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Fast cholinergic neurotransmission is mediated by acetylcholine-gated ion channels; in particular, excitatory nicotinic acetylcholine receptors play well established roles in virtually all nervous systems. Acetylcholine-gated inhibitory channels have also been identified in some invertebrate phyla, yet their roles in the nervous system are less well understood. We report the existence of multiple new inhibitory ion channels with diverse ligand activation properties inCaenorhabditis elegans. We identify three channels, LGC-40, LGC-57, and LGC-58, whose primary ligand is choline rather than acetylcholine, as well as the first evidence of a truly polymodal channel, LGC-39, which is activated by both cholinergic and aminergic ligands. Using our new ligand–receptor pairs we uncover the surprising extent to which single neurons in the hermaphrodite nervous system express both excitatory and inhibitory channels, not only for acetylcholine but also for the other major neurotransmitters. The results presented in this study offer new insight into the potential evolutionary benefit of a vast and diverse repertoire of ligand-gated ion channels to generate complexity in an anatomically compact nervous system.SIGNIFICANCE STATEMENTHere we describe the diversity of cholinergic signaling in the nematodeCaenorhabditis elegans. We identify and characterize a novel family of ligand-gated ion channels and show that they are preferentially gated by choline rather than acetylcholine and expressed broadly in the nervous system. Interestingly, we also identify one channel gated by chemically diverse ligands including acetylcholine and aminergic ligands. By using our new knowledge of these ligand-gated ion channels, we built a model to predict the synaptic polarity in theC. elegansconnectome. This model can be used for generating hypotheses on neural circuit function.

Tyramine beta-hydroxylase (TBH) is needed for the biosynthesis of the octopamine (OA) from tyramine (TA). Both OA and TA act as neurotransmitters, neurohormones, and neuromodulators in the invertebrate nervous system. In this study, TBH was identified in white shrimp, Litopenaeus vannamei, and further investigation on its potential function was conducted after inducing hypothermal stress and Vibrio alginolyticus infection. TBH of L. vannamei (LvTBH) was comprised 2178 nucleotide residues and contained an open reading frame encoding 408 amino acids, belonging to the Copper type II, ascorbate-dependent monooxygenases, was characterized by two Cu2_monooxygen domains and five glycosylation sites. LvTBH expression was especially abundant in muscle, and mainly in brain and thoracic ganglia of nervous system, eyestalk tissues, epithelium, and stomach, as determined by quantitative real-time PCR. The effects of hypothermal stress showed significant increases in LvTBH at 15, 30 and 60 min in brain and at 30 min in haemocyte, accompanied by an increase in OA level in haemolymph from 15 to 60 min. Significant increases in LvTBH occurred at 15, 30 and 60 min in haemocyte and at 60 min in brain tissue, and was proportional to the OA level of haemolymph under Vibrio alginolyticus infection from 30 to 60 min. Here, we demonstrated that LvTBH is functionally responsible for biogenic amine synthesis, suggesting that the increased release of OA in haemolymph for potential modulation of physiological and immunological responses is the consequence of the upregulated LvTBH gene expression in L. vannamei exposed to hypothermal stress and Vibrio alginolyticus infection.

Discrimination of sensory signals is essential for an organism to form and retrieve memories of relevance in a given behavioral context. Sensory representations are modified dynamically by changes in behavioral state, facilitating context-dependent selection of behavior, through signals carried by noradrenergic input in mammals, or octopamine (OA) in insects. To understand the circuit mechanisms of this signaling, we characterized the function of two OA neurons, sVUM1 neurons, that originate in the subesophageal zone (SEZ) and target the input region of the memory center, the mushroom body (MB) calyx, in larval Drosophila. We found that sVUM1 neurons target multiple neurons, including olfactory projection neurons (PNs), the inhibitory neuron APL, and a pair of extrinsic output neurons, but relatively few mushroom body intrinsic neurons, Kenyon cells. PN terminals carried the OA receptor Oamb, a Drosophila α1-adrenergic receptor ortholog. Using an odor discrimination learning paradigm, we showed that optogenetic activation of OA neurons compromised discrimination of similar odors but not learning ability. Our results suggest that sVUM1 neurons modify odor representations via multiple extrinsic inputs at the sensory input area to the MB olfactory learning circuit.

—Trace amines are similar in structure to catecholamines and serotonin of the central nervous system but are present at much lower concentrations. Trace amines such as tyramine, tryptamine, octopamine, and β-phenylethylamine, bind to highly specific receptors that have low affinity for catecholamines and serotonin. Several types of trace amine receptors have been identified. Trace amine-associated receptor 1 is localized in the prefrontal cortex and limbic structures. Localization of the other types of receptors is different. In particular, trace amine-associated receptor 5 is localized in the olfactory epithelium and structures of the olfactory brain. By interaction with dopaminergic and other neurotransmitter systems of the CNS, trace amines are involved in the regulation of many behavioral forms. In simplistic terms, we can talk about the functional antagonism of trace amines and the dopaminergic system. Trace amines are considered as promising antipsychotics, which is evidenced by the results of studies in animal models of schizophrenia.

Biogenic amines (BAs; 2-phenylethylamine, tyramine, dopamine, epinephrine, norepinephrine, octopamine, histamine, tryptamine, serotonin, agmatine, cadaverine, putrescine, spermidine, spermine and certain aliphatic amines) are widely distributed organic molecules that play basic physiological functions in animals, plants and microorganisms. Pseudomonas species can grow in media containing different BAs as carbon and energy sources, a reason why these bacteria are excellent models for studying such catabolic pathways. In this review, we analyse most of the routes used by different species of Pseudomonas (P. putida, P. aeruginosa, P. entomophila and P. fluorescens) to degrade BAs. Analysis of these pathways has led to the identification of a huge number of genes, catabolic enzymes, transport systems and regulators, as well as to understanding of their hierarchy and functional evolution. Knowledge of these pathways has allowed the design and collection of genetically manipulated microbes useful for eliminating BAs from different sources, highlighting the biotechnological applications of these studies.

Colonies of the red harvester ant, Pogonomyrmex barbatus, regulate foraging activity based on food availability and local conditions. Colony variation in foraging behavior is thought to be linked to biogenic amine signaling and metabolism. Measurements of differences in neurotransmitters have not been made among ant colonies in a natural environment. Here, for the first time, we quantified tissue content of 4 biogenic amines (dopamine, serotonin, octopamine, and tyramine) in single forager brains from 9 red harvester ant colonies collected in the field. Capillary electrophoresis coupled with fast-scan cyclic voltammetry (CE-FSCV) was used to separate and detect the amines in individual ant brains. Low levels of biogenic amines were detected using field-amplified sample stacking by preparing a single brain tissue sample in acetonitrile and perchloric acid. The method provides low detection limits: 1 nM for dopamine, 2 nM for serotonin, 5 nM for octopamine, and 4 nM for tyramine. Overall, the content of dopamine (47 ± 9 pg/brain) was highest, followed by octopamine (36 ± 10 pg/brain), serotonin (20 ± 4 pg/brain), and tyramine (14 ± 3 pg/brain). Relative standard deviations were high, but there was less variation within a colony than among colonies, so the neurotransmitter content of each colony might change with environmental conditions. This study demonstrates that CE-FSCV is a useful method for investigating natural variation in neurotransmitter content in single ant brains and could be useful for future studies correlating tissue content with colony behavior such as foraging. Graphical abstract.

Monoamine neuromodulators such as dopamine (DA), norepinephrine (NE), serotonin (5-HT), octopamine, and tyramine are signaling molecules in the nervous system, where they play critical roles in both health and disease. Given the complex spatio-temporal dynamics, similar structural features, and different receptors, studying their dynamics has been limited using conventional methods such as microdialysis and electrochemistry. However, recent advances in optics have facilitated the development of imaging-based detection methods. In this review, we summarize current detecting approaches for specific monoamines, emphasizing their design strategies, detection properties, applications, and limitations. We highlight the genetically encoded GPCR-based sensors for DA and NE, which have a high signal-to-noise ratio and selectivity, and can be used in vivo in different species. Finally, we discuss the potential for using this approach to generate new neuromodulator sensors with non-overlapping spectra, which will ultimately pave the way for studying the interplay between various neuromodulators and neurotransmitters.

In insects, neuropeptides and their receptors not only play a critical role in insect physiology and behavior but also are the potential targets for novel pesticide discoveries. Aphidius gifuensis is one of the most important and widespread aphid parasitoids, and has been successfully used to control aphid. In the present work, we systematically identified neuropeptides and their receptors from the genome and head transcriptome of A. gifuensis. A total of 35 neuropeptide precursors and 49 corresponding receptors were identified. The phylogenetic analyses demonstrated that 35 of these receptors belong to family-A, four belong to family-B, two belong to leucine-rich repeat-containing GPCRs, four belong to receptor guanylyl cyclases, and four belong to receptor tyrosine kinases. Oral ingestion of imidacloprid significantly up-regulated five neuropeptide precursors and four receptors whereas three neuropeptide precursors and eight receptors were significantly down-regulated, which indicated that these neuropeptides and their receptors are potential targets of some commercial insecticides. The RT-qPCR results showed that dopamine receptor 1, dopamine receptor 2, octopamine receptor, allatostatin-A receptor, neuropeptides capa receptor, SIFamide receptor, FMRFamide receptor, tyramine receptor and short neuropeptide F predominantly were expressed in the head whilst the expression of ion transport peptide showed widespread distribution in various tissues. The high expression levels of these genes suggest their important roles in the central nervous system. Taken together, our study provides fundamental information that may further our understanding of neuropeptidergic signaling systems in the regulation of the physiology and behavior of solitary wasps. Furthermore, this information could also aid in the design and discovery of specific and environment-friendly insecticides.

The Varroa destructor mite is a devastating parasite of Apis mellifera honeybees. They can cause colonies to collapse by spreading viruses and feeding on the fat reserves of adults and larvae. Amitraz is used to control mites due to its low toxicity to bees; however, the mechanism of bee resistance to amitraz remains unknown. In this study, we found that amitraz and its major metabolite potently activated all four mite octopamine receptors. Behavioral assays using Drosophila null mutants of octopamine receptors identified one receptor subtype Octβ2R as the sole target of amitraz in vivo. We found that thermogenetic activation of octβ2R-expressing neurons mimics amitraz poisoning symptoms in target pests. We next confirmed that the mite Octβ2R was more sensitive to amitraz and its metabolite than the bee Octβ2R in pharmacological assays and transgenic flies. Furthermore, replacement of three bee-specific residues with the counterparts in the mite receptor increased amitraz sensitivity of the bee Octβ2R, indicating that the relative insensitivity of their receptor is the major mechanism for honeybees to resist amitraz. The present findings have important implications for resistance management and the design of safer insecticides that selectively target pests while maintaining low toxicity to non-target pollinators.

Sublethal exposure to neonicotinoids affects honey bee olfaction, but few studies have investigated the sublethal effects of the enantioselective neonicotinoid dinotefuran on honey bee olfaction. This study assessed the sublethal olfactory toxicity of dinotefuran enantiomers to honey bees. Compared to R-dinotefuran, S-dinotefuran had higher acute oral toxicity, sucrose sensitivity effects, octopamine concentrations, lower learning ability, and memory effects on honey bees. High-throughput circular RNA sequencing of the honey bee brain revealed that R-dinotefuran caused more gene regulatory changes than S-dinotefuran. Gene ontology enrichment and Kyoto Encyclopedia of Genes and Genomes pathway analyses demonstrated that the SERCA, Kca, and Maxik genes may be related to the enantioselective effects of dinotefuran isomers on honey bee olfaction. These results indicated that the current ecotoxicological safety knowledge about chiral dinotefuran effects on honey bees should be amended.

Significance Physiological regulation and behavior depend less on neurons than on neuronal circuits. Neurosignal integration is the basis of neurocircuit function. The modalities of neuroinformation integration are evolutionarily conserved in animals and humans. Here, we identified two modalities of neurosignal integration in two different circuits by which serotonergic ADFs regulate pharyngeal pumping in Caenorhabditis elegans: disinhibition in a feedforward circuit consisting of ADF, RIC, and SIA neurons and disexcitation, a modality of neurosignal integration suggested by this study, in a feedback circuit consisting of ADF, RIC, AWB, and ADF neurons., Feeding is vital for animal survival and is tightly regulated by the endocrine and nervous systems. To study the mechanisms of humoral regulation of feeding behavior, we investigated serotonin (5-HT) and octopamine (OA) signaling in Caenorhabditis elegans, which uses pharyngeal pumping to ingest bacteria into the gut. We reveal that a cross-modulation mechanism between 5-HT and OA, which convey feeding and fasting signals, respectively, mainly functions in regulating the pumping and secretion of both neuromodulators via ADF/RIC/SIA feedforward neurocircuit (consisting of ADF, RIC, and SIA neurons) and ADF/RIC/AWB/ADF feedback neurocircuit (consisting of ADF, RIC, AWB, and ADF neurons) under conditions of food supply and food deprivation, respectively. Food supply stimulates food-sensing ADFs to release more 5-HT, which augments pumping via inhibiting OA secretion by RIC interneurons and, thus, alleviates pumping suppression by OA-activated SIA interneurons/motoneurons. In contrast, nutrient deprivation stimulates RICs to secrete OA, which suppresses pumping via activating SIAs and maintains basal pumping and 5-HT production activity through excitation of ADFs relayed by AWB sensory neurons. Notably, the feedforward and feedback circuits employ distinct modalities of neurosignal integration, namely, disinhibition and disexcitation, respectively.

Adrenergic signaling profoundly modulates animal behavior. For example, the invertebrate counterpart of norepinephrine, octopamine, and its biological precursor and functional antagonist, tyramine, adjust motor behavior to different nutritional states. In Drosophila larvae, food deprivation increases locomotor speed via octopamine-mediated structural plasticity of neuromuscular synapses, whereas tyramine reduces locomotor speed, but the underlying cellular and molecular mechanisms remain unknown. We show that tyramine is released into the CNS to reduce motoneuron intrinsic excitability and responses to excitatory cholinergic input, both by tyraminehonoka receptor activation and by downstream decrease of L-type calcium current. This central effect of tyramine on motoneurons is required for the adaptive reduction of locomotor activity after feeding. Similarly, peripheral octopamine action on motoneurons has been reported to be required for increasing locomotion upon starvation. We further show that the level of tyramine-β-hydroxylase (TBH), the enzyme that converts tyramine into octopamine in aminergic neurons, is increased by food deprivation, thus selecting between antagonistic amine actions on motoneurons. Therefore, octopamine and tyramine provide global but distinctly different mechanisms to regulate motoneuron excitability and behavioral plasticity, and their antagonistic actions are balanced within a dynamic range by nutritional effects on TBH.

This work deals with the molecular modeling and vibrational spectra of all the twenty conformers of an important biomolecule octopamine which have been investigated using the DFT/B3LYP level of theory in combination with the 6-31++g(d,p) as a suitable basis set. The experimental FTIR and FTRaman spectra of octopamine neurotransmitter were recorded in the spectral region 400–4000 cm−1 and 50–4000 cm−1 respectively and correlated with the calculated spectra of the most stable conformer. The effect of hydrochloride on the important geometrical parameters of most stable conformer of octopamine was also studied. The normal coordinate analysis was performed to scale the theoretical frequencies and to calculate potential energy distributions for precise normal mode assignment. Most of the frequencies were in good agreement with experimental one. However, some have been modified. Natural bond orbital analysis was performed in order to confirm the stability of electronic structure of octopamine molecule. HOMO-LUMO analysis for all the twenty conformers was also performed to give the transition profile and to study the chemical reactivity of octopamine.

Monoamines are a class of neuromodulators that are crucial for a variety of brain functions, including control of mood, movement, sleep and cognition. From mammals to insects, the nervous system is enriched in monoamines such as dopamine, serotonin and melatonin, analytes which range from being highly polar to non-polar. Here we developed a method using liquid chromatography coupled with mass spectrometry (LC-MS) to quantify in a single run the amounts of six distinct monoamines in extracts from dissected Drosophila and mouse brain tissues. The measured monoamines were dopamine (DA), serotonin (also known as 5-hydroxytryptamine (5-HT)), octopamine (OA, an insect equivalent of norepinephrine), tyramine (TA), melatonin (MT) and N-acetyl-hydroxy-serotonin (NAS). The analytical range of these monoamines was between 0.25 to 5.0 ng/mL.

Resistance to currently utilized chemical insecticidal agents represents a significant threat to public health and food security worldwide. Better understanding the neurophysiological effects of available and candidate insecticidal molecules is valuable for characterizing the mechanisms of insecticide resistance, as well as the design and study of novel control chemistries. In this paper, we describe a method of recording nerve firing from the central nervous system of Aedes aegypti fourth instar larvae. In short, mosquito larvae were immobilized by placing small pins through the head and siphon of the larvae in a wax dish, ventral side down. A single, longitudinal, dorsal incision from the distal abdomen to the pronotum of the larva was made, the alimentary canal removed, and the ventral nerve cord severed between the second and third abdominal ganglia. A recording suction electrode was connected directly to axons within the severed end of the connective in a novel way to record nerve firing in the ventral nerve cord at a high signal-to-noise ratio with conventional electrophysiological equipment. Using this novel method, we report the effects of four neuroactive compounds using this method: octopamine, pilocarpine, nicotine, and γ-aminobutyric acid (GABA). The utility of this recording technique for elucidating target site mechanisms involved in insecticide resistance is demonstrated with p,p’-dichlorodiphenyltrichlorethane (DDT) and its difluoro analog (DFDT).

Genomic and phylogenetic analyses of various invertebrate phyla revealed the existence of genes that are evolutionarily related to the vertebrate’s decapeptide gonadotropin-releasing hormone (GnRH) and the GnRH receptor genes. Upon the characterization of these gene products, encoding peptides and putative receptors, GnRH-related peptides and their G-protein coupled receptors have been identified. These include the adipokinetic hormone (AKH) and corazonin (CRZ) in insects and their cognate receptors that pair to form bioactive signaling systems, which network with additional neurotransmitters/hormones (e.g., octopamine and ecdysone). Multiple studies in the past 30 years have identified many aspects of the biology of these peptides that are similar in size to GnRH and function as neurohormones. This review briefly describes the main activities of these two neurohormones and their receptors in the fruit fly Drosophila melanogaster. The similarities and differences between Drosophila AKH/CRZ and mammalian GnRH signaling systems are discussed. Of note, while GnRH has a key role in reproduction, AKH and CRZ show pleiotropic activities in the adult fly, primarily in metabolism and stress responses. From a protein evolution standpoint, the GnRH/AKH/CRZ family nicely demonstrates the developmental process of neuropeptide signaling systems emerging from a putative common ancestor and leading to divergent activities in distal phyla.

The biogenic monoamine octopamine (OA) is a crucial regulator of invertebrate physiology and behavior. Since its discovery in the 1950s in octopus salivary glands, OA has been implicated in many biological processes among diverse invertebrate lineages. It can act as a neurotransmitter, neuromodulator and neurohormone in a variety of biological contexts, and can mediate processes including feeding, sleep, locomotion, flight, learning, memory, and aggression. Here, we focus on the roles of OA in female reproduction in insects. OA is produced in the octopaminergic neurons that innervate the female reproductive tract (RT). It exerts its effects by binding to receptors throughout the RT to generate tissue- and region-specific outcomes. OA signaling regulates oogenesis, ovulation, sperm storage, and reproductive behaviors in response to the female's internal state and external conditions. Mating profoundly changes a female's physiology and behavior. The female's OA signaling system interacts with, and is modified by, male molecules transferred during mating to elicit a subset of the post-mating changes. Since the role of OA in female reproduction is best characterized in the fruit fly Drosophila melanogaster, we focus our discussion on this species but include discussion of OA in other insect species whenever relevant. We conclude by proposing areas for future research to further the understanding of OA's involvement in female reproduction in insects.

Simple Summary This review aims to describe the type 1 tyramine receptors (TAR1s) in insects with a multidisciplinary approach and might be an important tool for a wide scientific audience, including biochemists, molecular physiologists, ethologists, and neurobiologists with a biological entomology background. In fact, in the last years, TAR1 has received much attention due to its broad general interest. The review is composed of a general introduction about the tyraminergic and octopaminergic systems and the corresponding tyramine (TA) and octopamine (OA) receptors, including the recent classification as well as their brief structural and functional information. The four chapters then describe TAR1s: (1) Molecular and structural characterization, with the purpose to provide a clear biochemical overview of the receptor that ensures a well-defined TAR1 identity; (2) pharmacology, in which a clear TAR1-mediated intracellular signaling pathway is detailed; (3) physiology and behavior, focusing on the TAR1-controlled traits in insects; (4) insecticide target, in which the knowledge on TAR1 roles in insects is associated with the growing evidence about the pest management strategies based on this receptor. The conclusions summarize TAR1 features as well as future directions on which the receptor research should move. Abstract Tyramine is a neuroactive compound that acts as neurotransmitter, neuromodulator, and neurohormone in insects. Three G protein-coupled receptors, TAR1-3, are responsible for mediating the intracellular pathway in the complex tyraminergic network. TAR1, the prominent player in this system, was initially classified as an octopamine receptor which can also be activated by tyramine, while it later appeared to be a true tyramine receptor. Even though TAR1 is currently considered as a well-defined tyramine receptor and several insect TAR1s have been characterized, a defined nomenclature is still inconsistent. In the last years, our knowledge on the structural, biochemical, and functional properties of TAR1 has substantially increased. This review summarizes the available information on TAR1 from different insect species in terms of basic structure, its regulation and signal transduction mechanisms, and its distribution and functions in the brain and the periphery. A special focus is given to the TAR1-mediated intracellular signaling pathways as well as to their physiological role in regulating behavioral traits. Therefore, this work aims to correlate, for the first time, the physiological relevance of TAR1 functions with the tyraminergic system in insects. In addition, pharmacological studies have shed light on compounds with insecticidal properties having TAR1 as a target and on the emerging trend in the development of novel strategies for pest control.

Identifying mechanisms underlying alcohol-related behaviors could provide important insights regarding the etiology of alcohol use disorder. To date, most genetic studies on alcohol-related behavior in model organisms have focused on neurons, leaving the causal roles of glial mechanisms less comprehensively investigated. Here, we report our studies on the role of Tyrosine decarboxylase 2 (Tdc2), which converts tyrosine to the catecholamine tyramine, in glial cells in Drosophila alcohol sedation. Using genetic approaches that drove transgene expression constitutively in all glia, constitutively in astrocytes and conditionally in glia during adulthood, we found that knockdown and overexpression of Tdc2, respectively, increased and decreased the sensitivity to alcohol sedation in flies. Manipulation of the genes tyramine β-hydroxylase and tyrosine hydroxylase, which respectively synthesize octopamine and dopamine from tyramine and tyrosine, had no discernable effect on alcohol sedation, suggesting that Tdc2 affects alcohol sedation by regulating tyramine production. We also found that knockdown of the vesicular monoamine transporter (VMAT) and disruption of the SNARE complex in all glia or selectively in astrocytes increased sensitivity to alcohol sedation and that both VMAT and the SNARE complex functioned downstream of Tdc2. Our studies support a model in which the synthesis of tyramine and vesicle-mediated release of tyramine from adult astrocytes regulates alcohol sedation in Drosophila. Considering that tyramine is functionally orthologous to norepinephrine in mammals, our results raise the possibility that gliotransmitter synthesis release could be a conserved mechanism influencing behavioral responses to alcohol as well as alcohol use disorder.

Foraging behavior is crucial for the development of a honeybee colony. Biogenic amines are key mediators of learning and the transition from in-hive tasks to foraging. Foragers vary considerably in their behavior, but whether and how this behavioral diversity depends on biogenic amines is not yet well understood. For example, forager age, cumulative foraging activity or foraging state may all be linked to biogenic amine signaling. Furthermore, expression levels may fluctuate depending on daytime. We tested if these intrinsic and extrinsic factors are linked to biogenic amine signaling by quantifying the expression of octopamine, dopamine and tyramine receptor genes in the mushroom bodies, important tissues for learning and memory. We found that older foragers had a significantly higher expression of Amdop1, Amdop2, AmoctαR1, and AmoctβR1 compared to younger foragers, whereas Amtar1 showed the opposite pattern. Surprisingly, our measures of cumulative foraging activity were not related to the expression of the same receptor genes in the mushroom bodies. Furthermore, we trained foragers to collect sucrose solution at a specific time of day and tested if the foraging state of time-trained foragers affected receptor gene expression. Bees engaged in foraging had a higher expression of Amdop1 and AmoctβR3/4 than inactive foragers. Finally, the expression of Amdop1, Amdop3, AmoctαR1, and Amtar1 also varied with daytime. Our results show that receptor gene expression in forager mushroom bodies is complex and depends on both intrinsic and extrinsic factors.

The biogenic monoamines, serotonin, octopamine, tyramine, dopamine and histamine are present within insect nervous systems, where they modulate multiple and diverse neuronal pathways. In this context, these biogenic amines may be involved in a cascade of events that leads to the initiation and maintenance of a new behavioural act; they bias the nervous and peripheral systems towards a new behavioural state. This review examines the role of these biogenic amines in triatomine physiology, with an emphasis on the most studied triatomine, Rhodnius prolixus. Each biogenic amine is reviewed with regard to its biosynthesis and removal, distribution, receptors and physiological relevance, with reference to insects in general and R. prolixus in particular. The biogenic amines control various behaviours within R. prolixus, including, feeding, reproduction, cuticle tanning and photoreception.

Drosophila melanogaster express vesicular transporters for the storage of neurotransmitters acetylcholine, biogenic amines, GABA, and glutamate. The large array of powerful molecular-genetic tools available in Drosophila enhances the use of this model organism for studying transporter function and regulation.

Arylalkylamine N-acetyltransferase (aaNAT) catalyzes the acetylation of dopamine, 5-hydroxy-tryptamine, tryptamine, octopamine, norepinephrine and other arylalkylamines to form respective N-acetyl-arylalkylamines. Depending on the products formed, aaNATs are involved in a variety of physiological functions. In the yellow fever mosquito, Aedes aegypti, a number of aaNATs and aaNAT-like proteins have been reported. However, the primary function of each individual aaNAT is yet to be identified. In this study we investigated the function of Ae. aegypti aaNAT1 (Ae-aaNAT1) in cuticle pigmentation and development of morphology. Ae-aaNAT1 transcripts were detected at all stages of development with highest expressions after pupation and right before adult eclosion. Ae-aaNAT1 mutant mosquitoes generated using clustered regularly interspaced palindromic repeats (CRISPR) - CRISPR-associated protein 9 had no obvious effect on larval and pupal development. However, the mutant mosquitoes exhibited a roughened exoskeletal surface, darker cuticles, and color pattern changes suggesting that Ae-aaNAT1 plays a role in development of the morphology and pigmentation of Ae. aegypti adult cuticles. The mutant also showed less blood feeding efficiency and lower fecundity when compared with the wild-type. The mutation of Ae-aaNAT1 influenced expression of genes involved in cuticle formation. In summary, Ae-aaNAT1 mainly functions on cuticular pigmentation and also affects blood feeding efficiency and fecundity.

High-resolution electron microscopy (EM) of nervous systems enables the reconstruction of neural circuits at the level of individual synaptic connections. However, for invertebrates, such as Drosophila melanogaster, it has so far been unclear whether the phenotype of neurons or synapses alone is sufficient to predict specific functional properties such as neurotransmitter identity. Here, we show that in Drosophila melanogaster artificial convolutional neural networks can confidently predict the type of neurotransmitter released at a synaptic site from EM images alone. The network successfully discriminates between six types of neurotransmitters (GABA, glutamate, acetylcholine, serotonin, dopamine, and octopamine) with an average accuracy of 87% for individual synapses and 94% for entire neurons, assuming each neuron expresses only one neurotransmitter. This result is surprising as there are often no obvious cues in the EM images that human observers can use to predict neurotransmitter identity. We apply the proposed method to quantify whether, similar to the ventral nervous system (VNS), all hemilineages in the Drosophila melanogaster brain express only one fast acting transmitter within their neurons. To test this principle, we predict the neurotransmitter identity of all identified synapses in 89 hemilineages in the Drosophila melanogaster adult brain. While the majority of our predictions show homogeneity of fast-acting neurotransmitter identity within a single hemilineage, we identify a set of hemilineages that express two fast-acting neurotransmitters with high statistical significance. As a result, our predictions are inconsistent with the hypothesis that all neurons within a hemilineage express the same fast-acting neurotransmitter in the brain of Drosophila melanogaster.

Oviposition is an important reproductive behavior that is triggered by mating in insects, and biogenic amines might be involved in its regulation. The effects of biogenic amines on oviposition have only been studied in a few insect species, and the findings to date have not been conclusive. In addition, there are few studies on the effects of biogenic amines on oviposition of the diamondback moth, Plutella xylostella L. Here, we tested how mating and biogenic amines regulate oviposition of P. xylostella by injecting amines and amine receptor antagonists into virgin and mated females and counting the number of eggs laid afterward. Biogenic amines of octopamine and tyramine could induce virgin adults of P. xylostella to lay eggs, while dopamine and serotonin had no such effect on oviposition. Furthermore, the octopamine antagonists mianserin, epinastine, and phentolamine inhibited oviposition by mated females. The tyramine antagonist yohimbine, dopamine antagonist SCH23390, and serotonin antagonist ketanserin did not block oviposition by mated females, and octopamine and tyramine-inducing oviposition by virgin females could be inhibited by the octopamine antagonists mianserin and epinastine instead of the tyramine antagonist yohimbine. We conclude that octopamine and its receptors are involved in mating-triggered oviposition in P. xylostella, while tyramine acts as a subsidiary. Further, the inducing effect of tyramine on oviposition is achieved via octopamine receptors instead of tyramine receptors. This experiment is helpful to further understand the role of biogenic amines in mating regulation and to provide a new strategy for controlling P. xylostella.

The function of the central nervous system to regulate food intake can be disrupted by sustained metabolic challenges such as high-fat diet (HFD), which may contribute to various metabolic disorders. Previously, we showed that a group of octopaminergic (OA) neurons mediated starvation-induced hyperactivity, an important aspect of food-seeking behavior (Yu et al., 2016). Here we find that HFD specifically enhances this behavior. Mechanistically, HFD increases the excitability of these OA neurons to a hunger hormone named adipokinetic hormone (AKH), via increasing the accumulation of AKH receptor (AKHR) in these neurons. Upon HFD, excess dietary lipids are transported by a lipoprotein LTP to enter these OA+AKHR+ neurons via the cognate receptor LpR1, which in turn suppresses autophagy-dependent degradation of AKHR. Taken together, we uncover a mechanism that links HFD, neuronal autophagy, and starvation-induced hyperactivity, providing insight in the reshaping of neural circuitry under metabolic challenges and the progression of metabolic diseases.

Background The response of organisms to nanoplastic exposure has gradually received the attention. Nevertheless, the role of neurons in response to nanoplastic exposure and the underlying mechanism are still largely unclear. We here examined the role of neuronal JNK MAPK signaling in response to low-dose of polystyrene (100 nm) in Caenorhabditis elegans. Results Exposure to nanopolystyrene in the range of μg/L could increase the expression of genes (jkk-1, mek-1, and jnk-1) encoding JNK MAPK signaling pathway. Meanwhile, RNAi knockdown of any of these genes induced a susceptibility to nanopolystyrene toxicity. In the neurons, SNB-1/synaptobrevin was identified as the downstream target of JNK-1/JNK, suggesting the alteration in neurotransmitter signals in nanopolystyrene-exposed nematodes. In nanopolystyrene-exposed nematodes, JNK-1 modulated TBH-1-mediated octopamine signal and CAT-2-mediated dopamine signal. TBH-1 and CAT-2 further regulated the response to nanopolystyrene by affecting the function of corresponding intestinal octopamine receptors (SER-6 and OCTR-1) and intestinal dopamine receptor (DOP-1). In the intestine, DOP-1 regulated the response to nanopolystyrene by activating the downstream signaling cascade in p38 MAPK signaling pathway. Conclusions Exposure to low-dose of nanopolystyrene could induce the response of neuronal JNK MAPK signaling pathway in nematodes. Our data further highlight the crucial role of neuronal JNK MAPK signaling-activated alteration in octopamine and dopamine signals in regulating the response to nanopolystyrene in organisms.

In both Drosophila and mammals, sleep is regulated by the circadian clock and homeostatic processes, especially after deprivation. Its function is also similar in different organisms, since the lack of sleep affects learning and memory but also development and metabolic processes. The circadian clock, the pacemaker in the brain, is composed of 150 neurons and some of them contact sleep regulating neurons located in mushroom bodies, a center of olfaction memory, and in the central complex. Wake or sleep promoting neurons are regulated by several neurotransmitters, and among them dopamine and octopamine promote wake, serotonin and GABA promote sleep, while glutamine and acetylcholine have dual function. Besides neurons, also glial cells are important in sleep regulation, especially those expressing clock genes, so-called glial oscillators.

While research into the biology of animal behaviour has primarily focused on the central nervous system, cues from peripheral tissues and the environment have been implicated in brain development and function1. There is emerging evidence that bidirectional communication between the gut and the brain affects behaviours including anxiety, cognition, nociception and social interaction1-9. Coordinated locomotor behaviour is critical for the survival and propagation of animals, and is regulated by internal and external sensory inputs10,11. However, little is known about how the gut microbiome influences host locomotion, or the molecular and cellular mechanisms involved. Here we report that germ-free status or antibiotic treatment results in hyperactive locomotor behaviour in the fruit fly Drosophila melanogaster. Increased walking speed and daily activity in the absence of a gut microbiome are rescued by mono-colonization with specific bacteria, including the fly commensal Lactobacillus brevis. The bacterial enzyme xylose isomerase from L. brevis recapitulates the locomotor effects of microbial colonization by modulating sugar metabolism in flies. Notably, thermogenetic activation of octopaminergic neurons or exogenous administration of octopamine, the invertebrate counterpart of noradrenaline, abrogates the effects of xylose isomerase on Drosophila locomotion. These findings reveal a previously unappreciated role for the gut microbiome in modulating locomotion, and identify octopaminergic neurons as mediators of peripheral microbial cues that regulate motor behaviour in animals.

Insects utilize an open circulatory system to transport nutrients, waste, hormones and immune factors throughout the hemocoel. The primary organ that drives hemolymph circulation is the dorsal vessel, which is a muscular tube that traverses the length of the body and is divided into an aorta in the head and thorax, and a heart in the abdomen. The dorsal vessel is myogenic, but its rhythmicity is modulated by neuropeptides and neurotransmitters. This review summarizes how neuropeptides such as crustacean cardioactive peptide (CCAP), FMRFamide-like peptides, proctolin, allatotropin and allatostatin modulate the heart contraction rate and the directionality of heart contractions. Likewise, it discusses how neurotransmitters such as serotonin, octopamine, glutamate and nitric oxide influence the heart rate, and how transcriptomic and proteomic approaches are advancing our understanding of insect circulatory physiology. Finally, this review argues that the immune system may modulate heart rhythmicity, and discusses how the myotropic activity of cardioactive factors extends to the accessory pulsatile organs, such as the auxiliary hearts of the antennae.

Background Tyramine, known as a “trace amine” in mammals, modulates a wide range of behavior in invertebrates; however, the underlying cellular and circuit mechanisms are not well understood. In the nematode Caenorhabditis elegans (C. elegans), tyramine affects key behaviors, including foraging, feeding, and escape responses. The touch-evoked backward escape response is often coupled with a sharp omega turn that allows the animal to navigate away in the opposite direction. Previous studies have showed that a metabotropic tyramine receptor, SER-2, in GABAergic body motor neurons controls deep body bending in omega turns. In this study, we focused on the role of tyramine in GABAergic head motor neurons. Our goal is to understand the mechanism by which tyraminergic signaling alters neural circuit activity to control escape behavior. Results Using calcium imaging in freely moving C. elegans, we found that GABAergic RME motor neurons in the head had high calcium levels during forward locomotion but low calcium levels during spontaneous and evoked backward locomotion. This calcium decrease was also observed during the omega turn. Mutant analyses showed that tbh-1 mutants lacking only octopamine had normal calcium responses, whereas tdc-1 mutants lacking both tyramine and octopamine did not exhibit the calcium decrease in RME. This neuromodulation was mediated by SER-2. Moreover, tyraminergic RIM neuron activity was negatively correlated with RME activity in the directional switch from forward to backward locomotion. These results indicate that tyramine released from RIM inhibits RME via SER-2 signaling. The omega turn is initiated by a sharp head bend when the animal reinitiates forward movement. Interestingly, ser-2 mutants exhibited shallow head bends and often failed to execute deep-angle omega turns. The behavioral defect and the abnormal calcium response in ser-2 mutants could be rescued by SER-2 expression in RME. These results suggest that tyraminergic inhibition of RME is involved in the control of omega turns. Conclusion We demonstrate that endogenous tyramine downregulates calcium levels in GABAergic RME motor neurons in the head via the tyramine receptor SER-2 during backward locomotion and omega turns. Our data suggest that this neuromodulation allows deep head bending during omega turns and plays a role in the escape behavior in C. elegans. Electronic supplementary material The online version of this article (10.1186/s40851-018-0103-1) contains supplementary material, which is available to authorized users.

Feeding behavior is the most fundamental behavior in C. elegans. Our previous results have dissected the central integration circuit for the regulation of feeding, which integrates opposing sensory inputs and regulates feeding behavior in a nonlinear manner. However, the peripheral integration that acts downstream of the central integration circuit to modulate feeding remains largely unknown. Here, we find that a Gαi/o-coupled tyramine receptor, TYRA-2, is involved in peripheral feeding suppression. TYRA-2 suppresses feeding behavior via the AIM interneurons, which receive tyramine/octopamine signals from RIM/RIC neurons in the central integration circuit. Our results reveal previously unidentified roles for the receptor TYRA-2 and the AIM interneurons in feeding regulation, providing a further understanding of how biogenic amines tyramine and octopamine regulate feeding behavior.

Nitric oxide (NO) plays various roles in insect immunity: as a cytotoxic component and as a signalling molecule; and immune-reactive lysozymes (IrLys) provide a first line of humoral immune functions against invading bacteria. Although there is considerable literature on eicosanoid and biogenic monoamine actions on insect immunity, there is no information on the role(s) of these chemicals in inducing NO and IrLys. We addressed this gap by challenging third instarSarcophaga(Liopygia)argyrostoma(Robineau-Desvoidy) with the Gram-positive bacteriumMicrococcus luteus. Here, we report that bacterial challenge induces elevation of NO and IrLys concentrations in haemocytes and in the fat body. The plasma pool content is comparatively low. Eicosanoid biosynthesis inhibitors (EBIs) lead to suppression of both NO and IrLys levels. Control larvae have low constitutive levels of NO and lysozyme concentrations. Octopamine (OA) elicits elevation of NO and IrLys concentrations. A similar effect is obtained by 5-hydroxytryptamine (5-HT) for NO. These data indicate immune-mediating roles of eicosanoids, OA and 5-HT in NO and IrLys activities.

Amitraz is an important product for the control of cattle ticks around the world. In comparison with other products for the control of ticks, it is quite affordable and it has a rapid knock-down effect. It binds with and activates adrenergic neuro-receptors of animals and it inhibits the action of monoamine oxidases (MAO). Resistance to amitraz has been documented in Rhipicephalus microplus, R. decoloratus and R. appendiculatus. Four mechanisms of resistance have been proposed, each of which is supported by evidence but none of which has been definitively confirmed as the cause of resistance in the field. The proposed mechanisms include genetic target site insensitivity in two G protein-coupled receptors, the beta-adrenergic octopamine receptor (BAOR) and the octopamine/tyramine receptor (OCT/Tyr), increased expression or activity of monoamine oxidases and increased expression or activity of the ATP binding cassette transporter.

To find a causal mechanism of learning and memory is a heuristically important topic in neuroscience. In the pond snail Lymnaea stagnalis, the following experimental facts have accrued regarding a classical conditioning procedure known as conditioned taste aversion (CTA): (1) one-day food-deprived Dutch snails have superior CTA memory formation; (2) the one-day food-deprived snails have a low monoamine content (e.g., serotonin, dopamine, octopamine) in their central nervous system (CNS); (3) fed or five-day food-deprived snails have poorer CTA memory and a higher monoamine content; (4) the Dutch snails form better CTA memory than the Canadian TC1 strain; and, (5) the F1 cross snails between the Dutch and Canadian TC1 strains also form poor CTA memory. Here, in one-day food-deprived snails, we measured the monoamine content in the CNSs of the 3 populations. In most instances, the monoamine content of the Dutch strain was lower than in the other two populations. The F1 cross snails had the highest monoamine content. A lower monoamine content is correlated with the better CTA memory formation.

The biogenic amines, tyramine and octopamine, in the octopaminergic synthesis pathway play critical roles in regulating physiological and immunological homeostasis in Litopenaeus vannamei. Tyrosine decarboxylase (TDC) is an enzyme catalyzing the first decarboxylation step in the biosynthesis of tyramine and octopamine. The full-length gene sequence of TDC cloned from the brain of L. vannamei (LvTDC) was predicted to encode a 779-amino acid protein with a pyridoxal-dependent decarboxylase-conserved domain in close phylogenetic relationship with arthropod TDCs. LvTDC gene expression was found to be abundant in nervous thoracic ganglia. RNA interference was used to assess the immune and physiological function of LvTDC. The LvTDC knockdown shrimp revealed significant decreases in the total haemocyte count, hyaline cells, antimicrobial peptides, respiratory bursts, gene expression, respiratory bursts of haemocytes per unit of haemolymph, and phagocytic activity and clearance efficiency toward Vibrio alginolyticus. Furthermore, LvTDC knockdown was accompanied by decreases in octopamine deficiency. In the V. alginolyticus challenge test, the survival rate of LvTDC knockdown shrimp was lower than the shrimp injected with DEPC-water or GAPDH-dsRNA. In conclusion, the cloned LvTDC was responsible for octopaminergic synthesis, which then regulated physiological and immune responses in L. vannamei.

Amitraz is one of the most used acaricides for the control of ticks of domestic animals, however, extensive use of this active ingredient has favored the development of resistant populations of Rhipicephalus microplus worldwide. The possible mechanisms of metabolic and/or target-site alterations mechanisms of amitraz resistance were investigated in a Brazilian field population of R. microplus (Sao Gabriel strain). Bioassays with the synergists piperonylbutoxide, triphenylphosphate and diethyl-maleate were used to evaluate the metabolic mechanisms involved. Target-site insensitivity was investigated by amplification and sequencing of a fragment of the octopamine/tyramine (OCT/TYR) receptor gene. Piperonylbutoxide synergism (synergism ratio = 2.8) indicated the participation of the P450 pathway in the detoxification of amitraz. Previously reported single nucleotide polymorphisms that confer amino acid changes in the OCT/TYR receptor, threonine to proline (T8P) and leucine to serine (L22S), were found in the amitraz-resistant strain but not in the susceptible reference strain. The results suggest that amitraz resistance in the studied strain is multi-factorial and may result from cytochrome P450 detoxification and mutations in octopamine receptors.

(R)-Octopamine (OA), a major invertebrate biogenic amine, plays an important role in a wide variety of physiological processes as a neurohormone, neuromodulator, and neurotransmitter in insects. OA receptors (OARs) are class A G protein-coupled receptors that specifically bind OA to activate downstream signaling cascades by coupling to G proteins and presumably other regulatory proteins. These receptors are broadly classified as α- and β-adrenergic-like OARs (α- and β-ALOARs). OARs are considered important targets of insecticides and acaricides. In the present study, we examined the actions of an array of 13 heterocyclic OAR agonists with the moieties that correspond to the phenyl group and the basic nitrogen atom of OA on α- and β-ALOARs from the silkworm (Bombyx mori) and the signaling pathways activated through these actions. The results indicated that these compounds display structure-dependent receptor subtype selectivity and G protein subtype preference, underscoring the need to determine which subtype and signaling pathway mediates toxicologically relevant effects for the efficient discovery of novel pest control chemicals. The results of insecticidal assays using B. mori larvae suggested that the activation of signal transduction pathways via α-ALOARs might be mainly responsible for the toxicological effects of the heterocycles.

A society of bumble bees is primitively eusocial, with an annual life cycle, and can be used as a physiological model of social bees for comparative studies with highly eusocial hymenopterans. We investigated the dynamics of biogenic amine levels in the brain, meso-metathoracic ganglia, terminal abdominal ganglion, and hemolymph in queens 1 day after mating (1DAM), during diapause (Dp), and during colony founding (CF) in the bumble bee, Bombus ignitus . Dopamine levels in the brain of CF queens were significantly lower than in 1DAM and Dp queens, and the levels in the thoracic ganglia and hemolymph in CF queens were lower than in 1DAM queens, but did not differ from other groups in the abdominal ganglion. Octopamine levels in the brains were higher in Dp queens than in 1DAM queens. Serotonin and tyramine levels did not differ between the groups in different compartments of the central nervous system (CNS) that we examined. The dopamine levels in the brains were significantly positively correlated with those in the thoracic ganglia, abdominal ganglion, and hemolymph, suggesting the regulation of dopamine levels among three different compartments of the CNS. In isolated virgin queens, there were no significant correlations between the brain levels of biogenic amines that we examined and the lengths of the largest terminal oocytes, whereas, in isolated workers, the brain dopamine levels were positively correlated with oocyte lengths. These results suggest that dopamine is associated with ovarian activity in reproductive workers, but not in either virgin or mated queens.

The parasitic wasp, Trichogramma evanescens, is an extremely small insect, with a body length as small as 0.3 mm. To facilitate this miniaturization, their brains may have evolved to contain smaller neural components and/or reduced neural complexity than larger insects. Here, we study whether the size and number of neurons are reduced in the miniaturized brain of T. evanescens, focusing on neurons that express serotonin (5HT), octopamine (OA) and dopamine (DA). We provide the first description of the distribution, projection patterns and number of 5HT-, OA- and DA-like immunoreactive cell bodies in T. evanescens and compare our observations with descriptions of much larger insects. The brains of T. evanescens contain comparable numbers of monoaminergic neurons to those of larger insects. Serotonergic neurons appear to be especially conserved; most of the clusters contain a similar number of neurons to those described in Apis mellifera and Drosophila melanogaster. This maintained complexity may have been facilitated by miniaturization of neuron size. However, many dopaminergic and some octopaminergic neuron clusters in T. evanescens contain fewer neurons than in larger insects. Modification of the complexity of these monoaminergic systems may have been necessary to maintain neuron functionality during brain miniaturization in T. evanescens. Our results reveal some of the evolutionary adaptations that may enable behavioural and cognitive complexity with respect to miniaturized brains. Electronic supplementary material The online version of this article (doi:10.1007/s00441-017-2642-8) contains supplementary material, which is available to authorized users.

The biogenic monoamines norepinephrine and epinephrine regulate important physiological functions in vertebrates. Insects such as honeybees do not synthesize these neuroactive substances. Instead, they employ octopamine and tyramine for comparable physiological functions. These biogenic amines activate specific guanine nucleotide-binding (G) protein-coupled receptors (GPCRs). Based on pharmacological data obtained on heterologously expressed receptors, α- and β-adrenergic-like octopamine receptors are better activated by octopamine than by tyramine. Conversely, GPCRs forming the type 1 tyramine receptor clade (synonymous to octopamine/tyramine receptors) are better activated by tyramine than by octopamine. More recently, receptors were characterized which are almost exclusively activated by tyramine, thus forming an independent type 2 tyramine receptor clade. Functionally, type 1 tyramine receptors inhibit adenylyl cyclase activity, leading to a decrease in intracellular cAMP concentration ([cAMP]i). Type 2 tyramine receptors can mediate Ca2+ signals or both Ca2+ signals and effects on [cAMP]i. We here provide evidence that the honeybee tyramine receptor 2 (AmTAR2), when heterologously expressed in flpTM cells, exclusively causes an increase in [cAMP]i. The receptor displays a pronounced preference for tyramine over octopamine. Its activity can be blocked by a series of established antagonists, of which mianserin and yohimbine are most efficient. The functional characterization of two tyramine receptors from the honeybee, AmTAR1 (previously named AmTYR1) and AmTAR2, which respond to tyramine by changing cAMP levels in opposite direction, is an important step towards understanding the actions of tyramine in honeybee behavior and physiology, particularly in comparison to the effects of octopamine.

The biogenic amine octopamine (OA) modulates invertebrate behavior by changing neuronal responses from sensory inputs to motor outputs. However, the OA modulation of visual sensitivity and its possible coupling to diurnal cycles remains unexplored. Here we studied the diurnal variations in the OA levels in the hemolymph of the crayfish Procambarus clarkii , its release from the structures in the eyestalk and its modulation of the retinal light sensitivity. The hemolymph concentration of OA and its amino acid precursor tyrosine was measured by high-resolution liquid chromatography; OA varied along the 24-h cycle. The peak value appeared about 2 h before the light offset which preceded the peak locomotor activity. OA was found in every structure of the eyestalk but displayed higher levels in the retina– lamina ganglionaris . Moreover, OA was released from isolated eyestalks at a rate of 92 nmol/eyestalk/min and a calcium-dependent release was evoked by incubation in a high potassium solution. OA injected into dark-adapted crayfish or applied to the isolated retina at concentrations of 1, 10 and 100 μM produced a proportionally increasing reduction in the amplitude of the photoreceptor light responses. These OA concentrations did not affect the position of the visual accessory pigments. Our results suggest that OA release in the crayfish eyestalk is coupled to the 24-h cycle to regulate the diurnal reduction of the photoreceptor sensitivity and to favor the expression of exploratory locomotion during the dark phase of the circadian cycle.

Bugula neritina is a sessile marine bryozoan with a pelagic larval stage. Larvae frequently settle on boat hulls, facilitating the introduction of B. neritina to bays and estuaries worldwide. Adrenergic agonists, such as norepinephrine, inhibit larval settlement in a variety of marine invertebrate species, including B. neritina. Light also inhibits larval settlement of B. neritina, yet the underlying mechanisms by which light and adrenergic compounds exert their effects on larvae are largely unknown. Octopamine is considered the invertebrate analog of norepinephrine, and may be one endogenous compound involved in larval settlement pathways. In this study, we investigated the effects of norepinephrine and the adrenergic antagonist phentolamine on larval settlement, and found that norepinephrine inhibited larval attachment and increased larval swimming behavior, while phentolamine increased larval attachment and decreased larval swimming behavior. We used fluorescent labeling and immunocytochemistry to localize sensory system components, and found that larvae possess adrenergic-like receptors and octopamine-like immunoreactivity. We also exposed larvae to phentolamine in both dark and light conditions, and found that light inhibited larval attachment, but phentolamine blocked those inhibitory effects. Based on these results, we put forth a putative mechanistic explanation for the effects of both light and adrenergic compounds on B. neritina larval settlement behavior. This study sheds light on previously unknown pathways underlying larval settlement behavior of bryozoans, and may aid in the development of effective, non-toxic biofouling control strategies.

In decapods, dopamine, octopamine, serotonin, and histamine function as locally released/hormonally delivered modulators of physiology/behavior. Although the functional roles played by amines in decapods have been examined extensively, little is known about the identity/diversity of their amine receptors. Recently, a Homarus americanus mixed nervous system transcriptome was used to identify putative neuronal amine receptors in this species. While many receptors were identified, some were fragmentary, and no evidence of splice/other variants was found. Here, the previously predicted proteins were used to search brain- and eyestalk ganglia-specific transcriptomes to assess/compare amine receptor complements in these portions of the lobster nervous system. All previously identified receptors were reidentified from the brain and/or eyestalk ganglia transcriptomes, i.e., dopamine alpha-1, beta-1, and alpha-2 (Homam-DAα2R) receptors, octopamine alpha (Homam-OctαR), beta-1, beta-2, beta-3, beta-4, and octopamine–tyramine (Homam-OTR-I) receptors, serotonin type-1A, type-1B (Homam-5HTR1B), type-2B, and type-7 receptors; and histamine type-1 (Homam-HA1R), type-2, type-3, and type-4 receptors. For many previously partial proteins, full-length receptors were deduced from brain and/or eyestalk ganglia transcripts, i.e., Homam-DAα2R, Homam-OctαR, Homam-OTR-I, and Homam-5HTR1B. In addition, novel dopamine/ecdysteroid, octopamine alpha-2, and OTR receptors were discovered, the latter, Homam-OTR-II, being a putative paralog of Homam-OTR-I. Finally, evidence for splice/other variants was found for many receptors, including evidence for some being assembly-specific, e.g., a brain-specific Homam-OTR-I variant and an eyestalk ganglia-specific Homam-HA1R variant. To increase confidence in the transcriptome-derived sequences, a subset of receptors was cloned using RT-PCR. These data complement/augment those reported previously, providing a more complete picture of amine receptor complement/diversity in the lobster nervous system.

Animals coexist in commensal, pathogenic or mutualistic relationships with complex communities of diverse organisms including microbes1. Some bacteria produce bioactive neurotransmitters which have been proposed to modulate host nervous system activity and behaviors2. However, the mechanistic basis of this microbiota-brain modulation and its physiological relevance is largely unknown. Here we show that inC. elegans, the neuromodulator tyramine (TA) produced by gut-colonizing commensalProvidenciabacteria can bypass the requirement for host TA biosynthesis to manipulate a host sensory decision. Bacterially-produced TA is likely converted to octopamine (OA) by the host tyramine beta-hydroxylase enzyme. OA, in turn, targets the OCTR-1 receptor on the ASH/ASI sensory neurons to modulate an aversive olfactory response. We identify genes required for TA biosynthesis inProvidencia, and show that these genes are necessary for modulation of host behavior. We further find thatC. eleganscolonized byProvidenciapreferentially select these bacteria in food choice assays, and that this selection bias requires bacterially-produced TA. Our results demonstrate that a neurotransmitter produced by gut microbiota mimics the functions of the cognate host molecule to override host control of a sensory decision, thereby promoting fitness of both host and microbe.

Zinc-α2-glycoprotein (ZAG) is a major plasma protein whose levels increase in chronic energy-demanding diseases and thus serves as an important clinical biomarker in the diagnosis and prognosis of the development of cachexia. Current knowledge suggests that ZAG mediates progressive weight loss through β-adrenergic signalling in adipocytes, resulting in the activation of lipolysis and fat mobilization. Here, through cross-linking experiments, amine oxidase copper-containing 3 (AOC3) is identified as a novel ZAG binding partner. AOC3—also known as vascular adhesion protein 1 (VAP-1) and semicarbazide sensitive amine oxidase (SSAO)—deaminates primary amines, thereby generating the corresponding aldehyde, H 2 O 2 and NH 3 . It is an ectoenzyme largely expressed by adipocytes and induced in endothelial cells during inflammation. Extravasation of immune cells depends on amine oxidase activity and AOC3-derived H 2 O 2 has an insulinogenic effect. The observations described here suggest that ZAG acts as an allosteric inhibitor of AOC3 and interferes with the associated pro-inflammatory and anti-lipolytic functions. Thus, inhibition of the deamination of lipolytic hormone octopamine by AOC3 represents a novel mechanism by which ZAG might stimulate lipolysis. Furthermore, experiments involving overexpression of recombinant ZAG reveal that its glycosylation is co-regulated by oxygen availability and that the pattern of glycosylation affects its inhibitory potential. The newly identified protein interaction between AOC3 and ZAG highlights a previously unknown functional relationship, which may be relevant to inflammation, energy metabolism and the development of cachexia.

International audience; The combined use of 3D-fluorescence spectroscopy and independent component analysis using a differential fingerprinting approach has been applied with success to detect physiological effects of dimethoate in honeybees. Biochemical determinations combined with the identification of fluorescence zones that may correspond to proteins, NADH or neurotransmitters/neurohormones (octopamine, dopamine and serotonin) related to the physiological stress caused by the pesticide enabled phenomenological modeling of the physiological response in the honeybee using a simple and rapid method. The signals associated with the fluorophores involved in the response to stress were extracted from the fluorescence spectra using an unsupervised algorithm such as independent component analysis. The signals of different neurotransmitters were isolated on separated factorial components, thus facilitating their biochemical interpretation.

Temperature has profound effects on the neural function and behaviour of insects. When exposed to low temperature, chill-susceptible insects enter chill coma, a reversible state of neuromuscular paralysis. Despite the popularity of studying the effects of low temperature on insects, we know little about the physiological mechanisms controlling the entry to, and recovery from, chill coma. Spreading depolarization (SD) is a phenomenon that causes a neural shutdown in the central nervous system (CNS) and it is associated with a loss of K+ homeostasis in the CNS. Here, we investigated the effects of rapid cold hardening (RCH) on chill tolerance of the migratory locust. With an implanted thermocouple in the thorax, we determined the temperature associated with a loss of responsiveness (i.e. the critical thermal minimum – CTmin) in intact male adult locusts. In parallel experiments, we recorded field potential (FP) in the metathoracic ganglion (MTG) of semi-intact preparations to determine the temperature that would induce neural shutdown. We found that SD in the CNS causes a loss of coordinated movement immediately prior to chill coma and RCH reduces the temperature that evokes neural shutdown. Additionally, we investigated a role for octopamine (OA) in the locust chill tolerance and found that OA reduces the CTmin and mimics the effects of prior stress (anoxia) in locust.

High population density alters insect prophylactic immunity, with density-dependent prophylaxis (DDP) being reported in many polyphonic insects. However, the molecular mechanism for DDP remains unclear. In current study, the role of tyramine &beta, hydroxylase (T&beta, h) in the immune response of M. separata larvae that were subject to different rearing densities conditions was investigated. The tyramine &beta, hydroxylase activity of larvae from high density treatments (10 and 30 larvae per jar) was significantly higher than that of the larvae from low density treatments (one, two, and five larvae/jar). A tyramine &beta, hydroxylase (designated MsT&beta, h) containing a 1779 bp open reading frame was identified. Multiple sequence alignment and phylogenetic analysis indicated that MsT&beta, h was orthologous to the T&beta, h that was found in other lepidopterans. Elevated MsT&beta, h expression was observed in larvae under high density (10 larvae per jar). Silencing MsT&beta, h expression by the injection of dsRNA in larvae from the high density treatment produced a 25.1% reduction in octopamine levels, while at the same time, there was a significant decrease in phenoloxidase (PO) and lysozyme activity, total haemocyte counts, and survival against Beauveria infection 56.6%, 88.5%, 82.0%, and 55.8%, respectively, when compared to control larvae. Our findings provide the first insights into how MsT&beta, h mediates the octopamine level, which in turn modulates the immune response of larvae under different population densities.

In decapod crustaceans, the amines dopamine, octopamine, serotonin, and histamine are known to serve as locally released and/or circulating neuromodulators. While many studies have focused on determining the modulatory actions of amines on decapod nervous systems, comparatively little is known about the identity of the receptors through which they exert their actions. Here, a crayfish, Procambarus clarkii, tissue-specific transcriptome was used to identify putative amine receptors in the eyestalk, a structure composed largely of the eyestalk ganglia, including the neuroendocrine X-organ-sinus gland system, and retina. Transcripts encoding 17 distinct putative amine receptors, three dopamine (one dopamine 1-like, one dopamine 2-like, and one dopamine/ecdysteroid-like), five octopamine (one alpha-like, three beta-like, and one octopamine/tyramine-like), three serotonin (two type-1-like and one type-7-like), and six histamine (five histamine-gated chloride channel A-like and one histamine-gated chloride channel B-like) were identified in the assembly. Comparison of the nucleotide sequence of the transcript encoding one predicted type-1-like serotonin receptor with that cloned previously from the P. clarkii nervous system shows the two sequences to be essentially identical, providing increased support for the validity of the transcripts used to deduce the proteins reported here. Reciprocal BLAST and structural/functional domain analyses support the protein family annotations ascribed to the putative P. clarkii receptors. These data represent the first large-scale description of amine receptors from P. clarkii, and as such provide a new resource for initiating gene-based studies of aminergic control of physiology/behavior at the level of receptors in this species.