Effect of short neuropeptide F signaling on larval feeding in Mythimna separata

Mythimna separata is a notorious phytophagous pest which poses serious threats to cereal crops owing to the gluttony of the larvae. Because short neuropeptide F (sNPF) and its receptor sNPFR are involved in a diversity of physiological functions, especially in functions related to feeding in insects, it is a molecular target for pest control. Herein, an sNPF and 2 sNPFRs were identified and cloned from M. separata. Bioinformatics analysis revealed that the sNPF and its receptors had a highly conserved RLRFamide C-terminus and 7 transmembrane domains, respectively. The sNPF and its receptor genes were distributed across larval periods and tissues, but 2 receptors had distinct expression patterns. The starvation-induced assay elucidated that sNPF and sNPFR expression levels were downregulated under food deprivation and recovered with subsequent re-feeding. RNA interference knockdown of sNPF, sNPFR1, and sNPFR2 by injection of double-stranded RNA into larvae not only suppressed food consumption and increased body size and weight, but also led to decrease of glycogen and total lipid contents, and increase of trehalose compared with double-stranded green fluorescent protein injection. Furthermore, molecular docking was performed on the interaction mode between sNPFR protein and its ligand sNPF based on the 3-dimensional models constructed by AlphaFold; the results indicated that both receptors were presumably activated by the mature peptide sNPF-2. These results revealed that sNPF signaling played a considerably vital role in the feeding regulation of M. separata and represents a potential control target for this pest.

Exploring the proteins and metabolites associated with male antennae responses to female exposure of Antheraea pernyi (Lepidoptera: Saturniidae) moths

Detection of sex pheromones of insects relies on the antennae. The female pheromone signal transmission in the male antennae ultimately initiates the courtship and mating behaviors of males. To investigate the proteins and metabolites involved in this neural transduction, integrative proteomics and metabolomics analysis including tandem mass tag (TMT) proteomic quantification and liquid chromatography tandem mass spectrometry (LC/MS)-based metabolomics was adopted for comparing proteomic and metabolic changes between the antennae of male moths following stimulation by females and the non-stimulated males of Antheraea pernyi (Guérin-Méneville, Lepidoptera: Saturniidae) in this study. A total of 92 differentially expressed proteins (DEPs) containing 52 upregulated and 40 downregulated proteins and 545 differentially expressed metabolites (DEMs) including 218 upregulated and 327 downregulated metabolites were identified from the antennae of female-stimulated male moths based on the proteome and metabolome data, respectively. Bioinformatics analysis was performed for the 45 DEPs and 160 DEMs, including Gene Ontology (GO), Clusters of Orthologous Groups (COG), and Kyoto Encylopaedia of Genes and Genomes (KEGG) enrichment analysis and Human Metabolome Database (HMDB) annotation. A number of DEPs and DEMs related to neural transmission of female pheromone signals in the male antennae of A. pernyi were screened, including tyrosine hydroxylase, cryptochrome-1, tachykinin, arylalkylamine N-acetyltransferase, cadherin-23, glutathione S-transferase delta 3, tyramine, tryptamine, n-oleoyl dopamine, n-stearoyl dopamine, and n-stearoyl tyrosine. The altered expression levels of those proteins or metabolites were speculated involved in regulating the neuron activity for enhanced transmission of neural impulses and continuous perception, reception, and transduction of female pheromone signals. Our findings yielded novel insights into the potential mechanisms in the antennae of male A. pernyi responding to female attraction.

Threat gates visual aversion via theta activity in Tachykinergic neurons

Animals must adapt sensory responses to an ever-changing environment for survival. Such sensory modulation is especially critical in a threatening situation, in which animals often promote aversive responses to, among others, visual stimuli. Recently, threatened Drosophila has been shown to exhibit a defensive internal state. Whether and how threatened Drosophila promotes visual aversion, however, remains elusive. Here we report that mechanical threats to Drosophila transiently gate aversion from an otherwise neutral visual object. We further identified the neuropeptide tachykinin, and a single cluster of neurons expressing it ("Tk-GAL42 ∩ Vglut neurons"), that are responsible for gating visual aversion. Calcium imaging analysis revealed that mechanical threats are encoded in Tk-GAL42 ∩ Vglut neurons as elevated activity. Remarkably, we also discovered that a visual object is encoded in Tk-GAL42 ∩ Vglut neurons as θ oscillation, which is causally linked to visual aversion. Our data reveal how a single cluster of neurons adapt organismal sensory response to a threatening situation through a neuropeptide and a combination of rate/temporal coding schemes.

Identification and expression of short neuropeptide F and its receptors in the tick Ixodes ricinus

In Europe, the tick Ixodes ricinus is the most important vector of numerous pathogens that are transmitted during blood feeding on their vertebrate hosts. To elucidate mechanisms controlling blood intake and associated transmission of pathogens we identified and described expression of short neuropeptide F (sNPF) and its receptors which are known to regulate feeding in insects. Using in situ hybridization (ISH) and immunohistochemistry (IHC) we stained numerous neurons producing sNPF in the central nervous system (CNS; synganglion), while a few peripheral neurons were detected anteriorly to the synganglion, and on the surface of the hindgut and leg muscles. Apparent sNPF expression was also found in enteroendocrine cells individually scattered in anterior lobes of the midgut. In silico analyses and BLAST search for sNPF receptors revealed two putative G protein-coupled receptors (sNPFR1 and sNPFR2) in the I. ricinus genome. Aequorin-based functional assay in CHO cells showed that both receptors were specific and sensitive to sNPF in nanomolar concentrations. Increased expression levels of these receptors in the gut during blood intake suggest that sNPF signaling may be involved in regulation of feeding and digestion processes of I. ricinus.

Effect of Kisspeptin-Type Neuropeptide on Locomotor Behavior and Muscle Physiology in the Sea Cucumber Apostichopus japonicus

Kisspeptins are neuropeptides encoded by the kiss1 gene, and little is known about them outside the vertebrate lineage. Two kisspeptin-type neuropeptides (KPs) have been discovered in Apostichopus japonicus (AjK1 and AjK2), an edible sea cucumber, and have been linked to reproductive and metabolic regulation. In this study, we evaluated how KPs affected locomotor behavior in one control group and two treatment groups (AjK1 and AjK2). We discovered that AjK1 had a significant dose effect, primarily by shortening the stride length and duration of movement to reduce the sea cucumber movement distance, whereas AjK2 had little inhibitory effect at the same dose. The levels of phosphatidylethanolamine (PE), phosphatidylcholine (PC), uridine, glycine, and L-serine in the longitudinal muscle of A. japonicus treated with AjK1 differed significantly from those of the control, which may explain the observed changes in locomotor behavior. Treatment with AjK2 induced changes in aspartate levels. Our results imply that AjK1 is more likely than AjK2 to have a role in the regulation of A. japonicus locomotion.

Parkin Knockdown Modulates Dopamine Release in the Central Complex, but Not the Mushroom Body Heel, of Aging Drosophila

Parkinson's disease (PD) is characterized by progressive degeneration of dopaminergic neurons leading to reduced locomotion. Mutations of parkin gene in Drosophila produce the same phenotypes as vertebrate models, but the effect of parkin knockdown on dopamine release is not known. Here, we report age-dependent, spatial variation of dopamine release in the brain of parkin-RNAi adult Drosophila. Dopamine was repetitively stimulated by local application of acetylcholine and quantified by fast-scan cyclic voltammetry in the central complex or mushroom body heel. In the central complex, the main area controlling locomotor function, dopamine release is maintained for repeated stimulations in aged control flies, but lower concentrations of dopamine are released in the central complex of aged parkin-RNAi flies. In the mushroom body heel, the dopamine release decrease in older parkin-RNAi flies is similar to controls. There is not significant dopaminergic neuronal loss even in older parkin knockdown flies, which indicates that the changes in stimulated dopamine release are due to alterations of neuronal function. In young parkin-RNAi flies, locomotion is inhibited by 30%, while in older parkin-RNAi flies it is inhibited by 85%. Overall, stimulated dopamine release is modulated by parkin in an age and brain region dependent manner. Correlating the functional state of the dopaminergic system with behavioral phenotypes provides unique insights into the PD mechanism. Drosophila can be used to study dopamine functionality in PD, elucidate how genetics influence dopamine, and test potential therapies to maintain dopamine release.

Interneurons of fan-shaped body promote arousal in Drosophila

Sleep is required to maintain physiological functions and is widely conserved across species. To understand the sleep-regulatory mechanisms, sleep-regulating genes and neuronal circuits are studied in various animal species. In the sleep-regulatory neuronal circuits in Drosophila melanogaster, the dorsal fan-shaped body (dFB) is a major sleep-promoting region. However, other sleep-regulating neuronal circuits were not well identified. We recently found that arousal-promoting T1 dopamine neurons, interneurons of protocerebral bridge (PB) neurons, and PB neurons innervating the ventral part of the FB form a sleep-regulatory circuit, which we named "the PB-FB pathway". In the exploration of other sleep-regulatory circuits, we found that activation of FB interneurons, also known as pontine neurons, promoted arousal. We then found that FB interneurons had possible connections with the PB-FB pathway and dFB neurons. Ca2+ imaging revealed that FB interneurons received excitatory signals from the PB-FB pathway. We also demonstrated the possible role of FB interneurons to regulate dFB neurons. These results suggested the role of FB interneurons in sleep regulation.

Physiological Signatures of Changes in Honeybee's Central Complex During Wing Flapping

Many kinds of locomotion abilities of insects-including flight control, spatial orientation memory, position memory, angle information integration, and polarized light guidance are considered to be related to the central complex. However, evidence was still not sufficient to support those conclusions from the aspect of neural basis. For the locomotion form of wing flapping, little is known about the patterns of changes in brain activity of the central complex during movement. Here, we analyze the changes in honeybees' neuronal population firing activity of central complex and optic lobes with the perspectives of energy and nonlinear changes. Although the specific function of the central complex remains unknown, evidence suggests that its neural activities change remarkably during wing flapping and its delta rhythm is dominative. Together, our data reveal that the firing activity of some of the neuronal populations of the optic lobe shows reduction in complexity during wing flapping. Elucidating the brain activity changes during a flapping period of insects promotes our understanding of the neuro-mechanisms of insect locomotor control, thus can inspire the fine control of insect cyborgs.

Suppression of host nocifensive behavior by parasitoid wasp venom

The parasitoid wasp Ampulex compressa envenomates the brain of its host the American cockroach (Periplaneta americana), thereby making it a behaviorally compliant food supply for its offspring. The target of venom injection is a locomotory command center in the brain called the central complex. In this study, we investigate why stung cockroaches do not respond to injuries incurred during the manipulation process by the wasp. In particular, we examine how envenomation compromises nociceptive signaling pathways in the host. Noxious stimuli applied to the cuticle of stung cockroaches fail to evoke escape responses, even though nociceptive interneurons projecting to the brain respond normally. Hence, while nociceptive signals are carried forward to the brain, they fail to trigger robust nocifensive behavior. Electrophysiological recordings from the central complex of stung animals demonstrate decreases in peak firing rate, total firing, and duration of noxious-evoked activity. The single parameter best correlated with altered noxious-evoked behavioral responses of stung cockroaches is reduced duration of the evoked response in the central complex. Our findings demonstrate how the reproductive strategy of a parasitoid wasp is served by venom-mediated elimination of aversive, nocifensive behavior in its host.

Endocrine cybernetics: neuropeptides as molecular switches in behavioural decisions

Plasticity in animal behaviour relies on the ability to integrate external and internal cues from the changing environment and hence modulate activity in synaptic circuits of the brain. This context-dependent neuromodulation is largely based on non-synaptic signalling with neuropeptides. Here, we describe select peptidergic systems in the Drosophila brain that act at different levels of a hierarchy to modulate behaviour and associated physiology. These systems modulate circuits in brain regions, such as the central complex and the mushroom bodies, which supervise specific behaviours. At the top level of the hierarchy there are small numbers of large peptidergic neurons that arborize widely in multiple areas of the brain to orchestrate or modulate global activity in a state and context-dependent manner. At the bottom level local peptidergic neurons provide executive neuromodulation of sensory gain and intrinsically in restricted parts of specific neuronal circuits. The orchestrating neurons receive interoceptive signals that mediate energy and sleep homeostasis, metabolic state and circadian timing, as well as external cues that affect food search, aggression or mating. Some of these cues can be triggers of conflicting behaviours such as mating versus aggression, or sleep versus feeding, and peptidergic neurons participate in circuits, enabling behaviour choices and switches.

The Role of Central Complex Neurons in Prey Detection and Tracking in the Freely Moving Praying Mantis (Tenodera sinensis)

Complex tasks like hunting moving prey in an unpredictable environment require high levels of motor and sensory integration. An animal needs to detect and track suitable prey objects, measure their distance and orientation relative to its own position, and finally produce the correct motor output to approach and capture the prey. In the insect brain, the central complex (CX) is one target area where integration is likely to take place. In this study, we performed extracellular multi-unit recordings on the CX of freely hunting praying mantises (Tenodera sinensis). Initially, we recorded the neural activity of freely moving mantises as they hunted live prey. The recordings showed activity in cells that either reflected the mantis's own movements or the actions of a prey individual, which the mantises focused on. In the latter case, the activity increased as the prey moved and decreased when it stopped. Interestingly, cells ignored the movement of the other prey than the one to which the mantis attended. To obtain quantitative data, we generated simulated prey targets presented on an LCD screen positioned below the clear floor of the arena. The simulated target oscillated back and forth at various angles and distances. We identified populations of cells whose activity patterns were strongly linked to the appearance, movement, and relative position of the virtual prey. We refer to these as sensory responses. We also found cells whose activity preceded orientation movement toward the prey. We call these motor responses. Some cells showed both sensory and motor properties. Stimulation through tetrodes in some of the preparations could also generate similar movements. These results suggest the crucial importance of the CX to prey-capture behavior in predatory insects like the praying mantis and, hence, further emphasize its role in behaviorally and ecologically relevant contexts.

A three-dimensional atlas of the honeybee central complex, associated neuropils and peptidergic layers of the central body

The central complex (CX) in the brain of insects is a highly conserved group of midline-spanning neuropils consisting of the upper and lower division of the central body, the protocerebral bridge, and the paired noduli. These neuropils are the substrate for a number of behaviors, most prominently goal-oriented locomotion. Honeybees have been a model organism for sky-compass orientation for more than 70 years, but there is still very limited knowledge about the structure and function of their CX. To advance and facilitate research on this brain area, we created a high-resolution three-dimensional atlas of the honeybee's CX and associated neuropils, including the posterior optic tubercles, the bulbs, and the anterior optic tubercles. To this end, we developed a modified version of the iterative shape averaging technique, which allowed us to achieve high volumetric accuracy of the neuropil models. For a finer definition of spatial locations within the central body, we defined layers based on immunostaining against the neuropeptides locustatachykinin, FMRFamide, gastrin/cholecystokinin, and allatostatin and included them into the atlas by elastic registration. Our honeybee CX atlas provides a platform for future neuroanatomical work.

Functional analysis of LFRFamide signaling in Pacific abalone, Haliotis discus hannai

The invertebrate LFRFamide (LFRFa) and short neuropeptide F (sNPF), consisting of 6 to 10 amino acids, are orthologs for bilaterian NPF/Y, which consist of 36 to 40 amino acids. Recently, a molluscan G protein-coupled receptor (GPCR) for NPF was characterized in Pacific abalone (Haliotis discus hannai). To address the functional evolutionary route of the invertebrate LFRFa and NPF signaling system, in this study, we identified cDNAs encoding LFRFa precursors and the sNPF receptor (Hdh-sNPFR) in Pacific abalone. Four LFRFa mature peptides with 6 or 7 amino acids were predicted: GSLFRFa, GGLFRFa, GTLFRFa, and GSTLFRFa. Hdh-sNPFR was identified as a classical rhodopsin-like GPCR and classified into a molluscan sNPFR group. In HEK293 cells, Hdh-sNPFR was mainly localized in the cell membranes and internalized in the cytoplasm following treatment with LFRFa peptides. Reporter assays demonstrated that LFRFa peptides inhibit forskolin-stimulated cAMP accumulation in Hdh-sNPFR-expressing HEK293 cells. LFRFa precursor and Hdh-sNPFR transcripts were more strongly expressed in the cerebral and pleural-pedal ganglia of Pacific abalone than in the peripheral tissues such as the ovary, gills, intestine, and hepatopancreas. The levels of LFRFa transcripts in the ovary, intestine, and hepatopancreas were significantly higher in mature female abalone than in immature females. Injection of LFRFa induced the egg release and spawning behavior of mature abalone, but suppressed food intake. These results suggest that LFRFa peptides are endogenous ligands for Hdh-sNPFR involved in food intake and reproduction through a Gαi-protein dependent signaling pathway.

Short Neuropeptide F and Its Receptor Regulate Feeding Behavior in Pea Aphid (Acyrthosiphon pisum)

Simple Summary

We know that neuropeptides and G protein-coupled receptors regulate the physiology and behavior of animals and that the pea aphid (Acyrthosiphon pisum) is a serious agricultural pest and model insect. In this study, we investigated the short neuropeptide F and its receptor in pea aphid. Feeding analysis showed that the probing time and total phloem duration significantly decreased in response to sNPF and predicted sNPFR gene silencing in RNAi assays. The silencing of sNPF significantly reduced the aphid’s reproduction but not survival. Our findings will help in the design of control strategies by using the molecular biological approach.

Abstract

Insect short neuropeptide F (sNPF), an ortholog of prolactin-releasing peptide of invertebrates, regulates diverse biological processes, including feeding, olfaction, locomotion, and sleep homeostasis in insects. However, its function is still unclear in an important model insect and agricultural pest, the pea aphid (Acyrthosiphon pisum). Here, we investigated short neuropeptide F (ApsNPF) and its receptor (ApsNPFR) in A. pisum. The sNPF gene contains three exons and two long introns. In addition, the genome contains a single sNPF receptor with seven transmembrane domains. Stage- and tissue-specific transcript profiling by qRT-PCR revealed that ApsNPF and ApsNPFR were mainly expressed in the central nervous system. The receptor was also detected in antennae, midgut, and integument. The highest expression levels were found in first instar nymphs compared to other developmental stages. Besides, the starvation-induced pattern indicated that the sNPF network depends on the nutritional state of the insect. An electrical penetration graph showed that probing time and phloem duration of A. pisum on broad bean plants decreased in response to dssNPF and dssNPFR in RNAi assays. sNPF silencing reduced the number of nymphs per female but not aphid survival. We believe that our results advance in-depth knowledge of the sNPF/sNPFR signaling cascade and its place in regulating feeding behavior in insects. In turn, it may contribute to the potential design of new strategies to control aphids, with a focus on the sNPF system.

Nutrient Sensing via Gut in Drosophila melanogaster

Nutrient-sensing mechanisms in animals' sense available nutrients to generate a physiological regulatory response involving absorption, digestion, and regulation of food intake and to maintain glucose and energy homeostasis. During nutrient sensing via the gastrointestinal tract, nutrients interact with receptors on the enteroendocrine cells in the gut, which in return respond by secreting various hormones. Sensing of nutrients by the gut plays a critical role in transmitting food-related signals to the brain and other tissues informing the composition of ingested food to digestive processes. These signals modulate feeding behaviors, food intake, metabolism, insulin secretion, and energy balance. The increasing significance of fly genetics with the availability of a vast toolbox for studying physiological function, expression of chemosensory receptors, and monitoring the gene expression in specific cells of the intestine makes the fly gut the most useful tissue for studying the nutrient-sensing mechanisms. In this review, we emphasize on the role of Drosophila gut in nutrient-sensing to maintain metabolic homeostasis and gut-brain cross talk using endocrine and neuronal signaling pathways stimulated by internal state or the consumption of various dietary nutrients. Overall, this review will be useful in understanding the post-ingestive nutrient-sensing mechanisms having a physiological and pathological impact on health and diseases.

The short neuropeptide F receptor regulates olfaction-mediated foraging behavior in the oriental fruit fly Bactrocera dorsalis (Hendel)

The short neuropeptide F (sNPF) signaling system, consisting of sNPF and its receptor (sNPFR), influences many physiological processes in insects, including feeding, growth and olfactory memory. We previously showed that sNPF regulates olfactory sensitivity in the oriental fruit fly Bactrocera dorsalis (Hendel) during starvation. However, the functional analysis of sNPFR is constrained by the failure of RNA interference in this species. Here, we generated a null sNPFR mutant using the CRISPR/Cas9 system to investigate the physiological roles of this receptor in more detail. G0 adults were produced at a frequency of 60.8%, and sNPFR^-/- mutants were obtained after several generations of backcrossing followed by self-crossing among heterozygous flies. We found that the mutants were significantly less successful at foraging for certain foods and showed increased foraging latency. Electroantennogram (EAG) assays indicated that the mutants had significantly lower electrophysiological responses to three tested odorants. Furthermore, qPCR data revealed the inhibition of several olfactory receptor genes, including Orco. Immunohistochemistry showed that BdsNPFR was localized in cells under the sensillum on the antennae. Based on their shape and size, the BdsNPFR⁺ cells differ from odorant receptor neurons (ORNs), which were labeled using a Drosophila melanogaster Orco antibody. Our data suggest that sNPFR regulates olfaction-mediated foraging behavior by mediating interactions between BdsNPFR⁺ cells and selected ORNs.

Internal state effects on behavioral shifts in freely behaving praying mantises (Tenodera sinensis)

How we interact with our environment largely depends on both the external cues presented by our surroundings and the internal state from within. Internal states are the ever-changing physiological conditions that communicate the immediate survival needs and motivate the animal to behaviorally fulfill them. Satiety level constitutes such a state, and therefore has a dynamic influence on the output behaviors of an animal. In predatory insects like the praying mantis, hunting tactics, grooming, and mating have been shown to change hierarchical organization of behaviors depending on satiety. Here, we analyze behavior sequences of freely hunting praying mantises (Tenodera sinensis) to explore potential differences in sequential patterning of behavior as a correlate of satiety. First, our data supports previous work that showed starved praying mantises were not just more often attentive to prey, but also more often attentive to further prey. This was indicated by the increased time fraction spent in attentive bouts such as prey monitoring, head turns (to track prey), translations (closing the distance to the prey), and more strike attempts. With increasing satiety, praying mantises showed reduced time in these behaviors and exhibited them primarily towards close-proximity prey. Furthermore, our data demonstrates that during states of starvation, the praying mantis exhibits a stereotyped pattern of behavior that is highly motivated by prey capture. As satiety increased, the sequenced behaviors became more variable, indicating a shift away from the necessity of prey capture to more fluid presentations of behavior assembly.

Neuropeptides and Behaviors: How Small Peptides Regulate Nervous System Function and Behavioral Outputs

One of the reasons that most multicellular animals survive and thrive is because of the adaptable and plastic nature of their nervous systems. For an organism to survive, it is essential for the animal to respond and adapt to environmental changes. This is achieved by sensing external cues and translating them into behaviors through changes in synaptic activity. The nervous system plays a crucial role in constantly evaluating environmental cues and allowing for behavioral plasticity in the organism. Multiple neurotransmitters and neuropeptides have been implicated as key players for integrating sensory information to produce the desired output. Because of its simple nervous system and well-established neuronal connectome, C. elegans acts as an excellent model to understand the mechanisms underlying behavioral plasticity. Here, we critically review how neuropeptides modulate a wide range of behaviors by allowing for changes in neuronal and synaptic signaling. This review will have a specific focus on feeding, mating, sleep, addiction, learning and locomotory behaviors in C. elegans. With a view to understand evolutionary relationships, we explore the functions and associated pathophysiology of C. elegans neuropeptides that are conserved across different phyla. Further, we discuss the mechanisms of neuropeptidergic signaling and how these signals are regulated in different behaviors. Finally, we attempt to provide insight into developing potential therapeutics for neuropeptide-related disorders.

Short-term maintenance on a high-sucrose diet alleviates aging-induced sleep fragmentation in drosophila

Sleep is a fundamental behavior in an animal’s life influenced by many internal and external factors, such as aging and diet. Critically, poor sleep quality places people at risk of serious medical conditions. Because aging impairs quality of sleep, measures to improve sleep quality for elderly people are needed. Given that diet can influence many aspects of sleep, we investigated whether a high-sucrose diet (HSD) affected aging-induced sleep fragmentation using the fruit fly, Drosophila melanogaster. Drosophila is a valuable model for studying sleep due to its genetic tractability and many similarities with mammalian sleep. Total sleep duration, sleep bout numbers (SBN), and average sleep bout length (ABL) were compared between young and old flies on a normal sucrose diet (NSD) or HSD. On the NSD, old flies slept slightly more and showed increased SBN and reduced ABL, indicating increased sleep fragmentation. Short-term maintenance of flies in HSD (up to 8 days), but not long-term maintenance (up to 35 days), suppressed aging-induced sleep fragmentation. Our study provides meaningful strategies for preventing the deterioration of sleep quality in the elderly.

A connectome of the Drosophila central complex reveals network motifs suitable for flexible navigation and context-dependent action selection

Flexible behaviors over long timescales are thought to engage recurrent neural networks in deep brain regions, which are experimentally challenging to study. In insects, recurrent circuit dynamics in a brain region called the central complex (CX) enable directed locomotion, sleep, and context- and experience-dependent spatial navigation. We describe the first complete electron microscopy-based connectome of the Drosophila CX, including all its neurons and circuits at synaptic resolution. We identified new CX neuron types, novel sensory and motor pathways, and network motifs that likely enable the CX to extract the fly's head direction, maintain it with attractor dynamics, and combine it with other sensorimotor information to perform vector-based navigational computations. We also identified numerous pathways that may facilitate the selection of CX-driven behavioral patterns by context and internal state. The CX connectome provides a comprehensive blueprint necessary for a detailed understanding of network dynamics underlying sleep, flexible navigation, and state-dependent action selection.

Identification of the Short Neuropeptide F and Short Neuropeptide F Receptor Genes and Their Roles of Food Intake in Dendroctonus armandi

The short neuropeptide F (sNPF) is an essential signaling molecule that is evolutionarily conserved and involved in a broad range of physiological functions in the invertebrates, by interacting with sNPF receptors, which belong to G protein-coupled receptors (GPCR). However, the function of sNPF in regulating the food intake of Dendroctonus armandi has been unclear. In this study, we cloned and characterized cDNAs encoding sNPF and sNPF receptor in the D. armandi and made bioinformatics predictions on the deduced amino acid sequences. They had a high degree of similarity to that of Dendroctonus ponderosa. Quantitative real-time reverse transcription PCR (qRT-PCR) revealed that the transcript levels of both sNPF and sNPFR varied across developmental stages and body parts. In addition, the sNPF and sNPFR expression levels were upregulated in starved beetles, and the expression levels recovered after re-feeding. Furthermore, RNAi knockdown by the injection of sNPF and sNPFR dsRNA into beetles significantly increased mortality and reduced their food intake and body weight, and also caused decrease of glycogen and free fatty acid and increase of trehalose. These results indicate that sNPF signaling pathway plays an important role in the regulation of food intake and provides a potential molecular target for the eco-friendly control strategies of this pest.

Expression patterns and functional analysis of the short neuropeptide F and NPF receptor genes in Rhopalosiphum padi

The short neuropeptide F (sNPF) and NPF receptor (NPFR) genes play important roles in many physiological processes. However, information on the survival-related functions of sNPF and NPFR under different stress conditions is lacking in aphids. In this study, we cloned sNPF and NPFR, and investigated the expression levels of these genes in different developmental stages, wing morphs, and stress conditions of the bird cherry-oat aphid (Rhopalosiphum padi L.), an important agricultural pest. The sNPF and NPFR transcript levels varied among developmental stages, and their expression levels in alate females were significantly higher than those in apterous females. In addition, starvation resulted in significantly increased sNPF expression, which then recovered after refeeding. Heat stress and insecticides significantly affected transcription of both genes. sNPF and NPFR knockdown in R. padi using RNA interference revealed optimal interference efficiency at 48 h post-injection. sNPF knockdown significantly decreased adult longevity, 15-d fecundity, and food intake. Additionally, mortality under starvation, insecticides, and heat stress conditions was significantly higher after injection with double-stranded sNPF in R. padi. NPFR knockdown significantly affected food intake and starvation resistance in R. padi. These results strongly indicate that sNPF plays vital roles in food intake, longevity, and reproduction in R. padi, and it can significantly affect the pest's response to stress conditions.

Metabolic control of daily locomotor activity mediated by tachykinin in Drosophila

Metabolism influences locomotor behaviors, but the understanding of neural curcuit control for that is limited. Under standard light-dark cycles, Drosophila exhibits bimodal morning (M) and evening (E) locomotor activities that are controlled by clock neurons. Here, we showed that a high-nutrient diet progressively extended M activity but not E activity. Drosophila tachykinin (DTk) and Tachykinin-like receptor at 86C (TkR86C)-mediated signaling was required for the extension of M activity. DTk neurons were anatomically and functionally connected to the posterior dorsal neuron 1s (DN1_ps) in the clock neuronal network. The activation of DTk neurons reduced intracellular Ca²⁺ levels in DN1_ps suggesting an inhibitory connection. The contacts between DN1_ps and DTk neurons increased gradually over time in flies fed a high-sucrose diet, consistent with the locomotor behavior. DN1_ps have been implicated in integrating environmental sensory inputs (e.g., light and temperature) to control daily locomotor behavior. This study revealed that DN1_ps also coordinated nutrient information through DTk signaling to shape daily locomotor behavior.

Lee and colleagues report the effect of a high-sucrose diet on Drosophila locomotor activity via DTk-TkR86C neuropeptide signalling. This signalling pattern appears to involve a circadian element, with pacemaker neuron involvement having a possible time-of-day effect on locomotor behaviour.

Neuropeptides as potential modulators of behavioral transitions in the ant Cataglyphis nodus

Age-related behavioral plasticity is a major prerequisite for the ecological success of insect societies. Although ecological aspects of behavioral flexibility have been targeted in many studies, the underlying intrinsic mechanisms controlling the diverse changes in behavior along the individual life history of social insects are not completely understood. Recently, the neuropeptides allatostatin-A, corazonin, and tachykinin have been associated with the regulation of behavioral transitions in social insects. Here, we investigated changes in brain localization and expression of these neuropeptides following major behavioral transitions in Cataglyphis nodus ants. Our immunohistochemical analyses in the brain revealed that the overall branching pattern of neurons immunoreactive (ir) for the three neuropeptides is largely independent of the behavioral stages. Numerous allatostatin-A- and tachykinin-ir neurons innervate primary sensory neuropils and high-order integration centers of the brain. In contrast, the number of corazonergic neurons is restricted to only four neurons per brain hemisphere with cell bodies located in the pars lateralis and axons extending to the medial protocerebrum and the retrocerebral complex. Most interestingly, the cell-body volumes of these neurons are significantly increased in foragers compared to freshly eclosed ants and interior workers. Quantification of mRNA expression levels revealed a stage-related change in the expression of allatostatin-A and corazonin mRNA in the brain. Given the presence of the neuropeptides in major control centers of the brain and the neurohemal organs, these mRNA-changes strongly suggest an important modulatory role of both neuropeptides in the behavioral maturation of Cataglyphis ants.

A novel satiety sensor detects circulating glucose and suppresses food consumption via insulin-producing cells in Drosophila

Sensing satiety is a crucial survival skill for all animal species including human. Despite the discovery of numerous neuromodulators that regulate food intake in Drosophila, the mechanism of satiety sensing remains largely elusive. Here, we investigated how neuropeptidergic circuitry conveyed satiety state to influence flies' food consumption. Drosophila tackykinin (DTK) and its receptor TAKR99D were identified in an RNAi screening as feeding suppressors. Two pairs of DTK⁺ neurons in the fly brain could be activated by elevated D-glucose in the hemolymph and imposed a suppressive effect on feeding. These DTK⁺ neurons formed a two-synapse circuitry targeting insulin-producing cells, a well-known feeding suppressor, via TAKR99D⁺ neurons, and this circuitry could be rapidly activated during food ingestion and cease feeding. Taken together, we identified a novel satiety sensor in the fly brain that could detect specific circulating nutrients and in turn modulate feeding, shedding light on the neural regulation of energy homeostasis.

Transcriptomic, peptidomic, and mass spectrometry imaging analysis of the brain in the ant Cataglyphis nodus

Behavioral flexibility is an important cornerstone for the ecological success of animals. Social Cataglyphis nodus ants with their age-related polyethism characterized by age-related behavioral phenotypes represent a prime example for behavioral flexibility. We propose neuropeptides as powerful candidates for the flexible modulation of age-related behavioral transitions in individual ants. As the neuropeptidome of C. nodus was unknown, we collected a comprehensive peptidomic data set obtained by transcriptome analysis of the ants' central nervous system combined with brain extract analysis by Q-Exactive Orbitrap mass spectrometry (MS) and direct tissue profiling of different regions of the brain by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) MS. In total, we identified 71 peptides with likely bioactive function, encoded on 49 neuropeptide-, neuropeptide-like, and protein hormone prepropeptide genes, including a novel neuropeptide-like gene (fliktin). We next characterized the spatial distribution of a subset of peptides encoded on 16 precursor proteins with high resolution by MALDI MS imaging (MALDI MSI) on 14 µm brain sections. The accuracy of our MSI data were confirmed by matching the immunostaining patterns for tachykinins with MSI ion images from consecutive brain sections. Our data provide a solid framework for future research into spatially resolved qualitative and quantitative peptidomic changes associated with stage-specific behavioral transitions and the functional role of neuropeptides in Cataglyphis ants.

Identification and Characterization of Breakpoints and Mutations on Drosophila melanogaster Balancer Chromosomes

Balancers are rearranged chromosomes used in Drosophila melanogaster to maintain deleterious mutations in stable populations, preserve sets of linked genetic elements and construct complex experimental stocks. Here, we assess the phenotypes associated with breakpoint-induced mutations on commonly used third chromosome balancers and show remarkably few deleterious effects. We demonstrate that a breakpoint in p53 causes loss of radiation-induced apoptosis and a breakpoint in Fucosyltransferase A causes loss of fucosylation in nervous and intestinal tissue—the latter study providing new markers for intestinal cell identity and challenging previous conclusions about the regulation of fucosylation. We also describe thousands of potentially harmful mutations shared among X or third chromosome balancers, or unique to specific balancers, including an Ankyrin 2 mutation present on most TM3 balancers, and reiterate the risks of using balancers as experimental controls. We used long-read sequencing to confirm or refine the positions of two inversions with breakpoints lying in repetitive sequences and provide evidence that one of the inversions, In(2L)Cy, arose by ectopic recombination between foldback transposon insertions and the other, In(3R)C, cleanly separates subtelomeric and telomeric sequences and moves the subtelomeric sequences to an internal chromosome position. In addition, our characterization of In(3R)C shows that balancers may be polymorphic for terminal deletions. Finally, we present evidence that extremely distal mutations on balancers can add to the stability of stocks whose purpose is to maintain homologous chromosomes carrying mutations in distal genes. Overall, these studies add to our understanding of the structure, diversity and effectiveness of balancer chromosomes.

Orcokinin in the central complex of the locust Schistocerca gregaria: Identification of immunostained neurons and colocalization with other neuroactive substances

The central complex is a group of highly interconnected neuropils in the insect brain. It is involved in the control of spatial orientation, based on external compass cues and various internal needs. The functional and neurochemical organization of the central complex has been studied in detail in the desert locust Schistocerca gregaria. In addition to classical neurotransmitters, immunocytochemistry has provided evidence for a major contribution of neuropeptides to neural signaling within the central complex. To complement these data, we have identified all orcokinin-immunoreactive neurons in the locust central complex and associated brain areas. About 50 bilateral pairs of neurons innervating all substructures of the central complex exhibit orcokinin immunoreactivity. Among these were about 20 columnar neurons, 33 bilateral pairs of tangential neurons of the central body, and seven pairs of tangential neurons of the protocerebral bridge. In silico transcript analysis suggests the presence of eight different orcokinin-A type peptides in the desert locust. Double label experiments showed that all orcokinin-immunostained tangential neurons of the lateral accessory lobe cluster were also immunoreactive for GABA and the GABA-synthesizing enzyme glutamic acid decarboxylase. Two types of tangential neurons of the upper division of the central body were, furthermore, also labeled with an antiserum against Dip-allatostatin I. No colocalization was found with serotonin immunostaining. The data provide additional insights into the neurochemical organization of the locust central complex and suggest that orcokinin-peptides of the orcokinin-A gene act as neuroactive substances at all stages of signal processing in this brain area.

The Effect of Pedal Peptide-Type Neuropeptide on Locomotor Behavior and Muscle Physiology in the Sea Cucumber Apostichopus japonicus

Neuropeptides are endogenous active substances that are present in nervous tissues and participate in behavioral and physiological processes of the animal system. Locomotor behavior is basic to predation, escape, reproduction in animals, and neuropeptides play an important role in locomotion. In this study, the function of pedal peptide-type neuropeptide (PDP) in the process of locomotor behavior of the sea cucumber Apostichopus japonicus was evaluated. The locomotor behavior of A. japonicus was recorded by infrared camera before and after PDP administration, and muscle physiology was studied by ultra performance liquid chromatography and quadrupole time-off-light mass spectrometry (UPLC-Q-TOF-MS) to clarify the potential physiological mechanisms. The results showed that PDP enhanced the cumulative duration of moving significantly at the 7th h after injection, and reduced the mean and maximum velocity by 16.90 and 14.22% in A. japonicus. The data of muscle metabolomics suggested that some significantly changed metabolites were related to locomotor behavior of sea cucumbers. The decreases of phosphatidylethanolamine (PE) and phosphatidylcholine (PC) might result in the increases of lysophosphatidylcholines (lysoPC) and lysophosphatidylethanolamine (lysoPE), and suggested the change of fluidity and permeability in the muscle cell membrane, which would affect the physiology and function of muscle cells, and finally alter the locomotor behavior. In addition, the increased level of arachidonic acid (ARA) might activate K⁺ ion channels and then affect the signaling of muscle cells, or promote the sensitivity of muscle cells to Ca²⁺ and then result in the contractility of longitudinal muscles in sea cucumbers. ARA was also involved in the linoleic acid metabolism which was the only pathway that disturbed significantly after PDP administration. In conclusion, PDP participated in the regulation of locomotor behavior in the sea cucumber, and the decreased PE and PC, increased lysoPC, lysoPE and ARA might be the potential physiological mechanisms that responsible for behavioral effects of PDP in A. japonicus.

Better Sleep at Night: How Light Influences Sleep in Drosophila

Sleep-like states have been described in Drosophila and the mechanisms and factors that generate and define sleep-wake profiles in this model organism are being thoroughly investigated. Sleep is controlled by both circadian and homeostatic mechanisms, and environmental factors such as light, temperature, and social stimuli are fundamental in shaping and confining sleep episodes into the correct time of the day. Among environmental cues, light seems to have a prominent function in modulating the timing of sleep during the 24 h and, in this review, we will discuss the role of light inputs in modulating the distribution of the fly sleep-wake cycles. This phenomenon is of growing interest in the modern society, where artificial light exposure during the night is a common trait, opening the possibility to study Drosophila as a model organism for investigating shift-work disorders.

Neuroarchitecture of the central complex in the brain of the honeybee: Neuronal cell types

The central complex (CX) in the insect brain is a higher order integration center that controls a number of behaviors, most prominently goal directed locomotion. The CX comprises the protocerebral bridge (PB), the upper division of the central body (CBU), the lower division of the central body (CBL), and the paired noduli (NO). Although spatial orientation has been extensively studied in honeybees at the behavioral level, most electrophysiological and anatomical analyses have been carried out in other insect species, leaving the morphology and physiology of neurons that constitute the CX in the honeybee mostly enigmatic. The goal of this study was to morphologically identify neuronal cell types of the CX in the honeybee Apis mellifera. By performing iontophoretic dye injections into the CX, we traced 16 subtypes of neuron that connect a subdivision of the CX with other regions in the bee's central brain, and eight subtypes that mainly interconnect different subdivisions of the CX. They establish extensive connections between the CX and the lateral complex, the superior protocerebrum and the posterior protocerebrum. Characterized neuron classes and subtypes are morphologically similar to those described in other insects, suggesting considerable conservation in the neural network relevant for orientation.

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.

Dopamine modulates the optomotor response to unreliable visual stimuli in Drosophila melanogaster

State-dependent modulation of sensory systems has been studied in many organisms and is possibly mediated through neuromodulators such as monoamine neurotransmitters. Among these, dopamine is involved in many aspects of animal behaviour, including movement control, attention, motivation and cognition. However, the precise neural mechanism underlying dopaminergic modulation of behaviour induced by sensory stimuli remains poorly understood. Here, we used Drosophila melanogaster to show that dopamine can modulate the optomotor response to moving visual stimuli including noise. The optomotor response is the head-turning response to moving objects, which is observed in most sight-reliant animals including mammals and insects. First, the effects of the dopamine system on the optomotor response were investigated in mutant flies deficient in dopamine receptors D1R1 or D1R2, which are involved in the modulation of sleep-arousal in flies. We examined the optomotor response in D1R1 knockout (D1R1 KO) and D1R2 knockout (D1R2 KO) flies and found that it was not affected in D1R1 KO flies; however, it was significantly reduced in D1R2 KO flies compared with the wild type. Using cell-type-specific expression of an RNA interference construct of D1R2, we identified the fan-shaped body, a part of the central complex, responsible for dopamine-mediated modulation of the optomotor response. In particular, pontine cells in the fan-shaped body seemed important in the modulation of the optomotor response, and their neural activity was required for the optomotor response. These results suggest a novel role of the central complex in the modulation of a behaviour based on the processing of sensory stimulations.

Neuropeptides in modulation of Drosophila behavior: how to get a grip on their pleiotropic actions

Neuropeptides constitute a large and diverse class of signaling molecules that are produced by many types of neurons, neurosecretory cells, endocrines and other cells. Many neuropeptides display pleiotropic actions either as neuromodulators, co-transmitters or circulating hormones, while some play these roles concurrently. Here, we highlight pleiotropic functions of neuropeptides and different levels of neuropeptide signaling in the brain, from context-dependent orchestrating signaling by higher order neurons, to local executive modulation in specific circuits. Additionally, orchestrating neurons receive peptidergic signals from neurons conveying organismal internal state cues and relay these to executive circuits. We exemplify these levels of signaling with four neuropeptides, SIFamide, short neuropeptide F, allatostatin-A and leucokinin, each with a specific expression pattern and level of complexity in signaling.

Tachykinins: Neuropeptides That Are Ancient, Diverse, Widespread and Functionally Pleiotropic

Tachykinins (TKs) are ancient neuropeptides present throughout the bilaterians and are, with some exceptions, characterized by a conserved FX1GX2Ramide carboxy terminus among protostomes and FXGLMamide in deuterostomes. The best-known TK is the vertebrate substance P, which in mammals, together with other TKs, has been implicated in health and disease with important roles in pain, inflammation, cancer, depressive disorder, immune system, gut function, hematopoiesis, sensory processing, and hormone regulation. The invertebrate TKs are also known to have multiple functions in the central nervous system and intestine and these have been investigated in more detail in the fly Drosophila and some other arthropods. Here, we review the protostome and deuterostome organization and evolution of TK precursors, peptides and their receptors, as well as their functions, which appear to be partly conserved across Bilateria. We also outline the distribution of TKs in the brains of representative organisms. In Drosophila, recent studies have revealed roles of TKs in early olfactory processing, neuromodulation in circuits controlling locomotion and food search, nociception, aggression, metabolic stress, and hormone release. TK signaling also regulates lipid metabolism in the Drosophila intestine. In crustaceans, TK is an important neuromodulator in rhythm-generating motor circuits in the stomatogastric nervous system and a presynaptic modulator of photoreceptor cells. Several additional functional roles of invertebrate TKs can be inferred from their distribution in various brain circuits. In addition, there are a few interesting cases where invertebrate TKs are injected into prey animals as vasodilators from salivary glands or paralyzing agents from venom glands. In these cases, the peptides are produced in the glands of the predator with sequences mimicking the prey TKs. Lastly, the TK-signaling system appears to have duplicated in Panarthropoda (comprising arthropods, onychophores, and tardigrades) to give rise to a novel type of peptides, natalisins, with a distinct receptor. The distribution and functions of natalisins are distinct from the TKs. In general, it appears that TKs are widely distributed and act in circuits at short range as neuromodulators or cotransmitters.

Evolutionary trends of neuropeptide signaling in beetles - A comparative analysis of Coleopteran transcriptomic and genomic data

Insects employ neuropeptides to regulate their growth & development, behaviour, metabolism and their internal milieu. At least 50 neuropeptides are known to date, with some ancestral to the insects and others more specific to particular taxa. In order to understand the evolution and essentiality of neuropeptides, we data mined publicly available high quality genomic or transcriptomic data for 31 species of the largest insect Order, the Coleoptera, chosen to represent the superfamilies' of the Adephaga and Polyphaga. The resulting neuropeptide distributions were compared against the habitats, lifestyle and other parameters. Around half of the neuropeptide families were represented across the Coleoptera, suggesting essentiality or at least continuing utility. However, the remaining families showed patterns of loss that did not correlate with any obvious life history parameter, suggesting that these neuropeptides are no longer required for the Coleopteran lifestyle. This may perhaps indicate a decreasing reliance on neuropeptide signaling in insects.

Predatory behavior changes with satiety or increased insulin levels in the praying mantis (Tenodera sinensis)

At any given moment, behavior is controlled by a combination of external stimuli and an animal's internal state. As physiological conditions change, vastly different behaviors might result from the same stimuli. For example, the motivation to hunt and hunting strategy are influenced by satiety. Here, we describe how sensory responsiveness and motor activity of a praying mantis (Tenodera sinensis) change as the insect feeds, leading to an altered hunting strategy. We further show that these changes can be induced by injection of insulin, which likely functions as a metabotropic indicator. Praying mantises directed their attention toward real and simulated prey less often as they fed and became sated. The range of distance and azimuth at which prey was detected decreased as did pursuit of prey, while opportunistic close-range attacks persisted. Together, these sensorimotor changes are indicative of a behavioral paradigm shift from 'pursuit' to 'ambush'. A similar effect was induced in starved praying mantises injected with 0.05 ml of 200 μg ml^-1 bovine insulin. These experiments showed that insulin injection into the circulating hemolymph is sufficient to decrease prey orientation as well as in prey-directed locomotor behaviors (tracking and pursuit). The effects of prey consumption and insulin injection were similarly dose dependent. These results suggest that insulin is a signal of internal, physiological conditions that can modify responses to external stimuli. A change in hunting strategy thus results from coordinated effects of a neurohormone on a set of independent sensorimotor processes and the overall activity level of the animal.

Recent advances in neuropeptide signaling in Drosophila, from genes to physiology and behavior

This review focuses on neuropeptides and peptide hormones, the largest and most diverse class of neuroactive substances, known in Drosophila and other animals to play roles in almost all aspects of daily life, as w;1;ell as in developmental processes. We provide an update on novel neuropeptides and receptors identified in the last decade, and highlight progress in analysis of neuropeptide signaling in Drosophila. Especially exciting is the huge amount of work published on novel functions of neuropeptides and peptide hormones in Drosophila, largely due to the rapid developments of powerful genetic methods, imaging techniques and innovative assays. We critically discuss the roles of peptides in olfaction, taste, foraging, feeding, clock function/sleep, aggression, mating/reproduction, learning and other behaviors, as well as in regulation of development, growth, metabolic and water homeostasis, stress responses, fecundity, and lifespan. We furthermore provide novel information on neuropeptide distribution and organization of peptidergic systems, as well as the phylogenetic relations between Drosophila neuropeptides and those of other phyla, including mammals. As will be shown, neuropeptide signaling is phylogenetically ancient, and not only are the structures of the peptides, precursors and receptors conserved over evolution, but also many functions of neuropeptide signaling in physiology and behavior.

Members of the neuropeptide transcriptional network in Helicoverpa armigera and their expression in response to light stress

Neuropeptides and peptide hormones play central roles in the regulation of various types of insect physiology and behavior. Artificial light at night, a form of environmental stress, has recently been regarded as a source of light stress on nocturnal insects. Because related genomic information is not available, molecular biological studies on the response of neuropeptides in nocturnal insects to light stress are limited. Based on the de novo sequencing of the Helicoverpa armigera head transcriptome, we obtained 124,960 unigenes. Of these, the number of unigenes annotated as neuropeptides and peptide hormones, neurotransmitter precursor processing enzymes, and neurotransmitter receptors were 34, 17, and 58, respectively. Under light stress, there were sex-specific differences in gene expression measured by qRT-PCR. The IMFamide, leucokinin and sNPF genes were differentially expressed at the mRNA level in males but not in females in response to light stress. The results provide new insights on the diversity of the neuropeptide transcriptional network of H. armigera. In addition, some neuropeptides exhibited sex-specific differential expression in response to light stress. Taken collectively, these results not only expand the catalog of known insect neuropeptides but also provide a framework for future functional studies on the physiological roles they play in the light stress response behavior of nocturnal moths.

Analysis and evaluation of (neuro)peptides in honey bees exposed to pesticides in field conditions

During the last years, declines in honey bee colonies are being registered worldwide. Cholinergic pesticides and their extensive use have been correlated to the decline of pollinators and there is evidence that pesticides act as neuroendocrine disruptors affecting the metabolism of neuropeptides. However, there is a big absence of studies with quantitative results correlating the effect of pesticide exposure with changes on neuropeptides insects, and most of them are conducted under laboratory conditions, typically with individual active ingredients. In this study, we present an analytical workflow to evaluate pesticide effects on honey bees through the analysis of (neuro)peptides. The workflow consists of a rapid extraction method and liquid chromatography with triple quadrupole for preselected neuropeptides. For non-target analysis, high resolution mass spectrometry, multivariate analysis and automatic identification of discriminated peptides using a specific software and protein sequence databases. The analytical method was applied to the analysis of target and non-target (neuro)peptides in honey bees with low and high content of a wide range of pesticides to which have been exposed in field conditions. Our findings show that the identification frequency of target neuropeptides decreases significantly in honey bees with high concentration of pesticides (pesticide concentrations ≥ 500 μg kg^-1) in comparison with the honey bees with low content of pesticides (pesticide concentrations ≤ 20 μg kg^-1). Moreover, the principal component analysis in non-target search shows a clear distinction between peptide concentration in honey bees with high level of pesticides and honey bees with low level. The use of high resolution mass spectrometry has allowed the identification of 25 non-redundant peptides responsible for discrimination between the two groups, derived from 18 precursor proteins.

Neuronal and molecular mechanisms of sleep homeostasis

Sleep is necessary for survival, and prolonged waking causes a homeostatic increase in the need for recovery sleep. Homeostasis is a core component of sleep regulation and has been tightly conserved across evolution from invertebrates to man. Homeostatic sleep regulation was first identified among insects in cockroaches several decades ago, but the characterization of sleep rebound in Drosophila melanogaster opened the use of insect model species to understand homeostatic functions and regulation of sleep. This review describes circuits in two neuropil structures, the central complex and mushroom bodies, that influence sleep homeostasis and neuromodulatory systems that influence the accrual of homeostatic sleep need.

Bombyx neuropeptide G protein-coupled receptor A7 is the third cognate receptor for short neuropeptide F from silkworm

The short neuropeptide F (sNPF) neuropeptides, closely related to vertebrate neuropeptide Y (NPY), have been suggested to exert pleiotropic effects on many physiological processes in insects. In the silkworm (Bombyx mori) two orphan G protein-coupled receptors, Bombyx neuropeptide G protein-coupled receptor (BNGR) A10 and A11, have been identified as cognate receptors for sNPFs, but other sNPF receptors and their signaling mechanisms in B. mori remain unknown. Here, we cloned the full-length cDNA of the orphan receptor BNGR-A7 from the brain of B. mori larvae and identified it as a receptor for Bombyx sNPFs. Further characterization of signaling and internalization indicated that BNGR-A7, -A10, and -A11 are activated by direct interaction with synthetic Bombyx sNPF-1 and -3 peptides. This activation inhibited forskolin or adipokinetic hormone-induced adenylyl cyclase activity and intracellular Ca²⁺ mobilization via a G_i/o-dependent pathway. Upon activation by sNPFs, BNGR-A7, -A10, and -A11 evoked ERK1/2 phosphorylation and underwent internalization. On the basis of these findings, we designated the receptors BNGR-A7, -A10, and -A11 as Bommo-sNPFR-1, -2, and -3, respectively. Moreover, the results obtained with quantitative RT-PCR analysis revealed that the three Bombyx sNPF receptor subtypes exhibit differential spatial and temporal expression patterns, suggesting possible roles of sNPF signaling in the regulation of a wide range of biological processes. Our findings provide the first in-depth information on sNPF signaling for further elucidation of the roles of the Bombyx sNPF/sNPFR system in the regulation of physiological activities.

The short neuropeptide F modulates olfactory sensitivity of Bactrocera dorsalis upon starvation

The insect short neuropeptide F (sNPF) family has been shown to modulate diverse physiological processes, such as feeding, appetitive olfactory behavior, locomotion, sleep homeostasis and hormone release. In this study, we identified the sNPF (BdsNPF) and its receptor (BdsNPFR) in an important agricultural pest, the oriental fruit fly Bactrocera dorsalis (Hendel). Afterwards, the receptor cDNA was functionally expressed in Chinese hamster ovary cell lines. Activation of BdsNPFR by sNPF peptides caused an increase in intracellular calcium ions, with a 50% effective concentration values at the nanomolar level. As indicated by qPCR, the BdsNPF and BdsNPFR transcripts were mainly detected in the central nervous system and antennae, and they showed significantly starvation-induced expression patterns. Furthermore, we found that the starved flies had an increased electroantennogram response compared to the normally fed flies. However, this enhanced olfactory sensitivity was reversed when we decreased the expression of BdsNPF by double-stranded RNA injection in adults. We concluded that sNPF plays an important role in modulating the olfactory sensitivity of B. dorsalis upon starvation. Our results will facilitate the understanding of the regulation of early olfactory processing in B. dorsalis.

Behavioral Senescence and Aging-Related Changes in Motor Neurons and Brain Neuromodulator Levels Are Ameliorated by Lifespan-Extending Reproductive Dormancy in Drosophila

The lifespan of Drosophilamelanogaster can be extended substantially by inducing reproductive dormancy (also known as diapause) by lowered temperature and short days. This increase of longevity is accompanied by lowered metabolism and increased stress tolerance. We ask here whether behavioral senescence is ameliorated during adult dormancy. To study this we kept flies for seven or more weeks in normal rearing conditions or in diapause conditions and compared to 1-week-old flies in different behavioral assays of sleep, negative geotaxis and exploratory walking. We found that the senescence of geotaxis and locomotor behavior seen under normal rearing conditions was negligible in flies kept in dormancy. The normal senescence of rhythmic activity and sleep patterns during the daytime was also reduced by adult dormancy. Investigating the morphology of specific neuromuscular junctions (NMJs), we found that changes normally seen with aging do not take place in dormant flies. To monitor age-associated changes in neuronal circuits regulating activity rhythms, sleep and walking behavior we applied antisera to tyrosine hydroxylase (TH), serotonin and several neuropeptides to examine changes in expression levels and neuron morphology. In most neuron types the levels of stored neuromodulators decreased during normal aging, but not in diapause treated flies. No signs of neurodegeneration were seen in either condition. Our data suggest that age-related changes in motor neurons could be the cause of part of the behavioral senescence and that this is ameliorated by reproductive diapause. Earlier studies established a link between age-associated decreases in neuromodulator levels and behavioral decline that could be rescued by overexpression of neuromodulator. Thus, it is likely that the retained levels of neuromodulators in dormant flies alleviate behavioral senescence.

A Neurocomputational Model of Goal-Directed Navigation in Insect-Inspired Artificial Agents

Despite their small size, insect brains are able to produce robust and efficient navigation in complex environments. Specifically in social insects, such as ants and bees, these navigational capabilities are guided by orientation directing vectors generated by a process called path integration. During this process, they integrate compass and odometric cues to estimate their current location as a vector, called the home vector for guiding them back home on a straight path. They further acquire and retrieve path integration-based vector memories globally to the nest or based on visual landmarks. Although existing computational models reproduced similar behaviors, a neurocomputational model of vector navigation including the acquisition of vector representations has not been described before. Here we present a model of neural mechanisms in a modular closed-loop control—enabling vector navigation in artificial agents. The model consists of a path integration mechanism, reward-modulated global learning, random search, and action selection. The path integration mechanism integrates compass and odometric cues to compute a vectorial representation of the agent's current location as neural activity patterns in circular arrays. A reward-modulated learning rule enables the acquisition of vector memories by associating the local food reward with the path integration state. A motor output is computed based on the combination of vector memories and random exploration. In simulation, we show that the neural mechanisms enable robust homing and localization, even in the presence of external sensory noise. The proposed learning rules lead to goal-directed navigation and route formation performed under realistic conditions. Consequently, we provide a novel approach for vector learning and navigation in a simulated, situated agent linking behavioral observations to their possible underlying neural substrates.

Insect-Like Organization of the Stomatopod Central Complex: Functional and Phylogenetic Implications

One approach to investigating functional attributes of the central complex is to relate its various elaborations to pancrustacean phylogeny, to taxon-specific behavioral repertoires and ecological settings. Here we review morphological similarities between the central complex of stomatopod crustaceans and the central complex of dicondylic insects. We discuss whether their central complexes possess comparable functional properties, despite the phyletic distance separating these taxa, with mantis shrimp (Stomatopoda) belonging to the basal branch of Eumalacostraca. Stomatopods possess the most elaborate visual receptor system in nature and display a fascinating behavioral repertoire, including refined appendicular dexterity such as independently moving eyestalks. They are also unparalleled in their ability to maneuver during both swimming and substrate locomotion. Like other pancrustaceans, stomatopods possess a set of midline neuropils, called the central complex, which in dicondylic insects have been shown to mediate the selection of motor actions for a range of behaviors. As in dicondylic insects, the stomatopod central complex comprises a modular protocerebral bridge (PB) supplying decussating axons to a scalloped fan-shaped body (FB) and its accompanying ellipsoid body (EB), which is linked to a set of paired noduli and other recognized satellite regions. We consider the functional implications of these attributes in the context of stomatopod behaviors, particularly of their eyestalks that can move independently or conjointly depending on the visual scene.

Molecular characterization of a short neuropeptide F signaling system in the tsetse fly, Glossina morsitans morsitans

Neuropeptides of the short neuropeptide F (sNPF) family are widespread among arthropods and found in every sequenced insect genome so far. Functional studies have mainly focused on the regulatory role of sNPF in feeding behavior, although this neuropeptide family has pleiotropic effects including in the control of locomotion, osmotic homeostasis, sleep, learning and memory. Here, we set out to characterize and determine possible roles of sNPF signaling in the haematophagous tsetse fly Glossina morsitans morsitans, a vector of African Trypanosoma parasites causing human and animal African trypanosomiasis. We cloned the G. m. morsitans cDNA sequences of an sNPF-like receptor (Glomo-sNPFR) and precursor protein encoding four Glomo-sNPF neuropeptides. All four Glomo-sNPF peptides concentration-dependently activated Glomo-sNPFR in a cell-based calcium mobilization assay, with EC50 values in the nanomolar range. Gene expression profiles in adult female tsetse flies indicate that the Glomo-sNPF system is mainly restricted to the nervous system. Glomo-snpfr transcripts were also detected in the hindgut of adult females. In contrast to the Drosophila sNPF system, tsetse larvae lack expression of Glomo-snpf and Glomo-snpfr genes. While Glomo-snpf transcript levels are upregulated in pupae, the onset of Glomo-snpfr expression is delayed to adulthood. Expression profiles in adult tissues are similar to those in other insects suggesting that the tsetse sNPF system may have similar functions such as a regulatory role in feeding behavior, together with a possible involvement of sNPFR signaling in osmotic homeostasis. Our molecular data will enable further investigations into the functions of sNPF signaling in tsetse flies.

Neural mechanisms of insect navigation

We know more about the ethology of insect navigation than the neural substrates. Few studies have shown direct effects of brain manipulation on navigational behaviour; or measure brain responses that clearly relate to the animal's current location or spatial target, independently of specific sensory cues. This is partly due to the methodological problems of obtaining neural data in a naturally behaving animal. However, substantial indirect evidence, such as comparative anatomy and knowledge of the neural circuits that provide relevant sensory inputs provide converging arguments for the role of some specific brain areas: the mushroom bodies; and the central complex. Finally, modelling can help bridge the gap by relating the computational requirements of a given navigational task to the type of computation offered by different brain areas.