Spontaneous Axonal Dystrophy in the Brain and Spinal Cord in Naïve Beagle Dogs.

Axonal dystrophy (AD) is a common age-related neurohistological finding in vertebrates that can be congenital or induced by xenobiotics, vitamin E deficiency, or trauma/compression. To understand the incidence and location of AD as a background finding in Beagle dogs used in routine toxicity studies, we examined central nervous system (CNS) and selected peripheral nervous system (PNS) tissues in twenty 18- to 24-month-old and ten 4- to 5-year-old control males and females. Both sexes were equally affected. The cuneate, gracile, and cochlear nuclei and the cerebellar white matter (rostral vermis) were the most common locations for AD. Incidence of AD increased with age in the cuneate nucleus, cerebellar white matter (rostral vermis), trigeminal nuclei/tracts, and lumbar spinal cord. Axonal dystrophy in the CNS was not accompanied by neuronal degeneration/necrosis, nerve fiber degeneration, and/or glial reaction. Axonal dystrophy was not observed in the PNS (sciatic nerve, vagus nerve branches, or gastrointestinal mural autonomic plexuses).