Paraventricular nucleus: a primary site mediating adrenergic stimulation of feeding and drinking.

Central injection of norepinephrine (NE) has been found to elicit preprandial drinking and feeding responses in the satiated rat. In the present study, 35 different brain areas, in over 500 rats, were examined to localize the precise region of NE sensitivity. Essentially all sites outside the hypothalamus, as well as in the lateral portion of the hypothalamus, were relatively or totally unresponsive to NE. In the medial hypothalamic area, the paraventricular nucleus (PVN) was clearly distinguished as the most effective site for initiating both feeding and drinking with noradrenergic activation in the satiated animal. Sites greater than 0.5 mm rostral, caudal, dorsal, ventral or lateral to this nucleus yielded significantly smaller effects. In mildly hungry rats, NE was found to potentiate the ongoing feeding response, and anatomical analyses of this phenomenon showed the PVN to be most responsive, with a smaller but reliable potentiation occurring along the periventricular hypothalamus adjacent to the third ventricle. Norepinephrine injected into the lateral perifornical hypothalamic area actually produced a suppression of feeding in these hungry animals. These findings, together with results from other studies, converge on the medial PVN region as being a key link in the process of increased food and water consumption associated with increased noradrenergic activity.