Department of Integrative Medical Biology, Section of Anatomy, Umeå University, Umeå, Sweden.
PLoS One. 2013;8(2):e56484. doi: 10.1371/journal.pone.0056484. Epub 2013 Feb 7.
Despite advances in surgical techniques for peripheral nerve repair, functional restitution remains incomplete. The timing of surgery is one factor influencing the extent of recovery but it is not yet clearly defined how long a delay may be tolerated before repair becomes futile. In this study, rats underwent sciatic nerve transection before immediate (0) or 1, 3, or 6 months delayed repair with a nerve graft. Regeneration of spinal motoneurons, 13 weeks after nerve repair, was assessed using retrograde labeling. Nerve tissue was also collected from the proximal and distal stumps and from the nerve graft, together with the medial gastrocnemius (MG) muscles. A dramatic decline in the number of regenerating motoneurons and myelinated axons in the distal nerve stump was observed in the 3- and 6-months delayed groups. After 3 months delay, the axonal number in the proximal stump increased 2-3 folds, accompanied by a smaller axonal area. RT-PCR of distal nerve segments revealed a decline in Schwann cells (SC) markers, most notably in the 3 and 6 month delayed repair samples. There was also a progressive increase in fibrosis and proteoglycan scar markers in the distal nerve with increased delayed repair time. The yield of SC isolated from the distal nerve segments progressively fell with increased delay in repair time but cultured SC from all groups proliferated at similar rates. MG muscle at 3- and 6-months delay repair showed a significant decline in weight (61% and 27% compared with contra-lateral side). Muscle fiber atrophy and changes to neuromuscular junctions were observed with increased delayed repair time suggestive of progressively impaired reinnervation. This study demonstrates that one of the main limiting factors for nerve regeneration after delayed repair is the distal stump. The critical time point after which the outcome of regeneration becomes too poor appears to be 3-months.
尽管外周神经修复的手术技术取得了进展，但功能恢复仍然不完全。手术时机是影响恢复程度的一个因素，但尚未明确界定延迟多久后修复就变得无效。在这项研究中，大鼠的坐骨神经被切断，然后立即（0 天）或延迟 1、3 或 6 个月进行神经移植修复。神经修复后 13 周，通过逆行标记评估脊髓运动神经元的再生情况。还从近端和远端残端以及神经移植物中收集神经组织，以及内侧腓肠肌（MG）肌肉。在延迟 3 个月和 6 个月的组中，远端神经残端中再生运动神经元和有髓轴突的数量明显下降。延迟 3 个月后，近端残端中的轴突数量增加了 2-3 倍，伴随着较小的轴突面积。对远端神经节段的 RT-PCR 分析显示 Schwann 细胞（SC）标志物下降，尤其是在延迟 3 个月和 6 个月的修复样本中。随着延迟修复时间的增加，远端神经中的纤维化和蛋白聚糖瘢痕标志物也逐渐增加。随着修复时间的延迟，从远端神经段分离出的 SC 的产量逐渐下降，但所有组的培养 SC 以相似的速度增殖。延迟 3 个月和 6 个月修复的 MG 肌肉重量明显下降（与对侧相比分别下降 61%和 27%）。随着延迟修复时间的增加，观察到肌肉纤维萎缩和神经肌肉接头的变化，表明神经再支配逐渐受损。本研究表明，延迟修复后神经再生的主要限制因素之一是远端残端。在这个时间点之后，再生的结果变得太差，似乎是 3 个月。
