Receptor subtypes mediating depressor responses to microinjections of nicotine into medial NTS of the rat

Abstract

Microinjections (50 nl) of nicotine (0.01–10 μM) into the nucleus of the solitary tract (NTS) of adult, urethan-anesthetized, artificially ventilated, male Wistar rats, elicited decreases in blood pressure and heart rate. Prior microinjections of α-bungarotoxin (α-BT) and α-conotoxin ImI (specific toxins for nicotinic receptors containing α7 subunits) elicited a 20–38% reduction in nicotine responses. Similarly, prior microinjections of hexamethonium, mecamylamine, and α-conotoxin AuIB (specific blockers or toxin for nicotinic receptors containing α3β4 subunits) elicited a 47–79% reduction in nicotine responses. Nicotine responses were completely blocked by prior sequential microinjections of α-BT and mecamylamine into the NTS. Complete blockade of excitatory amino acid receptors (EAARs) in the NTS did not attenuate the responses to nicotine. It was concluded that 1) the predominant type of nicotinic receptor in the NTS contains α3β4 subunits, 2) a smaller proportion contains α7 subunits, 3) the presynaptic nicotinic receptors in the NTS do not contribute to nicotine-induced responses, and 4) EAARs in the NTS are not involved in mediating responses to nicotine.