Stretch-induced growth in chicken wing muscles: nerve-muscle interaction in muscular dystrophy.

Skeletal muscle growth following denervation and denervation plus passive stretch was characterized in the patagialis muscle of normal and dystrophic chicks until 8 wk of age. In both genotypes, muscles denervated at 1 wk of age grew at reduced rates compared with contralateral control muscles whether or not they were passively stretched. Histograms of fiber size distributions as well as morphological criteria showed that passive stretch of denervated dystropic muscles substantially delayed the development of pathology. Denervation alone provided less protection. There was no evidence of fiber necrosis in any denervated dystrophic muscle, although many fibers did exhibit extreme hypertrophy and abnormal morphology. When denervated dystrophic muscles were allowed to reinnervate, growth and development of pathology was rapid. Because denervation, denervation with passive stretch, or passive stretch alone retards, but does not prevent, the development of pathology, it is concluded that dystrophy in the chick is a myogenic defect that is exacerbated by neurally mediated contractile activity.