Maturation, dystrophic changes and the continuous production of fibers in skeletal muscle regenerating in absence of the nerve

To investigate how much skeletal muscle depends on influences coming from peripheral nerve, we studied muscle regeneration induced by bupivacaine in the permanently denervated soleus muscle of adult rats. Using light and electron microscopy, we studied the extent of maturation attained by regenerated myofibers and their ability to regenerate again after repeated bupivacaine injury. Morphometric analyses showed that within the first two weeks after injury, the regenerated denervated fibers increased in diameter, matured and then became atrophic. By electron microscopy the morphological characteristics of mature fibers are evident, but final differentiation into adult fiber types is not attained. This is in keeping with previously reported biochemical results. A new phase of massive regeneration occurred when bupivacaine treatment was repeated, thus demonstrating that regenerated myofibers devoid of innervation keep their intrinsic ability to regenerate after injury. Spontaneous though s...