Ethanol-induced inhibition of NMDA receptor channels.

Ethanol is a potent inhibitor of the N-methyl-D-aspartate (NMDA)-receptor subtype of glutamate receptor in a number of brain areas. The mechanism of ethanol action has been investigated by means of patch-clamp recording of ionic currents and fura-2 measurement of intracellular Ca2+ concentration in cell culture systems; the subunit composition of NMDA receptors and their influence on the effect of ethanol was determined by molecular biology methods. Ethanol does not appear to interact with NMDA either at the glutamate recognition site of the receptor, or at any of the hitherto known multiple modulatory sites, such as the glycine or polyamine site. Moreover, ethanol does not cause an open channel block by itself and fails to interact with Mg2+ at the site where it causes open channel block. The ability of ethanol to inhibit responses to NMDA is dependent on the subunit combination of NMDA receptors. The NR1/NR2A and NR1/NR2B combinations are preferentially sensitive to ethanol inhibition. Chronic treatment with ethanol leads to an increase of the NMDA receptor number at the transcriptional and posttranscriptional level; the receptor function is also facilitated. This causes withdrawal-type seizures after termination of chronic treatment with ethanol. The inhibition of NMDA receptors by ethanol leads to the depression of excitatory synaptic potentials mediated by this type of excitatory amino acid receptor. Ethanol-induced disturbances in certain regions of the brain, i.e. hippocampus, nucleus accumbens or locus coeruleus may lead to cognitive disorders or drug dependence. Brain slices containing the locus coeruleus may be used as an in vitro test system to investigate the addictive properties of ethanol.