TRANSCRIPTIONAL CONTROL OF GLIAL FIBRILLARY ACIDIC PROTEIN AND GLUTAMINE-SYNTHETASE IN-VIVO SHOWS OPPOSITE RESPONSES TO CORTICOSTERONE IN THE HIPPOCAMPUS

Transcriptional regulation of two astrocyte genes, glial fibrillary ac idic protein (GFAP) and glutamine synthetase (GS), by glucocorticoids was determined by nuclear run-on assay with hippocampal tissues from a dult male F344 rats. Transcriptional responses of GFAP to corticostero ne were slower than those observed for GS, but were more sensitive to changes in plasma corticosterone. The transcription of GFAP did not ch ange 2 h after the injection of 10 mg corticosterone, but was reduced by 50% at 6 and 24 h. In contrast, corticosterone increased GS transcr iption at 2 and 6 h. Seven days after adrenalectomy, GFAP, but not GS, transcription was increased. Corticosterone replacement (200 mu g/ml in the drinking water) suppressed GFAP, but did not increase GS transc ription in adrenalectomized rats. Therefore, GFAP transcription is mor e sensitive to low physiological levels of corticosterone than transcr iption of GS. The slower response of GFAP than GS to corticosterone su ggests that glucocorticoids may have indirect effects on GFAP expressi on that require additional transcriptional regulators besides the gluc ocorticoid receptor.