Further observations on myelinated axon numbers in normal and dystrophic mice

Counts of the number of myelinated axons in the nerves to slow-twitch soleus and fast-twitch plantaris muscles of 129 ReJ dy/dy dystrophic mice at 4, 15 and 24 weeks of age have shown statistically significant reductions when compared to normal values. In addition muscle fibre losses had occurred in both muscles at the earliest age point studied. There was no suggestion of a progressive loss of myelinated axons. There was a greater percentage reduction in the soleus than in the plantaris nerves. The number of myelinated axons in the nerves to the plantaris and soleus muscles of the 129 ReJ +/+ normal animals was approximately the same, in contrast to the C57BL/6J strain where the soleus nerve always contained a greater number. Statistically significant reductions in the number of myelinated axons in the nerves to the medial gastrocnemius muscles of C57BL/6J dy2J/dy2J dystrophic mice have been observed at both 15 and 72 weeks of age. Muscle fibre losses have also been recorded in 72 weeks dystrophic medial gastrocnemius muscles.