The significance of the radial nerve cords in asteroids and echinoids

Summary The radial nerve cords of a number of different species of echinoids and asteroids have been examined with the electron microscope. They have been shown to consist of tracts of small naked axons with discrete regions of neuropile. Synapses within these areas of neuropile have been described and their significance discussed. A careful examination has failed to reveal any connections between the ectoneural nerve and the mesodermal nerves and muscles. Synapses across the connective tissue sheet separating these regions have been proposed to account for known functional connection. A hypothetical model of the nervous system has been proposed to account for known structure and function.The author wishes to acknowledge the help of Prof. M. S. Laverack during this study. Part of this work was carried out while the author was in receipt of a Queen Elizabeth Fellowship from the Commonwealth Government of Australia.     

Developmental origin of the adult nervous system in a holothurian: an attempt to unravel the enigma of neurogenesis in echinoderms

In adult echinoderms, the nervous system includes the ectoneural and hyponeural subsystems. The former has been believed to develop from the ectoderm, whereas the latter is considered to be mesodermal in origin. However, this view has not been substantially supported by embryological examinations. Our study deals with the developmental origin of the nervous system in the direct-developing sea cucumber Eupentacta fraudatrix. The rudiment of the adult nervous system develops from ectodermally derived cells, which ingress into the primary body cavity from the floor of the vestibule. At the earliest stages, only the rudiment of the ectoneural nerve ring is laid down. The radial nerve cords and tentacular nerves grow out from this subcutaneous rudiment. The ectoneural cords do not develop simultaneously but make their appearance in the following order: unpaired mid-ventral cord, paired dorsal lateral cords, and ventral lateral cords. These transitional developmental stages probably recapitulate the evolution of the echinoderm body plan. The holothurian hyponeural subsystem, as other regions of the metazoan nervous system, has an ectodermal origin. It originally appears as a narrow band of tissue, which bulges out of the basal region of the ectoneural neuroepithelium. Our data combined with those of other workers strongly suggest that the adult nervous tissue in echinoderms develops separately from the superficial larval system of ciliary nerves. Therefore, our data are neither in strict accordance with Garstang's hypothesis nor do they allow to refuse it. Nevertheless, in addition to ciliary bands, other areas of neurogenetic epidermis must be taken into account.     

The structure of the larval nervous system of Pisaster ochraceus (Echinodermata: Asteroidea)

Ultrastructural observations and glyoxilic acid-induced fluorescence of catecholamines indicate that tracts of axons lie at the base of the ciliary bands and run throughout their length in bipinnaria and brachiolaria larvae of Pisaster ochraceus. Two types of nerve cells occur at regular intervals within the ciliary bands. Type I nerve cells are associated with the axonal tracts, and type II nerve cells, which are ciliated, occur along the edge of the ciliary bands. Two prominent ganglia, which appear as accumulations of nerve cells and neuropile, occur on the lower lip of the larval mouth. Smaller ganglia occur irregularly throughout the ciliary band. Synapses were never clearly identified and were assumed to be unspecialized. Nervous tissues were also found associated with the esophageal muscles, the attachment organ, and the larval arms. Organization of the nervous system and its association with effectors suggest it controls swimming and feeding. Several similarities exist between the nervous systems of larval asteroids, larval echinoids, and adult echinoderms.     

Monoaminergic mechanisms in the nervous system of Lumbricus terrestris (L.)

Summary The localization and intraneuronal distribution of the monoaminergic transmitters in the nervous system of the earthworm, Lumbricus terrestris, have been investigated in detail with the aid of the histochemical fluorescence method of Falck and Hillarp.In the ventral nerve cord, many yellow fluorescent, 5-hydroxytryptamine containing neurons are found, but only few green fluorescent noradrenaline containing cell bodies, which, however, are numerous in the peripheral nervous system. There is an abundance of both fibre types in the neuropile.The 5-hydroxytryptaminergic neurons probably have a motor (possibly inhibitor) function; the adrenergic neurons in the body segments are supposed to have a receptor (exteroceptive and possibly proprioceptive) function.In the cerebral ganglion, both 5-hydroxytryptamine and noradrenaline containing neurons are found in large numbers, and there are closely packed numerous fibres of both types in the neuropile. Their function is more obscure, though an associative function can be presumed for some adrenergic neurons; smaller 5-hydroxytryptaminergic neurons might have a motor (perhaps inhibitor) function.Adrenergic sensory cells are found in the body integument, most frequently in the clitellum segments, in the prostomium, and in the roof of the buccal cavity. These cells give off varicose fibres that form a basi-epithelial network which is in communication with the green fluorescent sensory fascicles in the ventral nerve cord via the epidermal nerves, the ring nerves, and the segmental nerves. No direct adrenergic sensory-effector innervation of either circular and/or longitudinal musculature or gland cells seems to exist. No adrenergic free nerve endings in the body integument have been observed. Instead, there must be a synaptic contact with the motoneurons, either directly in the neuropile or via an interjacent neuron.No synaptic contacts have been observed in the ventral nerve cord between adrenergic or 5-hydroxytryptaminergic fibres and either the giant fibres or fluorescent or nonfluorescent perikarya.An adrenergic innervation of the pharynx musculature has been found, and sensory cells of a different type are present in and below the epithelium; here, a direct senso-motoric innervation of the pharyngeal musculature cannot be excluded. It is established that the adrenergic neurons in the stomatogastric nervous system have an exciting function on the pharynx, whereas a direct monoaminergic influence of the muscular movements of the intestine probably does not exist.Abbreviations Used A adrenaline - CA catecholamine - DA dopamine - 5-HT 5-hydroxytryptamine - MA monoamine - NA noradrenaline The research reported in this document has been sponsored by the Air Force Office of Scientific Research under Grant AF EOAR 67-15 through the European Office of Aerospace Research (OAR), United States Air Force, by the Swedish Natural Science Research Council (99-34, 6627), and by the Swedish Medical Research Council (B67-12X-712-02A).     

Developmental stage-specific antigens in the nervous system of the cockroach

A specific effort was made to obtain monoclonal antibodies that bind to macromolecules that play a role in the development of the nervous system. It was considered that good candidates for such molecules were those that were only transiently present in the embryonic nervous system. Hybridomas were prepared from spleen cells taken from mice that had been immunized with nerve cords from cockroach embryos at the 43-50% stage of development. The hybridoma supernatants were screened for antibody binding to frozen sections of both embryonic and adult thoracic ganglia. Cell lines that produced monoclonal antibodies that transiently bound to the embryonic nervous system were saved and cloned. These developmental stage-specific monoclonal antibodies either did not bind to the adult nervous system or bound to it with a pattern very different from that in the embryonic nervous system. The developmental stage-specific antigens detected by these monoclonal antibodies were organized into four categories based on the part of the embryonic nervous system in which they were transiently localized. These include binding to the cell bodies of all neurons, cell bodies of subsets of neurons or neuroblasts, subsets of axons, and the neuropile. Preliminary biochemical characterization of the antigens showed that many of these antibodies were recognizing carbohydrate epitopes. Functions for these antigens, most of which are components of the cell surface, are tentatively proposed.     

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.     

Novel Insights into the Echinoderm Nervous System from Histaminergic and FMRFaminergic-Like Cells in the Sea Cucumber Leptosynapta clarki

Understanding of the echinoderm nervous system is limited due to its distinct organization in comparison to other animal phyla and by the difficulty in accessing it. The transparent and accessible, apodid sea cucumber Leptosynapta clarki provides novel opportunities for detailed characterization of echinoderm neural systems. The present study used immunohistochemistry against FMRFamide and histamine to describe the neural organization in juvenile and adult sea cucumbers. Histaminergic- and FMRFaminergic-like immunoreactivity is reported in several distinct cell types throughout the body of L. clarki. FMRFamide-like immunoreactive cell bodies were found in the buccal tentacles, esophageal region and in proximity to the radial nerve cords. Sensory-like cells in the tentacles send processes toward the circumoral nerve ring, while unipolar and bipolar cells close to the radial nerve cords display extensive processes in close association with muscle and other cells of the body wall. Histamine-like immunoreactivity was identified in neuronal somatas located in the buccal tentacles, circumoral nerve ring and in papillae distributed across the body. The tentacular cells send processes into the nerve ring, while the processes of cells in the body wall papillae extend to the surface epithelium and radial nerve cords. Pharmacological application of histamine produced a strong coordinated, peristaltic response of the body wall suggesting the role of histamine in the feeding behavior. Our immunohistochemical data provide evidence for extensive connections between the hyponeural and ectoneural nervous system in the sea cucumber, challenging previously held views on a clear functional separation of the sub-components of the nervous system. Furthermore, our data indicate a potential function of histamine in coordinated, peristaltic movements; consistent with feeding patterns in this species. This study on L. clarki illustrates how using a broader range of neurotransmitter systems can provide better insight into the anatomy, function and evolution of echinoderm nervous sytems.     

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.     

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.     

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.     

Growth cones stall and collapse during axon outgrowth in Caenorhabditis elegans.

During nervous system development, neurons form synaptic contacts with distant target cells. These connections are formed by the extension of axonal processes along predetermined pathways. Axon outgrowth is directed by growth cones located at the tips of these neuronal processes. Although the behavior of growth cones has been well-characterized in vitro, it is difficult to observe growth cones in vivo. We have observed motor neuron growth cones migrating in living Caenorhabditis elegans larvae using time-lapse confocal microscopy. Specifically, we observed the VD motor neurons extend axons from the ventral to dorsal nerve cord during the L2 stage. The growth cones of these neurons are round and migrate rapidly across the epidermis if they are unobstructed. When they contact axons of the lateral nerve fascicles, growth cones stall and spread out along the fascicle to form anvil-shaped structures. After pausing for a few minutes, they extend lamellipodia beyond the fascicle and resume migration toward the dorsal nerve cord. Growth cones stall again when they contact the body wall muscles. These muscles are tightly attached to the epidermis by narrowly spaced circumferential attachment structures. Stalled growth cones extend fingers dorsally between these hypodermal attachment structures. When a single finger has projected through the body wall muscle quadrant, the growth cone located on the ventral side of the muscle collapses and a new growth cone forms at the dorsal tip of the predominating finger. Thus, we observe that complete growth cone collapse occurs in vivo and not just in culture assays. In contrast to studies indicating that collapse occurs upon contact with repulsive substrata, collapse of the VD growth cones may result from an intrinsic signal that serves to maintain growth cone primacy and conserve cellular material.     

Fine structure of glial cells in the central nervous system of the tapeworm Grillotia erinaceus (Cestoda: Trypanorhyncha)

The problem of glial cells existing in parasitic and free living flatworms is correlated with organization of parenchyma in platyhelmintes. In the contrary to the widespread opinion that myelin-like envelopes and glial cells do not exist in the nervous system of parasitic flatworms, it has been shown by ultrastructural researches that Amphilina foliacea (Cestoda, Amphilinidea) has well developed glial cells and myelin-like envelopes in the ganglia and main cords, which include both glial cells and intercellular components. The aim of our research was to reveal and investigate in details structural components corresponding to the concept of the glial cell in the CNS of Grillotia erinaceus (Cestoda: Trypanorhyncha). Three types of glial cells have been found. The first type is the fibroblast-like glial cells; cells locate in the cerebral ganglion, contain in cytoplasm and extract out fibrillar matrix, form desmosomes and have supporting function. The glial cells of the second type form myeline-like envelope of the giant axons and bulbar nerves in scolex and have laminar cytoplasm. These cells are numerous and exceed in number the neurons bodies into the nerve. The glial cells of the third type form multilayer envelopes in the main nerve cords; extra cellular fibers and gap-junctions take place between the layers. There are contacts between the glial cells of the third type and excretory epithelium but specialized contacts with neurons have been not found. The existing of glial cells in free living and parasitic flatworms is discussed.     

Dorsal unpaired median neurons, and ventral bilaterally paired neurons, project to a visceral muscle in an insect

Cobalt backfilling, Lucifer yellow injection and neurophysiological recordings have been used to identify the neurons, in particular dorsal unpaired median neurons, which contribute axons to the oviducal muscles of the locust Locusta migratoria. A total of eight neurons within the VIIth abdominal ganglion have axons passing to the oviducts. Three pairs of bilaterally symmetrical neurons have ventrally located cell bodies. One neuron from each pair projects to the left side of the oviducts and the other the right side of the oviducts. These cells lie ipsilateral to the nerve root through which they exit. The neuropilar branches are intraganglionic and lie mainly in the ipsilateral neuropile, however one of the neurons from each side possesses a giant process, reaching 10 micron in diameter, which passes dorsally to the contralateral side of the ganglion. The other two neurons are dorsal unpaired median neurons, and have large cell bodies which lie at the posterior end of the ganglion. Lucifer yellow injection into these two dorsal unpaired median neurons reveals a single neurite passing anteriorly from the cell body which bifurcates into two bilaterally symmetrical processes which exit to the oviducts through both the left and right sternal roots. Similar to other identified dorsal unpaired median neurons, the cell bodies stain with neutral red and can support overshooting action potentials. The possibility that these two cells contain octopamine is discussed.     

Helicostatins: brain-gut peptides of the moth, Helicoverpa armigera (Lepidoptera: Noctuidae)

Gene expression and immunolocalisation studies have determined that the helicostatins are brain-gut peptides in larvae of the lepidopteran, Helicoverpa armigera. Mapping of the distribution of these peptides in the nervous system and alimentary canal has provided evidence for multifunctional regulatory roles. In situ hybridisation studies have shown that the helicostatin precursor gene is expressed in neurones of the central and stomatogastric nervous systems, and endocrine cells of the midgut demonstrating that the helicostatins are true brain-gut peptides. Antisera raised against Leu-callatostatin 3 (ANRYGFGL-NH(2)), a peptide isolated from the blowfly, Calliphora vomitoria was used to map the distribution of allatostatin-like immunoreactive (Ast-ir) material in H. armigera to elucidate possible functions of the helicostatins. In situ hybridisation studies verified that the helicostatin precursor gene is expressed in neurones shown to contain Ast-ir, providing strong evidence that the Ast-ir material is helicostatins. Extensive immunoreactive axonal projections into complex regions of neuropile indicate that the helicostatins may have a neuromodulatory role in the brain and segmental ganglia of the ventral nerve cord. The presence of large amounts of immunoreactive material in axons within the corpora cardiaca (CC) and transverse nerves of the perisympathetic nervous system, two known neurohaemal organs, provides evidence for a neurohormonal role. The corpora allata (CA) were innervated only sparsely by Ast-ir axons suggesting that the CA are not a neurohaemal release site or a target. Thus, it is unlikely that the helicostatins regulate juvenile hormone (JH) biosynthesis or release. Ast-ir axons extended from the frontal ganglion through the recurrent nerve and many branches were closely associated with muscles of the foregut, stomodeal valve, and anterior midgut, implicating helicostatins in regulation of foregut motility. Ast-ir material was also present in nerves associated with muscles of the pyloric valve and rectum, and in endocrine cells of the midgut.     

The Sense Organs and Ventral Ganglion of Sagitta (Chaetognatha)

This paper describes some features of the chaetognath nervous system from ultrastructural observations and observations on material stained with specific techniques for nervous tissue, and from records of the activity of the locomotor muscles and ventral ganglion. Sensory cells grouped on the ventral surface of the head bear ciliary processes (some with multiple tubules), and are probably in connexion with the central nervous system by their own axons, unlike the sensory cells of the hair fan vibration receptors of head and body. The ventral ganglion is motor to the locomotor muscles of the body, and controls the rhythmic locomotor activity of the animal. Electrical events associated with contraction of these muscles are compound non-overshooting spike-like potentials. The ventral ganglion contains several large nerve fibres constant in position and connexions in different individuals. Some of these arise from cells in the ganglia of the head, and pass to the ventral ganglion, others from cells within the ventral ganglion, and probably supply the ciliary hair fan receptors of the body, whilst the motor axons issuing from the ventral ganglion are smaller in diameter. The ganglion is arranged on a ladder-like plan, and axons of the lateral cell bodies cross the central neuropil transversely before they contribute to the longitudinal tracts or pass out in the radial nerves. Synapses in the neuropil contain 30–40 nm electron lucent vesicles; the transmitter is unknown, but is unlikely to be either acetylcholine or l -glutamate. Occasional larger electron dense vesicles up to 70 nm in diameter are also found within nerve fibres of the neuropil. It is concluded that the arrangement of the peripheral nervous system is unlike that of several groups which have been suggested as related to chaetognaths.     

Metabolism of acetylcholine in the nervous system of Aplysia californica. II. Reginal localization and characterization of choline uptake

The choline required for synthesis of acetylcholine is derived exogenously by Aplysia ganglia. Under physiological conditions choline was taken up primarlily by neuropile and nerves and not by cholinergic cell bodies. In addition, compared with their contents of choline acetyltransferase, those components of nervous tissue which contain nerve terminals and axons synthesized acetylcholine far more efficiently. Choline was accumulated by high and low affinity uptake processes; the high affinity process appeared to be characteristic of cholinergic nuerons (Swartz, J. H., M. L. Eisenstadt, and H. Cedar.1975. J. Gen. Physiol. 65:255). The two uptake processes were similarly affected by temperature with a Q10 of 2.8. Both were dependent on a variety of ions in a complicated manner. High affinity uptake seemed to be more dependent on Na+, showed greater inhibition by ouabain, and was selectively inhibited by oxotremorine. We found that the functional state of neurons did not alter uptake of radioactive choline by either process, nor did it change the conversion to radioactive acetylcholine.     

Anatomy of the sensory nervous system in Craspedella pedum (Plathelminthes, Temnocephalida): DiO staining after fixation and in vivo

 The microanatomy of the nervous system of Craspedella pedum is described based on staining of the sensory nerves with DiO (3,3′-dioctadecyloxacarbocyanine perchlorate) in whole worms after fixation. The high resolution and reproducibility of this method revealed that the microanatomy of the nervous system is uniform within this species to rather minute details. Although the lateral and ventral cords have a similar diameter, the ventral nerve cords are very poor in sensory fibres. Such a high level of functional differentiation of nerve cords has not been known in representatives of the Plathelminthes. In vivo staining reveals numerous DiO-accumulating sensory neurons in the anterior portion of the body and a few pairs in its posterior half. The morphology of some neurons is described. Several neurons were identified and our data suggest that most, if not all, sensory neurons are identificable cells. Accepted: 16 December 1997     

Effect of the microiontophoretic feed of acetylcholine and noradrenaline on the neuronal reactivity of the motor cortex to specific stimuli

In the forelimb area of the motor cortex after microiontophoretic injection of acetylcholine a group of nervous cells revealed more rapid, more stable and more effective reactions to afferent stimuli. The interrelation of impulsive activity of some of these neurons and electromyographic activity of forelimb muscles has given a possibility to propose that acetylcholine mobilizes the motor cortex for motor function regulations. The only result of noradrenaline application to motor cortex neurons was the prolongation of their responses to specific afferent stimulation.