Bice T N, Beal J A
Department of Cellular Biology and Anatomy, Louisiana State University Medical Center in Shreveport, 71130, USA.
J Comp Neurol. 1997 Dec 1;388(4):550-64. doi: 10.1002/(sici)1096-9861(19971201)388:4<550::aid-cne4>3.0.co;2-1.
The total neuron population of the superficial dorsal horn (SDH), i.e., laminae I and II, was quantitated in Nissl preparations of spinal segment L1 in the rat. Subpopulations of the SDH, defined by axon projection, were quantitated following strategic intraspinal injections of dual retrograde tracers (Fluoro-Gold and true blue). These methods were used in conjunction with [3H]thymidine (delivered in utero) autoradiography for neurogenic pattern analysis. Following stereological correction, each dorsal horn in spinal segment L1 contained 11 neurons in lamina I and 42.6 neurons in lamina II per 10-microm transverse section. Neurons with long projections, i.e., neurons with projections rostral to spinal segment T5, were only slightly more numerous in lamina I than in lamina II. These neurons made up 34% of the total neuron population in lamina I and 7.0% in lamina II. Most of these neurons did not demonstrate descending connections, and many (presumed supraspinal projection neurons) did not demonstrate short, ascending, intersegmental connections. Neurons with short propriospinal projections, i.e., neurons with connections caudal to spinal segment T5, made up approximately half of the total neuron population in both lamina I and lamina II: 55% and 52%, respectively. Of these, 79% had both short ascending and descending projections; the remaining 21% had only descending projections. Neurons that were not labeled with retrograde tracers (presumed local circuit cells) represented 11% of the neurons in lamina I and 41% in lamina II. Neurogenesis in the SDH proceeded along an axon-length gradient, whereby neurons with the longest axons completed neurogenesis first, and those with the shortest completed neurogenesis last. The generation of both propriospinal and supraspinal projection neurons began on embryonic day 13 (E13). Nearly equal numbers of neurons in this group were generated in laminae I and II through E14. On E15, neuron production slowed in lamina I and accelerated in lamina II as local circuit neurons and the remaining propriospinal neurons were generated. Neuron production ceased simultaneously in both lamina I and lamina II on E16.
在大鼠脊髓L1节段的尼氏染色标本中，对浅背角（SDH），即I层和II层的神经元总数进行了定量分析。通过在脊髓内进行策略性注射双逆行示踪剂（荧光金和真蓝），对由轴突投射定义的SDH亚群进行了定量分析。这些方法与[3H]胸腺嘧啶核苷（子宫内注射）放射自显影术联合使用，用于神经发生模式分析。经过立体定向校正后，脊髓L1节段的每个背角在每10微米横切面上，I层含有11个神经元，II层含有42.6个神经元。具有长投射的神经元，即投射到脊髓T5节段以上的神经元，在I层中的数量仅比II层略多。这些神经元在I层中占神经元总数的34%，在II层中占7.0%。这些神经元中的大多数没有下行连接，许多（推测为脊髓上投射神经元）也没有短的、上行的节段间连接。具有短脊髓固有投射的神经元，即连接到脊髓T5节段以下的神经元，在I层和II层中分别约占神经元总数的一半：分别为55%和52%。其中，79%的神经元既有短的上行投射也有下行投射；其余21%只有下行投射。未被逆行示踪剂标记的神经元（推测为局部回路细胞）在I层中占神经元总数的11%，在II层中占41%。SDH中的神经发生沿着轴突长度梯度进行，轴突最长的神经元最先完成神经发生，轴突最短的神经元最后完成神经发生。脊髓固有投射神经元和脊髓上投射神经元的产生均始于胚胎第13天（E13）。在E14之前，I层和II层中产生的这组神经元数量几乎相等。在E15时，随着局部回路神经元和其余脊髓固有神经元的产生，I层中的神经元生成速度减慢，II层中的神经元生成速度加快。在E16时，I层和II层中的神经元生成同时停止。
