Head Ganglia Research Articles

Cellular-resolution gene expression mapping reveals organization in the head ganglia of the gastropod, Berghia stephanieae.

Gastropod molluscs such as Aplysia, Lymnaea, and Tritonia have been important for determining fundamental rules of motor control, learning, and memory because of their large, individually identifiable neurons. Yet only a small number of gastropod neurons have known molecular markers, limiting the ability to establish brain-wide structure-function relations. Here we combine high-throughput, single-cell RNA sequencing with in situ hybridization chain reaction in the nudibranch Berghia stephanieae to identify and visualize the expression of markers for cell types. Broad neuronal classes were characterized by genes associated with neurotransmitters, like acetylcholine, glutamate, serotonin, and GABA, as well as neuropeptides. These classes were subdivided by other genes including transcriptional regulators and unannotated genes. Marker genes expressed by neurons and glia formed discrete, previously unrecognized regions within and between ganglia. This study provides the foundation for understanding the fundamental cellular organization of gastropod nervous systems.

Descending interneurons of the stick insect connecting brain neuropiles with the prothoracic ganglion.

Stick insects respond to visual or tactile stimuli with whole-body turning or directed reach-to-grasp movements. Such sensory-induced turning and reaching behaviour requires interneurons to convey information from sensory neuropils of the head ganglia to motor neuropils of the thoracic ganglia. To date, descending interneurons are largely unknown in stick insects. In particular, it is unclear whether the special role of the front legs in sensory-induced turning and reaching has a neuroanatomical correlate in terms of descending interneuron numbers. Here, we describe the population of descending interneurons with somata in the brain or gnathal ganglion in the stick insect Carausius morosus, providing a first map of soma cluster counts and locations. By comparison of interneuron populations with projections to the pro- and mesothoracic ganglia, we then estimate the fraction of descending interneurons that terminate in the prothoracic ganglion. With regard to short-latency, touch-mediated reach-to-grasp movements, we also locate likely sites of synaptic interactions between antennal proprioceptive afferents to the deutocerebrum and gnathal ganglion with descending or ascending interneuron fibres. To this end, we combine fluorescent dye stainings of thoracic connectives with stainings of antennal hair field sensilla. Backfills of neck connectives revealed up to 410 descending interneuron somata (brain: 205 in 19 clusters; gnathal ganglion: 205). In comparison, backfills of the prothorax-mesothorax connectives stained only up to 173 somata (brain: 83 in 16 clusters; gnathal ganglion: 90), suggesting that up to 60% of all descending interneurons may terminate in the prothoracic ganglion (estimated upper bound). Double stainings of connectives and antennal hair field sensilla revealed that ascending or descending fibres arborise in close proximity of afferent terminals in the deutocerebrum and in the middle part of the gnathal ganglia. We conclude that two cephalothoracic pathways may convey cues about antennal movement and pointing direction to thoracic motor centres via two synapses only.

Morphology and immunohistochemical characteristics of the otic ganglion in the chinchilla (Chinchilla laniger Molina).

The available literature provides relatively little information on the morphology of the autonomic head ganglia in rodents including their neurochemical codding. Morphological investigations of the otic ganglion of the chinchilla were performed using the modified acetylcholinesterase method. The cellular structure was investigated with histological techniques and neurochemical properties were studied with the double-labelling immunofluorescence method. Macromorphological investigations allowed the otic ganglion to be identified as a compact, oval agglomeration of neurons and nerve fibers. Multidimensional cross-sections revealed densely arranged neuronal perikarya and two populations of nerve cells differing in size were distinguished. The large cells (40-50 μm) accounted for about 80% of the neurons in the cross-sections. Moreover, a small number of intraganglionic nerve fibers was observed. Immunohistochemical staining revealed that over 85% of the neuronal cell bodies in the otic ganglion contained immunoreactivity to VAChT or ChAT. VIP-immunoreactive perikarya comprised approximately 10% of the ganglionic cells. Double staining revealed the presence of VAChT+ and NOS+ neurons which amounted to about 45% of the nerve cells in the otic ganglion. NOS+ only perikarya comprised approx. 15% of all the neurons. Immunoreactivity to enkephalins, substance P, somatostatin, and galanin was expressed in single nerve cell bodies and nerve fibers except numerous substance P+ intraganglionic nerve fibers. Some of them were stained also for CGRP. Single neurons stained for tyroxine hydroxylase. Our results, compared with findings in other rodent species suggest the existence of interspecies differences in the morphology, cellular structure, and immunohistochemical properties of the head autonomic ganglia in mammals.

Investigating the role of low level reinforcement reflex loops in insect locomotion

Insects are highly capable walkers, but many questions remain regarding how the insect nervous system controls locomotion. One particular question is how information is communicated between the ‘lower level’ ventral nerve cord (VNC) and the ‘higher level’ head ganglia to facilitate control. In this work, we seek to explore this question by investigating how systems traditionally described as ‘positive feedback’ may initiate and maintain stepping in the VNC with limited information exchanged between lower and higher level centers. We focus on the ‘reflex reversal’ of the stick insect femur-tibia joint between a resistance reflex (RR) and an active reaction in response to joint flexion, as well as the activation of populations of descending dorsal median unpaired (desDUM) neurons from limb strain as our primary reflex loops. We present the development of a neuromechanical model of the stick insect (Carausius morosus) femur-tibia (FTi) and coxa-trochanter joint control networks ‘in-the-loop’ with a physical robotic limb. The control network generates motor commands for the robotic limb, whose motion and forces generate sensory feedback for the network. We based our network architecture on the anatomy of the non-spiking interneuron joint control network that controls the FTi joint, extrapolated network connectivity based on known muscle responses, and previously developed mechanisms to produce ‘sideways stepping’. Previous studies hypothesized that RR is enacted by selective inhibition of sensory afferents from the femoral chordotonal organ, but no study has tested this hypothesis with a model of an intact limb. We found that inhibiting the network’s flexion position and velocity afferents generated a reflex reversal in the robot limb’s FTi joint. We also explored the intact network’s ability to sustain steady locomotion on our test limb. Our results suggested that the reflex reversal and limb strain reinforcement mechanisms are both necessary but individually insufficient to produce and maintain rhythmic stepping in the limb, which can be initiated or halted by brief, transient descending signals. Removing portions of this feedback loop or creating a large enough disruption can halt stepping independent of the higher-level centers. We conclude by discussing why the nervous system might control motor output in this manner, as well as how to apply these findings to generalized nervous system understanding and improved robotic control.

Facial Ganglia - Anatomy, Symptomatology of Lesions and Biological Relevance

The article summarizes information about the head ganglia (the sympathetic ganglia and in the sensory cranial nerves). Gives а brief historical background on the history issue and relevance of the topic. Characterized by each node with its topography and lesion clinic. The described process of treatment, and prospects for new therapies. Raised the issue of the significance of the defeat ganglia, namely, the suffering of the sick and forced treatment costs (due to the complex differential diagnosis). In a biological sense, pain first appears in chordates and during evolution, as well as transformations of the brain and spinal cord, it acquires new types, localization and significance for the performance of a living organism. And facial pain, being a nosology with a multidisciplinary approach in diagnosis and treatment, demonstrates both its complexity and importance in human life.

Serotonin Signalling in Flatworms: An Immunocytochemical Localisation of 5-HT7 Type of Serotonin Receptors in Opisthorchis felineus and Hymenolepis diminuta.

The study is dedicated to the investigation of serotonin (5-hydroxytryptamine, 5-HT) and 5-HT7 type serotonin receptor of localisation in larvae of two parasitic flatworms Opisthorchis felineus (Rivolta, 1884) Blanchard, 1895 and Hymenolepis diminuta Rudolphi, 1819, performed using the immunocytochemical method and confocal laser scanning microscopy (CLSM). Using whole mount preparations and specific antibodies, a microscopic analysis of the spatial distribution of 5-HT7-immunoreactivity(-IR) was revealed in worm tissue. In metacercariae of O. felineus 5-HT7-IR was observed in the main nerve cords and in the head commissure connecting the head ganglia. The presence of 5-HT7-IR was also found in several structures located on the oral sucker. 5-HT7-IR was evident in the round glandular cells scattered throughout the larva body. In cysticercoids of H. diminuta immunostaining to 5-HT7 was found in flame cells of the excretory system. Weak staining to 5-HT7 was observed along the longitudinal and transverse muscle fibres comprising the body wall and musculature of suckers, in thin longitudinal nerve cords and a connective commissure of the central nervous system. Available publications on serotonin action in flatworms and serotonin receptors identification were reviewed. Own results and the published data indicate that the muscular structures of flatworms are deeply supplied by 5-HT7-IR elements. It suggests that the 5-HT7 type receptor can mediate the serotonin action in the investigated species and is an important component of the flatworm motor control system. The study of the neurochemical basis of parasitic flatworms can play an important role in the solution of fundamental problems in early development of the nervous system and the evolution of neuronal signalling components.

The neuromuscular system in flatworms: serotonin and FMRFamide immunoreactivities and musculature in Prodistomum alaskense (Digenea: Lepocreadiidae), an endemic fish parasite of the northwestern Pacific

Using the immunocytochemical method and confocal scanning laser microscopy, we obtained pioneering data on the muscle system organization and presence and localization of biogenic amine serotonin and FMRFamide-related peptides in the nervous system of the trematode Prodistomum alaskense (Ward and Fillingham, 1934) Bray and Merrett 1998 (family Lepocreadiidae). This flatworm is an intestinal parasite of endemic representatives of the marine fauna of the northwestern Pacific Ocean — the prowfish (Zaprora silenus Jordan, 1896) and the lumpfish (Aptocyclus ventricosus (Pallas, 1769)). We provide data of scanning electron microscopy on the tegumental topography of P. alaskense. The body wall musculature of P. alaskense has three layers of muscle fibres — the outer circular, intermediate longitudinal, and inner diagonal. The muscle system elements are well developed in the attachment organs, digestive and reproductive systems, and in the excretory sphincter. Serotonin– and FMRFamide–immunopositive neurons and neurites are found in the head ganglia, circular commissure, longitudinal nerve cords, and in the transversal connective commissures. The innervation of the oral and ventral suckers, pharynx, and the reproductive system compartments by the serotonergic and FMRFamide–immunopositive neurites is revealed. The results discus connection with the published data on the presence and functional roles of the serotonin and FMRFamide-related peptides in Platyhelminthes.

Descending and Ascending Signals That Maintain Rhythmic Walking Pattern in Crickets.

The cricket is one of the model animals used to investigate the neuronal mechanisms underlying adaptive locomotion. An intact cricket walks mostly with a tripod gait, similar to other insects. The motor control center of the leg movements is located in the thoracic ganglia. In this study, we investigated the walking gait patterns of the crickets whose ventral nerve cords were surgically cut to gain an understanding of how the descending signals from the head ganglia and ascending signals from the abdominal nervous system into the thoracic ganglia mediate the initiation and coordination of the walking gait pattern. Crickets whose paired connectives between the brain and subesophageal ganglion (SEG) (circumesophageal connectives) were cut exhibited a tripod gait pattern. However, when one side of the circumesophageal connectives was cut, the crickets continued to turn in the opposite direction to the connective cut. Crickets whose paired connectives between the SEG and prothoracic ganglion were cut did not walk, whereas the crickets exhibited an ordinal tripod gait pattern when one side of the connectives was intact. Crickets whose paired connectives between the metathoracic ganglion and abdominal ganglia were cut initiated walking, although the gait was not a coordinated tripod pattern, whereas the crickets exhibited a tripod gait when one side of the connectives was intact. These results suggest that the brain plays an inhibitory role in initiating leg movements and that both the descending signals from the head ganglia and the ascending signals from the abdominal nervous system are important in initiating and coordinating insect walking gait patterns.

On the Role of the Head Ganglia in Posture and Walking in Insects

In insects, locomotion is the result of rhythm generating thoracic circuits and their modulation by sensory reflexes and by inputs from the two head ganglia, the cerebral and the gnathal ganglia (GNG), which act as higher order neuronal centers playing different functions in the initiation, goal-direction, and maintenance of movement. Current knowledge on the various roles of major neuropiles of the cerebral ganglia (CRG), such as mushroom bodies (MB) and the central complex (CX), in particular, are discussed as well as the role of the GNG. Thoracic and head ganglia circuitries are connected by ascending and descending neurons. While less is known about the ascending neurons, recent studies in large insects and Drosophila have begun to unravel the identity of descending neurons and their appropriate roles in posture and locomotion. Descending inputs from the head ganglia are most important in initiating and modulating thoracic central pattern generating circuitries to achieve goal directed locomotion. In addition, the review will also deal with some known monoaminergic descending neurons which affect the motor circuits involved in posture and locomotion. In conclusion, we will present a few issues that have, until today, been little explored. For example, how and which descending neurons are selected to engage a specific motor behavior and how feedback from thoracic circuitry modulate the head ganglia circuitries. The review will discuss results from large insects, mainly locusts, crickets, and stick insects but will mostly focus on cockroaches and the fruit fly, Drosophila.

Nociceptive Pathway in the Cockroach Periplaneta americana.

Detecting and avoiding environmental threats such as those with a potential for injury is of crucial importance for an animal’s survival. In this work, we examine the nociceptive pathway in an insect, the cockroach Periplaneta americana, from detection of noxious stimuli to nocifensive behavior. We show that noxious stimuli applied to the cuticle of cockroaches evoke responses in sensory axons that are distinct from tactile sensory axons in the sensory afferent nerve. We also reveal differences in the evoked response of post-synaptic projection interneurons in the nerve cord to tactile versus noxious stimuli. Noxious stimuli are encoded in the cockroach nerve cord by fibers of diameter different from that of tactile and wind sensitive fibers with a slower conduction velocity of 2–3 m/s. Furthermore, recording from the neck-connectives show that the nociceptive information reaches the head ganglia. Removing the head ganglia results in a drastic decrease in the nocifensive response indicating that the head ganglia and the nerve cord are both involved in processing noxious stimuli.

DICROCOELIUM LANCEATUM (TREMATODA, DICROCOELIIDAE): THE STUDY OF THE NEURO-MUSCULAR SYSTEM

The work provides data on the presence and localization in the nervous system of the causative agent of dicroceliosis, Dicrocoelium lanceatum serotonergic and FMRFaminergic structures. Using the immunocytochemical method and confocal scanning laser microscopy, the test substances were found in the central and peripheral parts of the parasite's nervous system — in the head ganglia, the central nervous commissure, the longitudinal nerve trunks and the transverse commissures connecting them. The innervation of the nerve fibers of the attachment organs of trematodes by immunoreactive to serotonin and neuropeptide is shown.Trematode Dicrocoelium lanceatum (Stiles and Hassal, 1896) (Dicrocoeliidae) is the causative agent of Dicroceliosis, a widespread helminthiasis of domestic and wild animals. Dwelling in the bile ducts of the liver and in the gallbladder, dicroceliums cause irreversible pathological changes in the host organism, chronic inflammation of the bile ducts, cirrhosis of the liver, and metabolic processes in animals occur. As a result of the disease, animals are depleted, their productivity decreases, growth and development lag, and the nutritional and caloric value of meat decrease.In the cycle of development of the causative agent of dicroceliasis, the intermediate hosts are land mollusks, while the additional hosts are ants. The eggs of the parasite along with the bile enter the host intestine, and then with the feces into the external environment. Mollusks swallow eggs, miracidia come out from the eggs in the intestines of the mollusk, and penetrate the liver, where daughter sporocysts develop, in which cercariae form. Of the daughter sporocysts, cercariae are introduced into the respiratory cavity of the mollusk, where they are covered with sticky mucous substance. The formed mucous lumps are pushed by the respiratory movements of the mollusk into the external environment. Infection of ants occurs when eating these mucous balls. Once in the intestinal tract, cercariae enter the ant's abdominal cavity, where they turn into metacercariae. The definitive owners infect on pastures, swallowing invasive ants along with grass.

Relationship between normalized distributional pattern and functional outcome in patients with acute cardiogenic cerebral embolism.

This study aimed to elucidate spatial characteristics for magnetic resonance imaging (MRI) of cardiogenic cerebral embolism, to determine imaging biomarkers predicting patient outcome and cerebral herniation in cardioembolic stroke. This retrospective study assessed 90 patients with cardiogenic cerebral embolism. All images from MRI were normalized using a voxel-based symptom lesion mapping technique. Patients were categorized into two subgroups based on the outcome and presence of cerebral herniation. Each subgroup was assessed individually. The distribution map of all analyzed patients revealed accumulated ischemic lesions in bilateral middle cerebral artery areas. Ischemic lesions for the poor outcome group accumulated at the corona radiata on the right side and throughout the entire left hemisphere. Receiver operating characteristic (ROC) analysis suggested that a normalized ischemic volume of 62.8 mL allowed optimal differentiation between good and poor outcomes (sensitivity, 0.923; specificity, 0.923; area under the curve (AUC), 0.91) for left-side-dominant infarction. The distribution map for the cerebral herniation group revealed large ischemic areas in the left hemisphere. The analysis of differential involvement map with random permutation analysis showed that left anterior circulation infarcts were associated with midline shift. Receiver operating characteristic analysis revealed that a normalized infarction volume of 192.9 mL was highly predictive of cerebral herniation (sensitivity, 0.929; specificity, 0.750; AUC, 0.895). The medial frontal and occipital lobes, caudate head and basal ganglia were significantly involved in those patients who developed cerebral herniation. Ischemic volume contributed to outcomes and cerebral herniation. Ischemic lesions of the anterior and posterior cerebral arteries and basal ganglia in addition to middle cerebral artery area were identified as differences on MRI images between with and without cerebral herniation patients.

The functional connectivity between the locust leg pattern generators and the subesophageal ganglion higher motor center

Higher motor centers and central pattern generators (CPGs) interact in the control of coordinated leg movements during locomotion throughout the animal kingdom. The subesophageal ganglion (SEG) is one of the insect head ganglia reported to have a role in the control of walking behavior. Here we explored the functional relations between the SEG and the thoracic leg CPGs in the desert locust. Backfill staining revealed about 300 SEG descending interneurons (DINs) altogether. Recordings from an in-vitro isolated chain of thoracic ganglia, with intact or severed connections to the SEG, during pharmacological activation were used to determine how the SEG affects the centrally generated motor output to the legs. The SEG was demonstrated to both activate leg CPGs and synchronize their bilateral activity. The role of the SEG in insect locomotion is discussed in light of these findings.

The subesophageal ganglion modulates locust inter-leg sensory-motor interactions via contralateral pathways

The neural control of insect locomotion is distributed among various body segments. Local pattern-generating circuits at the thoracic ganglia interact with incoming sensory signals and central descending commands from the head ganglia. The evidence from different insect preparations suggests that the subesophageal ganglion (SEG) may play an important role in locomotion-related tasks. In a previous study, we demonstrated that the locust SEG modulates the coupling pattern between segmental leg CPGs in the absence of sensory feedback. Here, we investigated its role in processing and transmitting sensory information to the leg motor centers and mapped the major related neural pathways. Specifically, the intra- and inter-segmental transfer of leg-feedback were studied by simultaneously monitoring motor responses and descending signals from the SEG. Our findings reveal a crucial role of the SEG in the transfer of intersegmental, but not intrasegmental, signals. Additional lesion experiments, in which the intersegmental connectives were cut at different locations, together with double nerve staining, indicated that sensory signals are mainly transferred to the SEG via the connective contralateral to the stimulated leg. We therefore suggest that, similar to data reported for vertebrates, insect leg sensory-motor loops comprise contralateral ascending pathways to the head and ipsilateral descending ones.

Do Quiescence and Wasp Venom-Induced Lethargy Share Common Neuronal Mechanisms in Cockroaches?

The escape behavior of a cockroach may not occur when it is either in a quiescent state or after being stung by the jewel wasp (Ampulex compressa). In the present paper, we show that quiescence is an innate lethargic state during which the cockroach is less responsive to external stimuli. The neuronal mechanism of such a state is poorly understood. In contrast to quiescence, the venom-induced lethargic state is not an innate state in cockroaches. The Jewel Wasp disables the escape behavior of cockroaches by injecting its venom directly in the head ganglia, inside a neuropile called the central complex a ‘higher center’ known to regulate motor behaviors. In this paper we show that the coxal slow motoneuron ongoing activity, known to be involved in posture, is reduced in quiescent animals, as compared to awake animals, and it is further reduced in stung animals. Moreover, the regular tonic firing of the slow motoneuron present in both awake and quiescent cockroaches is lost in stung cockroaches. Injection of procaine to prevent neuronal activity into the central complex to mimic the wasp venom injection produces a similar effect on the activity of the slow motoneuron. In conclusion, we speculate that the neuronal modulation during the quiescence and venom-induced lethargic states may occur in the central complex and that both states could share a common neuronal mechanism.

De novo transcriptome assembly of the marine gastropod Reishia clavigera for supporting toxic mechanism studies

The intertidal whelk Reishia clavigera is commonly used as a biomonitor of chemical contamination in the marine environment along Western Pacific region, and as a model for mechanistic studies of organotin-mediated imposex development. However, limited genomic resources of R. clavigera have restricted its role for the investigation of molecular mechanisms of such endocrine disruptions. This study, therefore, aimed to establish tissue-specific transcriptomes of the digestive gland, gonad, head ganglia, penis and the remaining body part of the male and female R. clavigera. By combining the results, a global transcriptome was obtained. A total of 578,134,720 high-quality filtered reads were obtained using Illumina sequencing. The R. clavigera transcriptome comprised of 38,466 transcripts and 32,798 unigenes with predicted open reading frames. The average length of transcripts was 1,709bp with N50 of 2,236bp. Based on sequence similarity searches against public databases, 28,657 transcripts and 24,403 unigenes had at least one BLAST hit. There were 17,530 transcripts and 14,897 unigenes annotated with at least one Gene Ontology (GO) term. Moreover, 5,776 transcripts and 5,137 unigenes were associated with 333 Kyoto Encyclopaedia of Genes and Genomes (KEGG) pathways. The numbers of unigenes were similar among the five target tissues and between sexes, but tissue-specific expression profiles were revealed by multivariate analyses. Based on the functional annotation, putative steroid hormone-associated unigenes were identified. In particular, we highlighted the presence of steroid hormone receptor homologues that could be the targets for mechanistic studies of the organotin-mediated imposex development in marine gastropods. This newly generated transcriptome assembly of R. clavigera provides a valuable molecular resource for ecotoxicological and environmental genomic studies.

Pan-neuronal imaging in roaming Caenorhabditis elegans

We present an imaging system for pan-neuronal recording in crawling Caenorhabditis elegans. A spinning disk confocal microscope, modified for automated tracking of the C. elegans head ganglia, simultaneously records the activity and position of ∼80 neurons that coexpress cytoplasmic calcium indicator GCaMP6s and nuclear localized red fluorescent protein at 10 volumes per second. We developed a behavioral analysis algorithm that maps the movements of the head ganglia to the animal's posture and locomotion. Image registration and analysis software automatically assigns an index to each nucleus and calculates the corresponding calcium signal. Neurons with highly stereotyped positions can be associated with unique indexes and subsequently identified using an atlas of the worm nervous system. To test our system, we analyzed the brainwide activity patterns of moving worms subjected to thermosensory inputs. We demonstrate that our setup is able to uncover representations of sensory input and motor output of individual neurons from brainwide dynamics. Our imaging setup and analysis pipeline should facilitate mapping circuits for sensory to motor transformation in transparent behaving animals such as C. elegans and Drosophila larva.

Neuronal control of walking: studies on insects

Abstract The control of walking in insects is to a substantial amount a function of neuronal networks in the thoracic ganglia. While descending signals from head ganglia provide general commands such as for walking direction and velocity, it is the thoracic central nervous system that controls movements of individual joints and legs. The coordination pattern of legs is velocity dependent. However, a clear stereotypic coordination pattern appears only at high velocities. In accordance with the unit burst oscillator concept, oscillatory networks (central pattern generators (CPGs)) interlocked with movement and load sensors control the timing and amplitude of joint movements. For a leg’s movements different joint CPGs of a leg are mainly coupled by proprioceptors. Differential processing of proprioceptive signals allows a task specific modulation of leg movements, for example, for changing movement direction. A switch between walking and searching movements of a leg is under local control. When stepping into a gap missing sensory input and the activation of a local command neuron evokes stereotypic searching movements of the leg.

Neuronal control of walking: studies on insects

The control of walking in insects is to a substantial amount a function of neuronal networks in the thoracic ganglia. While descending signals from head ganglia provide general commands such as for walking direction and velocity, it is the thoracic central nervous system that controls movements of individual joints and legs. The coordination pattern of legs is velocity dependent. However, a clear stereotypic coordination pattern appears only at high velocities. In accordance with the unit burst oscillator concept, oscillatory networks (central pattern generators (CPGs)) interlocked with movement and load sensors control the timing and amplitude of joint movements. For a leg’s movements different joint CPGs of a leg are mainly coupled by proprioceptors. Differential processing of proprioceptive signals allows a task specific modulation of leg movements, for example, for changing movement direction. A switch between walking and searching movements of a leg is under local control. When stepping into a gap missing sensory input and the activation of a local command neuron evokes stereotypic searching movements of the leg.

Serotonin and neuropeptide FMRFamide in the nervous system of Opisthioglyphe ranae (Trematoda: Plagiorchiidae). An iimmunocytochemical study

The presence and localization of the serotoninergic and FMRFamidergic structures in the nervous system of the trematode Opisthioglyphe ranae, the marsh frog intestinal parasite, was studied using immunocytochemistry. The serotonin-immunoreactive nerve cells and fibers were revealed in the head ganglia, circular commissure, longitudinal nerve cords and their connective commissures, as well as around the oral and ventral suckers, oesophagus and genital pore. FMRF-specific immunoreactivity was observed in the head ganglia, longitudinal nerve cords and terminal parts of the reproductive system. The results obtained are discussed in light of the available data on the presence and functional significance of the above-mentioned neurotransmitters in trematodes.