极低频电磁场对大鼠创伤性颅脑损伤后神经保护时间窗的影响

Effects of extremely low-frequency electromagnetic fields on time window of neuroprotection after traumatic brain injury in rats

目的研究极低频电磁场对大鼠颅脑损伤后神经保护时间窗的影响。方法522只雄性SD大鼠建立侧向液压打击模型后，分别置于无电磁场中和频率为15HZ强度为1G、3G、5G的电磁场中[分别为N-EMF组、EMF-1G（15Hz）组、EMF-3G（15Hz）组、EMF-5G（15Hz）组]，时间分别为0．5h、1h、6h、12h、18h、24h、30h，然后腹腔注射海人酸诱导海马部位神经元凋亡模拟颅脑损伤后的二次损伤。应用水迷宫实验观察二次损伤后各组大鼠的学习与记忆能力，TUNEL法检测大鼠海马部位神经元凋亡情况，脑组织含水量检测大鼠脑水肿情况，Westernblotting法检测缺氧诱导因子-1α（HIF-1α）蛋白的表达情况。结果EMF-1G（15Hz）组、EMF-3G（15Hz）组、EMF-5G（15Hz）组大鼠颅脑损伤后神经保护窗口时间（损伤后1～12h）与N-EMF组（损伤后1-6h）相比明显延长。在神经保护时间窗内（1h、6h、12h），EMF-1G（15Hz）组、EMF-3G（15Hz）组、EMF-5G（15Hz）组大鼠到达高台所需时间比N-EMF组相对时间点明显缩短，诱导的神经元凋亡数目明显少于N-EMF组相对时间点，大鼠脑组织含水量明显低于N-EMF组相应时间点，差异均有统计学意义（P〈0．05）。在EMF-1G（15Hz）组、EMF-3G（15Hz）组、EMF-5G（15Hz）组侧向液压打击后12h、18h、24h注射海人酸后，HIF-1α蛋白的表达明显低于N-EMF组相应时间点，差异有统计学意义（P〈0．05）。结论电磁场照射可以明显延长创伤性颅脑损伤后的神经保护时间窗，并加强神经保护时间窗内的保护强度。

Objective To explore the effects of extremely low-frequency electromagnetic fields （ELFEF） on time window of neuroprotection after traumatic brain injury （TBI）. Methods Sprague-Dawley rats were subjected to models of lateral fluid percussion injury （LFP）. The rats were placed in non-electromagnetic fields （N-EMF） and 15 Hz electromagnetic fields （EMF） with the intensity of 1, 3 and 5 G, respectively （N-EMF group, EMF-1G [15 Hz] group, EMF-3G[15 Hz] group and EMF-5G [15 Hz] group）. Then KA was injected to the rat abdominal cavity to induce the apoptosis of hippocampus cells at 0.5, 1, 6, 12, 18, 24 and 30 h, respectively. The rats were taken into water maze test to testify the ability of cognitive and memory after KA injection, the apoptosis was examined using TUNEL, the cerebral edema was examined using brain water content and the HIF-1α protein expression was detected in the rat brain by Western blotting. Results ELFEF significantly prolonged the time window of neuroprotection after TBI; the time window of neuroprotection was 1 to 6 h after TBI in N-EMF, while it was 1 to 12 h after TBI in EMF. In the time window ofneuroprotection, rats in the EMF-1G [15 Hz] group, EMF-3G[15 Hz] group and EMF-5G [15 Hz] group needed obviously shorter time to reach to the high platform, had significantly decreased neuronal apoptosis amount and watercontent than rats in the N-EMF group （P〈0.05）; 12, 18 and 24 h after kainic acid injection in the EMF-1G [15 Hz] group, EMF-3G[15 Hz] group and EMF-5G [15 Hz] group, the HIF-1α in these groups was dramatically reduced as compared with that in the N-EMF group （P〈0.05）. Conclusion ELFEF could obviously prolong the time window of neuroprotection after TBI and enhance the intensity of protection in the time window.