Ethanol inhibits NMDA‐induced toxicity and trophism in cultured cerebellar granule cells

In cerebellar granule cell cultures, glutamate and N-methyl-D-aspartate (NMDA) caused either neurotoxic or trophic effects, depending on the developmental stage of the neurones. Ethanol (100 mM) partly inhibited delayed neurotoxicity induced by the excitatory amino acids (25 microM glutamate for 15 min or 100 microM NMDA for 30 min) assessed 24 h after the incubations in mature cultures in the absence of Mg2+. Glycine (5 microM) potentiated the toxicity of glutamate and the ethanol inhibition, and was routinely added in these experiments. The viability of neurones in the presence of 25 mM K+ and 0.8 mM Mg2+ was not impaired when maintained in 40-50 mM ethanol for the whole culture period of 7 days. However, ethanol almost completely inhibited the trophic effects of NMDA on developing cultures in 12.5 mM K+/0.8 mM Mg2+ medium. Glutamate (25 microM) and NMDA (100 microM) potently induced 45Ca2+ uptake by granule cells from day 2 in vitro onward. Sixty-five per cent of the 15-min 45Ca2+ influx induced by glutamate and 80% of that induced by NMDA were inhibited by ethanol (100 mM). MK-801 (a non-competitive antagonist of NMDA receptors; 100 nM) completely inhibited the toxic and trophic actions of glutamate and NMDA, as well as the 45Ca2+ influx induced by NMDA, but only 80% of the 45Ca2+ influx induced by glutamate. These results show that the toxic and trophic actions of glutamate are mediated mainly by Ca2+ influx through NMDA receptors. Both of these actions and the underlying Ca2+ influx are significantly inhibited by ethanol at pharmacological concentrations (< or = 100 mM), although the mechanisms of inhibition still need further study.