Neuroprotective Effect of Delayed Moderate Hypothermia After Focal Cerebral Ischemia: An MRI Study

Abstract

Background and Purpose— In contrast to early hypothermia, the effects of delayed hypothermia in focal cerebral ischemia have not been widely addressed. We examined the influence of delayed hypothermia on secondary ischemic injury, MRI lesion size, and neurological outcome after transient focal cerebral ischemia in a rat model. Methods— Rats (n=30) were subjected to transient middle cerebral artery occlusion (MCAO, 120 minutes) by use of the intraluminal filament model. Animals of the treatment group (n=12) were exposed to whole-body hypothermia of 33°C for 5 hours starting 3 hours after MCAO, whereas the control group (n=18) was kept at 37°C throughout the whole experiment. The normothermia- and hypothermia-treated animals were investigated daily by using the Menzies neurological score. Serial MRI was performed 1, 3, and 6 hours after MCAO and on days 1, 2, 3, and 5. After the final MRI scan, the rats were euthanized, and brain slices were stained by 2,3,5-triphenyltetrazolium chloride. Results— Delayed hypothermia resulted in a significant increase of survival rate and a significant improvement of the Menzies score. Moreover, a significant decrease in the extent of hyperintense volumes in T2-weighted scans and a reduction of cerebral edema as calculated from T2-weighted scans throughout the examination period were obvious. The extent of cerebral infarct volume and cerebral brain edema examined by MRI was consistent with 2,3,5-triphenyltetrazolium chloride staining. Conclusions— Our results suggest that even delayed postischemic hypothermia can reduce the extent of infarct volume and brain edema after transient focal cerebral ischemia.