Effects of Transient Forebrain Ischemia on the Hippocampus of the Mongolian Gerbil (Meriones unguiculatus): An Immunohistochemical Study

In the Mongolian gerbil, bilateral common carotid artery occlusion (BCCAO) for several minutes induces ischemia and delayed neuronal cell death in the CA1 region of the hippocampus due to their incomplete Circle of Willis. In the present study, the expression of fibroblast growth factor 2 (FGF2), its receptors (FGFR1 and FGFR2), glial fibrillary acidic protein (GFAP), and isolectin B4 (ISLB4) was investigated by immunohistochemical and lectin-binding methods after BCCAO was performed for 5 min in gerbils. One day after BCCAO, the pyramidal cells of the CA1 region of the hippocampus showed degenerative changes and lowered expression of FGF2, FGFR1, and FGFR2. Three days after BCCAO, there was an increase in GFAP-positive astrocytes and ISLB4-positive microglial cells. From five to 10 days after BCCAO, intense neuronal cell death in the stria pyramidale of the hippocampal CA1 region was observed, as well as an increase in GFAP-positive astrocytes and decrease in ISLB4-positive microglial cells. These results indicate that transient forebrain ischemia induces neuronal cell death with lowered expression of FGF2 and its receptors, and that the activation of glial cells may not directly lead to neuronal cell death.