Abstract： Objective To investigate the effect of cannabinoid CB2 receptor on ischemic tolerance of rat models with focal cerebral ischemia induced by electroacupuncture(EA)pretreatment.Methods The first experiment was performed as follows:40 adult male SD rats were randomized into 5 groups(middle cerebral artery occlusion[MCAO]group[vehicle],EA+MCAO group,AM630[the antagonist of CB2 receptor]+EA+MCAO group,V[the solvent of AM630]+EA+MCAO group and AM630+MCAO group,n=8).Suture method was employed to induce th eMCAO models.Pretreatment with EA was given 2h before the model making;pretreatment with AM630 or other solvents were given 5.5 h before the model making.The changes of infarction volume percentage were detected by 2,3,5-triphenoltetrazolium chloride (TTC)staining and neurobehavioral scores were evaluated 72 h after the success of model making.In the second experiment,40 adult male SD rats were performed the same treatment with the first experiment;pretreatment with EA was performed 24h before the model making;pretreatment with AM630 or other solvents were performed 27.5 h before the model making;the measurements and detection times were the same with the first one.In the third experiment,36 adult male SD rats were randomized into 6 groups(n=6):control group and EA-treated groups(2,6,12,18 and 24 h after the treatment). RT-PCR and Western blotting Were employed to detect the expression of CB2 receptor on the right side of rat brain. Results Compared with the vehicle and AM630+MCAO groups,the EA+MCAO group,AM630+EA+MCAO group and V+EA+MCAO group showed significantly higher scores of nerve function and a statistically lower percentage of infarction volume(P<0.05).Compared with the vehicle group,EA+MCAO group and V+EA+MCAO group showed significantly higher neurobehavioral scores and a lower percentage of infarction volume (P<0.05);compared with the EA+MCAO group,the AM630+EA+MCAO group and AM630+MCAO group showed significantly lower neurobehavioral scores and a higher percentage of infarction volume (P<0.05).The mRNA and protein expressions of CB2 receptor were significantly up-regulated in the EA-treatedgroups 18 and 24h after the treatment,respectively,as compared with those in the control group(P<0.05). Conclusion Cannabinoid CB2 receptor involves in the protective effect of delayed tolerance to focal cerebral ischemia induced by pretreatment with EA.