Hypothermic and normothermic ischemia-reperfusion activate microglia differently in hippocampal formation.

Using immunohistochemical methods, we investigated microglial profiles under normothermic ischemia and hypothermic ischemia using an anti-ionized calcium-binding adapter molecule 1 (Iba-1) antibody. In the early stages of ischemia-reperfusion, Iba-1-immunoreactive microglial cells under normothermic ischemia were characterized by swollen somata with short and thick processes, while fine long-branched processes in greater numbers were seen emanating from microglial somata under hypothermic ischemia. In animals subjected to hypothermic ischemia, immunoreactive microglial areas in the hippocampal CA1 sector were significantly increased after 5 and 8 h of reperfusion when compared with those under normothermic ischemia. In the dentate gyrus, an increase in the microglial area under hypothermic ischemia was already evident at 2 h after reperfusion; this increased level was maintained up to 8 h. Considering the various neuroprotective roles of hypothermic ischemia, the characteristic features of microglia under hypothermic ischemia may be associated with the formation of a neuroprotective environment.