Reinnervation events in long term denervated rat muscles

In spite of the surgical approaches utilized to prevent reinnervation from the sciatic proximal stump, some reinnervation of the distal leg muscles occurs, resulting in minimal or substantial recovery of muscle mass and function. These reinnervation events are recognizable at the light microscopy level by size and morphology of the reinnervated myofibers and by the recovery of the fascicle muscle structure. A clear type grouping (clustering of muscle fibers with the same contractile and metabolic profile) is the golden standard of muscle reinnervation. The fascicles are made of well packed fibers positive for either fast or slow ATPase. Mitochondrial activity is demonstrated by succinic acid deidrogenase staining. While in normal soleus muscles a low percentage of type II fibers are sparsely distributed among type I fibers, in some area of the sciatectomized-reinnervated muscles type II and Type I fibers are grouped. The innervated fibers neither express embryonic myosin nor NCAM (outside the synapse). The lack of expression of N-CAM confirms the re-innervation of the type-grouped fibers.