Characteristics of tail-tremor induced by nicotine in rats

To characterize the tail-tremor and locomotor hyperactivity induced by repeated nicotine administration, the effects of nicotinic, alpha-adrenergic and dopaminergic blockers were investigated in rats. Daily administration of nicotine (0.5 mg/kg, s.c.) induced tail-tremor from the 4th day, which became more marked in intensity by subsequent administration. Locomotor hyperactivity was also induced by nicotine, which was enhanced by daily administration. The tail-tremor and locomotor hyperactivity induced by repeated nicotine administration were inhibited by mecamylamine (0.1-1 mg/kg, i.p.) but not by hexamethonium (0.5 and 1 mg/kg, i.p.). Clonidine (0.02 and 0.04 mg/kg, i.p.) and prazosin (0.5 and 1 mg/kg, i.p.) reduced tail-tremor more markedly than hyperactivity. However, haloperidol (0.05-0.2 mg/kg, i.p.) and chlorpromazine (1-5 mg/kg, i.p.) reduced hyperactivity more markedly than tail-tremor. These results suggest that nicotine-induced tail-tremor and hyperactivity are due to an increased susceptibility of central nicotinic receptors of nicotine followed by catecholaminergic mechanisms, and that tail-tremor may be more associated with the noradrenergic system than the dopaminergic system.