Ethanol inhibition of NMDA receptor stimulation by the high-affinity selective agonist d,l-(tetrazol-5-yl)glycine (T5G) was studied using acutely dissociated neonatal whole-brain neurons loaded with the fluorescent indicator fura-2. T5G induced a concentration-dependent increase in intracellular calcium with a maximal increase above basal of 70 nM at 16 μM T5G (EC 5 0 of 0.66 +/- 0.18 μM). T5G agonist specificity was verified using the NMDA antagonists MK-801 (40 nM), APV (100 μM), and Mg 2 + (1 mM). The T5G stimulation of calcium entry was both blocked and reversed by these antagonists. Ethanol significantly inhibited the T5G-mediated increase in intracellular calcium only at concentrations =< 100 mM. In addition, the effect of increasing concentrations of ethanol in the presence of the glycine-site antagonist 5,7-dichlorokynurenic acid (DCKA, 0.37 μM) on T5G-stimulated calcium entry was examined. A significant inhibition of the T5G-stimulated response in the presence of DCKA was observed at ethanol concentrations as low as 20 mM. These results support previous findings that T5G is a potent agonist of the NMDA receptor and indicate that stimulation of calcium entry by this agonist is less sensitive to ethanol inhibition than stimulation by NMDA.