Role of central nicotinic and β-adrenergic receptors in the onset and further development of tail-tremor induced by repeated nicotine administration to rats

The effects of nicotinic and β-adrenergic receptor antagonists on tail-tremor induced by repeated nicotine administration were investigated in rats. The daily administration of nicotine (0.5mg/kg/day, s.c.) for 8 days resulted in an augmentation of tail-tremor. However, repeated administration of dimethyl phenyl piperazinium iodide (1mg/kg/day, s.c.) for 8 days did not cause tail-tremor. Mecamylamine (0.5mg/kg, i.p), administered before the nicotine injection on each day, abolished the tail-tremor. After discontinuation of the mecamylamine treatment, nicotine injections caused tail-tremor augmentation. Propranolol (20mg/kg, i.p.), administered before the nicotine on each day, suppressed the appearance of tail-tremor. After the discontinuation of propranolol treatment, the degree of tail-tremor induced by a single injection of nicotine on day 9 was much greater in the propranolol-treated group than in the saline-treated control group. Neither carteolol (20mg/kg, i.p.) nor metoprolol (20mg/kg, i.p.) treatment showed such effects. Intraspinal injection of 6-hydroxydopamine markedly enhanced the tail-tremor induced on the first day of nicotine injection. This effect became more intense on subsequent administration of nicotine. The enhanced tail-tremor following 6-hydroxydopamine treatment was abolished by mecamylamine (0.5 and 1mg/kg, i.p.), and was suppressed by propranolol (5–20mg/kg, s.c.) in a dose-dependent manner. These results suggest that central nicotinic receptors are essential for the onset and for the further development of tail-tremor induced by the repeated administration of nicotine, and that β2-adrenoceptors are associated with the tremor mechanism. Moreover, spinal noradrenergic mechanisms may be involved in the manifestation of this phenomenon.