Dynamics of NMDAR-mediated neurotoxicity during chronic ethanol exposure and withdrawal

We have utilized a hippocampal brain slice explant system to assess cellula r and synaptic mechanisms underlying the expression of alcohol withdrawal h yperexcitability. Previously, we observed a role for NMDA receptors in the expression of electrographic seizures (EGS) observed immediately upon withd rawal from chronic ethanol exposure in this system One possible cellular me chanism responsible for these prior results involves NMDAR-mediated neuroto xicity, which was assessed in the present study. Explants were exposed to 3 5 or 75 mM ethanol for 6 or 12 days and incubated with propidium iodide (PI ) to label non-viable cells and then imaged digitally. PI labeling was sign ificantly reduced (36% of control levels) following chronic ethanol exposur e (75 mM). When tested following ethanol withdrawal, PT labeling remained s ignificantly reduced in the 75 mM exposed group. We next assessed the effec t of an NMDA challenge 24 h following withdrawal. The 35 mM and 75 mM ethan ol exposed groups displayed significant 6-fold and 13-fold NMDAR-mediated i ncreases in PI labeling respectively; control explants displayed a 3-fold i ncrease. These data suggest that chronic ethanol exposure prior to withdraw al has a minor neuroprotective effect that slightly diminishes within 24 h of ethanol withdrawal. Furthermore, the data indicate that direct NMDAR act ivation is required for induction of ethanol withdrawal neurotoxicity. (C) 2000 Elsevier Science Ltd. All rights reserved.