| Objective Chronic cerebral hypoperfusion(CCH)is an important risk factor and pathophysiological basis for cognitive impairment.Transient receptorpotential vanilloid 1(TRPV1)is a non-selective cation channel with high permeability of calcium ions,and capsaicin is a highly selective agonist.The regulation of TRPV1 is involved in various physiological and pathophysiological processes of the brain.It can regulate brain activity by regulating neurotransmitter release,synaptic plasticity and nerve network excitability.Previous studies have found that the rats of CCH established by bilateral common carotid anery occlusion(BCCAO)can induce persistented impairment of spatial learning and memory for up to 6 months in experimental animals,accompanied by imbalance of silent synapses and functional synapses in hippocampal CAl,especially at 4 weeks after modeling.Therefore,by observing the effects of capsaicin on emotional arousal level and learning memory of CCH rats,we quantitatively analyze the changes of TRPV1 and synaptic loss in hippocampus of rats,and explore the mechanism and effective treatment of CCH-related cognitive impairment.Methods Sixty adult male SD rats were randomly divided into control group(SHAM group,n = 15),chronic cerebral hypoperfusion group(CCH group,n = 15),placebo control group(PC group,n = 15),capsaicin group(CAP group,n = 15).A rat model of CCH was established by BCCAO.Capsaicin and placebo were injected twice a week for 4 weeks on the basis of CCH model in capsaicin group and placebo control group.The open-field experiment and Morris water maze were used to evaluate the emotional level and spatial learning and memory function of rats;the immunofluorescence double labeling experiment was conducted on TRPV1 and synaptophysin in hippocampus,analyzed by laser confocal microscopy;the expression of TRPV1 and synaptophysin in hippocampus was analyzed by Western Blot;the ultrastructure of hippocampus synapse was observed by transmission electron microscope,including the changes of synaptic density and postsynaptic density.Results(1)Four weeks after the successful construction of CCH model,the level of emotional arousal and learning memory dysfunction appeared.After capsaicin intervention,the level of emotional arousal and learning memory dysfunction of CCH model rats were improved.Open-field experiment and Morris water maze experiment showed that compared with the control group [(22.60±4.60)times],the standing times of CCH group [(12.10±2.80)times] decreased(P<0.01),capsaicin group [(19.30±4.16)] times increased compared with placebo control group [(12.50±2.68)].Multivariate variance analysis of repeated measurements showed that the escape latency time and total swimming distance of CCH group increased significantly(P<0.01)compared with the control group.The escape latency time and total swimming distance of capsaicin group decreased compared with placebo control group(P<0.05),and there was significant difference on the 3rd day(P<0.05).On the 6th day,space exploration training was conducted.The results of single factor analysis of variance showed that the number of crossings [(0.75±0.89)times] decreased in CCH group compared with control group [(1.87±0.64)times](P<0.01).The capsaicin group [(2.38±0.74)times] was higher than the placebo control group [(1.00±0.93 times)](P<0.01);the crossing latency [(9.73±3.40)s] was higher than that of the control group [(29.78±9.80)s](P<0.01),and the capsaicin group [(9.33±7.38)s] was lower than that of the placebo control group [(35.10±1.85)s](P<0.01).(2)The expression of TRPV1 and synaptophysin decreased significantly 4 weeks after the successful construction of CCH model,while the expression of TRPV1 and synaptophysin increased significantly after capsaicin intervention.Immunofluorescence double label assay showed that TRPV1 and synaptophysin were expressed in all four groups of experimental animals,but the expression levels were different.The fluorescence intensity of TRPV1 in SHAM group,CCH group,PC group and CAP group was 56.18±2.66,13.88±1.37,15.08 ±2.59,55.15±2.12,and synaptophysin was 38.83±1.85,14.36±0.84,13.96±2.94,36.91±0.81,respectively.The results showed that the expression of TRPV1 and synaptophysin decreased in CCH group compared with SHAM group(P<0.05),while the expression in CAP group increased significantly compared with PC group(P<0.05).(3)CCH could significantly decrease the expression of TRPV1 and synaptophysin in hippocampus of rats,while capsaicin could significantly increase the content of TRPV1 and synaptophysin in hippocampus of CCH rats and improve synaptic loss.Western Blot experiment showed that the expression levels of TRPV1 in SHAM group,CCH group,PC group and CAP group was 1.00±0.00,0.73±0.66,0.75±0.61,1.05±0.82;the synaptophysin was 1.00±0.00,0.70±0.06,0.71±0.08,1.05±0.08.Compared with the control group,the expression of TRPV1 and synaptophysin in CCH group decreased significantly(P<0.05),while the expression of TRPV1 and synaptophysin in CAP group increased significantly(P<0.05)compared with PC group.(4)Synaptic loss was observed in the hippocampus of CCH rats,and the synaptic loss in the hippocampus of CCH rats was significantly improved after capsaicin intervention.TEM experiments showed that the synaptic density in SHAM group,CCH group,PC group and CAP group was 7.33±0.58,4.33±0.58,4.67±0.58,7.67±0.58;postsynaptic densities were 65.67±2.61,48.09±3.47,48.15±1.92,64.0±1.73.The results showed that the density of synapses and the thickness of postsynaptic densities in CCH group were significantly lower than those in SHAM group(P<0.05),while those in CAP group were significantly higher than those in PC group(P<0.05)Conclusion BCCAO can induce chronic cerebral hypoperfusion,which leads to cognitive impairment in emotional arousal level and learning memory,accompanied by decreased expression of TRPV1 and synaptophysin in hippocampus and decreased synaptic density and thickness of postsynaptic densities in synaptic ultrastructure.After capsaicin intervention,cognitive impairment in rats with CCH was significantly restored.The expression of TRPV1 and synaptophysin in hippocampus of rats increased,and the synaptic density and the thickness of postsynaptic densities in synaptic ultrastructure also increased.Therefore,it is speculated that synaptic loss and TRPV1 decrease in hippocampus caused by CCH are the important pathological basis of cognitive impairment,and capsaicin intervention can activate TRPV1 and improve cognitive impairment caused by synaptic loss in rats. |
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