Pathology of experimentally re-innervated skeletal muscle.

Abstract

The effects of cross-union of the nerves to fast and slow muscle on the structural and histochemical properties of skeletal muscle was studied in adult cats, newborn kittens and newborn rabbits. Nerves to the soleus and flexor hallucis longus or flexor digitorum longus were cross-united. In some cases denervation was affected by removing a 3 to 5 mm nerve segment. Tenotomy of the distal end of these individual muscles was performed between nylon sutures. Unoperated limbs served as controls. Contractile properties of the 3 muscles studied were measured by means of a strain gauge and a recorder. Tissue sections were studied histologically and assessed histochemically for activity of phosphorylase, reduced nicotinamide adenine dinucleotide (NADH2) diaphorase and myosin ATPase. After cross-union of the nerves to the soleus and flexor hallucis longus in the cats and kittens the flexor muscle showed areas composed entirely of fibers rich in NADH2 diaphorase, poor in phosphorylase and ATPase and indistinguishable from normal soleus. The cross-innervated and self-innervated muscle showed no histological abnormality and resembled quiescent normal muscle while many of the denervated and tenotomized muscles showed marked histological changes of varying degrees of atrophy. In the regenerating muscles marked variation in fiber size and shape appeared in many accompanied by excessive perimusial adipose tissue. The pattern was similar to that seen in muscular dystrophy. These muscle fibers had a marked variation in mitochondrial size and localization. Isolated giant fibers with a very intense NADH2 diaphorase reaction were seen. Structur-ally abnormal fibers took various forms and were frequently aggregated in groups. Core fibers took various forms but in the majority an inner zone devoid of enzyme activity and an outer apparently normal zone were apparent. Some fibers appeared to be vacuolated. In addition to the influence of the nervous system on the contractile properties of muscle, a marked influence on metabolic activity was demonstrated by changes in enzymatic pattern and an influence on structure was expressed in terms of abnromal fibers. Neurogenic atrophies were described traditionally as resulting from structural degeneration or mechanical interruption of the lower motor neuron.