Evidence for transsynaptic regulation of calmodulin-dependent cyclic nucleotide phosphodiesterase in cerebellar Purkinje cells.

Calmodulin-dependent phosphodiesterase (CaM-PDE) is selectively expressed in specific neuronal populations in adult rat brain. In cerebellar cortex, it is expressed at high levels in Purkinje cells (soma and dendrites). Climbing fiber ablation by intraperitoneal injections of 3-acetylpyridine resulted in a selective depression of cerebellar CaM-PDE expression using Western immunoblot procedures; neither calcineurin (calmodulin-dependent protein phosphatase) nor other calmodulin binding proteins, detected by biotinylated calmodulin overlays, were affected. Immunocytochemical staining of cerebellum revealed a loss of detectable CaM-PDE immunoreactivity in Purkinje cells, with no appreciable change in calcineurin immunoreactivity. Cerebral cortex was examined as a control for a direct effect of 3-acetylpyridine on CaM-PDE expression, independent of climbing fiber deafferentation. There were no detectable changes in CaM-PDE or calcineurin immunoreactivity in cortical pyramidal cells, and no changes were detected, either in Western blot analyses for CaM-PDE or calcineurin or in biotinylated calmodulin overlays. These data suggest that CaM-PDE expression in Purkinje cells is regulated transsynaptically by climbing fiber inputs.