The effects of (+)-amphetamine and fenfluramine on feeding in starved and satiated mice.

(+)-Amphetamine and fenfluramine depressed both the food intake during the first 2 h of feeding of mice adapted to feed between 12:00 and 15:00 daily and the food intake of free feeding mice between 24:00 and 02:00 (lighting on, 09:00-21:00) in a dose-dependent manner. Higher doses of each drug were needed to produce a significant depression in the latter case. However, (+)-amphetamine (0.5-2 mg/kg) markedly increased the negligible food intake of free feeding mice between 12:00 and 14:00, an effect which rapidly disappeared at higher doses. Fenfluramine at doses up to 40 mg/kg had no effect on the feeding of these mice. Nevertheless, as caffeine (10-40 mg/kg) also increased feeding, behavioural arousal might be an important factor in this anomalous feeding response, although a specific action by (+)-amphetamine and caffeine on the feeding centres of the satiated mouse cannot be ruled out.