Delayed response to denervation in muscles of C57BL/Ola mice

Muscle fibre areas and numbers, tetanic force, resident macrophage numbers and acetylcholine sensitivity were measured in normal and denervated soleus muscles of C57BL/Ola mice for comparison with data from outbred and other inbred strains. Serum creatine kinase levels were also measured. The muscles of normal C57BL/Ola mice had more fibres, generated more tension, had fewer resident macrophages and had a lower acetylcholine sensitivity than muscles of other strains. The normal level of serum creatine kinase was lower in C57BL/Ola mice than in Balb/c mice. Following denervation, the mean cross-sectional area of muscle fibres in Balb/c mice started to fall from day 1 but a fall was not seen in muscles from C57BL/Ola mice until day 5. The development of increased acetylcholine sensitivity was slower in the C57BL/Ola mice although the values in all mouse strains had converged by five days. The levels of serum creatine kinase also rose more slowly following denervation in C57BL/Ola mice. The differences between the data from C57BL/Ola mice and others are ascribed to the slow rate of Wallerian degeneration in that strain. The results support the view that the effects of denervation on muscle are due to both inactivity and an inflammatory effect contributed by nerve degeneration. The mutation that causes slow nerve degeneration may, however, also affect muscle directly, making it more resistant to catabolism.