Jensen K F, Killackey H P
Proc Natl Acad Sci U S A. 1984 Feb;81(3):964-8. doi: 10.1073/pnas.81.3.964.
There is a high degree of specificity in the efferent connections of the cerebral cortex. In the rodent neocortex, the characteristic band of corticospinal neurons within layer V is present at birth even though changes still occur in the areal distribution of these neurons. Disruption of neocortical development with ionizing radiation before, during, or after the production of neurons destined for layer V results in abnormally located corticospinal neurons. One abnormal location in which corticospinal neurons are found is in ectopic cell clusters beneath the cortical white matter bordering the dorso-medial aspect of the lateral ventricle. Corticospinal neurons only occur in these periventricular ectopias in adult rats irradiated on or before embryonic day 17. A second abnormal location of corticospinal neurons is between layer V and the pial surface. These scattered supragranular corticospinal neurons occur in all adult animals irradiated on embryonic days 16, 17, 18, or 19. The fact that neurons having an unusual position project to a subcortical target appropriate for one neocortical sublayer indicates that neither migratory path nor final position is essential to specifying a subcortical target. In addition, the fact that labeled corticospinal neurons are located in periventricular ectopias only when irradiation occurs on or before embryonic day 17 suggests that the initial projections of corticospinal neurons are determined early in their individual ontogeny prior to migration.
大脑皮层的传出连接具有高度特异性。在啮齿动物的新皮层中，尽管这些神经元的区域分布仍会发生变化，但第V层内皮质脊髓神经元的特征带在出生时就已存在。在注定进入第V层的神经元产生之前、期间或之后，用电离辐射破坏新皮层发育会导致皮质脊髓神经元位置异常。皮质脊髓神经元的一个异常位置是在与侧脑室背内侧缘相邻的皮质白质下方的异位细胞簇中。皮质脊髓神经元仅在胚胎第17天或之前接受照射的成年大鼠的这些脑室周围异位中出现。皮质脊髓神经元的第二个异常位置是在第V层和软膜表面之间。这些散在的颗粒上层皮质脊髓神经元出现在胚胎第16、17、18或19天接受照射的所有成年动物中。具有异常位置的神经元投射到适合一个新皮层亚层的皮质下靶点，这一事实表明，迁移路径和最终位置对于确定皮质下靶点都不是必需的。此外，只有当在胚胎第17天或之前进行照射时，标记的皮质脊髓神经元才位于脑室周围异位，这表明皮质脊髓神经元的初始投射在其个体发育早期迁移之前就已确定。
