Study On The Role And Mechanism Of Sevoflurane In Alleviating Depressant Behavior In Mice

Part 1 Effect of sevoflurane inhalation on depression-like behavior in miceBackground:With the development of modern society,depression has become the first major psychological disease that plagues human.An epidemiological investigation of depression in general hospital in China showed that 30%of inpatients have clinical symptoms of depression,15%had apparent mood with anxiety,and 6%had repeated suicidal ideation.The mental stress caused by the disease itself,various environmental and surgical factors,which make it easier to result in the anxiety and depression and induce the adverse effect for patients recovery,therefore,clinical doctors should pay more attention to this problem.Most of the classic antidepressants commonly used in clinical effect slowly and the patients lack of response to these medicine.Patients with drug resistance always be treated with electroconvulsive therapy(ECT),but repeated treatments of ECT will produce side effects like cognitive impairment.Thus,it is an urgent problem to develop a drug that can alleviate anxiety and depression and treat depression.Ketamine is an anesthetic that has been proved to have a definite antidepressant effect.A single doses ketamine can significantly alleviate the symptoms of depression.It is worth to investigate whether the sevoflurane can also improve the state of anxiety and depression in patients.Methods:In this section we detect depression-like behavior in mice in an acute stress environment,mice were divided into two groups:CON group(continuously inhaled 30%oxygen at flow of 2L/min,n=24)and SEV group(inhaled sevoflurane at three different concentration for 30 min,n=72).Then SEV group is divided into three sub-groups(n=24):1.5SEV group(inhaled 1.5%sevoflurane for 30 minutes),2.5SEV group(inhaled 2.5%sevoflurane for 30min)and 3.5SEV group(inhaled 3.5%sevoflurane for 30min).After the end of inhalation,the animals were subdivided into three groups for each behavioral experiment(n=8),including spontaneous activity testing for 30 minutes immediately after the end of inhalation in the open field experimental device,and the forced swimming test and the novelty-suppressed feeding test were performed after the end of inhalation until the mice were fully awake to perform depression-related behavioral tests.Chronic unpredictable mild stress(CUMS)model was administered to mice for six weeks to establish the chronic depression model in mice and divided into two groups(n=32):CUMS group(30%oxygen inhalation in chronic depression mice for 30 min)and CUMS-SEV group(inhalation of 2.5%sevoflurane in chronically depressed mice for 30 min).Mice without CUMS model is as the CON group(inhalation of 30%oxygen for 30 min,n=32).After the end of inhalation,the animals were subdivided into four groups to have behavioral test(n=8),including spontaneous activity testing for 30 minutes immediately after the end of inhalation in the open field experimental device,and at 15 minutes after the end of inhalation to detect depression-related behavior used OFT,FST and NSFT.Results:In the experiment of detecting depression-like behavior in mice under acute stress environment,compared with the CON group,the result of the exercise ability test in the open field device for 30-minutes has showed that the spontaneous activity of the 1.5SEV group and the 2.5SEV group recovered after 15 minutes of inhalation and the 3.5SEV group recovered after 20 minutes of inhalation.Therefore,in the nest behavior experiments,we performed behavioral tests of the 1.5SEV group and 2.5SEV group after 15 minutes of inhalation and the 3.5SEV group after 20 minutes of inhalation.In the 2.5SEV group,the depression-like behavior was reduced in the acute stress environment,which showed a significant decrease in the immobility time in the FST an the feeding latency in the NSFT,while the mice in 1.5SEV and 3.5SEV group did not show a reduction of depression-like behavior in behavioral test,so we use 2.5%sevoflurane concentration for subsequent experiments.Mice with the CUMS chronic depression model,compared with the CON group,the CUMS group showed significantly increase in depression-like behavior in behavioral testing,including a decrease in the time to enter the central region in the OFT and an increase in the number of fecal particles,as well as the increase of immobility time in the FST and the increase of feeding latency in the NSFT.Compared with the CUMS group,the CUMS-SEV group had an increased time to enter the central zone in the OFT and a decrease in the number of fecal particles,a decrease in the immobility time in the FST,and a significant reduction in the feeding latency in the NSFT.Conclusion:The results of the behavioral test showed that sevoflurane alleviate the depressant behavior caused by the stress environment or chronic depressionPart 2 Sevoflurane exerts antidepressant effect in mice through BDNF-TrkB pathwayBackground:The main target of classical antidepressants is the levels of different neurotransmitters in the brain,which relieve the symptoms of depression by increasing the level of monoamine neurotransmitters.As an NMDA receptor antagonist,the antidepressant effect of ketamine mainly depends on the activation of BDNF-TrkB-mTOR pathway,and exerts rapid antidepressant effect by increasing the expression of brain-derived neurotrophic factor(BDNF).According to the research,isoflurane can significantly alleviate the depressant behavior of learned helpless model mice,the mechanism is to rapidly increase the expression of phosphorylation of TrkB.Therefore,we assume that the mechanism of antidepressant effects of sevoflurane involves the changes in the BDNF-TrkB pathway.Methods:Mice that detected depression-like behavior in an acute stress environment were divided into two groups(n=3):CON group(continuously inhaled 30%oxygen at flow of 2L/min)and SEV group(inhaled sevoflurane at three different concentration for 30 min).CUMS model mice were divided into two group(n=3):CUMS group(30%oxygen inhalation in chronic depression mice for 30 min)and CUMS-SEV group(inhalation of 2.5%sevoflurane in chronically depressed mice for 30 min),mice without CUMS model is as the CON group(30%oxygen inhalation for 30 min).Remove the brain immediately at the moment of inhalation of oxygen or sevoflurane for 30 minutes and separated the hippocampus and prefrontal cortex.Then we detect the expression of BDNF,TrkB and p-TrkB on hippocampus and prefrontal cortex region by Western blot.Results:According to the Western Blot results,compared with CON group,the level of p-TrkB in HC and PFC sites in 2.5SEV group increased significantly,but the expression of BDNF did not change significantly.In chronic depression mice,compared with the CUMS group,the levels of pTrkB in the HC and PFC sites in the CUMS-SEV group also increased significantly,but the content of BDNF did not change significantly.Conclusion:The mechanism of antidepressant effects of sevoflurane in mice under stress environment and suffer from chronic depression is mediated by the BDNF-TrkB pathway and induces the increase of phosphorylation of TrkB.Part 3 Sevoflurane exerts antidepressant effect in mice through BDNF-TrkB pathwayBackground:From the above two studies,we learned that sevoflurane inhalation has a role in alleviating depression-like behavior of mice in acute stress environment and CUMS model mice,and by increasing pTrkB in the BDNF-TrkB signaling pathway.The level of pTrkB,as an active form of TrkB,is required for antidepressant behavioral effects including the fast-acting antidepressant ketamine and the inhaled anesthetic isoflurane,so in this section,we will investigate the changes of antidepressant effects induced by sevoflurane after down-regulation of TrkB protein.Methods:Lateral ventricle injection of small interfering RNA(siRNA)is divided into four groups(n=24):siRNA group(inhaled 30%oxygen with the injection of siRNA into lateral ventricle),siRNA-SEV(inhaled 2.5%sevoflurane with the injection of siRNA into lateral ventricle),CON group(inhaled 30%oxygen with the injection of control siRNA into lateral ventricle)and CON-SEV group(inhaled 2.5%sevoflurane with the injection of control siRNA into lateral ventricle).Inhalation of 30%oxygen or sevoflurane for 30 min at 72 h after the injection of the lateral ventricle,then mice would be subdivided into three groups for each behavioral experiment(n=8),including the detection of spontaneous activity in open field device for 30min immediately after the end of inhalation.The depression-related behavioral tests FST and NSFT performed 15 minutes after the end of inhalation were used to investigate the changes in antidepressant effects of sevoflurane after down-regulation of total TrkB protein.Results:Compared with CON group,the immobility time in the FST of the siRNA group was significantly reduced,and the feeding latency was significantly decreased in the NSFT.Compared with siRNA group,the immobility time in the FST and the feeding latency in NSFT of the siRNA-SEV group were significantly increased.Conclusion:After down-regulating the expression of total TrkB protein,the antidepressant effect of sevoflurane has disappeared,suggesting that the antidepressant effect of sevoflurane is associated with the BDNF-TrkB pathway.However,mice that down-regulated the expression of total TrkB protein showed a decrease in depression-like behavior after inhalation of 30%oxygen,suggesting that the pathogenesis of depression is closed related to the TrkB protein itself.