大鼠全脑照射后早期海马区磁共振波谱研究

H-MR Spectroscopy of the rat hippocampus after whole brain irradiation： an in vivo study

目的 探讨放射性脑损伤模型大鼠海马区代谢变化与认知功能障碍及早期病理演变的关系。方法 雌性SD大鼠65只，随机分为对照组5只和10、20、30Gy单次照射组各20只，于照射后2及4周、2及6个月（各5只）Y迷宫法测定大鼠的学习、记忆能力，定量分析照射后2及4周海马区N-乙酰天门冬氨酸／肌酸（NAA／Cr）、胆碱复合物／肌酸（Cho／Cr）的参数变化，电子显微镜观察海马区的超傲结构改变。结果照射后2及4周、2及6个月大鼠学习、记忆能力较对照组下降，照射剂量越大，学习记忆力下降越明显。10Gv照射组2及4周NAA／Cr与Cho／Cr比值低于对照组（t=2．345、2．578与2．503、3．025，P〈0．05），20Gv照射组（t=5．755、4．700与4．606、4．658，P〈0．01），30Gv照射组（t=10．956、6．766与9．571、6．377，P〈0．01）显著低于对照组。电镜观察显示：照射后4周海马区神经元有不同程度的线粒体肿胀、毛细血管内皮水肿及髓鞘板层解离。结论 ^1H—MRS能无创性动态监测放射性陆损伤海马区生化代谢改变，对早期海马异常的检测比MRI更敏感，^1H—MRS变化可在一定程度上反映脑损伤严重程度。

Objective To study the relationships between dynamic changes of the hippocampus metabolites, cognitive impairment and uhrastructural changes of hippocampus in rats during the initial 4 weeks after 6 MV X-ray whole-brain irradiation, Methods 65 rats were randomly divided into four groups as sham control （ n = 5）, 10 Gy, 20 Gy and 30 Gy groups （ n = 20）. The learning and memory ability was measured with the Y maze test 4, 8 weeks, 2,6 months after irradiation. ^1H-MRS was performed after 2 or 4 weeks＇ brain irradiation. The uhrastructural changes of the hippocampus were observed by electronic microscope. Results The learning and memorizing ability of irradiation groups was significantly different from that of control group. Compared with control group, the NAA/Cr and Cho/Cr ratio in the left hippocampus in 10 Gy, 20 Gy and 30 Gy groups at 2 weeks and 4 weeks decreased significantly. Neuronal mitochondria edema, endothelial cells swelling and lamina dissociation in myelin sheath were demonstrated in various degrees by electromicroscope at 4 weeks following whole brain irradiation. Conclusions ^1H-MRS can be used to non-invasively monitor the metabolic changes, both quantitatively and dynamically, of the irradiated rat brain. ^1H-MRS is superior to MRI in detecting early abnormality of the brain. The NAA/Cr and Cho/Cr ratio in irradiated hippocampus could reflect the severity of the brain injury to some extent.