Roberts A, Alford S T
J Comp Neurol. 1986 Aug 8;250(2):253-61. doi: 10.1002/cne.902500212.
We describe the distribution of "descending" interneurons in late Xenopus laevis embryos after retrograde filling with horseradish peroxidaze via their ipsilateral, descending axons in the spinal cord. These multipolar neurons, with dendrites spread throughout the marginal zone, form a longitudinal column extending from midtrunk spinal cord into the brainstem to the level of the vagus. In the hindbrain these neurons are part of the uncrossed reticulospinal projection. They are most numerous in the caudal brainstem, their density falling by half at the eighth postotic segment. To examine their possible role in swimming we reduced the population of descending interneurons by making progressive transections of the brainstem or spinal cord at the first to fifth postotic segments. These led to progressive reduction in the initial frequency of fictive swimming in immobilized embryos, even when the brainstem was divided sagittally. Transecting the spinal cord at the fourth postotic segment did not reduce initial frequency rostral to the lesion. The effects of these lesions on the duration of fictive swimming episodes were similar. The results suggest that descending interneurons could provide excitatory drive during swimming and that some reticulospinal and spinal interneurons may form single homogeneous populations.
我们通过辣根过氧化物酶经非洲爪蟾晚期胚胎同侧脊髓下行轴突逆行填充，描述了“下行”中间神经元的分布。这些多极神经元的树突遍布边缘区，形成一个从脊髓中干延伸至脑干迷走神经水平的纵柱。在后脑中，这些神经元是未交叉的网状脊髓投射的一部分。它们在脑干尾部数量最多，在耳后第八节段密度减半。为了研究它们在游泳中可能发挥的作用，我们通过在耳后第一至第五节段逐步横断脑干或脊髓来减少下行中间神经元的数量。这些操作导致固定胚胎中虚构游泳的初始频率逐渐降低，即使脑干被矢状切开也是如此。在耳后第四节段横断脊髓不会降低损伤部位头侧的初始频率。这些损伤对虚构游泳发作持续时间的影响类似。结果表明，下行中间神经元可能在游泳过程中提供兴奋性驱动，并且一些网状脊髓和脊髓中间神经元可能形成单一的同质群体。
