Xu Xiaohong, Ye Lingjing, Ruan Qin
Zhejiang Normal University, Chemistry and Life Sciences College, Yinbin Road, Jinhua, Zhejiang 321004, China.
Exp Biol Med (Maywood). 2009 Mar;234(3):296-305. doi: 10.3181/0804-RM-128.
Environmental enrichment (EE), where animals are exposed to a complex novel environment, has been shown to induce synaptic plasticity in both intact and injured animals. The purpose of this study was to investigate the effects of EE on spatial memory and structural modifications of synaptic junctions in rats following transient focal cerebral ischemia. Adult male Sprague-Dawley rats underwent right middle cerebral artery occlusion (MCAO) for 40 min and reperfusion. On day 3 after MCAO or sham surgery, rats were randomly assigned for 14 days to enriched or standard environmental housing. Spatial memory was then tested by the Morris water maze. Parietal cortex and the CA1 region of hippocampus were processed for electron microscopy and stereological techniques were used to evaluate plasticity of synaptic junctions. EE after MCAO improved spatial memory, with shortened escape length, increased frequency of crossings at the location of the platform, and increased percentage of time spent in the quadrant where the platform was previously located. Synaptic ultrastructural analysis showed that EE after MCAO increased numeric synaptic density in parietal cortex, and induced structural changes in synaptic junctions, with a decreased width of synaptic clefts and increased thickness of postsynaptic densities (PSD) in parietal cortex and hippocampus, accompanying improved performance on the spatial memory task. Using Western blot analysis, we determined the expression of glutamate receptor NMDAR1, and PSD-95, the best characterized protein member of the PSD-95 family, that was abundantly expressed in the PSD of excitatory synapses. The results showed that the content of NMDAR1 was not altered in MCAO rats of EE; however, the phosphorylated NMDAR1 increased significantly when compared with the standard environment housing MCAO rats. In addition, EE inhibited the impaired expression of PSD-95 induced by MCAO in parietal cortex and hippocampus. These data suggest that improved spatial memory of cerebral ischemic rats by EE is associated with structural modifications of synaptic junctions in several brain regions.
环境富集（EE），即让动物暴露于复杂的新环境中，已被证明能在完整动物和受伤动物中诱导突触可塑性。本研究的目的是探讨EE对短暂局灶性脑缺血后大鼠空间记忆及突触连接结构改变的影响。成年雄性Sprague-Dawley大鼠接受右侧大脑中动脉闭塞（MCAO）40分钟后再灌注。在MCAO或假手术后第3天，将大鼠随机分为两组，分别置于富集环境或标准环境饲养14天。然后通过莫里斯水迷宫测试空间记忆。对顶叶皮质和海马CA1区进行电子显微镜处理，并采用体视学技术评估突触连接的可塑性。MCAO后进行EE可改善空间记忆，表现为逃避路径缩短、平台位置穿越频率增加以及在先前平台所在象限停留时间百分比增加。突触超微结构分析显示，MCAO后进行EE可增加顶叶皮质的突触数量密度，并诱导突触连接的结构变化，顶叶皮质和海马的突触间隙宽度减小，突触后致密物（PSD）厚度增加，同时空间记忆任务表现得到改善。通过蛋白质免疫印迹分析，我们检测了谷氨酸受体NMDAR1以及PSD-95（PSD-95家族中特征最明确的蛋白质成员，在兴奋性突触的PSD中大量表达）的表达。结果显示，EE组MCAO大鼠的NMDAR1含量未改变；然而，与标准环境饲养的MCAO大鼠相比，磷酸化NMDAR1显著增加。此外，EE抑制了MCAO诱导的顶叶皮质和海马中PSD-95的表达受损。这些数据表明，EE改善脑缺血大鼠的空间记忆与多个脑区突触连接的结构改变有关。
