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* To whom correspondence should be addressed. E-mail: ramorris{at}mail.utexas.edu.
To discriminate between pre- and post-synaptic effects of ethanol on NMDAR-signaling in hippocampus, we adapted the technique of Sr2+-substitution to the hippocampal blind slice patch-clamp preparation. Hippocampal slices were isolated from 12-20 day old rats sacrificed in accordance with University of Texas IACUC guidelines. NMDAR mEPSCs were evoked from CA1 pyramidal neurons in the presence of Sr2+ (4 mM), causing the synchronous EPSC observed in the presence of Ca2+ to be supplanted by asynchronous mEPSCs. Amplitudes typically ranged from 5-40 pA and responded to the NMDAR antagonist (DL)-APV (50µM) with a statistically significant reduction in mean amplitude. Ethanol (25, 50, and 75 mM) exerted dose-dependent effects on mEPSC amplitude and frequency. Peak amplitude inhibition was observed at 75 mM ethanol. Notably, ethanol significantly decreased event frequency at 50 and 75 mM ethanol. Ethanol (75 mM) also significantly increased the paired-pulse ratio of NMDAR EPSCs. Cumulative comparisons of decay time constants derived from single-exponential fitting of mEPSCs revealed significantly accelerated current decay kinetics in the presence of 75 mM ethanol. Taken together, these reductions in miniature event frequency and amplitude, concurrent with an increased rate of decay, suggest that the acute effects of ethanol on NMDAR signaling at hippocampal synapses are multifocal in nature. This finding of pre-and post-synaptic effects of ethanol on NMDAR signal strength in a brain region central to cognition is wholly consistent with previous reports of ethanol inhibition of NMDAR-LTP in vitro and with the profound cognitive deficits associated with binge-level intoxication in vivo.
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