COCAINE SELF-ADMINISTRATION INCREASES PREPRODYNORPHIN, BUT NOT C-FOS,MESSENGER-RNA IN RAT STRIATUM

THE impact of cocaine self-administration on the expression of striata l preprodynorphin and c-fos mRNA was examined with in situ hybridizati on histochemistry. Cocaine significantly increased preprodynorphin mRN A in the dorsal, but not ventral, striatum. Expression of c-fos mRNA i n cocaine-administering rats did not differ from that in controls in a ll structures examined. These results indicate that the expression of preprodynorphin, but not c-fos, is upregulated in rat striatum as a co nsequence of cocaine self-administration. Furthermore, these data indi cate that the regulation of preprodynorphin is dissociable from the ex pression of c-fos in rats exposed to repeated doses of cocaine.