GONADAL-STEROIDS REGULATE THE EXPRESSION OF GLIAL FIBRILLARY ACIDIC PROTEIN IN THE ADULT MALE-RAT HIPPOCAMPUS

This study demonstrates that gonadal steroids (estradiol, testosterone , dihydrotestosterone) can regulate the expression of glial fibrillary acidic protein in the adult male rat brain. Previously, we showed tha t castration of adult male rats increased glial fibrillary acidic prot ein messenger RNA in the hippocampus and that this increase was additi ve with the increase induced by deafferenting entorhinal cortex lesion s [Day et al. (1990) Molec. Endocr. 4, 1995-2002]. We extended these e ffects of castration and entorhinal cortex lesion to glial fibrillary acidic protein, using immunoassays. Furthermore, we found regional dif ferences in responses to castration and sex steroid replacement. In th e hippocampus, glial fibrillary acidic protein expression was enhanced by castration and inhibited by sex steriods. In contrast, hypothalami c glial fibrillary acidic protein expression was inhibited by castrati on. Similar regional differences were also shown for astrocyte glial f ibrillary acidic protein distribution by immunocytochemistry. The regi onal specificity of glial fibrillary acidic protein expression after c astration and sex steroid replacement is pertinent to the role of astr ocytes in synaptic plasticity in unlesioned adults as well as in respo nses to lesions where the steroid milieu has been shown to influence s prouting.