Effects of chronically administered fluoxetine and fenfluramine on food intake, body weight and the behavioural satiety sequence.

Rats were administered fenfluramine (FF: 3 mg/kg) or fluoxetine (FX: 6 mg/kg) daily for 3 weeks. On acute administration, FF suppressed consumption of 35% sucrose (in a 40 min test) and overnight chow intake. Repeated administration saw the rapid development of extensive tolerance to these effects. FF had no effects on body weight, and no withdrawal effects were apparent. FX reduced chow intake and body weight throughout the treatment period, but there was evidence of some tolerance to the suppression of chow intake and sucrose drinking. Following FX withdrawal, normal body weight was restored in 4 days; food intake was normal during this period. A delayed rebound hyperphagia commenced on day 5 of withdrawal, and persisted for at least 6 days. The behavioural satiety sequence (drinking--activity--grooming--resting) was disrupted by acute FF; on chronic treatment, FF advanced the onset of postprandial resting, but also increased drinking time. FX advanced the behavioural satiety sequence on acute administration, but not after chronic treatment. We consider the implications of these results for the use of resting behaviour as an indicator of postprandial satiety.