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 that castration of adult male rats increased glial fibrillary acidic protein messenger RNA in the hippocampus and that this increase was additive with the increase induced by deafferenting entorhinal cortex lesions [ Day el al. (1990) Molec. Endocr. 4, 1995–2002]. We extended these effects of castration and entorhinal cortex lesion to glial fibrillary acidic protein, using immunoassays. Furthermore, we found regional differences in responses to castration and sex steroid replacement. In the hippocampus, glial fibrillary acidic protein expression was enhanced by castration and inhibited by sex steriods. In contrast, hypothalamic glial fibrillary acidic protein expression was inhibited by castration. Similar regional differences were also shown for astrocyte glial fibrillary acidic protein distribution by immunocytochemistry. The regional specificity of glial fibrillary acidic protein expression after castration and sex steroid replacement is pertinent to the role of astrocytes in synaptic plasticity in unlesioned adults as well as in responses to lesions where the steroid milieu has been shown to influence sprouting.