Objectives To investigate the neuroprotective mechanism of vagus nerve stimulation ( VNS) by stimulating the vagus nerve in ischemic cerebral tissue in a rat model of transient focal cerebral ischemia. Methods Twenty-six adult male Sprague-Dawley ( SD ) rats were randomly divided into sham operation group (n=6),model group (n=10),and VNS-treated group (n=10) . The model of rat transient focal cerebral ischemia was induced by the intraluminal suture method. At 30 min after modeling,the right side neck VNS in the VNS-treated group was stimulated ( stimulus intensity 0. 5 mA, interval 0. 5 ms, frequency 20 Hz),once every 5 min within 1 h,and once for 30 s. The model group repeated the steps of the VNS-treated group,but did not stimulate. The sham operation group repeated the experimental steps,but it neither embolized the vessels nor stimulated nerves. The changes of cerebral blood flow were monitored with a laser Doppler flowmeter. The rats were sacrificed after 24 h. The expressions of interleukin 6(IL-6) and caspase-3 in brain tissue were determined by immunohistochemistry staining. The neuronal apoptosis was observed by the in situ end-labelling technique. Results ( 1 ) Compared with the sham operation group, the number of positive cells of IL-6,caspase-3,and the numbers of neuronal apoptosis in the model group were significantly increased (20. 7 ± 5. 0 cells/HP vs. 2. 3 ± 1. 0 cells/HP,44. 5 ± 9. 5 cells/HP vs. 0,30. 9 ± 9. 0 cells/HP vs.0).Thereweresignificantdifferences(P<0.05).(2)Comparedwiththemodelgroup,thenumber of positive cells of IL-6(10. 9 ± 3. 7 cells/HP),the caspase-3 (18. 9 ± 6. 7 cells/HP),and the numbers of neuronal apoptosis (14. 0 ± 5. 2 cells/HP) in the VNS-treated group decreased significantly. There were significant differences (P<0. 01). (3) Before and after modeling,there were no significant differences in cerebral blood flow in various periods between the model group and the VNS-treated group (P>0. 05). Conclusion The neuroprotective mechanism of VNS for cerebral ischemia may be associated with the inhibition of neuronal apoptosis and decreasing inflammatory response. It may not be associated with the changes of cortical cerebral blood flow.%目的：通过刺激短暂性局灶性脑缺血大鼠模型迷走神经,探讨迷走神经刺激( VNS)对脑缺血神经保护的作用机制。方法成年雄性 Sprague-Dawley( SD)大鼠26只,根据体质量大小编号,计算机随机分成假手术组(6只)、模型组(10只)、VNS治疗组(10只)。采用线栓法建立大鼠短暂性局灶性脑缺血模型,VNS治疗组于模型建立30 min后开始刺激颈部右侧迷走神经,刺激强度0．5 mA,间期0．5 ms,频率20 Hz,在1 h内每隔5 min刺激1次,每次持续30 s。模型组重复VNS治疗组步骤,但不予刺激。假手术组重复实验步骤,但既不栓塞血管也不刺激神经。使用激光多普勒血流仪监测脑血流变化。24 h后处死大鼠,取脑组织行免疫组化检测白细胞介素6(IL-6)、半胱氨酸天冬氨酸蛋白酶3(caspase-3)的表达,及原位末端标记法观察神经细胞凋亡情况。结果(1)与假手术组相比,模型组的 IL-6、caspase-3阳性细胞数、神经细胞凋亡计数明显增加[(20．7±5．0)个/高倍镜(HP)比(2．3±1．0)个/HP,(44．5±9．5)个/HP比0,(30．9±9．0)个/HP比0],差异有统计学意义(P<0．01)；(2)与模型组相比,VNS治疗组的IL-6阳性细胞数[(10．9±3．7)个/HP]、caspase-3的阳性细胞数[(18．9±6．7)个/HP]及神经细胞凋亡计数[(14．0±5．2)个/HP]明显减少,差异有统计学意义(P<0．01)；(3)模型组与VNS治疗组在造模前及造模后各个时期的脑血流量比较,差异无统计学意义( P>0．05)。结论 VNS对脑缺血的神经保护作用机制与通过抑制神经细胞凋亡及减少炎性反应有关,可能与皮质脑血流改变无关。
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