Sensory innervation of the tentacles of the polychaete,Sabella pavonina

Summary Following observation of conical groups of stiff, but motile cilia on the tentacles of the branchial crown of Sabella pavonina, these were examined with the electron microscope. The bundles consist of about 40 unenclosed standard cilia supported by one or two primary sense cells with centrally directed axons of 0.1–0.2 diameter. Axons in the distal portions of the branchial crown occur in small bundles surrounded by a basement membrane. More centrally, glial elements appear and the nerves are surrounded by a collagenous sheath. The branchial nerve trunk shows similarities in organisation to other previously investigated annelid central nervous tissue in that the whole nerve is surrounded by a fibrous sheath central to which there is a layer of glial cells with processes penetrating a central neuropile. The 0.1–0.2 axons commonly occur in glial-enveloped groups of < 40 whilst other axons of larger and mixed diameter are found together.Each tentacle has two branchial nerves on the oral side, and each nerve gives rise to two small 75-axon branches running to each pinnule. The branchial nerves fuse to form the branchial nerve trunk running to the supra-oesophageal ganglia.Sections of the branchial nerves of the branchial crown at progressively more central levels show that the branchial nerve trunk contains enough axons of 0.1–0.2 diameter to account for all the sensory cells on the tentacles. This is taken as evidence for the sensory cells having axons terminating within the central nervous system and that there is no peripheral confluence or fusion of these afferent axons.     

Serotonergic and FMRFamidergic nervous systems in gymnolaemate bryozoan larvae

A growing body of data from nervous systems of marine invertebrate larvae provides an ideal background for comparisons among higher taxa. The currently available data from Bryozoa, however, do not allow for a consistent hypothesis of an ancestral state for this taxon, which would be necessary for phylogenetic inferences. The larval nervous systems of the four gymnolaemate species Flustrellidra hispida, Bugula fulva, Alcyonidium gelatinosum, and Bowerbankia gracilis are examined by means of antibody staining against the neurotransmitters serotonin and FMRFamide, as well as against acetylated α-tubulin. Despite considerable variation, a comparison reveals a common pattern of the distribution of serotonin. The neurotransmitter is found in at least two cells in the apical organ as well as in paired axial and lateral nerves emerging from a central nerve nodule. A ring nerve is present below the corona and at least two serotonergic cells are found between the corona cells. Serotonergic coronal cells might represent unique bryozoan features, whereas the remaining elements show resemblance to the situation found in most spiralian taxa. The data do not provide support for a closer relationship of Bryozoa to Phoronida or Brachiopoda.     

Topology of the nervous system of Notommata copeus (Rotifera: Monogononta) revealed with anti-FMRFamide, -SCPb, and -serotonin (5-HT) immunohistochemistry

Abstract. The nervous system of the benthic freshwater rotifer, Notommata copeus , was examined using antibody probes, epifluorescence and confocal laser scanning microscopy, and digital imaging to highlight similarities with other monogonont rotifers. Immunoreactivity to anti-FMRFamide (Phe–Met–Arg–Phe–NH₂), -SCPb (small cardioactive peptide b), and -serotonin (5-HT, 5-hydroxytryptamine) was present in the central, peripheral, and stomatogastric nervous system. Specifically, anti-FMRFamide and -SCPb staining was abundant in perikarya and neurites of the cerebral ganglion, ventrolateral nerve cords, and mastax. In addition, a single loop-like neurite was present in between the nerve cords at the posterior end of the body. Serotonergic neurites were also abundant, and highlighted several cerebral pathways that included connections to the nerve cords and possibly the mastax. Novel neural pathways were also present in the posterior trunk region, where serotonergic neurites innervated the foot and lateral body wall. The results presented herein also highlight the utility of 3D visualization software to gain further insights into the organization and architecture of the rotifer cerebral ganglion.     

The nervous system of the tube-worm Chaetopterus variopedatus (Polychaeta)

Silver impregnation of serial histological sections of the tubeworm Chaetopterus variopedatus revealed the presence of a subepidermal nervous system. The anterior nervous system is delimited by the first 11 segments and comprises (1) two dorsolateral cerebral ganglia and lateral instead of ventral nerve cords which are widely separated and thus connected by unusually long commissures, (2) a pharyngeal ganglion in the fourth segment which is connected to the cerebral ganglia by pharyngeal nerves and constitutes along with the pharyngeal plexus a stomatogastric or enteric nervous system, and (3) small, presumably segmental ganglionic swellings along the lateral nerve cords from which emerge commissures and parapodial nerves. No subesophageal ganglion or periesophageal connective could be identified. The lateral nerve cords converge toward the midline in the 12th segment to form the posterior nervous system comprising a pair of ventromedian nerve cords with their repetitive segmental ganglia from which emerge numerous short commissures and three segmental nerves coursing toward the dorsal and ventral regions of parapods and toward the neuropod. Light and electron microscopic investigations of cerebral and segmental ganglia showed an arrangement of inner neuropile and of unipolar neuron somata at the periphery. The neuropile comprises numerous neurites ranging in diameter from 0.5 to 10 μm and making polarized or symmetrical synaptic junctions with each other. The pharyngeal ganglion consists of a similar neuropile and of a large mass of cell bodies which is traversed by an elaborate network of sinuses and harbors three types of neurosecretory cells in addition to the conventional neuron somata. These findings are interpreted in the framework of the highly specialized morphological features and habits of Chaetopterus, and the welldeveloped stomatogastric system is considered to be related to control of the feeding activities.     

The nervous system of <Emphasis Type="Italic">Paludicella articulata</Emphasis> - first evidence of a neuroepithelium in a ctenostome ectoproct

Introduction

Comparatively few data are available concerning the structure of the adult nervous system in the Ectoprocta or Bryozoa. In contrast to all other ectoprocts, the cerebral ganglion of phylactolaemates contains a central fluid-filled lumen surrounded by a neuroepithelium. Preliminary observations have shown a small lumen within the cerebral ganglion of the ctenostome Paludicella articulata. Ctenostome-grade ectoprocts are of phylogenetic relevance since they are considered to have retained ancestral ectoproct features. Therefore, the ctenostome Paludicella articulata was analyzed in order to contribute to the basal neural bauplan of ctenostomes and the Ectoprocta in general.

Results

The presence of a lumen and a neuroepithelial organization of the nerve cells within the cerebral ganglion are confirmed. Four tentacle nerves project from the cerebral ganglion into each tentacle. Three of the tentacle nerves (one abfrontal and two latero-frontal nerves) have an intertentacular origin, whereas the medio-frontal nerve arises from the cerebral ganglion. Six to eight visceral nerves and four tentacle sheath nerves are found to emanate from the cerebral ganglion and innervate the digestive tract and the tentacle sheath, respectively.

Conclusions

The situation in P. articulata corresponds to the situation found in other ctenostomes and supports the notion that four tentacle nerves are the ancestral configuration in Ectoprocta and not six as proposed earlier. The presence of a lumen in the ganglion represents the ancestral state in Ectoprocta which disappears during ontogeny in all except in adult Phylactolaemata and P. articulata. It appears likely that it has been overlooked in earlier studies owing to its small size.

     

Phylogenetic development of myelin glycosphingolipids

Myelin is a highly specialized membrane, which enwraps axons and facilitates saltatory nerve conduction in vertebrates. Galactocerebroside and its sulfate ester, sulfatide, are highly localized in myelin. To understand the role played by these galactosphingolipids we investigated the changes of these myelin-specific compounds during the course of the evolution of myelin. We found that urodele nerve myelin lacks alpha-hydroxy fatty acid-containing galactosphingolipids. Our morphological and physiological studies of urodele nerves indicated that these hydroxy fatty acid-containing galactosphingolipids probably contribute to fast nerve conduction. Also it is suspected that they are involved in the regulation of the thickness of myelin in relation to the size of the axon. In another study, we discovered that glucocerebroside, which has glucose instead of galactose as its carbohydrate component, is abundantly present in the myelin-like sheath membrane of crustacean nerves. Subsequently, the phylogenetic study indicated that galactocerebrosides were limited to the nervous system of deuterostomes, while all protostome nerves contain glucocerebrosides. The role of glucocerebrosides in multilayered membranes and in the conduction velocity of the protostome nervous system is discussed.     

Immunocytochemistry of the neuromuscular systems of Loxosomella vivipara and L. parguerensis (Entoprocta: Loxosomatidae)

Little detailed information exists on the anatomy of the nervous system and the musculature of Entoprocta. Herein we describe the distribution of the neurotransmitters RFamide and serotonin as well as the myo-anatomy of adults and asexually produced budding stages of the solitary entoproct species Loxosomella vivipara and L. parguerensis using immunocytochemistry and epifluorescence as well as confocal microscopy. The development of the RFamidergic and serotonergic nervous system starts in early budding stages. In the adults, RFamide is present in the bilateral symmetric cerebral ganglion, a pair of oral nerves that innervate two pairs of nerve cell clusters in the heel of the foot, a pair of aboral nerves, the paired lateral nerves, the calyx nerves, the atrial ring nerve, the tentacle nerves, the stomach nerves, and the rectal nerves. Serotonin is only found in the cerebral ganglion, the oral nerves, and in the tentacle nerves. Some differences in the distribution of both neurotransmitters were found between L. vivipara and L. parguerensis and are most obvious in the differing number of large serotonergic perikarya associated with the oral nerves. Nerves arising from the cerebral ganglion and running in a ventral direction have not been described for Entoprocta before, and the homology of these to the ventral nerve cords of other Spiralia is considered possible. The body musculature of both Loxosomella species comprises longitudinal and diagonal muscles in the foot, the stalk, and the calyx. We found several circular muscles in the calyx. The stalk and parts of the foot and the calyx are surrounded by a fine outer layer of ring muscles. In addition to the congruent details regarding the myo-anatomy of both species, species-specific muscle structures could be revealed. The comparison of our data with recent findings of the myo-anatomy of two Loxosoma species indicates that longitudinal and diagonal body muscles, atrial ring muscles, tentacle muscles, esophageal and rectal ring muscles, as well as intestinal and anal sphincters are probably part of the ancestral entoproct muscle bauplan.     

Ultrastructure of the adhesive tentacles of the limnomedusa Vallentinia gabriella (Hydrozoa,Olindiadidae)

Summary The specialized adhesive exumbrellar tentacles of the limnomedusa Vallentinia gabriella were examined by light microscopy and scanning and transmission electron microscopy. The adhesive region first differentiates some distance from the tentacle tip. As differentiation proceeds the distal part is reduced and the adhesive region comes to lie at the tentacle tip. The adhesive epithelium consists of flagellated and non-flagellated glandular cells, a few nematocytes, and a nerve plexus. The glandular cells are characterized by electron-dense granules and bundles of microtubules. The microtubules, being anchored to the mesoglea, are oriented parallel to the longitudinal axis of the cell and extend up to the cell apex. It can be assumed that the microtubules are involved in the transport of secretory granules to the cell apex. Bundles of neurites run adjacent to the mesoglea between the basal processes of the glandular cells. The neurites form interneural synapses and synapses with glandular cells. It is suggested that detachment of the specialized adhesive tentacles is under nervous control.     

Tentacle development in dermophis mexicanus (amphibia,gymnophiona) with an hypothesis of tentacle origin

The development of the tentacle, a chemosensory and perhaps tactile structure unique among vertebrates to gymnophione amphibians is described in Dermophis mexicanus and Gymnopis multiplicata. The tentacle is associated with the vomeronasal organ and its glands, and utilizes several structures usually associated with the eye, such as the Harderian gland, the retractor and levator muscles, and their nerves. Innervation of the tentacle itself is from the trigeminal nerve. We present an hypothesis that the tentacle originated from modified eye components.     

Le système nerveux des cténaires

Summary Ultrastructural evidence is given of the occurrence of nervous elements in the mesoglea of Ctenophores based on the presence of the typical synapses of this phylum.In Beroids, nervous fibers from the ectodermal nerve-net cross the epithelial basal membrane and run through the mesoglea; they are devoid of any ensheathing cell. These neurites build highly differentiated synapses upon the muscles and upon peculiar cells, tentatively named mesenchymal cells.In Cydippids, nerve fibers and nerve cell-bodies have been observed in the mesoglea of the tentacles. The mesogleal core of each tentacle contains mesenchymal cells and a thick strand of neurons and neurites, forming a kind of elongated ganglion. Neurites of either the axial neurones or the epithelial nerve-net neurones form numerous radial nerve strands across the tentacular muscles. Interneural, neuro-muscular and neuro-mesenchymal junctions are very frequent in the tentacle.As far as the organization of the mesoglea is concerned, the Ctenophora thus appear closer to Turbellaria than to Cnidaria.

Ce travail a bénéficié de la collaboration technique de Madame J. Amsellem que nous remercions vivement.     

Polymer hollow fiber-encapsulated peripheral nerve extracts change their activity towards injured hippocampal neurites in rats

The regeneration of the adult mammalian central nervous system (CNS) requires changes of the nonpromising environment. Applying peripheral nerve grafts and their extracts are both the useful method to induce regeneration of injured CNS neurites. Our previous reports showed that degeneration of peripheral nerves enhanced their neurotrophic activity in a time-dependent manner. Electrophoretical analysis of proteins obtained from degenerating sciatic nerves revealed significant changes in fractions of low molecular mass. The aim of the present work was to examine the influence of fractionated extracts from 7-day-predegenerated and non-predegenerated peripheral nerves upon injured hippocampal neurites in adult rats. The extracts were closed in fibrin-filled connective tissue chambers (CTC) or within CTC-wrapped polymer hollow fibers (PHF) of 30 kDa cut-off. The cell bodies of regrowing fibers were labeled with FITC-HRP. The CTCs appeared to be useful tool for implantation of artificial grafts into mammalian CNS. Full-spectrum nerve extracts induced strong regeneration of injured hippocampal neurites. The number of labeled cells within hippocampus was significantly lower in PHF groups than in CTC ones, indicating that low-mass proteins present in peripheral nerve extracts are not sufficient to induce successful regeneration.     

Myoanatomy and serotonergic nervous system of plumatellid and fredericellid phylactolaemata (lophotrochozoa,ectoprocta)

The phylogenetic position of the Ectoprocta within the Lophotrochozoa is discussed controversially. For gaining more insight into ectoproct relationships and comparing it with other potentially related phyla, we analysed the myoanatomy and serotonergic nervous system of adult representatives of the Phylactolaemata (Plumatella emarginata, Plumatellavaihiriae, Plumatella fungosa, Fredericella sultana). The bodywall contains a mesh of circular and longitudinal muscles. On its distal end, the orifice possesses a prominent sphincter and continues into the vestibular wall, which has longitudinal and circular musculature. The tentacle sheath carries mostly longitudinal muscle fibres in Plumatella sp., whereas F. sultana also possesses regular circular muscle fibres. Three groups of muscles are associated with the lophophore: 1) Lophophoral arm muscles (missing in Fredericella), 2) epistome musculature and 3) tentacle musculature. The epistome flap is encompassed by smooth muscle fibres. A few fibres extend medially over the ganglion to its proximal floor. Abfrontal tentacle muscles have diagonally arranged muscle fibres in their proximal region, whereas the distal region is formed by a stack of muscles that resemble an inverted ‘V’. Frontal tentacle muscles show more variation and either possess one or two bases. The digestive tract possesses circular musculature which is striated except at the intestine where it is composed of smooth muscle fibres. The serotonergic nervous system is concentrated in the cerebral ganglion. From the latter a serotonergic nerve extends to each tentacle base. In Plumatella the inner row of tentacles at the lophophoral concavity lacks serotonergic nerves. Bodywall musculature is a common feature in many lophotrochozoan phyla, but among other filter feeders like the Ectoprocta is only present in the ‘lophophorate’ Phoronida. The longitudinal tentacle musculature is reminiscent of the condition found in phoronids and brachiopods, but differs to entoproct tentacles. Although this study shows some support for the ‘Lophophorata’, more comparative analyses of possibly related phyla are required. J. Morphol., 2011. © 2011 Wiley Periodicals, Inc.     

The nervous system of <Emphasis Type="Italic">Convolutriloba</Emphasis> (Acoela) and its patterning during regeneration after asexual reproduction

We describe the serotonergic and cholinergic nervous system of the asexually reproducing acoel Convolutriloba longifissura Bartolomaeus & Balzer, 1997 by means of immunohistochemistry, conventional histochemistry and transmission electron microscopy. Immunocytochemical staining for serotonin revealed neurons in the brain, in a pair of ventral main longitudinal cords, in two pairs of smaller dorsal longitudinal nerve cords, and in a submuscular nerve net. The brain comprises a ventral-anterior commissure and a less intensely stained dorsal commissure joined together by connectives into a three-ringed scaffold from which the longitudinal nerves extend. We followed the regeneration of the serotonergic part of the nervous system up to the second day after fission. Within this time period, the offspring reestablished bilateral symmetry in the nervous system and developed full motor control. The presence of aminergic cell bodies associated with the main lateral nerve cords of C. longifissura shows that the acoelan nervous system is more similar to that of other platyhelminths (triclads, rhabditophorans) than previously assumed. The presence of serotonergic cell bodies along the main nerve cord correlates with the capacity for asexual reproduction via fissioning. We also describe the single fission mode of C. hastifera Winsor 1990, which brings the modes of asexual reproduction employed by members of the Convolutrilobinae to three.     

The ring nerve of the box jellyfish <Emphasis Type="Italic">Tripedalia cystophora</Emphasis>

Box jellyfish have the most elaborate sensory system and behavioural repertoire of all cnidarians. Sensory input largely comes from 24 eyes situated on four club-shaped sensory structures, the rhopalia, and behaviour includes obstacle avoidance, light shaft attractance and mating. To process the sensory input and convert it into the appropriate behaviour, the box jellyfish have a central nervous system (CNS) but this is still poorly understood. The CNS has two major components: the rhopalial nervous system and the ring nerve. The rhopalial nervous system is situated within the rhopalia in close connection with the eyes, whereas the ring nerve encircles the bell. We describe the morphology of the ring nerve of the box jellyfish Tripedalia cystophora as ascertained by normal histological techniques, immunohistochemistry and transmission electron microscopy. By light microscopy, we have estimated the number of cells in the ring nerve by counting their nuclei. In cross sections at the ultrastructural level, the ring nerve appears to have three types of neurites: (1) small “normal”-looking neurites, (2) medium-sized neurites almost completely filled by electron-lucent vacuoles and (3) giant neurites. In general, only one giant neurite is seen on each section; this type displays the most synapses. Epithelial cells divide the ring nerve into compartments, each having a tendency to contain neurites of similar morphology. The number and arrangement of the compartments vary along the length of the ring nerve. Dan Nilsson acknowledges grant no. 621-2002-4873 from the Swedish Research Council. Anders Garm acknowledges grant no. 2005-1-74 from the Carlsberg Foundation.     

Localization of a substance P-like material in the central and peripheral nervous system of the snail Helix aspersa

Summary A monoclonal antibody against substance P was used for immunocytochemical staining of the central ganglia of the snail Helix aspersa and several peripheral tissues including the gut, reproductive system, cardiovascular system, tentacle and other muscles.Within the central ganglia many neurones, and many fibres in the neuropile and the nerves entering the ganglia, were stained for the SP-like material. The largest numbers of reactive cell bodies were in the pleural ganglia and on the dorsal surfaces of the pedal ganglia. A group of cells was also found, surrounding the right pedal-cerebral connective, that did not fluoresce, but were enveloped by reactive processes terminating directly onto the neurone somata.Specific staining was observed in all peripheral tissues examined and always appeared to be concentrated in nerve terminals. Most particularly these occurred in the heart and aorta, the pharyngeal retractor muscle and the tentacle. Although mostly present in muscular tissues, some fluorescence was also observed in the nervous layer surrounding the retina. The tentacular ganglion also contained immunoreactive cell bodies.     

Organization and ultrastructure of the nervous system in Catenulida (Turbellaria)

Summary The fine structure of the nervous system of lower fresh-water Turbellaria was investigated. This system consists of a brain, short nerve trunks and a network of subepithelial nerve cells. The brain structure shows ganglion cells and their proccesses, forming a neuropil. The ganglion cells are most probably unipolar. The perikaryon contains numerous ribosomes, few mitochondria, and golgi complexes. Thus it corresponds structurally to neuroblasts of higher animals. The neurites contain mitochondria, neurotubules, and empty or dense core vesicles. All (inStenostomum sp.) or some of the nerve cells (inCatenula sp.) have neurosecretory vesicles.