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Early postnatal ethanol intubation blunts GABA(A) receptor up-regulation and modifies 3alpha-hydroxy-5alpha-pregnan-20-one sensitivity in rat MS/DB neurons.

Previously we found postnatal binge-like ethanol exposure using an artificial-rearing method in the rat delayed developmental up-regulation of GABA(A) receptors (GABA(A)Rs) in both medial septum/diagonal band (MS/DB) and cerebellar Purkinje neurons. In the present study, the impact of ethanol on developing GABA(A)Rs in MS/DB neurons was further tested under conditions not requiring anesthesia or maternal deprivation. Nursing rat pups received ethanol (4.5-5.25 g/kg/day) on postnatal days (PD) 4-9, which was administrated manually by oral intragastric intubation. This treatment caused dose-dependent blunting of peak GABA(A) receptor whole cell currents in acutely dissociated MS/DB cells on PD 12-15. The threshold with oral intubation was slightly higher than previously observed for artificial-rearing (4.9 vs. 4.5 g/kg/day). The previously observed reduced sensitivity of GABA(A)Rs to Zn(2+)-inhibition after ethanol was not found with the intubation model. In studies only carried out using the intubation method, 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha-OH-DHP) caused an allosteric concentration-dependent potentiation of currents activated by non-saturated concentrations of GABA. A bicuculline sensitive direct activation of GABA(A)Rs also occurred with higher concentrations of 3alpha-OH-DHP alone. Ethanol intubation up-regulated allosteric neurosteroid potentiation with low concentrations of GABA, but did not change direct agonist actions of 3alpha-OH-DHP. Finally, 3alpha-OH-DHP did not prime ethanol insensitive GABA(A)Rs to become sensitivity to acute ethanol potentiation. These results indicate ethanol consistently blunts postnatal GABA(A) receptor up-regulation across early postnatal binge-type ethanol exposure models and may increase positive modulation of GABA(A) receptors by endogenous neurosteroids.