Locust Nervous System Research Articles

Piwi/piRNAs control food intake by promoting neuropeptide F expression in locusts

Animal feeding, which directly affects growth and metabolism, is an important physiological process. However, the contribution of PIWI proteins and PIWI‐interacting RNAs (piRNAs) to the regulatory mechanism of animal feeding is unknown. Here, we report a novel function of Piwi and piRNAs in regulating food intake in locusts. Our study shows that the locust can serve as a representative species for determining PIWI function in insects. Knockdown of Piwi1 expression suppresses anabolic processes and reduces food consumption and body weight. The reduction in food intake by knockdown of Piwi1 expression results from decreased expression of neuropeptide NPF1 in a piRNA‐dependent manner. Mechanistically, intronic piRNAs might enhance RNA splicing of NPF1 by preventing hairpin formation at the branch point sites. These results suggest a novel nuclear PIWI/piRNA‐mediated mechanism that controls food intake in the locust nervous system.

An Algorithm for Tracking the Position and Velocity of Multiple Neuronal Signals Using Implantable Microelectrodes In Vivo.

Increasingly complex multi-electrode arrays for the study of neurons both in vitro and in vivo have been developed with the aim of tracking the conduction of neural action potentials across a complex interconnected network. This is usually performed through the use of electrodes to record from single or small groups of microelectrodes, and using only one electrode to monitor an action potential at any given time. More complex high-density electrode structures (with thousands of electrodes or more) capable of tracking action potential propagation have been developed but are not widely available. We have developed an algorithm taking data from clusters of electrodes positioned such that action potentials are detected by multiple sites, and using this to detect the location and velocity of action potentials from multiple neurons. The system has been tested by analyzing recordings from probes implanted into the locust nervous system, where recorded positions and velocities correlate well with the known physical form of the nerve.

A Furcated Visual Collision Avoidance System for an Autonomous Microrobot

This paper proposes a secondary reactive collision avoidance system for microclass of robots based on a novel approach known as the furcated luminance-difference processing (FLDP) inspired by the lobula giant movement detector, a wide-field visual neuron located in the lobula layer of a locust nervous system. This paper addresses some of the major collision avoidance challenges: obstacle proximity and direction estimation, and operation in GPS-denied environment with irregular lighting. Additionally, it has proven effective in detecting edges independent of background color, size, and contour. The FLDP executes a series of image enhancement and edge detection algorithms to estimate collision threat-level which further determines whether the robot’s field of view must be dissected where each section’s response is compared against the others to generate a simple collision-free maneuver. Ultimately, the computation load and the performance of the model are assessed against an eclectic set of offline as well as real-time real-world collision scenarios validating the proposed model’s asserted capability to avoid obstacles at more than 670 mm prior to collision, moving at 1.2 ms−1 with a successful avoidance rate of 90% processing at 120 Hz on a simple single-core microcontroller, sufficient to conclude the system’s feasibility for real-time real-world applications that possess fail-safe collision avoidance system.

Optogenetic manipulation of medullary neurons in the locust optic lobe.

The locust is a widely used animal model for studying sensory processing and its relation to behavior. Due to the lack of genomic information, genetic tools to manipulate neural circuits in locusts are not yet available. We examined whether Semliki Forest virus is suitable to mediate exogenous gene expression in neurons of the locust optic lobe. We subcloned a channelrhodopsin variant and the yellow fluorescent protein Venus into a Semliki Forest virus vector and injected the virus into the optic lobe of locusts ( Schistocerca americana). Fluorescence was observed in all injected optic lobes. Most neurons that expressed the recombinant proteins were located in the first two neuropils of the optic lobe, the lamina and medulla. Extracellular recordings demonstrated that laser illumination increased the firing rate of medullary neurons expressing channelrhodopsin. The optogenetic activation of the medullary neurons also triggered excitatory postsynaptic potentials and firing of a postsynaptic, looming-sensitive neuron, the lobula giant movement detector. These results indicate that Semliki Forest virus is efficient at mediating transient exogenous gene expression and provides a tool to manipulate neural circuits in the locust nervous system and likely other insects. NEW & NOTEWORTHY Using Semliki Forest virus, we efficiently delivered channelrhodopsin into neurons of the locust optic lobe. We demonstrate that laser illumination increases the firing of the medullary neurons expressing channelrhodopsin and elicits excitatory postsynaptic potentials and spiking in an identified postsynaptic target neuron, the lobula giant movement detector neuron. This technique allows the manipulation of neuronal activity in locust neural circuits using optogenetics.

Complex object motion represented by context-dependent correlated activity of visual interneurones.

Accurate and adaptive encoding of complex, dynamic visual information is critical for the survival of many animals. Studies across a range of taxa have investigated behavioral and neuronal responses to objects that represent a threat, such as a looming object approaching along a direct collision course. By investigating neural mechanisms of avoidance behaviors through recording multineuronal activity, it is possible to better understand how complex visual information is represented in circuits that ultimately drive behaviors. We used multichannel electrodes to record from the well‐studied locust nervous system to explore how object motion is reflected in activity of correlated neural activity. We presented locusts (Locusta migratoria) with objects that moved along one of 11 unique trajectories and recorded from descending interneurons within the ventral nerve cord. Spike sorting resulted in 405 discriminated units across 20 locusts and we found that 75% of the units responded to some form of object motion. Dimensionality reduction through principal component (PCA) and dynamic factor (DFA) analyses revealed population vector responses within individuals and common firing trends across the pool of discriminated units, respectively. Population vector composition (PCA) varied with the stimulus and common trends (DFA) showed unique tuning related to changes in the visual size and trajectory of the object through time. These findings demonstrate that this well‐described collision detection system is more complex than previously envisioned and will drive future experiments to explore fundamental principles of how visual information is processed through context‐dependent dynamic ensembles of neurons to initiate and control complex behavior.

Na+-K+-ATPase trafficking induced by heat shock pretreatment correlates with increased resistance to anoxia in locusts.

The sensitivity of insect nervous systems to anoxia can be modulated genetically and pharmacologically, but the cellular mechanisms responsible are poorly understood. We examined the effect of a heat shock pretreatment (HS) on the sensitivity of the locust (Locusta migratoria) nervous system to anoxia induced by water immersion. Prior HS made locusts more resistant to anoxia by increasing the time taken to enter a coma and by reducing the time taken to recover the ability to stand. Anoxic comas were accompanied by surges of extracellular potassium ions in the neuropile of the metathoracic ganglion, and HS reduced the time taken for clearance of excess extracellular potassium ions. This could not be attributed to a decrease in the activity of protein kinase G, which was increased by HS. In homogenates of the metathoracic ganglion, HS had only a mild effect on the activity of Na(+)-K(+)-ATPase. However, we demonstrated that HS caused a threefold increase in the immunofluorescent localization of the α-subunit of Na(+)-K(+)-ATPase in metathoracic neuronal plasma membranes relative to background labeling of the nucleus. We conclude that HS induced trafficking of Na(+)-K(+)-ATPase into neuronal plasma membranes and suggest that this was at least partially responsible for the increased resistance to anoxia and the increased rate of recovery of neural function after a disturbance of K(+) homeostasis.

A modified model for the Lobula Giant Movement Detector and its FPGA implementation

Bio-inspired vision sensors are particularly appropriate candidates for navigation of vehicles or mobile robots due to their computational simplicity, allowing compact hardware implementations with low power dissipation. The Lobula Giant Movement Detector (LGMD) is a wide-field visual neuron located in the Lobula layer of the Locust nervous system. The LGMD increases its firing rate in response to both the velocity of an approaching object and the proximity of this object. It has been found that it can respond to looming stimuli very quickly and trigger avoidance reactions. It has been successfully applied in visual collision avoidance systems for vehicles and robots. This paper introduces a modified neural model for LGMD that provides additional depth direction information for the movement. The proposed model retains the simplicity of the previous model by adding only a few new cells. It has been simplified and implemented on a Field Programmable Gate Array (FPGA), taking advantage of the inherent parallelism exhibited by the LGMD, and tested on real-time video streams. Experimental results demonstrate the effectiveness as a fast motion detector.

Bio-Inspired Real-Time Robot Vision for Collision Avoidance

A mixed analog-digital integrated vision sensor was designed to detect an approaching object in real-time. To respond selectively to approaching stimuli, the sensor employed an algorithm inspired by the visual nervous system of a locust, which can avoid collisions robustly by using visual information. An electronic circuit model was designed to mimic the architecture of the locust nervous system. Computer simulations showed that the model provided appropriate responses for collision avoidance. We implemented the model with a compact hardware system consisting of a silicon retina and field-programmable gate array (FPGA) circuits; the system was confirmed to respond selectively to approaching stimuli that constituted a collision threat.

2P1-D04 衝突回避のためのアナログ・デジタル混在型ロボットビジョン(ロボットビジョン)

A mixed analog-digital integrated vision sensor was designed to detect an approaching object in real time. To respond selectively to looming stimuli, the sensor employed an algorithm inspired by a visual nervous system in the locust, which can avoid a collision robustly by use of visual information. An electronic circuit model was designed to mimic the architecture of the locust nervous system. Computer simulations showed that the model provided appropriate responses for collision avoidance. We implemented the model with a compact hardware system consisting of a silicon retina and FPGA circuits and the system was confirmed to be available in real-world scenes.

The distribution of putative nitric oxide releasing neurones in the locust abdominal nervous system: a comparison of NADPHd histochemistry and NOS-immunocytochemistry

Nitric oxide is well established as a signalling molecule in the nervous system of vertebrates and invertebrates. In this study we evaluate the usefulness of NADPHdiaphorase histochemistry and immunocytochemistry for detecting the presence of nitric oxide synthase in locusts. We describe the distribution of putative nitric oxide releasing neurones and stained neuropiles in the locust ventral nerve cord, in particular the abdominal ganglia and abdominal neuromeres. NADPHdiaphorase histochemistry revealed prominent staining in all neuropilar regions and a specific distribution pattern of stained cell bodies in all examined ganglia. Nitric oxide synthase immunocytochemistry, using a commercially available universal antibody, labelled cells in corresponding positions within the ganglia. This was confirmed by double labelling of alternate sections. Western blot analysis demonstrated that in locusts this universal NOS-antibody binds to a protein of similar size to nitric oxide synthase identified in other insect species. The antibody also labelled axons in most peripheral nerves of all examined ganglia, whereas NADPHdiaphorase histochemistry only revealed such stained fibres within peripheral nerves in some preparations, because they may have been masked by intense background staining. We therefore conclude that nitric oxide synthase-immunocytochemistry and NADPHd histochemistry are both good markers for the presence of nitric oxide synthase in the locust ventral nerve cord, and that nitric oxide may be used as a signalling molecule by efferent neurones in locusts.

Cholinergic transmission via central synapses in the locust nervous system.

In this study we examine the nature of chemical synaptic transmission between identified filiform hair receptors on the prothoracic segment of a locust and the identified postsynaptic projection interneuron (A4I1). The effects of pressure ejected acetylcholine, and various ligands of acetylcholine receptors on the activity of the postsynaptic neuron A4I1, or on wind-elicited responses in A4I1 are reported. It is suggested that the transmitter of the afferent fibers is acetylcholine, and that fast transmission is mediated by nicotinic acetylcholine-receptors. Both nicotine and carbachol act as agonists, whereas d-tubocurarine and alpha-bungarotoxin act as antagonists. The presence of muscarinic acetylcholine receptors was also evident from the modulatory effects of muscarine, oxotremorine and pilocarpine, which were blocked by bath application of atropine. GABA, and its agonists muscimol and cis-4-amino-crotonic-acid lead to inhibition of A4I1 responses. This inhibition was prevented by the additional application of picrotoxin. This suggests involvement of a ligand-gated GABA receptor which, most likely, increases chloride conductance. Metabotropic GABA-receptors do not seem to be involved, since baclofene, diazepam and bicuculline ejections had no effects. Glutamate also inhibits wind elicited A4I1 responses. Although attempts were made to further characterize the receptor involved, tested substances such as kainic acid, glycine, CNQX or GDEE had no effect.

Octopamine receptors in the honey bee and locust nervous system: pharmacological similarities between homologous receptors of distantly related species

Honey bees are perhaps the most versatile models to study the cellular and pharmacological basis underlying behaviours ranging from learning and memory to sociobiology. For both aspects octopamine (OA) is known to play a vital role. The neuronal octopamine receptor of the honey bee shares pharmacological similarities with the neuronal octopamine receptor of the locust. Both, agonists and antagonists known to have high affinities for the locust neuronal octopamine receptor have also high affinities for the bee neuronal octopamine receptor. The distribution of receptors is more or less congruent between locusts and bees. Optic lobes and especially the mushroom bodies are areas of greatest octopamine receptor expression in both species, which mirrors the physiological significance of octopamine in the insect nervous system. The neuronal octopamine receptor of insects served as a model to study the pharmacological similarity of homologous receptors from distantly related species, because bees and locusts are separated by at least 330 million years of evolution.

Tyramine injections reduce locust viability

In the locust nervous system, tyramine is the direct precursor for octopamine synthesis and, as an octopamine analogue, it can activate octopamine receptors. Furthermore, the identification of specific tyramine receptors in Locusta migratoria and Drosophila melanogaster suggests that it is an important transmitter or modulator candidate. In this paper, we report that repeated tyramine injections reduced the viability of last instar larvae of Locusta and Schistocerca. In addition, a retardation of the last ecdysis was observed as a sublethal effect of the repeated tyramine treatment. Moreover, egg deposition by adult females was also retarded and/or drastically reduced. These effects show similarity to sublethal effects described for certain "insecticidal" octopamine receptor agonists, such as formamidines and phenyliminoimidazolidines. Since certain formamidine compounds were also shown to be agonists for the cloned tyramine receptors, it cannot be excluded that some lethal or sublethal consequences of tyramine administration are the result of an interaction with specific tyramine receptors.

Distribution of SchistoFLRFamide-like immunoreactivity in the adult ventral nervous system of the locust, Schistocerca gregaria.

SchistoFLRFamide (PDVDHVFLRF-NH2) is one of the major endogenous neuropeptides of the FMRFamide family found in the nervous system of the locust, Schistocerca gregaria. To gain insights into the potential physiological roles of this neuropeptide we have examined the distribution of SchistoFLRFamide-like immunoreactivity in the ventral nervous system of adult locusts by use of a newly developed N-terminally specific antibody. SchistoFLRFamide-like immunoreactivity in the ventral nerve cord is found in a subgroup of the neurones that are immunoreactive to an antiserum raised against bovine pancreatic polypeptide (BPP). In the suboesophageal ganglion three groups of cells stain, including one pair of large posterior ventral cells. These cells are the same size, in the same location in the ganglion and have the same branching pattern as a pair of BPP immunoreactive cells known to innervate the heart and retrocerebral glandular complex of the locust. In the thoracic and abdominal ganglia two and three sets of cells, respectively, stain with both the SchistoFLRFamide and BPP antisera. In the abdominal ganglia the immunoreactive cells project via the median nerves to the intensely immunoreactive neurohaemal organs.

Distribution of myomodulin-like immunoreactivity in the adult and developing ventral nervous system of the locust Schistocerca gregaria.

The distribution of myomodulin-like immunoreactivity in the ventral nervous system of an insect, the locust Schistocerca gregaria, both in the adult and during development, is described. The results suggest the presence of a novel modulatory system in insects which uses myomodulin-like neuropeptides. The study also indicates that the myomodulins, which were first identified in mollusks, may represent another interphyletic family of neuropeptides. In the suboesophageal ganglion, immunoreactive cells occur in five groups. The processes from the two anterior ventral midline groups of cells project to the corpora allata via nervi corpora allata II. Thus myomodulin-like neuropeptides may be involved in the control of the release of juvenile hormone from the corpora allata. The thoracic ganglia contain three groups of immunoreactive cells, including a bilaterally symmetrical group of 12-15 posterior lateral cells, which project to the median nerve and its neurohaemal organs, suggesting a possible neurohaemal role for myomodulin-like peptides. Each thoracic neuromere also contains a single, intensely stained, dorsal unpaired median (DUM) cell that may correspond to the so-called H cell. In the abdominal ganglia, the staining shows sexual dimorphism, both in terms of the number of dorsal and ventral midline cells stained and in terms of the distribution of their immunoreactive processes. Myomodulin-like immunoreactivity is one of the earliest neurotransmitter/neurohormone phenotypes detectable during the development of the locust nervous system. It first appears in the single DUM cells in each of the thoracic neuromeres at 50% development, and the complete adult pattern of staining is present at 85-90% of development.

The effects of myomodulin and structurally related neuropeptides on skeletal neuromuscular transmission in the locust

1. The modulatory actions of myomodulin A on tension generated in the extensortibiae muscle of the locust hindleg by stimulation of the slow excitatory motoneurone (SETi) depend upon the frequency of stimulation. Myomodulin A has no consistent effect on the tension induced by the fast extensor motoneurone (FETi) or upon the myogenic rhythm present in the extensor. The effects of a range of structurally related neuropeptides have also been assessed. 2. At low frequencies of SETi stimulation (1 Hz and below), the predominant modulatory effects are increases in the amplitude, contraction rate and relaxation rate of twitch tension. At higher frequencies, where twitches summate but tetanus is incomplete (up to 20 Hz), these effects are superimposed upon an increase of maintained tension. 3. The modulatory actions of myomodulin-like peptides show some similarities to and some differences from the modulatory actions of octopamine, proctolin and FMRFamide-like neuropeptides in this preparation, but are likely to be mediated via a distinct set of receptors. 4. The results of the present study, taken together with the localization of myomodulin-like immunoreactivity in specific sets of neurones in the locust nervous system, suggest the presence of a novel modulatory system in insects that uses myomodulin-like neuropeptides. It also indicates that myomodulins, which were first identified in molluscs, may represent another interphyletic family of neuropeptides.

Sequence and functional expression of a single alpha subunit of an insect nicotinic acetylcholine receptor.

We report the isolation and sequence of a cDNA clone that encodes a locust (Schistocerca gregaria) nervous system nicotinic acetylcholine receptor (AChR) subunit (alpha L1). The calculated molecular weight of the unglycosylated polypeptide, which contains in the proposed extracellular domain two adjacent cysteine residues which are characteristic of alpha (ligand binding) subunits, is 60,641 daltons. Injection into Xenopus oocytes, of RNA synthesized from this clone in vitro, results in expression of functional nicotinic receptors in the oocyte membrane. In these, nicotine opens a cation channel; the receptors are blocked by both alpha-bungarotoxin (alpha-Bgt) and kappa-bungarotoxin (kappa-Bgt). Reversible block of the expressed insect AChR by mecamylamine, d-tubocurarine, tetraethylammonium, bicuculline and strychnine has also been observed. These data are entirely consistent with previously reported electrophysiological studies on in vivo insect nicotinic receptors and also with biochemical studies on an alpha-Bgt affinity purified locust AChR. Thus, a functional receptor exhibiting the characteristic pharmacology of an in vivo insect nicotinic AChR can be expressed in Xenopus oocytes by injection with a single subunit RNA.

FMRFamide-like peptides in the locust: distribution, partial characterization and bioactivity

The quantitative distribution of FMRFamide-like peptides in the nervous system and in their putative target sites in the locust Schistocerca gregaria is described using radioimmunoassay techniques. The nature of the immunoreactive material has been characterized by high-pressure liquid chromatography. At least six peaks of FMRFamide-like immunoreactivity can be separated in extracts of locust nervous tissue. The relative proportions of these peaks vary from tissue to tissue, suggesting a differential expression of FMRFamide-like peptides in different parts of the locust nervous system. The bioactivity of the endogenous FMRFamide-like peptides has been assessed on the extensor tibiae neuromuscular preparation and on the locust heart. The results suggest that FMRFamide-like peptides in the locust function both as circulating neurohormones and as locally released neuromodulators or neurotransmitters.

Occurrence of crustacean cardioactive peptide (CCAP) in the nervous system of an insect,Locusta migratoria

Using a radioimmunoassay developed for the determination of crustacean cardioactive peptide (CCAP), immunoreactive material was detected in extracts of locust nervous tissue. Serial dilutions of a brain extract gave a displacement curve parallel to the CCAP standard curve. One locust nervous system was calculated to contain approximately 1.4 pmol CCAP-like material. In order to investigate whether the immunoreactive substance was similar or identical to the crustacean neuropeptide, isolation and complete characterization was carried out using 800 locust nervous systems. The isolation procedure consisted of pre-purification of the crude extract on a Sep-Pak cartridge, affinity chromatography on a column which was prepared by coupling of anti-CCAP antibody to CNBr-activated Sepharose, and reversed phase high performance liquid chromatography (HPLC). In the HPLC-profile immunoreactivity was confined to a single peak which co-chromatographed with authentic CCAP. The peptide was carboxymethylated and analyzed in an automated gas-phase sequencer. Its amino acid sequence, is identical to that of CCAP fromCarcinus maenas. Synthetic CCAP was tested on the isolated locust hindgut in vitro. The peptide proved to be a potent enhancer of gut contractions, with a significant effect being observable at concentrations of 10−10 M. It is concluded that in the locust CCAP may function as a myotropic peptide.

NPY-like peptides occur in the nervous system and midgut of the migratory locust, Locusta migratoria and in the brain of the grey fleshfly, Sarcophaga bullata

The distribution of the NPY-like substances in the nervous system and the midgut of the migratory locust, Locusta migratoria and in the brain of the grey fleshfly, Sarcophaga bullata was determined by immunocytochemistry using an antiserum directed against synthetic porcine NPY. The peroxidase-antiperoxidase procedure revealed that NPY immunoreactive cell bodies and nerve fibers were observed in the brain, optic lobes, corpora cardiaca, suboesophageal ganglion and ventral nerve cord of the locust and in the brain, optic lobes and suboesophageal ganglion of the fleshfly. In the locust midgut, numerous endocrine cells and nerve fibers penetrating the outer musculature contained NPY-like immunoreactivity. The concentrations of NPY immunoreactive material in acetic acid extracts of locust brain, optic lobes, thoracic ganglia, ovaries and midguts was measured using a specific radioimmunoassay technique. The dilution curves of the crude tissue extracts were parallel to the standard curve. The highest amount of NPY-like immunoreactivity was found in the locust ovary and midgut. Reverse-phase high-performance liquid chromatography (RP-HPLC) and radioimmunoassay were used to characterize the NPY-like substances in the locust brain and midgut. HPLC-analysis revealed that NPY-immunoreactivity in the locust brain eluted as three separate peaks. The major peak corresponded to a peptide less hydrophobic than synthetic porcine NPY. RP-HPLC analysis of midgut extracts revealed the presence of an additional NPY-immunoreactive peak which had a retention time similar to the porcine NPY standard. The present data show the existence of a widespread network of NPY immunoreactive neurons in the nervous system of the locust and the fleshfly. Characterization of the immunoreactive substances indicates that peptides similar but not identical to porcine NPY are present in the central nervous system and midgut of insects.