The effects of NPY and 5-TG on responding to cues for fats and carbohydrates.

Previous research has shown that glucoprivic and lipoprivic metabolic challenges selectively augment the performance of appetitive responses conditioned to carbohydrate- and fat-associated cues, respectively. The present experiment investigated whether intracerebroventricular (i.c.v.) infusion of neuropeptide Y (NPY) has a similar selective effect on appetitive behavior. We trained rats to associate two different conditioned stimuli (CSs) with two different macronutrient (peanut oil and sucrose pellets) unconditioned stimuli (USs). After training, the rats were food sated and responding to each CS was then tested in extinction. In one test session, the effects of NPY were compared to isotonic saline. A second test compared the effects of these two treatments with i.c.v. infusion of the glucose antimetabolite 5-thio-d-glucose (5-TG). Replicating our earlier result, 5-TG selectively promoted conditioned responding to the CS for sucrose pellets. In contrast, the capacity of NPY to promote appetitive behavior did not depend on the macronutrient that was signaled by the CS. These results suggest that NPY and 5-TG promote appetitive behavior via different mechanisms.