Schreyer D J, Jones E H
Department of Anatomy and Neurobiology, University of California, Irvine 92717.
Brain Res. 1988 Jan 1;466(1):89-101. doi: 10.1016/0165-3806(88)90088-0.
The retrogradely transported dye, Fast blue, was injected into cervical or lumbar segments of the spinal cord of rats during the first days of life in order to label the cell bodies of origin of the corticospinal tract which is growing down the cord during that period. The first corticospinal axons arrive at cervical levels immediately after birth and all arise from a circumscribed group of layer V pyramidal cells in a small region of dorsal parietal cortex. This same cell group provides the corticospinal projection to lumbar segments of the spinal cord, the axons reaching those segments at the end of the first postnatal week. The area of lumbar projecting cells undergoes relatively little expansion and no diminution during subsequent weeks and into adulthood. The area occupied by cortical cells projecting to the spinal cord expands during the first postnatal week, but the axons of all these additional cells do not appear to invade the lower sequents of the spinal cord. By the end of the first week, corticospinal cells can be labeled in a continuous sheet throughout most of the extent of the frontal, parietal and cingulate cortex. During the second and third postnatal weeks, the area sending axons to the upper levels of the spinal cord diminishes and large areas bereft of retrogradely labeled corticospinal cells appear: laterally, in lateral frontal and lateral parietal cortex; dorsally, at the border of frontal and parietal cortex; medially, in medial frontal and cingulate cortex. The more restricted adult pattern is established at the end of the third week. Hence, the first cortical axons to advance down the spinal cord are those that will innervate the lumbar segments in the adult. Later addition of corticospinal axons involves only those projecting to upper cord segments. Within this group there are those which will establish persistent connections from appropriate cortical areas and others that will shortly be eliminated from inappropriate areas.
在大鼠出生后的头几天，将逆行运输染料快蓝注入脊髓的颈段或腰段，以标记在此期间沿脊髓下行生长的皮质脊髓束的起源细胞体。第一批皮质脊髓轴突在出生后立即到达颈段水平，并且全部起源于背侧顶叶皮质小区域中V层锥体细胞的一个限定组。同一细胞组向脊髓腰段提供皮质脊髓投射，轴突在出生后第一周结束时到达这些节段。在随后的几周直至成年期，投射到腰段的细胞区域扩张相对较小且没有缩小。投射到脊髓的皮质细胞所占区域在出生后第一周会扩大，但所有这些额外细胞的轴突似乎并未侵入脊髓的更低节段。到第一周结束时，在额叶、顶叶和扣带皮质的大部分范围内，皮质脊髓细胞可以被标记在一个连续的层面上。在出生后的第二和第三周，向脊髓上部节段发送轴突的区域缩小，出现大片没有逆行标记皮质脊髓细胞的区域：在外侧，位于额叶外侧和顶叶外侧皮质；在背侧，位于额叶和顶叶皮质的边界；在内侧，位于额叶内侧和扣带皮质。在第三周结束时建立了更具局限性的成年模式。因此，第一批向下延伸至脊髓的皮质轴突是那些在成年期将支配腰段的轴突。后来添加的皮质脊髓轴突仅涉及那些投射到脊髓上部节段的轴突。在这个群体中，有一些将从适当的皮质区域建立持久连接，而另一些将很快从不适当的区域被消除。
