Fernández J, Nicholls J G
Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, Chile.
J Comp Neurol. 1998 Jul 6;396(3):338-50.
The aim of these experiments was to determine the state of maturity of dorsal root ganglia and axons in opossums (Monodelphis domestica) at birth and to assess quantitatively changes that occur in early life. Counts made of dorsal root ganglion cells at cervical levels showed that the numbers were similar in newborn and adult animals, approximately 1,600 per ganglion. In cervical dorsal root ganglia of newborn animals, division of neuronal precursors cells had ceased. The number of axons in cervical dorsal roots was similar in newborn and adult animals (about 4,500). For each ganglion cell body, approximately three axons were counted in the dorsal root. At birth, dorsal roots contained several bundles about 30 microns in diameter consisting of small axons (0.05-2 microns in diameter). A few non-neural cells were identified as Schwann cell perikarya, each enclosing a number of neurites. Later, marked changes occurred in Schwann cells and in their relationship to axons in the roots. Thus, at 12 days, an increase occurred in the number of Schwann cells and fibroblasts, and the bundles had enlarged to about 80 microns with little increase in axon diameter (0.1-2 microns). By 18 days, the bundles were larger, and myelination had already started. At 23 days, the dorsal root contained more than 500 myelinated axons that could reach 5 microns in diameter. The adult dorsal root enclosed about 900 myelinated axons. Throughout this time, the relationship between the Schwann cells and axons changed. Together, these results indicate that the number of axons and cell bodies of sensory dorsal root ganglia in opossum do not show major changes after birth. In addition, these results set the stage for quantitative studies of regeneration of dorsal column fibers in injured neonatal opossum nervous system.
这些实验的目的是确定负鼠（Monodelphis domestica）出生时背根神经节和轴突的成熟状态，并定量评估生命早期发生的变化。对颈部水平的背根神经节细胞进行计数显示，新生动物和成年动物的细胞数量相似，每个神经节约1600个。在新生动物的颈部背根神经节中，神经元前体细胞的分裂已经停止。新生动物和成年动物颈部背根中的轴突数量相似（约4500条）。对于每个神经节细胞体，在背根中大约可计数到三条轴突。出生时，背根包含几条直径约30微米的束，由小轴突（直径0.05 - 2微米）组成。少数非神经细胞被鉴定为雪旺细胞周核，每个包绕着许多神经突。后来，雪旺细胞及其与根中轴突的关系发生了显著变化。因此，在12天时，雪旺细胞和成纤维细胞数量增加，束直径增大到约80微米，而轴突直径增加很少（0.1 - 2微米）。到18天时，束更大，并且已经开始髓鞘形成。在23天时，背根包含超过500条直径可达5微米的有髓轴突。成年背根包绕约900条有髓轴突。在整个这段时间里，雪旺细胞和轴突之间的关系发生了变化。总之，这些结果表明，负鼠感觉背根神经节的轴突和细胞体数量在出生后没有显示出重大变化。此外，这些结果为对受伤新生负鼠神经系统中背柱纤维再生的定量研究奠定了基础。
