• N Kawai, M Okauchi, K Morisaki, and S Nagao.
• Department of Neurological Surgery, Kagawa Medical University, Japan. nobu@kms.ac.jp
• Stroke. 2000 Aug 1;31(8):1982-9; discussion 1989.

Background And PurposeIntraischemic mild hypothermia has been shown to be neuroprotective in reducing cerebral infarction in transient focal ischemia. As a more clinical relevant issue, we investigated the effect of delayed intraischemic and postischemic hypothermia on cerebral infarction in a rat model of reversible focal ischemia. We also examined the effect of hypothermia on the inflammatory response after ischemia-reperfusion to assess the neuroprotective mechanism of brain hypothermia.MethodsRats were subjected to 2 hours of middle cerebral artery occlusion followed by 22 hours of reperfusion under the following protocols: (1) rats were treated with normothermia (37.0 degrees C, 4 hours) and then housed in room temperature (25 degrees C, 18 hours) and (2) rats were treated with hypothermia (33.0 degrees C, 4 hours, brain temperature modulation was started 30 minutes before the reperfusion) and then housed in cold temperature (5 degrees C, 18 hours). Animals were killed 24 hours after the onset of ischemia. The infarct volume was examined with 2,3,5-triphenyl-tetrazolium chloride staining. The accumulation of polymorphonuclear leukocytes (PMNLs) and the expression of intercellular adhesion molecule-1 mRNA were evaluated in both groups.ResultsA significant reduction (P<0.05) in infarct volume was found in the hypothermia group compared with the normothermia group. Compared with the normothermia group, hypothermic treatment also significantly reduced the accumulation of PMNLs (P<0.01) and inhibited the overexpression of intercellular adhesion molecule-1 mRNA at 22 hours of reperfusion after 2 hours of ischemia.ConclusionsIschemic brain damage can be reduced with delayed intraischemic and prolonged postischemic hypothermia in a focal model of transient cerebral ischemia in rats. The neuroprotective mechanism of hypothermia may be mediated by suppression of PMNL-mediated inflammatory response after ischemia-reperfusion in this model.

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