Structural repair and functional recovery following cerebral ganglion removal in the pulmonate snail Melampus

Abstract

SYNOPSIS. Regeneration of the nervous system of Melampus following cerebral ganglion removal proceeds through tract, bud, and ganglion stages Each stage can represent a terminal condition in some animals Early events of regeneration appear to include roles for chemotactic and growth-promoting agents and axonal guidance by preferential adhesion to a connective tissue sheath This latter proposed mechanism accounts for the observed sequence in which the neural elements unite in the tract stage and for the pattern of failures that result when the sheath is disrupted In the tract stage of regeneration, communication through the site of the missing ganglion is restored within the central nervous system, and between neurons of non-excised ganglia and the denervated periphery Some behavioral recovery results The bud stage of regeneration is characterized by neuropil development and associated swelling at the site of confluence of the tracts Serotonin immunohistochemistry of bud stage preparations and retrograde dye transport via bud nerves show tracts and numerous synaptic vancosities, but the neuron somata that are labeled are located in other ganglia Ultrastructural examination of late bud/early ganglion stage tissue reveals the presence of small undifferentiated cells By six to seven months postoperative, some snails have clearly reached a ganglion stage of regeneration characterized by the appearance of differentiated neurons within the bud The origin of these new neurons is currently under investigation. © 1988 by the American Society of Zoologists.