The Effects Of Repetitive Transcranial Magnetic Stimulation And Its Molecular Mechanism On Ability Of Learning And Memory In Vascular Dementia Rat Model

ObjectiveVascular dementia(VaD)is one of main types of senile dementia.While the definite pathogenesis is still not clear.Repetitive transcranial magnetic stimulation (rTMS)plays an important role in the recovery of cerebral ischemia.We investigated the effect of repetitive transcranial magnetic stimulation on the ability of learning and memory and studied its molecular mechanism.This will provide therapy foundation in clinical rTMS application on vascular dementia and help to discover more effective therapy of vascular dementia.MethodsTwo-vessel occlusion(2VO)was employed to make vascular dementia rat models. Morris water-maze test was performed to study the ability of learning and memory in each group of rats.The expression of BDNF,NMDAR1,Synaptophysin(SYN)in hippocampal CA1 region were determined by immunohistochemistry assay.The ultrastucture changes of the synapses were observed with electron microscopy.1.Animals36 male Wistar rats weighting 290±20g were randomly divided into control group, vascular dementia group,vascular dementia with low frequency stimulation group and vascular dementia with high frequency stimulation group.2.Vascular dementia rat modelTwo-vessel occlusion(2VO)method was used to make vascular dementia animal model.The rats were performed fasting while could drink 8-12h before operation. Apply abdominal anesthesia with 10%chloral hydrate(0.3ml/100g body weight). Fixed the rats lying on the back,selected median incision on abdomen,and performed blunt dissection to expose double-side common carotid.The artery was occlusion by 4 type line.In the control group,rats were not performed 2VO operation.3.Repetitive transcranial magnetic stimulationLow frequency rTMS group rats were given 0.5 Hz rTMS for six weeks.High frequency rTMS group rats were given 5 Hz rTMS for six weeks. 4.Morris water maze testBefore Morris water maze test,a free swimming trail was run in which the platform was removed so that all rats were adapted to temperature and environment of Morris water maze.The rats that had poor ability of swimming were ticked out of test.During the place navigation test,a submerged platform was placed in the Morris water maze and rats were studied to learn the location of the platform that could be used to escape from swimming.The rats were placed in the maze in different starting positions that were equally distributed around the perimeter of the maze.The trail was lasted for 4 days.Record the escape latencies in each group.In the 5^thday,a spatial probe test was given which consisted of a 120 seconds free swimming period without the platform.Times of crossing the former site of the removed hidden platform were calculated statistically.5.Immunohistochemistry assayThe expression of BDNF,NMDAR1,SYN in hippocampal CA1 region were detected with immunohistochemistry assay.6.Statistical analysisUse SPSS 13.0 software for statistical disposition.All results were shown by mean±standard deviation.Differences between three groups were evaluated using one-way ANOVA,and differences between two groups were evaluated using Student's t test for statistical analysis.P＜0.05 was considered as the level of significance.Results1.Morris water maze test resultsThere was significant difference among four groups.The escape latencies in VaD group were statistically longer than those in control group significantly(p＜0.05),and the escape latencies in the low frequency rTMS group and in the high frequency rTMS group were shorter than those in VaD group significantly(P＜0.05).The time and distance of crossing the former site of the removed hidden platform in VaD group were less than those in control group(P＜0.05),and the time and distance of crossing the former site of the removed hidden platform in the low frequency rTMS group and in the high frequency rTMS group were longer than those in VaD group significantly (P＜0.05).Low frequency rTMS group had no statistical difference with high frequency rTMS group(P＞0.05).2.The expression of BDNF,NMDAR1,SYN in hippocampus CA1 regionThe average expression of BDNF,NMDAR1,SYN protein in VaD group was lower than that in control group(P＜0.05).The average expression of BDNF, NMDAR1,SYN protein expression in low frequency rTMS group and in the high frequency rTMS group were higher than that in VaD group(P＜0.05).Low frequency rTMS group had no statistical difference with high frequency rTMS group(P＞0.05).3.The morphology of nerve cell in hippocampus CA1 regionThe morphology of nerve cell in hippocampus CA1 reginon in VaD group disordered and damaged obviously compared with control group.The damaged changes of nerve cell morphology not only in low frequency rTMS group but also in high frequency rTMS group improved compared with VaD group.There was no statistical difference with low frequency rTMS group and high frequency rTMS group.4.The ultra-micro structure changes of the synapsesThe structure of synapses in VaD group disordered and damaged obviously compared with control group.The damaged changes of synapses structure not only in low frequency rTMS group but also in high frequency rTMS group improved compared with VaD group.There was no statistical difference with low frequency rTMS group and high frequency rTMS group.ConclusionsVascular dementia rats have deficiency in the ability of spatial learning and memory,rTMS can improve the ability of spatial learning and memory in vascular dementia rats.Our research proved that rTMS could increase the expression of BDNF, NMDAR1 and SYN protein,and influence the plasticity of synapses,thus in the end it improve the function of behavior,learning and memory.