Ondansetron, a selective 5-HT3 receptor antagonist, reduces palatable food consumption in the nondeprived rat

This study investigated the effects of ondansetron, a selective 5-HT3 receptor antagonist, on palatable food consumption in nondeprived male rats, under conditions of familiarity. The results showed that ondansetron (3.0-30 micrograms/kg, i.p.) significantly reduced food intake at each dose tested. The reduction in food intake was due not to a change in the rate of eating but to a reduction in the time spent eating. This, in turn, was due to a reduction in the mean duration of feeding bouts but not due to a change in the frequency of feeding bouts. Hence, the feeding-suppressant effect of ondansetron resulted from a quite specific alteration in the microstructural characteristics of feeding behaviour. In the 60-min observation period, ondansetron did not affect either locomotor activity or rearing, indicating that it did not have general excitatory or behavioural-suppressant effects. Following ondansetron, animals continued to show a typical decline in feeding over time, indicative of the development of within-meal satiety, but the level of feeding was reduced in such a way as to suggest that ondansetron enhances satiety. As a result, as feeding declined, the level of grooming which typically follows the end of feeding, was increased in ondansetron-treated animals. In a supplementary experiment, ondansetron had no effect on deprivation-induced feeding. Present evidence does not allow these data for a 5-HT3 receptor antagonist to be easily accommodated into the major current hypothesis dealing with serotonergic control of feeding responses. Therefore, the role of 5-HT3 receptor-mediated changes in ingestive behaviour requires further investigation.