The effects of prostaglandin (PG) E2 on glutamate-induced cytotoxicity were examined using primary cultures of rat cortical neurons. The cell viability was significantly reduced when cultures were briefly exposed to either glutamate or N-methyl-D-aspartate (NMDA) then incubated with normal medium for 1 h. Similar cytotoxicity was observed with the brief application of ionomycin, a calcium ionophore, and S-nitrosocysteine, a nitric oxide (NO)-generating agent. PGE2 at concentrations of 0.01-1 microM dose-dependently ameliorated the glutamate-induced cytotoxicity. PGE1, butaprost, an EP2 receptor agonist, and 8-bromo-cAMP were also effective in protecting cultures against glutamate cytotoxicity. By contrast, neither 17-phenyl-omega-trinor-PGE2, an EP1 receptor agonist, nor M&B 28767, an EP3 receptor agonist, affected glutamate-induced cytotoxicity. NMDA-induced cytotoxicity was ameliorated by PGE2, butaprost, MK-801, N-omega-nitro-L-arginine, a NO synthase inhibitor, and hemoglobin, which binds NO. These agents excluding MK-801 ameliorated the ionomycin-induced cytotoxicity. The cytotoxicity induced by S-nitrosocysteine was prevented only by hemoglobin but not by the other agents including PGE2. These findings indicate that PGE2 protects cultured cortical neurons against NMDA receptor-mediated glutamate neurotoxicity via EP2 receptors. EP2 receptor stimulation may suppress a step in NO formation triggered by Ca(2+)-influx through NMDA receptors.