直线加速器不同剂量全脑单次与分割外照射对大鼠学习记忆能力的影响

Different effects of fractionated and single fraction irradiation on learning and memory ability in rats

目的 探讨不同照射方法对大鼠学习记忆能力的影响，以期为放射性脑损伤进一步研究建立更精确放射性脑损伤大鼠模型。方法 采用直线加速器对Sprague—Dawley大鼠分别进行单次和分割全脑照射，剂量分别为20Gy、30Gy，并设未照射组为对照。在照射后2周、8周分别进行Morris水迷宫实验，分析各组大鼠行为学检测结果，采用平均逃避潜伏期和搜索策略两个指标评价大鼠学习记忆能力，同时观察各组脑组织病理变化。结果 相同剂量常规分割照射2组大鼠与单次照射2组大鼠相比，照射后不同时间点平均潜伏期和搜索策略差异有显著性（P〈0．05），且30Gy分割照射后8周时平均潜伏期[（105．62±9．58）s]和搜索策略（9．37±0．81）％差异最为明显。单次照射两个剂量组其平均逃避潜伏期和搜索策略得分在照射后2周和8周时差异无显著性，而分割照射2组在照射后不同时间点其平均逃避潜伏期和搜索策略得分均差异有显著性（P〈0．05），以30Gy组最为明显（P〈0．01）[平均潜伏期2周（83．52±7．79）s，8周（105．62±9．58）s；搜索策略2周（11．52±1．02）％，8周（9．37±0．81）％]。20Gy分割照射组和30Gy两照射组病理检查显示神经元萎缩变性，白质梳松，以30Gy分割照射组在照射后8周时上述病变最为严重。结论 全脑分割照射比单次大剂量照射更易造成远期的放射性脑损伤，对大鼠进行全脑常规分割照射可以建立更贴近临床病理过程的放射性脑损伤动物模型。

Objective To explore the effects of different irradiation methods on learning and memory ability and to establish exact animal model of radiation brain injuries for further studies. Methods Sprague-Dawley rats were treated respectively with fractionated and single fraction irradiation with different irradiation doses. On the 2nd week and 8th week after radiation, Morris maze tests were taken to study the learning and memory ability of rats in each group. Average escape latency and search strategy were scaled and analyzed. Pathology examinations were taken in every group. Results Statistic differences of average escape latency and search strategy were found between fractionated and single fraction irradiation groups with the same irradiation dose （ P 〈 0.05 ）, and the differences were the most significant on 8th week after irradiation. No statistic differences of average escape latency and search strategy were found between 20Gy and 30Gy groups treated with single fraction irradiation. However, statistic differences were found between two groups with fractionated irradiation （ P 〈 0.05 ）. Neurons were atrophic degenerated and whiter matter were loosen in 30Gy group with single fraction irradiation and two groups with fractionated irradiation, but not in other groups. Conclusions Delayed radiation brain injuries were more easily caused with fractionated irradiation than with single fraction irradiation. The animal model which was much closer to clinical pathological process of radiation brain injuries can be developed by fractionated irradiation.