Quantitative ultrastructural differences in the development of normal and dystrophic muscle

Abstract

Ultrastructural alterations in developing dystrophic muscle, which can be clues to the initiation and timing of the dystrophic lesion, have not yet been carefully studied. We studied ultrastructural changes in the developing pectoral muscle of a line of dystrophic chickens and closely related normal chickens using stereological methods. These methods provided a quantitative estimate of the relative volume and surface area of cell structures and can often detect subtle changes. We found that most ultrastructural differences between normal and dystrophic fibers were not apparent unitl between 18 days in ovo and 1 week posthatching, but that differences in myofibril development were apparent as early as 10 days in ovo. This relative lack of myofibril development may be related to the increased myosin and myofibril degradation that has been shown in young chicks.