Food intake in baboons: effects of d-amphetamine and fenfluramine

Food intake of four adult male baboons (Papio c. anubis) was monitored during daily experimental sessions lasting 22 hours. Food was available under a two-component operant schedule. Following completion of the first "procurement component" response requirement, access to food, i.e., a meal, became available under the second "consumption component" during which each response produced a one-g food pellet. After a 10-minute interval in which no response occurred, the consumption component was terminated. The effects of oral d-amphetamine (AMPH: 0.03-1.0 mg/kg) and fenfluramine (FEN: 0.25-2.0 mg/kg) were determined by having the baboons drink a dose on Tuesdays and Fridays 45 to 60 min before the daily session. Dose-dependent decreases in food intake were observed with AMPH being four times as potent as FEN. Although both drugs were equally efficacious in decreasing food intake, they had dissimilar effects on the topography of feeding behavior. AMPH decreased food intake by increasing the latency to the first meal, decreasing the size of the first meal, and decreasing the number of meals within a session. FEN, in contrast, had no significant effect on latency to the first meal or size of the first meal, but decreased the number of meals within a session. In addition, the drugs had different effects on the patterning of responding within the first meal. Finally, at the doses tested, there was no evidence of nonspecific motor deficits disrupting food intake. Although there are some differences between these results and the previously reported effects of these drugs, it is clear that AMPH and FEN influence feeding behavior in different ways.