[The involvement of the cholinergic system in the tremor induced by phenol]

The effect of cholinergic drugs on the tremor induced by subcutaneous (s.c.) injection of a 1 v/v% phenol solution was investigated. Male dd-Y strain mice weighing 18-24 g were used in all experiments. Intraperitoneal (i.p.) administration of physostigmine (0.05-0.1 mg/kg) did not alter the tremor. Neostigmine (0.05-0.1 mg/kg i.p.) increased the strength of the tremor weakly and shortened the latency of the tremor. I.p. administrations of methacholine, atropine, methylatropine, and scopolamine did not produce significant effects on the tremor. I.p. injection of nicotine (0.5-1 mg/kg) shortened the duration of the tremor. Intracerebro-ventricular (i.c.v.) infusions of nicotine (4 micrograms/mouse) and carbachol (5 micrograms/mouse) prolonged the latency of the tremor. Furthermore, i.c.v. infusion of nicotine (4 micrograms/mouse) reduced the strength of the tremor slightly. On the contrary, i.p. (10-20 mg/kg) or i.c.v. (20-60 micrograms/mouse) administration of mecamylamine potentiated the strength and prolonged the duration of the tremor in a dose dependent manner. Hexamethonium (10-20 micrograms/mouse, i.c.v.) also potentiated the strength and prolonged the duration of the tremor. These results suggest that a peripheral increase of acetylcholine level may potentiate the tremor induced by phenol, and the tremor may be suppressed by a negative feedback mechanism involving the nicotinic cholinergic system of the central nervous system.