Differential expression of preproenkephalin and preprodynorphin mRNAs in striatal neurons: high levels of preproenkephalin expression depend on cerebral cortical afferents.

Preproenkephalin and preprodynorphin mRNAs can be detected by in situ hybridization in medium-sized striatal neurons in normal rats and in rats with unilateral cerebral cortical lesions. Hybridization of 35S-labeled oligonucleotide cDNAs complementary to specific regions of each mRNA reveals that preproenkephalin-expressing neurons are more numerous than cells expressing preprodynorphin. Hybridization densities above enkephalin-positive neurons are also more than twice those noted above preprodynorphin-expressing cells. Northern analyses of mRNA extracted from the striatum are consistent with these relationships. The striatal preproenkephalin hybridization densities are decreased ipsilateral to cerebral cortical lesions; this change evolves largely between 1 and 5 d following the lesion. Striatal preproenkephalin mRNA is thus more prominent than preprodynorphin mRNA and depends on cerebral cortical inputs for its full expression.