Differential Roles of NMDA Receptor Subtypes in Ischemic Neuronal Cell Death and Ischemic Tolerance

Abstract

Activation of NMDA subtypes of glutamate receptors is implicated in cell damage induced by ischemia as well as for the establishment of ischemic tolerance after ischemic preconditioning in animal models. We investigated the contributions of NR2A- and NR2B-containing NMDA receptors to ischemic cell death and ischemic tolerance in a rat model of transient global ischemia. Transient global ischemia was produced in rats by 4-vessel occlusion. Neuronal injury was analyzed by Fluoro-Jade B and Nissl staining. Phosphorylation of CREB was detected by Western blotting and immunohistochemistry. In situ hybridization and reverse transcriptase-polymerase chain reaction were used to evaluate the mRNA level of cpg15 and bdnf. NR2A subtype-specific antagonist NVP-AAM077 enhanced neuronal death after transient global ischemia and abolished the induction of ischemic tolerance. In contrast, NR2B subtype-specific antagonist ifenprodil attenuated ischemic cell death and enhanced preconditioning-induced neuroprotection. Furthermore, selectively blocking NR2A-, but not NR2B-, containing NMDA receptors inhibited ischemia-induced phosphorylation of CREB and the subsequent upregulation of CREB target genes such as cpg15 and bdnf. We found that NR2A- and NR2B-containing NMDA receptor subtypes play differential roles in ischemic neuronal death and ischemic tolerance, suggesting attractive new strategies for the development of drugs for patients with stroke.