NMDA receptor antagonism does not inhibit induction of ischemic tolerance in gerbil brain in vivo.

Effects of high and moderate affinity uncompetitive NMDA receptor antagonists (+)MK-801 and memantine on ischemic tolerance were compared in relation to telemetrically controlled brain temperature. The tolerance to an injurious 3 min test of global forebrain ischemia in Mongolian gerbils was induced 48 h earlier by 2 min preconditioning ischemia. Normothermic preconditioning was virtually harmless, and greatly reduced neurodegeneration evoked by test ischemia. In hyperthermic animals it was injurious and failed to induce tolerance. Memantine (5 mg/kg) and (+)MK-801 (3 mg/kg) injected i.p. 1 h before preconditioning did not inhibit ischemic tolerance in the normothermic gerbils, while in hyperthermic animals treated with (+)MK-801 ischemic tolerance was partially restored. Subchronic 3 day infusion of memantine (30 mg/kg/day) significantly decreased neurodegeneration, and preconditioning in the normothermic gerbils further reduced neuronal damage. Hyperthermia exacerbated preconditioning ischemia and in this way reduced expression of tolerance, while (+)MK-801 partially reversed this effect. Our results do not confirm previous reports on the role of NMDA receptors in the induction of ischemic tolerance in gerbils.