Background-Nicotine and methamphetamine are both abused in similar settings, sometimes together. Because there are known interactions between central nicotinic acetylcholine receptors and dopamine receptors, it is of interest to characterize the nature of the interaction of these two compounds in vivo.Methods-The purpose of this study was to characterize the extent to which these two compounds produce similar discriminative stimulus effects and to identify pharmacological mechanisms for their interaction. Male Sprague-Dawley rats were trained to discriminate methamphetamine or nicotine from saline. First, the ability of methamphetamine and nicotine to cross-substitute in rats trained to the other compound was tested. Subsequently, the ability of a dopamine antagonist (haloperidol) and a centrally-acting nicotinic antagonist (mecamylamine) to block the discriminative stimulus effects of methamphetamine and nicotine were also tested.Results-Nicotine fully substituted in methamphetamine-trained rats, but methamphetamine only partially substituted in nicotine-trained rats. In nicotine-trained rats, mecamylamine fully antagonized the discriminative stimulus effects of nicotine, but haloperidol had no effect. The partial substitution of methamphetamine was partially attenuated by haloperidol, but not altered by mecamylamine. In methamphetamine-trained rats, mecamylamine failed to antagonize the discriminative stimulus effects of methamphetamine, but haloperidol fully blocked the methamphetamine cue. Mecamylamine blocked the ability of nicotine to substitute for methamphetamine, but haloperidol had no effect.Conclusions-These results indicate that nicotine and methamphetamine share discriminative stimulus effects in some subjects and that the two compounds do not act at the same site, but produce their interaction indirectly. These findings suggest that these two compounds might be at least partially interchangeable in human users, and that there are potentially interesting pharmacological reasons for the commonly observed co-administration of nicotine and methamphetamine.

This study tested the time course of the discriminative stimulus effects of inhibitors of monoamine oxidase (MAO) alone or in combination with cocaine. Male Sprague-Dawley rats were trained to discriminate cocaine (10 mg/kg, i.p.) from saline using a two-lever choice methodology. The nonselective MAO inhibitors tranylcypromine (0.01 to 5 mg/kg) and phenelzine (1 to 25 mg/kg), the MAO-A selective compound clorgyline (1 to 25 mg/kg), and the MAO-B selective compounds pargyline (0.005 to 50 mg/kg) and selegiline (1 to 25 mg/kg) were tested for substitution 15 min or 24 hr following administration, and in combination with 10 mg/kg of cocaine 24 and 48 hr after administration. At 15 min, selegiline fully substituted for the discriminative stimulus effects of cocaine, whereas all other compounds partially substituted. At 24 hr, substitution of cocaine was diminished for all compounds except phenelzine, which produced a greater amount of substitution at 24 hr than at 15 min. When cocaine was administered 24 hr following clorgyline, selegiline, pargyline, and phenelzine, cocaine-appropriate responding was attenuated at intermediate doses of these drugs, whereas the highest doses did not alter cocaine-lever responding. All compounds except selegiline substantially decreased response rate and produced various adverse effects. At 48 hr, the effects of all compounds except phenelzine were markedly reduced. Selectivity for MAO-A or B did not predict the ability to substitute for or attenuate the subjective effects of cocaine. These findings suggest that MAO inhibitors can modulate the discriminative stimulus effects of cocaine for at least 24 hr, and may be useful for treatment of cocaine abuse.

No abstract

No abstract