Neuroscience Vol. 55, No. 2, pp. 435-443, 1993 Printed in Great Britain 0306-4522/93 86.00 + 0.00 Pergamon Press Ltd IBRO zyxwvut GONADAL STEROIDS REGULATE THE EXPRESSION OF GLIAL FIBRILLA RY ACIDIC PROTEIN IN THE ADULT M A LE RAT HIPPOCAMPUS J. R. DAY,* N. J. LAPING, M. LAMPERT-ETCHELLS, S. A. BROWN, J. P. ~‘CALLAGHAN,~ T. H. MCNEILL and C. E. FINCH Neurogerontology Division, Andrus Gerontology Center, and Department of Biological Sciences, University of Southern California, Los Angeles, CA 90089-0191, U.S.A. Abstract-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 et al. (1990) Molec. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIH Endocr. 4, 1995-20021. 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 immuno- cytochemistry. 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. Gonadal steroids have organizational effects on the developing mammalian nervous system that persist as gender differences in adult neural structures. How- ever, the role of steroids in maintaining synaptic organization or in regulating plasticity is compara- tively undefined in adults. Recently, we found that castration of adult male rats increased levels of two astrocyte mRNAs whose expression in the adult hippocampus was not known to be responsive to gonadal steroids. Castration for three weeks elevated the expression of glial fibrillary acidic protein (GFAP) and clusterin (SGP-2) in male rat hippo- campus, as shown by northern blots and immuno- cytochemistry. These two astrocytic mRNAs were known to increase during lesion-induced neurodegen- eration; prior castration additively increased the prevalence of these transcripts.6 These data suggest that testicular hormones regulate hippocampal astro- *To whom correspondence should be addressed at: Depart- ment of Biology, Pennsylvania State University, Univer- sity Park, PA 16802, U.S.A. (present address). j-Present address: Health Effects Laboratory, U.S. Environ- mental Protection Agency, Research Triangle Park, NC, 27711, U.S.A. Abbreviations: AR, androgen receptor; DHT, dihydro- testosterone; ECL, entorhinal cortex lesion; EDTA, ethylenediaminetetra acetate; ELISA, enzyme-linked im- munosorbant assay; ER, estrogen receptor; GFAP, glial fibrillary acidic protein; -IR, immunoreactive, im- munoreactivity; SDS, sodium dodecyl sulfate; SGP-2, clusterin; SSC, standard sodium citrate; SSPE, standard sodium phosphate with EDTA. cyte activity in intact adult rats and may influence astrocyte activities during lesion-induced synaptic reorganization. Anatomical studies show important influences of adrenal and gonadal steroids on synaptic reorganiza- tion. Entorhinal cortex lesions (ECLs) that interrupt the perforant path to the granule neuron molecular layer induce synaptic reorganization in the hippo- campus. *o-44 ECL-induced synaptic reorganization is inhibited by glucocorticoids.22,36 Gender differences of adult rats in dendritic branching of hippocampal granule cellsI and CA3 pyramidal neuronsI are evidence of gonadal steroid participation in the organization of the adult hippocampus. The effects of castration on ECL-induced plasticity also differ between genders: sprouting is stimulated by castration in females, but not in males.23,37 Astrocytes are strongly implicated in the regulation of reactive synaptic reorganization after lesions in the adult brain, e.g. in the production of growth fac- tors1~8~12~16~17~19~24 and removal of degenerating termi- nals 33In vitro models also suggest a role in guiding axon growth.7*14,27,39 Astrocytic reactivity may be monitored by the expression of the astrocyte-specific cytoskeletal protein, GFAP. Both GFAP and its mRNA are increased in the hippocampus following deafferentation.8~32~42 Effects of sex steroids on astrocytes in the brain might be indirect, because astrocytes that display mRNA or immunoreactivity for estrogen (ER) or androgen (AR) receptors are rare compared to 435