The nervous system component of the mesentery of the sea cucumber Holothuria glaberrima in normal and regenerating animals

The mesenterial tissues play important roles in the interactions between the viscera and the rest of the organism. Among these roles, they serve as the physical substrate for nerves connecting the visceral nervous components to the central nervous system. Although the mesenterial nervous system component has been described in vertebrates, particularly in mammals, a description in other deuterostomes is lacking. Using immunohistochemistry in tissue sections and whole mounts, we describe here the nervous component of the intestinal mesentery in the sea cucumber Holothuria glaberrima. This echinoderm has the ability to regenerate its internal organs in a process that depends on the mesentery. Therefore, we have also explored changes in the mesenterial nervous component during intestinal regeneration. Extensive fiber bundles with associated neurons are found in the mesothelial layer, extending from the body wall to the intestine. Neuron-like cells are also found within a plexus in the connective tissue layer. We also show that most of the cells and nerve fibers within the mesentery remain during the regenerative process, with only minor changes: a general disorganization of the fiber bundles and a retraction of nerve fibers near the tip of the mesentery during the first days of regeneration. Our results provide a basic description of mesenterial nervous component that can be of importance for comparative studies as well as for the analyses of visceral regeneration.