EVIDENCE FOR SEXUAL-DIFFERENTIATION OF GLIA IN RAT-BRAIN

It is well established that gonadal steroids mediate sexual differenti ation of the brain via direct effects on neurons during a restricted c ritical period. In addition, estrogen can influence glial morphology i n the adult brain, and in vitro studies suggest estrogen induces glial differentiation. However, there is a lack of in vivo evidence for ste roid effects on glia during the critical period. We report here a horm one-mediated sexual differentiation of arcuate glia as early as Postna tal Day 1. Using glial fibrillary acidic protein immunoreactivity (GFA P-ir), we compared the responsiveness of astroglia in the rat arcuate nucleus among five hormonally different groups. The results indicate i ncreased GFAP-ir cell surface area 24 hr after hormonal manipulation i n castrate males compared to intact males, intact females (ANOVA; P < 0.01), and females injected with testosterone propionate (50 mu g; ANO VA; P < 0.05). However, astroglia in intact males extended their proce sses significantly greater distances from the cell body compared to al l other treatment groups (ANOVA; P < 0.01). The GFAP-ir cells were cat egorized into four distinct classes ranging from a simple bipolar to a fully stellate morphology. The frequency distribution of classes vari ed between groups with more stellate cells found in intact males. Fina lly, these sex differences in arcuate glia persisted into adulthood. W e hypothesize that during the critical period, testosterone, or its me tabolite estrogen, induce sexual differentiation of glia. We further h ypothesize that in females glial cells remain partially undifferentiat ed and this may be important to glial plasticity seen in adult female arcuate. (C) 1996 Academic Press.