Food deprivation-induced vs. drug-induced feeding: A behavioral evaluation

Several neuroactive substances including neuropeptide Y (NPY), muscimol, and norepinephrine (NE) stimulate feeding in satiated rats. In the present study, we observed the behavioral patterns of rats stimulated to eat by food deprivation or by intracerebroventricular (icv) injection of orexigenic agents to explore the hypothesis that such agents produce a behavioral state resembling hunger. Animals that were food deprived for 24 h spent the majority of their time eating (35%), drinking (5%), resting (44%), and moving (13%) when food was available. If food was removed and substituted with a chewable substrate (plastic tube), they chewed on tubes for a brief period (5%) but spent most of their time moving (14%) or resting (77%). In the absence of food or tubes, they briefly moved about the cage (4%) and spent almost all of their time resting (94%). The patterns observed with the orexigenic drugs were different, particularly in the absence of food. NPY-injected rats were more active than deprived rats, spending 22% of their time moving in the presence of food, 47% in the presence of tubes, and 37% in the absence of food or tubes. Rats injected with muscimol demonstrated a marked increase in the time spent chewing and eating. These rats spent 67% of their time eating in the presence of food and chewed 25% of the time in the absence of either food or tubes. NE-injected rats also chewed when tubes were present (17%) or when no food or tubes were present (10%). Lag sequential analysis further documented differences in behavioral patterns amongst the various treatments. Depriving rats for 48 h failed to induce the increased locomotor activity or nonspecific chewing observed in drug-exposed rats when food was absent or when tubes were present. Thus we found that three orexigenic agents given icv share with food deprivation the ability to induce feeding, but the neuroactive agents differ from deprivation in the pattern of behavior observed in association with feeding.