Reelin在小鼠穿通纤维及大脑连合纤维寻径中的作用

Reelin's roles in the pathfinding of perforant fibers and commissural fibers in mice

目的通过对比野生型小鼠和Reeler小鼠穿通通路及连合纤维的发育,探讨Reelin在穿通通路及连合纤维寻径中的作用。方法共取野生型小鼠(WT)和Reelin基因缺失小鼠(Reeler),从胚龄16 d(E16)至出生7d(P7)各年龄点,共123例。采用Di I/Di O离体示踪技术对不同年龄点的WT小鼠及Reeler小鼠的穿通通路及连合纤维进行顺行和逆行示踪。结果 1.穿通通路主要由内嗅皮质第Ⅱ层和第Ⅳ层神经元所发出,在E16时进入海马腔隙分子层,P1时穿通纤维出现在齿状回,P7时穿通纤维形成致密纤维束终止于齿状回外分子层2/3;Reeler小鼠的穿通通路出现明显的发育延迟并且投射纤维分布紊乱;2.穹隆连合纤维主要由海马CA3锥体细胞,门细胞及内嗅皮质Ⅱ~Ⅳ层神经元发出,在E16时形成;Reeler小鼠穹隆纤维与WT小鼠在发育中无明显区别;3.胼胝体连合纤维主要由新皮质Ⅱ~Ⅳ层神经元及纹状体神经元所投射,在E18时形成并向对侧皮质进行纤维投射,并且投射部位出现对称分布,P3时一侧胼胝体纤维到达对侧纹状体。Reeler小鼠胼胝体投射的皮质神经元向对侧新皮质投射出现延迟。结论 Reelin可能是穿通通路及连合纤维发育的导向因子。Reelin的缺失导致穿通通路发育延迟,并且连合纤维在皮质的细胞来源及穿通通路细胞来源紊乱。

Objective To understand Reelin＇ s roles in the pathfinding of perforant fibers and commissural fibers between wild-type （WT） and Reeler mice. Methods A total of 123 WT mice and Reeler mice from embryonic day 16 （El6） to postnatal day 7 （PT） were used for this study. The perforant fibers and commissural fibers were labeled with DiI and DiO tracing （anterograde and retrograde）. Results 1. Perforant fibers were mainly projected from the neurons in the layers Ⅱ to Ⅳ of entorhinal cortex. They entered the stratum laeunosum-molecular layer in hippoeampus proper as early as El6, while the perforant fibers reached the dentate gyrus （DG） at P1. The perforant fibers terminated in the outer two thirds of the molecular layer of the dentate gyrus at P7. Compared with WT miee, the perforant fibers in Reeler mice developed retardantly and distributed in disorder. 2. Fornix commissural fibers rose from the pyramidal cells of the CA3, hilus neurons and the Ⅱ -Ⅳ layers neurons of the entorhinal cortex at El6. Compared with WT mice, Reeler mice almost had no significant difference in the development of fornix fiber. 3. Corpus callosum was mainly projected from the neurons of layers Ⅱ -Ⅳ of neoeortex and corpus striatum, which started to project toward contralateral cortex at El8 and reached the eontralateral striatum at P3. However, the corpus eallosum fibers of Reeler mice entered to the eontralateral neocortex later than in WT mice. Conclusion Reelin may serve as a guiding cue for the development of perforant pathway and commissural fibers. Without Reelin, the commissural and perforant pathways develop retardantly, and their original neurons in cortical plate are in disorder.