Radial Nerve Cord Research Articles

Ultrastructure of the circumoral nerve ring and the radial nerve cords in holothurians (Echinodermata)

The circumoral nerve ring and the radial nerve cords (RNCs) of Eupentacta fraudatrix and Pseudocnus lubricus (Holothuroidea) were examined as an example of holothurian nervous tissue. The RNC is composed of outer ectoneural and inner hyponeural layers, which are interconnected with one another via short neural bridges. The circumoral nerve ring is purely ectoneural. Both ectoneural and hyponeural components are epithelial tubes with a thick neuroepithelium at one side. A thin ciliated non-neuronal epithelium complements the neuroepithelium to form a tube, thereby enclosing the epineural and hyponeural canals. The whole of the ectoneural and hyponeural subsystems is separated from the surrounding tissue by a continuous basal lamina. The nerve ring and the ectoneural and hyponeural parts of the radial nerves are all neuroepithelia composed of supporting cells and neurons. Supporting cells are interpreted as being glial cells. Based on ultrastructural characters, three types of neurons can be distinguished: (1) putative primary sensory neurons, whose cilium protrudes into the epineural or hyponeural canal; (2) non-ciliated neurons with swollen rough endoplasmic reticulum cisternae; (3) monociliated neurons that are embedded in the trunk of nerve fibers. Different types of synapses occur in the neuropile area. They meet all morphological criteria of classical chemical synapses. Vacuolated cells occur in the neuroepithelium of E. fraudatrix, but are absent in P. lubricus; their function is unknown. The cells of the non-neuronal epithelia that overlie the ectoneural and hyponeural canals are hypothesized to belong to the same cell type as the supporting cells of the neuroepithelium.

Homology of echinoderm radial nerve cords and the chordate neural tube???

Evolution & DevelopmentVolume 8, Issue 1 p. 1-2 Homology of echinoderm radial nerve cords and the chordate neural tube??? Claus Nielsen, Claus Nielsen Zoological Museum, University of Copenhagen, Universitetsparken 15, DK-2100 Copenhagen, DenmarkSearch for more papers by this author Claus Nielsen, Claus Nielsen Zoological Museum, University of Copenhagen, Universitetsparken 15, DK-2100 Copenhagen, DenmarkSearch for more papers by this author First published: 06 January 2006 https://doi.org/10.1111/j.1525-142X.2006.05068.xCitations: 14 (email: [email protected]) Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article.Citing Literature Volume8, Issue1January 2006Pages 1-2 RelatedInformation

Engrailed is expressed in larval development and in the radial nervous system of Patiriella sea stars

We documented expression of the pan-metazoan neurogenic gene engrailed in larval and juvenile Patiriella sea stars to determine if this gene patterns bilateral and radial echinoderm nervous systems. Engrailed homologues, containing conserved En protein domains, were cloned from the radial nerve cord. During development, engrailed was expressed in ectodermal (nervous system) and mesodermal (coeloms) derivatives. In larvae, engrailed was expressed in cells lining the larval and future adult coeloms. Engrailed was not expressed in the larval nervous system. As adult-specific developmental programs were switched on during metamorphosis, engrailed was expressed in the central nervous system and peripheral nervous system (PNS), paralleling the pattern of neuropeptide immunolocalisation. Engrailed was first seen in the developing nerve ring and appeared to be up-regulated as the nervous system developed. Expression of engrailed in the nerve plexus of the tube feet, the lobes of the hydrocoel along the adult arm axis, is similar to the reiterated pattern of expression seen in other animals. Engrailed expression in developing nervous tissue reflects its conserved role in neurogenesis, but its broad expression in the adult nervous system of Patiriella differs from the localised expression seen in other bilaterians. The role of engrailed in patterning repeated PNS structures indicates that it may be important in patterning the fivefold organisation of the ambulacrae, a defining feature of the Echinodermata.

Patterns of gene expression in the developing adult sea urchin central nervous system reveal multiple domains and deep-seated neural pentamery.

The adult sea urchin central nervous system (CNS) is composed of five radial nerve cords connected to a circular nerve ring. Although much is known about the molecular mechanisms underlying the development and function of the nervous systems of many invertebrate and vertebrate species, virtually nothing is known about these processes in echinoderms. We have isolated a set of clones from a size-selected cDNA library prepared from the nervous system of the sea urchin Heliocidaris erythrogramma for use as probes. A total of 117 expressed sequence clones were used to search the GenBank database. Identified messages include genes that encode signaling proteins, cytoskeletal elements, cell surface proteins and receptors, cell proliferation and differentiation factors, transport and channel proteins, and a RNA DEAD box helicase. Expression was analyzed by RNA gel blot hybridization to document expression through development. Many of the genes have apparently neural limited expression and function, but some have been co-opted into new roles, notably associated with exocytotic events at fertilization. Localization of gene expression by whole-mount in situ hybridization shows that the morphologically simple sea urchin radial CNS exhibits complex organization into localized transcriptional domains. The transcription patterns reflect the morphological pentamery of the echinoderm CNS and provide no indication of an underlying functional bilateral symmetry in the CNS.

Molecular approach to echinoderm regeneration.

Until very recently echinoderm regeneration research and indeed echinoderm research in general has suffered because of the lack of critical mass. In terms of molecular studies of regeneration, echinoderms in particular have lagged behind other groups in this respect. This is in sharp contrast to the major advances achieved with molecular and genetic techniques in the study of embryonic development in echinoderms. The aim of our studies has been to identify genes involved in the process of regeneration and in particular neural regeneration in different echinoderm species. Our survey included the asteroid Asterias rubens and provided evidence for the expression of Hox gene homologues in regenerating radial nerve cords. Present evidence suggests: 1) ArHox1 expression is maintained in intact radial nerve cord and may be upregulated during regeneration. 2) ArHox1 expression may contribute to the dedifferentiation and/or cell proliferation process during epimorphic regeneration. From the crinoid Antedon bifida, we have been successful in cloning a fragment of a BMP2/4 homologue (AnBMP2/4) and analysing its expression during arm regeneration. Here, we discuss the importance of this family of growth factors in several regulatory spheres, including maintaining the identity of pluripotent blastemal cells or as a classic skeletal morphogenic regulator. There is clearly substantial scope for future echinoderm research in the area of molecular biology and certain aspects are discussed in this review.

The enteric nervous system of echinoderms: unexpected complexity revealed by neurochemical analysis.

Echinoderms are one of the most important groups of metazoans from the point of view of evolution, ecology and abundance. Nevertheless, their nervous system has been little studied. Particularly unexplored have been the components of the nervous system that lie outside the ectoneural and hyponeural divisions of the main nerve ring and radial nerve cords. We have gathered information on the nervous components of the digestive tract of echinoderms and demonstrate an unexpected level of complexity in terms of neurons, nerve plexi, their location and neurochemistry. The nervous elements within the digestive system consist of a distinct component of the echinoderm nervous system, termed the enteric nervous system. However, the association between the enteric nervous system and the ectoneural and hyponeural components of the nervous system is not well established. Our findings also emphasize the importance of the large lacunae in the neurobiology of echinoderms, a feature that should be addressed in future studies.

Localization of the neuropeptide NGIWYamide in the holothurian nervous system and its effects on muscular contraction

NGIWYamide is a peptide recently isolated from the sea cucumber Apostichopus japonicus. It stiffens the connective tissue of the holothurian body wall. Localization of NGIWYamide was investigated by immunohistochemical staining with antiserum raised against NGIWYamide. In holothurian nervous systems NGIWYamide-like immunoreactivity (NGIWYa-LI) was observed in the hyponeural and ectoneural regions of the radial nerve cord, as well as in the circumoral nerve ring, podial nerves, tentacular nerves, the basiepithelial nerve plexus of the intestine and in cellular processes running through the body wall dermis. Labelled nerve fibres from the hyponeural part of the radial nerve running towards the circular muscle and from the podial nerve into the body wall dermis suggest that NGIWYamide controls both muscle and connective tissue. We examined the effect on muscle activity of the sea cucumber. NGIWYamide (10-7 to 10-4 M) caused contraction of the longitudinal body wall muscle. Tentacles showed contraction only at a higher dose (10-4 M). NGIWYamide (10-4 M) inhibited spontaneous contraction of the intestine.

Secretory Radial Glia in the Ectoneural System of the Sea Star Asterias rubens (Echinodermata)

AbstractPrevious studies of epithelial nervous systems have focused on the neuronal elements, but generally neglected the origin of neuro–glial interactions. In this study, we use a polyclonal antiserum directed against Reissner's substance to label non‐neuronal bipolar cells in the ectoneural part of the radial nerve cord in the sea star Asterias rubens. Ultrastructural results show secretory activity in these bipolar cells. Immunolabelled material is released into the extracellular matrix in the hyaline layer as well as in the region of the basal end‐feet. As a first step towards characterising the antigen, a specific protein band of 36 kD was demonstrated with immunoprecipitation. Cells of this type: (1) traverse the epithelium to full extent from the outer surface to the basal lamina; (2) carry a single apical cilium; (3) contain conspicuous bundles of intermediate filament; (4) produce a secretion which is, at least in part, homologous to the Reissner's substance which is produced by a primitive radial glia cell type in chordates. It is concluded that the bipolar cells in the ectoneural part of the surface epithelium of the sea star Asterias rubens are secretory radial glia, which evidently have a common origin to the radial glia which secretes Reissner's substance in chordates.

Patterns of bromodeoxyuridine incorporation and neuropeptide immunoreactivity during arm regeneration in the starfish Asterias rubens

Regeneration of the arm of the starfish,Asterias rubens(L.) (Echinodermata: Asteroidea) was examined using two preparations. The first 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 starfish neuropeptide, GFNSALMFamide (S1). BrdU labelling indicated that initial events occur by morphallaxis, with cell cycle activity first 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 fixation, the possible migration or differentiation of labelled cells was investigated. Neuropeptide ICC indicated the extension of S1–IR nerve fibres into the regenerating area, soon after initial wound healing processes were complete. These fibres 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 confirmed whether S1–IR neurons were derived from proliferating cells of epithelial origin, or from transdifferentiation of epithelial cells, although the former mechanism is suggested. Differentiation of the regenerating structures to replace cells such as S1–containing neurons, is thought to involve cell cycle activity and differentiation of epithelial cells in the epidermal tissue, possibly in association with certain types of coelomocytes which move into the regenerating area.

Localization of S1- and S2-like immunoreactivity in the nervous system of the brittle star Amphipholis squamata (Delle Chiaje 1828).

The recent isolation and characterization of the SALMFanide neuropeptides S1 GFNSALMFamide; and S2 (SGPYSFNSGLTFamide) from the sea stars. Asterias rubens and Asterias forbesi have initiated numerous studies on their morphological localization and distribution within the phylum Echinodermata. It has been shown by immunocytochemistry and radioimmunoassay that these peptides are widely distributed in the nervous system of some asteroids, echinoids and ophiuroids. A physiological approach has also shown that S1 and S2 potentiate the luminescence of the small ophiuroid Amphipholis squamata. In the present study. S1- and S2-like immunoreactivity have been localized in A. squamata by immunocytochemistry on both wholemount preparation and histological sections. The results reveal a widespread neuronal distribution of S1-like immunoreactivity in the circumoral ring, radial nerve cord, and tube feet. S1-like immunoreactivity was found to be associated with axons and cell bodies in both the ectoneural and hyponeural components of the nervous. S2-like immunoreactivity was detected only in the ectoneural plenus of the circumoral ring and radial nerve cord.

Ultrastructure of the Statocysts in the Apodous Sea Cucumber Leptosynapta inhaerens (Holothuroidea, Echinodermata)

AbstractThe burrowing sea cucumber Leptosynapta inhaerens possesses five pairs of statocysts, one pair on either side of each radial nerve cord where it arises from the circumoral nerve ring. The nerve cords exhibit only ectoneural components at the level of the statocysts. A sinus‐like epineural canal lies superjacent to each cord. This canal is lined by a robust monociliated neuroepithelium which lacks any special support cells. Beneath the neuroepithelium, the somata of the ectoneural neurons form a perikaryal layer whereas the axons are located within the proximal parts of the cords. Glial cells have not been found. Each statocyst is a hollow sense organ. Its central cavity is lined by a monolayer of monociliated parietal cells. Axons of these parietal cells extend towards the statocyst nerve which connects each statocyst with the ectoneural pathways of the cord. A single lithocyte floats within each central statocyst cavity. This unciliated cell contains a voluminous vacuole with the statolith and several smaller vacuoles. It is concluded that statocysts do not belong to the basic organization of the Holothuroidea but have been evolved within this group. The statement, that the statocysts of apodous sea cucumbers and that of the enigmatic Xenoturbella bocki are homologous organs, is rejected.

Distribution and action of SALMFamide neuropeptides in the starfish Asterias rubens.

The SALMFamides S1 and S2 are two structurally related neuropeptides that are present in starfish, and which share the C-terminal amino acid sequence SXLXFamide, where X is variable. To establish the distribution of S1 and S2 in starfish, we have raised antisera that recognise specifically the C-terminal pentapeptide sequence of either S1 or S2. Here we describe the production and characterisation of an S2-specific antiserum designated CLII. This antiserum, together with an S1-specific antiserum (BLII), has been used in a radioimmunoassay to measure S1 and S2 levels in extracts of body parts from the starfish Asterias rubens. High concentrations (250-400 pmol g-1) of both peptides were detected in the radial nerve cords of the nervous system and lower concentrations were detected in other body parts, including neuromuscular organs such as the tube feet, apical muscle and cardiac stomach. We have examined the pharmacological effects of S1 and S2 on the contractility of these three preparations. Neither S1 nor S2 influenced the tone of tube foot and apical muscle preparations but S2 caused relaxation of cardiac stomach preparations, antagonising the contracting action of acetylcholine.

Tissue distribution of the SALMFamide neuropeptides S1 and S2 in the starfish Asterias rubens using novel monoclonal and polyclonal antibodies. I. Nervous and locomotory systems

The recent isolation and characterization of the SALMFamide neuropeptides (S1 and S2) from the starfish Asterias rubens has initiated a series of single- and double-labelling immunocytochemical studies to ascertain their tissue distribution and cellular localization. Specific novel monoclonal and polyclonal antisera have been raised against these neuropeptides and used in optical immunocytochemistry (ICC). The results of the present study reveal, for the first time, the widespread neuronal distribution of S2 localized to axons and perikarya of the radial nerve cord and tube foot ectoneural nerve plexus. Double labelling revealed a predominantly separate localization for S1 and S2 immunoreactivity. The potential functional roles of S1 and S2 in the radial nerve cord (RNC) and tube feet of Asterias rubens are discussed.

Localization of the heptapeptide GFSKLYFamide in the sea cucumber holothuria glaberrima (echinodermata): A light and electron microscopic study

Two peptides, Gly-Phe-Ser-Lys-Leu-Tyr-Phe-NH2 (GFSKLYFamide) and Ser-Gly-Tyr-Ser-Val-Leu-Tyr-Phe-NH2 (SGYSVLYFamide), recently isolated from the sea cucumber Holothuria glaberrima [Díaz-Miranda et al. (1992) Biol. Bull. 182:241-247] represent the first neuropeptides isolated from holothurians. Using an antibody against GFSKLYFa, we describe here the localization and distribution pattern of GFSKLYFa-like immunoreactivity in H. glaberrima, where immunoreactive fibers form a prominent and extensive peptidergic nervous system component. Neuron-like cells and nerve fibers expressing GFSKLYFa-like immunoreactivity are found in the ectoneural and hyponeural divisions of the radial nerve cords as well as in the digestive, haemal, respiratory, and reproductive systems; in the tentacles; and in tube feet. Neuroendocrine-like cells are found in the mucosal layer of the intestine. Ultrastructure immunocytochemical analysis revealed that, in nerve cells and fibers in the serosal layer of the intestine, the immunoreactivity is concentrated in vesicles. The immunoreactive nerve fibers are found mainly within a dense nerve plexus overlying and in close contact with smooth muscle cells of the intestine. The exclusive expression of GFSKLYFa-like immunoreactivity in neuronal or neuroendocrine tissue together with the close apposition of some fibers to muscle cells suggests that GFSKLYFa acts as a neuromuscular transmitter or neuromodulator in H. glaberrima. The wide occurrence of GFSKLYFa-like immunoreactivity throughout the nervous system of the sea cucumber suggests that GFSKLYFa plays an important role in the control of multiple action systems, including digestion, respiration, circulation, reproduction, and locomotion.

Localization of neuropeptides in the nervous system of the brittle star Ophiura ophiura

Immunocytochemical investigations using antisera against the SALMFamide neuropeptide S1 and RFamide were carried out on whole mounts of the radial nerve cord and circumoral ring of the brittle star Ophiura ophiura. Both antisera show an abundant immunoreactivity in the ectoneural tissue and give similar patterns of distribution. They show that in the radial nerve cord there are discrete populations of neurons organized in an identical pattern in each segment. At the junction with the ring, however, the two proximal segments of the nerve cord are differentiated from the distal ones by increased numbers of immunoreactive neurons. This is probably due to the more complex integrative function in that area. In the ring, immunolabelling is simple and consists of fibre tracts and two local ganglia. In each segment both antisera label either one or two giant neurons the shape of which is similar to that of a class of fibres that have been described from intra-cellular dyefills. The S1- and RFamide-like distributions, although very similar, show some neurons which are only labelled by one antiserum. Since preabsorption controls indicate no cross-reactivity between antisera, there is evidence of two distinct neuropeptides in the nervous system of the brittle star.

Localisation of gamma aminobutyric acid (GABA)-like immunoreactivity in the echinoderm Asterias rubens.

Gamma amino butyric acid (GABA) is believed to be the principal inhibitory neurotransmitter in the mammalian central nervous system, a function that has been extended to a number of invertebrate systems. We have used a specific antiserum raised against GABA to demonstrate GABA-like immunoreactivity in the radial nerve cord (RNC), tube feet and the digestive system of the asteroid Asterias rubens. In the RNC, immunoreactivity was restricted to ectoneural fibres and cell bodies while in the tube feet fibres were revealed in the basal nerve ring and longitudinal nerve. In the gut, extensive labelling was apparent in the basi-epithelial plexus as well as in mucosal perikarya.

Nitric oxide (NO) synthase immunoreactivity in the starfish Marthasterias glacialis

The neuroendocrine system of the starfish Marthasterias glacialis was investigated immunocytochemically using antisera specific for rat neuronal, bovine aortic endothelial, and mouse macrophage, nitric oxide (NO) synthases. Immunoreactivity was detected only with the antibodies specific for the neural enzyme, in the ectoneural and hyponeural tissues of the radial nerve cords and in the basiepithelial plexus and endocrine cells of the digestive tract. The pyloric stomach showed more immunoreactive structures than the other digestive organs, with the rectal caeca showing the least activity. Immunoreactive endocrine cells were located in the cardiac and pyloric stomachs and in the pyloric caeca. Co-localization of the enzyme immunoreactivity, and the staining for NADPH-diaphorase, demonstrate the presence of NO synthase in echinoderms. These results provide further evidence that NO is a neuronal messenger of early phylogenetic origin which has been conserved throughout evolution.

Immunocytochemical mapping of the novel echinoderm neuropeptide SALMFamide 1 (S1) in the starfish Asterias rubens.

The recent isolation and characterization of the SALMFamide neuropeptides S1 and S2 from the starfish Asterias rubens has initiated a series of studies on their distribution. Specific antisera have been raised against S1 and used in light-microscopical immunocytochemistry. The results of this study reveal for the first time a possible hyponeural innervation of the visceral musculature of the gut and the widespread neuronal distribution of S1, (i) in axons and cell bodies of both ectoneural and hyponeural regions of the radial nerve cord and circumoral nerve ring, (ii) in the nerve ring and nerve plexus of the tube feet, (iii) in the apical muscle, (iv) in skin, and (v) extensively throughout the digestive system. These discoveries are of particular interest in terms of the possible functional roles for S1 in Asterias rubens.

Ultrastructure and organization of the epineural canal and the nerve cord in sea urchins (Echinodermata, Echinoida)

The radial nerve cord ofMespilia globulus has been examined as an example of echinoid nerve cords. In the radius of echinoids only the ectoneural component of the nerve cord is present which is a derivative of the ectoderm. The nerve cord runs in the interior of the body and is accompanied by the epineural canal. In echinoids, the neuroepithelium makes up the upper and side walls of the epineural canal. Each lateral branch of the nerve cord forms a sort of neural tube. It encloses a branch of the epineural canal which represents an open connection with the sea water. Thus, the epineural canal exhibits numerous openings which probably allow sea water to flow back and forth. This organization is unique in echinoderms. — The neuroepithelium exhibits the organization of an epidermis with well-developed nervous elements. Glial cells are not present. The support cells are the true epithelial cells. Their monociliated cell bodies border the lumen and, by means of cytoplasmic stems that contain a bundle of filaments, they reach up to the basal lamina. The nerve cells and their trunk of nerve fibres fill the spaces between the support cells. — Three types of nerve cells can be distinguished according to their polarity: (1) Primary sensory cells that project a cilium into the epineural canal, the axon hillock region is at the opposite pole. (2) Subluminal cells whose cilium originates in the axon hillock region. (3) Neurones that lie within the trunk of nerve fibres. They are highly stretched in the direction of the nerve cord and are also provided with a cilium. Types 2 and 3 may be homologized with the basal nerve cells of the epidermis. They are possibly multipolar. — The lateral nerve cords make contact with the ampulla and pass the ambulacral plate parallel to the channel that connects the ampulla and the tube foot. The activity of the tube foot-ampulla system is possibly controlled by means of transmitter substances that diffuse through the connective tissue layer between the nerve cord and the myoepithelia of the ampulla and the tube foot respectively.

Isolation of the neuropeptide SALMFamide-1 from starfish using a new antiserum

We have raised antisera in rabbits to a conjugate of thyroglobulin and Lys-Tyr-Ser-Ala-Leu-Met-Phe-NH 2 (KYSALMFamide), a synthetic analog of the starfish neuropeptide S1 (Gly-Phe-Asn-Ser-Ala-Leu-Met-Phe-NH 2). The sensitivity and specificity of two antisera (BL and SL) for S1 were established by testing the ability of S1 and structurally related peptides (SALMFamide-2 and various FMRFamide-related peptides) to displace iodinated KYSALMFamide from the serum antibodies in an RIA. Both antisera are sensitive to femtomolar amounts of S1. BL is highly specific for S1 but SL is not, since it is also able to detect femtomolar amounts of the FMRFamide-related peptides. We have used the BL antiserum in the RIA to monitor the purification of S1 immunoreactivity from radial nerve cord extracts of both Asterias rubens and Pycnopodia helianthoides. The partial amino acid sequence GFNSALM was obtained from automated Edman degradation sequencing of pure immunoreactive peaks from both species.