EMERGENCE OF CONNECTIVITY IN THE EMBRYONIC RAT PARIETAL CORTEX
EMERGENCE OF CONNECTIVITY IN THE EMBRYONIC RAT PARIETAL CORTEX
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DOI：
10.1093/cercor/2.4.336
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发表时间：
1992-07-01
期刊：
影响因子：
3.7
通讯作者：
JHAVERI, S
中科院分区：
文献类型：
--
作者：
ERZURUMLU, RS;JHAVERI, S
为了了解皮层回路是如何组合在一起的，我们检查了皮质投射细胞的出现和皮层下传入事件在胚胎大鼠大脑顶叶皮层的到达。应用亲脂示踪剂Dil和DiA选择性标记12-18 d龄大鼠胚胎（E12-E18；妊娠期21 d）醛固定脑内的传入和传出投射。在E12和E13，新皮质区由心室区和预板组成，没有皮质外连接。到了E14，就在皮质板出现之前，位于脑端囊腹外侧预板的多形性细胞向神经节隆起发出第一组皮质轴突。此后不久，皮层板出现为致密的放射状细胞带，这些细胞也有助于皮质投射。到E15，早期皮质投射细胞的轴突级联穿过纹状体原基，即内囊的未来位置。在皮质板形成和皮质轴突最初生长时，上行皮质轴突系统尚未到达新皮层。在双标记实验中，一种染料被放置在新皮层，另一种染料被放置在同侧丘脑背侧，结果表明皮层传出神经在纹状体水平遇到丘脑轴突的第一个上升波。总的来说，这两个轴突系统连接了新皮层和间脑。当它们在E16到达新皮层时，丘脑轴突在中间区域沿腹外侧到背内侧的路线运动。丘脑轴突是第一个到达新皮层的皮层下传入系统。其他由中脑被盖产生的上行传入系统在E17之后进入新皮层。对同一大脑的两个半球和不同胚胎年龄的丘脑皮质和被盖皮质投影的比较清楚地揭示了这两种投影系统在其轨迹和到达时间上的差异。目前的观察结果挑战了皮质下轴突的早熟为皮质成熟提供动力的观点，并表明皮质板分化和皮质投射模式的初始组织独立于上升通路发生。
In order to understand how cortical circuitry is put together, we examined the emergence of corticofugal projection cells and the arrival of subcortical afferents in the presumptive parietal cortex of the embryonic rat cerebrum. Afferent and efferent projections were selectively labeled by applications of the lipophilic tracers Dil and DiA in aldehyde-fixed brains of 12-18-d-old rat embryos (E12-E18; gestation: 21 d). On E12 and E13, the neocortical anlage consists of a ventricular zone and a preplate, with no extracortical connections. By E14, just prior to the appearance of the cortical plate, polymorphic cells located in the ventrolateral preplate of the telencephalic vesicle send out the first group of corticofugal axons toward the ganglionic eminence. Shortly thereafter, the cortical plate emerges as a dense band of radially oriented cells that also contribute to the corticofugal projection. By E15, axons of the early cortical projection cells cascade through the striatal primordium, the future site of the internal capsule. At the time of cortical plate formation and initial corticofugal axon outgrowth, ascending corticopetal axon systems have not yet arrived in the neocortex.Double-labeling experiments in which one dye is placed in the neocortex and the other in the ipsilateral dorsal thalamus reveal that cortical efferents encounter the first ascending wave of thalamofugal axons at the level of the striatum. Collectively, these two axonal systems bridge the neocortex and the diencephalon. Upon their arrival in the neocortex on E16, thalamic axons follow a ventrolateral to dorsomedial course within the intermediate zone.Thalamic axons are the first subcortical afferent system to arrive in the neocortex. Other ascending afferent systems arising from the midbrain tegmentum enter the neocortex after E17. Comparison of thalamocortical and tegmentocortical projections in two halves of the same brain and across various embryonic ages clearly reveals that the two projection systems differ in their trajectories as well as in their time of arrival. Present observations challenge the view that the precocious arrival of subcortical axons provides the impetus for cortical maturation, and suggest that cortical plate differentiation and the initial organization of corticofugal projection patterns occur independent of ascending pathways.