Hypothalamic norepinephrine in the rat during feeding and push-pull perfusion with glucose, 2-DG, or insulin

Abstract
The pattern of norepinephrine (NE) release within sites in the diencephalon of the fasted rat was determined under 2 conditions: as the animal fed and during the localized perfusion of its hypothalamus or adjacent structures with glucose, 2-deoxy-D-glucose (2-DG) or insulin. The endogenous neuronal stores of NE in the unrestrained animal were first radiolabeled with 2.0 .mu.Ci of either [14C]NE or [3H]NE injected into hypothalamic sites in a volume of 1.0 .mu.l. Then, each site was perfused by means of push-pull cannulas, with an artificial CSF for 5 min at a rate of 25 .mu.l/min. After 3 samples of perfusate were collected at 15 min intervals, 1 of 2 experimental procedures was undertaken. In 1 case, the rat was offered food pellets, which were readily consumed. In the other, 1 of 3 compounds was added to the perfusion solution: 55 .mu.g/.mu.l of D-glucose; 4 mU[units]/.mu.l of insulin; or 10 .mu.g/.mu.l of 2-DG. As the rat fed, the efflux of labeled NE was enhanced at circumscribed sites distributed mainly within ventral and medial hypothalamic areas. The release of NE within the same loci was suppressed by the addition of glucose, whereas 2-DG augmented the efflux of this catecholamine. Insulin also caused an inconsistent rise in the efflux of NE which was temporally delayed. An analysis of selected hypothalamic perfusates by TLC showed generally that the alteration in NE activity was reflected in the profile of the catecholamine metabolites. The local level of glucose within the hypothalamus of the rat can modify the activity of noradrenergic neurons, which in turn influences the animal''s subsequent intake of food.