Dopaminergic regulation of proenkephalin-A gene expression in the basal ganglia.

Dopaminergic denervation by 6-hydroxydopamine (6-OHDA) increased proenkephalin-A gene expression in the striatum as evidenced by increases in the levels of Met5-enkephalin (ME), precursor and preproenkephalin mRNA (PE-mRNA). This and other lines of evidence support the hypothesis that nigrostriatal dopamine input is inhibitory to striatal enkephalin neurons and that the removal of this inhibitory influence leads to an acceleration of ME biosynthesis. These findings suggest that the enkephalin system may be associated with the progression of adaptive changes subsequent to dopaminergic dysfunction in basal ganglia.