Abstract

A reliable eating response was obtained on injection of 2.5 µg of aqueous norepinephrine into the rostral hypothalamus. When the diameter of the guide cannula was decreased to a delivery orifice of 76 µ, the norepinephrine concentration optimum was similar to that with the much larger cannulae used in earlier work. l-Norepinephrine and l-epinephrine gave responses of similar intensity. A negligible eating response was obtained with l-isoproterenol, d-norepinephrine, normetanephrine, metanephrine, tyramine, octopamine, ephedrine, phenylephrine, amphetamine and histamine. Angiotensin elicited drinking but no eating. Phenoxybenzamine and phentolamine prevented the eating response to norepinephrine but propranolol did not. Local administration of desmethylimipramine 20 min before norepinephrine augmented the eating response. Injected norepinephrine-H² was present in sedimentable subcellular fractions by the time the eating response began. The results provide further evidence consistent with the hypothesis that alpha adrenergic modulation of postsynaptic activity by norepinephrine from nerve endings is involved in the hypothalamic control of feeding in the rat.