Batardiere A, Barone P, Dehay C, Kennedy H
Cerveau et Vision Unité 371, INSERM, Bron, France.
J Comp Neurol. 1998 Jul 13;396(4):493-510. doi: 10.1002/(sici)1096-9861(19980713)396:4<493::aid-cne6>3.0.co;2-x.
Corticocortical pathways can be classified as feedback and feedforward, in part according to the laminar distribution of the parent cell bodies. Here, we have developed exhaustive sampling procedures to determine unambiguously this laminar distribution. This shows that individual extrastriate areas in the adult cat have highly stereotyped proportions of supragranular layer neurons with respect to the total population of neurons back-projecting to area 17. During development, these adult laminar patterns emerge from an initially uniform radial distribution through a process of selective reorganization, which is highly specific to each area. Injections of fluorescent retrograde tracers were made in area 17. In areas 19, 20, posteromedial lateral suprasylvian area, and anteromedial lateral suprasylvian area, we defined a projection zone as the region containing retrogradely labeled neurons. In the neonate, counts of labeled neurons throughout the projection zones show constant percentages of 40% in the supragranular layers. During development, there is an area-specific reduction in the percentage of supragranular labeled neurons generating the laminar distributions characteristic of each area. Numbers of labeled neurons were estimated at different eccentricities of the projection zone. This finding indicates that during development there is a relative decrease in the numbers of labeled neurons of the periphery of the projection zone in the supragranular layers but not in the infragranular layers. This decrease is accompanied by a relative decrease in the dimensions of the supragranular projection zone with respect to the infragranular projection zone. These findings suggest that each extrastriate area precisely adjusts the proportions of supragranular layer neurons back-projecting to striate cortex in part by developmental changes in the divergence-convergence values of individual neurons. This shaping of corticocortical connectivity occurs relatively late in postnatal development and could, therefore, be under epigenetic control.
皮质-皮质通路可分为反馈和前馈通路，部分依据是母细胞体的层状分布。在此，我们开发了详尽的采样程序，以明确确定这种层状分布。这表明，成年猫的各个纹外区域相对于反向投射到17区的神经元总数而言，具有高度刻板的颗粒上层神经元比例。在发育过程中，这些成年层状模式通过选择性重组过程从最初均匀的径向分布中形成，这一过程对每个区域都具有高度特异性。在17区注射荧光逆行示踪剂。在19区、20区、后内侧外侧上薛氏区和前内侧外侧上薛氏区，我们将投射区定义为包含逆行标记神经元的区域。在新生猫中，对整个投射区内标记神经元的计数显示颗粒上层中恒定比例为40%。在发育过程中，颗粒上层标记神经元的百分比出现区域特异性降低，从而产生每个区域特有的层状分布。在投射区的不同偏心度处估计标记神经元的数量。这一发现表明，在发育过程中，颗粒上层投射区周边的标记神经元数量相对减少，而颗粒下层则没有。这种减少伴随着颗粒上层投射区相对于颗粒下层投射区尺寸的相对减小。这些发现表明，每个纹外区域通过单个神经元发散-会聚值的发育变化，部分地精确调整反向投射到纹状皮质的颗粒上层神经元的比例。皮质-皮质连接的这种塑造在出生后发育过程中相对较晚发生，因此可能受表观遗传控制。
