| Objective:This study compare the changes in neurobehavioral,hippocampal volume,ultrastructure of hippocampal neurons after exposure to sevoflurane anesthesia in aging rats with d-galactose,and further evaluate the effects after intervention withα7nAChR agonist and antagonist.The purpose of this study was to explore the effect ofα7nAChR regulation on the changes of hippocampal structure and cognitive function in aging rats after sevoflurane anesthesia,so as to seek a convenient and reliable clinical diagnosis basis for postoperative cognitive dysfunction（POCD）.Methods:Total of 72 adult SPF healthy male Sprague-Dawley rats（4 weeks）,were subcutaneously injected with 10%d-galactose（0.125 g/kg.d）through the neck and back for 6 weeks,and the aging model rats were constructed by referring to literature[1,2].The rats were randomly divided into four groups:control group（n=18）,sevoflurane group（n=18）,α7nAChR agonist group（n=18）,α7nAChR antagonist group（n=18）.Control group inhaled the carrier gas（1 L/min O2+1 L/min air）for 6 h;Sevoflurane group inhaled3.2%sevoflurane+carrier gas for 6 h;α7nAChR agonist group received a single intraperitoneal injection ofα7nAChR agonist（PNU-282987）5 mg/kg,the same treatment as sevoflurane group after 24 hours;α7nAChR antagonist group received a single intraperitoneal injection ofα7nAChR antagonist（MLA）3 mg/kg,the same treatment as sevoflurane group after 24 hours.The rats in the above groups were divided into three subgroups（n=6）according to 2h,1w and 4w for follow-up experiments:（1）Morris water maze experiment was used to evaluate the learning and memory ability of rats;（2）MRI brain scanning was used to observe the volume change of hippocampus;（3）Immediately after the MRI was taken,the hippocampus tissue was taken,and morphological changes of hippocampal cells and synapses were observed under transmission electron microscopy.Results:1.General situation:1)During the d-galactose injection,The rats in each group developed well,with no significant difference in body weight.There were no accidents occurred during the injection.2)During sevoflurane inhalation anesthesia,the rats in each group had stable breathing,no obvious cyanosis,and recovered well.2.Morris water maze experiment results:1)Adaptive training:all rats are capable of swimming,without visual or swimming disturbance.2)Navigation test:with the increase of experimental days,the trend and straight-line searching strategies gradually increased,and the average escape latency of rats in each group was shortened.There was no significant difference in the escape latency between day3,-4,-5.It is suggested that all rats have a stable learning and memory ability to the platform.（3）Spatial probe test:（1）Compared with the control group,the entry times of the platform,the original platform quadrant and the effective area of the sevoflurane group were significantly reduced 2 hours after awakening（P<0.05）,while the entry times of the original platform and the original platform quadrant of the sevoflurane group were significantly lower than that of the control group（P<0.05）.Compared with the control group,theα7nAChR agonist group showed no statistically significant difference at any time point.The platform retention time,primary platform entry times and effective area entry times of theα7nAChR antagonist group were all significantly lower than those of the control group 2 hours after anaesthesia（P<0.05）.The retention time of the original platform and the entry times of the platform at 1 w after anesthesia were both reduced compared with the control group（P<0.05）.（2）Compared with sevoflurane group,2 hours after anaesthesia,the primary platform and primary platform quadrant entry times of theα7nAChR agonist group increased significantly（P<0.05）,and 1week after anaesthesia,the primary platform retention time,primary platform entry times,effective area entry times and primary platform quadrant entry times all increased significantly（P<0.05）.And the above indexes ofα7nAChR antagonistic group showed a decreasing trend compared with sevoflurane group 2 hours after anaesthesia.There was no significant difference in the observed indexes among the groups at 4 week after anaesthesia（P>0.05）.3.The MRI imaging results:In this study,MRI scans were performed on the brains of rats in each group,and the MRI results of left hippocampal volume（LHV）,left maximum hippocampal length（LHL）,left maximum hippocampal width（LHW）,right hippocampal volume（RHV）,right maximum hippocampal length（RHL）and right maximum hippocampal width（RHW）were statistically analyzed.1)The actual measured indexes:（1）Compared with the control group,2 hours after anesthesia,RHV,LHV and RHL in sevoflurane group were significantly reduced（P<0.05）,and 1week after anesthesia,RHV,LHV and RHW in sevoflurane group were significantly reduced（P<0.05）.RHV,RHW and LHW were significantly reduced in theα7nAChR agonist group 2 hours after anaesthesia,and 1week after anaesthesia in theα7nAChR agonist group,LHV was significantly reduced（P<0.05）.In theα7nAChR antagonist group,LHV decreased significantly 2 hours after anaesthesia,and RHV and LHV decreased significantly 1week after anaesthesia（P<0.05）.（2）Compared with sevoflurane group:2 hours after the rats in theα7nAChR agonist group were awakened from anesthesia,the RHL was significantly increased,and the RHV of 1week was significantly increased（P<0.05）.RHV increased significantly 2 hours after anaesthesia withα7nAChR antagonist（P<0.05）,and RHW reduced significantly 1week after anaesthesia（P<0.05）.2)Standardized results of MRI indicators（‰）:2 hours after anesthesia,RHV/BV in sevoflurane group was significantly less than that in the control group,RHW/BW in theα7nAChR agonist group and the antagonist group was significantly less than that in the control group,RHV/BV in theα7nAChR antagonist group was significantly less than that in the control group（P<0.05）.1week after anesthesia,LHV/BV in theα7nAChR agonist group was significantly less than the other three groups（P<0.05）,and RHW/BW in the sevoflurane group were significantly greater than the other three groups,and LHW/BW in the sevoflurane group were significantly greater than control group and agonist group（P<0.05）.4.The ultrastructure observation of hippocampus neurons in rats:2 hours after anesthesia,edema was observed in neurons and intercellular substance in hippocampus of rats in sevoflurane group,α7nAChR agonist group group and theα7nAChR antagonist group,but the degree of edema was different.The sequence from more to less is:theα7nAChR antagonist group,sevoflurane group,α7nAChR agonist group.At high magnification,the mitochondria of theα7nAChR antagonist group showed significant changes in edema and vacuolation,while the mitochondria of the other groups showed no significant changes.1week after anesthesia,neurons and interstitial edema increased significantly in sevoflurane group andα7nAChR antagonist group,but did not increase significantly in theα7nAChR agonist group.Neurons and interstitial edema fluid in theα7nAChR antagonist group were progressively increased,and the structure of hippocampal neurons was disordered,and the damage degree was obviously aggravated.Conclusion:1.After inhalation of 3.2%sevoflurane by d-galactose-induced aging model rats,it would cause cognitive impairment in a short time,and MRI measurement of hippocampal volume could be used as an auxiliary examination method to judge cognitive impairment and recovery effect.2.The change of hippocampal ultrastructure may be the pathological basis of the cognitive dysfunction caused by sevoflurane,and transmission electron microscopy can be used to determine the damage of hippocampal neurons and the recovery process.3.α7nAChR agonist can improve the cognitive impairment caused by sevoflurane anesthesia to a certain extent,and can be used as a potential prophylactic drug for POCD for further research. |
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