A comparison of the effects of ethanol and the competitive glycine antagonist 7-chlorokynurenic acid on N-methyl-D-aspartic acid-induced neurotransmitter release from rat hippocampal slices.

N-Methyl-D-aspartate (NMDA; 500 microM) stimulated the net release of preloaded tritiated norepinephrine from rat hippocampal slices. Both ethanol and the competitive glycine antagonist 7-chlorokynurenic acid (7-CK) dose-dependently inhibited NMDA-stimulated release without affecting basal, nonstimulated efflux. These inhibitory effects were readily reversed upon washout of the drugs. Over the concentration range tested (25-200 mM), ethanol inhibited approximately 65% of NMDA-stimulated release with an estimated IC50 of approximately 70 mM. In contrast, 7-CK fully inhibited release (> 95%) at a concentration of 30 microM with half-maximal inhibition occurring at approximately 2 microM. The combination of 7-CK (1-30 microM) and ethanol (25-100 mM) had an additive inhibitory effect on NMDA-stimulated release but did not alter the inhibitory potency of 7-CK. Calculated IC50 values for 7-CK in the presence of 25, 50, or 100 mM ethanol were (mean +/- SEM; microM) 2.33 (0.11), 2.38 (0.23), and 1.99 (0.30), respectively. 7-CK (3 microM) inhibited NMDA-stimulated [3H]norepinephrine release by approximately 50%. This inhibition was fully attenuated by the addition of the glycine agonist D-serine with complete reversal occurring at 30 microM D-serine. Increasing the 7-CK concentration to 10 microM shifted the D-serine dose-effect curve to the right in a parallel fashion as expected for a competitive antagonist. In contrast, the inhibitory effects of ethanol or the combination of 7-CK (3 microM) and ethanol (25 or 50 mM) were not reversed by the addition of D-serine (0.1-1,000 microM).(ABSTRACT TRUNCATED AT 250 WORDS)