Mid-term Progress Report for Community of Scholars
Team researching Binge Eating in Laboratory Rats.
Binge eating is a disorder that affects many people, yet serious ethical issues
arise when scientists and physicians attempt to study its causes in human
subjects. Therefore, it is highly desirable to develop animal models to gain
an understanding of the mechanisms responsible for binge eating and to
experiment with treatments that can potentially be used on humans who
suffer from this eating disorder.
Binge eating often occurs after periods of self-restriction such as dieting.
When a dieter “breaks” her diet, she may consume abnormally large
amounts of food. Binge eating may also be a means by which persons
suffering from depression activate regions of the brain that are associated
with pleasure and/or reward. Relying again upon animal models, it may be
possible to understand the relationship between mood disorders such as
depression and binge eating by manipulating conditions in the laboratory
such that the symptoms of depression are experimentally induced in
laboratory animals and the effect of depression upon food intake can be
investigated.
This summer, two Wofford College Biology majors are developing an
animal model using laboratory rats to study the conditions that trigger binge
eating and the impact of stress upon feeding behaviors. Relying upon
previous reports that certain conditions of limited access to a highly
palatable food results in episodes of binge eating, Robynn Mackechnie is
conducting experiments on four groups of 10 laboratory rats each in which
the access to Froot Loops is carefully controlled every day for 28
consecutive days. Abundant research conducted in research courses at
Wofford College has shown that rats avidly consume Froot Loops (and yes,
this is the trademark spelling!) In our Community of Scholars 2007
research, the amount of rat chow and Froot Loops is carefully monitored
each day so that eating patterns can be observed. One of the four groups
(control) never gets Froot Loops. One group gets Froot Loops 2 hours per
day seven days a week (R7 on graphs at end of this document.) Another
group receives Froot Loops for 2 hours on Monday, Wednesday, and Fridays
(R3 on graphs.) A fourth group is provided Froot Loops on a carefully
planned irregular schedule (I on graphs.) On day 14 half way through the
scheduled experiments, Robynn’s experimental rats are providing some
unanticipated results. Unlike previous studies in which rats binge eat on a
high fat food, it seems that her lab rats are regulating their caloric intake at
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about 100 kcal per day. On days when Froot Loops are available, they eat a
combination of chow and Froot Loops that totals 100 kcal. On days when
deprived of Froot Loops, Robynn’s rats consume the same reduced amount
of rat chow such that overall energy intake is decreased. These results were
not predicted based on how rats behave when given a high fat food
intermittently. Rats binge eat (consume a much larger caloric intake) on
days when fats are available. Thus, Robynn’s data suggests that rats respond
in different ways to highly palatable foods depending on the chemical
composition of those foods (fat vs. carbohydrate.) It will be interesting to
see if this behavior persists throughout the four weeks of Robynn’s
experiments. When her experiments are completed on July 20th, she will
need the remaining portion of the Community of Scholar’s 10 weeks
duration to delve into the scientific literature on this topic to see how her
findings relate to what is known concerning binge eating in laboratory rats.
Kishan Govind’s experiments are conducted in parallel with Robynn’s. In
addition to the same schedule of access to a highly palatable food, Kishan’s
40 laboratory rats are subjected to a variety of mild stressors that previous
researchers have used to induce the symptoms of depression in laboratory
rats. These stressors include 36 hours of continuous light once a week
which disrupts the diurnal cycling much like severe jet lag. Twice each
week, each animal’s cage is tilted at nearly 45 degrees for 3 hours. Also
twice each week, eat rat is deprived of water for 18 hours. At the end of 18
hours, an empty water bottle is given to each rat. One hour later, water is
finally provided. Another stressor involves keeping the rats in cages for 24
hours in wet bedding. This stressor is akin to the discomfort of lying in a
wet sleeping bag for a protracted period. Kishan had to devise a schedule of
stressors that would be sufficient to induce what is termed “chronic mild
stress” in the literature and characteristics similar to clinical depression in
humans.
The standard protocol for chronic mild stress used by other laboratories
always incorporates food deprivation which, for our purposes, is
inappropriate since Kishan is measuring food intake as it is affected by
depression. Also, the most effective stressor employed in previous
experiments is paired caging of these male rats. Again, since we must
accurately measure food intake for each rat, we were unable to include
paired caging as a stressor in our experimental protocol. Since all of the
previous studies we are aware of have included food deprivation and paired
caging as stressors, we were concerned that our protocol might not induce
depression. According to the literature, depressed rats don’t eat any less
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than control rats, but after about 2 weeks of repeated exposure to the
stressors, rats subjected to the protocol gain weight at a slower rat that
control rats. We were delighted to observe that 10 days into the experiment,
Kishan’s stressed rats weighed slightly but statistically significantly less that
Robynn’s non-stressed rats which serve as the control animals for his
experiments. By day 14, the differences were more pronounced.
Furthermore, careful measurements of food intake each day for Kishan’s
stressed rats reveals that some stressors have a more profound effect than
others. Very interestingly, those rats that are provided Froot Loops only on
Mondays, Wednesdays, and Fridays show signs of binge eating although at
the midpoint of our experiments, the differences from control animals has
yet to reach statistical significance. According to the literature, full
manifestation of the symptoms of chronic mild stress often require 2-3
weeks so we eagerly look forward to the completion of our 4 week study.
At the moment, it seems likely that stressed rats like stressed humans may
eat more palatable foods as a way to “self-medicate” to reduce stress.
To reach this point in our research many technical challenges had to be dealt
with before the actual experiments could begin. During the week in which
our rats acclimated to their new environment and adjusted to their new
light/dark schedule (lights on at 4 am, lights off at 4 pm), we conducted
several experiments on rats that had been used for other studies in the spring
of 2007.
For instance, we had to devise a way to provide Froot Loops to rats that
would make it convenient to measure how much was consumed (without
losing Froot Loops in the bedding of each cage) and in a manner that is
similar to the way in which rats eat standard laboratory chow. It was
necessary to run a series of pilot studies in which we tested various modes of
making Froot Loops available (strung on a hoop of stiff wire, threaded onto
a flexible chain, or slipped individually on a stiff rod that could be
positioned atop each cage.) The outcome of this set of trials revealed that
the optimal mode by which to provide Froot Loops is placing them on a 9
inch long plexiglass rod of 3/16 inch diameter. We discovered that rats
don’t eat as much from any of the other modes, including rods of 1/8 inch
diameter. Unfortunately, this knowledge forces us to spend considerable
time each day making “Froot Loop shish-ke-bobs” for use in our daily
experiments. These pilot studies required the same thoughtful planning as
our main experiments, the same careful measurement of food intake, and the
same types of statistical analysis that we use in our main experiment. The
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data, statistical analysis, and abstracts of those pilot studies are posted on our
website at http://webs.wofford.edu/davisgr/researchsummer2007/
Our mornings spent making shish-ke-bobs, discussing relevant papers from
the existing scientific literature, entering data from the previous day’s
experiment, and reviewing experimental results. Five days a week including
Saturday mornings it is necessary to provide stressors to Kishan’s rats.
Twice a week we have to weigh all 80 rats, and for two days each week we
are making or cleaning up wet bedding. Since our experiments call for
measuring food intake every day for 28 days and since the experiments are
conducted simultaneously on 40 rats each kept in two adjoining rooms in the
Animal Care Facility, two researchers must be at work every afternoon from
1 pm until 4:30. During that time, in each room we must weigh 130-190
samples of food depending on how many groups of rats are given access to
Froot Loops that day. All of us look forward to the end of the experiment at
which time our schedule will permit us to spend sufficient time analyzing
our results and preparing a report of our findings. To do so, we will
continue to develop expertise in the use of spreadsheets, software for
statistical analysis, and software used to present results in graphical form.
G.R. Davis, Jr.
8 July 2007
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Daily Caloric Intake (Non-Stressed Rats)
130
120
kcal/ 24 hr
110
100
90
80
Control
R7
70
60
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
5
6
7
8
9
10
11
12
13
14
15
5
6
7
8
9
10
11
12
13
14
15
130
120
kcal/ 24 hr
110
100
90
80
Control
70
R3
60
0
1
2
3
4
130
120
kcal/ 24 hr
110
100
90
80
Control
70
Irregular
60
0
1
2
3
4
Day
Symbol for each day is total caloric intake as mean ± standard error for each group
(n= 10 rats per group.) Day 1 is a Saturday.
C = Control (no access to Froot Loops); these animals are given only rat chow.
R7 = regular daily 2hr access to Froot Loops seven days per week.
R3 = regular daily 2hr acces to Froot Loops Monday, Wednesday, and Friday.
I = irregular access to Froot Loops.
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Daily Caloric Intake (Stressed Rats)
130
120
kcal/ 24 hr
110
100
90
80
CS
R7S
70
60
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
3
4
5
6
7
8
9
10
11
12
13
14
15
3
4
5
6
7
8
9
10
11
12
13
14
15
130
120
kcal/ 24 hr
110
100
90
80
CS
R3S
70
60
0
1
2
130
120
kcal/ 24 hr
110
100
90
80
CS
IS
70
60
0
1
2
Day
Symbol for each day is total caloric intake as mean ± standard error for each group
(n= 10 rats per group.) All animals in these four groups are subjected to stressors (S).
CS= Control (no access to Froot Loops); these animals are given only rat chow.
R7S = regular daily 2hr access to Froot Loops seven days per week.
R3S = regular daily 2hr acces to Froot Loops Monday, Wednesday, and Friday.
I S= irregular access to Froot Loops.
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