Therapeutic time window of post-ischemic mild hypothermia and the gene expression associated with the neuroprotection in rat focal cerebral ischemia

Hypothermia is the only neuroprotective therapy proven to be clinically effective. Identifying the molecules that play important roles in the efficacy of hypothermia, we developed a multi-channel computer-controlled system, in which the brain temperatures of freely moving rats were telemetrically monitored and maintained below 35 degrees C, and examined the time window necessary to exert its significant neuroprotective effects. Eight-week-old SD rats were subjected to a 2h middle cerebral artery occlusion (MCAO) with an intraluminal filament, and post-ischemic hypothermia was introduced at 0, 2, 4, or 6h after reperfusion until the rats were killed 2 days after MCAO. Since a significant protection was observed when hypothermia was started within 4h after reperfusion, it was concluded that the therapeutic time window of mild hypothermia lasts for 4h after reperfusion in our model. On the basis of the window, comprehensive gene expression analyses using oligonucleotide microarrays were conducted and identified potential genes related to the efficacy of hypothermia, which included inflammatory genes like osteopontin, early growth response-1, or macrophage inflammatory protein-3alpha. Therefore, the neuroprotective effects of post-ischemic mild hypothermia were strongly suggested to be mainly associated with the reduction of neuronal inflammation.