Protein kinase C negatively regulates the intrinsic excitability in zebrin-negative cerebellar Purkinje cells

Protein kinase C gamma (PKC gamma), a neuronal isoform present exclusively in the central nervous system, is most abundantly expressed in cerebellar Purkinje cells (PCs). Targeted deletion of PKC gamma causes a climbing fiber synapse elimination in developing PCs and motor deficit. However, physiological roles of PKC gamma in adult mouse PCs are little understood. In this study, we aimed to unravel the roles of PKC gamma in mature mouse PCs by deleting PKC gamma from adult mouse PCs of PKC gamma fl/fl mice via cerebellar injection of adeno-associated virus (AAV) vectors expressing Cre recombinase under the control of the PC-specific L7-6 promoter. Whole cell patch-clamp recording of PCs showed higher intrinsic excitability in PCs virally lacking PKC gamma [PKC gamma-conditional knockout (PKC gamma-cKO) PCs] than in wild-type (WT) mouse PCs in the zebrin-negative module, but not in the zebrin-positive module. AAV-mediated PKC gamma re-expression in PKC gamma-deficient mouse PCs in the zebrin-negative module restored the enhanced intrinsic excitability to a level comparable to that of wild-type mouse PCs. In parallel with higher intrinsic excitability, we found larger hyperpolarization-activated cyclic nucleotide-gated (HCN) channel currents in PKC gamma-cKO PCs located in the zebrin-negative module, compared with those in WT mouse PCs in the same region. However, pharmacological inhibition of the HCN currents did not restore the enhanced intrinsic excitability in PKC gamma-cKO PCs in the zebrin-negative module. These results suggested that PKC gamma suppresses the intrinsic excitability in zebrin-negative PCs, which is likely independent of the HCN current inhibition.