ten Donkelaar H J, de Boer-van Huizen R
Department of Anatomy and Embryology, University of Nijmegen, The Netherlands.
Anat Embryol (Berl). 1991;183(6):589-603. doi: 10.1007/BF00187908.
The development of ascending spinal pathways has been studied in the clawed toad, Xenopus laevis. From stage 35 (hatching) on, HRP was applied at the spinomedullary border or to the area of the developing dorsal column nucleus, to analyze the development of ascending spinal pathways to the brain stem, and the onset and development of spinal projections to the dorsal column nucleus, respectively. Several populations of spinal neurons with ascending projections at least as far as the spinomedullary border were successively labeled. In early stages ascending spinal projections arise from Rohon-Beard cells and ascending interneuron populations located at the margin of the gray and white matter, i.e., marginal neurons. The ascending interneuron populations could be characterized as dorsolateral commissural and commissural interneurons projecting contralaterally, and as ipsilaterally projecting ascending interneurons and distinguished by Roberts and co-workers. Such a subdivision could be made until about stage 57. Then these ascending and commissural interneuron populations become intermingled with other populations of ascending tract neurons. Rohon-Beard cells could be labeled, more or less shrunken, until stage 55. Around stage 48 (at the time of the appearance of the limb buds) spinal ganglion cells could be labeled from the spinomedullary border and the developing dorsal column nucleus. At stage 48 such ascending primary spinal afferents were found to arise only from non-limb-bud-innervating dorsal root ganglia. Gradually also the limb-bud-innervating ganglia give rise to ascending collaterals, so that by stage 53 all spinal ganglia send ascending collaterals to the brain stem. The number of cells of origin of secondary spinal afferents to the brain stem increases during development, and their distribution becomes more extensive. Particularly impressive is a large population of neurons in the dorsal horn projecting ipsilaterally to the dorsal column nucleus. Part of the latter population represents non-primary spinal afferents to the dorsal column nucleus.
人们已经在爪蟾（非洲爪蟾）中研究了脊髓上行通路的发育情况。从第35期（孵化期）开始，将辣根过氧化物酶（HRP）应用于脊髓延髓边界或发育中的薄束核区域，分别分析脊髓上行通路向脑干的发育情况以及脊髓向薄束核投射的起始和发育情况。相继标记了几群至少投射到脊髓延髓边界的具有上行投射的脊髓神经元。在早期阶段，脊髓上行投射起源于罗霍恩 - 比尔兹细胞和位于灰质和白质边缘的上行中间神经元群，即边缘神经元。上行中间神经元群可分为对侧投射的背外侧连合和连合中间神经元，以及同侧投射的上行中间神经元，这是由罗伯茨及其同事区分出来的。这种细分可以持续到大约第57期。然后，这些上行和连合中间神经元群与其他上行束神经元群混合在一起。罗霍恩 - 比尔兹细胞在第55期之前或多或少会萎缩并被标记。在大约第48期（肢体芽出现时），可以从脊髓延髓边界和发育中的薄束核标记脊髓神经节细胞。在第48期，发现这种上行的初级脊髓传入纤维仅来自不支配肢体芽的背根神经节。逐渐地，支配肢体芽的神经节也产生上行侧支，因此到第53期时，所有脊髓神经节都向脑干发送上行侧支。向脑干的二级脊髓传入纤维的起源细胞数量在发育过程中增加，并且它们的分布变得更加广泛。特别引人注目的是背角中有一大群神经元同侧投射到薄束核。后一群中的一部分代表薄束核的非初级脊髓传入纤维。
