Ultrastructural changes in muscle and motor end-plate of the dystrophic mouse.

A comparative study of dystrophic mice (C57BL/6J-dy2J) and normal littermates, 6 to 9 months old, has revealed numerous ultrastructural changes in the dystrophic soleus. Vacuoles, swollen mitochondria, vesicular aggregates, membranous bodies, Z-line degradation, localized hypercontraction, myofibrillar disorientation, and focal necrosis were common. We report here new observations. Discontinuous, dense bands (240 A wide) were observed rarely between inner and outer membranes in some nuclei. Closely associated with infoldings of nuclear membrane were paracrystalline, vesicular structures, actin-like filaments, and autophagic vacuoles. With the degeneration of the nuclear membrane, actin-like filaments were observed within the nucleus. The primary synaptic clefts were widened and contained osmophilic-dense granules (diameter 0.2 to 0.7 micrometer). There was loss of secondary synaptic folds. Discontinuity of pre- and postsynaptic membranes could be observed, though rarely. Lysosome-like dense bodies were present among myofilaments. The myeloid bodies and autophagic vacuoles that were associated with nuclei, sarcoplasmic reticulum, and mitochondria gave a positive acid phosphatase reaction. Such degeneration changes were not observed in the normal soleus.