Acute amphetamine or methamphetamine alters opioid peptide mRNA expression in rat striatum

The effects of a single dose of amphetamine or methamphetamine on opioid peptide gene expression in the dorsal and ventral striatum of rats were investigated by quantitative in situ hybridization 3, 6, or 18 h after injection. Although amphetamine-treated rats exhibited significantly different behaviors than those treated with methamphetamine, both drugs caused a patchy increase in preprodynorphin, but not preproenkephalin, mRNA in the caudate at all 3 time points. No changes were detected in the nucleus accumbens. These data indicate that prolonged elevation of preprodynorphin expression may alter the responsiveness of striatonigral neurons to subsequent amphetamine exposure.