Kageyama G H, Robertson R T
Department of Anatomy and Neurobiology, College of Medicine, University of California, Irvine 92717.
J Comp Neurol. 1993 Sep 1;335(1):123-48. doi: 10.1002/cne.903350109.
Anterograde movement of DiI and transneuronal transport of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) were used to study the temporal and laminar patterns of ingrowth of the geniculocortical projection to visual cortex in fetal and postnatal rats. The development of this projection was compared to patterns of migration and settling of [3H]-thymidine-labeled neurons destined for cortical layer IV, and to geniculocortical synapse formation. DiI-labeled geniculocortical axons were found in the intermediate zone beneath the lateral cerebral mantle at embryonic day (E)17 and in the subplate layer underlying visual cortex by E18. On E19 they appeared to accumulate and grow radially into an expanding subplate layer and into the deep part of developing cortical layer VI. By postnatal day (P)0, DiI or WGA-HRP-labeled geniculocortical axons were found in developing cortical layers VI and V. By P1, they invaded the deep portion of the cell-dense cortical plate, where they were in position to make initial contact with neurons that would later form layer IV. A few axons traversed the cortical plate to reach the marginal zone. Layer IV became an identifiable layer on P2, and a clear projection to layer IV was evident by P3. These results suggest that geniculocortical afferents grow continuously from the intermediate zone, initially into an expanding subplate layer and then sequentially into each of the developing cortical layers without evidence of "waiting." Electron microscopic data suggest that geniculocortical axons begin to form immature synapses with dendrites and neuronal perikarya as they first encounter cortical neurons, first in the subplate layer and then in developing layers VI, V and marginal zone, in addition to the primary target layer IV. The precise targeting and overall temporal and laminar patterns of ingrowth and synaptogenesis suggest that geniculocortical axons are directed to the visual cortex by guidance cues within the internal capsule and subplate. Further, they reach the occipital pole early enough to influence the specification and histogenesis of cortical area 17, perhaps by exerting an influence on the deep-to-superficial "wave" of neuronal differentiation in sequentially developing subplate and cortical layers VI, V and IV.
运用碘化丙啶（DiI）的顺行运输和小麦胚凝集素-辣根过氧化物酶（WGA-HRP）的跨神经元运输，研究胎鼠和新生大鼠视皮质膝状皮质投射向内生长的时间和分层模式。将该投射的发育情况与注定要进入皮质第IV层的[3H] - 胸腺嘧啶核苷标记神经元的迁移和定居模式以及膝状皮质突触形成进行比较。在胚胎第17天（E17），在大脑外侧皮质下方的中间带发现了DiI标记的膝状皮质轴突，到E18时，在视皮质下方的板下层中发现了这些轴突。在E19时，它们似乎聚集并径向生长到不断扩展的板下层以及发育中的皮质第VI层深部。到出生后第0天（P0），在发育中的皮质第VI层和第V层中发现了DiI或WGA-HRP标记的膝状皮质轴突。到P1时，它们侵入了细胞密集的皮质板深部，在那里它们能够与后来形成第IV层的神经元进行初步接触。一些轴突穿过皮质板到达边缘区。第IV层在P2时成为可识别的层，到P3时，向第IV层的清晰投射明显可见。这些结果表明，膝状皮质传入纤维从中带持续生长，最初进入不断扩展的板下层，然后依次进入每个发育中的皮质层，没有“等待”的迹象。电子显微镜数据表明，膝状皮质轴突在首次遇到皮质神经元时就开始与树突和神经元胞体形成不成熟的突触，首先在板下层，然后在发育中的第VI层、第V层和边缘区，此外还有主要目标层第IV层。向内生长和突触形成的精确靶向以及总体时间和分层模式表明，膝状皮质轴突是由内囊和板层内的引导线索导向视皮质的。此外，它们足够早地到达枕极，可能通过对依次发育的板层以及皮质第VI层、第V层和第IV层中神经元分化的由深至浅的“波”施加影响，从而影响皮质17区的特化和组织发生。
