Differential Localization of the γ 3 and γ 12 Subunits of G Proteins in the Mammalian Brain

The localization of two forms of the γ subunit of G proteins, γ 3 and γ 12 , was examined in the mammalian brain. Concentrations of these two γ subunits increased markedly, as did those of glial fibrillary acidic protein, during postnatal development in the rat cerebral cortex. In aged human brains, by contrast, the concentration of γ 3 tended to decrease with age, whereas that of γ 12 in the temporal cortex increased slightly. An immunohistochemical study of human brains revealed that γ 3 was abundant in the neuropil, whereas γ 12 was localized in glial cells. In the hippocampal formation of aged human brains, levels of γ 12 ‐positive cells, as well as levels of glial fibrillary acidic protein‐ and vimentin‐positive astrocytes, increased, in particular in the CA1 subfield and the prosubiculum, in which there was a decrease in the number of pyramidal cells. The appearance of γ 12 ‐positive cells associated with the loss of pyramidal cells was also observed in the hippocampus of rats that had been treated with kainic acid. These results indicate that γ 12 is strongly expressed in reactive astrocytes. In a study of cultured neural cells, we found that γ 12 was predominant in glioma cells, such as C6 and GA‐1 cells, in contrast with the specific localization of γ 3 in PC12 pheochromocytoma cells, which are neuron‐like cells. Taken together, the results indicate that γ 3 and γ 12 are selectively expressed in neuronal and glial cells, respectively, and that concentrations of γ 3 and γ 12 in the brain are related to the numbers and/or extent of maturation of these cells.