Selective brain cooling during and after prolonged global ischemia reduces cortical damage in rats

Studies of the cerebroprotective effects of selective brain cooling have failed to show amelioration of ischemic injury in the cerebral cortex. This study was designed to test the hypothesis that mild-to-moderate selective brain cooling initiated after the onset of global brain ischemia in rats protects the cerebral cortex and improves neurological outcome.

Global forebrain ischemia for 30 minutes in 27 fasted adult male Wistar rats was achieved by bilateral carotid occlusion and hypotension. In group 1, brain temperature, measured in the temporalis muscle, was maintained at 37-38 degrees C throughout the experiment. In group 2, brain temperature fell spontaneously during ischemia to 34.7 +/- 0.1 degrees C and rose spontaneously to 36-37 degrees C after 10 minutes of recirculation. In group 3, brain temperature was lowered with ice packs placed around the head after 15 minutes of ischemia to 24.1 +/- 0.9 degrees C by the end of ischemia, maintained at 30.0 +/- 1.0 degrees C for the first hour of recirculation, then allowed to rise to 36-37 degrees C.

Seven-day survival was 0% (0 of 6) in group 1, 73% (8 of 11) in group 2, and 100% (6 of 6) in group 3. Severity of neuronal damage was less in group 2 than in group 1 in the cortex (p < 0.05) and hippocampal CA1 (p < 0.05) and CA3 regions (p < 0.05). Group 3 had less neuronal damage than group 2 in both cortex (p < 0.02) and striatum (p < 0.02). Furthermore, postischemic weight loss was less and neurobehavioral scores were significantly higher in group 3.

This study shows that selective brain cooling increases survival from prolonged global ischemia and reduces neuronal injury in the cerebral cortex as well as the striatum and hippocampus.