Nicotine-induced tail-tremor and drug effects.

Tail-tremor induced by repeated and daily administration (0.5 mg/kg SC x 6 times/day) of nicotine as well as effects of various drugs on this response were investigated in Wistar strain male rats. Daily administration of nicotine in doses of 0.5 mg/kg SC caused tail-tremors to appear beginning on the 3rd day. Tail-tremor induced by the first injection of each day gradually increased with the daily injections, however, the heightened effect of this first injection at the beginning of each day decreased during the day upon repeated administration of 6 times/day at 2-hr intervals. Basically, tail-tremor appeared about 5 min after SC administration of nicotine and reached a peak approximately 7-9 min after injection, declining to zero afterwards. Different drugs showed various effects on this response. While mecamylamine (0.5 and 1.0 mg/kg IP) abolished nicotine-induced tail-tremor, arecoline (0.5 and 1.0 mg/kg IP), atropine (2.5 and 5.0 mg/kg IP), scopolamine (1.0 and 2.0 mg/kg IP) and hexamethonium (0.5 and 1.0 mg/kg IP) showed no such effects. Furthermore, physostigmine (0.1 mg/kg IP) actually potentiated this action. These results suggest that tail-tremor induced by nicotine may be mediated through central nicotine receptor system.