Abstract
We investigated the effects of various parasympathetic drugs on the head-twitch response (HTR), as induced by intracerebroventricular (i.c.v.) administration of tyramine in mice pretreated with safrazine, a monoamine oxidase inhibitor. Intraperitoneal administration of neostigmine, methacholine, carbamylcholine, methylatropine or hexamethonium did not alter the HTR induced by tyramine. The i.c.v. infusion of acetylcholine, physostigmine, nicotine, carbamylcholine or atropine slightly inhibited the tyramine-response. The i.c.v. infusion of pilocarpine, methacholine, mechamylamine, hexamethonium or tetraethylammonium resulted in a slight or significant potentiation of the HTR. These results suggest that the HTR induced by tyramine is accelerated by mechanisms related to muscarinic receptors within the central nervous system and that the tyramine-response is suppressed by mechanisms related to nicotinic receptors.
