Conditions of protection by hypothermia and effects on apoptotic pathways in a rat model of permanent middle cerebral artery occlusion

Abstract

Object Hypothermia is protective in stroke models, but findings from permanent occlusion models are conflicting. In this article the authors induced focal ischemia in rats by permanent distal middle cerebral artery (MCA) occlusion plus transient occlusion of the common carotid arteries (CCAs). This models a scenario in which the MCA remains occluded but partial reperfusion occurs through collateral vessels. The authors also determined whether hypothermia mediates ischemic damage by blocking apoptotic pathways. Methods The left MCA was occluded permanently and the CCAs were reopened after 2 hours, leading to partial reperfusion in rats maintained at 37°C, 33°C (mild hypothermia), or 30°C (moderate hypothermia) for 2 hours during and/or after CCA occlusion (that is, for a total of 2 or 4 hours of hypothermia or normothermia). Infarct size was measured 2 days after the stroke. Immunofluorescence staining and Western blot analysis were used to detect cytochrome c and apoptosis inducing factor (AIF) translocation. Results Four hours of prolonged mild hypothermia (33°C) reduced the infarct size 22% in the model of permanent MCA occlusion, whereas 2 hours of such mild hypothermia maintained either during CCA occlusion or after CCA release did not attenuate ischemic damage. However, moderate hypothermia (30°C) during CCA occlusion was significantly more protective than 4 hours of 33°C (46% decrease in infarct size). Four hours of mild or moderate hypothermia reduced cytosolic cytochrome c release and both nuclear and cytosolic AIF translocation in the penumbra 2 days after stroke. Conclusions These findings suggest that hypothermic neuroprotection might be achieved by blocking AIF and cytochrome c–mediated apoptosis.