Silos-Santiago I, Snider W D
Department of Neurology and Neurological Surgery (Neurology), Washington University School of Medicine, St. Louis, Missouri 63110.
J Comp Neurol. 1994 Apr 8;342(2):221-31. doi: 10.1002/cne.903420206.
Considerable progress has been made in recent years in identifying molecules with restricted expression in mammalian spinal cord at early developmental stages. However, the significance of the different expression patterns for most of these molecules is unclear because so little is known about the development of various classes of spinal interneurons. Recently, we have characterized the development of rat spinal cord interneurons with an axon that crosses in the ventral commissure (Silos-Santiago and Snider, J. Comp. Neurol., 325:514, 1992). In the current study, we describe the morphological development of ipsilaterally projecting spinal interneurons in laminae V-VIII of the thoracic spinal cord. These neurons were labelled by retrograde lateral diffusion of DiI after crystals were placed in various locations in the embryonic thoracic cord. By E14, approximately 48 hours after the first interneurons are generated, eight different groups of ipsilateral interneurons are present in the spinal cord. By E15, these groups of ipsilateral interneurons have reached distinct locations within the gray matter. Even at this early stage, different groups of cells have elaborated characteristic dendritic arborizations. By E19, at least 17 different types of ipsilateral interneurons can be identified on the basis of location and dendritic morphology. In general, ipsilateral interneurons are located more dorsally and laterally than commissural interneurons at all stages of embryonic development. Furthermore, in comparison with commissural neurons, fewer ipsilateral interneurons have dendritic arbors with a mediolateral orientation in the transverse plane. This work demonstrates that rat embryonic spinal cord contains a large number of morphologically distinct classes of interneurons that extend axons into the ipsilateral lateral funiculus. These neurons can be distinguished from commissural neurons on the basis of location and morphology. These results, taken together with those from our previous study, provide a framework for the localization of gene expression to different classes of spinal interneurons at early developmental stages.
近年来，在识别哺乳动物脊髓发育早期阶段表达受限的分子方面取得了相当大的进展。然而，由于对各类脊髓中间神经元的发育了解甚少，这些分子大多数不同表达模式的意义尚不清楚。最近，我们已经描述了具有在腹侧连合交叉轴突的大鼠脊髓中间神经元的发育情况（西洛斯 - 圣地亚哥和斯奈德，《比较神经学杂志》，325:514，1992）。在当前的研究中，我们描述了胸段脊髓V - VIII层中同侧投射脊髓中间神经元的形态发育。在胚胎胸段脊髓的不同位置放置晶体后，通过DiI的逆行侧向扩散对这些神经元进行标记。到胚胎第14天，即第一批中间神经元产生后约48小时，脊髓中存在八组不同的同侧中间神经元。到胚胎第15天，这些同侧中间神经元组已到达灰质内不同的位置。即使在这个早期阶段，不同组的细胞已经形成了特征性的树突分支。到胚胎第19天，根据位置和树突形态可以识别出至少17种不同类型的同侧中间神经元。一般来说，在胚胎发育的所有阶段，同侧中间神经元比连合中间神经元更靠背侧和外侧定位。此外，与连合神经元相比，在横切面上具有中外侧方向树突分支的同侧中间神经元较少。这项工作表明，大鼠胚胎脊髓包含大量形态上不同类别的中间神经元，其轴突延伸至同侧外侧索。这些神经元可以根据位置和形态与连合神经元区分开来。这些结果与我们之前研究的结果一起，为早期发育阶段不同类别的脊髓中间神经元基因表达的定位提供了一个框架。
