LeSage, M. G., Stafford, D., & Glowa, J. R. (2004).
Effects of anorectic drugs on food intake under progressive-ratio and free-access conditions in rats.
Journal of the Experimental Analysis of Behavior, 82, 275-292.
The effects of two anorectic drugs, dexfenfluramine and phentermine, on food intake
under different food-access conditions were examined. Experiment 1 compared the
effects of these drugs on food intake under a progressive-ratio (PR) schedule and
free-access conditions. Dexfenfluramine decreased food intake under both conditions,
but the doses required to decrease intake under free-access conditions were higher
than those required to reduce intake under the PR condition. Intermediate doses of
phentermine sometimes increased breaking points, and higher doses decreased them.
Phentermine decreased food intake at the same doses under both access conditions.
Thus the potency of dexfenfluramine, but not phentermine, to decrease food-maintained
behavior depended upon the food-access condition. Experiment 2 used a novel mixed
progressive-ratio schedule of food delivery to study the duration of drug effects.
Sessions consisted of five components separated by 3-hr timeouts. The ratio
requirement reset at the beginning of each component and a new breaking point
was obtained. Both dexfenfluramine and phentermine dose-dependently decreased
breaking points early in the session. In some rats, compensatory increases in
breaking point were observed. That is, breaking points later in the session
increased over control levels, resulting in no change in the total number of
food pellets earned for the session compared to control. The present findings
suggest that the effects of some anorectic drugs depend upon the access conditions
for food; increasing the effort to obtain food may enhance their ability to
decrease food-maintained behavior.
Key words: progressive-ratio schedule, food-maintained behavior, food intake,
dexfenfluramine, phentermine, lever press, rats