Ethanol withdrawal tremor potentiates the tremorogenic action of nicotine

The tremorogenic effect of nicotine was studied in control rats and in rats withdrawn for 16-48 h from six to nine days' ethanol administration. The frequency and the intensity of tremor were measured electronically. A single dose of nicotine 5 mg/kg caused shortlasting (2-3 min) convulsions within 1 min after injection in control rats. Tremor occurred first after five repeated injections of nicotine (5 mg/kg) at half-hour intervals. This tremor encompassed peak frequencies of 6, 10 and 15 Hz. Hexamethonium at a dose of 10 mg/kg did not inhibit the tremor but eliminated the highest peak frequency (15 Hz) and tended to increase the intensity. Propranolol 5 mg/kg completely abolished the nicotine-induced tremor in control rats. Rats withdrawn from repeated ethanol administration showed a marked hypersensitivity to the tremorogenic action of nicotine so that a single dose of 1 mg/kg of nicotine caused clear tremor. The frequency spectra of this tremor showed peak frequencies at 6, 10 and 12 Hz. Hexamethonium did not change these frequencies. Furthermore, it tended to increase the intensity of nicotine-induced tremor in ethanol-withdrawn rats. Propranolol did not inhibit the tremor although it eliminated the 12 Hz peak frequency. The results suggest that the hypersensitivity to the tremorogenic action of nicotine in ethanol-withdrawn rats is not mediated by a sympathetic beta-adrenergic mechanism.