Cocaine self-administration increases preprodynorphin, but not c-fos, mRNA in rat striatum.

The impact of cocaine self-administration on the expression of striatal preprodynorphin and c-fos mRNA was examined with in situ hybridization histochemistry. Cocaine significantly increased preprodynorphin mRNA in the dorsal, but not ventral, striatum. Expression of c-fos mRNA in cocaine-administering rats did not differ from that in controls in all structures examined. These results indicate that the expression of preprodynorphin, but not c-fos, is upregulated in rat striatum as a consequence of cocaine self-administration. Furthermore, these data indicate that the regulation of preprodynorphin is dissociable from the expression of c-fos in rats exposed to repeated doses of cocaine.