Abstract
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 ARs) in both medial septum/diagonal band (MS/DB) and cerebellar Purkinje neurons. In the present study, the impact of ethanol on developing GABA ARs 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 ARs to Zn 2+-inhibition after ethanol was not found with the intubation model. In studies only carried out using the intubation method, 3α-hydroxy-5α-pregnan-20-one (3α-OH-DHP) caused an allosteric concentration-dependent potentiation of currents activated by non-saturated concentrations of GABA. A bicuculline sensitive direct activation of GABA ARs also occurred with higher concentrations of 3α-OH-DHP alone. Ethanol intubation up-regulated allosteric neurosteroid potentiation with low concentrations of GABA, but did not change direct agonist actions of 3α-OH-DHP. Finally, 3α-OH-DHP did not prime ethanol insensitive GABA ARs 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.
Published Version
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