The nervous system ofNectonema munidae andGordius aquaticus,with implications for the ground pattern of the Nematomorpha

 The nervous system of Nectonema munida is shown to be composed of a brain, a ventral nerve cord with an anterior and a posterior enlargement, a dorsal nerve cord and a plexus-like basiepidermal nervous system. The ultrastructure of these parts is given. Additionally, the ventral nerve cord of Gordius aquaticus is ultrastructurally described. The results are compared with the literature to work out the ground pattern of the Nematomorpha according to the nervous system. This contains a circumpharyngeal brain with a main subpharyngeal portion and a weak suprapharyngeal portion, a ventral and dorsal intraepidermal nerve cord and a peripheral nervous system. The ground pattern of the nervous system of Nematomorpha is then compared to that of other Nemathelminthes. The form of the brain and the distribution of perikarya are derived characters of the Nematomorpha. The existence of an unpaired ventral and an unpaired dorsal nerve cord and the position of these two cords in epidermal cords are synapomorphies of the Nematomorpha and the Nematoda. Accepted: 7 July 1996     

Localisation of GYIRFamide immunoreactivity inMacrostomum hystricinum marinum (Plathelminthes,Macrostomida)

The distribution of GYIRFamide immunoreactivity in the nervous system ofMacrostomum hystricinum marinum has been demonstrated by an indirect fluorescence technique in conjunction with confocal scanning laser microscopy (CSLM). Immunostaining was extensive in both the central (CNS) and peripheral (PNS) nervous systems, revealing detailed information on the microanatomy of the peptidergic nervous system of this free-living plathelminth. In the CNS, immunoreactive nerve cell bodies and nerve fibres occurred in the brain and along two pairs of longitudinal nerve cords: the main nerve cords and the ventral nerve cords. In the PNS, immunostaining was prevalent in nerve cells and fibres innervating the pharynx and the gut. The employed antibody is directed against a recently characterised FMRF-amide-related peptide (FaRP), GYIRFamide, isolated from two species of the Tricladida,Dugesia tigrina andBdelloura candida. Phylogenetically, GYIRFamide represents the most ancient neuropeptide thus far identified within the Bilateria     

Ciliary and nervous structures in juvenile females of the annelid Dinophilus gyrociliatus (O. Schmidt, 1848) (Annelida: Polychaeta)

Ciliary and nerve structures were described in juvenile female Dinophilus gyrociliatus (O. Schmidt, 1848) after immunochemical staining with tubulin, serotonin, and FMRFamide antibodies. Anti-tubulin antibodies revealed the following external structures: two head and seven body ciliary bands, a ventral ciliary band, and head ciliary fields. Gut cilia and five pairs of protonephridia were detected inside the body. The nervous system consists of an oval headed neuropile with anterior and posterior nerves extending from it, seven longitudinal nerve cords, commissures, and circular nerves. Anti-serotonin antibodies revealed the head neuropile, neurons at the base of the ventral ciliary band, an oesophageal ring, and seven longitudinal ventral cords. Anti-FMRFamide antibodies revealed approximately ten neurons in the cerebral ganglion, five longitudinal cords, and the oesophageal and caudal-nerve rings. The presented data suggest the simplification of the nervous system structure in D. gyrociliatus, which probably reflects pedomorphosis.     

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.     

Glyoxylic acid induced fluorescence in the nervous system of Gyratrix hermaphroditus (Kalyptorhynchia,Polycystididae)

Catecholamines (CAs) are found in the neuropile of the brain, in 3 pairs of longitudinal nerve cords, in the transverse ventral commissure, in anterior ventral and dorsal nerves, in two pharyngeal nerve rings and in 24 neurons in the nervous system of Gyratrix hermaphroditus. The CA distribution pattern in compared with those of other neuroactive substances. Homology of neurons in the family of Polycystididae and in Plathelminthes in general is discussed.     

Muscle fibers in the central nervous system of nemerteans: Spatial organization and functional role

The system of muscle fibers associated with the brain and lateral nerve cords is present in all major groups of enoplan nemerteans. Unfortunately, very little is known about the functional role and spatial arrangement of these muscles of the central nervous system. This article examines the architecture of the musculature of the central nervous system in two species of monostiliferous nemerteans (Emplectonema gracile and Tetrastemma cf. candidum) using phalloidin staining and confocal microscopy. The article also briefly discusses the body‐wall musculature and the muscles of the cephalic region. In both species, the lateral nerve cords possess two pairs of cardinal muscles that run the length of the nerve cords and pass through the ventral cerebral ganglia. A system of peripheral muscles forms a meshwork around the lateral nerve cords in E. gracile. The actin‐rich processes that ramify within the nerve cords in E. gracile (transverse fibers) might represent a separate population of glia‐like cells or sarcoplasmic projections of the peripheral muscles of the central nervous system. The lateral nerve cords in T. cf. candidum lack peripheral muscles but have muscles similar in their position and orientation to the transverse fibers. The musculature of the central nervous system is hypothesized to function as a support system for the lateral nerve cords and brain, preventing rupturing and herniation of the nervous tissue during locomotion. The occurrence of muscles of the central nervous system in nemerteans and other groups and their possible relevance in taxonomy are discussed. J. Morphol. 2012. © 2012 Wiley Periodicals, Inc.     

The organization of the nervous system in Plathelminthes. The neuropeptide F-immunoreactive pattern in Catenulida,Macrostomida, Proseriata

The organization of the nervous system of Archilopsis unipunctata Promonotus schultzei and Paramonotus hamatus (Monocelididae, Proseriata) and Stenostomum leucops (Catenulida) and Microstomum lineare (Macrostomida) was studied by immunocytochemistry, using antibodies to the authentic flatworm neuropeptide F (NPF) (Moniezia expansa). The organization of the nervous system of the Monocelididae was compared to that of the nervous system of Bothriomolus balticus (Otoplanidae), a previously studied species of another family of the Proseriata. The results show that the main nerve cords (MCs), independent of lateral or ventral position in the Monocelididae and the Otoplanidae, correspond to each other. The study also confirms the status of the lateral cords as main cords (MCs) in S. leucops and M. lineare. Common for MCs in the members of the investigated taxa are the following features: MCs consist of many fibres, originate from the brain and are adjoined to 5-HT-positive neurons. In Monocelididae and Otoplanidae, the MCs additionally have the same type of contact to the pharyngeal nervous system. Also common for both proseriate families is the organization of the two lateral nerve cords, with weaker connections to the brain, and the pair of dorsal cords running above the brain. The organization of the minor cords differs. The Monocelididae have a pair of thin ventral cords forming a mirror image of the dorsal pair. Furthermore, an unpaired ventral medial cord connecting medial commissural cells was observed in P. schultzei. Marginal nerve cords, observed in Otoplanidae, are absent in Monocelididae. All minor nerve cords are closely connected to the peripheral nerve plexus. The postulated trends of condensation of plexal fibres to cords and/or the flexibility of the peripheral nerve plexus are discussed. In addition, the immunoreactivity (IR) pattern of NPF was compared to the IR patterns of the neuropeptide RFamide and the indoleamine, 5-HT (serotonin). Significant differences between the distribution of IR to NPF and to 5-HT occur. 5-HT-IR dominates in the submuscular and subepidermal plexuses. In the stomatogastric plexus of M. lineare, only peptidergic IR is observed in the intestinal nerve net. The distribution of NPF-IR in fibres and cells of the intestinal wall in M. lineare indicates a regulatory function for this peptide in the gut, while a relationship with ciliary and muscular locomotion is suggested for the 5-HT-IR occurring in the subepidermal and submuscular nerve, plexuses. In M. lineare, the study revealed an NPF- and RFamide-positive cell pair, marking the finished development of new zooids. This finding indicates that constancy of these cells is maintained in this asexually reproducing and regenerating species.     

Architecture of the nervous system in two Dactylopodola species (Gastrotricha, Macrodasyida)

Immunohistochemical stainings have become standard tools to describe the nervous system, but usually only singular or few markers are used and consequently show only subsets of neurons within the nervous system. We investigated two species of Dactylopodola (Gastrotricha, Macrodasyida) with a broad set and combination of markers, to represent the nervous system in a more holistic approach. We suggest that markers for both neurotubuli (tubulin) and neurotransmitters (e.g. serotonin, FMRF-amides, histamine) should be used. Combinations with markers for the musculature (phalloidin) and nuclei (propidiumiodide or other markers) help to reveal spatial patterns and when used with TEM can provide a more precise picture of the spatial relationships of particular nerves. Species of Dactylopodola have a brain consisting of a solid dorsal commissure and a fine ventral commissure. Cell somata of brain cells are arranged lateral to the dorsal commissure and form a dumbbell-like brain. Additionally, projections into the head region, head sensory organs, one pair of lateroventral nerve cords with three commissures and stomatogastric nerves are described. Obviously, some longitudinal transmitter-specific fibres run in parallel to the main longitudinal nerve and represent additional longitudinal fibres. In comparison with the nervous system architecture of other gastrotrich species and that of different bilaterian animals it is speculated that the gastrotrich nervous system retains several ancestral features, such as being commissural and not a compact brain.     

Distribution and partial characterization of CREB-like immunoreactivity in the medicinal leech Hirudo

The presence and distribution of immunoreactivity to the cyclic AMP response element binding protein (CREB) were determined in the central nervous system (CNS) and in peripheral tissues of the medicinal leech Hirudo. Western blots revealed several CREB-immunoreactive (CREB-IR) bands including one whose molecular weight (43–44 kDa) was similar to mammalian CREB. The 43–44 kDa CREB-like protein was detected in nuclear extracts of the ventral nerve cord and was not observed following preincubation of the primary antiserum with the epitope sequence. CREB-like immunoreactivity was detected in extracts from each of six regions of the leech CNS, and in extracts from leech body wall musculature, crop, intestine, jaw musculature, pharynx, and salivary tissues. Whole mounts of leech ganglia revealed specific CREB-IR in a restricted population of neurons distributed throughout the leech CNS. Apparent homologues to a pair of CREB-IR dorsolateral neurons were observed in most ganglia along the ventral nerve cord. Several CREB-IR neurons exhibited segmental specificity. A number of neurons stained with an antiserum to the cyclic AMP response element modulator (CREM). These neurons showed no overlap in location with CREB-IR neurons, and this staining was not eliminated with a preabsorption control. Possible roles for a CREB-like protein in the leech are discussed. Electronic Publication     

Serotonin-and FMRFamide-immunoreactive nerve elements in the chiton Lepidopleurus asellus (Mollusca,Polyplacophora)

The distribution of serotonin-like and FMRFamide-like immunoreactive (5HT-ir and FMRFa-ir, respectively) neurons in the nervous system of the chiton Lepidopleurus asellus (Mollusca, Polyplacophora) was studied using an immunocytochemical technique. The neurons were distributed in characteristic patterns in the central nervous system, the 5HT-ir neurons predominating in the ventral (pedal) cords and FMRFa-ir neurons in the lateral cords. In the body wall including the foot, a tight network of 5HT-ir and FMRFa-ir nerve fibers is found, the former being mostly attributed to the musculature whereas the latter seems to be associated with the blood sinuses. Intraepithelial neurons of both types are abundant in the fore-and hindgut. The presence and general distribution in the central and peripheral nervous system of the 5HT-ir and FMRFa-ir elements seems thus to be similar in simple and advanced molluscs. The relationship between these neurons and their targets in the body also appears to be well conserved in molluscs.     

Organization of the nervous system in Opisthorchis viverrini investigated by histochemical and immunohistochemical study

The structure and organization of the nervous system has been documented for various helminth parasites. However, the neuroanatomy of the carcinogenic liver fluke, Opisthorchis viverrini has not been described. This study therefore investigated the organization of the nervous system of this fluke using cholinesterase activity, aminergic and peptidergic (FMRFamide-like peptides) immunostaining to tag major neural elements. The nervous system, as detected by acetylcholinesterase (AchE) reaction, was similar in newly excysted metacercariae, migrating juveniles and adult parasites. In these stages, there were three pairs (dorsal, ventral and lateral) of bilaterally symmetrical longitudinal nerve cords and two cerebral ganglia. The ventral nerve cords and the cerebral ganglia were well-developed and exhibited strong AchE reactivity, as well as aminergic and FMRFamide-like immunoreactivity. Numerous immunoreactive nerve cell bodies were observed around the inner surface of the ventral sucker. Fine FMRFamide-like peptides immunopositive nerve fiber was rarely observed. Overall, the organization of the nervous system of O. viverrini is similar to other trematodes.     

The nervous system of Bothriomolus balticus (Proseriata) —a contribution to the knowledge of the orthogon in the Plathelminthes

Summary The nervous system (NS) of Bothriomolus balticus (Proseriata) was studied by the immunocytochemical (ICC) method with antisera to RFamide, SALMFamide and serotonin and with the histochemical GAIF method. The use of the ICC technique provided a much more precise morphological account of the nervous system than had previously been possible. The obtained data are discussed in connection with the comparative morphology of the nerve cords of the Plathelminthes. A similar position does not grant direct correspondence between nerve cords in the taxon Seriata. Marginal cords had probably an independent origin in the Monocelididae and Otoplanidae. The ventral (main) cords of B. balticus seem to correspond to the lateral (main) cords of the Monocelididae. It can be hypothesized that both: (1) a shift of the main cords accompanied by formation of new cords from the plexus and fusion of other cords and (2) a redistribution of nerve processes and perikarya between the cords, take part in the evolution of cords in the Plathelminthes. The first hypothesis seems to explain the difference in the position of main cords in proseriates, though, the second hypothesis might dominate, for example, in the Neorhabdocoela and the Neodermata. The correctness of the evolutionary analysis of the nerve cords in plathelminths can only be provided by neurons or neuron groups marking these structures.     

Ventral nerve cord in Phoronopsis harmeri larvae

The nervous system organization is considered a phylogenetically important character among metazoans. The phylum Phoronida is included in a supraphyletic taxon known as Lophotrochozoa. Many lophotrochozoans possess a metameric ventral nerve cord as adults or larvae. Phoronids do not exhibit external metamery either as larvae or as adults. The current study describes the ventral nerve cord in the young larva of Phoronopsis harmeri. This structure is apparent both in the serotonergic and FMRF-amidergic nervous system in young larvae. The ventral nerve cord extends from the mouth to the tentacular ridge. Both serotonergic and FMRF-amidergic components consist of two ventrolateral nerves, each with several unipolar neurons. The ventrolateral nerves connect to each other by means of thin repetitive transversal nerves ("commissures"). The abundance of neurons and nerves in the epidermis of the oral field of actinotrocha larva likely reflects the importance of this area in collection of food particles. The ventral nerve cords of the actinotrocha and the metatrochophore differ in their positions with respect to ciliated bands: the cord is located between the preoral and postoral ciliated bands in the actinotrocha but between the postoral ciliated band and telotroch in the metatrochophore. The presence of the ventral nerve cord, which contains repetitive elements (neurons and "commissures"), in the early development of P. harmeri may recapitulate some stages of nervous system development during phoronid phylogeny. The larval nervous system does not contain nervous centers under the tentacular ridge that can correlate with the catastrophic metamorphosis and unique body plan of phoronids.     

Nervous network in larvae of the ascidian Ciona intestinalis

 With the use of the monoclonal antibody UA301, which specifically recognizes the nervous system in ascidian larvae, the neuronal connections of the peripheral and central nervous systems in the ascidian Ciona intestinalis were observed. Three types of peripheral nervous system neurons were found: two located in the larval trunk and the other in the larval tail. These neurons were epidermal and their axons extended to the central nervous system and connected with the visceral ganglion directly or indirectly. The most rostral system (rostral trunk epidermal neurons, RTEN) was distributed bilateral-symmetrically. In addition, presumptive papillar neurons in palps were found which might be related to the RTEN. Another neuron group (apical trunk epidermal neurons, ATEN) was located in the apical part of the trunk. The caudal peripheral nervous system (caudal epidermal neurons, CEN) was located at the dorsal and ventral midline of the caudal epidermis. In the larval central nervous system, two major axon bundles were observed: one was of a photoreceptor complex and the other was connected with RTEN. These axon bundles joined in the posterior sensory vesicle, ran posteriorly through the visceral ganglion and branched into two caudal nerves which ran along the lateral walls of the caudal nerve tube. In addition, some immunopositive cells existed in the most proximal part of the caudal nerve tube and may be motoneurons. Received: 8 September 1997 / Accepted: 14 December 1997     

Demonstration of motoneuron-12 sparing in cultured Manduca sexta ventral nerve cords

The emergence of the adult Manduca sexta moth is accompained by the death of half of the neurons present in the pupal abdominal nervous system (Truman, 1983). This developmental neuronal death is highly selective, so that the same neurons die at the same time relative to emergence in every moth. In the case of the MN-12 motoneurons, this cell death is regulated both by hemolymph concentrations of a steroid hormone, 20-hydroxyecdysone, and by actions exerted by adjacent ganglia (Truman and Schwartz, 1984; Fahrbach and Truman, 1987). This latter effect, which has been previously described in isolated abdomens and in moths with transected ventral nerve cords, has now been reproduced under controlled culture conditions in which the selectivity and extent of postemergence neuronal death is comparable to that seen in vivo. With respect to the MN-12 neurons found in the most anterior unfused abdominal ganglion, A₃, the pterothoracic ganglion appears to be the source of a factor that permits these neurons to die according to their usual developmental schedule. © 1992 John Wiley & Sons, Inc.     

Immunolocalization of serotonin in Onychophora argues against segmental ganglia being an ancestral feature of arthropods

Background  

Onychophora (velvet worms) represent the most basal arthropod group and play a pivotal role in the current discussion on the evolution of nervous systems and segmentation in arthropods. Although there is a wealth of information on the immunolocalization of serotonin (5-hydroxytryptamine, 5-HT) in various euarthropods, as yet no comparable localization data are available for Onychophora. In order to understand how the onychophoran nervous system compares to that of other arthropods, we studied the distribution of serotonin-like immunoreactive neurons and histological characteristics of ventral nerve cords in Metaperipatus blainvillei (Onychophora, Peripatopsidae) and Epiperipatus biolleyi (Onychophora, Peripatidae).     

Cadmium induces alterations in the human spinal cord morphogenesis

The effects of cadmium on the central nervous system are still relatively poorly understood and its role in neurodegenerative diseases has been debated. In our research, cultured explants from 25 human foetal spinal cords (10–11 weeks gestational age) were incubated with 10 and 100 μM cadmium chloride (CdCl₂) for 24 h. After treatment, an immunohistochemical study [for Sglial fibrillary acidic protein (GFAP) and choline acetyltransferase (ChAT)], a Western blot analysis (for GFAP, β-Tubulin III, nerve growth factor receptor, Caspase 8 and poly (ADP-ribose) polymerase), and a terminal deoxynucleotidyl transferase biotin-dUTP nick end labelling (TUNEL) assay (for detection of apoptotic bodies) were performed. The treatment with CdCl₂ induced a significant and dose-dependent change in the ratio motor neurons/glial cells in the ventral horns of human foetal spinal cord. The decrease of the choline acetyltransferase-positive cells (motor neurons) and the reduction of β Tubulin III indicate that CdCl₂ specifically affects motor neurons of the ventral horns. While the number of motor neurons decreased for the activation of apoptotic pathways (as shown by the increased expression of Caspase 8, nerve growth factor receptor, and poly (ADP-ribose) polymerase), glial cells, both in the subependymal zone and in the gray matter of the ventral horns, increased (as shown by the increase of GFAP expression). These results provide the evidence that during human spinal cord development, CdCl₂ may affect the fate of neural and glial cells thus, being potentially involved in the etiopathogenesis of neurodegenerative diseases.     

The fate of specific motoneurons and sensory neurons of the pregenital abdominal segments inTenebrio molitor (Insecta : Coleoptera) during metamorphosis

The anatomy and innervation of the lateral external muscle and sensory cells located in the ventral region of pregenital abdominal segments were examined at the larval and adult stages ofTenebrio molitor (Coleoptera). All seven muscles located in this region degenerate during the pupal stage, whilst only the lateral external median (lem) appears in the adult. Backfillings of the motor nerve innervating this muscle reveal that, at both larval and adult stages, it is innervated by ten neurons. Intracellular records from the muscle fibres show that two neurons are inhibitory, and at least five are excitatory. There are also two unpaired neurons. A variety of sensory organs are located in the ventral region of the larvae, whilst only campaniform sensilla are found in the adult. At both stages, the innervation pattern of the sensory nerve branches is very similar. Also, the central projections of the sensory cells occupy similar neuropilar areas. Finally, prolonged intracellular records from the lem muscle revealed that, at the larval stage, it participates only in segmental or intersegmental reflexes, whilst in the adult it has a primary expiratory role in ventilation. The results show that extensive changes occur in the number of muscles located in the ventral region of the pregenital abdominal segments, as well as in the arrangement and number of sensory neurons, in the structure of the exoskeleton, and even in the central nervous system. In contrast, only minor changes are observed in the sensory and motor nerve branches, in the sensory projections, and in the number and the location of the motoneurons innervating the lateral external median muscle. Correspondence to: G. Theophilidis     

Absence of sensory input does not affect persistent neurons in Tenebrio molitor metamorphosis (Insecta: Coleoptera)

Summary The ventral nerve cord of holometabolous insects is reorganized during metamorphosis. Certain elements, however, persist from the larval to the adult stage. A group of dorsal unpaired median neurons and a set of thoracic serotonin-immunoreactive interneurons are shown to be persistent elements in the ventral nerve cord of Tenebrio molitor. These persistent neurons retain their bauplan even after deprivation of the sensory neurons projecting onto them. These persistent neurons might provide a network into which newly developing sensory neurons fit during reorganization of the nervous tissue.