Gonadal steroids regulate GABAA receptor subunit mRNA expression in NT2-N neurons

Changes in gonadal steroid hormone levels during the menstrual cycle affect seizure frequency in women with catamenial epilepsy. Since GABA(A) receptors (GABARs) contribute to the prevention and termination of seizures by reducing neuronal excitability, we hypothesized that fluctuating gonadal steroid levels might affect GABAR subunit expression, which could alter inhibitory tone leading to increased seizure activity. To address this question in a simplified environment in vitro, we examined the effects of gonadal steroids on NT2-N neuronal cells. We have previously shown that NT2-N cells express functional GABARs, and that the expression pattern of GABAR subunits is regulated by chronic benzodiazepine exposure and hypoxia. NT2-N neurons were exposed to progesterone (0.1 mu M), beta-estradiol (3 nM), or vehicle (DMSO) for 2 days or 7 days prior to RNA harvesting. GABAR subunit mR-NA levels were assessed by semiquantitative RT-PCR normalized to actin levels. Progesterone exposure for 7 days increased alpha 2 and gamma 3 and decreased alpha 5 subunit mRNAs, while beta-estradiol caused significant increases in alpha 3, beta 3 and epsilon expression. Further analysis revealed differential regulation of alpha 4, alpha 5, epsilon and pi subunit expression. Plots of relative PCR density in progesterone-treated cells for alpha 2 vs. alpha 5, alpha 5 vs. gamma 3 and alpha 2 vs. gamma 3 showed correlation between samples, suggesting coordinate regulation. Both progesterone and estrogen nuclear receptor mR-NAs were detected by RT-PCR, and 2 days but not 7 days estrogen exposure upregulated progesterone receptor mRNA. Gonadal steroid fluctuations regulate GABAA receptor subunit expression in NT2-N cells. Such changes, if observed in vivo, could affect seizure frequency. (c) 2005 Elsevier B.V. All rights reserved.