Peroneal muscular atrophy （pma）マウスの末梢神経異常—坐骨，腓骨，腓腹および脛骨神経における総有髄線維数の分析

PERIPHERAL NERVE ABNORMALITIES OF MUTANT (PMA) MOUSE: MYELINATED FIBER COUNTS OF SCIATIC, PERONEAL, SURAL AND TIBIAL NERVES

　抄録　腓骨筋萎縮を主徴とし，常染色体性劣性遺伝を示すpmaマウス（江崎ら，1981）の坐骨神経，腓骨神経，腓腹神経，脛骨神経の定性的な組織学的観察に加え，これらの神経の神経束総横断面積および総有髄線維数を算定し，対照マウスと比較検討した。その結果，この異常マウスでは，腓骨神経の欠如と同時に対照マウスに比較して坐骨神経の神経束総横断面積および総有髄線維数が低値を，腓腹神経の神経束総横断面積および総有髄線維数が高値を示した。それ故この異常マウスでは腓骨神経を走行する有髄線維が欠如し，同時に本来腓骨神経を走行する有髄線維の一部が腓腹神経に含まれるような異常走行も存在すると判断された。この異常マウスの末梢神経には，軸索変性，節性脱髄，onion bulb形成などの所見はみられなかった。この異常マウスの末梢神経異常はCharcot-Marie-Tooth　病患者の末梢神経病変と明らかに異なる。

A mutant mouse characterized by peroneal mus-cular atrophy and congenital absence of the pero-neal nerve has been described by Esaki et al. and investigated as a possible animal model of Charcot-Marie-Tooth disease or spinal muscular atrophy. However, the nature of the peripheral nerve abnormality of this mutant mouse has not been precisely defined yet.

In this study, in addition to the qualitative eva-luation of teased fiber and Epon-embedded prepa-rations, the total transverse fascicular area and the total numbers of myelinated fibers per nerve in sciatic, peroneal (proximal and distal), sural (pro-ximal and distal) and tibial (proximal and distal) nerves on both right and left sides were compared between six peroneal muscular atrophy (pma) mice with autosomal recessive gene manifesting mainly the peroneal muscular atrophy and their six cont-rol mice to understand and define the peripheral nerve abnormalities.

The pma mice showed per equinovarus bilate-rally and their peroneal nerves were absent. No myelinated fibers showing axonal degeneration or segmental demyelination were found on teased fiber preparation. Onion bulb, demyelinated or remyelinated axons and myelin ovoids were notobserved in Epon-embedded sections.

The mean total transverse fascicular area and mean total number of myelinated fibers per nerve in the sciatic nerve in pma mice was significantly less (p<0.02) than that in control mice. On the other hand they were significantly greater (p< 0.0001) in the sural nerve in pma mice than in control mice. The difference of the number of myelinated fibers between proximal and distal tibial nerves was similar in between pma and control mice, suggesting the lack of anomalous myelinated fibers innervating leg muscles in pma mice. The sum of the number of the myelinated fibers in the proximal peroneal, sural and tibial nerves was similar to the number of the myelina-ted fibers in the sciatic nerve in both pma and control mice.

Therefore, congenital absence of myelinated fibers proximal to the sciatic nerve probably de-termined genetically and as revealed in the lite-rature, and subsequent anomalous course of the myelinated fibers destined for the peroneal nerve through the sural nerve may explain the differences of the numbers of total myelinated fibers of both peroneal and sural nerves between pma and cont-rol mice obtained in this study.

Although the mutant mouse shows the typical peroneal muscular atrophy, the absence of the peroneal nerve and the lack of the ongoing dege-nerative findings of myelinated fibers in any nerve studied are entirely different from those in patients with Charcot-Marie-Tooth disease.