20Gyγ射线不同分割模式头部照射对小鼠学习记忆的影响

The effects of 20Gyγ-ray cranial irradiation with different fractionation regimen on learning and memory in mice

目的:探讨20 Gy γ射线不同分割模式头部照射对小鼠学习记忆的影响。方法:48只成年雄性C57BL/6小鼠随机分为对照组(control)、20 Gy单次照射组(20 Gy)、大分割照射组(5 Gy×4 d)和常规分割照射组(2 Gy×10 d),各照射组小鼠均头部接受γ射线照射,总剂量为20 Gy。照后4周采用Morris水迷宫对小鼠空间学习记忆能力进行测试;放射免疫法检测血清脑损伤标志物S100钙结合蛋白B(S100B)和神经元特异性烯醇化酶(NSE)水平;HE和Nissl染色观察脑组织形态结构;Western Blot检测脑海马组织学习记忆相关蛋白c AMP反应元件结合蛋白(CREB)的表达及磷酸化水平变化。结果:各照射组小鼠在Morris水迷宫定位航行实验中逃避潜伏期显著延长,空间探索实验中逃避潜伏期显著延长且平台穿越次数显著减少;20 Gy组和5 Gy×4d组NSE水平显著升高,各照射组S100B水平显著升高;20 Gy组小鼠海马组织结构紊乱,细胞结构模糊;与control组相比,各照射组海马CA1区神经元数量明显减少;与control组相比,20 Gy组CREB表达水平明显下调,各照射组CREB磷酸化水平显著下降,20 Gy组和5 Gy×4 d组p-CREB/CREB比值显著降低。结论:20 Gy γ射线不同分割模式头部照射后4周均可造成小鼠空间学习记忆障碍,其中,20 Gy单次照射对小鼠空间学习记忆的损伤最重,大分割照射次之,常规分割照射较轻。

Objective:To investigate the impact of 20 Gyγ-ray cranial irradiation with single or fractionated dosing regimen on learning and memory in mice.Methods:48 male C57BL/6 mice were randomly divided into control group(control),20 Gy single dose group(20 Gy),large fractionated dose group(5 Gy×4 d)and conventional fractionated dose group(2 Gy×10 d),12 mice in each group.The radiation was delivered over the whole brain and the total dose was 20 Gy.Morris water maze was used to detect spatial learning and memory ability at 4 weeks after irradiation.The serum levels of S100 calcium binding protein B(S100B)and neuron specific enolase(NSE)were detected by radioimmunoassay.The pathology of brain staining was observed by HE and Nissl.Western Blot was used to detect the protein levels of cAMP response element binding protein(CREB)and phosphorylated cAMP response element binding protein(p-CREB)in hippocampus of mice.Results:Compared with control group,4 weeks after 20 Gyγ-ray cranial irradia-tion,the escape latencies of mice in irradiation groups were significantly prolonged in morris water maze navigation test.In addition,in the probe test,the escape latencies were significantly prolonged and platform crossing times were significantly reduced.The results of radioimmunoassay showed that,compared with control group,the levels of NSE in 20 Gy group and 5 Gy×4 d group were significantly increased.The S100B levels were significantly increased in irradiation groups.The results of HE staining and Nissl staining showed that the structure of hippocampus in 20 Gy group was disordered and the cell structure was fuzzy.Compared with the control group,the number of neurons in hippocampus CA1 area in irradiation groups were decreased significantly.Western Blot results showed that the CREB protein level in 20 Gy group was significantly down-regulated compared with control group,the protein levels of p-CREB in all irradiation groups were significantly down-regulated,the ratios of p-CREB/CREB in 20 Gy group and 5 Gy×4 d group were significantly decreased.Conclusion:After 20 Gyγ-ray cranial irradiation with single dose or fractionated dose could cause spatial learning and memory impairment in mice.Among the three different fractionated regimens,the 20 Gy group may have the most serious damage,the large fractionated dose has less damage and conventional fractionated dose has minimum damage on spatial learning and memory.