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.

Factors affecting the histochemical composition of reinnervated soleus muscle of rat.

The myofibrillar ATPase reaction was utilized to determine the relative proportion of type II fibres in reinnervated soleus muscle 6 months after transection and reunion of the nerve at various distances from the muscle. In self-reinnervated soleus muscle, a highly significant decrease in the percentage of type II fibres from 10.5 +/- 1.6% in normal muscle to 0.7 +/- 0.4% was noted. In randomly reinnervated soleus muscle the percentage of type II fibres gradually increased with the distance of the site of nerve transection from the muscle. After transection and reunion of the muscular branch of the tibial nerve, the type II fibres constituted 34.0 +/- 1.5% and that of the reinnervated soleus muscle after transection and reunion of the sciatic nerve stump was 73.7 +/- 1.7% of the total fibre population. Different factors which might be responsible for the observed differences in the degree of cytochemical transformation of muscle fibre types in the process of reinnervation are discussed.

Classification of muscle fiber types based on succinic dehydrogenase and myofibrillar ATPase reactions in normal and randomly reinnervated rat skeletal muscles.

In the normal and randomly reinnervated plantaris muscle of rat staining for succinic dehydrogenase (SDH) activity differentiates three fiber types (A, B and C), staining for myofibrillar adenosine triphosphatase (ATPase) differentiates three fiber types (alpha, beta and alpha beta). Here we present our finding type A corresponds to alpha beta fibers, B to beta or alpha beta, C to alpha or alpha beta. In normal soleus muscle both classifications were found to be compatible and B fibers correspond to beta and C to alpha fibers. An exception is the small percent of alpha beta fibers which correspond to B type. In randomly reinnervated soleus muscle changes in ATPase activity are not followed by changes in SDH staining and B fibers correspond to alpha, beta or alpha beta types.