SEXUAL DIMORPHISM AND SEX STEROID MODULATION OF GLIAL FIBRILLARY ACIDIC PROTEIN MESSENGER-RNA AND IMMUNOREACTIVITY LEVELS IN THE RAT HYPOTHALAMUS

By using the techniques of in situ hybridization histochemistry and im munocytochemistry, we have found that both glial fibrillary acidic pro tein messenger RNA levels and glial fibrillary acidic protein immunore active surface density in the arcuate nucleus and median eminence are modulated by both the neonatal and adult sex steroid environments. No effect was seen on the number of immunoreactive glia. Intact adult mal es had significantly higher glial fibrillary acidic protein messenger RNA levels and glial fibrillary acidic protein immunoreactive surface density than females. Both adult and neonatal castration of male anima ls significantly reduced glial fibrillary acidic protein messenger RNA levels and glial fibrillary acidic protein immunoreactive surface den sity. Neonatal and adult testosterone treatment increased both of thes e parameters in both sexes; however, there was no additive effect of t he steroid treatments. Glial cells are involved in the proliferation, survival, migration and maturation of neurons, as well as in the modul ation of synaptic connectivity, and therefore it follows that hormonal modulation of glia may mediate some of the known steroid effects on n eurons. The data reported here show that astroglia are significantly i nfluenced by both the neonatal and adult sex steroid environments and suggest that some of the steroid effects on neurons during both of the se developmental periods may be mediated, at least in part, through mo dulation of glial cells.