High-magnification photomicrographs showing IL-1β immunoreactivity (A, C, E, G) and B4-isolectin-positive microglia (B, D, F, H) in coronal sections of the CA1 (A–D) and CA3 (E–H) areas of the rat dorsal hippocampus 3 hr after a local injection of 12.5% PEG (A, B, E, F) or 0.77 nmol of bicuculline methiodide in PEG (C, D, G, H). IL-1β immunoreactivity was enhanced in darkly stained cells with ramified processes in stratum radiatum (sr) of CA1 pyramidal layer (C, arrowheads). A diffuse pattern of lightly stained cells was observed in CA3 (G, arrowheads). B4-isolectin-positive microglia was enhanced in stratum radiatum (sr) CA1 (D, arrowheads) and in stratum lucidum (sl) CA3 (H, arrowheads). Microglia processes were interposed between pyramidal cells in CA3.f, Fissura hippocampi; so, stratum oriens. Scale bar, 200 μm.