| Ischemic stroke is a lethal cerebral vascular disease caused by thedisturbance of cerebral blood supply which leads to cerebral ischemia andhypoxia. Ischemic stroke ranked as the second most common single causeof death in the developed world after ischemic heart disease. There are morethan8million stroke patients (ischemic stroke patients are considered asprimarily cases) in China and the number is still rising by8.7%every year.Our government spends40billion yuan in taking care of them. Advances inthe diagnosis and treatment of ischemic stroke have been made over the pasttwo decades, but mortality after stroke is still high. The majority of patientshave lost the effective treatment due to the limited time window of early detection and thrombolytic therapy. Thereby, how to reveal the mechanism ofischemic stroke, find out reasonable and effectively ways to prevent and treatthem is always the hot spot issue in the study of neuroscience.One interesting avenue developed in recent years for neuroprotection isthe concept of “conditioning”. In1990, Kitagawa found that ischemicpreconditioning induced ischemic tolerance which activated severalendogenous signaling pathways that result in protection against ischemia. Inthe following studies, researchers proved that many drugs (e.g. LPS, TNF-α,IL-1) also mimicked the same neuroprotective effect as that of ischemicpreconditioning. However, they are all difficult to be used in clinic because ofthe limitations of these ways. Isoflurane, as a safety inhalation anesthetics,has a wide range of clinical applications. Immediately after the first report ofNewberg that isoflurane could reduce the oxygen consumption of the brain, alot of research activities had proved the protection for central nervous systemof isoflurane preconditioning. However, the underlying mechanisms ofconditioning induced by isoflurane are not fully understood.Endocannabinoids are important components of the brain’s first-linedefense against excitotoxic damage. Previous study during brain trauma inanimal models demonstrated that the protective effects against cerebralischemic insult induced by treating with endocannabinoid or cannabinoidreceptor agonists is attenuated by a specific CB1receptor antagonist AM251. CB1turns out to be one of the most abundant neuromodulatory receptors andis expressed at high levels in the brain. And Data suggests thatendocannabinoids are synthesized by neurons in response to Ca2+influx andisoflurane preconditioning increase the Ca2+influx in neurons. This impliesthat isoflurane preconditioning may promote the synthesis of endogenouscannabinoid.Therefore, we speculate that:(1) Isoflurane preconditioning upregulatedthe neuronal expression of CB1receptor in the rat brains.(2) CB1receptormay be involved in the tolerance induced by isoflurane preconditioning in theanimal model of cerebral ischemic.Objective: The study is presented to investigate whether CB1receptorparticipates in the neuroprotective effects induced in transient middle cerebralartery occlusion (MCAO) in rat models by isoflurance preconditioning.Methods:(1) Sprague Dawley (SD) rats were randomly divided into twogroups: control group and isoflurane preconditioning group. Observe thedistribution and levels of CB1receptor in brain tissue between the twogroups via immunofluorescent and Western Blot, respectively. Two groupsreceived the middle cerebral artery occlusion for2h. Then we detected theinfarct volume and neurobehavioral score of the rats in tow groups at24hafter reperfusion.(2) Forty-eight male SD rats were randomly assigned to6groups: Sham group only received sham operation, control group underwent ischemic for2h and reperfusion for24h, isoflurane preconditioning groupinhaled isoflurane (1.5%) for1h a day for5consecutive days, vehicle plusisoflurane preconditioning group and CB1receptor antagonist plus isofluranepreconditioning group inhaled isoflurance for1h and were respectivelyinjected with vehicle3ml/kg and AM2511mg/kg (i.p.)30min prior to theonset of isoflurane preconditioning once a day for5consecutive days,antagonist group received AM251(i.p.) once a day for5consecutive days.Twenty-four hours after last treatment, all groups except sham group receivedthe middle cerebral artery occlusion (120min). The neurobehavioral score ofall rats were evaluated at24h after reperfusion.The infarct volume, as apercentage of volume at normal cerebral hemisphere, was then assessed by2,3,5triphenyltetrazolium chloride (TTC) staining after the evaluation ofneurobehavioral score.Results:(1) In comparison with the control group, isoflurane pretreatmentenhanced the CB1receptor levels in rat brain tissue significantly (P<0.05).Neurobehavioral score in isoflurane preconditioning group was superior thanthat in control group; The infarct volume of isoflurane preconditioning wasmarkedly smaller than control group.(2) In sham group, no neurologicaldeficits and infarct volume were observed. The infarct volume in isofluranepreconditioning group and vehicle plus isoflurane preconditioning groupwas significantly smaller than that in control group, CB1receptor antagonist group and antagonist plus isoflurane preconditioning group (p<0.05). Theneurobehavioral score in isoflurane preconditioning group and vehicle plusisoflurane preconditioning group were significantly higher than that incontrol group, antagonist group, and antagonist plus isofluranepreconditioning group (P<0.05). No significantly difference was observedbetween antagonist group, antagonist plus isoflurane preconditioning groupand control group.Conclusion: Compared with control group, pretreatment with isoflurane for5consecutive days significantly increased the brain tissue content of theneuronal CB1receptor. Isoflurane preconditioning reduced infarct volumeof brain tissue and improved neurological outcome. The neuroprotectiveeffects were attenuated by AM251. The CB1receptor is possibly involved inthe brain ischemic tolerance induced by isoflurane preconditioning. |
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