Nerve Strands Research Articles

A cadaveric study on superior hypogastric plexuses

Introduction: The superior hypogastric plexus (SHP) is found around the level of aortic bifurcation. It is important in surgical procedures in the pelvis.Methods: Ten (5; M & 5; F) fresh intact adult human cadavers were dissected. Following the initial dissection, all of them were further sectioned sagittal in the midline and separated in to half pelvises, and assessed. The study was carried out in the Department of Anatomy, Faculty of medicine Ragama, Sri Lanka from 2022 to 2024. The ethical clearance was obtained.Results: In all specimens, left connecting fibers from the inferior mesenteric plexuses (IMA) crossed the left common iliac artery and joining to the superior hypogastric plexuses. In 80%, right connecting nerve fibers from the inferior mesenteric plexuses crossed the right common iliac artery and joined the superior hypogastric plexus (SHP). Eighty percent of the specimens had, well-defined nerve strands, whereas 20% contained a delicate and irregular meshwork. In all of the specimens, the median root, or a nerve root from abdominal aortic plexus from the IMA were present. In 80% specimens, the SHP was located between the aortic bifurcation and the sacral promontory. In 20%, it extended across the pelvic brim and ended on the body of the S1 vertebra.Conclusion: The majority of the SHP were located below the aortic bifurcation and had well-defined nerve strands, rest traversed the pelvic brim and terminated on the body of the S1 vertebra. Further larger sample studies are recommended.

Antihypertrophic Effect of Menthol from Mentha x Piperita Concerning Cardiac Hypertrophy: A Review

Background: The abnormal enlargement or thickening of the heart muscle leads to diminishment of ventricular wall tension which helps to keep up the outstanding task at hand in terms of capacity and effectiveness. There are two kinds of hypertrophy: physiological and pathological. Initially, what evolves as an adaptive reaction, advances to heart failure. Different cellular signaling pathways control each type of hypertrophy. Peppermint - Mentha x piperita, a hybrid of Mentha spicata and Mentha aquatica belongs to the family of Lamiaceae. The peppermint oil has high menthol content and has many useful targets in cardiovascular disorders, such as hypertension, coronary heart disease, etc., Objective: The objective of this review article is to investigate the antihypertrophic activity of Mentha x piperita which is not yet established Methods: For manuscript preparation, we had used all accessible international databases, traditional books (Regular books in English), and electronic resources (Google Scholar, PubMed, Science Direct, Springer, Wiley, etc.,), unpublished data (thesis, R&D reports, and dissertations). Results: Menthol may activate Transient receptor potential cation channel subfamily M (melastatin) member 8 (TRMP8) channels resulting in increased cytosolic calcium concentration and vasorelaxation activity. Menthol is known to stimulate the elevation of TRPM8 protein in the endothelium, Vascular Smooth Muscle (VSM), and vascular afferent nerve strands, while obstructing VSM L-type Calcium Channels (LCC), contributing to both the cardiovascular and vasoactive properties of peppermint. In vivo experiments proved that glucagon plays a significant role in the preventive effect of menthol (as TRPM8 modulator) against a high-fat diet (HFD) induced weight gain and related complications. Conclusion: Due to the efficacy of Menthol (Mentha x piperita) in its cardioprotective properties, understanding the actual mechanisms related to the efficacy of Menthol on CVD can be the subject of future studies.

Innervation of internal female genital organs in the pig during prenatal development.

This study investigated the innervation of internal genital organs in 5-, 7- and 10-week-old female pig foetuses using single and double-labelling immunofluorescence methods. The structure and topography of the organs was examined using a scanning electron microscope (SEM). The investigations revealed differences in the innervation between the three developmental periods. Immunostaining for protein gene product 9.5 (PGP; general neural marker) disclosed solitary nerve fibres in the external part of the gonadal ridge and just outside of the mesenchyme surrounding mesonephric ducts in 5-week-old foetuses. Double-labelling immunohistochemistry revealed that nerve fibres associated with the ridge expressed dopamine β-hydroxylase (DβH; adrenergic marker) or vesicular acetylcholine transporter (VAChT; cholinergic marker). In 7-week-old foetuses, the PGP-positive nerve terminals were absent from the gonad but some of them ran outside and along, and sometimes penetrated into the mesenchyme surrounding the tubal and uterine segments of the paramesonephric ducts and uterovaginal canal. Few axons penetrated into the mesenchyme. DβH-positive fibres were found in single nerve strands or bundles distributed at the edge of the mesenchyme. VAChT-positive nerve terminals formed delicate bundles located at the edge of the mesenchyme, and the single nerves penetrated into the mesenchyme. DβH was also expressed by neurons which formed cell clusters comprising also DβH- or VAChT-positive nerve fibres. In 10-week-old foetuses, PGP-positive nerve fibres were still absent from the ovary but some were distributed in the mesenchyme associated with the uterovaginal canal and uterine and a tubal segment of the paramesonephric ducts, respectively. DβH- or VAChT-positive nerve fibres were distributed at the periphery of the mesenchyme associated with the uterovaginal canal. Some DβH- and many VAChT-positive nerve fibres were evenly distributed throughout the mesenchyme. The clusters of nerve cells comprised DβH-positive perikarya and DβH- or VAChT-positive nerve fibres. The investigations revealed no DβH/VAChT-positive nerve fibres or neurons as well as no nerve structures stained for calcitonin gene-related peptide and/or substance P (sensory markers) associated with the genital organs in the studied prenatal periods.

Stretchable Low Impedance Electrodes for Bioelectronic Recording from Small Peripheral Nerves

Monitoring of bioelectric signals in peripheral sympathetic nerves of small animal models is crucial to gain understanding of how the autonomic nervous system controls specific body functions related to disease states. Advances in minimally-invasive electrodes for such recordings in chronic conditions rely on electrode materials that show low-impedance ionic/electronic interfaces and elastic mechanical properties compliant with the soft and fragile nerve strands. Here we report a highly stretchable low-impedance electrode realized by microcracked gold films as metallic conductors covered with stretchable conducting polymer composite to facilitate ion-to-electron exchange. The conducting polymer composite based on poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) obtains its adhesive, low-impedance properties by controlling thickness, plasticizer content and deposition conditions. Atomic Force Microscopy measurements under strain show that the optimized conducting polymer coating is compliant with the micro-crack mechanics of the underlying Au-layer, necessary to absorb the tensile deformation when the electrodes are stretched. We demonstrate functionality of the stretchable electrodes by performing high quality recordings of renal sympathetic nerve activity under chronic conditions in rats.

Technical feasibility of visualizing myenteric plexus using confocal laser endomicroscopy.

In preceding studies, we identified that the myenteric plexus (MP) could be visualized with confocal laser endomicroscopy (CLE) by applying neural fluorescent probes lacking clinical safety profiling data from the submucosal side. In this study, we evaluated the technical feasibility of MP visualization using probe-based CLE (pCLE) from the serosal side with cresyl violet (CV), which has been used clinically for chromoendoscopy. The dye affinity of CV for MP was first explored in an in vivo transgenic mouse model using neural crest derivatives labeled with green fluorescent protein. We also tested the feasibility of CV-assisted visualization of MP in human surgical specimens, wherein the tissue dying and pCLE observation were performed from the serosal side. In the human study, rate of MP visualization by pCLE was evaluated as the primary outcome. We also evaluated the sensitivity and specificity of MP visualization by pCLE, using pathological presence/absence of MP as the gold standard. We confirmed the dye affinity of CV to MP in all tested models. The MP appeared as brightly stained ladder-like structures with pCLE, and in the human study, MP was visualized in 12/14 (85.7%) samples, with 92.3% sensitivity and 100% specificity. In positive cases showing the ladder-like structure of MP by pCLE, the mean maximum and minimum widths of nerve strands were 54.3 (±23.6) and 19.7 (±6.0)μm, respectively. A ganglion was detected by pCLE in 10 cases (10/12, 83.3%). This study demonstrated the technical feasibility of visualizing the MP in real time by CV-assisted pCLE (UMIN-CTR number, UMIN000015056).

Clinical, physiological and pathological characterisation of the sensory predominant peripheral neuropathy in copper deficiency

IntroductionMyelopathy is considered the most common neurological complication of copper deficiency. Concurrent peripheral neuropathy has been recognised in association with copper deficiency but has not been well characterised.ObjectivesTo characterise the...

A Narrative Study of Diagnosing Various Retinal Diseases using Optical Coherence Tomography

Objectives: The aim of the study is to review working principles of Optical Coherence Tomography (OCT), and to describe its use in the diagnosis and management of various retinal diseases in medical field. Methods/Analysis: Qualitative analysis such as Morphological alterations, Anomalous structures, 3-D & C-scan studies, increased and decreased reflectivity. Quantitative analysis includes retinal layer thickness measurement, volume and mapping. Interpretations of Spectral Domain OCT (SD-OCT), images to analyze abnormalities in retinal layers in z-depth or 3D scan or C-scan. SD-OCT visualizes ocular structures of retinal diseases in unprecedented 3-D views. It provides an accurate analytic and synthetic study of Retinal Deformations, Retinal edema, Macular Pucker, Macular hole, irregular foveal depression. Findings: In 3-D studies of macular cube, B-scan of the retinal profile gives an absolute representation of optical tissue for the study and measurement. The thickness of Fovea is about 160 - 180 microns and the resolving power measured using the A-scan study is under 4 microns. In case of ARMD-Age- related Macular degeneration (Drusen), the yellow deposits in between RPE (Retinal Pigment Epithellium) and Choroid layer is identified clearly. OCT finds that the RPE atrophy is dynamic and also the external membrane or layers of the retina. In case of Pseudo-vitelliform macular degeneration OCT shows a nontransparent yellow-orange sub-retinal deposit and a central retinal detachment. For Glaucoma disease OCT provides accurate images and this allows us to understand the physical structure (morphology) of the optical disc and the peripapillary nerve strands. In Central Serous Chorio Retinopathy (CSCR) OCT display a little gaps/discontinuity in the RPE at the dispersion location within the serous RPE separation. Various diffusion points shall be visible around the area towards Bruch’s membrane around RPE. Cystoid Macular Edema displayed by showing destruction of the Muller glia cells, leading to cystoid cavity formation inside the retina. Novelty/improvement: Future work is towards the study of determining and analyzing macular degeneration by SD-OCT tool to diagnose possible symptoms for the disease by identifying affected retinal layers through OCT images using improved mmethodologies like image pre-processing, segmentation and classification based on specific algorithm in neural networks.

A new method for spike extraction using velocity selective recording demonstrated with physiological ENG in Rat

BackgroundThis paper describes a series of experiments designed to verify a new method of electroneurogram (ENG) recording that enables the rate of neural firing within prescribed bands of propagation velocity to be determined in real time. Velocity selective recording (VSR) has been proposed as a solution to the problem of increasing the information available from an implantable neural interface (typically with electrodes in circumferential nerve cuffs) and has been successful in transforming compound action potentials into the velocity domain. New methodThe new method extends VSR to naturally-evoked (physiological) ENG in which the rate of neural firing at particular velocities is required in addition to a knowledge of the velocities present in the recording. ResultsThe experiments, carried out in rats required individual spikes to be distinct and non-overlapping, which could be achieved by a microchannel or small-bore cuff. In these experiments, strands of rat nerve were laid on ten hook electrodes in oil to demonstrate the principle. Comparison with existing methodThe new method generates a detailed overview of the firing rates of neurons based on their conduction velocity and direction of propagation. In addition it allows real time working in contrast to existing spike sorting methods using statistical pattern processing techniques. ConclusionsResults show that by isolating neural activity based purely on conduction velocity it was possible to determine the onset of direct cutaneous stimulation of the L5 dermatome.

Neuropathic alterations of the myenteric plexus neurons following subacute intraperitoneal administration of salsolinol

Impairment of the enteric nervous system has been suggested to occur within the pathogenesis of neurodegenerative diseases. Thus, in the current study, we consider salsolinol (1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline, SAL) as a substance that can potentially induce myenteric neurodegen-eration. Male Wistar rats were subjected to continuous intraperitoneal dosing of salsolinol (200 mg/kg in total) with osmotic mini-pumps for either two or four weeks. An equivalent group of rats served as the control. Jejunal myenteric neurons were subjected to immunofluorescence staining to detect neuron specific protein - protein gene product (pan-neuronal marker, PGP 9.5), nitric oxide synthase (NOS), choline acetyltransferase (ChAT), Bax-protein and alpha-synuclein. In search of any functional impairment within the gastrointestinal tract, gut motility was assessed by determining the residual solid food contents in the stomach and the small and large intestine transit. The myenteric neuron count, the mean size of the neuron body, the area of ganglia and the diameter of nerve strands were decreased in both of the salsolinol-treated groups compared with the controls. The number of NOS-positive cells was lower in the salsolinol-treated groups, while the number of ChAT-positive cells remained unchanged in comparison with the controls. Neurons expressing the pro-apoptotic Bax protein and alpha-synuclein deposits were observed among the myenteric neurons of the salsolinol-treated rats. Salsolinol evokes enteric neuronal cell death via initiation of apoptosis and leads to the formation of pathological aggregates of alpha-synuclein. Impairment of myenteric neurons, mainly the inhibitory motor neurons, might be responsible for the abnormal intestinal transit. Thus, salsolinol might be regarded as a suitable compound for inducing experimental enteric neurodegeneration in rats.

Potential of the use of an antioxidant compound to promote peripheral nerve regeneration after injury

The peripheral nervous system is a vital part of the body because it transfers information to coordinate all actions. Peripheral nerve injuries are detrimental to the proper function of this system and can cause loss of sense and movement. It is of utmost importance to research approaches to the treatment of peripheral nerve damage because such injuries can drastically change a person's life, and these traumatic injuries are a significant cause of physical disabilities that primarily affect the lives of young adults of working age. The aetiologies of traumatic peripheral nerve injury include penetrating injury, crush, traction, ischemia, and less common mechanisms, such as thermal-, electric shock-, radiation-, percussion-, and vibration-induced injuries (Robinson, 2004). Lacerations, for example, by glass, knives, fans, saw blades, auto metal, and long bone fractures, account for approximately 30% of serious nerve injuries. Another common injury mechanism is compression, which may involve mechanical deformation and ischemia. Manipulation of the nerve can generate a severe inflammatory reaction in the nerve, and these reactions have been likened to chemical burns with dense scarring accompanied by considerable pain (Bagheri et al., 2011).

FRI0518 A Loss of Telocytes Accompanies Fibrosis of Multiple Organs in Systemic Sclerosis

BackgroundTelocytes are a distinct population of stromal (interstitial) cells recently identified in a variety of tissues and organs. By their extremely long cytoplasmic processes telocytes form a three-dimensional network that...

C-opsin Expressing Photoreceptors in Echinoderms

Today's progress in molecular analysis and, in particular, the increased availability of genome sequences have enabled us to investigate photoreceptor cells (PRCs) in organisms that were formerly inaccessible to experimental manipulation. Our studies of marine non-chordate deuterostomes thus aim to bridge a gap of knowledge regarding the evolution of deuterostome PRCs prior to the emergence of vertebrates' eyes. In this contribution, we will show evidence for expression of a c-opsin photopigment, which, according to our phylogenetic analysis, is closely related to an assemblage of chordate visual c-opsins. An antibody raised against sea urchins' c-opsin protein (Sp-Opsin1) recognizes epitopes in a variety of tissues of different echinoderms. While in sea urchins this c-opsin is expressed in locomotory and buccal tube feet, spines, pedicellaria, and epidermis, in brittlestars and starfish we found the immuno-reaction to be located exclusively in cells within the animals' spines. Structural characteristics of these c-opsin+ PRC types include the close vicinity/connection to nerve strands and a, so far unexplored, conspicuous association with the animals' calcite skeleton, which previously has been hypothesized to play a role in echinoderm photobiology. These features are discussed within the context of the evolution of photoreceptors in echinoderms and in deuterostomes generally.

High sensitivity recording of afferent nerve activity using ultra-compliant microchannel electrodes: an acute in vivo validation

Neuroprostheses interfaced with transected peripheral nerves are technological routes to control robotic limbs as well as convey sensory feedback to patients suffering from traumatic neural injuries or degenerative diseases. To maximize the wealth of data obtained in recordings, interfacing devices are required to have intrafascicular resolution and provide high signal-to-noise ratio (SNR) recordings. In this paper, we focus on a possible building block of a three-dimensional regenerative implant: a polydimethylsiloxane (PDMS) microchannel electrode capable of highly sensitive recordings in vivo. The PDMS ‘micro-cuff’ consists of a 3.5 mm long (100 µm × 70 µm cross section) microfluidic channel equipped with five evaporated Ti/Au/Ti electrodes of sub-100 nm thickness. Individual electrodes have average impedance of 640 ± 30 kΩ with a phase angle of −58 ± 1 degrees at 1 kHz and survive demanding mechanical handling such as twisting and bending. In proof-of-principle acute implantation experiments in rats, surgically teased afferent nerve strands from the L5 dorsal root were threaded through the microchannel. Tactile stimulation of the skin was reliably monitored with the three inner electrodes in the device, simultaneously recording signal amplitudes of up to 50 µV under saline immersion. The overall SNR was approximately 4. A small but consistent time lag between the signals arriving at the three electrodes was observed and yields a fibre conduction velocity of 30 m s−1. The fidelity of the recordings was verified by placing the same nerve strand in oil and recording activity with hook electrodes. Our results show that PDMS microchannel electrodes open a promising technological path to 3D regenerative interfaces.

Three-dimensional demonstration of the interstitial cells of Cajal associated with the submucosal plexus in guinea-pig caecum

The guinea-pig caecum was studied by using immunohistochemistry for Kit receptors and nerves to clarify whether interstitial cells of Cajal (ICC) were localized in association with the submucosal plexus (ICC-SP). A large area of the guinea-pig caecum was nearly devoid of longitudinal muscles, because they were concentrated into three bundles of the taenia caeci (coli) and this allowed clear observation of the myenteric and submucosal plexus as separate networks in whole-mount stretch preparations. The myenteric plexus was observed as a loose polygonal network consisting in elongated ganglia and long connecting nerve strands, whereas the submucosal plexus was identified as smaller ovoid ganglia connected to much thinner nerve strands in different tissue layers. Three-dimensional reconstruction of confocal images revealed multipolar-shaped ICC-SP located around the submucosal ganglion in a basket formation. Bipolar ICC-SP were also observed along the connecting nerve strands of the submucosal plexus. The functional involvement of ICC-SP in mucosal activity is discussed in relation to fluid transportation. This three-dimensional study of ICC-SP thus provides a candidate for the most suitable material available for functional experiments examining the physiological significance of ICC-SP.

Experimental Physiology -Viewpoints: Parasympathetic control of blood flow to the activated human brain

Experimental Physiology -<i>Viewpoints</i>: Parasympathetic control of blood flow to the activated human brain

Age-related changes in substance P-immunoreactive nerve structures of the rat recto-anal region

Abstract The recto-anal region is innervated by extrinsic and intrinsic nerves and a number of neuropeptides including substance P (SP) have been suggested to participate in the regulation of intestinal movements. We examined the age-related changes in the distribution of SP-immunoreactive nerve structures in the distal part of the rat large intestine. Using immunohistochemistry, the presence of SP was studied in fresh tissues from Wistar rats at different ages taken at three sampling sites, the distal rectum, anal canal and internal anal sphincter. In the 15-day old rats the myenteric plexus of the distal rectum and anal canal was well outlined by numerous SP-immunoreactive varicose nerve fibres encircling immunonegative perikarya. In the circular muscle layer, nerve fibres and small nerve bundles ran parallel to the muscle cells, while in the longitudinal muscle layer, only occasional nerve fibres were seen. At the level of the internal anal sphincter, no myenteric ganglia were present. Here, thin varicose fibers ran parallel to the smooth muscle cells. In the 3-month old rats, a larger number of intensely staining SP-immunoreactive nerve fibres were found and in the circular muscle layer, thicker nerve strands were observed. In the 26-month old rats, the density and staining intensity of SP-immunopositive nerve fibres in the myenteric plexus was lower than in the 3-month-old rats. Similar changes in the SP-immunostained fibres in the internal anal sphincter were observed. Degenerative alterations in SP-containing fibres during aging appear to play a role in ano-rectal motility and sphincter control.

Kinetic and thermodynamic properties of MAG antagonists

Paraplegia is caused by injuries of the central nervous system (CNS) and especially young people suffer from these severe consequences as, for example, the loss of motor functions. The lack of repair of the injured nerve strands originates from the inhibitory environment for axon regeneration in the CNS. Specific inhibitory proteins block the regrowth of nerve roots. One of these neurite outgrowth inhibitors is the myelin-associated glycoprotein (MAG), which is a member of the Siglec family (sialic acid-binding immunoglobulin-like lectin). In previous studies, we identified potent small molecule MAG antagonists. In this communication, we report new neuraminic acid derivatives modified in the 4- and 5-position, and the influence of various structural modifications on their kinetic and thermodynamic binding properties.

Capitellid connections: contributions from neuromuscular development of the maldanid polychaete Axiothella rubrocincta (Annelida).

BackgroundNumerous phylogenetic analyses on polychaete annelids suggest a taxon Capitellida that comprises the three families Maldanidae, Arenicolidae and Capitellidae. Recent molecular studies support the position of the Echiura, traditionally ranked as a separate phylum, within the capitellids. In order to test the robustness of this molecular-based hypothesis we take a different approach using comparative analyses of nervous and muscle system development in the maldanid Axiothella rubrocincta. Employing immunocytochemistry in combination with confocal laserscanning microscopy, we broaden the database on capitellid organogenesis, thereby incorporating classical histological data in our analysis. Besides assessing possible shared features with the echiurans, we also discuss the variability of neural and muscular characters within the Capitellida.ResultsThe scaffold of the adult central nervous system, which is already established in early developmental stages of Axiothella, consists of cerebral commissures that give rise to simple circumesophageal connectives with fused ventral and dorsal roots and a single ventral neurite bundle. From the latter arise segmental neurites that innervate the peripheral bodywall. Since there is no observable regular pattern, and individual neurites are lost during ontogeny, their exact arrangement remains elusive. The pharynx is encircled by a prominent stomatogastric nerve ring, with a pair of anterior and lateral proboscis neurites directly connecting it to the central nervous system. One pair of ventral and one pair of dorsal longitudinal muscles form the earliest rudiments of the bodywall musculature in late larval stages, while a continuous layer of circular muscles is lacking throughout ontogeny.ConclusionsComparative neurodevelopmental analysis of capitellid and echiuran species reveals several common characters, including simple circumesophageal connectives, a single fused ventral nerve strand, and a stomatogastric ring nerve, that support a close relationship of both taxa, thus corroborating recent molecular phylogenetic analyses. The data on myogenesis show that four longitudinal muscle bands most likely represent an ancestral character not only for the Capitellida, but for the Annelida in general. Whether or not circular muscles are part of the annelid groundpattern remains uncertain.

The Enteric Nervous System In The Goat: Regional Morphological Differences And The Organization Of Submucosal And Intramucosal Plexuses

Regional differences, submucosal and intramucosal organization of ganglia in the enteric nervous system (ENS) of large mammals are not yet clear. The ENS of eight adult goats was studied by S-100 protein, neurofilament proteins, and substance P immunohistochemistry. Numerical density was used to establish intramucosal ganglia distribution. The outer submucosal plexus (OSP) and inner submucosal plexus (ISP) were differentiated using submucosal vascular arcade landmark. Primary nerve strands emerged beneath OSP ganglia and the latter were coarse textured and their primary nerve strands displayed a definitive orientation relative to circular muscle. The OSP and ISP were subdivided into the plexus submucous extremus and intermediate plexus, respectively based on topography, size, shape, outline and density of ganglia and nerve meshworks, and size of nerve cell bodies. Mucosal plexus contained many ganglia and isolated nerve cell bodies with higher numerical densities in caecum, colon and ileum. Myenteric, OSP, ISP and mucosal plexuses showed a similar pattern of regional differences in the size of ganglia and nerve strands. Larger ganglia and large nerve strands were found in the colon and caecum. They were medium sized in the duodenum, rectum, ileum and distal jejunum and smaller in the proximal and middle jejunum. The present study elaborates on the morphological features to differentiate OSP from ISP and suggests that plexus submucous extremus and intermediate plexus exist in intestine of goat. Regional variations of the sizes of ganglia and nerves, stratification of submucosal and intramucosal ganglia suggest a functional significance in regulating muscle, vascular, immune system and mucosal functions. Tanzania Veterinary Journal Vol. 24 (1) 2007: pp. 1-22

Distribution of serotonin in the trunk of Metaperipatus blainvillei (Onychophora, Peripatopsidae): Implications for the evolution of the nervous system in Arhropoda

Onychophora ("velvet worms") are a key taxon in the discussion of arthropod phylogeny. Studies that analyze neuroanatomical characters against a phylogenetic background have recently provided new insights into this debate. However, to date only a few studies on nervous system organization, particularly in the trunk, are available in Onychophora. To close this gap and to compare the onychophoran nervous system with that of other bilaterians, we have analyzed the pattern of serotonin-like immunoreactivity in Metaperipatus blainvillei (Peripatopsidae). In addition to confirming previous histological observations, our experiments revealed many new aspects of nervous system organization in Onychophora. The serotonergic nervous system of M. blainvillei consists of five longitudinal nerve strands (the paired dorsolateral nerves, the heart nerve, and the paired ventral cords), which are interconnected at regular intervals by ring commissures as well as median commissures. The ring commissures are absent in the leg-bearing regions. In addition to the main nerve tracts, there are several extensive fiber networks innervating the integument, the nephridial organs, and the body musculature. The leg nerves and nephridial nerves represent the only strictly segmental neuronal structures. We conclude that the general architecture of the onychophoran nervous system in the trunk closely resembles the orthogonal organization that is present in various other groups of Bilateria, which suggests that the arthropod nervous system is derived from such an orthogonal pattern. This finding implies that the "rope ladder-like" nervous system may have arisen independently in Panarthropoda and Annelida and does not represent a synapomorphy of these groups.