[Temperature effect on ischemic brain injury].

The effect of manipulating the brain temperature during cerebral ischemia was investigated in Wistar rats subjected to 30 min 4-vessel occlusion. Three brain temperature profiles were compared: 1. Spontaneous decrease in brain temperature during ischemia from 36 to 31 degrees C (spontaneous hypothermia; n = 5); 2. Constant brain temperature of 30 degrees C induced by selective head cooling (induced hypothermia; n = 5); and 3. Constant brain temperature of 36 degrees C induced by selective heating of the head (normothermia; n = 5). The core temperature was maintained constant at 37 degrees C in all groups. In the spontaneously hypothermic brains, 16% of the CA1 neurons survived after 30 min ischemia. Induced hypothermia significantly increased this percentage to 69%, but maintenance of the brain temperature at normothermia decreased neuronal survival to 1%. Normothermia of the brain also led to morphological injury outside the vulnerable regions, greater variability of the morphologic lesions, an increase in mortality, a marked loss of body weight, and prolongation of EEG suppression, as compared to in both hypothermic groups. These findings clearly demonstrate that maintaining the brain temperature at normothermia by selective heating of the head aggravates ischemic injury and, in consequence, should not be used to investigate the effectiveness of protective drugs for brain ischemia.