Correlative histochemical study of skeletal muscle after suprasegmental denervation, peripheral nerve section, and skeletal fixation

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Abstract
Changes which occurred in the gastrocnemius and soleus muscles of adult and newborn guinea pigs after high thoracic cordotomy were studied with histochemical techniques and compared to the effects of peripheral nerve section and skeletal fixation. In the adult gastrocnemius, moderate atrophy of both histochemical fiber types developed after cordotomy and to a lesser extent after skeletal fixation. In contrast, denervation resulted in preferential atrophy of the type II fibers. The normal newborn guinea pig soleus were histochemically mixed, containing about an even number of type I and II fibers, and by 6 weeks of age it becomes uniform, containing only type 1 extrafusal fibers. Neonatal cordotomy, sciatic nerve section, and skeletal fixation impaired this normal histochemical change such that by 6 weeks of age the soleus remained mixed. In the adult soleus, 30 days after cordotomy, about 30% type n fibers appeared and, after skeletal fixation, only about 5%. Sciatic nerve section in the adult guinea pig resulted in the appearance of type II fibers in the soleus only after 3 to 6 months. In the soleus muscle of adult animals, cordotomy was followed by myo-pathic-like changes friecrosis, increased endomysial connective and adipose tissue, vacuoles, ringed fibers, and snake coils). The caution necessary in interpreting such changes as specifically myopathic was indicated. The pathogenic factors possibly playing a role in the studied experimental models were discusssed.