Effect of tenotomy on self-reinnervated and randomly reinnervated soleus muscle of rat.

The time course and degree of atrophic changes caused by tenotomy were compared in normal, self-reinnervated and randomly reinnervated soleus muscle 6 months after transsection and reunion of the nerve at different distances from the muscle. Comparison was made between the behaviour of Type I and Type II fibers, distinguished on the basis of histochemical myofibrillar ATPase and succinic dehydrogenase reactions. Cross-sectional areas of individual muscle fibers were measured using Quantimet 720 image analyser. Selective atrophy of Type I muscle fibers as determined by structural and histochemical changes was observed after tenotomy of normal, self-reinnervated and randomly reinnervated soleus muscles after transsection of the muscular branch of the tibial nerve, Type II muscle fibers in randomly reinnervated muscles were found to be relatively insensitive to tenotomy, as in normal muscle. In randomly reinnervated muscles after transsection and reunion of the sciatic nerve, tenotomy did not cause any visible structural and histochemical abnormalities although a decrease of muscle weight and cross-sectional surface area of fibers was noted. Since in these muscles Type II fibers increased to about 70% of the muscle fiber population, it is suggested that the increased percentage of Type II fibers seemed to prevent the atrophic changes in Type I fibers after tenotomy.