Effects of anorectic drugs and prior feeding on food-rewarded runway behavior

Two treatments that act through central catecholamine pathways and are normally found to be strongly anorectic (d-amphetamine, 1.25 mg/kg and diethylpropion, 5.00 mg/kg) failed to influence either latency to run or running velocity in single trial running for food reward. In contrast, d-fenfluramine (2.5 mg/kg), which normally has similar anorectic potency but acts via a serotoninergic mechanism, significantly increased latency and decreased running velocity. Prior feeding (30 min ad lib access to food) also decreased runway performance to a similar degree. Further studies, using a 3 trial procedure where rats were allowed to feed for 30 sec following each run, revealed that d-amphetamine (1.25 mg/kg), both with and without penfluridol pretreatment (2.5 mg/kg), failed to affect running velocity or the amount of food eaten. However, d-fenfluramine (2.5 mg/kg) and a postsynaptic serotonin receptor agonist, m-chlorophenylpiperazne (1.0, 2.0 mg/kg) led to a significant reduction in these measurements. Thus it appears that "serotoninergic" anorectic drugs, like the state induced by prefeeding, depress food-rewarded runway behavior whereas "catecholaminergic" anorectic agents lack such effect.