Transient global ischemia leads to glutamate mediated delayed neuronal death in the CA1 but not in the CA3 region of the rat hippocampus, and changes in AMPA receptor subunit composition has been proposed to cause a difference in excitatory input to the CA1 and CA3 regions. In situ hybridization with riboprobes for AMPA receptor subtype GluR1-4 mRNA was performed on sections from the brain of sham operated and ischemic rats in two models (neck cuff and 4-vessel occlusion combined with hypotension) with identical results: the content of the GluR1-3 mRNA species was down regulated in the hippocampal regions CA1 and CA3 but only weak changes were observed in the dentate gyrus. The down regulation observed in CA1 was non-selective among GluR1-3, i.e. all GluR mRNA species showed approximately the same degree of down regulation. A change in calcium permeability of the AMPA channels mediated by a shift in channel sub-unit composition and corroborating an increased calcium influx is thus not supported by these findings.