Ethanol Inhibition of N-Methyl-D-Aspartate-Stimulated Endogenous Dopamine Release from Rat Striatal Slices: Reversal by Glycine

N-Methyl-D-aspartate stimulated a concentration-dependent release of endogenous dopamine from rat striatal slices. The threshold for activation was between 10 and 25 microM and reached a maximum at 1 mM. Release was completely blocked by magnesium or tetrodotoxin. Ethanol (10-200 mM) significantly inhibited the N-methyl-D-aspartate-stimulated release of dopamine by 20-45%, with half-maximal inhibition occurring at approximately 21 mM. Addition of ethanol plus increasing concentrations of magnesium resulted in a greater inhibition of N-methyl-D-aspartate-stimulated dopamine release than that observed with magnesium alone. However, this effect appeared to be due to a noninteractive additive effect of the two antagonists, as the IC50 value for magnesium inhibition was not significantly altered by ethanol. Glycine, which had no effect on dopamine release by itself, completely reversed the inhibitory effects of ethanol (25 mM) at low micromolar concentrations. These results suggest that ethanol may produce its effects in striatal slices by interfering with a glycine modulatory site of the N-methyl-D-aspartate receptor-ionophore complex.