NICOTINIC-CATECHOLAMINERGIC INTERACTIONS IN RAT-BRAIN - EVIDENCE FOR CHOLINERGIC NICOTINIC AND MUSCARINIC INTERACTIONS WITH HYPOTHALAMIC EPINEPHRINE

Abstract

The i.p. injection of nicotine produced several changes in regional catecholamine concentrations in rat brain. These changes were blocked by the centrally active nicotinic antagonist mecamylamine, but not by the quaternary nicotinic antagonist hexamethonium. An examination of the effects of various cholinergic agents on hypothalamic epinephrine concentrations revealed several interesting findings. Central muscarinic antagonism or peripheral muscarinic agonism decreased hypothalamic epinephrine concentrations. The anticholinesterase physostigmine decreased hypothalamic epinephrine concentrations and this effect was blocked by the centrally acting nicotinic antagonist mecamylamine, but not by hexamethonium, scopolamine or methscopolamine. An interaction of cholinergic receptors, both nicotinic and muscarinic, with hypothalamic epinephrine was indicated.