Cannabinoid CB2 receptor participates in the delayed tolerance to focal cerebral ischemia induced by electroacupuncture pretreatment

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. Key words: CB2 receptor;  Cerebral ischemia;  Electroacupuncture; Pretreatment