EXPRESSION OF IONOTROPIC GLUTAMATE-RECEPTOR SUBUNITS IN GLIAL-CELLS OF THE HIPPOCAMPAL CA1 AREA FOLLOWING TRANSIENT FOREBRAIN ISCHEMIA

We examined by immunohistochemistry the expression of ionotropic gluta mate receptor subunits (GluRs) in glial cells of the rat dorsal hippoc ampus 3 to 28 days after transient forebrain ischemia. In general, the expression of GluRs at all time points studied underwent a drastic re duction that was primarily restricted to the CAI region. In addition t o the disappearance of GluRs as a result of neuronal cell death, we ob served their expression in reactive glial cells. The time course of ex pression and the subunits involved were different for astrocytes and m icroglia. Reactive astrocytes exhibited kainate, GluR5-7, and N-methyl -D-aspartate (NMDA), NR2A/B, receptor subunits, both of which were max imally expressed approximately 4 weeks after ischemia. In contrast, re active microglia expressed GluR4 and NR1 subunits, alpha-amino-3-hydro xy-5-methyl-4-isoxazole propionic acid (AMPA), and NMDA receptor subty pes, respectively, with maximal expression observed between 3 and 7 da ys after ischemia. These results demonstrate that specific types of Gl uRs are expressed in reactive glial cells after ischemia and that, ove rall, their expression levels peak around or after the periods of maxi mal astrogliosis and microgliosis. Thus, modulation of GluR expression may be one of the molecular components accompanying the gliotic proce ss.