Fine Structural Analysis of the Central Nervous System in the Spider, Achaearanea tepidariorum (Theridiidae: Araneae)

ABSTRACT Central nervous system (CNS) of arachnids is still mysterious and has a rich unexplored field compare to what is known in insects or crustaceans. The CNS of the spider, Achaearanea tepidariorum, consists of a dorsal brain or supraesophageal ganglion and circumesophageal connectives joining it to the subesophageal mass. As the segmentation of the arachnid brain is still under discussion, we classify the brain as a protocerebral and tritocerebral ganglion depending on the evidences which generally accepted. The subesophageal nerve mass underneath the brain is the foremost part of the ventral nerve cord. All of this nerve mass is totally fused together, and forming subesophageal ganglia in this spider. In the brain, the nerve cells are packed in the frontal, dorsal and lateral areas, but are not absent from the posterior and ventral regions. In addition, the nerve cells of the subesophageal and abdominal ganglia are only restricted to the ventral and ventolateral regions. The CNS of the spider, Achaearanea tepidariorum is similar in feature to the Family Araneidae.     

The morphology and anatomy of the vestimentiferan worm <Emphasis Type="Italic">Oasisia alvinae</Emphasis> Jones, 1985 (Annelida: Siboglinidae). I. External morphology,obturaculae and tentacles

This study describes the tube structure, external morphology, and histological organization of the obturacula and tentacles of the small hydrothermal-vent vestimentiferan worm Oasisia alvinae. The tubes are considerably twisted and bear collars, thus suggesting a step-like growth of the worm. The total length of the studied specimens is 32–41 mm. The trunk region comprises 75% of the total body length and is differentiated into a broadened forepart and a narrowed posterior part. The ratio between the lengths of the obturacular and vestimental regions is 0.62–0.63. The examined specimens of O. alvinae have 13 to 17 pairs of tentacular lamellae; the total number of tentacles is about 550. The muscular bands in the obturacula of O. alvinae lie in the parafrontal planes. Polymorphism occurs in the number and arrangement of the denticles of the opistosomal chaetae in O. alvinae.     

Structure and anterior regeneration of musculature and nervous system in Cirratulus cf. cirratus (Cirratulidae,Annelida)

Annelids provide suitable models for studying regeneration. By now, comprehensive information is restricted to only a few taxa. For many other annelids, comparative data are scarce or even missing. Here, we describe the regeneration of a member of the Cirratulus cirratus species complex. Using phalloidin‐labeling and antibody‐stainings combined with subsequent confocal laser scanning microscopy, we provide data about the organization of body wall musculature and nervous system of intact specimens, as well as about anteriorly regenerating specimens. Our analyses show that C. cf. cirratus exhibits a prominent longitudinal muscle layer forming a dorsal muscle plate, two ventral muscle strands and a ventral‐median muscle fiber. The circular musculature forms closed rings which are interrupted in the area of parapodia. The nervous system of C. cf. cirratus shows a typical rope‐ladder like arrangement and the circumesophageal connectives exhibit two separate roots leading to the brain. During regeneration, the nervous system redevelops remarkably earlier than the musculature, first constituting a tripartite loop‐like structure which later become the circumesophageal connectives. Regeneration of longitudinal musculature starts with diffuse ingrowth and subsequent structuring into the blastema. In contrast, circular musculature develops independently inside the blastema. Our findings constitute the first analysis of regeneration for a member of the Cirratuliformia on a structural level. Summarizing the regeneration process in C. cf. cirratus, five main phases can be subdivided: 1) wound closure, 2) blastema formation, 3) blastema differentiation, 4) resegmentation, and 5) growth, respectively elongation. Additionally, the described tripartite loop‐like structure of the regenerating nervous system has not been reported for any other annelid taxon. In contrast, the regeneration of circular and longitudinal musculature originating from different groups of cells seems to be a general pattern in annelid regeneration. J. Morphol. 275:1418–1430, 2014. © 2014 Wiley Periodicals, Inc.     

Anatomy of synganglia, including their neurosecretory regions, in unfed, virgin female Ixodes scapularis say (Acari: Ixodidae).

The central nervous system of Ixodes scapularis is fused into a single compact synganglion. The esophagus runs through the synganglion and divides it into supraesophageal and subesophageal parts. The supraesophageal portion contains a single protocerebrum with four pairs of glomeruli, paired optic lobes and cheliceral ganglia, and a single stomodeal bridge. The subesophageal portion contains a centrally located network of commissures and connectives, a pair of palpal ganglia, paired olfactory lobes of the first pedal ganglia, four pairs of pedal ganglia, and a single opisthosomal ganglion. A retrocerebral organ complex (ROC) in close vicinity of the digestive tract, as described in some other tick species, apparently is lacking. Perhaps the function of the ROC is performed by the paired, large, ganglion-like bodies that lie anterolaterad to the cheliceral ganglia. The rind, which is formed from the neuronal somata and glial cells, surrounds the central fibrous core or neuropile. Neurosecretory cells (NSC) are distinct among rind cells due to their large size and concentration of cytoplasmic neurosecretions. NSC are present throughout the synganglion, although the subesophageal portion contains larger groups of these cells. Histological serial sections, stained with Meola's (Trans Am Microsc Soc 89:66-71, '70) paraldehyde fuchsin (PAF) procedure revealed 24 PAF-stained, putative neurosecretory regions in the synganglion of virgin, unfed females. All of these regions appear to be connected and associated with the nearest ganglion and are correspondingly named. Eighteen PAF-positive regions occur in the synganglion. In addition, PAF-negative (green-stained) cells occupy 6 distinct regions in the synganglion of unfed, unmated females.     

Morphological and physiological properties of the giant interneuron of the hermit crab (Pagurus pollicaris)

The physiological and morphological properties of the giant interneurons in the hermit crab Pagurus pollicaris are described. The cell bodies are located anteriorly in the supraesophageal ganglion, close to the mid-line. Each cell sends a neurite posteriorly and then laterally, so that they cross over in the center of the ganglion. Each axon then branches: one branch runs laterally while the other travels posteriorly and leaves the ganglion in the circumesophageal connective on the side contralateral to the cell body. The giant axons travel in the circumesophageal connectives and through the thoracic and abdominal ganglia without branching. Each giant axon makes synaptic contact with its ipsilateral giant abdominal flexor motor neuron and with a second flexor motor neuron that has its axon in the contralateral third root. In the supraesophageal ganglion there is a bidirectional synapse between the two giant interneurons. Intracellular recordings from the giant axons show that there is a delay of 0.5 to 0.75 ms that cannot be accounted for by spike propagation along the axons, and may be accounted for by a chemical synapse between the giant interneurons.     

The distribution of an immunoreactive endothelin-like substance in the nervous system of the nereid,Neanthes diversicolor (Annelida)

Summary The distribution of an immunoreactive endothelin-1-like peptide was investigated in the nereid, Neanthes diversicolor, using an antiserum raised against synthetic endothelin-1. Immunoreactive perikarya were localized in the brain, and nerve fibers containing endothelin-1-like material were found in the neuropil occupying the central portion of the brain. No immunostained fiber elements were traced in the circumesophageal connectives. Immunoreactive perikarya occurred in the subesophageal ganglion. From this ganglion, specifically stained fibers run posteriorly toward the ventral nerve cord. In each segmental ganglion, immunoreactive neurons were observed in medio-ventral and latero-ventral regions, and one or two marked fibers extended to the parapodium. In the parapodium, small immunoreactive perikarya and fiber elements were visible. Immunolabeled fibers occurred in the stomatogastric nerves, in the wall of the buccal cavity, and in the pharynx, esophagus, intestine and its anal region. Immunoreactive perikarya and nerve fibers were visualized between the circular muscle layer and epithelial cell layer in the esophagus and intestine. The endothelin-1-like substance shown to occur in N. diversicolor appears to function as a neurotransmitter or neuromodulator.     

Mechanism of neuronal coordination of the rhythmic activities of developing flight muscles and a neurosecretory cell population in the silkmoth, Bombyx mori

Ultradian rhythmic firing activity (period of 40-90 min) of a population of neurosecretory cells (NSCs) producing FXPRLamide peptides in the subesophageal ganglion (SG) of the silkmoth, Bombyx mori, is closely coordinated with periodically occurring electrical activity of developing flight muscles (FMs) during metamorphosis. To examine neuronal mechanisms and pathways that mediate the coordination of the NSC and flight motor systems, the ventral nerve cord (VNC) or circumesophageal connectives were transected. Transection of the VNC between the SG and thoracic ganglia greatly shortened the period of activity rhythm of the FMs (5-15 min) with no effect on the rhythmicity of NSCs. Bilateral transsection of the circumesophageal connectives between the brain and SG abolished the rhythmic activity of NSCs, thereby suggesting that the coordination of the two systems may be mediated by a common oscillatory mechanism in the brain. Further, bisection of the brain in the midline failed to abolish the ultradian rhythmicity of FMs. Thus, each brain hemisphere may have an ultradian oscillator that activates the NSC system in the SG, and modulates the short-period oscillation of the flight motor system located in the thoracic ganglia.     

Specialized brain regions and sensory inputs that control locomotion in leeches

Locomotor systems are often controlled by specialized cephalic neurons and undergo modulation by sensory inputs. In many species, dedicated brain regions initiate and maintain behavior and set the duration and frequency of the locomotor episode. In the leech, removing the entire head brain enhances swimming, but the individual roles of its components, the supra- and subesophageal ganglia, in the control of locomotion are unknown. Here we describe the influence of these two structures and that of the tail brain on rhythmic swimming in isolated nerve cord preparations and in nearly intact leeches suspended in an aqueous, “swim-enhancing” environment. We found that, in isolated preparations, swim episode duration and swim burst frequency are greatly increased when the supraesophageal ganglion is removed, but the subesophageal ganglion is intact. The prolonged swim durations observed with the anterior-most ganglion removed were abolished by removal of the tail ganglion. Experiments on the nearly intact leeches show that, in these preparations, the subesophageal ganglion acts to decrease cycle period but, unexpectedly, also decreases swim duration. These results suggest that the supraesophageal ganglion is the primary structure that constrains leech swimming; however, the control of swim duration in the leech is complex, especially in the intact animal.     

The morphology and anatomy of the vestimentiferan worm Oasisia alvinae Jones, 1985 (Annelida: Siboglinidae). III. Coelomic cavity, trophosome and blood, excretory and reproductive systems

This study deals with the organization of the coelom in the all the parts of the body of the vestimentiferan Oasisia alvinae. The localization of the dissepiment between the vestimental and trunk regions in males and females differs. The histological structure and anatomy of the trophosome and the vascular, excretory, and reproductive systems is described. Three cell types are distinguishable in each trophosome lobe. Up to four bacteriocytes could be found in a row from the central blood vessel to the surface of the organ. The main blood vessels in almost all parts of the body have a well-developed muscle sheath and an endothelium that is expressed in varying degrees. In the trunk region, an intravasal body, which is represented by two modifications, is observed in the dorsal blood vessel. The excretory tree is located under the brain. The reproductive system is symmetrical in males and dissymmetrical in females. The gonoducts of females are extensive; in males, they are short and open in the front part of the reproductive coelom. The genital coeloms of both sexes perform the functions of gamete production and storage.     

Localization of allatostatin-immunoreactive material in the central nervous system,stomatogastric nervous system,and gut of the cockroach Blattella germanica

Immunoreactivity against peptides of the allatostatin family having a typical YXFGL-NH₂ C-terminus has been localized in different areas of the central nervous system, stomatogastric nervous system and gut of the cockroach Blattella germanica. In the protocerebrum, the most characteristic immunoreactive perikarya are situated in the lateral and median neurosecretory cell groups. Immunoreactive median neurosecretory cells send their axons around the circumesophageal connectives to form arborizations in the anterior neuropil of the tritocerebrum. A group of cells in the lateral aspect of the tritocerebrum project to the antennal lobes in the deutocerebrum, where immunoreactive arborizations can be seen in the periphery of individual glomeruli. Nerve terminals were shown in the corpora allata. These terminals come from perikarya situated in the lateral neurosecretory cells in the pars lateralis and in the subesophageal ganglion. Immunoreactive axons from median neurosecretory cells and from cells positioned in the anteriormost part of the tritocerebrum enter together in the stomatogastric nervous system and innervate foregut and midgut, especially the crop and the valve between the crop and the midgut. The hindgut is innervated by neurons whose perikarya are located in the last abdominal ganglion. Besides immunoreactivity in neurons, allatostatin-immunoreactive material is present in endocrine cells distributed within the whole midgut epithelium. Possible functions for these peptides according to their localization are discussed. Arch. Insect Biochem. Physiol. 37:269–282, 1998. © 1998 Wiley-Liss, Inc.     

Second-order ocellar neurons in the brain of the honeybee (Apis mellifera)

Summary Electrophoretic injection of Procion Yellow M-R4 into the ocellar tract of the worker bee has revealed the following:Two types of giant axon run from the lateral ocellus to the circumesophageal neuropile, where one branches ipsilaterally and the other contralaterally. A third type comes from the median ocellus and can be traced into the cervical connectives. The largest dendritic complex is in the circumesophageal neuropile; in addition, fiber endings have been demonstrated in the following areas: in the subretinal region, along the optic commissure, in the medulla interna, in the subesophageal ganglion and between the neurosecretory cells of the pars intercerebralis. — The giant fibers are enclosed in a glial sheath.Three types of cell body are described. One is associated with the glia; another, larger cell type comprises giant-axon somata. The third type of cell is small, and cannot yet be identified.Some of the histological results are discussed with respect to the possible function of the ocellus.     

Structure of the nervous system of Myzostoma cirriferum (Annelida) as revealed by immunohistochemistry and cLSM analyses

The nervous systems of juvenile and adult Myzostoma cirriferum Leuckart, 1836, were stained with antisera against 5-HT (5-hydroxytryptamine, serotonin), FMRFamide, and acetylated alpha-tubulin in combination with the indirect fluorescence technique and analyzed by confocal laser scanning microscopy. The central nervous system consists of two small cerebral ganglia, connected by a dorsal commissure, a ventral nerve mass, and a pair of long circumesophageal connectives joining the former to the latter. The two neuropil cords within the ventral nerve mass curve outward and are joined to one another anteriorly and posteriorly. They are connected by 12 commissures, forming a ladder-like system. A single median nerve runs along the midventral axis. In addition to the circumesophageal connectives, 11 peripheral nerves arise from each main cord. The first innervates the anterior body region. The others form five groups of two nerves each, the first and thicker nerve of which is the parapodial nerve, innervating the parapodium and two corresponding cirri. Except for those in the most posterior group, the second nerves innervate the lateral organs and the body periphery. Serotonergic perikarya are arranged in six more or less distinct clusters, the first lying in front of and the other five between the main nerve cords. The distribution pattern of the FMRFamidergic perikarya is less clear and the somata lie between and outside the cords. One pair of dorsolateral longitudinal nerves was visualized by tubulin staining. Peripheral nerves and the commissures, in particular, demonstrate a segmental organization of the nervous system of M. cirriferum. Furthermore, their arrangement indicates that the body consists of six segments, the first of which is identifiable only by the first pair of peripheral nerves, the first two commissures, and the anteriormost ventral ganglion. The nervous system M. cirriferum thus exhibits several structures also found in the basic plan of the polychaete nervous system.     

Existence and distribution of gonadotropin-releasing hormone-like peptides in the central nervous system and ovary of the Pacific white shrimp, <Emphasis Type="Italic">Litopenaeus vannamei</Emphasis>

We used antibodies against octopus gonadotropin-releasing hormone (octGnRH) and tunicate GnRH (tGnRH-I) in order to investigate the existence and distribution of GnRH-like peptides in the central nervous system (CNS) and in the ovary during various stages of the ovarian cycle of the white shrimp, Litopenaeus vannamei. OctGnRH-immunoreactive and tGnRH-I-immunoreactive neurons and fibers were present in several regions of the supraesophageal ganglion (brain), subesophageal ganglion (SEG), thoracic ganglia, and abdominal ganglia. In the brain, both octGnRH immunoreactivity (ir) and tGnRH-I-ir were detected in neurons of clusters 6, 11, 17, and associated fibers, and the anterior medial protocerebral, posterior medial protocerebral, olfactory, and tegumentary neuropils. In the SEG and thoracic ganglia, octGnRH-immunoreactive and tGnRH-I-immunoreactive neurons and fibers were present in dorsolateral and ventromedial cell clusters and in surrounding fibers. Only immunoreactive fibers were detected in the abdominal ganglia. In the ovary, both octGnRH and tGnRH-I were detected at medium intensity in the cytoplasm of early step oocytes (Oc2) and, at high intensity, in Oc3. Furthermore, octGnRH-ir and tGnRH-I-ir were intense in follicular cells surrounding Oc2 and Oc3. The presence of GnRH-ir in the CNS and ovary indicates that GnRH-like peptides occur in the white shrimp, and that GnRHs are involved in the reproductive process, especially ovarian maturation and the differentiation of oocytes, as reported in other species.     

New vistas on the initiation and maintenance of insect motor behaviors revealed by specific lesions of the head ganglia

In insects, thoracic pattern generators are modulated by the two head ganglia, the supraesophageal ganglion (brain) and the subesophageal ganglion, which act as higher-order neuronal centers. To explore the contribution of each head ganglion to the initiation and maintenance of specific motor behaviors in cockroaches (Periplaneta americana), we performed specific lesions to remove descending inputs from either the brain or the subesophageal ganglion or both, and quantified the behavioral outcome with a battery of motor tasks. We show that ‘emergency’ behaviors, such as escape, flight, swimming or righting, are initiated at the thoracic level independently of descending inputs from the head ganglia. Yet, the head ganglia play a major role in maintaining these reflexively initiated behaviors. By separately removing each of the two head ganglia, we show that the brain excites flight behavior and inhibits walking-related behaviors, whereas the subesophageal ganglion exerts the opposite effects. Thus, control over specific motor behaviors in cockroaches is anatomically and functionally compartmentalized. We propose a comprehensive model in which the relative permissive versus inhibitory inputs descending from the two head ganglia, combined with thoracic afferent sensory inputs, select a specific thoracic motor pattern while preventing the others.     

Central nervous system projections to and from the commissural ganglion of the crab Cancer borealis

Higher-order inputs provide important regulatory control to motor circuits, but few cellular-level studies of such inputs have been performed. To begin studying higher-order neurons in an accessible model system, we have localized, in the supraesophageal ganglion (brain), neurons that are candidates for influencing the well-characterized motor circuits in the stomatogastric nervous system (STNS) of the crab Cancer borealis. The STNS is an extension of the central nervous system and includes four ganglia, within which are a set of motor circuits that regulate the ingestion and processing of food. These motor circuits are locally regulated by a set of modulatory neurons, most of which are located in the paired commissural ganglia (CoGs). These modulatory neurons are well-positioned to receive input from brain neurons because the circumesophageal commissures (CoCs) connect the brain with the CoGs. We have performed a series of CoC backfills to localize the brain neurons that are likely to innervate the CoGs and are, therefore, candidates for influencinng the STNS motor patterns. CoC backfill-labeled neuronal somata within the brain are clustered around a subset of anatomically defined neuropil regions. We have concomitantly localized many CoG neurons that project into the brain. This latter pathway presumably includes neurons that provide feedback regarding ongoing STNS activity. Interestingly, nearly all of these brain and CoG neurons project through the medial aspect of the CoC. This work provides an initial framework for future studies to determine the way that higher-order input regulates rhythmic motor patterns. This work was supported by a grant from the National Institute of Neurological Disorders and Strokes (NS42813 to M.P.N.) and a National Science Foundation Fellowship (DGE9616278 to M.S.K.).     

Hyalomma dromedarii (Acari: Ixodoidea: Ixodidae): Central and peripheral nervous system anatomy

TheHyalommadromedarii central nervous system, the synganglion, is an integrated nerve mass concentrated around the esophagus and formed by fusion of a small anterodorsal supraesophageal part an a large posteroventral subesophageal part. The supraesophageal part consists of the protocerebrum including a pair of optic ganglia, a pair of cheliceral ganglia, a pair of pedipalpal ganglia, and the stomodeal pons. The subesophageal part includes four paired pedal ganglia and the complex opisthosomatic ganglion. The peripheral nervous system includes the following pairs of nerves: optic, cheliceral, pedipalpal, primary and accessory (histologically traced); also unpaired pharyngeal and recurrent nerves, four pairs of pedal nerve trunks, each with a hemal branch, and two pairs of opisthosomatic nerves. Each peripheral nerve is traced distally to the innervation site. The salivary glands are innervated anteriorly by branches of the pedipalpal nerve and medially by branches of the hemal nerves associated with the third pedal nerves.Reprint request should be sent to: Medical Zoology Department, NAMRU-3, Fleet Post Office, New York 09527, U.S.A.     

Immunohistochemical and ultrastructural analysis of the muscular and nervous systems in the interstitial polychaete Polygordius appendiculatus (Annelida)

The systematic position of Polygordiidae is still under debate. They have been assigned to various positions among the polychaetes. Recent molecular analyses indicate that they might well be part of a basal radiation in Annelida, suggesting that certain morphological characters could represent primitive character traits adopted from the annelid stem species. To test this hypothesis, an investigation of the muscular and nervous systems by means of immunological staining and confocal laser scanning microscopy and transmission electron microscopy was conducted. With the exception of the brain, the nervous system is entirely basiepidermal and consists of the brain, the esophageal connectives, the subesophageal region, the ventral nerve cord and several smaller longitudinal nerves. These are connected by a considerable number of ring nerves in each segment. The ventral nerve cord is made up of closely apposed longitudinal neurite bundles, a median and two larger lateral ones. Since distinct ganglia are lacking, it represents a medullary cord. The muscular system mainly consists of longitudinal fibers, regularly distributed oblique muscles and strong septa. The longitudinal fibers form a right and a left unit separated along the dorsal midline, each divided into a dorsal and ventral part by the oblique muscles. Anteriorly, the longitudinal musculature passes the brain and terminates in the prostomium. There is no musculature in the palps. In contrast to earlier observations, regularly arranged minute circular muscle fibers are present. Very likely, a basiepithelial and non-ganglionic organization of the ventral nerve cord as well as an orthogonal nervous system represent plesiomorphic characters. The same applies for the predominance of longitudinal muscle fibers.     

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.