Noradrenergic receptor interactions in feeding elicited by stimulation of the para-ventricular hypothalamus

Food intake and feeding behaviour were examined after the administration of noradrenaline (NA) or clonidine to the para-ventricular nucleus of the hypothalamus, or after systemic administration of clonidine. In 20-hr deprived animals all treatments dose-dependently reduced pellet consumption; however, at a low dose (2-5 micrograms) central clonidine increased eating time and bout length. In 4-hr deprived animals all treatments increased sucrose consumption. Clonidine (peripheral and central) increased feeding time but did not alter feeding rate; NA did not alter feeding time, but did increase feeding rate; NA also increased activity and decreased resting. The effects of NA on feeding rate, activity and resting were blocked by propranolol; however, the propranolol-NA combination increased feeding time. Thus, NA and clonidine increased feeding by different mechanisms, but after propranolol pretreatment the effects of NA were similar to those of clonidine. It is concluded that clonidine enhances feeding by inhibiting satiety and that the feeding stimulant effect of NA is mediated by a complex interaction of alpha- and beta-receptors.