Structural analysis of the actions of amphetamine and fenfluramine on food intake and feeding behaviour in animals and man

The drug pair of amphetamine and fenfluramine was used in a series of studies to investigate the mechanisms controlling food intake and the elements of feeding behaviour. In rats, the results of lesion experiments failed to reveal a brain zone whose destruction led to the attenuation of fenfluramine anorexia. In every case, however, the results dissociated the anorexic effects of amphetamine and fenfluramine, suggesting that the two drugs operate via separate anatomical systems and that they differentially influence the mechanism of the feeding process. The microstructure of eating in rats was analyzed using such parameters as latency to begin eating, bout size, bout duration, and the local rate of eating. Whereas amphetamine increased latency and the local rate of eating, fenfluramine failed to delay the onset of eating but slowed the rate of consumption and tended to bring eating to apremature end. The macrostructure of eating was continually monitored, using an eatometer, in freely-feeding rats. Fenfluramine reduced the overall size of meals taken and reduced the intra-meal rate of feeding. The effects of amphetamine were paradoxical and dependent on both the dose used and on the state of the animal. Using a different experimental procedure in which freely-feeding rats were allowed to self-select high or low protein-containing diets, amphetamine caused rats to restrict protein intake severely whereas, on fenfluramine, rats reduced food intake but maintained a normal proportion of protein. Similar effects of the two drugs on the structure of feeding and on food preference and selection have been detected in studies carried out in man.