Sexual differentiation of astrocyte morphology in the developing rat preoptic area

The preoptic area is an important brain region controlling sex-typic behaviour and physiology, and astrocytes of this region are responsive to steroids perinatally. Utilizing glial fibrillary acidic protein immunocytochemistry, the morphology of astrocytes in the preoptic area of male and female rat pups was examined on the day of birth and on postnatal day 3. As early as the day of birth, astrocytes of the male preoptic area exhibit both significantly greater primary process length and number of primary processes, and these differences remain at postnatal day 3. Application of exogenous steroid to females suggested that gonadal steroids, in particular oestradiol, mediate the sex difference. Pups received 100 mug of steroid on the day of birth and again on postnatal day 1, and astrocyte morphology was assessed on postnatal day 3. Both oestradiol and testosterone induced significant changes in process length and number compared to vehicle-treated controls. Astrocytes of oestradiol-treated females did not differ on PN3 from those of PN3-untreated males. Exposure to the nonaromatizable steroid, dihydrotestosterone, had no effect on any attribute of astrocyte morphology. This suggests the effects induced by testosterone are mediated by oestradiol following local aromatization of the steroid, and not through direct activation of the androgen receptor. Astrocytes are important in synapse formation and efficacy, and we hypothesize a role for astrocyte complexity and differentiation in the establishment of synaptic patterning.