行为学训练对低剂量X线照射后SD大鼠认知能力的改善作用研究

Abilities of learning and memory could be improved by behavioral training in SD rats received low doses X-ray

目的探讨行为学训练对低剂量X线照射后幼年SD大鼠学习记忆的影响及其相关机制。方法出生后35d的SD大鼠按抽签法随机分为训练组、照射组及对照组，每组各16只。照射组、训练组每天均接受1次低剂量[以临床中婴幼儿（0～6岁）所采用剂量为基准]X线照射，共7d。对照组接受假照射。通过Morris水迷宫训练其学习记忆能力，7．0TMR检测3组大鼠海马区N-乙酰．天门冬氨酸／肌酸（NAA／Cr）比值。荧光免疫组化法和Western blotting检测各组大鼠海马区细胞色素C氧化酶亚基Ⅳ（COXⅣ）蛋白表达的变化。HE染色观察海马CA1区神经元形态，透射电镜观察神经元线粒体形态。结果（1）照射组NAA／Cr值（1．611±0．013）较对照组（1．873±0．032）明显降低，训练组NAA／Cr值（1．870±0．018）较照射组明显升高，差异均有统计学意义（P〈0．05）。（2）定位航行实验中照射组大鼠第1-4天逃避潜伏期均长于对照组大鼠，差异有统计学意义（P〈0．05）；训练组大鼠第1-4天逃避潜伏期与对照组大鼠无明显区别，差异无统计学意义（P〉0．05）。空间探索实验中，照射组大鼠穿越原站台次数、原站台象限停留时间均明显少于对照组，差异有统计学意义（P〈0．05）；训练组大鼠穿越原站台次数、原站台象限停留时间与对照组大鼠无明显区别，差异无统计学意义（P〉0．05）。（3）荧光免疫组化结果显示照射组大鼠海马CA1区COXⅣ蛋白表达减少，训练组COXⅣ表达增加。Westem blotting结果显示照射组大鼠海马CA1区COXⅣ蛋白表达（0．298±0．049）较对照组（0.998±0．056）明显减少，差异有统计学意义（P〈0．05）；训练组COXIV表达（0．987±0．053）接近训练组，差异无统计学意义（P〉0．05）。（4）照射组大鼠可见核固缩及较多受损的线粒体，训练组大鼠仅见少量受损线粒体。结论行为学训练可能通过增加COXⅣ蛋白表达，改善线粒体形态及功能来恢复低剂量X线照射后幼年SD大鼠受损的学习记忆能力。

Objective To explore the effect of behavior training on abilities of learning and memory in young SD rats received low doses of X-ray and their relevant mechanism. Methods A total of 48 SD rats aged 35 d were randomly divided into irradiated group, training group and control group （n=16）; rats in the irradiated group and training group received X-ray once daily for seven d; rats in the training group also received behavior training. Abilities of learning and memory were detected by Morris water maze test; changes ofN-acetyl aspartate/creatine （NAA/Cr） in the hippocampus were observed; the protein expression levels of cytochrome c oxidase IV （COXIV） in hippocampal regions were observed by immunofluorescence staining and Western blotting. Morphology of neurons in hippocampal CA1 region was detected by HE staining, and mitochondrial morphology was observed via transmission electron microscopy. Results （1） As compared with that in control group （1.873±0.032）, the ratio of NAA/Cr in the irradiated group （1.611±0.013） was significantly decreased, while that in the training group （1.870± 0.018） was significantly higher than that in the irradiated group （P〈0.05）. （2） The escape latency, times crossing the platform and duration of staying in the platform in rats of the irradiated group were significantly longer/fewer than those in the control group, while no significant differences were noted between the training group and control group （P〉0.05）. （3） Immunofluorescence indicated decreased COXIV protein expression in the CA1 area of irradiated group and increased COXIV protein expression in the CA1 area of training group; Western blotting showed that the COXIV protein expression in the hippocampal regions of irradiated group （0.298±0.049） was significantly decreased as compared with that in the control group （0.998±0.056, P〈0.05）, while no significant differences were noted between the training group （0.987±0.053） and control group （P〉0.05）. （4） Karyopyknosis and more damaged mitochondria were found in the irradiated group, while more normal neurons were observed in hippocampal CA1 area of the control and training groups by HE staining. Conclusion Learning and memory abilities of SD rats received low doses of X-ray could be recovered by behavior training, which could be related to the increment of COXIV protein expression and mitochondria improvement by behavior training, and neuron damage in the hippocampus would be reversible in an extent.