Norepinephrine: reversal of anorexia in rats with lateral hypothalamic damage.

Injection of norepinephrine in the lateral ventricles of rats recovering from lateral hypothalamic anorexia caused immediate feeding and, frequently, overeating. Intraventricular administration of the alpha-noradrenergic blocker, phentolamine, suppressed feeding in both normal rats and rats that had recovered from lateral hypothalamic lesions. Feeding is reinforced by ascending medial forebrain bundle fibers that form alpha-noradrenergic synapses in the hypothalamus and forebrain. Damage to these fibers suppresses feeding by reducing noradrenergic transmission and, hence, the rewarding value of food. Recovery of feeding after hypothalamic lesions coincides with the recovery of noradrenergic reward function.