坐骨神經移植老鼠其具髓鞘神經生長速率之比較

Abstract

當周邊神經受傷時，軸索(axon)被切斷時，在軸索的遠端會進行一種陳規性的退化現象，稱為瓦勒氏退化(Wallerian degeneration)，此退化現象將提供適當的細胞及分子環境做為神經再生的環境。但是對於有神經缺損(尤其是運動神經缺損)的周邊神經損傷來說，無法以直接端對端的方法直接縫合，神經移植(nerve graft)則是一個標準的手術方法。不同種類的神經再生速度也不盡相同。許多研究報告指出：運動神經和感覺神經的再生速度存在著差異，但是何種神經有較快的再生速度仍有許多爭議。本實驗的目的是希望利用坐骨神經截斷的老鼠，以自體神經原位移植(orthotopically re-implantation)的方式將一小段神經(6mm)縫回原來截斷的位置，在不同的時間點(術後一週、一、三及六個月)以型態學的方法觀察脛神經和腓腸神經中具髓鞘神經軸索恢復的密度和軸索直徑大小的變化來比較運動神經和感覺神經的再生速度。本研究中，我們發現：(1)脛神經內再生之具髓鞘神經軸索數目和腓腸神經相等。(2)神經移植使得再生神經軸索直徑變小(shift to left)，數目也比原來少，功能的恢復會比壓傷或截斷傷直接縫合不好。(3)脛神經與腓腸神經增生的神經軸索在神經受傷的三個月內即增生完成。由於脛神經屬於混合型神經(mix nerve)，而腓腸神經為純感覺神經(sensory nerve)，之前學者推論脛神經內運動神經軸索的比例應該小於全部軸索30% (Schmalbruch , 1986; Brown et al., 1992)，根據我們的實驗，在六個月時脛神經再生軸索恢復的比例為1.67±0.28，腓腸神經為1.21±0.19，推算出運動神經：感覺神經的再生神經軸索為0.67：0.2，因此我們初步認為運動神經的再生效率比感覺神經快速;如此的推論仍需更進一步的實驗驗證。

Peripheral nerves have inherent potential for regeneration because of the ideal microenvironment for axonal regeneration provided by the distal nerve stump after Wallerian degeneration. If primary repair is not possible when the nerve is transected, clinical use of autologous nerve grafts has become the gold standard for repairing the injured nerve. The recovery of function after nerve graft not only depends on types of nerve graft but also depends on types of injured nerves. Sensory or motor nerve inherents better nerve regeneration efficiency still exists debates in previous literatures. In the present study, we use morphometric analysis to compare the myelinated nerve regeneration efficiency between tibia nerve and sural nerve in sciatic nerve graft mice. There are significant difference in regenerated axon number and density ratio between post operative seven days (POD7), one (POM1) and three (POM3) months in both tibia and sural nerve (p<0.05). In post operative six months (POM6), the regeneration axon density ratio is higher in tibia nerve than in sural nerve (p<0.05). The histogram of myelinated axon fiber in POM3 and POM6 showed a shift-to-left phenomenon in both tibia and sural nerves. These datas indicate regenerated myelinated axon number and density increased from POD7 to POM3 but maintained from POM3 to POM6. The size of regenerated axon is smaller than control side in POM3 and POM6 mice.