We previously reported the late onset reduction of muscarinic acetylcholine receptors (LORMAR) which begins 7 days after a 5-min period of experimentally induced forebrain ischemia in the gerbil hippocampus. This study demonstrated that post-ischemic administration of cyclosporin A (CsA) reduced LORMAR 10 days after 5 min of forebrain ischemia in the gerbil hippocampus, suggesting that immunosuppression by CsA may reduce damage to the cholinergic system after ischemia. Microglia positive for HLA-DR class II antigen which presented in the hippocampal CA1 area, the region most vulnerable to ischemia, were also reduced by CsA. CsA may suppress microglial activation especially with regard to the antigen-presenting function, and LORMAR may be attenuated by this modulation of microglial function.