The Effect of Denervation and Subsequent Reinnervation on the Morphology of Rat Soleus Muscles

To investigate the effect of denervation and subsequent reinnervation on skeletal muscle, a histochemical study was performed on the soleus muscles of rats. Partial denervation was carried out by freezing the sciatic nerve locally, and the change in the nerve and the soleus muscles was examined for 5 weeks. The muscle fiber cross-sectional area of the denervated soleus muscles progressively declined to a minimum 2 weeks after the injury (type I fibers, 1209.1 ± 248.3 μm2; type II fibers, 802.4 ± 126.8 μm2) and began to reverse the decline at 3 weeks. The type II fiber ratios to total fiber of the denervated sides were consistently higher than the control levels, and muscle fibers stained in both acid preincubation and alkaline preincubation were observed. The proportion of type II fibers in the soleus muscles showed an increase and consequently a decrease with a short delay in response to denervation and consequent reinnervation. These data suggest that denervation elicits an alteration in fiber type composition and a reduction in fiber size. The increase of type II fibers seemed to occur in hybrid fibers containing both myosin heavy chains I and II at varying ratios in the same fibers. The reinnervation took the crucial role of recovering from atrophy and composing the integrity of the soleus muscles. However, the ability to generate muscle tension needs a much longer time to recover. This suggests a need to investigate interventions to facilitate the functional recovery of partially-denervated muscle.