Morphine-induced anorexia in lateral hypothalamic rats.

The anorexic effect of morphine in rats with lateral hypothalamic lesions was examined. Morphine (15 mg/kg) produced an anorectic effect which was greater in lesioned rats than in controls. However, in lesioned rats, morphine anorexia was completely reversed by naloxone (2 mg/kg), while in controls there was mild anorexia. Repeated morphine injections caused decreasing anorectic effects, an effect which developed more rapidly in control than in lesioned subjects. The effects of morphine on food intake in lesioned rats were similar to the effects of fenfluramine, rather than amphetamine, suggesting involvement of serotonergic, rather than catecholaminergic mediation of morphine anorexia.