Nandi K N, Knight D S, Beal J A
Louisiana State University School of Medicine, Shreveport 71130.
J Comp Neurol. 1993 Feb 8;328(2):252-62. doi: 10.1002/cne.903280207.
The purpose of the present study was to determine the relationship between the duration of a spinal neuron's neurogenic period and the length of its axon or level of projection. Spinal segment L1 was chosen for examination and neurons were divided into four projection groups: 1) supraspinal projection (SSp), 2) long ascending propriospinal (LAPr), 3) short ascending propriospinal (SAPr), and 4) descending propriospinal (DPr). To determine the duration of the neurogenic period for each group, 3H-thymidine was administered to fetal rats during the proliferative period for spinal neuroblasts on one of embryonic (E) days E13 through E16. Between 50 and 100 days after birth neurons in each group were labeled with the retrograde fluorescent tracer Fluoro-Gold. To demonstrate nerve cells with SSp projections, spinal cords were hemisected at spinal segment C3 in one group of animals and Fluoro-Gold was applied to the sectioned surface of the cord. Three additional sets of animals were used to label nerve cells with LAPr, SAPr, and DPr projections by injecting Fluoro-Gold into the gray matter at spinal segments C6, T12, and L5, respectively. Neurons labeled with both Fluoro-Gold and 3H-thymidine and neurons labeled with Fluoro-Gold alone in each animal in each group were counted and the data statistically analyzed. Results showed that within each spinal lamina neurons with different projections were generated, i.e., completed cell division, at significantly different rates. Neurons with the longest axons, those with SSP projections, were generated first. These were followed by those with LAPr projections, and finally those with SAPr and DPr projections. In most laminate there was no significant difference between the neurogenic periods of rostrally projecting short propriospinal (SAPr) neurons versus caudally projecting short propriospinal (DPr) neurons. It was concluded that the duration of the neurogenic period for a given group of neurons within each spinal lamina is inversely related to the distance between the nerve cell and its projection site regardless of the direction of its projection.
本研究的目的是确定脊髓神经元神经源性期的持续时间与其轴突长度或投射水平之间的关系。选择腰1脊髓节段进行检查，并将神经元分为四个投射组：1）脊髓上投射（SSp），2）长升支固有脊髓投射（LAPr），3）短升支固有脊髓投射（SAPr），4）降支固有脊髓投射（DPr）。为了确定每组的神经源性期持续时间，在胚胎（E）期第13至16天的其中一天，在脊髓成神经细胞增殖期给胎鼠注射3H-胸腺嘧啶核苷。出生后50至100天，用逆行荧光示踪剂荧光金标记每组中的神经元。为了显示具有SSp投射的神经细胞，在一组动物的颈3脊髓节段将脊髓半横切，并将荧光金应用于脊髓的切面。另外三组动物分别通过将荧光金注入颈6、胸12和腰5脊髓节段的灰质来标记具有LAPr、SAPr和DPr投射的神经细胞。对每组中每只动物中同时用荧光金和3H-胸腺嘧啶核苷标记的神经元以及仅用荧光金标记的神经元进行计数，并对数据进行统计分析。结果表明，在每个脊髓板层内，具有不同投射的神经元以明显不同的速率产生，即完成细胞分裂。轴突最长的神经元，即具有SSP投射的神经元，最先产生。其次是具有LAPr投射的神经元，最后是具有SAPr和DPr投射 的神经元。在大多数板层中，向头端投射的短固有脊髓（SAPr）神经元与向尾端投射的短固有脊髓（DPr）神经元的神经源性期之间没有显著差异。得出的结论是，每个脊髓板层内给定神经元组的神经源性期持续时间与神经细胞与其投射部位之间 的距离成反比，而与其投射方向无关。
