Estradiol enhances excitatory gamma-aminobutyric [corrected] acid-mediated calcium signaling in neonatal hypothalamic neurons.
Contrary to the situation in adulthood, gamma-aminobutyric [corrected] acid (GABA)(A) receptor activation during early brain development depolarizes neurons sufficiently to open L-type voltage-gated Ca(2+) channels. Because GABA is excitatory during the sensitive period of steroid-mediated brain sexual differentiation, we investigated whether estradiol modulates excitatory GABA during this period, by examining two parameters: 1) magnitude of GABA-induced calcium transients; and 2) developmental duration of excitatory GABA. Dissociated hypothalamic neurons from embryonic-day-15 rat embryos were loaded with the Ca(2+) indicator, fura-2, and transient rises in [Ca(2+)](i) (Ca(2+) transient) were measured after application of 10 microM muscimol, a GABA(A) receptor agonist. Cells were treated with 10(-10) M estradiol or vehicle from 0-3 days in vitro (DIV) and imaged on 4 DIV, whereas others were treated from 3-6 DIV and imaged on 7 DIV. The mean amplitude of Ca(2+) transients after muscimol administration were 68% and 61% higher in estradiol-treated neurons on 4 DIV and 7 DIV, respectively, relative to controls. Consistent with GABA becoming inhibitory in mature neurons, 50% fewer control neurons responded on DIV 7, relative to DIV 4. However, estradiol treatment maintained excitatory GABA on DIV 7 (72% in estradiol-treated vs. 35% in control). This is the first report of hormonal modulation of excitatory GABA, and it suggests that estradiol may mediate sexual differentiation by enhancing GABA-induced increases in intracellular Ca(2+).
Perrot-Sinal
T S
TS
Department of Physiology, University of Maryland School of Medicine, Baltimore 21201, USA. tperr001@umaryland.edu
Davis
A M
AM
Gregerson
K A
KA
Kao
J P
JP
McCarthy
M M
MM
D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D004958:Estradiol / Q000494:pharmacology*; D018698:Glutamic Acid / Q000494:pharmacology; D007031:Hypothalamus / Q000378:metabolism*; D009118:Muscimol / Q000494:pharmacology; D009474:Neurons / Q000378:metabolism; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects*; D013997:Time Factors; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
D020746:Calcium Channels, L-Type; D009118:Muscimol; D018698:Glutamic Acid; D004958:Estradiol; D005680:gamma-Aminobutyric Acid; D002118:Calcium