant (p<
0.0001). The number of nests built by fornix-column lesion subjects, variance of 1 nest,
and the number of nests built by fornix-septum lesion subjects, variance of 0.5, were also
significantly different from that of normal hamsters (p= 0.0001 and p= 0.0003,
respectively). Not only did the fornix-lesion subjects build lower numbers of nests, but
the quality of the nests were also worse. Most of the nests built by fornix-lesion subjects
were not enclosed, but instead were found on top of the bedding inside the den.
37
Nesting
4.5
4
3.5
3
2.5
2
a 1.5
0.5
0
NH
DF
DE
FC
FS
Subject Group
Figure 9. The mean number of nests maintained by the five groups of
subjects tested. Statistical difference from normal group: DE p> 0.9999; DF
p< 0.000 1; FC p= 0.000 1; FS p= 0.0003. (NH=normal hamster (n=20),
DE=bilateral dorsal fornix exposure (n=4), DF=bilateral dorsal fornix lesion
(n=4), FC=bilateral fornix-column lesion (n=4), FS=bilateral fornix-septum
lesion (n=4)).
4.1.3
In-Cage Activity
Analysis of the sanitary tray of each subject, as well as visual observation,
revealed that normal hamsters and bilateral dorsal fornix exposure subjects spent the
majority of their active and inactive times "underground" inside their den. The majority
of their feeding, feces depositing and urination occurred in the nests located in the den of
their experimental cages. Although fornix-lesion subjects did build nests in their den,
they did not utilize them nearly to the extent that the control subjects did. Furthermore,
the fornix lesion groups were in general less active than the control groups and were
often found sleeping outside of their den, a behavior that was not observed with any of
the normal hamsters.
Key:
= feces
/
=
pebbles
= urine
/J)= pellet dust
Figure 10. The key to the illustrations used in the sanitary tray analysis
figures.
38
Normal Hamsters
Back I
IiOJ
NJ 1- 1
Nil-I
trot
Back
7J
NI-2
HNf-2.3
B~Hfx
NI Frlxnl I
~ck
1
Frot|
4i~
7 ,
J3Uif-34
Back
-
NII-1
e
NH-1.
Rack
___
r
NH-I
-.
=
rt
c~
r
I
r
H 5ck]
tRackj
Fra*mi
i Fck
N
IHf CA-3
N V_
I F-x-gJ
Figure 11. Summary of the tray analysis of all the normal hamsters. Notice that most of
the activity occurs in the den, back bottom portion of the experimental cage.
39
4~
Bilateral Dorsal Fornix Exposure
t a
ackl
FrH -2a8
FrxtBc]
Back' I
raJ
Hfx.8
Hf-'c 1
-1(k
Bilateral Dorsal Fornix Lesion
Fr~IBick
flfN
I!
t Ji]~
t1
18
Bas ]
rji
Rack
111V34
2j
V
T
i
71:471)
Bilateral Fornix-Column iber Lesion
Fruj
"Back,!
Back
Fui
MAC-,%
Ill'
I f-24
ii
Ilk
J
~t4
r
Bilateral Fornix-Septum Fiber Lesion
Bc
Fr-Ml
r_
Al
Fr
IBA
I
'13
rI~UI
HIxM'
jjft
j4. ~x~4
r.~
~,
-I
Figure 12. Summazy of the tray analysis of all the subjects who underwent surgery.
Notice that most of the activity for the bilateral dorsal fornix exposure subjects occurs in
the den, the back bottom portion of the experimental cage, while most of the activity for
all the fornix-lesion subjects occurs in the front portion of the experimental cage, except
for two bilateral fornix-column lesion subjects (Hfx-24 and Hfx-26).
40
4.1.4
Before and After Surgerv: In-Cage Behavior Comparisons
Statistical analysis could not be done for the before and after surgery comparisons
because the experimental cages of the subjects were only analyzed once, after the
completion of the SNH behavioral tests.
Bilateral Dorsal Fornix Exposure
Both Hfx-19 and Hfx-22 were behaviorally tested before and after undergoing
bilateral dorsal fornix exposure surgery. The number of hoards maintained by Hfx- 19
went from 2, before surgery to 3, after surgery, while the number of hoards maintained by
HFx-22 remained the same. Likewise, the number and quality of the nests maintained
Hfx-22 also remained the same, while Hfx-19 maintained one less nest. Both subjects, in
general, behaved and were active in cage the same before the dorsal exposure surgery as
afterwards (See Figure 11 and 12).
Bilateral Dorsal Fornix Lesion
Hfx-18, Hfx-23, Hfx-34 and Hfx-35 were behaviorally tested before and after
undergoing bilateral dorsal fornix lesion surgery. All of the dorsal fornix-lesion subjects
hoarded before undergoing surgery and none of them hoarded after the surgery. The
number of nests maintained decreased for all the subjects after surgery by 2 or more.
Furthermore, the in cage activity for all the dorsal fornix-lesion subjects shifted from
being mostly inside the den to being mostly outside of the den (See Figure 11 and 12).
Bilateral Fornix-Column Lesion
The only bilateral fomix-column lesion subject that was behaviorally tested
before and after undergoing the surgery was Hfx-36. Although, Hfx-36 maintained a
hoard before undergoing lesioning of the fornix columns, she did not maintain a hoard
afterward. Like the dorsal fornix-lesion subjects, the number of nests maintained by Hfx36 decreased, from 5 to 3. Furthermore, the in cage activity for this bilateral fornixcolumn lesion subject shifted from being mostly inside the den to being mostly outside of
the den (See Figure 11 and 12).
Bilateral Fornix-Septum Lesion
The only bilateral fornix-septum lesion subject to be behaviorally tested before
and after undergoing the surgery was Hfx-37. Although, Hfx-37 maintained a hoard
before undergoing lesioning of the fornix-septum fibers, she did not maintain a hoard
afterward. Like Hfx-36, the number of nests maintained by Hfx-36 decreased after the
surgery, from 4 to 3. Furthermore, the in cage activity for this bilateral fornix-septum
lesion subject shifted from being mostly inside the den to being mostly outside of the den
(See Figure 11 and 12).
41
4.2
Arena Behavior
Syrian Golden hamster behavior was documented during the behavioral tests.
The primary behaviors observed were activity level, grooming, responses to novelty
objects, and foraging behavior. Videocassettes recorded during the behavioral test for the
first Experiment were lost, but information documented in writing during the behavioral
tests and summary reports were used to compile the results presented for Experiment 1
below whenever possible. The rest of the behaviors reported below were also
documented during behavioral tests in the Hamster Arena. Any uncertainty in the
documentation was double checked on the videocassette of the behavioral tests.
4.2.1
Activity Level
Activity level for all the subjects was determined by counting the number of times
each subject passed through regions of the Arena having the coordinates (3,1), (3,2) and
(3,3), during a behavioral test, except for the first Experiment where the regions having
the coordinates (1,3) and (3,3) were used. The number of passes through the regions of
interest was divided by the duration of the respective behavioral test and results from
each member of a subject group were combined and plotted against the time of day.
Cage4
Cage2 Cage3
Cagel
Cage6
Cage5
7
6
A
B
5
C
4
3
2
1
1
2
3
4
5
X-axis
Figure 13. Regions of the Hamster Arena were assigned Cartesian
coordinates. The number of times a subject passed through the regions
(3,1) and (3,2), region (3,3) for the first Experiment, was used in
determining its activity level.
42
Results obtained for normal hamster subjects suggest that activity level increases
slowly during the Day time period and peaks in the beginning of the Twilight time
period. It then plateaus off at a relatively high level (Figure 14-A). Most of the higher
levels of activity were due to the subjects from Experiment 1. In general, the bilateral
dorsal fornix exposure subjects displayed the same pattern of increase in overall activity
level as the normal hamster subjects (Figure 14-B). Both the bilateral dorsal fornixlesion subjects and the bilateral fornix-septum lesion subjects, on the other hand, showed
no change in activity level as the time of day progressed (Figure 14-C and E, ). Their
activity level was consistently low during any given time of day. The bilateral fornixcolumn lesion subjects also showed an abnormal pattern of activity compared to the
normal hamsters and the dorsal exposure subjects. Although their activity level was in
general higher than those of the dorsal fornix and fornix-septum lesion subjects, the
activity pattern remained relatively unchanged and seemed to decrease during the
Twilight time period (Figure 14-D).
Controls
B
A
Nmnsd Huwwer
13:55
1:43
1619
2
13:55
2W
The (A4r)
14
16:19
TM (A1r)
21W
Fornih Lesions
D
C
DTardFumix~mden
2-
2-
01
13-55
1619
194
1355
2117
16:19
14
2111)
T= (Wr)
The(24r)
E
1omx-hnumLe in
2-
1.5
F-
013 :55
1619
1843
21W
Tzz(24r)
Figure 14. Plots of the activity level of the five subject groups. Normal
and dorsal exposure subjects (A and B, respectively) show similar patterns
of increasing activity as time progresses. The activity level of the dorsal
fornix lesion and fornix-septum lesion subjects (C and E, respectively)
stay low and do not change with progressing time, while that of the fornixcolumn lesion subjects (D) decreases slightly with time.
43
4.2.2
Grooming
The grooming habits displayed by the subjects were documented and quantified.
Grooming in hamsters is known to be an indication of internal conflict. Grooming was
only documented if the investigator could see the subject grooming. Thus the grooming
reported in this thesis is an under-representation of the number of times the subject
actually did groom, especially concerning the grooming that occurred inside the dens of
the experimental cages where access was not easy for the investigator.
All the subject groups groomed more frequently while in the Arena than while in
their experimental cages. The length of each groom, on the other hand, was on average
longer for grooming that occurred inside the subject's cage (Figure 15) compared to those
that occurred while the subject was outside and away from her cage (Figure 16). This
was consistent across subject groups. No statistically significant difference was found
between the normal hamster and dorsal exposure controls and the other fornix-lesion
subjects for in-cage grooming. While outside of the experimental cages, dorsal fornixlesion subjects groomed significantly longer (p=0.0085) than normal hamsters and
fomix-septum lesion subjects groomed significantly longer (p=0.0425) compared to the
combined control groups (normal and dorsal exposure subjects).
In-Cage Grooming
5oo-
0
I.-
Nil
DE
DF
FC
FS
Subject Group
Figure 15. A box-plot of the average length of grooming inside the
experimental cages. Statistical difference compared to normal group: DE
p-=0.3297; DF p=0.5861; FC p= 0.5484; FS p= 0.2367. (NH=normal
hamster (n=16), DE=bilateral dorsal fornix exposure (n=4), DF=bilateral
dorsal fornix lesion (n=4), FC=bilateral fornix-column lesion (n=4),
FS=bilateral fornix-septum lesion (n=3)).
44
500
Outside-Cage Grooming
-
0-
Nil
DF
DE
FC
FS
Subject Group
Figure 16. A box-plot of the average length of grooming outside the
experimental cages. Statistical difference from normal group: DE p=0. 6 6 8 2 ;
DF p=0.0085; FC p= 0.3197; FS p= 0.0528, when compared to controls
(NH + DE) FS p=0.0425*. (NH=normal hamster (n=16), DE=bilateral dorsal
fornix exposure (n=4), DF=bilateral dorsal fornix lesion (n=4), FC= bilateral
fornix-column lesion (n=4), FS=bilateral fornix-septum lesion (n=3)).
4.2.3
Novelty Response
Exploration of the novel object was documented when the subjects sniffed the
bit
it, attempted to pouch it, or scent marked the object either vaginally or with
object,
their flank glands (Figure 17). There were no statistical significant differences between
the groups in their exploration of the novelty object (NO), although comparison between
normal hamsters and the dorsal fornix-lesion subjects gave a p= 0.0668 value. Many of
the subjects especially those from the fornix-lesion groups, never entered the novelty area
(NA) and almost 30% of all the subjects entered the NA less than twice during multiple
times they were tested.
45
Entering NA vs. Exploring NO
1.2
z
0.8
W
0 0.6
z
e0 0.4 -u0.2
0
NH
DF
DE
FC
FS
Subject Group
Figure 17. Histogram of the average number of times members of
each group explored the Novelty Object (NO) after entering the
Novelty Area (NA). Statistical difference from normal group: DE p=
0.9915; DF p= 0.0668; FC p= 0.8781; FS p= --. (NH=normal
hamster (n=19), DE=bilateral dorsal fornix exposure (n=4),
DF=bilateral dorsal fornix lesion (n=3), FC=bilateral fornix-column
lesion (n=2), FS=bilateral fornix-septum lesion (n=1)).
4.2.4
Foraging Behavior
A subject was considered to pouch a food pellet if she stuffed the pellet into the
pouches in her cheeks or carried it in her mouth. Hoarding was defined as the subject
taking the food pellet, that she had previously pouched in the Arena, from the Arena into
her experimental cage. The water in the lake area, though occasionally explored by the
subjects, was in general ignored.
There was no statistically significant difference between the normal hamster
subjects and the bilateral dorsal exposure subjects in their foraging behavior of pouching
food pellets from the foraging stations (p= 0.9213). There was also no statistically
significant difference between the normal hamster subjects and the bilateral fornixcolumn lesion subjects in their pouching of food pellets (p= 0.2732). However, highly
significant differences in pouching behavior were found between normal hamsters and
dorsal fornix-lesion subjects (p= 0.0077), as well as between normal subjects and fornixseptum lesion subjects (p= 0.0276). The average number of times food was pouched
from the foraging stations for each subject group is shown in Figure 18.
46
Foraging Behavior: Pouching
0.7-
-
S 0.6 -
U.*
U 0.5 -
93 0
U.
0.2 o 0.1
0NH
DE
DF
FC
FS
Subject Group
Figure 18. The average number of times food was pouched from the
foraging stations for each subject group. Statistical difference from
normal group: DE p= 0.9213; DF p= 0.0077; FC p= 0.2732; FS p=
0.0276. (NH=normal hamster (n-=19), DE=bilateral dorsal fornix
exposure (n=4), DF=bilateral dorsal fornix lesion (n=4), FC=bilateral
fornix-column lesion (n=4), FS=bilateral fornix-septum lesion (n=3)).
All controls, normal hamsters and bilateral dorsal exposure subjects, eventually
hoarded the food pellets they pouched from the foraging stations in their experimental
cages. Rarely were members of these two subject groups observed to eat food pellets
outside of their cages (Figure 19). There was no statistically significant difference
between the normal and the dorsal exposure subjects in their open field (outside of cage)
feeding behavior (p= 0.1477). Members of all three of the fornix lesion groups were
often observed to feed outside of the safety of their cages (Figure 19). The difference
between bilateral dorsal fornix-lesion subjects and normal subjects in their open field
feeding behavior was highly significant (p< 0.0001). The behavioral difference between
normal and fornix-column lesion subjects, as well as the difference between normal
hamsters and fornix-septum lesion subjects, were also highly significant (p= 0.00 18 and
p= 0.0006, respectively).
47
Foraging Behavior: Outside-Cage Feeding
0.07
0.06
0.05
0.04
0 0.03
0
.
0.02
(U
0.01
0
NH
DF
DE
FC
FS
Subject Group
Figure 19. The mean number of times pellets were eaten out side of the
experimental cages, while the subject was foraging in the SNH, for each
subject group. Experiment 1 subjects were not included. Statistical
difference from normal group: DE p=O.1 4 7 7 ; DF p<0.0001; FC p=0.00 18;
FS p=0.0006. (NH = normal hamster (n=16), DE = bilateral dorsal fornix
exposure (n=4), DF = bilateral dorsal fornix lesion (n=4), FC= bilateral
fornix-column lesion (n=4), FS=bilateral fornix-septum lesion (n=3)).
Normal hamsters and dorsal exposure subjects on average explored all four of the
foraging stations, as well as pouched food pellets from them. The most explored foraging
station was either A or B, depending on which was closest to the subjects cage. The least
explored foraging station was P, which was located out in the open, in the center of the
Arena. In contrast, subjects with fornix lesions did not explore the Arena to the extent of
the controls and they usually concentrated on one or two foraging stations. The mean
number of foraging stations explored by the dorsal fornix, fornix-column, and fornixseptum lesion subjects were all significantly lower than that of the normal subjects (p=
0.0001, p=0.0312 and p= 0.0089, respectively). Furthermore, members from all the
fornix lesion groups were observed to fall asleep during testing in the open-field of the
Arena.
48
Foraging Station Exploration
4.5
4
.e
3.5 3
2.5
2
E
1.5
1
0.5
0
NH
DE
DF
FC
FS
Subject Group
Figure 20. The mean number of foraging stations explored by each subject
group. Statistical difference from normal group: DE p=0.4109; DF
p<0.0001; FC p=0.0312; FS p=0.008 9 . (NH=normal hamster (n=19),
DE=bilateral dorsal fornix exposure (n=4), DF=bilateral dorsal fornix lesion
(n=4), FC = bilateral fornix-column lesion (n=4), FS= bilateral fornixseptum lesion (n=3)).
4.2.5
Before and After Surgerv: Arena Behavior Comparisons
Bilateral Dorsal Fornix Exposure
Both Hfx- 19 and Hfx-22 were behaviorally tested before and after undergoing
bilateral dorsal fornix exposure surgery. Before and after comparison of activity level in
the Arena revealed no significant difference for either of the dorsal fornix exposure
subjects. The same was true for the rest of the Arena behaviors observed for these two
subjects.
Bilateral Dorsal Fornix Lesion
Hfx-18, Hfx-23, Hfx-34 and Hfx-35 were behaviorally tested before and after
undergoing bilateral dorsal fornix lesion surgery. Activity level in the Arena decreased
after surgery for all the dorsal fornix-lesion subjects, except for Hfx-34 whose activity
level score was zero for before and after surgery. The change in activity level was
significant for Hfx-l 8 and Hfx-23 (p< 0.0001 and p= 0.0168, respectively), but not for
Hfx-35 (p= 0.1174). Changes in cage grooming and outside of cage grooming varied
among the subjects, but none of the changes were significant. The same non-significant
changes were found for their response to novel objects (NO) in the Novelty Area (NA).
49
Though most of the subjects showed a decrease in their food pellet pouching behavior
after the lesioning of the dorsal fornix bundle, only the decrease demonstrated by Hfx-34
was significant (p< 0.0001). On the other hand, Hfx-18 and Hfx-23 showed significant
increases in the number of times they ate pellets while foraging in the Arena (p= 0.0029
and p= 0.0130, respectively). Hfx-34 never foraged before surgery and Hfx-35 never
foraged for food pellets after surgery.
Bilateral Fornix-Column Lesion
The only bilateral fornix-column lesion subject that was behaviorally tested
before and after undergoing the surgery was Hfx-36, Arena activity level, as well as the
in cage and outside of cage length of grooming, decreased after the fornix columns of
Hfx-36 were lesioned, but none of the decreases were statistically significant. Hfx-36
never entered the Novelty Area so before and after comparisons could not be made.
However Hfx-36 did forage both before and after undergoing surgery and the number of
times she pouched after entering a foraging station decreased to zero after the surgery (p<
0.0001). Hfx-36 neither ate pellets before nor after undergoing the fornix column lesions.
Bilateral Fornix-Septum Lesion
The only bilateral fornix-septum lesion subject that was behaviorally tested before
and after undergoing the surgery was Hfx-37. Arena activity level for Hfx-37
significantly decreased after surgery (p= 0.00 10), as well as the average length of her incage grooming (p= 0.0006). Although the average length of her outside of experimental
cage grooming did increase, the increase was not statistically significant. And like most
of the subjects tested in Experiment 5, Hfx-37 did not enter the Novelty Area. Even
though Hfx-37 pouched more often before surgery, she also explored the foraging
stations, without pouching, more often. Thus the change in the number of times she
pouched, on entering a foraging station, before and after surgery was not statistically
significant, although the increase in her outside of cage pellet consumption after surgery
was significant (p=0.00 4 3 ).
50
4.3
Food Consumption and Weight
Both the control and the fornix lesion groups were given two food pellets a day in
their experimental cages, as well as being allowed to forage for additional pellets in the
Hamster Arena. Although the control subjects pouched and hoarded significantly more
pellets than their lesioned counterparts, the data obtained from weighing the subjects
before and after surgery, did not indicate a trend of weight gain or weight loss amongst
any of the surgery groups (Table 1). It must be noted that documentation of the weight of
the subjects were made more to determine the amount of anesthesia to give each subject,
before surgery and before sacrificing, rather than as an end in itself.
Weight Change
Group
Subject #
Before-Surgery-After
Change in Weight
Dorsal Fornix Exposure
Hfx-1 0*
Hfx-22
11Og
140g
120g
130g
+
Dorsal Fornix Lesion
Hfx-34
Hfx-35
125g
125g
140g
120g
+
Fornix-Column Lesion
Hfx-36
Hfx-38
130g
125g
125g
125g
Fomix-Septum Lesion
Hfx-37
Hfx-39
115g
11Og
120g
11Og
none
+
none
Table 1. Subjects that underwent surgery were weighed before surgery,
but after pre-surgical behavioral testing, and again at the conclusion of the
experiment, after post-surgical behavioral testing. *Hfx-10 did not
undergo pre-surgical behavioral testing.
51
5
Conclusion
All in-cage behaviors were significantly altered by the fornix lesions. Significant
alterations were also observed in the foraging, exploratory, activity level, and grooming
behaviors of the Syrian hamster, but not in the novelty response behavior. Of the
behaviors examined, those dealing with cage maintenance and activity, as well as the
behaviors dealing with food acquisition and consumption, were the most affected by the
lesion of the fornix fiber bundles.
Fornix-lesioned subjects displayed drastic shifting of in-cage activity from the
"underground" den region of the experimental cages to the "above-ground" front region.
Furthermore fornix-lesion groups also showed reduction of the number of nests built, as
well as the lack or drastic reduction in the number of food hoards maintained. These
results are consistent with the deficits in nest building and hoarding obtained by Shipley
and Kolb (1977) and Siegel (1985) in their observation of septal-lesioned hamsters,
although these deficits were observed with fornix-column lesion hamsters as well in this
study. Although the cause of these results are not entirely clear, a reduction in the level
of motivation of the lesioned subjects would be in agreement with Borer et al. (1985)
documented decrease in the in-cage wheel-running activity of hippocampal lesioned
Syrian Golden hamsters, which Borer et aL (1985) also concluded was due to a reduced
motivation to run and not to motor impairment nor lack of food.
All fornix lesioned groups on average pouched food pellets much less consistently
than the control groups. Instead, the fornix lesion groups were found to be significantly
more likely to eat the food pellets out in the open Arena rather than pouch and hoard
them in their cages. These results are consistent with foraging behavior deficits
documented in rats with hippocampal lesion (Osborne and Dodek, 1986) and with septal
lesion (Brodal, 1998). Fornix-lesion subjects were consistently unwilling to pouch,
although they had no motor impairment hindering them. They were also observed to
occasionally fall asleep while feeding on a food pellet in one of the foraging station in the
exposed Arena. Although they could smell the food pellets in the other foraging stations,
fornix-lesioned hamsters explored significantly fewer numbers of foraging stations than
their control counterparts.
The activity levels of the fornix lesion groups, while in the Arena, indicated that
overall these subjects were hypoactive compared to the control subjects. Although there
were insistances when fornix-lesioned subjects displayed hyperactivity, overall their
activity level remained relatively unchanged throughout the day and was consistently
low. These results are somewhat consistent with those obtained using Syrian hamsters
with hippocampal and septal damage by Borer et al. (1979a and 1983a, respectively), but
they disagree with Whishaw et aL. (1994) finding that rats with damage to the
hippocampal formation, in open-field, were consistently hyperactive. This disagreement
might however simply be due to species difference. Once again the higher activity level
observed for the fornix-column lesion subjects was probably due to some sparing of the
post-commissural fornix fibers in one or two of the subjects, Hfx-24 and Hfx-26.
52
Increase in weight would have been predicted with the hypoactivity of the fornixlesion subjects and was indeed observed by Borer et al. using hippocampal-damaged
hamsters (1979a) and septal damaged hamsters (1983a). However, in this study no such
change in weight was observed. One possible reason might be that in this study each
subject was given a fixed minimum of two food pellets a day and thus did not have
access to unlimited amount of food. Furthermore, fomix-lesion subjects did not pouch
and hoard the eight additional food pellets in the foraging stations, which they could then
consume at a later time. Normal hamsters, maintained at two pellets a day, displayed
normal activity patterns, so lack of additional food consumption was not the cause of the
hypoactivity. The results obtained for Syrian hamster response to novelty was also
inconclusive, since almost 1/3 of the subjects, both control and fornix lesion, entered the
Novelty Area less than twice.
The lack of statistical difference between the controls and the fornix-lesion
subjects in their in-cage grooming behavior was probably due to the under-representation
of the number of times that each subject actually groomed because of visual obstruction
and inaccessibility posed by the experimental setup. This is likely to be true because
statistical differences were found in grooming behavior out-side of the cage. It is
uncertain what the significance of the increase in length of grooming by fornix-lesion
subjects might indicate. One possibility is that while the fornix-lesion subjects were in
the Arena, they experienced higher levels of anxiety and conflicting emotions over
foraging for food pellets, exploring the Arena, or just doing nothing. They often did the
latter. This conclusion is not too different from Osborne and Dodek's (1986) hypothesis
that fornix lesions disrupt the sequencing of behaviors involved in foraging, eating and
drinking. Osborne and Dodek's hypothesis is discussed further in the Discussion Section.
Once again, the lack of difference between the fornix-column group and the control
subjects in grooming was probably due to some sparing of the post-commissural fornix
fibers.
53
6
Discussion
All the behaviors analyzed in this study involved instinctual responses, not visuospatial learning tasks. Surgery was done to some of the subjects after they had been
familiarized with the SNH, thus the results obtained could not have been due to a simple
spatial learning deficit. The possibility of the results being due to either anterograde or
retrograde amnesia is also unlikely since the fornix-lesion subjects seemed to remember
the location of the few foraging stations they did forage, but were not motivated enough
to explore further for additional foraging stations. Likewise, behaviors such as activity
level would be predicted to increase, not decrease, if the behavioral deficits exhibited
were solely due to amnesia. Increase in food consumption, shown by some studies to
occur after hippocampal or fornix lesions (Borer et al., 1979a; Osborne and Dodek, 1986)
might account for the lack of hoarding, but it cannot adequately account for the other
abnormal foraging behaviors displayed by the fornix-lesion subjects. For instance, why
did fornix-lesion subjects not first pouch the food pellets, carry them to the safety of their
cage, and then consume the food? Furthermore, fornix-lesion subjects did not show an
increase in weight after undergoing the surgery, which would be expected with increased
food consumption.
Although disruption of the circadian rhythms controlling food consumption and
activity level, as a possible explanation of some of the deficits demonstrated by the
fornix-lesion subjects, cannot be completely ruled out by the results obtained in this
study, it does not adequately explain the deficit in nesting building or the abnormal
disorganization of their living quarter. Neither of these in-cage behaviors have been
documented to be entrained by an internal biological clock mechanism. Furthermore,
disruption of the circadian rhythms cannot explain the difference between the fornixlesion subjects and controls in the length of their grooming, a behavior not entrained by
an internal biological clock..
Osborne and Dodek's (1986) hypothesized that the behavioral deficits displayed
by the fornix-lesion subjects were the result of disrupted micro-regulation of the
sequences of behaviors involved in foraging, eating, drinking, etc. Thus fornix fiber
bundles carry information used in determining which behavior in a sequence is
appropriate for a given situation and the continuation of this sequence to its natural
termination. This hypothesis would offer a possible explanation for the results obtained
for grooming, but would not explain or predict the overall hypoactivity of fornix-lesioned
subjects, unless the micro-regulator is assumed to be the motivational level of the animal.
Since the fornix is a component of Papez circuit, it is likely that disruption
of the fornix would alter either the expression or the experience of emotional states.
Lesions of another component of Papez circuit, the septum, has been demonstrated in
other studies to alter emotional and behavioral responses (Brodal, 1998), as well as
foraging behavioral deficits, like those displayed by the fornix-lesion subjects (Borer et
al. 1977, 1979b; Potegal et al. 1981 a). According to Borer et al. (1985) the difference
between septohypothalamic tract lesion hamsters and neurologically intact hamsters was
54
reduced motivation. A reduction in the level of motivation of fornix-lesioned subjects
would not only account for the deficits in foraging behavior, but would also predict the
hypoactivity, deficit in nest building behavior and poorer quality of the nests, as well as
to some degree the higher mortality rate exhibited by the fornix-lesion groups. Many of
the results obtained in this study support this hypothesis. We speculate that the fornix
fiber bundles carry information essential for the hypothalamus, the center for emotional
expression, to properly coordinate emotions necessary for the survival of the hamster.
This study was unable to determine which of the fornix trajectories to the hypothalamus
was the most crucial for this process.
55
7
Future Work
There are portions of this study which were not completed and need to be in order
to better understand the importance and consequences of the results obtained. One such
portion is the determination of the extent of the neuroanatomical damage caused by the
fomix lesion surgeries. Furthermore, it must also be determined if there is sparing of
post-commissural fibers in the fornix-column lesion subjects, Hfx-24 and Hfx-26, and
whether the sparing can account for the discrepancies in the results obtained for the
fornix-column subjects and the other fornix-lesion groups. Analysis of the
neuroanatomical structures will require histological staining, using cresyl violet and loyez
myelin stains, of all the hamster brains sectioned in this study and a thorough
reconstruction of the brain slices. Documentation of scent marking and other behavioral
results obtained during this study must also be analyzed to determine whether these
behaviors are also altered by the lesioning of the fornix fiber bundles.
A new paradigm needs to be devised to more accurately determine and quantify
differences in the response of fornix-lesion and normal Syrian Golden hamsters to novel
objects and environments. The response of these two groups to predatory or aggressive
cues might also be of interest, given that some studies have reported decreased fear and
increased levels of aggression (Shipley and Kolb, 1977; Siegel, 1985). The experiments
conducted in this study might also be repeated using male Syrian Golden hamsters to
determine whether sexual dimorphic differences exist in the functioning of fornix-fibers.
Attempts might also be made to recover the normal behaviors by regenerating the severed
fomix axonal fibers, via peripheral nerve grafts. Functional recovery of normal behaviors
by fornix lesion animals would be a good indication of the effectiveness of various CNS
regenerative techniques.
56
References
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
Ackroff, K. and A. Sclafani, Flavorpreferences conditionedby sugars:rats learn
to prefer glucose overfructose. Physiol Behav, 1991. 50(4): p. 815-24.
Alantar, A., et al., Potentiationoffentanyl suppressionof the jaw-opening reflex
by transcranialelectricalstimulation. Brain Res, 1997. 763(1): p. 14-20.
Ammassari-Teule, M. and C. Maho, Choice behavior offornix-damagedrats in
radialmaze error-freesituationsand subsequent learning.Physiol Behav, 1992.
51(3): p. 563-7.
Anderson, S. and Jones, J., Jr., Order and Families ofRecent Mammals
ofthe World. 1984. Wiley, New York.
Appenrodt, E. and H. Schwarzberg, Septal vasopressin modulates motility and
passive avoidance inpinealectomizedrats. Physiol Behav, 1999. 66(5): p. 757-61.
Asher, R.J., Morphologicaldiversity of anatomicalstrepsirrhinismand the
evolution of the lemuriform toothcomb. Am J Phys Anthropol, 1998. 105(3): p.
355-67.
Baldi, B., et al., Effects of combined medial septal area,fimbria-fornix and
entorhinalcortex tetrodotoxin inactivationson passive avoidance response
consolidationin the rat.Brain Res, 1999. 821(2): p. 503-10.
Balse, E., et al., Intrahippocampalgrafts containingcholinergicand serotonergic
fetal neurons amelioratespatialreference but not working memory in rats with
fimbria-fornix/cingularbundle lesions. Brain Res Bull, 1999. 49(4): p. 263-72.
Bartness, T.J., N.F. Ruby, and G.N. Wade, Dietaryobesity in exercisingor coldexposed Syrian hamsters. Physiol Behav, 1984. 32(1): p. 85-90.
Bauman, T.R., R.R. Anderson, and C.W. Turner, Thyroid hormone secretion rates
andfood consumption of the hamster (Mesocricetusauratus)at 25.5 degree and
4.5 degree C. Gen Comp Endocrinol, 1968. 10(1): p. 92-8.
Bear, M.F,, Connors, B.W., Paradiso, M.A., (Eds.) Neuroscience
Exploringthe Brain. 1996. Academic Press, Boston.
Bernardis, L.L. and L.A. Frohman, Effects ofhypothalamic lesions at different
loci on development of hyperinsulinemiaand obesity in the weanling rat. J Comp
Neurol, 1971. 141(1): p. 107-15.
Billingham, R. and Silvers, W. (1963). Skin transplants and the hamster. Sci.
Am. 208, 118-127.
Borer, K.T., Absence of weight regulation in exercising hamsters. Physiol Behav,
1974. 12(4): p. 589-97.
Borer, K.T., et al., The role ofthe septal area in the neuroendocrinecontrol of
growth in the adult golden hamster. Neuroendocrinology, 1977. 23(3): p. 133-50.
Borer, K.T., et al., Increasedserum growth hormone and somatic growth in adult
hamsters with hippocampaltransections.Neuroendocrinology, 1979a. 29(1): p.
22-33.
Borer, K.T., et al., Contributionof growth,fatness, andactivity to weight
disturbanceafter septohypothalamiccuts in adult hamsters. J Comp Physiol
Psychol, 1979b. 93(5): p. 907-18.
57
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
Borer, K.T., et al., Physiologicaland behavioralresponses to starvationin the
golden hamster. Am J Physiol, 1979b. 236(2): p. E105-12.
Borer, K.T., M.E. Trulson, and L.R. Kuhns, Role oflimbic system in the control of
hamster growth. Brain Res Bull, 1979a. 4(2): p. 239-47.
Borer, K.T., C.D. Potter, and N. Fileccia, Basisfor the hypoactivity that
accompanies rapidweight gain in hamsters. Physiol Behav, 1983c. 30(3): p. 38997.
Borer, K.T., et al., Exercise reversesphotoperiodicanestrusin golden hamsters.
Biol Reprod, 1983b. 29(1): p. 38-47.
Borer, K.T., B. Shapiro, and A.I. Vinik, A rolefor somatostatinin the control of
hamster growth. Brain Res Bull, 1983a. 11(6): p. 663-9.
Borer, K.T., et al., Recoveryfrom energy deficit in golden hamsters. Am J
Physiol, 1985. 248(4 Pt 2): p. R439-46.
Borer, K.T., Regulation of Energy Balance in the Golden Hamster. The
Hamster: Reproduction and Behavior, 1985. pp. 3-19. H.I. Siegel (Ed.). Plenum
Press, New York.
Bouton, M.E., Context, time, andmemory retrievalin the interferenceparadigms
ofPavlovian learning.Psychol Bull, 1993. 114(1): p. 80-99.
Brandner, C. and F. Schenk, Septal lesions impairthe acquisitionof a cued place
navigation task: attentionalor memory deficit? Neurobiol Learn Mem, 1998.
69(2): p. 106-25.
Brito, G.N. and G.J. Thomas, T-maze alternation,responsepatterning,and septohippocampalcircuitryin rats. Behav Brain Res, 1981. 3(3): p. 319-40.
Brito, G.N. and L.S. Brito, Lesions in the septo-hippocampalsystem orprelimbic
cortex ofrats do not alter the performance of a T-maze visual discriminationtask
but disruptthe performance of a T-maze alternationtask Braz J Med Biol Res,
1987. 20(3-4): p. 461-5.
Brito, G.N. and L.S. Brito, Septohippocampalsystem and the prelimbicsector of
frontal cortex: a neuropsychologicalbattery analysis in the rat.Behav Brain Res,
1990. 36(1-2): p. 127-46.
Brodal, A., The Olfactory Pathway. The Amygdala. The Hippocampus. The
"Limbic System ". Neurological Anatomy: In Relation to Clinical Medicine (3 rd
Ed.), 1981. pp. 640-697. Oxford University Press, New York.
Brodal, A., The Autonomic Nervous System. The Hypothalamus. Neurological
Anatomy: In Relation to Clinical Medicine (3 rd Ed.), 1981. pp. 698-787. Oxford
University Press, New York
Brodal, P., The Cerebral Cortex and Limbic Structures. The Central Nervous
System: Structure and Function (2 nd Ed.), 1998. pp. 553-620. Oxford University
Press, New York.
Brooks, A.I., et al., Repeated acquisitionandperformance chamberfor mice: a
paradigmfor assessment of spatiallearningand memory. Neurobiol Learn Mem,
2000. 74(3): p. 241-58.
Buhusi, C.V. and N.A. Schmajuk, Attention, configuration,and hippocampal
function. Hippocampus, 1996. 6(6): p. 621-42.
Bunnell, B.N., F.J. Sodetz, Jr., and D.I. Shalloway, Amygdaloid lesions and social
behavior in the golden hamster.Physiol Behav, 1970. 5(2): p. 153-61.
58
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
49.
50.
51.
Burton, S., et al., Combined lesions of hippocampus and subiculum Do not
produce deficits in a nonspatialsocial olfactory memory task J Neurosci, 2000.
20(14): p. 5468-75.
Bussey, T.J., et al., Distinctpatterns of behaviouralimpairmentsresultingfrom
fornix transectionor neurotoxic lesions ofthe perirhinalandpostrhinalcortices
in the rat. Behav Brain Res, 2000. 111(1-2): p. 187-202.
Buzsaki, G., et al., Spatial mapping, working memory, and thefimbria-fornix
system. J Comp Physiol Psychol, 1982. 96(1): p. 26-34.
Calabrese, P., et al., Fornix damage and memory. A case report.Cortex, 1995.
31(3): p. 555-64.
Canguilhem, B., et al., [Feedingbehavior, circannualbody weight and
hibernationrhythms in Europeanhamsters lesioned in the noradrenergic
ascendingbundles (author'stransl)]. Physiol Behav, 1977. 18(6): p. 1067-74.
Capone, F., et al., Oxotremorine-inducedmodifications of the behavioraland
neuroendocrineresponses toformalin pain in male rats. Brain Res, 1999. 830(2):
p. 292-300.
Cassaday, H.J., et al., 5,7-Dihydroxytryptaminelesions in thefornix-fimbria
attenuate latent inhibition.Behav Neural Biol, 1993. 59(3): p. 194-207.
Cassaday, H.J. and J.N. Rawlins, Fornix-fimbriasection and working memory
deficits in rats: stimulus complexity and stimulus size. Behav Neurosci, 1995.
109(4): p. 594-606.
Cassel, J.C., et al., The fimbria-fornix/cingularbundle pathways: a review of
neurochemicaland behaviouralapproachesusing lesions and transplantation
techniques. Prog Neurobiol, 1997. 51(6): p. 663-716.
Cassel, J.C., et al., Fimbria-fornixvs selective hippocampallesions in rats: effects
on locomotor activity and spatiallearningand memory. Neurobiol Learn Mem,
1998. 69(1): p. 22-45.
Chen, F. and A.J. Lawrence, Effect of chronic ethanol and withdrawalon the muopioidreceptor-and 5-Hydroxytryptamine(A) receptor-stimulatedbinding of
[(35)S]Guanosine-5'-O-(3-thio)triphosphatein the fawn-hooded rat brain:A
quantitative autoradiographystudy. J Pharmacol Exp Ther, 2000. 293(1): p. 15965.
Chozick, B.S., The behavioraleffects of lesions ofthe septum: a review. Int J
Neurosci, 1985. 26(3-4): p. 197-217.
Chudasama, Y. and J.L. Muir, A behaviouralanalysis of the delayed nonmatching to position task: the effects of scopolamine, lesions ofthe fornix andof
the prelimbic region on mediating behaviours by rats. Psychopharmacology
(Berl), 1997. 134(1): p. 73-82.
Clark, J.D., HistoricalPerspectivesand Taxonomy. Laboratory Hamsters, 1987.
pp. 3-10. G.L.V Hossier and C.W. McPherson (Eds.). Academic Press, Boston.
Clemens, L.G. and Witcher, J.A., Sexual Differentiationand Development. The
Hamster: Reproduction and Behavior, 1985. pp. 3-19. H.I. Siegel (Ed.). Plenum
Press, New York.
Collier, G.H., and Rovee-Collier, C.K., A comparativeanalysis ofoptimal
foraging behavior: Laboratorysimulation. Foraging Behavior, 1981. pp. 39-76.
A.C. Kamil and T.D. Sargent (Eds.). Garland STPM Press, New York.
59
52.
53.
54.
55.
56.
57.
58.
59.
60.
61.
62.
63.
64.
65.
66.
67.
68.
69.
Coolen, L.M. and R.I. Wood, Bidirectionalconnections of the medial amygdaloid
nucleus in the Syrian hamster brain: simultaneous anterogradeand retrograde
tract tracing.J Comp Neurol, 1998. 399(2): p. 189-209.
Coutureau, E., et al., Selective lesions of the entorhinalcortex, the hippocampus,
or thefimbria-fornix in rats: a comparison of effects on spontaneous and
amphetamine-inducedlocomotion. Exp Brain Res, 2000. 131(3): p. 381-92.
Dalrymple-Alford, J.C., Behavioraleffects of basalforebraingrafts after dorsal
septo- hippocampalpathway lesions. Brain Res, 1994. 661(1-2): p. 243-58.
Day, C.S.D. and Galef, B.G., Jr., Pup cannibalism: One aspect of maternal
behavior in golden hamsters. J. Comp. Psychol, 1977. 91: p. 1179-1189.
Decker, M.W., P. Curzon, and J.D. Brioni, Influence ofseparate and combined
septal and amygdala lesions on memory, acoustic startle, anxiety, and locomotor
activity in rats.Neurobiol Learn Mem, 1995. 64(2): p. 156-68.
Delbende, C., et al., [Role of alpha-MSHand relatedpeptides in the central
nervous system]. Rev Neurol, 1985. 141(6-7): p. 429-39.
Devinsky, 0., M.J. Morrell, and B.A. Vogt, Contributionsofanteriorcingulate
cortex to behaviour.Brain, 1995. 118(Pt 1): p. 279-306.
Devor, M. and G.E. Schneider, Attraction to home-cage odor in hamsterpups:
specificity andchanges with age. Behav Biol, 1974. 10(2): p. 211-21.
Dieterlen, F., Das Verhalten des syrischen Goldhamsters (Mesocricetusauratus
Waterhouse). Z. Tierpsychol., 1959. 16: p. 47-103.
Duncan, G.E., D.J. Knapp, and G.R. Breese, Neuroanatomicalcharacterizationof
Fos induction in rat behavioralmodels ofanxiety. Brain Res, 1996. 713(1-2): p.
79-91.
Ennaceur, A. and J.P. Aggleton, Spontaneous recognition ofobject configurations
in rats: effects offornix lesions. Exp Brain Res, 1994. 100(1): p. 85-92.
Ennaceur, A., N. Neave, and J.P. Aggleton, Spontaneous object recognition and
object location memory in rats: the effects of lesions in the cingulate cortices,the
medialprefrontal cortex, the cingulum bundle and the fornix. Exp Brain Res,
1997. 113(3): p. 509-19.
Flynn, F.W., et al., The relation offeeding and activityfollowing septal lesions in
rats. Behav Neurosci, 1986. 100(3): p. 416-21.
Francis, D.D., F.C. Champagne, and M.J. Meaney, Variationsin maternal
behaviourare associatedwith differences in oxytocin receptorlevels in the rat. J
Neuroendocrinol, 2000. 12(12): p. 1145-8.
Freeman, J.H., Jr., et al., Lesions of the entorhinalcortex disrupt behavioraland
neuronal responses to context change during extinction of discriminative
avoidance behavior. Exp Brain Res, 1997. 115(3): p. 445-57.
Freo, U., et al., Dose-dependent effects of buspirone on behavior and cerebral
glucose metabolism in rats. Brain Res, 1995. 677(2): p. 213-20.
Frost, P., et al., Biodynamic studies of hamsterflank organgrowth: hormonal
influences. J Invest Dermatol, 1973. 61(3): p. 159-67.
Fulton, G.P., The Golden Hamster in Biomedical Research. The Golden Hamster
its biology and use in medical research, 1968. pp.3-13. R.A. Hoffman, P.F.
Robinson, and H. Magalhaes (Eds.). The Iowa State University Press, Ames,
Iowa.
60
70.
71.
72.
73.
74.
75.
76.
77.
78.
79.
80.
81.
82.
83.
84.
85.
86.
Gabriel, M., et al., Mamillothalamictract transection blocks anteriorthalamic
training-induced neuronalplasticityand impairsdiscriminativeoffidance
behavior in rabbits. J Neurosci, 1995. 15(2): p. 1437-45.
Gaffan, D. and A. Parker, Interactionofperirhinalcortex with thefornix-fimbria:
memory for objects and "object-in-place"memory. J Neurosci, 1996. 16(18): p.
5864-9.
Gaffan, E.A. and M.J. Eacott, Spatial memory impairment in rats with fornix
transectionis not accompaniedby a simple encoding deficitfor directions of
objects in visual space. Behav Neurosci, 1997. 111(5): p. 937-54.
Garofalo, P., et al., CR 2249: a new putative memory enhancer.Behavioural
studies on learningand memory in rats and mice. J Pharm Pharmacol, 1996.
48(12): p. 1290-7.
Garritano, J., et al., The output of the hippocampus is inhibited duringsocial
behavior in the male rat.Exp Brain Res, 1996. 111(1): p. 35-40.
Georges, F. and G. Aston-Jones, Potentregulation of midbrain dopamine neurons
by the bed nucleus ofthe stria terminalis.J Neurosci, 2001. 21(16): p. RC160.
Gluck, M.A. and C.E, Myers, Integratingbehavioralandphysiologicalmodels of
hippocampalfunction.Hippocampus, 1996. 6(6): p. 643-53.
Goldman, L. and H. Swanson, Populationcontrol in confined colonies ofgolden
hamsters (Mesocricetusauratus Waterhouse). Z Tierpsychol, 1975. 37(3): p. 22536.
Goldman, L. and H.H. Swanson, Developmental changes in pre-adultbehavior in
confined colonies ofgolden hamsters. Dev Psychobiol, 1975. 8(2): p. 137-50.
Granneman, J.G. and G.N. Wade, Effects ofphotoperiodand castrationon postfastfood intake and body weight gain in golden hamsters.Physiol Behav, 1982.
28(5): p. 847-50.
Gray, T.S. and J.E. Morley, Neuropeptide Y: anatomicaldistributionandpossible
function in mammalian nervous system. Life Sci, 1986. 38(5): p. 389-401.
Greenough, W.T., et al., Sex differences in dentriticpatterns in hamsterpreoptic
area.Brain Res, 1977. 126(1): p. 63-72.
Harper, D.N., A.P. McLean, and J.C. Dalrymple-Alford, Forgettingin rats
following medial septum or mammillary body damage. Behav Neurosci, 1994.
108(4): p. 691-702.
Hart, M., A. Poremba, and M. Gabriel, The nomadic engram: overtraining
eliminates the impairment of discriminativeavoidance behaviorproduced by
limbic thalamic lesions. Behav Brain Res, 1997. 82(2): p. 169-77.
Hofferer, E., et al., A comparisonof behaviouraleffects and morphological
features of grafts rich in cholinergicneurons placed in two sites ofthe denervated
rat hippocampus.Exp Brain Res, 1996. 111(2): p. 187-207.
Hoffman, R.A., Robinson, P.F., and Magalhaes, H. (Eds.), The Golden Hamster
its biology and use in medical research. 1968. The Iowa State University Press,
Ames, Iowa.
Hoffman, R.A., K. Davidson, and K. Steinberg, Influence ofphotoperiodand
temperatureon weight gain,food consumption,fat pads and thyroxine in male
golden hamsters. Growth, 1982. 46(2): p. 150-62.
61
87.
88.
89.
90.
91.
92.
93.
94.
95.
96.
97.
98.
99.
100.
101.
102.
103.
104.
105.
Honacki, J., Kinman, K., and Koeppl, J., Mammal Species of the World. 1982.
Allen Press, Inc. and The Assoc. of Systematic Collections, Lawrence, Kansas.
Homer, P.J. and F.H. Gage, Regeneratingthe damagedcentral nervous system.
Nature, 2000. 407(6807): p. 963-70.
Insel, T.R. and L.E. Shapiro, Oxytocin receptordistributionreflects social
organizationin monogamous andpolygamous voles. Proc Natl Acad Sci U S A,
1992. 89(13): p. 5981-5.
Irvin, R.W., et al., Vasopressin in the septal areaof the golden hamster controls
scent marking and grooming. Physiol Behav, 1990. 48(5): p. 693-9.
Janis, L.S., T.W. Bishop, and G.L. Dunbar, Medial septal lesions in ratsproduce
permanent deficitsfor strategy selection in a spatialmemory task Behav
Neurosci, 1994. 108(5): p. 892-8.
Janzen, W.B. and B.N. Bunnell, Septal lesions and the recovery offunction in the
juvenile hamster. Physiol Behav, 1976. 16(4): p. 445-52.
Jeltsch, H., et al., The effects of intrahippocampalraphe and/orseptal grafts in
rats withfimbria-fornixlesions depend on the origin ofthe grafted tissue andthe
behaviouraltask used Neuroscience, 1994. 63(1): p. 19-39.
Johnston, R.E., Scent marking by male Golden Hamsters (Mesocricetusauratus)
III. Behavior in a seminaturalenvironment. Z Tierpsychol, 1975. 37(2): p. 21321.
Johnston, R.E., Scent marking by male golden hamsters (Mesocricetusauratus).
II The role of the flank gland scent in the causation of marking. Z Tierpsychol,
1975. 37(2): p. 138-44.
Johnston, R.E., Scent marking by male golden hamsters (Mesocricetusauratus)I.
Effects ofodors and social encounters. Z Tierpsychol, 1975. 37(1): p. 75-98.
Johnston, R.E. and T. Schmidt, Responses ofhamsters to scent marks ofdifferent
ages. Behav Neural Biol, 1979. 26(1): p. 64-75.
Johnston, R.E., Communication. The Hamster: Reproduction and Behavior,
1985. pp. 3-19. H.I. Siegel (Ed.). Plenum Press, New York.
Kalil, K. and G.E. Schneider, Retrograde corticalaandaxonal changesfollowing
lesions ofthe pyramidal tract. Brain Res, 1975. 89(1): p. 15-27.
Kelsey, J.E. and S.P. Grossman, Influence of central cholinergicpathways on
performance on free- operantavoidance and DRL schedules. Pharmacol Biochem
Behav, 1975. 3(6): p. 1043-50.
Kelsey, J.E. and H. Vargas, Medial septal lesions disruptspatial,but not
nonspatial,working memory in rats. Behav Neurosci, 1993. 107(4): p. 565-74.
Kempermann, G. and F.H. Gage, New nerve cellsfor the adult brain. Sci Am,
1999. 280(5): p. 48-53.
Kirkpatrick, B., J.W. Kim, and T.R. Insel, Limbic systemfos expression
associatedwith paternalbehavior. Brain Res, 1994. 658(1-2): p. 112-8.
Kordower, J.H. and M.S. Fiandaca, Response ofthe monkey cholinergic
septohippocampalsystem tofornix transection: a histochemicaland cytochemical
analysis.J Comp Neurol, 1990.298(4): p. 443-57.
Kornecook, T.J., T.E. Kippin, and J.P. Pinel, Basalforebraindamage and objectrecognitionin rats. Behav Brain Res, 1999. 98(1): p. 67-76.
62
106.
107.
108.
109.
110.
111.
112.
113.
114.
115.
116.
117.
118.
119.
120.
121.
Kumar, S. and S.K. Kulkarni, Influence of antidepressantdrugs on learningand
memory paradigmsin mice. Indian J Exp Biol, 1996. 34(5): p. 431-5.
Kyrkouli, S.E., B.G. Stanley, and S.F. Leibowitz, Bombesin-inducedanorexia:
sites ofaction in the rat brain.Peptides, 1987. 8(2): p. 237-41.
Laurent-Demir, C. and R. Jaffard, Paradoxicalfacilitatoryeffect offornix lesions
on acquisitionof contextualfear conditioningin mice. Behav Brain Res, 2000.
107(1-2): p. 85-91.
Le Moal, M. and B. Cardo, Rhythmic slow wave activity recorded in the ventral
mesencephalic tegmentum in the rat.Electroencephalogr Clin Neurophysiol,
1975. 38(2): p. 139-47.
Leutgeb, S. and S.J. Mizumori, Excitotoxic septal lesions result in spatialmemory
deficits and alteredflexibilityof hippocampalsingle-unitrepresentations.J
Neurosci, 1999. 19(15): p. 6661-72.
Lonstein, J.S., et al., Forebrainexpression of c-fos due to active maternal
behaviour in lactatingrats.Neuroscience, 1998. 82(1): p. 267-8 1.
Lowndes, M. and D.C. Davies, The effect ofarchistriatallesions on 'openfield'
andfear/avoidancebehaviour in the domestic chick. Behav Brain Res, 1995.
72(1-2): p. 25-32.
M'Harzi, M., et al., Effects ofselective lesions offimbria-fornix on learningset in
the rat. Physiol Behav, 1987. 40(2): p. 181-8.
M'Harzi, M. and L.E. Jarrard, Strategyselection in a task with spatialand
nonspatialcomponents: effects offimbria-fornix lesions in rats. Behav Neural
Biol, 1992. 58(3): p. 171-9.
Maeda, N., N. Matsuoka, and I. Yamaguchi, Septohippocampalcholinergic
pathway andpenile erections induced by dopaminergicand cholinergic
stimulants. Brain Res, 1990. 537(1-2): p. 163-8.
Maeda, N., N. Matsuoka, and I. Yamaguchi, Role ofthe dopaminergic,
serotonergicand cholinergic link in the expression ofpenile erection in rats.Jpn J
Pharmacol, 1994. 66(1): p. 59-66.
Maeda, N., N. Matsuoka, and I. Yamaguchi, Possible involvement of the septohippocampalcholinergicand raphe-hippocampalserotonergicactivationsin the
penile erection induced byfenfluramine in rats. Brain Res, 1994. 652(2): p. 1819.
Maeda, N., et al., Involvement of raphe-hippocampalserotonergicand septohippocampalcholinergicmechanisms in the penile erection induced by
FR121196, aputative cognitive enhancer.Jpn J Pharmacol, 1995. 68(1): p. 85-94.
Malan, A. and G. Hildwein, [Thermoregulationin ambiant heat ofa hibernant,
the European hamster (Cricetuscricetus). Comparisonwith the white rat].Arch
Sci Physiol, 1969. 23(2): p. 153-81.
Malsbury, C.W., L.M. Kow, and D.W. Pfaff, Effects ofmedial hypothalamic
lesions on the lordosis response and other behaviors in remale golden hamsters.
Physiol Behav, 1977. 19(2): p. 223-37.
Malsbury, C.W., D. Strull, and J. Daood, Half-cylinder cuts antero-lateralto the
ventromedialnucleus reduce sexual receptivity in female golden hamsters.
Physiol Behav, 1978. 21(1): p. 79-87.
63
122.
123.
124.
125.
126.
127.
128.
129.
130.
131.
132.
133.
134.
135.
136.
137.
138.
139.
140.
Malsbury, C.W., D.M. Marques, and J.T. Daood, Sagittal knife cuts in the farlateralhypothalamus reduce sexual receptivity infemale hamsters. Brain Res
Bull, 1979. 4(6): p. 833-42.
Maren, S. and M.S. Fanselow, Electrolytic lesions ofthe fimbria/fornix, dorsal
hippocampus, or entorhinalcortex produce anterogradedeficits in contextual
fear conditioningin rats.Neurobiol Learn Mem, 1997. 67(2): p. 142-9.
Maren, S., Long-term potentiationin the amygdala: a mechanismfor emotional
learningandmemory. Trends Neurosci, 1999. 22(12): p. 561-7.
McHugh, T.J., Blum K.I., Tsien, J.Z., Tonegawa, S., and Wilson, M.A., Impaired
hippocampalrepresentationof space in CAI-specific NMDARJ knockout mice.
Cell, 1996. 87(7): p. 1147-8.
Mehta, M.R., Quirk, M.C., and Wilson, M.A., Experience-dependentasymmetric
shape of hippocampalreceptivefields. Neuron, 2000. 25(3): p. 504-6.
Mesulam, M., Brain, mind, and the evolution of connectivity. Brain Cogn, 2000.
42(1): p. 4-6.
Morin, L.P., BiologicalRhythms. The Hamster: Reproduction and Behavior,
1985. pp. 3-19. H.I. Siegel (Ed.). Plenum Press, New York.
Morin, L.P. and Wood, R.I. A StereotaxicAtlas of The Golden Hamster Brain.
2000. Academic Press, Boston.
Murphy, M.R., History of the Captureand Domesticationof the Syrian Golden
Hamster (Mesocricetusauratus Waterhouse). The Hamster: Reproduction and
Behavior, 1985. pp. 3-19. H.I. Siegel (Ed.). Plenum Press, New York.
Nauta, W.J.H. and Feirtag, M., Anatomical Divisions. Fundamental
Neuroanatomy, 1986. pp. 39-49. Freeman, New York.
Nauta, W.J.H. and Feirtag, M., Affect and Motivation; The Limbic System.
Fundamental Neuroanatomy, 1986. pp. 120-131. Freeman, New York.
Neill, D.B., J.F. Ross, and S.P. Grossman, Comparison ofthe effects offrontal,
striatal,and septal lesions in paradigms thought to measure incentive motivation
or behavioral inhibition.Physiol Behav, 1974. 13(2): p. 297-305.
Northmore, D.P., Levine, E.S., and G.E. Schneider, Behavior evoked by electrical
stimulation ofthe hamster superiorcolliculus. Exp Brain Res, 1988. 73(3): p.
595-605.
Nosofsky, R.M., Choice, similarity, and the context theory of classification.J Exp
Psychol Learn Mem Cogn, 1984. 10(1): p. 104-14.
Nowak, R.M., and Paradiso, J.L., Walker's Mammals ofthe World 4* ed. 1983.
Johns Hopkins Univ. Press, Baltimore, Maryland.
Osborne, B. and A.B. Dodek, Disruptedpatternsofconsummatory behavior in
rats withfornix transections.Behav Neural Biol, 1986. 45(2): p. 212-22.
Osborne, B. and L.A. Flashman, Mealpatternsfollowingchanges in procurement
costfor rats with fornix transection.Behav Neural Biol, 1986. 46(2): p. 123-36.
Peinado-Manzano, M.A., The role of the amygdala and the hippocampusin
working memory for spatialand non-spatialinformation. Behav Brain Res, 1990.
38(2): p. 117-34.
Piazza, P.V. and M. Le Moal, The role ofstress in drug self-administration.
Trends Pharmacol Sci, 1998. 19(2): p. 67-74.
64
141.
142.
143.
144.
145.
146.
147.
148.
149.
150.
151.
152.
153.
154.
155.
156.
157.
158.
Polsky, R.H., Conspecific defeat, isolation/grouping,andpredatorybehavior in
golden hamsters. Psychol Rep, 1976. 38(2): p. 571-7.
Popik, P. and J.M. van Ree, Neurohypophysealpeptides and social recognitionin
rats. Prog Brain Res, 1998. 119: p. 415-36.
Poplawsky, A. and R.L. Isaacson, Changes in open-field behaviorsfollowing
septal lesions in rats.Behav Neural Biol, 1983. 38(1): p. 61-9.
Poremba, A. and M. Gabriel, Amygdala neurons mediate acquisitionbut not
maintenanceof instrumentalavoidance behavior in rabbits.J Neurosci, 1999.
19(21): p. 9635-41.
Poucet, B. and T. Herrmann, Septum and medialfrontal cortex contributionto
spatialproblem- solving. Behav Brain Res, 1990. 37(3): p. 269-80.
Pouzet, B., et al., The effects ofradiofrequency lesion or transectionof the
fimbria-fornix on latent inhibition in the rat.Neuroscience, 1999. 91(4): p. 135568.
Purves, D., Augustine, G.J., Fitzpatrick, D., Katz, L.C., LaMantia, A.S.,
McNamara, J.O., Ed., Neuroscience. 1997. Sinauer Associates, Inc.,
Sunderland, MA. .
Quillfeldt, J., et al., Biochemical and behavioraleffects of intraseptal
microinjectionoffasciculin, an irreversibleacetylcholinesteraseinhibitor. Braz J
Med Biol Res, 1991. 24(5): p. 499-507.
Rawlins, J.N., T.J. Maxwell, and J.D. Sinden, The effects offornix section on winstay/lose-shift andwin-shift/lose- stay performance in the rat. Behav Brain Res,
1988. 31(1): p. 17-28.
Richards, M.P.M., Effects of estrogen andprogesteroneon nest buildingin the
golden hamster. Anim. Behav, 1969. 17: p. 356-361.
Richards, M.P.M., Activity measured by running wheels and observationduring
the estrous cycle, pregnancy, andpseudopregnancy in the golden hamster. Anim.
Behav, 1966. 14: p. 450-458.
Roeling, T.A., et al., Efferent connections of the hypothalamic "groomingarea"in
the rat. Neuroscience, 1993. 56(1): p. 199-225.
Roeling, T.A., et al., Efferent connections ofthe hypothalamic "aggressionarea"
in the rat.Neuroscience, 1994. 59(4): p. 1001-24.
Roeser, C., J.C. Cassel, and C. Kelche, Behavioraleffects ofGM] ganglioside
treatment and intrahippocampalseptal grafts in rats withfimbria-fornix lesions.
Exp Brain Res, 1997. 115(3): p. 520-30.
Ross, J.F. and S.P. Grossman, Septal influences on operantresponding in the rat.
J Comp Physiol Psychol, 1975. 89(6): p. 523-36.
Rowland, N., Failureby deprivedhamsters to increasefood intake: some
behavioralandphysiologicaldeterminants.J Comp Physiol Psychol, 1982. 96(4):
p. 591-603.
Rowland, N., Physiologicaland behavioralresponses to glucoprivationin the
golden hamster.Physiol Behav, 1983. 30(5): p. 743-7.
Sandner, G., et al., What brain structuresare active during emotions? Effects of
brain stimulation elicitedaversion on c-fos immunoreactivityand behavior.
Behav Brain Res, 1993. 58(1-2): p. 9-18.
65
159.
160.
161.
162.
163.
164.
165.
166.
167.
168.
169.
170.
171.
172.
173.
174.
175.
176.
177.
Scheff, S.W., et al., Morris water maze deficits in ratsfollowingtraumaticbrain
injury: lateralcontrolledcortical impact. J Neurotrauma, 1997. 14(9): p. 615-27.
Schmajuk, N.A. and J.J. DiCarlo, Stimulus configuration,classicalconditioning,
and hippocampalfunction.Psychol Rev, 1992. 99(2): p. 268-305.
Schneider, G.E., Contrastingvisuomotorfunctions of tectum and cortex in the
golden hamster. Psychol Forsch, 1967.31(1): p. 52-62.
Schneider, G.E., Two visual systems. Science, 1969. 163(870): p. 895-902.
Schneider, G.E. (Unpublished). Four hours in the life of a Syrian Hamster.
Cambridge, MA.
Schoenfeld, T.A. and Leonard, C.M., BehavioralDevelopment in the Syrian
Golden Hamster.The Hamster: Reproduction and Behavior, 1985. pp. 3-19. H.I.
Siegel (Ed.). Plenum Press, New York.
Schwarting, R.K. and J.P. Huston, Behavioralconcomitantsofregional changes
in the brain's biogenic amines after apomorphineand amphetamine. Pharmacol
Biochem Behav, 1992. 41(4): p. 675-82.
Siegel, H.I., Aggressive Behavior. The Hamster: Reproduction and Behavior,
1985. pp. 3-19. H.I. Siegel (Ed.). Plenum Press, New York.
Siegel, H.I., ParentalBehavior. The Hamster: Reproduction and Behavior, 1985.
pp. 3-19. H.I. Siegel (Ed.). Plenum Press, New York.
Sodetz, F.J. and B.N. Bunnell, Septal ablation and the social behaviorofthe
golden hamster.Physiol Behav, 1970. 5(1): p. 79-88.
Sutherland, R.J. and A.J. Rodriguez, The role ofthefornix/fimbriaand some
relatedsubcorticalstructures in place learningand memory. Behav Brain Res,
1989. 32(3): p. 265-77.
Swanson, L.W., The anatomicalorganizationof septo-hippocampalprojections.
Ciba Found Symp, 1977. 58: p. 25-48.
Swanson, L.W. and W.M. Cowan, An autoradiographicstudy ofthe organization
of the efferent connections ofthe hippocampalformation in the rat. J Comp
Neurol, 1977. 172(1): p. 49-84.
Swanson, L.W. and R.W. Lind, Neuralprojectionssubserving the initiationofa
specific motivated behavior in the rat: new projectionsfrom the subfornical
organ. Brain Res, 1986. 379(2): p. 399-403.
Taylor, G., et al., Adult ontogeny of rat working memory of social interactions.J
Gerontol A Biol Sci Med Sci, 1999. 54(3): p. M145-51.
Tejani-Butt, S.M., W.P. Pare, and J. Yang, Effect ofrepeatednovel stressorson
depressive behavior and brain norepinephrinereceptorsystem in SpragueDawley and Wistar Kyoto (WKY) rats. Brain Res, 1994. 649(1-2): p. 27-35.
Thiel, C.M., J.P. Huston, and R.K. Schwarting, Hippocampalacetylcholine and
habituationlearning.Neuroscience, 1998. 85(4): p. 1253-62.
Thinus-Blanc, C., et al., The effects of reversible inactivationsofthe hippocampus
on exploratoryactivity and spatialmemory. Hippocampus, 1991. 1(4): p. 365-71.
Thomas, G.J. and P.S. Spafford, Deficitsfor representationalmemory inducedby
septal and corticallesions (singly and combined) in rats. Behav Neurosci, 1984.
98(3): p. 394-404.
66
178.
Thomas, G.J. and D.M. Gash, Differentialeffects ofposteriorseptal lesions on
dispositionaland representationalmemory. Behav Neurosci, 1986. 100(5): p.
712-9.
179. Treit, D. and C. Pesold, Septal lesions inhibitfear reactionsin two animal models
ofanxiolytic drug action. Physiol Behav, 1990. 47(2): p. 365-71.
180. Truong, D.D., et al., Glycine involvement in DDT-induced myoclonus. Mov
Disord, 1988. 3(1): p. 77-87.
181.
van Rijzingen, I.M., W.H. Gispen, and B.M. Spruijt, Postoperativeenvironmental
enrichment attenuatesfimbria-fornixlesion- induced impairments in Morris maze
performance.Neurobiol Learn Mem, 1997. 67(1): p. 21-8.
182. Vandenbergh, J.G., Effects ofgonadal hormones on theflank gland of the golden
hamster. Horm. Res., 1973. 4: p. 28-33.
183. Vandenbergh, J.G., Reproductive coordinationin the golden hamster: Female
influences on the male. Horm. Res., 1977. 9: p. 264-275.
184. Wade, G.N., Obesity without overeatingin golden hamsters. Physiol Behav,
1982. 29(4): p. 701-7.
185. Walker, J.A. and D.S. Olton, Spatial memory deficitfollowingfimbria-fornix
lesions: independent oftime for stimulus processing.Physiol Behav, 1979. 23(1):
p. 11-5.
186. Walker, J.A. and D.S. Olton, Fimbria-fornixlesions impair spatialworking
memory but not cognitive mapping.Behav Neurosci, 1984. 98(2): p. 226-42.
187. Wang, Z., C.F. Ferris, and G.J. De Vries, Role ofseptal vasopressin innervation
in paternalbehaviorin prairievoles (Microtusochrogaster).Proc Natl Acad Sci
U S A, 1994. 91(1): p. 400-4.
188. Warburton, E.C. and J.P. Aggleton, Differentialdeficits in the Morris water maze
following cytotoxic lesions of the anteriorthalamus andfornix transection.Behav
Brain Res, 1999. 98(1): p. 27-38.
189. Weiner, I., et al., Fimbria-fornixcut affects spontaneousactivity, two-way
avoidance and delayed non matching to sample, but not latent inhibition.Behav
Brain Res, 1998. 96(1-2): p. 59-70.
190. Whishaw, I.Q., et al., "Short-stops" in rats withfimbria-fornix lesions: evidence
for change in the mobility gradient.Hippocampus, 1994. 4(5): p. 577-82.
191.
Whishaw, I.Q. and J.A. Tomie, Rats withfimbria-fornix lesions can acquire and
retaina visual- tactile transwitching(configural)task Behav Neurosci, 1995.
109(4): p. 607-12.
192. Whishaw, I.Q. and J.A. Tomie, Pilotingand dead reckoning dissociatedby
fimbria-fornix lesions in a ratfoodcarryingtask Behav Brain Res, 1997. 89(1 2): p. 87-97.
193. Wible, C.G., J.R. Shiber, and D.S. Olton, Hippocampus,fimbria-fornix,
amygdala, and memory: object discriminationsin rats.Behav Neurosci, 1992.
106(5): p. 751-61.
194. Wiig, K.A., L.N. Cooper, and M.F. Bear, Temporally gradedretrogradeamnesia
following separateand combined lesions of the perirhinalcortex andfornix in the
rat. Learn Mem, 1996. 3(4): p. 313-25.
67
195.
196.
197.
198.
199.
200.
201.
202.
Wilensky, A.E., G.E. Schafe, and J.E. LeDoux, The amygdala modulates memory
consolidationoffear-motivated inhibitoryavoidance learningbut not classical
fear conditioning.J Neurosci, 2000. 20(18): p. 7059-66.
Wilson, M.A. and Tonegawa, S., Synapticplasticity,place cells and spatial
memory: study with second generationknockouts. Trends Neurosci, 1997. 20(3):
p. 102-6.
Yamazaki, M., et al., FK960 N-(4-acetyl-J-piperazinyl)-p-fluorobenzamide
monohydrate amelioratesthe memory deficits in rats through a novel mechanism
of action. J Pharmacol Exp Ther, 1996. 279(3): p. 1157-73.
Yerganian, G., History and cytogenetics ofhamsters. Prog Exp Tumor Res, 1972.
16: p. 2-34.
Yoganarasimha, D. and B.L. Meti, Amelioration offornix lesion induced learning
deficits by self-stimulation rewardingexperience. Brain Res, 1999. 845(2): p.
246-51.
Zafar, H.M., W.P. Pare, and S.M. Tejani-Butt, Effect ofacute or repeatedstress
on behaviorand brainnorepinephrinesystem in Wistar-Kyoto (WKY) rats. Brain
Res Bull, 1997. 44(3): p. 289-95.
Zucker, I., G.N. Wade, and R. Ziegler, Sexual and hormonal influences on eating,
taste preferences,and body weight ofhamsters. Physiol Behav, 1972. 8(1): p.
101-11.
Zucker, I. and F.K. Stephan, Light-dark rhythms in hamster eating, drinking and
locomotor behaviors. Physiol Behav, 1973. 11(2): p. 239-50.
68