高频重复经颅磁刺激对短暂全脑缺血大鼠学习记忆能力及海马长时程增强的影响

The influence of high frequency, repetitive transcranial magnetic stimulation on long-term potentiation in the hippocampus and on spatial learning and memory after global cerebral ischemia

目的观察高频重复经颅磁刺激（rTMS）对全脑缺血再灌注大鼠空间记忆能力及海马长时程增强（LTP）的影响，探讨rTMS是否通过增强LTP促进模型大鼠空间记忆能力的恢复。方法雄性Wistar大鼠83只，5只测定磁刺激运动诱发电位静息阈值，将余78只大鼠按随机数字表法分成正常组、模型组（制作脑缺血再灌注模型）和rTMS组（制作脑缺血再灌注模型，然后给予rTMS治疗）。用四血管夹闭法制作全脑缺血再灌注10min模型；术后第3天开始给予rTMS（10Hz，静息阈值，刺激5s），每天2次，连续刺激14d；分别在术前、术后3d、术后17d（即rTMS治疗14d）后，用Morris水迷宫检测大鼠空间学习记忆能力，电生理检测大鼠在体海马穿通纤维到齿状回颗粒细胞层（PP—DG）电刺激诱发电位（兴奋性突触后电位、群峰电位）及0波短脉冲群电刺激LTP诱导幅度的变化。结果术后第3天，模型大鼠PP—DG通路LTP诱发电位幅度较正常组显著降低，模型组与rTMS组间差异无统计学意义（P〉0．05）；治疗14d后，PP．DG通路LTP诱发电位幅度正常组、模型组和rTMS组之间组间差异有统计学意义（P〈0．05）；Morris水迷宫实验显示大鼠定位航行逃避潜伏期和空间探索在原平台所在象限时间及穿越平台位置时间的组间差异有统计学意义（P〈0．01），rTMS组逃避潜伏期显著缩短（P〈0．01）；rTMS组在原平台所在象限时间及穿越平台时间较模型组明显增多（P〈0．01）。结论高频rTMS促进全脑缺血再灌注后大鼠空间学习记忆能力的恢复，其作用主要是通过增强海马LTP的诱导幅度，原因可能与rTMS调节海马环路中间神经元功能状态及长期高频rTMS可增强神经递质的释放有关。

Objective To investigate the effects of repeated high frequency transcranial magnetic stimulation （rTMS） on spatial learning and memory function, and on long-term potentiation （LTP） after global cerebral isehemia and reperfusion, and to explore the mechanisms involved. Methods Eighty-three male Wistar rats were studied. Five were tested to determine their average motor threshold （Tin）. The others were divided into a normal control group, a cerebral ischemia and reperfusion model group and an rTMS group. Cerebral ischemia was induced with the four vessel occlusion method for 10 minutes. The rTMS treatment protocol （ 10 Hz stimulation for 5 s at the resting threshold, twice a day） was applied over a 2-week period from day 3 post-operation. The Morris water maze test was performed to observe spatial learning and memory at post-operation day 2 and day 4. The field excitatory postsynaptic potentials, population spike and the magnitude of long-term potentiation （LTP） induced by theta burst electric stimu- lation were recorded from the perforant path to the dentate gyrus （PP-DG）. Results At post-operation day 3, rats in the untreated cerebral ischemia and reperfusion model group exhibited a significant decrease in the magnitude of the PP-DG LTP as compared to the normal group. No significant difference in LTP was found between the model group and the rTMS group. After the 2 weeks of treatment the LTP levels in the rTMS treated group were significantly higher than in the two untreated groups. In the Morris water maze testing, the average escape latency in the rTMS group was significantly shorter than that of the cerebral ischemia and reperfusion model group （which was not treated）. In the probe trials, the time in the original quadrant of the platform and the time of crossing the platform were both signifi- cantly less for the rTMS-treated rats than for those not treated. Conclusions High frequency rTMS can improve spatial learning and memory after global cerebral ischemia and reperfusion by enhancing the LTP induced in the hip- pocampus. High frequency rTMS might exert this beneficial effect by modulating the function of intermediate neurons in the hippoeampal neuronal network and by promoting neurotransmitter release.