A scanning electron microscopic study of peripheral nerve degeneration and regeneration

Abstract

The left sciatic nerves of male Holtzman rats were exposed and crushed with a hemostat for 3 s at a point midway between the inferior gluteal nerve and the bifurcation into the tibial and common peroneal nerves. Normal myelinated axons appear in the scanning electron microscope as relatively smooth cylindrical structures with interweaving strands of collagen fibers coursing over their length. Nodes of Ranvier are seen as constrictions along the myelinated fibers. After crushing, the nerve fibers swell, and interruptions appear in the nodal and internodal regions causing a beaded morphology. The myelin sheaths fragment into numerous spherical bodies as the degenerative process progresses. Some remnants of myelin debris are found within the nerves 60 days following the lesion A few regenerating myelinated axons are observed within the connective tissue fibers and myelin debris distal to the crushed regions approx 15 days after placement of the lesion. By day 30 the nerves are relatively normal in appearance. The scanning electron micrographs provide a three-dimensional picture of the dynamic processes which occur during nerve degeneration and regeneration. These findings are correlated with previous studies and can serve as a basis for future scanning electron microscopic studies in this area of research.