Distribution and expression of G-protein in rat cerebral cortical cells. I. Intact tissue

Localization and developmental expression of guanine nucleotide-binding regulatory protein (G-protein) were investigated in cerebral cortical tissue of rat. Immunohistochemical techniques using a rabbit polyclonal antibody were applied to reveal the pattern of G-protein distribution. Fluorescent staining in cortical sections was localized mainly to neurons; cell bodies were stained along with the proximal region of processes, including apical dendrites. All neurons appeared to be equally stained, and thus the staining activity reflected the laminar pattern of these cells in cortex. Moreover, areas of neuropil, white matter, and layer I were immunonegative, although synaptic labelling could not be directly eliminated. Most glial cells also lacked staining; however, moderately intense labelling was observed in the choroid plexus, ependymal cells and a subpopulation of microglia. Using Western immunoblot analysis, the antigens recognized in rat cerebral cortex were shown to co-electrophorese with the alpha- and beta-subunits of bovine brain G-protein, thus supporting the specificity of the antibody preparation utilized. In contrast to the adult tissue, in fetal and neonatal cortex faint to moderate staining was uniformly exhibited by essentially all cells. As determined by the immunoblot procedure, the overall level of G-protein increased from the fetal stage through the neonatal and adolescent periods to reach a maximum concentration in young adult tissue. Based on cellular distribution, G-protein may function in the overall regulation of neuronal activity within cerebral cortex. Further, these results suggest that there is a selective developmental increase in expression of G-protein in specific cell populations, particularly neurons.