Effects of hypothalamic knife cuts on feeding induced by paraventricular norepinephrine injections.

The relationship between the fiber systems involved in the hypothalamic noradrenergic feeding response and the medial hypothalamic (MH) hyperphagia syndrome was appraised in male rats using knife cuts. Parasagittal knife cuts in the perifornical hypothalamus produced hyperphagia and excessive weight gain but failed to disrupt feeding in response to paraventricular hypothalamic injections of norepinephrine (NE). Coronal knife cuts in the posterior hypothalamus which extended from the midline to the lateral perifornical region also failed to disrupt NE feeding. These findings indicate that the output of the noradrenergic feeding system does not follow the feeding pathway implicated in the MH hyperphagia syndrome. They also suggest that the output of the noradrenergic feeding system is not directed laterally beyond the level of the fornix nor caudally into the lower brainstem over the medial forebrain bundle.