5-(alpha-methyl-4-bromobenzylamino)phosphonomethyl-1-4-dihydroquinoxaline-2-3-dione and Brain-Ischemia

Ischemic postconditioning (Post C), which involves administration of a brief ischemia after the initial ischemic event, has been demonstrated to be strongly neuroprotective against global cerebral ischemia (GCI) and to improve cognitive outcome. To enhance understanding of the underlying mechanisms, the current study examined the role of NMDA receptors in mediating the beneficial effects of Post C (3 min ischemia) administered 2 days after GCI in adult male rats. The results revealed that Post C was strongly neuroprotective against GCI, and that this effect was blocked by administration of the NMDA receptor antagonist MK-801. Further work revealed that the NR2A-type NMDA receptors mediate the Post C beneficial effects as administration of a NR2A-preferring antagonist (NVP-A) blocked Post C neuroprotection and cognitive enhancement, while administration of a NR2B-preferring antagonist (Ro25) was without effect. Post C significantly up-regulated NR2A levels and phosphorylation of NR2A in the hippocampal CA1 region after Post C. Post C also increased Ca(2+) influx and activation/phosphorylation of CamKIIα at Thr(286), effects that were NR2A mediated as they were blocked by NVP-A. Phosphorylation of ERK and CREB was also increased by Post C, as were two downstream CREB-dependent prosurvival factors, brain derived neurotropic factor (BDNF) and Bcl2, effects that were blocked by the NR2A antagonist, NVP-A. Taken as a whole, the current study provides evidence that NR2A-activation and downstream prosurvival signaling is a critical mediator of Post C-induced neuroprotection and cognitive enhancement following GCI.

Topics: Analysis of Variance; Animals; Brain Ischemia; Calcium; CREB-Binding Protein; Dizocilpine Maleate; Hippocampus; Immunoprecipitation; Male; Maze Learning; Neuroprotective Agents; Phenols; Piperidines; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Signal Transduction; Time Factors

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.

Topics: Animals; Brain Ischemia; Brain-Derived Neurotrophic Factor; Cell Death; Cyclic AMP Response Element-Binding Protein; Excitatory Amino Acid Antagonists; Humans; Ischemic Preconditioning; Membrane Proteins; Nerve Tissue Proteins; Neurons; Piperidines; Protein Isoforms; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate