Apomorphine anorexia: a further pharmacological characterization.

Low doses of apomorphine reduce food intake, primarily by decreasing the rate of eating and also by reducing eating time. We have previously reported that the effect on eating time is mediated by dopamine cell body autoreceptors in the ventral tegmental area. The present experiments were designed to elucidate the pharmacological basis of the effect of apomorphine on eating rate. In the first experiment dopamine was also found to reduce food intake, but mainly by an effect on eating time. The peripheral DA antagonist domperidone abolished the effects of DA, but enhanced the effects of apomorphine. In the second experiment phentolamine, yohimbine, propranolol, scopolamine, naloxone and methergoline all failed to reverse the effect of apomorphine on eating rate. However, in the third experiment, effects of apomorphine on total food intake, eating time and eating rate were all blocked by the neuroleptics, pimozide and sulpiride. It is concluded that the reduction of eating rate by apomorphine is also mediated by an interaction with central DA receptors, but that this receptor population is anatomically distinct from that responsible for the effect of apomorphine on eating time.