低剂量X射线照射对幼年大鼠学习记忆功能改变的影响

Effect of low doses X-ray exposure on learning ability and memory in young rats

关键词:  低剂量电离辐射  学习  记忆  Morris水迷宫  海马  大鼠

Key words:  low dose irradiation  learning  memory  Morris water maze  hippocampus  rat

摘要:

目的 探讨低剂量X射线持续照射幼年SD大鼠后对其学习记忆能力的影响及相关机制。方法 24只幼年SD大鼠随机分为对照组(0d照射组,接受假照射)、7、14d照射组,于出生后第35天起,每天接受1.0mGy的X射线照射。照射结束次日,Morris水迷宫测试各组大鼠的空间学习记忆能力,灌注取脑后H-E染色观察海马CA1区神经元形态,透射电镜观察海马CA1区超微结构的变化。结果 定位航行实验中,7、14d照射组逃避潜伏期均较对照组延长,14d照射组长于7d照射组(P<0.05)；空间探索实验中,对照组,7、14d照射组原站台象限停留时间分别为(66.66±8.83)、(44.57±8.77)、(29.74±5.47)s,组间比较,差异均有统计学意义(P<0.05)；对照组,7、14d照射组穿越原站台象限次数分别为(2.75±1.16)、(2.50±1.07)、(1.13±0.64)次,组间比较,差异均有统计学意义(P<0.05)。H-E染色对照组、7d照射组海马CA1区神经元形态未见异常,14d照射组可见核固缩。透射电镜下14d照射组神经元核固缩,线粒体空泡变,7及14d照射组均见突触后膜致密物(postsynaptic density, PSD)增多、不均匀,突触间隙显示不清,14d照射组受损更为明显。结论 幼年SD大鼠连续接受一定低剂量的X射线照射可以损伤大鼠海马CA1区神经元结构的完整性,降低大鼠的学习记忆能力,随着受照射时间的增加,大鼠的学习记忆能力受损程度增加。

Abstract:

Objective To investigate the effect of low doses X-ray exposure on learning ability and memory in young rats. Methods Twenty four Sprague-Dawley rats aged 35 days were randomly divided into two irradiated groups and one control group with 8 rats in each group. The rats in 7d-and 14d irradiated groups received X-ray irradiation at a dose of 1.0mGy/d for 7 or 14 days, respectively; and the control group received sham radiation. Morris water maze was used to examine the ability of sapatial learning and memory. The morphology of neurons in hippocampal CA1 area was observed by H-E staining and the ultrastructure of CA1 area was observed by electron microscopy. Results All irradiated groups showed increased latencies compared with that of control group, 14d-irradiated group presented longer latencies compared with 7d-irradiated group (P <0.01). The time staying in the quadrant of the original platform in control group, 7d and 14d irradiated groups were(66.66±8.83),(44.57±8.77) and(29.74±5.47)s, respectively (P=0.000). The number of crossing the platform of control group, 7d and 14d-irradiated groups was(2.75±1.16),(2.50±1.07),(1.13±0.64) times, respectively (P<0.01). H-E staining showed degeneration of neurons at hippocampal CA1 area only in 14d irradiated group, not in control and 7d irradiated groups. There was damage of postsynaptic density (PSD) at hippocampal CA1 area in all X-ray irradiated groups, especially in 14d irradiated group. Mitochondria swell and ridge disappearance and pyknotic nuclei were observed in 14d irradiated group. Conclusion Low dose X-ray exposure nay damage structure and function in neurons of hippocampal CA1 and further decrease the learning ability and memory in young rats, and the damage is increased with the exposure time.