Neural abnormalities in the dystrophic mouse.

Neural abnormalities (area of amyelination) have been found in the cranial nerves and in the ventral cervical and lumbosacral roots and in the mixed spinal nerves of bar harbor dystrophic mice of both the severe (129 Re/J dy/dy) and benign (dy-2J DY-2J) forms. The significance of these findings is discussed

Abnormalities of peripheral nerves in murine muscular dystrophy.

Mice of the Bar Harbor 129 Re dydy strain suffer from a progressive degeneration of the skeletal muscles similar in pathological characteristics to that of human Duchenne muscular dystrophy. Previously the nervous system of these animals has been described as being without abnormality. This report details striking abnormalities of the dorsal and ventral roots and proximal parts of the sciatic nerves of these animals. The abnormalities consist of non-myelinated axons of up to 6 μ diameter, without surrounding Schwann cell cytoplasm, collected into extensive areas between a few relatively normal myelinated axons. These areas are surrounded by sheets of Schwann cells, which show the morphological counterparts of active metabolism, and some of which show attempted myelination of axons. These abnormalities are equally extensive in older and in younger animals, though the appearance is very similar to that of foetal developing nerve. Minor evidence of axonal degeneration is present. The changes are interpreted as indicating a developmental abnormality of myelination by Schwann cells, perhaps as a result of the impaired mitotic division of these cells. They offer an experimental model for the investigation of a number of problems of nerve physiology. Preliminary studies of peripheral nerve and nerve roots from human cases of Duchenne muscular dystrophy and from dystrophic hamsters have not revealed a similar abnormality. The change is therefore likely to be a phenomenon confined to the dystrophic mouse, and one which is unrelated to the coexisting skeletal muscle degeneration

The nodes of ranvier in the nerves of mice with muscular dystrophy.

Light microscopic, and scanning and transmission electron microscopic studies of the nodes of Ranvier of the distal peripheral nerves of mice with muscular dystrophy (dy/dy) are reported. Extensive widening of the nodes, retraction of Schwann cell cytoplasm and myelin, paranodal thinning of the myelin sheaths, and loss of nodal gap substance were observed. There was no loss of myelinated fibers. The changes at the nodes of Ranvier probably explain the slowed maximum conduction velocity observed in dystrophic peripheral nerves

Structural changes in the early stages of Duchenne muscular dystrophy

The finding of a relative absence of degeneration and regeneration in a muscle biopsy taken at 2½ weeks of age from a boy who later showed the florid pathological changes of preclinical Duchenne muscular dystrophy prompted a review of muscle biopsies taken from boys in the preclinical and early clinical stages of this disease. Only one other biopsy obtained in the first year of life was available. In this, taken at 2 months, there were active changes present. These findings suggest that biopsies taken to detect preclinical cases should not be performed at less than 2 months of age, and raise the possibility of the existence of a stage in Duchenne muscular dystrophy before active degeneration when the muscle shows little or no change on light microscopy

Mitochondrial myopathies. A clinico-pathological study of cases with and without extra-ocular muscle involvement

The clinical and pathological features of 28 patients with mitochondrial myopathy were reviewed. The cases were divided into a group with involvement of the extra-ocular muscles alone or with limb muscle involvement, and a group with a facioscapulohumeral syndrome or generalised weakness without extra-ocular muscle involvement. Cardiac and central nervous system manifestations occurred particularly in the first group which included six patients with multisystemic features and two with the complete Kearns-Sayre syndrome. Diabetes mellitus occurred in the second group only. Quantitative histology on limb muscle biopsies showed a higher proportion of fibres with abnormal mitochondrial aggregates in the second group. No one type of mitochondrial inclusion or other ultrastructural change was specific for either group of cases. The findings illustrate the clinical heterogeneity of cases of mitochondrial myopathy and the lack of specificity of any of the myopathological changes for different subgroups of patients

Distribution of Ribosomal RNA in Fusing Myoblasts

THE syncytial structure of vertebrate striated muscle is considered to be formed, both in embryogenesis and in its regeneration after injury or disease, by the successive fusion of many individual initially uninucleate “myoblasts”. K. F. A. R. and Hudgson1 have recently reviewed the current literature on this subject