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Neurosteroids modulate the reaction of astroglia to high extracellular potassium levels

The extracellular concentration of potassium ([K+]0) in brain tissue is modified by neuronal activity and is increased under several pathological conditions. The influence of neurosteroids on the astroglia response to high [K+]0 was assessed on cultured slices from rat hippocampus. Exposure to [K+]0 above physiological (3 mM) levels resulted in the progressive appearance of cell processes immunoreactive for glial fibrillary acidic protein (GFAP). The maximal effect was observed at 50 mM [K+]0, and further increases of [K+]0 did not increase the extension of GFAP‐immunoreactive processes. The effect was observed as early as 10 min after increasing [K+]0, was independent of new protein synthesis, and was reversible, reaching control conditions by 15 h after resetting [K+]0 to physiological levels. Gonadal hormones and neurosteroids had prominent and variable effects on the stimulatory influence of high [K+]0 on astroglia morphology. At physiological [K+]0, 17β‐estradiol and pregnenolone, as well as its sulfate derivative, increased the extension of GFAP‐immunoreactive processes. However, at high [K+]0, testosterone, pregnenolone, and dehydroepiandrosterone and its sulfate derivative decreased the extension of GFAP‐immunoreactive processes. Effects of gonadal hormones and neurosteroids were blocked by the protein synthesis inhibitor cycloheximide. These results suggest that non‐genomic effects of high [K+]0 on glial cells interact with genomic effects of steroids to modulate astroglia morphology. © 1996 Wiley‐Liss, Inc.