INTRACELLULAR INCREASES OF CAMP INDUCE OPPOSITE EFFECTS IN GLUTAMIC-ACID DECARBOXYLASE (GAD(67)) AND GLIAL FIBRILLARY ACIDIC PROTEIN IMMUNOREACTIVITIES IN C6 CELLS

C6 is a cell line that expresses glial and neuronal markers. Treatment s that increase intracellular cAMP levels induce the differentiation o f these cells. We had previously demonstrated that forskolin, an agent that activates adenylate cyclase, produced changes in gene expression in C6 cells. As a consequence of this treatment, glutamic acid decarb oxylase (GAD) activity and the mRNA for GAD(67), one of the isoforms o f the enzyme, decreased. In contrast, this treatment increased the tra nscription of the glial fibrillary acidic protein (GFAP) gene. We now show, by immunocytochemistry, that the changes in gene expression are phenotypically reflected by corresponding changes in the levels of the proteins encoded by the GAD(67) and GFAP genes. Computer-assisted ima ge analysis demonstrated that both the increase in GFAP immunofluoresc ence, and the decrease in GAD(67) immunofluorescence are statistically significant. The changes in gene expression and in protein immunoreac tivity are part of the differentiation process of the C6 cells towards a more mature glial phenotype.