Wallerian Degeneration and Myelin Loss Secondary to Neuronal and Axonal Degeneration

Abstract

There are basically two causes of Wallerian degeneration in our definition: neuronal cell death and axonal lesion. It should be noted, that our definition is wider than usual and not only includes acute axonal lesions, but neuronal and axonal lesions of any kind. Degeneration of the entire arborization of a neuron with its axon and axonal branches inevitably follows necrosis of the neuronal cell body. Examples are degenerative diseases affecting neuronal cell bodies and axons, such as Friedreich’s disease, olivopontocerebellar atrophy, and neuronal ceroid lipofuscinosis. A lesion of the axon that leads to an interruption of its continuity gives rise to degeneration of the distal part, whereas the proximal portion survives. The myelin in the distal portion undergoes dissolution as a consequence of the axonal degeneration, as the integrity of the myelin sheaths depends on continued contact with a viable axon. The changes in the distal part of the interrupted nerve are called Wallerian degeneration in a narrower sense, following Waller’s original description of the changes that he observed after cutting the glossopharyngeal and hypoglossal nerves in the frog in 1850.