Regeneration of the enteric nervous system in the sea cucumber Holothuria glaberrima

Among higher metazoans, echinoderms exhibit the most impressive capacity fo r regeneration. Holothurians, or sea cucumbers, respond to adverse stimuli by autotomizing and ejecting their visceral organs, which are then regenera ted. Neuronal fibers and cell bodies are present within the viscera, but pr evious regeneration studies have not accounted for the nervous component. W e used light microscopic immunocytochemistry and ultrastructural studies to describe the regeneration of the enteric nervous system in the sea cucumbe r Holothuria glaberrima. This study provides evidence that the enteric nerv ous system of this echinoderm regenerates after evisceration and that in 3- 5 weeks the regenerated system is virtually identical to that of noneviscer ated animals. The regeneration of the enteric nervous system occurs paralle l to the regeneration of other organ components. Nerve fibers and cells are observed within the mesenterial thickenings that give rise to the new inte stine and within the internal connective tissue prior to lumen formation. W e also used bromodeoxyuridine incorporation to show that proliferation of t he neuronal population occurs in the regenerating intestine. The regenerati on of the nervous system commands high interest because members of the clos ely related phylum Chordata either lack or have a very limited capacity to regenerate their nervous system. Thus, holothurians provide a model system to study enteric nervous system regeneration in deuterostomes. J. Comp. Neu rol. 406:461-475, 1999. (C) 1999 Wiley-Liss, Inc.