Hormones and Behavior
Alison Bell
Animal Biology
University of Illinois
Today’s lecture
• Hormones
– What are they?
– Where are they made?
– What do they do?
• Hormones and behavior
– Organization-activation
• Relative plasticity hypothesis
– In utero and parental effects
– Challenge hypothesis
Hormones: What are they?
• Chemical substances, formed in a specialized
gland or group of cells, released into the blood
that affect target cells in another organ.
Distinct from:
•Neurotransmitters, substances
released by neurons that are
received by adjacent neurons &
alter their membrane potential.
•Pheromones, substances
released by an individual as scent
signals for another.
Hormones: What are they?
Testosterone
Chemically, they can be:
– Lipids (e.g. steroids such
as testosterone)
– Peptides/proteins (e.g.
vasopressin)
– Amines/other small
molecules (e.g.
epinephrine)
Hormones: Where are they made?
• Peripherally
– Endocrine glands, e.g. adrenal gland, thyroid
gland
– Gonads, e.g. testes, ovaries
• Centrally
– ‘Neurohormones’ are produced within the
brain, but travel to target via bloodstream
• e.g. hypothalamus, neurosteroidogenic cells
Hormones: What do they do?
Nonsteroid hormones: can’t enter cell
Steroid hormones: pass right through
• Many physiological effects: regulation of reproduction,
growth, osmotic balance, heart rate, etc.
• In the brain: influence neuronal responsiveness, or
activity of certain genes within the neuron, thus altering
the biochemistry of the brain to alter behavior
Hormone regulation:
Important vertebrate pathways
Hypothalamus-pituitary-gonad (HPG)
Hypothalamus-pituitary-adrenal (HPA)
Hormone regulation:
Synthesis and metabolism
Bells and whistles:
Receptors
Plasma binding proteins
Enzymes
How to study hormones?
• Remove the gland
• Add hormone
• Measure circulating levels
• Block receptor
Sexual Behavior: Females
• Estradiol and mice
– OVX mice: eliminates
female sexual
behavior (lordosis)
– Can be restored by
treatment with
estradiol followed by
progesterone
Estradiol
Sexual Behavior: Males
Red deer stag
– Sept/Oct become
aggressive, begin courting
females
– Testes generate sperm
and release testosterone
– Castrated males do not
fight or mate
– Testosterone implants
restore behavior
Hormones
If a male and female ring dove are
placed in a cage containing a bowl and
nesting material, and kept in simulated
spring, they will initiate the following
sequence:
bow and coo display, where the
male bows and coos to the female
select a nest site, marked by the
female sitting on it
build the nest – takes one week
copulate during nest building
female lays eggs, 2 eggs over 2
days
incubate the eggs – takes two weeks
the young hatch and the parents feed
the young by producing a “crop milk”
and regurgitating it for the young –
takes two weeks
initiate sequence again
Behavior
Role of progesterone…
Lehrman 1964
Important point
• Many shared
mechanisms, BUT
mechanisms often
differ between
species/groups
– Different selection
pressures result in
modifications of the
hormonal mechanisms
of behavior
Hunt et al 1995
Modes of Hormone Action
•
Activational effects
– Short-term, reversible effects that occur in the fully
developed organism (e.g. alteration of transmission
in neural networks that respond to certain aspects of
the environment)
•
Organizational effects
– Long-term, irreversible effects on tissue
differentiation and development (e.g. brain, ovary)
that can either directly (brain) or indirectly (ovary)
influence behavior
•
Critical or sensitive period
Activational Effect
• Oxytocin and maternal
behavior in mice
– Pre-maternal mice fear
pups and will attack them
– Oxytocin injections induce
maternal behavior
Another activational example
• Oxytocin and
maternal behavior in
sheep
– Stimulation of birth
canal during parturition
results in oxytocin
release in brain
– Oxytocin injections
cause non-pregnant
females to accept
alien lambs in 30
seconds!
Dolly the sheep and her
surrogate mom
Organizational Effect
Sexual differentiation via
exposure to steroids during
development
Figure 1. Sexual dimorphisms in the brain.
(a,b) The sexually dimorphic nucleus of the preoptic
area (SDN-POA) is larger in male rats (a) than in
females (b) because the testes secrete testosterone
during the perinatal sensitive period. After that time,
testosterone has little effect on SDN-POA volume.
(c,d) In contrast, the volume of the rat posterodorsal
medial amygdala (MePD), which is about 1.5 times
larger in males (c) than in females (d), retains its
responsiveness to testosterone throughout life. (e,f) In
zebra finches, the robustus archistriatum (RA) nucleus
is crucial for song production and has a greater volume
in males (e) than in females (f). Like the rat SDN-POA,
exposure to steroid hormones early in life is essential
for the RA to develop a masculine phenotype. For the
RA, however, the steroids may not originate from the
testes, but are rather synthesized locally in the brain
itself. SCN, suprachiasmatic nucleus; 3V, third
ventricle; ot, optic tract. All scale bars = 250 mum.
Morris et al 2004
Applying organization-activation theory to
alternative phenotypes
The relative plasticity hypothesis
Alternative phenotypes – within-sex
variation in phenotype (morphology,
behavior), e.g. sneakers vs territorial
males
Fixed: individual permanently,
irreversibly differentiated into one or
the other type and doesn’t change
phenotype during lifetime, e.g. satellite
vs territorial ruffs, hooknose or jack
salmon
Plastic: individual can change
phenotype, e.g. calling vs intercepting
frogs depending on local conditions
Moore et al 1998
The relative plasticity hypothesis
Moore et al 1998
Effects of exposure to hormones on
behavioral development
Mice and aggressiveness
– Subtle differences in the
hormonal environment
during embryonic
development influence
adult behavior
– E.g. Males: 2M more
aggressive later on.
– E.g. Females: 2M more
aggressive (correlated with
territory size as adults)
– Vom Saal et al
Another interesting way in
which developing embryos
are exposed to hormones…
Gil et al 1999, zebra finches
Females mated to
relatively attractive males
deposited more
testosterone in their eggs
compared to females
mated to unattractive
males
The differential allocation hypothesis (Burley 1988)
Testosterone in male birds
What explains the dynamics (change
over time) of T?
Costs of T
Aggression
T
Parental behavior
Level of behavior
The challenge
hypothesis
In species where males provide direct
parental care (feed the chicks), males
should increase T only when needed,
e.g. when challenged, but then return T
to level B. In contrast, in species where
males do not provide direct parental care
and spend most of their time defending
the territory, males should have high,
relatively unchanging, levels of T.
Wingfield et al 1990
Closer to home: hormones
and human behavior
Undoubtedly, hormones involved in
organizing and activating human sexual
behavior
What about unique human behaviors?
Testosterone and aggression
• Some studies find higher T
in CSF of aggressive males
– Meta-analysis of 45 studies:
weak, positive correlation
between T & aggressiveness
– May be more related to
“dominance”
– Serotonin may be more
important in aggression
• Ritualized aggression?
– Men experience a surge in T
after team/individual wins in
sports
– World Cup soccer fans show
increased T if their team wins