It has been well known that transient global ischemia of the brain induces delayed neuronal death of hippicampal CA1 pyramidal cells. Calcium influx is thought to play a critical role in the neuronal death after ischemia. Changes in AMPA receptor subunit composition has been proposed to determine calcium permeability and the delayed neuronal death. The present study is undertaken to examine the involvement of changes of AMPA receptor subunit composition in the delayed neuronal death. Global ischemia was produced in rats using 20-min 4-vessel occlusion model, and in situ hybridization with oligoprobes for GluR1, 2 and NMDAR1 was performed on sections from the brain of sham operated and ischemic rat. In CA1 region, the expressions of all three receptor subtype mRNAs decreased at day 1 after the ischemic insults, and almost abolished at day 5. In CA3 region, the expression of three mRNA also decreased at day 1 and then it somehow recovered at day 5. In dentate gyrus, the expression of three mRNA showed weak decreases at day 1. The expression of GluR1 and GluR2 mRNA were comparable to control (sham operated) but NMDAR1 mRNA expression was higher than control at day 5. These findings suggest that the changes of AMPA receptor subunit composition might not be correlated with the delayed neuronal death in hippocampal CA1 region.