UNCHANGED BALANCE BETWEEN LEVELS OF MESSENGER-RNA ENCODING AMPA GLUTAMATE-RECEPTOR SUBTYPES FOLLOWING GLOBAL CEREBRAL-ISCHEMIA IN THE RAT

Transient global ischemia leads to glutamate mediated delayed neuronal death in the CA1 but not in the CA3 region of the rat hippocampus, an d changes in AMPA receptor subunit composition has been proposed to ca use a difference in excitatory input to the CA1 and CA3 regions. In si tu hybridization with riboprobes for AMPA receptor subtype GluR1-4 mRN A was performed on sections from the brain of sham operated and ischem ic rats in two models (neck cuff and 4-vessel occlusion combined with hypotension) with identical results: the content of the GluR1-3 mRNA s pecies was down regulated in the hippocampal regions CA1 and CA3 but o nly weak changes were observed in the dentate gyrus. The down regulati on observed in CA1 was non-selective among GluR1-3, i.e. all GluR mRNA species showed approximately the same degree of down regulation. A ch ange 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.