Nicotine Abstinence Syndrome Precipitated by the Competitive Nicotinic Antagonist Dihydro-β-Erythroidine

Rats infused subcutaneously with 9 mg/kg/day nicotine tartrate for 7 days exhibit behavioral abstinence signs following either termination of nicotine infusion or injection of the noncompetitive nicotinic antagonists mecamylamine (SC) or hexamethonium (ICV). This study examined the abstinence precipitating effects of dihydro-β-erythroidine (DHβE), a competitive nicotinic antagonist. Twenty-four nicotine-dependent rats were injected in the third ventricle with 10, 18, or 25 μg DHβE in 20 μl saline or with saline alone and observed for abstinence signs over a 20-min period. There was a significant positive linear trend of overall abstinence signs as a function of dose, p < 0.01. In 12 nondependent rats, the high dose of DHβE did not induce more abstinence-like signs than saline alone. In a second experiment, 18 nicotine-dependent rats were injected SC with 1 or 6 mg/kg of the muscarinic antagonist scopolamine or with saline alone. Few abstinence signs were observed in any group; there was no significant drug effect. The results suggest that nicotine abstinence signs observed in the rat are specific to reduced stimulation of previously overstimulated nicotinic receptors.