MODULATION OF FEEDING BY HYPOTHALAMIC PARAVENTRICULAR NUCLEUS ALPHA-1-ADRENERGIC AND ALPHA-2-ADRENERGIC RECEPTORS

Noradrenergic receptor populations within the paraventricular hypothalamus (PVN) modulate feeding. Satiated rats exhibit enhanced feeding subsequent to activation of alpha2-adrenergic receptors within the PVN induced by exogenous infusion of either norepinephrine (NE) or clonidine (CLON). The feeding-stimulatory effect of alpha2-adrenergic agents presumably reflects an inhibitory action on receptors located on medial hypothalamic ''satiety'' cells. Adrenergic receptors of the alpha1-subclass have been identified within the PVN which are excitatory and which may function to suppress food intake. Microinjection into rat PVN of various alpha1-adrenergic agonists including cirazoline, methoxamine, phenylpropanolamine and phenylephrine suppress feeding; an effect that is reversed by pretreatment with alpha1-adrenergic receptor antagonists. The present review argues that alpha1- and alpha2-adrenoceptors within brain and specifically within the PVN are organized in an antagonistic fashion and that the effects of various adrenergic agonists on feeding may reflect the degree to which these agonists act at alpha1- and alpha2-adrenoceptors as well the relative balance of these receptors and their activity within the PVN.