Mild hypothermia increases Bcl-2 protein expression following global cerebral ischemia

Mild hypothermia protects the brain against experimental ischemia, but the reasons are not well known. We examined whether the protective effects of mild hypothermia could be correlated with alterations in expression of Bcl-2, an anti-apoptotic protein in a rat model of transient global ischemia. Following 10 min of forebrain ischemia, hippocampal neurons were examined 72 h later for survival, expression of Bcl-2 family proteins and apoptosis. Intraischemic mild hypothermia was applied for 3 h (33 degreesC, isch-33) or normal body temperature was maintained (37 degreesC, isch-37). Survival of CAI neurons was significantly improved in the inch-33 group compared to the isch-37 group (90 vs. 53% survival; P <0.01). The proportion of Bcl-2-positive cells among surviving CAI neurons in the isch-33 group was increased compared to that of sham and isch-37 groups (P <0.01). Bax expression in CAI was no different between sham and isch-33 groups, but was significantly decreased in isch-37 (P <0.05). TUNEL staining was positive in many isch-37 CAI neurons, but absent in isch-33. Utilizing electron microscopy, more cells meeting criteria for apoptosis were observed in the isch-37 than isch-33. These data suggest that mild hypothermia attenuates apoptotic death, and that this protection may be related to increases in Bcl-2. (C) 2001 Elsevier Science B.V. All rights reserved.