ROLE OF GABA(A) RECEPTORS IN THE GABA ATTENUATION OF ETHANOL NEUROTOXICITY

We have previously reported that GABA reverses the neuronotoxic effect s of ethanol in neuroblast-enriched cultures derived from 3-day-old wh ole chick embryo (E3WE). In the present study, we examined the effects of GABA agonists and antagonists on morphological growth patterns and on cholinergic neuronal phenotypic expression, using choline acetyltr ansferase (ChAT) activity as a marker. E3WE neuroblast-enriched cultur es showed positive immunoreactivity for neurofilament and as previousl y reported, control cultures exhibited the characteristic pattern of o utgrowth of neurites of varying thickness radiating from the aggregate s. In contrast, cultures grown in ethanol consisted of neuronal aggreg ates lacking fasciculation but having a complex network of individual thin neurites. Both GABA and GABA(A) agonist muscimol enhanced neuriti c fasciculation and arborization in control and ethanol-treated cultur es, and this growth enhancement was inhibited by GABA(A) antagonist bi cuculline. No effects were noted with GABA(B) agonist baclofen. GABA i ncreased ChAT activity in E3WE control cultures, as previously reporte d. A similar effect was seen with GABA(A) agonist muscimol, but not wi th GABA(B) agonist baclofen. However, the GABA effect was not apparent in the presence of GABA(B) antagonist phaclofen. Thus, it appears tha t the cholinotrophic effects of GABA are mediated by both GABA(A) and GABA(B) receptors. In ethanol-treated cultures the already-reported Ch AT decline was reversed by GABA and muscimol, but not by baclofen. Mor eover, the GABA effect in ethanol-treated cultures was not antagonized by GABA(B) antagonist phaclofen, suggesting that the GABA effect was mediated by a GABA(A) receptor. We conclude from these findings that t he cholinotrophic effects of GABA are mediated by GABA(A) and GABA(B) receptors, while the rescuing effects of GABA in the ethanol-treated c ultures are mediated via GABA(A) receptors. (C) 1996 Wiley-Liss, Inc.