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 immunocytochemistry, we have found that both glial fibrillary acidic protein messenger RNA levels and glial fibrillary acidic protein immunoreactive 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 males 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 animals significantly reduced glial fibrillary acidic protein messenger RNA levels and glial fibrillary acidic protein immunoreactive surface density. Neonatal and adult testosterone treatment increased both of these parameters in both sexes; however, there was no additive effect of the steroid treatments. Glial cells are involved in the proliferation, survival, migration and maturation of neurons, as well as in the modulation of synaptic connectivity, and therefore it follows that hormonal modulation of glia may mediate some of the known steroid effects on neurons. The data reported here show that astroglia are significantly influenced by both the neonatal and adult sex steroid environments and suggest that some of the steroid effects on neurons during both of these developmental periods may be mediated, at least in part, through modulation of glial cells.