DOPAMINE MECHANISMS PLAY AT BEST A SMALL ROLE IN THE NICOTINE DISCRIMINATIVE STIMULUS

The ability of D-1 and D-2 dopamine antagonists to reduce the subjective effects of nicotine was examined in rats trained to discriminate nicotine (0.3 mg/kg, base) from saline. Each of SCH 23390 (a D-1 antagonist) and spiperone (a D-2 antagonist) reduced responding on the drug-appropriate lever, and produced a reduction in overall response rates. The nicotine cue was also tested for generalization to the dopamine reuptake blocker GBR 12909. Doses of GBR 12909 that produced complete responding on the drug-appropriate lever in cocaine-trained animals led to only minimal selection of the nicotine-appropriate lever in nicotine-trained animals; as with the dopamine antagonists, response rates after GBR 12909 were markedly reduced in nicotine-trained, but not in cocaine-trained, rats. These data suggest that dopaminergic mechanisms play, at best, a small role in the discriminative stimulus properties of nicotine.