Anatomical studies of central regeneration of an identified molluscan interneuron

Abstract

Regeneration of the giant interneuron R. Pe. D. 1 within the central nervous system ofLymnaea stagnaliswas studied by intracellular injection of Lucifer Yellow. The major axon of R. Pe. D. 1 was severed by crushing the right–pleural–parietal connective and this initiates prolific sprouting from the proximal axon segment. Regeneration is highly specific in that neurites extend posteriorly across the crush site into regions of the c. n. s. where previously disconnected follower cells of R. Pe. D. 1 are located and project specifically to those nerve trunks that normally contain an axon branch of R. Pe. D. 1. Neurites also extend however, into regions of the anterior c. n. s. that are not normally occupied by R. Pe. D. 1 processes. This novel growth is a consistent consequence of lesioning the right pleural–parietal connective. Neuritic outgrowth is rapid, approximately 360–400 μm d-1and processes reach the former target cell regions in the posterior c. n. s. within three or four days. The extent of the regenerative response shown by the interneuron was found to depend upon the site of lesion of its major axon within the c. n. s. Novel sprouting, for instance, was particularly extensive in preparations where the R. Pe. D. 1 axon was severed close to the soma but entirely absent when axotomy was carried out distally within the posterior c. n. s. Regenerating neurites are able to extend to the former target cell areas via an alternative pathway through the left side of the c. n. s. when regrowth via the normal right-hand route is prevented.