[Comparison of the effects of nicotine and methamphetamine on extracellular dopamine in the nucleus accumbens of behaviorally sensitized rats].

Repeated administration of nicotine (NCT) and methamphetamine (MAP) produced a progressive enhancement (sensitization) in the increasing effects on spontaneous motor activity in rats. The purpose of this study was to compare the effects of NCT and MAP on the extracellular levels of dopamine (DA) and dihydroxyphenylacetic acid (DOPAC) in the nucleus accumbens of behaviorally sensitized rats by in vivo microdialysis. NCT 0.5 mg/kg, sc did not change the DA and DOPAC levels in drug-naive rats, but it showed an increase in the DA levels in rats sensitized to NCT. MAP 0.5 mg/kg, sc increased DA levels and decreased DOPAC levels in drug-naive rats, but it showed a smaller increase in DA levels in rats sensitized to MAP than in drug-naive rats. On the other hand, the basal levels of DA were increased in sensitized rats produced by MAP, but not in those produced by NCT. The present results suggest that NCT and MAP produce behavioral sensitization through the action on the mesolimbic dopaminergic system, but the manner of action of these drugs is different.