The influence of transient forebrain ischemia on the temporal alteration of NMDA receptor (NMDAR1) mRNAs in the hippocampal formation was analysed by in situ hybridization, RNA blot and in vitro receptor autoradiography ([3H]3-((+)2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid). In the CA1 subfield of the hippocampus, decrease of NMDAR1 mRNA levels was not observed until death of the CA1 pyramidal cells. Reactive astrocytes, which appear after CA1 pyramidal cell death, expressed few NMDAR1. The CA3 and dentate gyrus also showed a reduction of NMDAR1 mRNA levels 7 days after ischemia. Temporal profiles of NMDAR1 mRNA levels correlated well with those of NMDA receptor-binding in the CA1 and CA3/dentate gyrus. These results indicate that NMDA receptors in the CA1 are predominantly located on the CA1 pyramidal cells and that these receptors are preserved during early recriculation period. Histologically intact neurons in the CA3 and dentate gyrus also had marked modulation in glutamatergic neurotransmission after ischemia.
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