The present immunocytochemical study utilizes serotonin and SALMFamide antisera, together with confocal laser scanning microscopy, to provide new information about the development of the nervous system in the sea urchin Psammechinus miliaris (Echinodermata: Echinoidea). Special attention is paid to the extent of the nervous system in later larval stages (6-armed pluteus to metamorphic competency), a characteristic that has not been well described in this and other species of sea urchin. An extensive apical ganglion appears by the 6-armed pluteus stage, forming a complex of 10-20 cells and fibers, including discrete populations of both serotonin-like and SALMF-amide-like immunoreactive cells. At metamorphosis this complex is large, comprising at least 40 cells in distinct arrays. Serotonin-like immunoreactivity is also particularly apparent in the lower lip ganglion of 6- to 8-armed plutei; this ganglion consists of 15-18 cells that are distributed around the mouth. The ciliary nerves that lie beneath the ciliary bands in the larval arms, the esophagus, and a hitherto undescribed network associated with the pylorus all show SALMFamide-like immunoreactivity. The network of cells and fibers in the pyloric area develops later in larval life. It first appears as one cell body and fiber, then increases in size and complexity through the 8-armed pluteus stage to form a complex of cells that encircles the pylorus. SALMFamide-like, but not serotonin-like, immunoreactivity is seen in the vestibule wall, tube feet, and developing radial nerve fibers of the sea urchin adult rudiment as the larva gains metamorphic competency.

Regeneration of the arm of the star¢sh, Asterias rubens (L.) (Echinodermata: Asteroidea) was examined using two preparations. The ¢rst involved regeneration of the entire arm tip and its associated sensory structures and the second examined regeneration of a small section of radial nerve cord in the mid-arm region. Cell cycle activity was investigated by incorporation of the thymidine analogue, bromodeoxyuridine (BrdU). Details of neuroanatomy were obtained by immunocytochemistry (ICC) using an antiserum to the recently isolated star¢sh neuropeptide, GFNSALMFamide (S1). BrdU labelling indicated that initial events occur by morphallaxis, with cell cycle activity ¢rst apparent after formation of a wound epidermis. As regeneration proceeded, BrdU immunoreactive (IR) nuclei revealed cell cycle activity in cells at the distal ends of the radial nerve cord epidermis, in the coelomic epithelium, the perihaemal and water vascular canal epithelia, and in the forming tube feet of both preparations. By varying the time between BrdU pulses and tissue ¢xation, the possible migration or di¡erentiation of labelled cells was investigated. Neuropeptide ICC indicated the extension of S1-IR nerve ¢bres into the regenerating area, soon after initial wound healing processes were complete. These ¢bres were varicose and disorganized in appearance, when compared to the normal pattern of S1-IR in the radial nerve. S1-IR was also observed in cell bodies, which reappeared in the reforming optic cushion and radial nerve at later stages of regeneration. Double labelling studies with anti-BrdU and anti-S1 showed no co-localization in these cell bodies, in all the stages examined. It appeared that S1-IR cells were not undergoing, and had not recently undergone, cell cycle activity. It cannot be con¢rmed whether S1-IR neurons were derived from proliferating cells of epithelial origin, or from transdi¡erentiation of epithelial cells, although the former mechanism is suggested. Di¡er-entiation of the regenerating structures to replace cells such as S1-containing neurons, is thought to involve cell cycle activity and di¡erentiation of epithelial cells in the epidermal tissue, possibly in association with certain types of coelomocytes which move into the regenerating area.

Studies of the larval nervous system of two species of starfish were carried out using antisera to a recently isolated native echinoderm neuropeptide, GFNSALMFamide (S1), and to serotonin. S1-like immunoreactivity was found in the larvae of the asteroids Pisaster ochraceus and Asterias rubens (Echinodermata: Asteroidea), originating in the apical region and becoming concentrated as two groups of cells in the dorsal ciliary band, the preoral transverse and adoral ciliary bands in larvae up to the early brachiolarian stage (five weeks). The pattern of serotonin immunoreactivity, although appearing earlier in the apical nerve plexus, is very similar to that of the peptide, with paired groups of immuno- reactivity apparent in the dorsal ciliary band. This evidence, together with other recent studies, indicates that this neuropeptide is present in both the larval and adult nervous system, despite the complete reformation of the system at metamorphosis. The close localization of SI with serotonin may also suggest a possible function for the peptide in larval and adult nervous systems.

Background: An acidic polysaccharide, fCS, from the sea cucumber Holothuria forskali has a range of biological activities.Results: The conformation of fCS was determined, and resulting oligosaccharides were shown to retain desirable biological properties.Conclusion: The conformation of the fCS repeating unit underpins binding to L- and P-selectins.Significance: Exploitation of the fCS-selectin interaction may open new avenues for therapeutic intervention using fCS fragments or their mimetics.