Abnormalities of the sciatic nerves of dystrophic mice, with reference to nerve counts and mean area of axons.

Ultrastructural changes of the sciatic nerves of C57BL/ 6J dydy mice were examined. Nerve counts were calculated and the area of axons was measured in these nerve tissues. Many large bundles of unmyelinated nerves were observed at the proximal portion of the sciatic nerve, without cytoplasm or basement membrane of the Schwann cell. These bundles were composed of axons of various sizes and shapes, including some very large axons. The large unmyelinated axons decreased in number and size as nerves descended to the distal portion. The myelinated nerves showed irregular shapes. Some myelinated nerves were enveloped in very thin myelin sheaths for the mouse age. The destructed myelin was often observed from the radix to the distal portion of sciatic nerves. They lost their myelin sheaths at the Ranvier node, and descended for long distances with naked axons. The neighboring myelin segments of naked axons showed unusually bizarre shapes. They seemed to be the abnormal development of the demyelinated axons. Such findings were very similar to those of the embryonal developing peripheral nerves. It was concluded that the muscular dystrophy of the C57BL/6J-dydy mice might be related to dysmyelination and to the decrease in the number of myelinated nerves