Figure 14-18.

Wallerian Degeneration, Transverse Section of Spinal Cord, Dog.

A, Longitudinal section. Arrows illustrate swollen axons. H&E stain. B, Transverse section. Laceration and/or severe compression of myelinated nerves cause a specific sequence of structural and functional changes in the axon and the myelin (distal from the point of injury), referred to as Wallerian degeneration (see E-Fig. 14-5). Axons are initially swollen (arrows) and eventually removed by phagocytosis to leave clear spaces, which were once the sites of nerve fibers. The cell bodies of affected neurons usually have central chromatolysis, but are metabolically active in an attempt to regenerate the lost portion of the axon (not shown; see Fig. 14-19). H&E stain.

(Courtesy Dr. J.F. Zachary, College of Veterinary Medicine, University of Illinois.)