右美托咪定减轻老年小鼠心肌缺血再灌注诱发认知功能障碍的作用及突触可塑性机制

Effects of Dex on alleviating cognitive impairment induced by myocardial I/R in aged mice and its related synaptic plasticity mechanisms

目的 探究右美托咪定(dexmedetomidine,Dex)减轻老年小鼠心肌缺血再灌注(ischemia-reperfusion,I/R)诱发认知功能障碍的作用及突触可塑性机制。方法 采用随机数字表法将40只老年雄性C57BL/6小鼠分为假手术(Sham)组、Sham+Dex组、I/R组、I/R+Dex组,每组10只。再灌注第7天,采用八臂水迷宫、新物体识别评价小鼠认知功能,海马CA1区电生理记录体内长时程增强统计场兴奋性突触后电位(field excitatory postsynaptic potential,fEPSP),酶联免疫吸附法检测血清肌钙蛋白T(cardiac troponin T,cTnT)、乳酸脱氢酶(lactate dehydrogenase,LDH)、N末端B型钠尿肽前体(N-terminal pro-B-type natriuretic peptide,NT-proBNP)水平,Western blot检测海马组织脑源性神经营养因子(brain-derived neurotrophic factor,BDNF)、酪氨酸激酶受体B(tyrosine kinase receptor B,TrkB)-FL、TrkB-T1蛋白表达,Golgi-Cox染色观察海马CA1区树突棘密度,免疫荧光染色检测突触生长素(synaptic growth factor,SYN)、突触后致密蛋白95(postsynaptic dense protein 95,PSD95)表达。结果 再灌注第7天,与Sham组、Sham+Dex组比较,I/R组、I/R+Dex组工作记忆错误(working memory error,WME)、参考记忆错误(reference memory error,RME)、总记忆错误(total error,TE)、血清cTnT、LDH、NT-proBNP水平、TrkB-T1蛋白表达升高,识别指数、fEPSP斜率、BDNF、TrkB-FL蛋白表达、突触棘密度、SYN、PSD95表达降低(P<0.05)。与I/R组比较,I/R+Dex组TrkB-T1蛋白表达降低(0.86±0.07 vs 1.51±0.18,P<0.05),BDNF蛋白表达(0.70±0.07 vs 0.39±0.06)、TrkB-FL蛋白表达(0.67±0.10 vs 0.45±0.08)、SYN表达(20.53±0.59 vs 16.50±1.05)、PSD95表达(17.73±0.52 vs 14.71±0.91)升高(P<0.05)。结论 Dex对老年小鼠心肌I/R诱发的认知功能障碍具有保护性作用,具体机制可能与减轻心脏损伤,增加BDNF、SYN、PSD95表达,改善海马组织TrkB-FL与TrkB-T1比例失调,增强突触可塑性相关。

Objective To investigate the effect and synaptic plasticity mechanism of dexmedetomidine(Dex) on alleviating cognitive impairment induced by myocardial ischemia/reperfusion(I/R) in aged mice.Methods Forty elderly male C57BL/6 mice were randomly divided into sham group,Sham+Dex group,I/R group,and I/R+Dex group,with 10 mice in each group.On the 7th day of reperfusion,cognitive function was evaluated using an eight arm water maze and novel object recognition.Electrophysiological recordings of hippocampal CA1 area was performed to measure field excitatory postsynaptic potential(fEPSP) in in vivo long-term potentiation(LTP).The serum levels of cardiac troponin T(cTnT),lactate dehydrogenase(LDH),and N-terminal pro-B-type natriuretic peptide(NT-proBNP) were detected by ELISA.Western blotting was used to determine the expression of brain-derived neurotrophic factor(BDNF),tyrosine kinase receptor B(TrkB)-FL,and TrkB-T1 in hippocampal tissues.Golgi-Cox staining was utilized to observe the density of dendritic spines in hippocampal CA1 area.Immunofluorescence staining was performed to detect the expression of synaptic growth factor(SYN) and postsynaptic dense protein 95(PSD95).Results On the 7th day of reperfusion,the working memory error(WME),reference memory errors(RME) and total errors(TE) of the eight arm water maze and the expression levels of cTnT,LDH,NT-proBNP and TrkB-T1 were significantly higher,and the recognition index,fEPSP and expression levels of BDNF,TrkB-FL,SYN and PSD95 and density of dendritic spines were remarkably decreased in the I/R group and I/R+Dex group than the Sham group and Sham+Dex group(P<0.05).The I/R+Dex group had obviously reduced TrkB-T1 expression(0.86±0.07 vs 1.51±0.18),and increased expression levels of BDNF(0.70±0.07 vs 0.39±0.06),TrkB-FL(0.67±0.10 vs 0.45±0.08),SYN(20.53±0.59 vs 16.50±1.05) and PSD95(17.73±0.52 vs 14.71±0.91) when compared with the I/R group(P<0.05).Conclusion Dex exerts protective effect on cognitive impairment induced by myocardial I/R in elderly mice,and the specific mechanism may be related to alleviating cardiac injury,increasing the expression of BDNF,SYN and PSD95,improving the imbalance of TrkB-FL and TrkB-T1 ratio in hippocampal tissue,and enhancing synaptic plasticity.