Neurogranin expression by cerebellar neurons in rodents and non-human primates

Neurogranin (NG) is a brain-specific protein kinase C substrate involved in the regulation of calcium signaling and neuronal plasticity. A rostrocaudal expression profile, with large amounts in telencephalic brain regions and low expression levels in phylogenetically older brain structures, was reported previously. In the cerebellum, expression of NG has not been described. By using immunocytochemistry and in situ hybridization, we found that NG is expressed in the mouse (C57Bl/6), rat (Wistar), and monkey (Cercopithecus aetiops) cerebella. In the mouse cerebellum, Golgi cells were strongly immunoreactive for NG, whereas other cerebellar neurons were devoid of this protein. Cell counts showed 1.6-fold more immunopositive Golgi cells in the hemispheres (61.1 +/- 8.0 cells/mm(2)) than in the vermis (37.5 +/- 3.3 cells/mm(2)). Developmental studies showed detectable NG in the mouse cerebellum as early as on postnatal day 10 (P10). In contrast to the mouse, in the rat cerebellum we found only a few Golgi cells containing NG (hemispheres, 2.4 +/- 0.5 cells/mm(2); vermis, 1.5 +/- 0.3 cells/mm(2)). In the monkey cerebellum, unipolar brush cells, localized in the granular layer, were heavily labeled, whereas Golgi cells were devoid of NG. This study demonstrated that NG is strongly expressed in specific gamma-aminobutyric acidergic neurons in the rodent cerebellum. In addition, NG expression in the primate cerebellum by brush cells, which are excitatory, showed remarkable cell type-specific and species-specific expression patterns of a postsynaptic protein mediating calcium signaling mechanisms.