Release of norepinephrine from hypothalamus and amygdala by rewarding medial forebrain bundle stimulation and amphetamine.

Abstract

The hypothalamus and amygdala of 76 unanesthetized rats were perfused with Locke's solution through a permanently indwelling push-pull cannula after intraventricular injection of a radioactive norepinephrine tracer. Rewarding electrical stimulation of the medial forebrain bundle caused a marked increase in the radioactivity of the perfusate. Nonrewarding brain stimulation did not release radioactivity and, in some cases, even inhibited its spontaneous release. 3 mg/kg amphetamine, administered intraperitoneally, increased the radioactivity of the amygdaloid, but not the hypothalamic, perfusates. Chemical analyses revealed that O-methylated metabolites of norepinephrine accounted for 70% of the radioactivity in control samples and 88% of the radioactivity in samples collected during rewarding stimulation. These results demonstrate in vivo that norepinephrine can be released at central synapses by stimulation of a particular neural system. More specifically, the release of norepinephrine at terminal sites of the medial forebrain bundle in hypothalamus and limbic system is responsible at least in part for the positive reinforcement of behavior. (35 ref.) (PsycINFO Database Record (c) 2006 APA, all rights reserved)