exercise and anorexia
21, 2000, Gazette)
Drs. Virginia Grant and Bow Revusky of the Psychology department
look on as graduate
student Jennifer Smith gives one of the rats a chance to run
on the wheel in the laboratory.
by Chris Hammond
A pair of psychologists at Memorial are using rats and running
wheels to study the relationship between intense physical activity
and the development of anorexia nervosa. Dr. Bow Revusky and
Dr. Virginia Grant have received funding from NSERC for a project
called Activity-Induced Suppression of Eating and Related Phenomena.
This project stems from an experimental model called activity
anorexia. Activity anorexia is experimentally induced by
allowing rats to eat for 60 minutes each day and leaving them
to spend the rest of the day in a running wheel. The rats do
not have to run in the wheel but some spend almost all day running.
of them cover huge distances 12 kilometres or so,
Dr. Grant said. Rats tend to increase their running over days
and their eating is inadequate. It is not just that they dont
eat enough to compensate for their exercise. They actually eat
less than other rats that have the same feeding schedule but
are not allowed to run in the wheel. The rats that are allowed
to run in the wheel lose a lot of weight.
you let it go on too long meaning two weeks at most
rats could actually starve to death. This is actually an experimental
model of anorexia nervosa, Dr. Revusky explained.
in certain kinds of occupations like athletes, gymnasts, dancers,
and models tend to be excessively concerned about their weight.
When they go on diets, they are especially vulnerable to anorexia
nervosa because they engage in a high level of physical activity.
and exercise can be a deadly combination, said Dr. Grant.
You have to be careful. Once it gets to a certain level,
a vicious circle comes into effect. Exercise tends to decreases
eating, resulting in weight loss, leading to increased exercise
that tends to decrease eating, and so on.
started to work on this model about five years ago. In particular,
we are concerned with the rewarding or motivational processes
activated by wheel running, said Dr. Revusky.
run spontaneously in the wheel, even more when they are hungry.
Rats will also learn to press a lever to gain the opportunity
to run in the wheel, and they press more vigorously when they
are hungry. These findings indicate that wheel running is rewarding
to a rat and that its reward value is increased when the rat
wheel running is rewarding implies that it activates a reward
system in the brain. Lots of things, such as eating tasty food
or having sex, are presumed to do so. Wheel running, at least
for rats, is just one of these things. Drs. Grant and Revusky
hypothesized that a high level of continuing activation of the
reward system is responsible for the suppression of eating.
an important aspect of their hypothesis is the notion that the
reward system in the animals brain activated by wheel running
continues to be active for some amount of time after wheel running
they experience after wheel running is pleasant, Dr. Grant
said. When the animal is put in the feeding cage to eat after
wheel running, it tends to be less inclined to eat due to the
continuing activation of the reward system.
test that idea, Drs. Grant and Revusky did the following experiment.
On some occasions, the rats were allowed to run for a lengthy
period of time in the activity wheels to activate the reward
system or produce pleasant feelings. Then, the rats were removed
from the wheels and were each placed in a distinctive chamber.
This should result in an association between the distinctive
chamber and the pleasant feelings present after wheel running.
other occasions, these rats were put in a different chamber without
prior wheel running. No association should occur between the
second chamber and the pleasant feelings. Later, the rats were
given a test during which they could choose between the two chambers.
Consistent with the notion that the activation of the reward
system continues after wheel stops, the rats showed a preference
for the distinctive chamber that was associated with the pleasant
feelings present after wheel running.