The proximo-distal spread of axonal degeneration in the dorsal columns of the rat

Summary The pivotal event in Wallerian degeneration is the breakdown of the axon. Establishing the pathophysiology of axonal degeneration has implications for the understanding of the pathogenesis of other types of nerve degenerations. A key aspect of the pathophysiology is the spatiotemporal pattern of spread after transection, an issue that has remained controversial. We have studied the progression of axonal degeneration in the dorsal columns of the rat following L₄L₅L₆ dorsal radiculotomy. Axonal degeneration proceeds in a proximo-distal fashion, beginning near the site of transection and spreading up the dorsal columns at a net rate of about 3 mmh^–1. In addition, there was early degeneration of the preterminal axons in the gracile nuclei. This pattern suggests that the clearing of axonally transported materials from the distal stump by continued anterograde transport may underlie axonal breakdown after transection.