Post-ischemic hypothermia delayed neutrophil accumulation and microglial activation following transient focal ischemia in rats

Following ischemia, inflammation has been demonstrated to be involved in th e progression of the tissue damage. Intra-ischemic hypothermia has been sho wn to attenuate the adverse activities of neutrophils and microglia. We inv estigated whether neutrophil accumulation and/or microglial activation is a ttenuated in post-ischemic hypothermia following transient focal ischemia i n rats. After 1 h of ischemia, the neutrophil accumulation and the microgli al activation was evaluated immunohistochemically. Percent infarct area was compared at 1, 2, 3, 5, and 7 days after ischemia/reperfusion. In hypother mia, the neutrophil accumulation was delayed but not attenuated. In normoth ermia, the accumulation reached the peak at 2 days after ischemia. The peak shifted to 3 days in hypothermia. Similarly; the microglial activation was delayed in hypothermia. Comparison of the infarct area showed significant protection by hypothermia at 1 and 2 days after reperfusion. However, hypot hermia failed to show significant protection after 3 days and later. These results show that the delayed neutrophil accumulation and the microglial ac tivation can be responsible for the loss of persistent protection in post-i schemic hypothermia. (C) 2000 Elsevier Science B.V. All rights reserved.