Effects of Partial and Total Denervation on the Distribution of Fiber Size of Rat Soleus Muscles: A Quantitative Computer Imaging Analysis

The effects of partial and total denervation on muscle fibers were studied in rat soleus muscles by quantitative computer imaging analysis. Within 5 weeks after denervation, there was a progressive reduction of the soleus muscle weight in total denervation groups but a gradual recovery beginning in the third week and reaching 75% of the control in the fifth week in the partial denervation group. The reduction of muscle mass was mainly due to the replacement of large and medium-sized fibers by small atrophic fibers. In totally denervated muscles, cross-sectional fiber area showed a rapid decline after denervation, but the shape of fiber size distribution was nearly normal. On the other hand, partially denervated muscles showed an asymmetrical fiber size distribution with a shift toward large fibers. In control and totally denervated muscles, mean fiber area strongly correlated with the standard deviation from the mean, but in partially denervated muscles, this strong correlation no longer existed and was replaced by larger standard deviations. It is concluded that only partially denervated muscles show significant variations in fiber size.