Effects of mild hypothermia on neuronal cell apoptosis , Bcl-2 and Bax protein expression following global cerebral ischemia-reperfusion in rats

Objective To investigate the effects of mild hypothermia (32.5 - 33.5℃) on neuronal cell apoptosis , Bcl-2 and Bax protein expression in hippocampus following global cerebral ischemia-reperfusion (I/R) in rats. Methods Twenty-four male Wistar rats weighing 250-300 g were randomly divided into three groups of 8 animals : (A) control group-normothermia-sham operation; (B) normothermia-global cerebral I/R (N-I/R); (C) hypothermia-global cerebral I/R (H-I/R) . Global cerebral I/R was produced by occlusion of bilateral common carotid arteries combined with hypotension (MAP = 40mmHg) induced by exsanguinations. Global cerebral ischemia was confirmed by dilated pupils and EEG. Global cerebral ischemia was maintained for 20 min followed by 72 h reperfusion. Mild hypothermia was induced by alcohol spreyed over the rats combined with fanning and maintained at 32.5-33.51 for 3 h. At the end of 72 h reperfusion the animals were sacrificed and hippocampus was obtained for detection of neuronal cell apoptosis (TUNEL) and Bcl-2 and Bax protein expression (immuno -histochemistry technique) . Results The number of apoptotic neuronal cells increased significantly in group B (N-I/R) and C (H-I/R) compared with that in control group (A) (P 0.05 or 0.01). There was significantly less number of apoptotic neuronal cells in group C (H-I/R) than in group B (N-I/R) . Bcl-2 and Bax protein expression were significantly increased in group B and C compared with those in control group, but there was no significant difference in Bcl-2 and Bax protein expression between group B and C. Conclusion Mild hypothermia attenuates apoptotic neuronal cell death associated with I/R but does not alter Bcl-2 and Bax protein expression following global cerebral I/R.