处理时间窗对七氟醚后处理新生大鼠缺氧／缺血脑损伤长期保护作用的影响

The effects of time window on the long-term neuroprotection of sevoflurane postconditioning on neonatal rats with hypoxic/ ischemic brain injury

目的对七氟醚后处理新生大鼠缺氧／缺血（hypoxic/ischemic，H／I）脑损伤模型长期保护作用的有效处理时间窗进行研究探讨。方法新生7dSD大鼠240只，按随机数字表法分为假手术组（Sham组）、H／I组、0h后处理组（P0组）、3h后处理组（R组）、6h后处理组（P6组）、12h后处理组（P12组）（每组40只）。各组行左侧颈总动脉结扎术（Sham组不结扎），吸入8％0：＋92％N2混合气体处理2h，制备大鼠H／I脑损伤模型。制模后，P0组、P3组、P6组、P12组分别于0、3、6、12h吸入含2％七氟醚的湿化混合气体30min。于H／I处理后7d，测定死亡率、大鼠体重；取脑称重，测定左右脑质量比；左右脑切片尼氏染色，观察海马CA1区皮质神经元存活情况，计数神经元，计算左右侧正常神经元密度比值。于H／I处理后21-28d行悬吊实验检测运动能力，29-34d用Morris水迷宫实验检测大鼠学习、记忆能力。结果各组死亡率差异无统计学意义（P〉0．05）。与Sham组比较，其余各组左右脑质量比降低（P〈0．05），神经元计数减少（P〈0．05），逃避潜伏期延长、平台穿越次数减少。与H／I组比较，P0组、P，组、P6组左右脑质量比降低减少（P〈0．05），神经元计数改善（P〈0．05），逃避潜伏期明显缩短、平台穿越次数增加（P〈0．05）；P12组与H／I组比较，组间差异无统计学意义（P〉0．05）。各组悬吊时间差异无统计学意义（P〉0．05）。结论在七氟醚后处理大鼠脑H／I模型的保护作用上，6h以内是后处理保护作用最为有效的时间窗；这种保护作用具有可持续性，可改善由于H／I脑损伤而带来的学习、记忆功能障碍。

Objective To evaluate the effects of time window on long-term neuroprotection of sevoflurane postconditioning on neonatal rats with hypoxic/ischemic （H/I） brain injury. Methods Two hundred and forty 7-days-old SD rats, weighing 13-17 g, （male/female ratio, 1 ： 1）, were randomly divided into 6 groups （n=40） using a random number table： sham operation group（group Sham）, H/I injury group（group H/I）, according to the time of postconditioning, 0 h（group P0）, 3 h（group P3）, 6 h（group Pf）, 12 h（group P12）. To establish H/I brain injury model in neonatal rats, the left common carotid artery ligation was carried out, and then the rats were exposed to 8% O2＋92% N2 at 37 ℃ for 2 h in group H/I, P0, P3, P6 and P12- The rats of group Po, P3, P6, P12 inhaled 2% sevoflurane for 30 min at 0, 3, 6, 12 h after the H/I model was established. At 7 d after the model was established, the mortality was recorded in the rats. The survival rats were weighed and then sacrificed. The brains were removed and the right and left cerebral hemispheres were weighed separately, and the ratio between left/right cerebral hemispheres was calculated. The density of normal neurons in the hippocampal CA1 region of the left cerebral hemispheres were measured. In another experiment, the function of cognitive and memory were assessed in adolescence （28 d after H/I） using Morris water maze. Results There was no significant difference in the mortality among the five groups （P〉0.05）. Compared with group sham, the density of normal neurons in the hippocampal CA1 region in the left cerebral hemispheres, weight of left cerebral hemispheres, and ratio between left/fight cerebral hemispheres were significantly decreased, and left brain injury was more severe in group H/I and the postconditioned groups （P〈0.05）. Compared with group H/I, the density of normal neurons in the hippocampal CA1 region in the left cerebral hemispheres, weight of left cerebral hemispheres, and ratio between left/right cerebral hemispheres were less decreased in group P0, P3 and P6 （P〈0.05）. There were no significant changes in group P12 compared with group H/I （P〉0.05）. The measurement results coincided with the results of Morris water maze： compared with group H/I, the escape latency longations were decreased significantly and crossing platform times were increased in group P0, P3 and P6 （P〈0.05）; there were no significant changes in group P12 compared with group H/I （P〉0.05）. Conclusions 2% sevoflurane postconditioning within 6 h was most effective on attenuating neonatal rats＇ H/I brain injury, and the protection is long-term and can improve learning and memory function during adolescence.