Ultrastructural and histochemical correlations of experimental muscle regeneration

Abstract

A correlative ultrastructural and light microscopic histochemical investigation was performed in cold-injured gastrocnemius muscle in normal adult mice. Three zones were in evidence after the injury: undamaged muscle, a necrotic area, and an intermediate region. In the necrotic area, degenerating myofibres contain mainly fragments of myofibrils; they are stained by the myofibrillar ATP-ase and the menadione-mediated α-glycerophosphate dehydrogenase reactions. Necrotic fibres are not stained by the reactions for 4 oxidative enzymes (succinate, lactate, malate, and DPNH dehydrogenase) or the phosphorylase reaction. In the intermediate region, many persistent myofibres possess collections of enlarged mitochondria; they are darkly-stained with the 4 oxidative enzyme reactions mentioned above. Early regenerating sarcoblasts are rich in ribosomes, have central nuclei with adjacent accumulations of mitochondria, and myofibrils developing at the periphery of the cell; their cytoplasm is strongly basophilic and the myofibrils are well-stained with the myofibrillar ATP-ase. Sarcoblasts present dark irregular dots between myofibrils and centrally, adjacent to nuclei, with the oxidative enzyme reactions used. Later, regenerated myofibres are recognized by central nuclei, large mitochondria and an undeveloped sarcotubular system; they display an intense but irregular staining with the oxidative enzyme reactions and are darkly-stained by the ATP-ase reaction. Large regenerated myofibres acquire a positive phosphorylase reaction.