L-Dopa feeding suppression: effect on catecholamine neurons of the perifornical lateral hypothalamus.

Injection of L-Dopa (0.8--200 nmoles) into the perifornical hypothalamus produced a dose-dependent suppression of feeding in hungry rats. This effect was positively correlated in magnitude with the same effect produced by the catecholamine agonists dopamine and epinephrine, and by the catecholamine-releasing drug amphetamine. L-Dopa's action was partially antagonized by separate injections of the dopaminergic blocker haloperidol (58% blockade) and the beta-adrenergic blocker propranolol (38% blockade). Combined injections of these two antagonists produced a 90% blockade of L-Dopa's effect. Perifornical administration of the dopa decarboxylase inhibitors Ro 4-4602 and MK-486 was also shown to reverse L-Dopas feeding suppression, at doses that enhanced the effect of injected dopamine and epinephrine. On the basis of these findings, L-Dopa appears to suppress food consumption in part through increased catecholamine synthesis, specifically within dopaminergic and adrenergic neurons of the perifornical hypothalamic region.