Developmental expression of galanin-like immunoreactivity by members of the avian sympathoadrenal cell lineage.

The developmental coexpression of galanin-like immunoreactivity with the catecholamine-synthesizing enzyme tyrosine hydroxylase (TH) was studied in the avian embryo sympathoadrenal system using double-labeling immunocytochemistry. Galanin-like immunoreactivity is expressed by various catecholaminergic cell populations, namely sympathoblasts, chromaffin and small intensely fluorescent (SIF) cells, but not by principal neurons of the paravertebral sympathetic ganglia. Both galanin and somatostatin immunoreactivities are coexpressed in the adrenal and sympathetic ganglion primordia by the neural precursors, but the subsequent expression pattern of both peptides differs. Our results support the hypothesis that early sympathoblasts express a large repertoire of neuroactive substances and that the expression of these becomes restricted during further development as the sympathoblasts become principal neurons.

Cellular mechanisms of intestine regeneration in the sea cucumber, Holothuria glaberrima Selenka (Holothuroidea:Echinodermata).

Echinoderms are the deuterostome group with the most striking capacity to regenerate lost body parts. In particular, members of the class Holothuroidea are able to regenerate most of their internal organs following a typical evisceration process. Such formation of new viscera in an adult organism provides a unique model to study the process of organogenesis. We have studied this process in the sea cucumber Holothuria glabberrima by describing the spatial and temporal pattern of cellular events that occur during intestine regeneration following chemically induced evisceration. Regeneration begins as a thickening of the mesenteries that supported the autotomized organs to the body wall. The mesenterial thickening consists of tissues where most of the cellular populations found in the normal intestine are already present. However, the cell numbers differ, particularly those of hemocytes and amoebocytes, suggesting that some of these cells play an important role in the formation of the solid rod of hypertrophic mesentery that characterizes the intestinal primordia. The appearance of the luminal epithelium, together with the formation of the lumen, occurs during the second week of regeneration by proliferation and extensive migration of cells from the esophagus and cloacal ends into the thickenings. At this stage all tissue layers are present, but it takes an additional week for them to exhibit the proportions typical of the normal organ. Cell division, as determined by BrdU labeling, mainly occurs in the coelomic epithelia of the hypertrophic mesentery and in the regenerating luminal epithelium. Our study provides evidence that the process of new organ formation in holothurians can be described as an intermediate process showing characteristics of both epimorphic and morphallactic phenomena.

FMRFamide-like immunoreactivity in cells and fibers of the holothurian nervous system.

Immunoreactivity to FMRFamide (FMRFa) was detected in several components of the nervous system of the sea cucumber, Holothuria glaberrima. Neurons and fibers expressing immunoreactivity to this peptide were found in the radial nerves, and in nerve plexuses of the esophagus, and large and small intestine. The neurons in the enteric nervous system were located in the serosal layer and immunoreactive fibers appeared to innervate the longitudinal muscle. Co-existence of immunoreactivities to FMRFa and cholecystokinin was detected in most of the enteric fibers. Therefore, in the holothurians, neurons expressing FMRFa and FMRFa/cholecystokinin might be involved in the physiology of the digestive tract.

Cells in the intestinal system of holothurians (Echinodermata) express cholecystokinin-like immunoreactivity.

The presence of cholecystokinin (CCK), originally isolated from porcine small intestine, has been reported in a diversity of invertebrates ranging, from cnidarians to protochordates, but so far, not in echinoderms. We have used immunohistochemical techniques to demonstrate the presence of cells expressing CCK-like immunoreactivity in the intestine of three species of sea cucumber: Holothuria mexicana, H. glaberrima, and Stichopus badionotus. The immunoreactivity was observed within the cytoplasm of these cells, in what appeared to be granular or vesicle-like structures. The cell bodies were present in the outer connective tissue layer of the intestine and had a neuronal appearance, sending an axon-like structure into the circular muscle and internal connective tissue. A plexus of fibers expressing CCK-like immunoreactivity was found overlying the muscle layer. Contractility of H. mexicana intestinal strips was studied under partially isometric conditions. CCK and related peptides induced relaxation of the basal muscle tension, and of tension induced by ACh application, suggesting a role for this agent in the intestinal physiology of holothurians.