Hiroko Ishii

Electron microscopic examination of basal lamina in Fukuyama congenital muscular dystrophy.

By light microscopy we previously obtained immunocytochemical evidence for basal lamina (BL) abnormality of skeletal muscle in Fukuyama congenital muscular dystrophy (FCMD). To further elucidate the pathological involvement of the BL in FCMD, we examined by electron microscopy the skeletal muscle in 12 cases of FCMD, nine cases of age-matched neuromuscular diseases unrelated to FCMD, and a case of merosin-negative CMD (MCMD). We found that the BL of skeletal muscle fibres in all patients with FCMD and the MCMD patient had a thin, deranged and often disrupted appearance. These features were more prominent in large calibre (> 15 microns) fibres than in small calibre (approximately 8 microns) fibres. Replication of the BL was not observed in 11 of the 12 FCMD patients. Although the BL over the intact plasma membrane had occasional gaps, the plasma membrane under the disrupted BL was normal in some case. Our results indicate the presence of fragile BL which may precede plasma membrane damage in FCMD skeletal muscle.

Muscle fiber growth and necrosis in dystrophic muscles: a comparative study between dy and mdx mice

Histopathological and morphometric studies of murine dystrophic muscles in the early postnatal period were performed. In dy mice, obtained by in vitro fertilization, scattered necrotic fibers were noted at 10 days of age followed by poorly compensated regeneration leading to muscle fiber loss, marked variation in fiber size, and fibrous and adipose tissue proliferation. In mdx mice, clusters of necrotic muscle fibers seen at 10-15 days were followed by well compensated regeneration with little fibrosis. There appeared to be no delay in muscle fiber growth and fiber type differentiation in both dy and mdx mice up to 10 days of age since there was no distinct difference in muscle fiber size, fiber type differentiation and the incidence of myosatellite cells between dystrophic muscles and those from age-matched control mice. Muscle fibers appeared to undergo necrosis only when they had reached a certain stage of maturation since at early stages of development or regeneration they rarely became necrotic. The difference in clinical symptoms between dy and mdx mice may result from differences in their regenerative response to necrosis.

Congenital muscular dystrophies.

Considerable advances in the understanding of congenital muscular dystrophy made during the past year may allow a new clinical classification of this disease. In particular, (1) evidence has accumulated to suggest that a laminin alpha2-chain (alpha2 subunit of laminin-2 or merosin) deficiency causes a type of congenital muscular dystrophy, and (2) it has been postulated that Fukuyama-type congenital muscular dystrophy and Walker-Warburg syndrome (but not Finnish muscle-eye-brain disease) are genetically identical diseases.

Internodal microvillus-like Schwann cell fingers in myelinated fibres in mouse spinal roots

SummaryCollections of microvillus-like Schwann cell fingers identical to those described previously in the nodal gap substance were commonly found along the internodes of large myelinated fibres in the spinal roots of adult mice. They were covered by Schwann cell basal lamina and focally protruded from the outer cytoplasmic Schwann cell compartment. Unlike nodal Schwann cell fingers, these internodal fingers had no contact with the axolemma, but were directed toward the endoneurium. These were not recognized in the distal peripheral nerves. The frequent occurrence of internodal Schwann cell fingers in the spinal root fibres suggests that these structures may be involved in some electrophysiological regulatory mechanism in this particular region of the nervous system.

Internodal Schwann cell fingers in the ventral spinal roots in mice: Incidence and relationship to the diameter of myelinated fibers

Internodal Schwann cell fingers were present in the lumbar, cervical, and thoracic spinal roots of adult mice at the age of 3 months, but they were not recognized in five mice examined at the age of 3 weeks. In the L4 ventral roots of ICR mice aged 3 months, the incidence of internodal Schwann cell fingers was 0.79% at the central-peripheral transitional zone and 2.43% at the distal regions, respectively. The ratio of axon diameter to total fiber diameter of myelinated fibers with internodal Schwann cell fingers was lower than that of fibers without them. Therefore, we conclude that internodal Schwann cell fingers are probably related to the developmental increase in the thickness of the myelin sheaths in the ventral spinal roots at all levels of the spinal cord.