迷走神经刺激对老龄小鼠术后认知功能障碍的影响及海马IGF-1信号通路在其中的作用

Effects of vagus nerve stimulation on postoperative cognitive dysfunction and role of hippocampal insulin growth factor 1 signaling pathway in aged mice

目的探讨迷走神经刺激对老龄小鼠术后认知功能障碍(POCD)的影响及海马胰岛素生长因子1(IGF-1)信号通路在其中的作用。方法清洁级C57小鼠75只,雌雄不拘,21~23月龄,体重28~34 g,采用随机数字表法分为5组(n=15):假手术组(S组)、手术组(O组)、手术+迷走神经刺激组(O+V组)、手术+IGF-1 siRNA组(O+I组)和手术+迷走神经刺激+IGF-1 siRNA组(O+V+I组)。O组行剖腹探查术;O+V组剖腹探查术结束后行迷走神经刺激30 min(刺激强度0.5 mA,刺激频率20 Hz,刺激时间30 s,刺激6次,间隔5 min);O+I组行剖腹探查术,并于术前24 h、术后24和48 h经鼻吸入IGF-1 siRNA溶液10μl;V+I组剖腹探查术后行迷走神经刺激,并于术前24 h、术后24和48 h经鼻吸入IGF-1 siRNA溶液10μl。术后第14~18天行Morris水迷宫测试;术后第7天,处死小鼠取海马,采用Western blot法检测Bax、离子钙结合适配器分子1(Iba-1)、IGF-1、IGF受体1(IGF1R)、磷酸化IGF1R(p-IGF1R)、IL-1β和活化的caspase-3的表达。结果与S组比较,O组术后第16~18天时逃离潜伏期延长,穿越平台次数减少,目标象限停留时间缩短,海马IGF-1和p-IGF1R表达下调,Iba-1、IL-1β、活化的caspase-3和Bax表达上调(P<0.05);与O组比较,O+V组术后第16~18天时逃离潜伏期缩短,穿越平台次数增加,目标象限停留时间延长,海马IGF-1和p-IGF1R表达上调,Iba-1、IL-1β、活化的caspase-3和Bax表达下调(P<0.05),O+I组上述各指标差异无统计学意义(P>0.05);与O+V组比较,O+V+I组术后第16~18天时逃离潜伏期增长,穿越平台次数减少,目标象限停留时间缩短,海马IGF-1和p-IGF1R表达下调,Iba-1、IL-1β、活化的caspase-3和Bax表达上调(P<0.05)。4组间海马IGF1R表达比较差异无统计学意义(P>0.05)。结论迷走神经刺激可减轻老龄小鼠POCD,其机制与激活IGF-1信号通路,减轻海马神经炎症反应和神经元凋亡有关。

Objective To investigate the effects of vagus nerve stimulation on postoperative cognitive dysfunction and the role of hippocampal insulin growth factor 1 signaling pathway in aged mice.Methods Seventy-five clean-grade C57 mice of both sexes,aged 21-23 months,weighing 28-34 g,were divided into 5 groups(n=15 each)using a random number table method:sham operation group(group S),operation group(group O),operation+vagus nerve stimulation group(group O+V),operation+IGF-1 siRNA group(group O+I)and operation+vagus nerve stimulation+IGF-1 siRNA group(group O+V+I).Group O underwent exploratory laparotomy.Group O+V received a 30-min electrical stimulation of the vagus nerve(intensity 0.5 mA,frequency 20 Hz,time 30 s,6 times,interval 5 min)after the end of exploratory laparotomy.Group O+I underwent exploratory laparotomy and inhaled IGF-1 siRNA solution 10μl intranasally at 24 h before surgery and 24 and 48 h after surgery.Group O+V+I underwent electrical vagus nerve stimulation after exploratory laparotomy and inhaled IGF-1 siRNA solution 10μl intranasally at 24 h before surgery and 24 and 48 h after surgery.Morris water maze tests were performed on 14-18 days after operation.On day 7 after operation,the mice were sacrificed and the hippocampus was obtained for determination of the expression of Bax,ionized calcium-binding adapter molecule 1(Iba-1),insulin-like growth factor 1(IGF-1),insulin-like growth factor 1 receptor(IGF1R),phosphorylated IGF1R(p-IGF1R),interleukin-1beta(IL-1β)and activated caspase-3 by Western blot.Results Compared with group S,the escape latency was significantly prolonged on days 16-18 after operation,the frequency of crossing the platform was reduced,the time spent in the target quadrant was shortened,the expression of IGF-1 and p-IGF1R was down-regulated,and the expression of Iba-1,IL-1β,activated caspase-3 and Bax was up-regulated in group O(P<0.05).Compared with group O,the escape latency was significantly shortened on days 16-18 after operation,the frequency of crossing the platform was increased,the time spent in the target quadrant was prolonged,the expression of IGF-1 and p-IGF1R was up-regulated,and the expression of Iba-1,IL-1β,activated caspase-3 and Bax was down-regulated in group O+V(P<0.05),and no significant change was found in the parameters mentioned above in group O+I(P>0.05).Compared with group O+V,the escape latency was significantly prolonged on days 16-18 after operation,the frequency of crossing the platform was reduced,the time spent in the target quadrant was shortened,the expression of IGF-1 and p-IGF1R was down-regulated,and the expression of Iba-1,IL-1β,activated caspase-3 and Bax was up-regulated in group O+V+I(P<0.05).There was no significant difference in the expression of IGF1R among the four groups(P>0.05).Conclusions Vagus nerve stimulation can reduce postoperative cognitive dysfunction,and the mechanism is related to activation of IGF-1 signaling pathway and reduction of hippocampal neuroinflammation and neuronal apoptosis in aged mice.