AbstractRecent evidence indicates that astroglia may be involved in the synthesis of endogenous neurosteroids. The extension of glial fibrillary acidic protein (GFAP)‐immunoreactive astroglial cell processes was assessed in hippocampal slice cultures from adult gonadectomized male rats under the influence of the neurosteroids dehydroepiandrosterone, dehydroepiandrosterone sulfate, dehydroepiandrosterone estereate, pregnenolone, pregnenolone sulfate, and pregnenolone oleate. The effects of neurosteroids were compared to those induced by the gonadal steroids testosterone, 17ß‐estradiol and progesterone. Astrocytes in hippocampal slice cultures had a morphology that was indistinguishable from that observed in the hippocampus fixed in situ. Castration of adult male rats resulted in a significant decrease in the extension of GFAP‐immunoreactive processes, both in tissues fixed in situ and in slice cultures. In contrast, incubation of slice cultures from gonadectomized animals with pregnenolone, pregnenolone sulfate, 17ß‐estradiol, and testosterone enhanced the extension of GFAP‐immunoreactive processes. While other steroids tested did not affect this parameter, dehydroepiandrosterone and its sulfate and estereate derivatives induced the transformation of astroglial cells into hypertrophic and highly GFAP immunoreactive cells with the morphological characteristics of reactive astroglia. We conclude that neurosteroids regulate the morphology and/or GFAP distribution of astrocytes in hippocampal slice cultures from adult rats. © 1995 Wiley‐Liss, Inc.