Objective:To determine the expression of S100,S100B mRNA and the pathological change of canine cerebral tissue at 6 hours after CPR,and the effects of naloxone on CPR.Methods: 18 healthy adult hybrid dogs were randomly divided into blank group,control group and naloxone group(n=6 per group).The control group received standard CPR after induced ventricular fibrillation;the naloxone group received additional use of naloxone,while the blank group was not given any treatment.The three groups were collected for hippocampus tissues at 6 hours post-CPR to be detected for S100B concentration and pathological change. Results: The number of S100-positive cells in the naloxone group was significantly lower than that in the control group but higher than that in the blank group(P<0.01).The control group exhibited obvious pathological lesion of nerve cells including neuron loss,concentrated neuronal cytoplasma,ill-demarcated nucleolus and edematous capillaries,compared with the milder changes of neurons in the naloxone group.Conclusion: Naloxone may ameliorate post-CPR cerebral lesion in dogs,likely by associated with the decreased production of cerebral S100 after cardiopulmonary resuscitation.