Topographical distributions of 32K and 48K cAMP-regulated phosphoproteins: Relationships to dopamine and serotonin innervations in striatum, substantia nigra and cerebral cortex

The topographical distribution of a cAMP-regulated phosphoprotein of an apparent molecular weight (M_r) of 32,000 (32K) was examined in homogenates prepared from microdiscs punched out from serial frozen slices of the striatum. The amount of this phosphoprotein progressively diminished from the rostral to the caudal part of the striatum as did both the dopamine-innervation and the dopamine (D₁)-sensitive adenylate cyclase. After kainic acid lesion of the rostral part of the striatum, the 32K phosphoprotein disappeared in this area and we observed a 48% decrease in the amount of 32K phosphoprotein found in the substantia nigra. 6-Hydroxydopamine lesions of the nigro-striatal dopaminergic pathway did not affect the 32K phosphoprotein either in striatum or substantia nigra. These results suggest that in the nigro-striatal pathway, the 32K phosphoprotein is closely associated with dopaminoceptive neurons containing D₁ receptors. In the cerebral cortex the association of 32K phosphoprotein with dopaminoceptive neurons is more questionable since we did not find a higher density of this phosphoprotein in areas containing a high amount of D₁ receptor (frontal cerebral cortex) than in areas containing a low amount of D₁ receptor (parietal cerebral cortex). In the course of this study we found another cAMP-regulated phosphoprotein of an M_r of 48,000 (48K). The amount of this phosphoprotein increased progressively from the rostral to the caudal part of the striatum, a pattern of distribution close to that of serotonin terminals. This protein was also present in the substantia nigra. Kainic acid lesioning of the rostral part of the striatum did not affect the amount of the 48K phosphoprotein within the substantia nigra. 6-Hydroxydopamine lesions of the substantia nigra also did not alter the amount of 48K phosphoprotein in this brain region.