Age-related changes in peripheral nerves of the dog. I. A morphologic and morphometric study of single-teased fibers.

Incidence of lesions in single-teased myelinated fibers and the relationship between internodal length and fiber diameter were studied by morphologic and morphometric techniques on common peroneal and ulnar nerves of 28 dogs between three months and 15 years of age that were free of neuromuscular disease. Minimal lesions were seen in nerves of dogs under ten years of age, usually involving less than 3% of the teased fibers; however, in older dogs, the mean incidence of lesions that included axonal degeneration and segmental demyelination and remyelination, increased to 6% and 9% in ulnar and common peroneal nerves, respectively. A positive correlation (p less than 0.0001) between internodal length and fiber diameter was found in both nerves from immature and mature dogs, but slopes of regression lines were reduced in older dogs.