Effect of denervation and nerve extract on ultrastructure of muscle

Changes in denervated skeletal muscle result both from disuse and loss of neurogenic trophic substances. It had been shown that administration of nerve extract intramuscularly in rats or systemically in mice prevented the nondisuse component of atrophy in denervated muscle. Amelioration of atrophy was manifested as reduced losses of weight, protein, and cross-sectional areas of fiber in denervated hind-limb muscles. The present study assessed the effects of nerve extract on ultrastructural changes in different types of fiber (as classified by activity of ATPase) in mouse skeletal muscle denervated for 7 days. Denervated and contralateral innervated muscles of treated and untreated mice were examined by electron microscopy, and morphological parameters were quantitated by stereological techniques. Denervated muscles exhibited smaller reductions of several ultrastructural changes in treated than in untreated mice including sizes of mitochondria, and percentage volume per fiber of mitochondria, sarcoplasmic reticulum, and t-tubules. The magnitude of the myotrophic effects varied in the different types of fiber, with amelioration of between 50 and 95% of the postdenervation changes.