Effects of cholecystokinin, d-amphetamine and fenfluramine in rats trained to discriminate 3 from 22 hr of food deprivation.

Attempts to assess similarities between the interoceptive stimuli of anorectic drugs and food satiation have generally been limited to human verbal reports. The purpose of the present study was to develop a procedure for assessing similarities between the interoceptive stimuli of food in the gut and various drugs known to alter food intake in rats. Rats (n = 23) were trained in a two-lever, food-reinforced, discrimination paradigm to press one lever when deprived of food for 3 hr and another lever when deprived of food for 22 hr. Criteria for stimulus control over responding were achieved after a mean of 92 (range = 26-175) training sessions. In time course tests, rats were tested when 22, 12, 6 and 3 hr food-deprived. As the number of hours of food deprivation decreased, the percentage of responses that occurred on the 3-hr food deprivation lever increased. In substitution tests, rats that were 22-hr food-deprived consistently responded as if they were 3-hr food deprived after administration of sweetened condensed milk preloads or cholecystokinin, but only occasionally after administration of water preloads, LiCl, d-amphetamine or fenfluramine. These results demonstrate that the presence of food in the gut can function as a discriminative stimulus to control lever choice in rats. Furthermore, they suggest that the discriminative stimulus effects of cholecystokinin, but not d-amphetamine or fenfluramine, are similar to those of food in the gut, and support the hypothesis that cholecystokinin plays a role in the regulation of food intake.