Estradiol enhances excitatory gammabutyric acid-mediated calcium signalingin neonatal hypothalamic neurons

Contrary to the situation in adulthood, gammabutyric acid (GABA), receptor activation during early brain development depolarizes neurons sufficiently to open L-type voltage-gated Ca2+ channels. Because GABA is excitatory duri ng the sensitive period of steroid-mediated brain sexual differentiation, w e investigated whether estradiol modulates excitatory GABA during this peri od, by examining two parameters: 1) magnitude of GABA-induced calcium trans ients; and 2) developmental duration of excitatory GABA. Dissociated hypoth alamic neurons from embryonic-day-15 rat embryos were loaded with the Ca2indicator, fura-a, and transient rises in [Ca2+](i) (Ca2+ transient) were m easured after application of 10 muM muscimol, a GABA(A) receptor agonist. C ells were treated with 10 M estradiol or vehicle from 0-3 days in vitro (DI V) and imaged on 4 DIV, whereas others were treated from 3-6 DIV and imaged on 7 DIV. The mean amplitude of Ca2+ transients after muscimol administrat ion were 68% and 61% higher in estradiol-treated neurons on 4 DIV and 7 DIV , respectively, relative to controls. Consistent with GABA becoming inhibit ory in mature neurons, 50% fewer control neurons responded on DIV 7, relati ve to DIV 4. However, estradiol treatment maintained excitatory GABA on DIV 7 (72% in estradiol-treated us. 35% in control). This is the first report of hormonal modulation of excitatory GABA, and it suggests that estradiol m ay mediate sexual differentiation by enhancing GABA-induced increases in in tracellular Ca2+.