Development of the nervous system in Dugesia tigrina during regeneration after fission and decapitation

In the present study of Dugesia tigrina the development of the nervous system is followed and compared during regeneration after fission and after decapitation. Immunocytochemistry was used, with antisera raised against the biogenic amine, 5-hydroxytryptamine (5-HT) and the two neuropeptides, neuropeptide F (NPF), and FMRF amide. The results indicate that two processes are involved in the formation of the new cerebral ganglion. First, new processes sprouting from the original main longitudinal nerve cords bend transversely, indicating the position of the developing horseshoe-shaped anterior cerebral commissure. Then new nerve cells in front of the commissure differentiate from neoblasts and their growth cones fasciculate with the fibres from the old main longitudinal nerve cords. In the cerebral ganglion, 5-HT-IR cells appear before NPF-IR cells, in contrast to the pharynx where NPF-IR cells differentiate before the 5-HT-IR cells. In the peripheral nervous system, NPF-IR fibres and cells appear at a very early stage and dominate the whole regeneration process. A role for the PNS in early pattern formation is suggested.

Platyhelminth FMRFamide-related peptides

Platyhelminths are the most primitive metazoan phylum to possess a true central nervous system, comprising a brain and longitudinal nerve cords connected by commissures. Additional to the presence of classical neurotransmitters, the nervous systems of all major groups of flatworms examined have widespread and abundant peptidergic components, Decades of research on the major invertebrate phyla, Mollusca and Arthropoda, have revealed the primary structures and putative functions of several families of structurally related peptides, the best studied being the FMRFamide-related peptides (FaRPs). Recently, the first platyhelminth FaRP was isolated from the tapeworm, Moniezia expansa, and was found to be a hexapeptide amide, GNFFRFamide. Two additional PaRPs were isolated from species of turbellarians; these were pentapeptides, RYIRFamide (Artioposthia triangulata) and GYIRFamide (Dugesia tigrina). The primary structure of a monogenean or digenean FaRP has yet to be deduced. Preliminary physiological studies have shown that both of the turbellarian FaRPs elicit dose-dependent contractions of isolated digenean and turbellarian somatic muscle fibres. Unlike the high structural diversity of FaRPs found in molluscs, arthropods and nematodes, the complement of FaRPs in individual species of platyhelminths appears to be restricted to 1 or 2 related molecules. Much remains to be learnt about platyhelminth PaRPs, particularly from peptide isolation, molecular cloning of precursor proteins, receptor localization, and physiological studies. Copyright (C) 1996 Australian Society for Parasitology.

LOCALIZATION, QUANTITATION, AND CHARACTERIZATION OF NEUROPEPTIDE-F-IMMUNOREACTIVE AND FMRFAMIDE-IMMUNOREACTIVE PEPTIDES IN TURBELLARIANS AND A MONOGENEAN - A COMPARATIVE-STUDY

Over the past decade it has become clear that the nervous systems of platyhelminths are both complex and highly developed, particularly in peptidergic elements. The central position of an ancestral flatworm in the evolution of the Bilateria has placed a greater importance on the study of modern flatworms. Using antisera generated to the C-terminal region of platyhelminth neuropeptide F and the molluscan neuropeptide, FMRFamide, in immunocytochemistry at both Light and ultrastructural levels, immunoreactivities have been localised within the nervous systems of three species of triclad turbellarians, Dugesia lugubris, Dendrocoelum lacteum, and Polycelis nigra, and one species of monogenean trematode, Diclidophora merlangi. Extensive immunostaining was obtained with both antisera throughout the central and peripheral nervous systems of all species studied, but intensity and abundance was significantly greater in the turbellarians. Indirect electron-immunogold labeling demonstrated that immunoreactivity to both neuropeptides was often colocalised in neurosecretory vesicles, although discrete populations of vesicles were also observed. Radioimmunoassay of extracts of all species confirmed that neuropeptide F immunoreactivity was consistently more abundant than FMRFamide immunoreactivity, and that the levels of both in the three turbellarians were several orders of magnitude greater than those found in the monogenean. Chromatographic analyses of turbellarian extracts revealed that neuropeptide F and FMRFamide immunoreactivities were attributable to different peptides. These data imply that the neuropeptidergic systems of turbellarians are considerably more extensive than those of monogeneans, and would suggest that a regression has occurred in the latter as a consequence of the adoption of a more sedentary parasitic lifestyle. (C) 1995 Wiley-Liss, Inc.