17beta-estradiol affects GABAergic transmission in developing hippocampus.

Estrogens are potent modulators of the nervous system. In particular, 17beta-estradiol was shown to affect GABAergic synaptic transmission in hippocampus of adult animals in vivo but much less is known on the impact of this hormone on the GABAergic system in the developing brains. We have recently shown that phasic and tonic GABAergic transmissions are strongly modulated upon long-term treatment with exogenous 17beta-estradiol in hippocampal neurons developing in vitro. To check for the long-term estrogen effect in a more physiological developmental model, we have investigated the GABAergic transmission in developing brains of P7-P40 animals, injected daily with 17beta-estradiol. We have found that such a treatment clearly increased GABAergic mIPSC frequency and amplitude while the onset and decay of mIPSCs were shortened. These effects were statistically significant in the youngest considered age group (P7-P13) with a tendency to disappear in older animals. Long-term treatment with estradiol did not change the susceptibility of mIPSC amplitude to upregulation by flurazepam while mIPSC decay was prolonged by this drug to a larger extent in 17beta-estradiol-treated animals. 17beta-estradiol strongly upregulated GABAergic tonic current but again this effect was restricted to the youngest group of animals. We conclude that 17beta-estradiol strongly modulates the GABAergic synaptic transmission but this effect critically depends on the animal age being the most prominent in youngest animals.