Regionalized nervous system in Hydra and the mechanism of its development

The last common ancestor of Bilateria and Cnidaria is considered to develop a nervous system over 500 million years ago. Despite the long course of evolution, many of the neuron-related genes, which are active in Bilateria, are also found in the cnidarian Hydra. Thus, Hydra is a good model to study the putative primitive nervous system in the last common ancestor that had the great potential to evolve to a more advanced one. Regionalization of the nervous system is one of the advanced features of bilaterian nervous system. Although a regionalized nervous system is already known to be present in Hydra, its developmental mechanisms are poorly understood. In this study we show how it is formed and maintained, focusing on the neuropeptide Hym-176 gene and its paralogs. First, we demonstrate that four axially localized neuron subsets that express different combination of the neuropeptide Hym-176 gene and its paralogs cover almost an entire body, forming a regionalized nervous system in Hydra. Second, we show that positional information governed by the Wnt signaling pathway plays a key role in determining the regional specificity of the neuron subsets as is the case in bilaterians. Finally, we demonstrated two basic mechanisms, regionally restricted new differentiation and phenotypic conversion, both of which are in part conserved in bilaterians, are involved in maintaining boundaries between the neuron subsets. Therefore, this study is the first comprehensive analysis of the anatomy and developmental regulation of the divergently evolved and axially regionalized peptidergic nervous system in Hydra, implicating an ancestral origin of neural regionalization.     

Microscopic anatomy and ultrastructure of the nervous system of <Emphasis Type="Italic">Phoronopsis harmeri</Emphasis> Pixell, 1912 (Lophophorata: Phoronida)

The microscopic anatomy and ultrastructure of the nervous system of Phoronopsis harmeri was investigated using histological techniques and electron microscopy. The collar nerve ring is basically formed by circular nerve fibers originating from sensitive cells of tentacles. The dorsal nerve plexus principally consists of large motor neurons. It is shown for the first time that the sensitive collar nerve ring immediately passes into the motor dorsal nerve plexus. The basic components of the nervous system have similar cytoarchitectonics and a layered structure. The first layer is formed by numerous nerve fibers surrounded by the processes of glia-like cells. The bodies of glia-like cells constitute the second layer. The third layer consists of neuron bodies overarched by the bodies of epidermal cells. The giant nervous fiber is accompanied by more than one hundred nerve fibers of a common structure and, thus, marks the true longitudinal nerve. The phoronids possess one or two longitudinal nerves. It is supposed that the plexus nature of the nervous system in phoronids may be related to their phylogenesis. A comparison of the nervous system organization and body plans among the Lophophorata suggests that the nervous system of phoronids cannot be considered as a reductive variant of the brachiopod nervous system. At the same time, the structure of the nervous system of bryozoans can be derived from that of phoronids.     

The nervous system of Neodasys chaetonotoideus (Gastrotricha: Neodasys) revealed by combining confocal laserscanning and transmission electron microscopy: evolutionary comparison of neuroanatomy within the Gastrotricha and basal Protostomia

We present a reconstruction of the nervous system of Neodasys chaetonotoideus Remane, 1927 (Gastrotricha, Chaetonotida) based on different microscopical methods: (1) immunohistochemistry (anti-acetylated α- and β-tubulin-, anti-5-HT- and anti-FMRFamide labelling) and (2) histochemistry (labelling of musculature and nuclei) by the means of confocal laser scanning microscopy (cLSM) and (iii) ultrastructure by means of transmission electron microscopy (TEM). All parts of the nervous system contain structures with an immunoreaction against the used immunohistochemical markers and labelling of histochemical markers. Results of both techniques (cLSM, TEM) reveal that the nervous system of N. chaetonotoideus is composed of a “dumb-bell-shaped” brain and one pair of posterior longitudinal neurite bundles. The brain is made up of a pair of laterally located clusters of neuronal somata, a large dorsal interconnecting dorsal commissure and two tiny ventral commissures in the region of the lateral clusters. From this, it follows that the brain is circumpharyngeal in position. The innervation of the head region is conducted by three pairs of anterior-directed neurite bundles. We describe here the gross anatomy of the nervous system and give additional details of the ultrastructure and the 5-HT and RFamide-like IR components of the nervous system. We compare our newly obtained data with already published data on the nervous system of gastrotrichs to reconstruct the hypothetical ground pattern of the nervous system in Gastrotricha, respectively, in Macrodasyida.     

Evolution of eumetazoan nervous systems: insights from cnidarians

Cnidarians, the sister group to bilaterians, have a simple diffuse nervous system. This morphological simplicity and their phylogenetic position make them a crucial group in the study of the evolution of the nervous system. The development of their nervous systems is of particular interest, as by uncovering the genetic programme that underlies it, and comparing it with the bilaterian developmental programme, it is possible to make assumptions about the genes and processes involved in the development of ancestral nervous systems. Recent advances in sequencing methods, genetic interference techniques and transgenic technology have enabled us to get a first glimpse into the molecular network underlying the development of a cnidarian nervous system—in particular the nervous system of the anthozoan Nematostella vectensis. It appears that much of the genetic network of the nervous system development is partly conserved between cnidarians and bilaterians, with Wnt and bone morphogenetic protein (BMP) signalling, and Sox genes playing a crucial part in the differentiation of neurons. However, cnidarians possess some specific characteristics, and further studies are necessary to elucidate the full regulatory network. The work on cnidarian neurogenesis further accentuates the need to study non-model organisms in order to gain insights into processes that shaped present-day lineages during the course of evolution.     

Acetylcholinesterase activity in the developing and regenerating nervous system of the acoel Symsagittifera roscoffensis

Bery, A. and Martínez, P. 2010. Acetylcholinesterase activity in the developing and regenerating nervous system of the acoel Symsagittifera roscoffensis. —Acta Zoologica (Stockholm) 92 : 383–392. The use of the cholinergic system is widespread in the animal kingdom. It controls different processes, including reproduction and neural transmission. However, its evolutionary history is not yet well understood. For instance, the role played by the cholinergic system in the nervous system of basal bilaterian taxa, where the first signs of architectural complexity appear, is still unknown. Here, we describe the structure of the cholinergic system during the development and regeneration of the acoel flatworm Symsagittifera roscoffensis, using acetylcholinesterase (AchE) activity as a marker. In this species, AchE activity is observed at all developmental stages, including in the early embryos. The juvenile and adult patterns reveal the presence of a complex nervous system that includes three pairs of longitudinal neurite bundles, which are connected to an anterior centralized mass of neurons and neural processes formed by two pairs of connectives and four commissures. The power of the technique also allows the detection of newly born neurons as they are incorporated into the growing nervous system (during regeneration).     

Neural Circuit Recording from an Intact Cockroach Nervous System

The cockroach ventral nerve cord preparation is a tractable system for neuroethology experiments, neural network modeling, and testing the physiological effects of insecticides. This article describes the scope of cockroach sensory modalities that can be used to assay how an insect nervous system responds to environmental perturbations. Emphasis here is on the escape behavior mediated by cerci to giant fiber transmission in Periplaneta americana. This in situ preparation requires only moderate dissecting skill and electrophysiological expertise to generate reproducible recordings of neuronal activity. Peptides or other chemical reagents can then be applied directly to the nervous system in solution with the physiological saline. Insecticides could also be administered prior to dissection and the escape circuit can serve as a proxy for the excitable state of the central nervous system. In this context the assays described herein would also be useful to researchers interested in limb regeneration and the evolution of nervous system development for which P. americana is an established model organism.     

<Emphasis Type="Italic">Engrailed</Emphasis> is expressed in larval development and in the radial nervous system of <Emphasis Type="Italic">Patiriella</Emphasis> 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.     

The nervous system in the cyclostome bryozoan <Emphasis Type="Italic">Crisia eburnea</Emphasis> as revealed by transmission electron and confocal laser scanning microscopy

Introduction

Among bryozoans, cyclostome anatomy is the least studied by modern methods. New data on the nervous system fill the gap in our knowledge and make morphological analysis much more fruitful to resolve some questions of bryozoan evolution and phylogeny.

Results

The nervous system of cyclostome Crisia eburnea was studied by transmission electron microscopy and confocal laser scanning microscopy. The cerebral ganglion has an upper concavity and a small inner cavity filled with cilia and microvilli, thus exhibiting features of neuroepithelium. The cerebral ganglion is associated with the circumoral nerve ring, the circumpharyngeal nerve ring, and the outer nerve ring. Each tentacle has six longitudinal neurite bundles. The body wall is innervated by thick paired longitudinal nerves. Circular nerves are associated with atrial sphincter. A membranous sac, cardia, and caecum all have nervous plexus.

Conclusion

The nervous system of the cyclostome C. eburnea combines phylactolaemate and gymnolaemate features. Innervation of tentacles by six neurite bundles is similar of that in Phylactolaemata. The presence of circumpharyngeal nerve ring and outer nerve ring is characteristic of both, Cyclostomata and Gymnolaemata. The structure of the cerebral ganglion may be regarded as a result of transformation of hypothetical ancestral neuroepithelium. Primitive cerebral ganglion and combination of nerve plexus and cords in the nervous system of C. eburnea allows to suggest that the nerve system topography of C. eburnea may represent an ancestral state of nervous system organization in Bryozoa. Several scenarios describing evolution of the cerebral ganglion in different bryozoan groups are proposed.

     

Designing and Implementing Nervous System Simulations on LEGO Robots

We present a method to use the commercially available LEGO Mindstorms NXT robotics platform to test systems level neuroscience hypotheses. The first step of the method is to develop a nervous system simulation of specific reflexive behaviors of an appropriate model organism; here we use the American Lobster. Exteroceptive reflexes mediated by decussating (crossing) neural connections can explain an animal''s taxis towards or away from a stimulus as described by Braitenberg and are particularly well suited for investigation using the NXT platform.¹ The nervous system simulation is programmed using LabVIEW software on the LEGO Mindstorms platform. Once the nervous system is tuned properly, behavioral experiments are run on the robot and on the animal under identical environmental conditions. By controlling the sensory milieu experienced by the specimens, differences in behavioral outputs can be observed. These differences may point to specific deficiencies in the nervous system model and serve to inform the iteration of the model for the particular behavior under study. This method allows for the experimental manipulation of electronic nervous systems and serves as a way to explore neuroscience hypotheses specifically regarding the neurophysiological basis of simple innate reflexive behaviors. The LEGO Mindstorms NXT kit provides an affordable and efficient platform on which to test preliminary biomimetic robot control schemes. The approach is also well suited for the high school classroom to serve as the foundation for a hands-on inquiry-based biorobotics curriculum.     

Histamine is a major mechanosensory neurotransmitter candidate in Drosophila melanogaster

Histamine is known to be the neurotransmitter of insect photoreceptors. Histamine-like immunoreactivity is also found in a number of interneurons in the central nervous system of various insects. Here, we demonstrate by immunohistochemical techniques that, in Drosophila melanogaster (Acalypterae), most or all mechanosensory neurons of imaginal hair sensilla selectively bind antibodies directed against histamine. The histamine-like staining includes the cell bodies of these neurons as well as their axons, which form prominent fibre bundles in peripheral nerves, and their terminal projections in the central neuropil of head and thoracic ganglia. The specificity of the immunostaining is demonstrated by investigating a Drosophila mutant unable to synthesize histamine. Other mechanosensory organs, such as campaniform sensilla or scolopidial organs, do not stain. In the calypteran flies, Musca and Calliphora, we find no comparable immunoreactivity associated with either hair sensilla or the nerves entering the central nervous system, observations in agreement with earlier studies on Calliphora. Thus, histamine seems to be a major mechanosensory transmitter candidate of the adult nervous system of Drosophila, but apparently not of Musca or Calliphora.     

Chicken Acidic Leucine-rich EGF-like Domain Containing Brain Protein (CALEB), a Neural Member of the EGF Family of Differentiation Factors, Is Implicated in Neurite Formation

Chicken acidic leucine-rich EGF-like domain containing brain protein (CALEB) was identified by combining binding assays with immunological screens in the chicken nervous system as a novel member of the EGF family of differentiation factors. cDNA cloning indicates that CALEB is a multidomain protein that consists of an NH₂-terminal glycosylation region, a leucine-proline–rich segment, an acidic box, a single EGF-like domain, a transmembrane, and a short cytoplasmic stretch. In the developing nervous system, CALEB is associated with glial and neuronal surfaces. CALEB is composed of a 140/130-kD doublet, an 80-kD band, and a chondroitinsulfate-containing 200-kD component. The latter two components are expressed in the embryonic nervous system and are downregulated in the adult nervous system. CALEB binds to the extracellular matrix glycoproteins tenascin-C and -R. In vitro antibody perturbation experiments reveal a participation of CALEB in neurite formation in a permissive environment.     

Evidence and bioassay for diuretic factors in the nervous system of larvalHeliothis virescens

Summary Diuretic factors were studied in the central nervous system of larvae of the tobacco budworm,Heliothis virescens, using [¹⁴C]urea as a sensitive indicator for water movement through isolated Malpighian tubules. The assay required Na⁺ and a pH of 6.0–6.2 for maximum activity. Malpighian tubules had high secretory activity in feeding larvae of the fifth instar, but the activity declined during the burrowing-digging stage that preceded pupation. Malpighian tubules from starved larvae showed a greater response to extracts of nervous tissues than did tubules from feeding larvae, and extracts showed a dose-response relationship with fluid secretion. Diuretic activity was distributed throughout all parts of the central nervous system with the brain having the most activity. Brain extracts increased fluid secretion by in vitro Malpighian tubules by more than 3-fold and doubled the rate of dye clearance from the hemolymph in vivo. Diuretic activity in nervous tissue extracts was unaffected by boiling but sensitive to proteases. Fluid secretion by in vitro tubules was increased by cAMP, dbcAMP, theophylline, octopamine and dopa. These studies provide evidence for the presence of diuretic factors in the central nervous system ofH. virescens larvae and describe a sensitive bioassay for these factors.Abbreviations AR activation ratio - cAMP cyclic AMP - dbcAMP dibutyryl cyclic AMP - dbcGMP dibutyryl cyclic GMP - Dopa dihydroxyphenylalanine - 5-HT 5-hydroxytryptamine - L1 larval instar - VCNS ventral central nervous system     

The nervous system of Isodiametra pulchra (Acoela) with a discussion on the neuroanatomy of the Xenacoelomorpha and its evolutionary implications

Introduction

Acoels are microscopic marine worms that have become the focus of renewed debate and research due to their placement at the base of the Bilateria by molecular phylogenies. To date, Isodiametra pulchra is the most promising ??model acoel?? as it can be cultured and gene knockdown can be performed with double-stranded RNA. Despite its well-known morphology data on the nervous system are scarce. Therefore we examined this organ using various microscopic techniques, including histology, conventional histochemistry, electron microscopy, and immunocytochemistry in combination with CLSM and discuss our results in light of recently established phylogenies.

Results

The nervous system of Isodiametra pulchra consists of a bilobed brain with a dorsal posterior commissure, a frontal ring and tracts, four pairs of longitudinal neurite bundles, as well as a supramuscular and submuscular plexus. Serotonin-like immunoreactivity (SLI) is displayed in parts of the brain, the longitudinal neurite bundles and a large part of the supramuscular plexus, while FMRFamide-like immunoreactivity (RFLI) is displayed in parts of the brain and a distinct set of neurons, the longitudinal neurite bundles and the submuscular plexus. Despite this overlap SLI and RFLI are never colocalized. Most remarkable though is the presence of a distinct functional neuro-muscular system consisting of the statocyst, tracts, motor neurons and inner muscles, as well as the presence of various muscles that differ with regard to their ultrastructure and innervation.

Conclusions

The nervous system of Isodiametra pulchra consists of an insunk, bilobed brain, a peripheral part for perception and innervation of the smooth body-wall musculature as well as tracts and motor neurons that together with pseudostriated inner muscles are responsible for steering and quick movements. The insunk, bilobed brains with two to three commissures found in numerous acoels are homologous and evolved from a ring-commissural brain that was present in the stem species of acoelomorphs. The acoelomorph brain is bipartite, consisting of a Six3/6-dependend animal pole nervous system that persists throughout adulthood and an axial nervous system that does not develop by exhibiting a staggered pattern of conserved regulatory genes as in other bilaterians but by a nested pattern of these genes. This indicates that acoelomorphs stem from an ancestor with a simple brain or with a biphasic life cycle.     

Neuroanatomy of the tube feet and tentacles in Holothuria glaberrima (Holothuroidea, Echinodermata)

Echinoderms are a key group in understanding the evolution of the nervous system in the Metazoa. Remarkably, little is known about echinoderm neurobiology. The echinoderm podia, which are unique echinoderm modifications and comprise structures responsible for locomotion and feeding, have been largely neglected in nervous system studies. Here, we have applied immunohistological approaches using different neuronal markers to describe the neuroanatomy of the holothurian podia and its relation to the muscular component. We show, using the sea cucumber Holothuria glaberrima (Selenka, 1867), the direct innervation of the podia by the ectoneural component of the nervous system, as well as the existence of a connection between the nervous system components in the main nerves, the muscle, and the connective tissue. These findings confirm the ectoneural origin of the tube feet’s main nervous system and demonstrate its neuroanatomic complexity. We also show the presence of fibers and neurons within the tube feet mesothelium and connective tissue. The study of these simple structures will help us elucidate the echinoderms’ neuromuscular circuit and their evolutionary relationships.     

Immunohistochemical investigations of the development of Scoloplos armiger (“intertidalis clade”) indicate a paedomorphic origin of Proscoloplos cygnochaetus (Annelida,Orbiniidae)

The embryology of Scoloplos armiger (“intertidalis clade”) was described in detail using light microscopy in a landmark paper by DT Anderson in 1959. To expand these investigations, we used immunohistochemical staining techniques (phalloidin, anti‐FMRFamide, anti‐serotonin, and anti‐α‐tubulin) coupled with confocal laser scanning microscopy to describe the early development of musculature and nervous system of this species. Moreover, we applied the same methods (and Azan staining) to adults of the putatively paedomorphic orbiniid species Proscoloplos cygnochaetus. Our results showed comparable patterns for stainings of the nervous and muscle system for juveniles of Scoloplos and adults of Proscoloplos. Both show scarce transverse musculature and only a few dorsoventral muscle fibers in the anterior body region. For the nervous system, the observed immunoreactive pattern is nearly superimposable for juveniles of Scoloplos armiger and adults of Proscoloplos. Moreover, the intraepidermal and basiepithelial position of the ventral nervous system only found in juvenile Scoloplos is comparable with the conditions exhibited in adults of Proscoloplos. In summary, our data are in congruence with the hypothesis of a paedomorphic origin for Proscoloplos as derived from molecular phylogenetic analyses.     

On the phylogeny of the Phyllodocidae (Polychaeta Annelida): an alternative

The phylogeny of the Phyllodocidae (Polychaeta Annelida) is examined in an analysis which includes previously unnoticed characters of the nervous system. Concentrating on four problems of importance in understanding the phylogeny of the family, a study of the nervous system demonstrated that: 1. A median antenna, such as that present in species of Eulalia, is not homologous to the nuchal papilla of, for example, Eteone and Phyllodoce; 2. Nuchal organs, presumably found in all phyllodocids, are basically homologous, but four separate types may be recognized; 3. The anterior concentration of the first segments (particularly their tentacular cirri), which is evident in most phyllodocids, is accompanied by different alterations of the ventral nervous system. The polarities of these changes are not self-evident; 4. A study of the ventral nervous system of Eteone reveals that the first apparent segment, bearing two pairs of tentacular cirri, must be regarded as homologous to the second segment of all other phyllodocids. Furthermore, this genus descended from forms in which a segment was present anterior to the first apparent segment, the first two segments possibly bearing tightly packed tentacular cirri. In connection with other characters, this information was used to produce a cladogram, which has some surprising features. The most unexpected result is the prediction that Eteone is the sister group of a taxon containing the genera Paranaitis, Chaetoparia, and Phyllodoce. The results are discussed and compared to those of other investigators.     

Nervous system development of two crinoid species, the sea lily Metacrinus rotundus and the feather star Oxycomanthus japonicus

Nervous system development in echinoderms has been well documented, especially for sea urchins and starfish. However, that of crinoids, the most basal group of extant echinoderms, has been poorly studied due to difficulties in obtaining their larvae. In this paper, we report nervous system development from two species of crinoids, from hatching to late doliolaria larvae in the sea lily Metacrinus rotundus and from hatching to cystidean stages after settlement in the feather star Oxycomanthus japonicus. The two species showed a similar larval nervous system pattern with an extensive anterior larval ganglion. The ganglion was similar to that in sea urchins which is generally regarded as derived. In contrast with other echinoderm and hemichordate larvae, synaptotagmin antibody 1E11 failed to reveal ciliary band nerve tracts. Basiepithelial nerve cells formed a net-like structure in the M. rotundus doliolaria larvae. In O. japonicus, the larval ganglion was still present 1 day after settlement when the adult nervous system began to appear inside the crown. Stalk nerves originated from the crown and extended down the stalk, but had no connections with the remaining larval ganglion at the base of the stalk. The larval nervous system was not incorporated into the adult nervous system, and the larval ganglion later disappeared. The aboral nerve center, the dominant nervous system in adult crinoids, was formed at the early cystidean stage, considerably earlier than previously suggested. Through comparisons with nervous system development in other ambulacraria, we suggest the possible nervous system development pattern of the echinoderm ancestor and provide new implications on the evolutionary history of echinoderm life cycles.