The effects of denervation location on fiber type mix in self-reinnervated mouse soleus muscles.
Mouse soleus muscles were denervated by crushing the soleus nerve where it enters the muscle to determine if denervation followed by self-reinnervation can permanently alter the mix of fiber types in a muscle. Reinnervated and contralateral control muscles were sectioned at 2 and 7 months postdenervation and histochemically stained for myosin ATPase to determine the percentages of fast and slow twitch fibers in the muscles. It was found that, at both 2 and 7 months postdenervation, reinnervated muscles had a significantly higher percentage of slow twitch fibers than did contralateral control muscles (86.7 versus 67.8% at 2 months and 90.0 versus 69.3% at 7 months). Soleus muscles were also denervated by crushing the soleus nerve where it exists the gastrocnemius muscle (approximately 4 mm proximal to where the nerve enters the soleus muscle) to ascertain if the location of the nerve lesions plays a role in the ultimate outcome of the process of self-reinnervation. Reinnervated muscles and their contralateral muscles were sectioned at 2 months postdenervation and histochemically stained for myosin ATPase as before. It was found that, in contrast to muscles denervated at the point of nerve entry, muscles denervated 4 mm more proximal exhibited only a small increase in their percentage of slow twitch fibers which was not statistically significant (71.4 versus 68.4%). These results suggest that denervation followed by self-reinnervation can cause a permanent change in a muscle's fibers type mix and that the location of the nerve lesion strongly influences the final outcome of the reinnervation process.
Bishop
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Indiana University School of Medicine, Muncie Center for Medical Education, Ball State University 47306, USA.
Milton
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D000818:Animals; D005260:Female; D006614:Hindlimb; D008137:Longitudinal Studies; D051379:Mice; D009121:Muscle Denervation; D018657:Muscle Fibers, Slow-Twitch / Q000648:ultrastructure; D018482:Muscle, Skeletal / Q000201:enzymology / Q000294:innervation* / Q000648:ultrastructure; D009218:Myosins / Q000378:metabolism; D009416:Nerve Regeneration / Q000502:physiology*
D009218:Myosins