Contribution Of Increased Blood Pressure Variability To Learning Ang Memory Impairment And Abnormal Blood-brain Barrier In Rats And The Improvement Of Nitrendipine

BackgroundLearning and memory impairment is mainly manifested by the decline of cognitive function,which occurs in stroke,dementia and other diseases.They are often caused by the elderly,which seriously endangers their quality of life.Clinical reports have shown that increased blood pressure variability can lead to decreased learning and memory,cognitive impairment,but the mechanism is still unclear.Based on the abnormal function of blood-brain barrier is one of the mechanisms of learning and memory disorder,we propose a hypothesis: the mechanism of learning and memory impairment caused by elevated blood pressure variability is related to abnormal blood-brain barrier function,and the antihypertensive drug nitrendipine has an improving effect.PurposeTo explore the time-course relationship and molecular mechanism of learning and memory impairment and abnormal blood-brain barrier caused by increased blood pressure variability in rats,and observe the improvement of nitrendipine.Method1.A rat model of increased blood pressure variability was established by sinoaortic denervation(SAD)and divided into Sham operation group and SAD model group.Using hemodynamic monitoring method for conscious free-activity rats,detection of hemodynamic parameters,including SBP,DBP,MBP,SBP,DBPV,MBPV,BRS.Morris Water maze,new object recognition test and Barnes maze were used to detect the learning and memory function of rats at different time points 2 weeks,4 weeks,8 weeks and 16 weeks after operation.The function of blood-brain barrier(BBB)was detected by injecting EB into rat tail for 2 weeks,4 weeks,8 weeks and 16 weeks.The indexes included the amount of EB leakage in the brain and the fluorescence intensity of EB in brain slices.The function of BBB were measured by injecting FITC-dextran into the tail of rats for 2 and 4weeks,The indexes including the amount of FITC-dextran leakage in the brain and the fluorescence intensity of FITC-dextran in brain slices.The expression levels of blood brain barrier-related proteins occludin and ZO-1 were detected by Western blotting.2.The rats were divided into three groups: Sham group,SAD group and SAD+Nitrendipine group 2 weeks after SAD operation,0.5% CMC-Na,0.5% CMC-Na and nitrendipine(0.5 mg/Kg·d)were administered for 1 month.The hemodynamic,behavioral and BBB functions were measured by using the above methods.Result1.Time-course changes in learning and memory impairment and blood-brain barrier abnormalities induced by increased blood pressure fluctuation(1)Hemodynamic results: Compared with the Sham group,the SBP,DBP,and MBP are similar in the SAD group,while SBPV,DBPV,and MBPV increased significantly,and BRS and ?HR decreased significantly.The results suggest that the simple blood pressure variability model is successful.(2)Behavior experimental results2.1 Results of Morris water maze test: compared with Sham group,the latency of SAD group increased significantly at 2 weeks,4 weeks,8 weeks and 16 weeks after operation.The results of Morris water maze space exploration showed that the times of platform crossing in SAD group were significantly lower than those in Sham group at 4weeks,8 weeks and 16 weeks after operation,and the stay time in platform quadrant decreased significantly at 8 weeks and 16 weeks after operation.2.2 Results of the new object recognition test: In the training stage,compared with Sham group,there was no significant difference in the recognition index of two identical objects between SAD group at 2 weeks,4 weeks,8 weeks and 16 weeks after operation.In the memory stage,compared with the Sham group,there was no significant difference in the recognition index of different objects in the SAD group at 2 weeks,4 weeks and 8weeks after operation,but at 16 weeks after the operation,the recognition index of different objects in the SAD group decreased significantly.2.3 Results of Barnes maze: In the training stage,compared with the Sham group,there was no significant difference in the latency between the 2 and 4 week after surgery in the SAD group,and the latency increased significantly at 8 and 16 weeks after surgery.At the detection stage,the time taken to find the target hole was significantly longer in the SAD group than in the Sham group at 8 and 16 weeks after operation.Compared with Sham group,the correct numbers of finding target holes in SAD group were significantly lower at 4 and 16 weeks after operation.The above results suggest that the SAD group began to show learning and memory impairment in the Morris water maze test 2 weeks after surgery,and continued until 16 weeks.(3)The results of blood-brain barrier permeability test3.1 Results of EB leakage in brain: Compared with the Sham group,there was no significant difference in the amount of EB leakage in the brain of the SAD group at 2 and 4weeks after operation,but the amount of EB infiltration in the brain of the SAD group increased significantly at 8 and 16 weeks after operation.The results of EB fluorescence intensity in brain slices showed that compared with Sham group,the fluorescence intensity of EB in the hippocampus of SAD group was significantly higher at 8 and 16 weeks.In the cortex and striatum,the results were consistent with those of the hippocampus.3.2 Results of intracerebral FITC-dextran(10KD)permeability:Compared with Sham group,the infiltration of FITC-dextran in the brain of SAD group increased at the 2nd and4 th week after operation,but there was no obvious difference.The results of FITC-dextran fluorescence intensity in brain slices showed tha,compared with Sham group,the fluorescence intensity of FITC-dextran in the hippocampus of SAD group increased significantly at 2 weeks after operation,but there was no significant difference at 4 weeks after operation.Compared with Sham group,the fluorescence intensity of FITC-dextran in the cortex of SAD group increased significantly at 2 weeks and 4 weeks after operation.Compared with Sham group,the fluorescence intensity of FITC-dextran in the striatum of AD group increased significantly at 4 weeks after operation.(4)Changes in Occludin and ZO-1 in the brainOccludin protein expression results: in the cerebral cortex and striatal protein levels decreased at 2 weeks after SAD;4 weeks after surgery,cerebral cortex,hippocampus and striatum protein levels decreased;8 weeks after surgery,the hippocampus,striatum protein levels decreased;16 weeks after surgery,the cortex,hippocampus,and striatal protein levels were also reduced.The results suggest that the level of Occludin protein in the brain decreases after the fluctuation of blood pressure.ZO-1 protein expression results: Only in the 16 weeks after SAD surgery,the level of ZO-1 in the hippocampus of the brain decreased,and there was no significant change at other time points.It is suggested that the effect of ZO-1 may be less in the abnormal function of BBB in SAD rats.2.The improvement of nitrendipineAfter nitrendipine administration,there was no significant change in SBP,DBP and MBP in SAD group compared with Sham group,while SBPV,DBPV and MBPV increased significantly,and BRS and ?HR decreased significantly.Compared with SAD group,there was no significant difference in SBP,SBPV,DBPV,MBPV and BRS between SAD+nitrendipine group,DBP and MBP decreased significantly,and ?HR increased significantly.Compared with Sham group,BRS and ?HR were significantly decreased in the SAD+nitrendipine group.It is suggested that nitrendipine can reduce the BPV of SAD rats to some extent.Behavioral results after nitrendipine administration:(1)Results of Morris water maze test:Compared with Sham group,the latency of SAD group was significantly higher than that of SAD group,while that of,SAD+Nitrendipine group was significantly lower than that of SAD group.In the experiment of space exploration,compared with Sham group,the number of traversing platform in SAD group decreased significantly,and there was no significant difference in the stay time of platform quadrant among the three groups.(2)Results of the new object recognition test: There was no significant difference in the recognition index between Sham group,SAD group and SAD+Nitrendipine group in training stage and memory stage.Results of Barnes maze:Compared with(3)Sham group,the latency of SAD group increased significantly;Compared with SAD group,the latency of rats in SAD+nitrendipine group decreased significantly.The time taken to find the target hole was significantly higher in the SAD group than in the Sham group,while the time spent in SAD+nitrendipine group decreased significantly compared with SAD group.Compared with the Sham group,the correct numbers of finding target holes in the SAD group was significantly reduced;there was no significant difference between the SAD group and the SAD+nitrendipine group.correct numbers of finding target holes.BBB permeability test results after nitrendipine administration:1)Results of EB leakage in brain: Compared with the Sham group,the EB leakage in the brain of the SAD group was significantly increased;Compared with the SAD group,the SAD+nitrendipine group showed decreased.2)EB fluorescence intensity in brain sections: In the hippocampus,cortex and striatum areas of the brain slices,the EB fluorescence intensity of the SAD group increased compared with the Sham group;compared with the SAD group,the fluorescence intensity of the SAD+nitrendipine group significantly reduced.The results suggest that nitrendipine can reduce the blood-brain barrier penetration of SAD rats and have a protective effect on brain tissue.Effects of nitrendipine on Occludin and ZO-1 in brain of SAD rats: Compared with Sham group,the expression of Occludin in the cortex,hippocampus and striatum decreased in SAD group,and increased in SAD + nitrendipine group compared with SAD group.There was no significant difference between the groups for the amount of ZO-1 expression.The results suggest that the expression of Occludin in the brain increases after the intervention of nitrendipine,and the function of BBB is improved.Conclusion1.Increased blood pressure variability leads to learning and memory impairment in rats,which may be related to impaired BBB function.2.Nitrendipine can improve learning and memory impairment in rats caused by increased blood pressure variability,and the mechanism may be related to the improvement of BBB function.