Pharmacological Tests for the Function of Hypothalamic Norepinephrine in Eating Behavior
Drugs that affect peripheral adrenergic neurotransmission were injected via implanted cannulas into the perifornical region near the posterior part of the anterior hypothalamus of satiated rats, in order to test the hypothesis that in this part of the hypothalamus particularly norepinephrine (NE) functions as a modulator of the neural system involved in regulating eating behavior. The latency of the eating response to NE varied from approximately 2 min. to 8 min., presumably depending on small differences in the site of the injection. NE is highly localized at nerve terminals, mainly within synaptic vesicles. In the storage granules the NE is protected against the catabolic action of the enzyme monoamine oxidase. In rats that are especially good eaters, it can elicit eating by itself, presumably by conserving the endogenous NE that continuously leaks out at a subthreshold level from the presynaptic terminals.