Axonal regeneration and sprouting following injury to the cerebral–buccal connective in the snail Achatina fulica

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Abstract
Axonal sprouting and regeneration were studied in the land snail Achatina fulica following a unilateral crush to the cerebral–buccal connective. Both normal projection patterns and changes induced by injury were examined with axonal filling techniques. As expected, most staining was lost shortly after the crush when filling across the lesion site. Much of this decrease is attributable to the direct disruption of fiber pathways, but evidence also indicates that a limited amount of retraction of some neurites occurred during the first week. A subsequent, gradual increase in the numbers of stained elements culminated in supernumerary counts of fibers in many pathways and in some novel labeling of cell bodies, Maximum numbers of supernumerary fibers usually occurred 21–28 days after the lesion. Most of these extra neurites and cell bodies subsequently disappeared, and by day 35 the appearance of projections generally returned to within the ranges observed in normal, unlesioned animals. Together the results demonstrate the extent of neuritic regeneration, sprouting, and retraction that occurs in vivo within the gastropod nervous system following injury. The study also indicates the usefulness of such in vivo approaches to understand the long-term processes that contribute to the restoration of morphological and functional integrity.