Structural change in muscles of the dystrophic chicken. I. Quantitative indices.

The pectoral and posterior latissimus dorsi (PLD) muscles in the dystrophic chicken show many pathological changes. At 7 weeks of age, in a strain of these birds bred for early onset of this inherited disorder, physical weakness is established and these changes can be clearly assessed. Quantitative indices of these progressive changes were obtained by light and electron microscopic analyses; these indices cover fibre hypertrophy, fibre area variation, nuclei distribution, phagocytosis and satellite cell and fibroblast populations. The dystrophic pectoral muscle at 7 weeks is more severely affected than the PLD. In the former, there is an increase of peripheral myonuclei per fibre cross-section of over 200%, a hypertrophy factor nearly 200-fold greater than normal and longitudinal fibre splitting in 11% of the fibres. Many foci of degeneration are also present at this early stage. Although regenerating fibres are uncommon, an increased satellite cell population is observed. These indices provide a basis for assessing the effects of in vivo drug treatments, at the level of muscle structure.