Comparison of neuroprotective effects in ischemic rats with different hypothermia procedures.

OBJECTIVE: The neuroprotective effect of hypothermia has long been recognized. The aim of this work was to compare the neuroprotective effect of systemic, head and local vascular cooling hypothermia procedures in ischemic rats.

METHODS: Stroke in Sprague-Dawley rats (n=64) was induced by a 3 hour right middle cerebral artery occlusion using an intraluminal filament. Before reperfusion, ischemic animals (n=16 in each group) received hypothermia (systemic, head or local vascular) or no treatment. Brain temperature, infarction volume (n=8 in each group) and functional outcome (n=8 in each group) were compared.

RESULTS: Regarding brain temperature, vascular cooling significantly reduced the temperature of ischemic territory in cortex from 37.2 +/- 0.1 to 33.4 +/- 0.4 degrees C and in striatum from 37.5 +/- 0.2 to 33.9 +/- 0.4 degrees C within 5 minutes. This hypothermic condition remained for up to 60 minutes after reperfusion. However, systemic cooling reduced brain temperature at a similar level for six times longer. In the head cooling group, the target temperature was reached in 15 minutes, but returned to normal within 5 minutes. Although all hypothermia procedures induced neuroprotection, ischemic rats with vascular cooling showed significantly (p<0.001) better neuroprotection with 10.7 +/- 2.6% infarction, compared to 54.2 +/- 1.9% (no treatment), 37.1 +/- 1.0% (head cooling) and 29.1 +/- 3.4% (systemic cooling). Significantly (p<0.001) better effects on motor function were also detected in vascular cooling groups at 14 and 28 days.

CONCLUSION: Vascular cooling appears to be the most effective in reducing infarct volume and improving functional outcome than the other two hypothermia methods in a rat ischemia/reperfusion model.