Objective To evaluate the effect of hypothermia on the expression of dynamin-related protein 1(Drp1)in brain tissues during global cerebral ischemia-reperfusion(I/R)in rats. Methods Thirty-six healthy male Sprague-Dawley rats,weighing 280-320 g,were divided into 3 groups(n=12 each)using a random number table:sham operation group(group Sham),global cerebral I/R group(group I/R)and hypothermia group(group H).Cardiac arrest was induced by transoesophageal cardiac pacing followed by cardiopulmonary resuscitation to establish the global cerebral I/R model in anesthetized rats in I/R and H groups.In group H,the body temperature(rectal temperature)was cooled down to 32-34 ℃ within 15 min starting from the beginning of reperfusion,and maintained at this level for 6 h.At 72 h of reperfusion,neurological deficit was scored,and the rats were sacrificed,and the whole brain was removed for examination of the pathological changes in hippocampal CA1 region and for determination of normal pyramidal cell count and neuronal apoptosis in hippocampal CA1 region and expression of Drp1 and cytochrome c(Cyt c)in hippocampal tissues(by Western blot).The apoptosis rate was calculated. Results Compared with group S,the neurological deficit score and apoptosis rate were significantly increased,and the number of normal pyramidal cells was decreased in I/R and H groups,the expression of Drp1 and Cyt c in hippocampal tissues was significantly up-regulated in group I/R(P<0.05),and no significant change was found in the expression of Drp1 and Cyt c in hippocampal tissues in group H(P>0.05).Compared with group I/R,the neurological deficit score and apoptosis rate were significantly decreased,the number of normal pyramidal cells was increased,and the expression of Drp1 and Cyt c in hippocampal tissues was down-regulated in group H(P<0.05). Conclusion The mechanism by which hypothermia inhibits cell apoptosis during global cerebral I/R may be related to down-regulation of Drp1 expression in rats.