Localization of cyclic GMP-dependent protein kinase in rat basal ganglia neurons

Cyclic GMP-dependent protein kinase displays an uneven distribution in brain, being highly concentrated only in cerebellar Purkinje cells. Using DARPP-32 (dopamine- and cyclic AMP-regulated phosphoprotein, Mr 32,000) as exogenous substrate, and performing assays in the absence or presence of the protein inhibitor of cyclic AMP-dependent protein kinase, we have now identified both cyclic AMP-dependent and cyclic GMP-dependent protein kinase activities in the rat neostriatum and substantia nigra. Quinolinic acid-induced degeneration of neostriatal neurons and the straitonigral fibers emanating from neostriatal neurons decreased the activities of both cyclic nucleotide-dependent enzymes by 70-85% in the neostriatum, while cyclic GMP-dependent protein kinase was decreased by 44% and cyclic AMP-dependent protein kinase was decreased by 18% in the substantia nigra. In the basal ganglia, cyclic GMP-dependent protein kinase therefore appears enriched in striatonigral neurons, while cyclic AMP-dependent protein kinase is present both in striatonigral neurons and in other cells. The results indicate that cyclic GMP-regulated protein phosphorylation may play a role in the function of distinct basal ganglion neurons.