Abstract
The effects of sulpiride (25 μg in 0.5 μl) injected into either the dorsal striatum or nucleus accumbens on licking, gnawing and locomotion induced in rats by either methamphetamine (10 mg/kg) or apomorphine (2 and 4 mg/kg) were investigated. Sulpiride injected into the dorsal striatum enhanced methamphetamine-induced gnawing but not that induced by apomorphine, a directly-acting dopamine agonist. These results suggest that enhancement of the effect of methamphetamine may be due to the inhibition by sulpiride of the striatonigral negative feedback mechanisms controlling dopamine release. Sulpiride injected into the nucleus accumbens blocked methamphetamine-induced gnawing without affecting the effects of apomorphine. Antagonism of the effects of methamphetamine by blockade of dopamine receptors within the nucleus accumbens has not previously been reported and cannot be easily explained on the basis of present knowledge.
Hyperlocomotion produced by methamphetamine (10 mg/kg) was significantly reduced by injection of sulpiride into the nucleus accumbens but not into the dorsal striatum. Injection of sulpiride into the nucleus accumbens more markedly reduced hyperlocomotion produced by apomorphine (2 and 4 mg/kg) than did injection of sulpiride into the dorsal striatum. These results support the hypothesis that the nucleus accumbens more effectively generates dopamine-mediated locomotion via D2 receptors than the striatum.
