Fiber Type Profile Change after Partial and Total Denervation in Rat. Soleus Muscles

Abstract

The short-term effects after experimental partial and total denervation on histochemical fiber type profiles were studied in rat soleus muscles by the myofibrillar ATPase stain. In 58 control soleus muscles, a total of 155788 fibers were counted, comprising type 1 (75.1%), type 2A (13.3%), type 2B (1.4%) and type 2C (10.3%), respectively. In 34 animals with total denervation, including 17 with soleus nerve resection at 1cm before entering the soleus muscle and 17 with total sciatic neurectomy, the proportion of type 1 fiber was decreased in denervated muscles to 39.1% 5 weeks after the procedures. In parallel with a decrease in type 1 fiber proportion, undifferentiated type 2C fibers increased, thereby suggesting muscle fiber type dedifferentiation taking place in totally denervated muscle. In contrast, 24 muscles with partial denervation showed a decreased proportion of type 1 fibers at the initial stage followed by an increase in type 1 fiber to 89.0% 5 weeks after denervation, resulting from an active reinnervating process.