Octopamine Research Articles

Octopamine and Tyramine Contribute Separately to the Counter-Regulatory Response to Sugar Deficit in Drosophila.

All animals constantly negotiate external with internal demands before and during action selection. Energy homeostasis is a major internal factor biasing action selection. For instance, in addition to physiologically regulating carbohydrate mobilization, starvation-induced sugar shortage also biases action selection toward food-seeking and food consumption behaviors (the counter-regulatory response). Biogenic amines are often involved when such widespread behavioral biases need to be orchestrated. In mammals, norepinephrine (noradrenalin) is involved in the counterregulatory response to starvation-induced drops in glucose levels. The invertebrate homolog of noradrenalin, octopamine (OA) and its precursor tyramine (TA) are neuromodulators operating in many different neuronal and physiological processes. Tyrosine-ß-hydroxylase (tßh) mutants are unable to convert TA into OA. We hypothesized that tßh mutant flies may be aberrant in some or all of the counter-regulatory responses to starvation and that techniques restoring gene function or amine signaling may elucidate potential mechanisms and sites of action. Corroborating our hypothesis, starved mutants show a reduced sugar response and their hemolymph sugar concentration is elevated compared to control flies. When starved, they survive longer. Temporally controlled rescue experiments revealed an action of the OA/TA-system during the sugar response, while spatially controlled rescue experiments suggest actions also outside of the nervous system. Additionally, the analysis of two OA- and four TA-receptor mutants suggests an involvement of both receptor types in the animals' physiological and neuronal response to starvation. These results complement the investigations in Apis mellifera described in our companion paper (Buckemüller et al., 2017).

Mediation of inducible nitric oxide and immune-reactive lysozymes biosynthesis by eicosanoid and biogenic amines in flesh flies

AbstractNitric 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.

Octopamine enhances the immune responses of freshwater giant prawn, Macrobrachium rosenbergii, via octopamine receptors

Octopamine (OA) is known to play an important role in regulating insect immune responses. In Macrobrachium rosenbergii (18.0 ± 1.7 g), OA at 25.0 and 250.0 pmol/prawn significantly increased THC, semigranular cells (SGCs) and PO activity in hemocytes per 50 μL hemolymph, hyaline cells, granular cells (GCs) and RBs in hemocytes per 10 μL hemolymph, and RBs per hemocyte, and however, significantly decreased PO activity per granulocyte (GC + SGC), which returned to control levels after 4 h of injection. The significantly increased phagocytic activity and clearance efficiency of prawn received OA for 8 h returned to control levels after 16 h of injection. In addition, the significantly increased glucose and decreased lactate were observed within 1 h of OA injection. In the susceptibility test, prawn received OA at 25.0 or 250.0 pmol/prawn for 2 h then challenged with Lactococcus garvieae at 105 colony-forming units/prawn significantly increased the resistance of prawns by 23.3% and 30.0%, respectively, compared to the saline-challenged control after 144 h of challenge. In addition, the changes on immunocompetence induced by OA were observed to be blocked by adrenoceptors antagonists. These results suggest that OA administration at 250.0 pmol/prawn or less causes the mediate a transient up-regulation in immune and physiologic responses to promote the resistance of M. rosenbergii to L. garvieae, which are thought to be mediated by α- and β-adrenergic-like octopamine receptors.

Differential effects of predator cues versus activation of fight-or-flight behaviour on reproduction in the cricket Gryllus texensis

How prey animals determine predation risk remains uncertain. We propose that one signal of high predation risk is repeated activation of fight-or-flight behaviour. We activated escape runs in the cricket Gryllus texensis by blowing air on the cerci. Escape runs were induced for 5 min, three times per day, three times per week for 4 weeks. Repeated fight-or-flight behaviour led to a loss in mass and decreased life span, suggesting a decline in somatic maintenance. However, there was an increase in egg laying, which we interpret as terminal reproductive investment. Stress responses remained robust. Octopamine (OA), a stress neurohormone in insects, increased in concentration in the haemolymph after running, and the magnitude of the increase was the same even after repeated activation (i.e. there was no habituation of the response). There was also no increase in basal OA haemolymph levels. In a second experiment, crickets were exposed to a mantid (predator, Tenodera sinensis), a walking stick (nonpredator, Carausius morosus), or an empty container. None of the crickets exhibited fight-or-flight behaviour. However, mantid-exposed crickets decreased egg laying. There was no decrease in life span or mass. There was no change in basal levels of OA, or in the magnitude of the OA increase after running. These results are consistent with the hypothesis that repeated fight-or-flight behaviour induces reproductive responses that would be adaptive for a shortened life span. These responses differ from those produced by predator cues alone. Even short-lived animals, such as crickets, appear to alter reproduction depending on the relative predation risk and their residual reproductive potential.

Origins of Aminergic Regulation of Behavior in Complex Insect Social Systems.

Neuromodulators are conserved across insect taxa, but how biogenic amines and their receptors in ancestral solitary forms have been co-opted to control behaviors in derived socially complex species is largely unknown. Here we explore patterns associated with the functions of octopamine (OA), serotonin (5-HT) and dopamine (DA) in solitary ancestral insects and their derived functions in eusocial ants, bees, wasps and termites. Synthesizing current findings that reveal potential ancestral roles of monoamines in insects, we identify physiological processes and conserved behaviors under aminergic control, consider how biogenic amines may have evolved to modulate complex social behavior, and present focal research areas that warrant further study.

Tyramine Actions on Drosophila Flight Behavior Are Affected by a Glial Dehydrogenase/Reductase.

The biogenic amines octopamine (OA) and tyramine (TA) modulate insect motor behavior in an antagonistic manner. OA generally enhances locomotor behaviors such as Drosophila larval crawling and flight, whereas TA decreases locomotor activity. However, the mechanisms and cellular targets of TA modulation of locomotor activity are incompletely understood. This study combines immunocytochemistry, genetics and flight behavioral assays in the Drosophila model system to test the role of a candidate enzyme for TA catabolism, named Nazgul (Naz), in flight motor behavioral control. We hypothesize that the dehydrogenase/reductase Naz represents a critical step in TA catabolism. Immunocytochemistry reveals that Naz is localized to a subset of Repo positive glial cells with cell bodies along the motor neuropil borders and numerous positive Naz arborizations extending into the synaptic flight motor neuropil. RNAi knock down of Naz in Repo positive glial cells reduces Naz protein level below detection level by Western blotting. The resulting consequence is a reduction in flight durations, thus mimicking known motor behavioral phenotypes as resulting from increased TA levels. In accord with the interpretation that reduced TA degradation by Naz results in increased TA levels in the flight motor neuropil, the motor behavioral phenotype can be rescued by blocking TA receptors. Our findings indicate that TA modulates flight motor behavior by acting on central circuitry and that TA is normally taken up from the central motor neuropil by Repo-positive glial cells, desaminated and further degraded by Naz.

Octopamine Underlies the Counter-Regulatory Response to a Glucose Deficit in Honeybees (Apis mellifera).

An animal’s internal state is a critical parameter required for adaptation to a given environment. An important aspect of an animal’s internal state is the energy state that is adjusted to the needs of an animal by energy homeostasis. Glucose is one essential source of energy, especially for the brain. A shortage of glucose therefore triggers a complex response to restore the animal’s glucose supply. This counter-regulatory response to a glucose deficit includes metabolic responses like the mobilization of glucose from internal glucose stores and behavioral responses like increased foraging and a rapid intake of food. In mammals, the catecholamines adrenalin and noradrenalin take part in mediating these counter-regulatory responses to a glucose deficit. One candidate molecule that might play a role in these processes in insects is octopamine (OA). It is an invertebrate biogenic amine and has been suggested to derive from an ancestral pathway shared with adrenalin and noradrenalin. Thus, it could be hypothesized that OA plays a role in the insect’s counter-regulatory response to a glucose deficit. Here we tested this hypothesis in the honeybee (Apis mellifera), an insect that, as an adult, mainly feeds on carbohydrates and uses these as its main source of energy. We investigated alterations of the hemolymph glucose concentration, survival, and feeding behavior after starvation and examined the impact of OA on these processes in pharmacological experiments. We demonstrate an involvement of OA in these three processes in honeybees and conclude there is an involvement of OA in regulating a bee’s metabolic, physiological, and behavioral response following a phase of prolonged glucose deficit. Thus, OA in honeybees acts similarly to adrenalin and noradrenalin in mammals in regulating an animal’s counter-regulatory response.

The Role of Monoaminergic Neurotransmission for Metabolic Control in the Fruit Fly Drosophila Melanogaster.

Hormones control various metabolic traits comprising fat deposition or starvation resistance. Here we show that two invertebrate neurohormones, octopamine (OA) and tyramine (TA) as well as their associated receptors, had a major impact on these metabolic traits. Animals devoid of the monoamine OA develop a severe obesity phenotype. Using flies defective in the expression of receptors for OA and TA, we aimed to decipher the contributions of single receptors for these metabolic phenotypes. Whereas those animals impaired in octß1r, octß2r and tar1 share the obesity phenotype of OA-deficient (tβh-deficient) animals, the octß1r, octß2r deficient flies showed reduced insulin release, which is opposed to the situation found in tβh-deficient animals. On the other hand, OAMB deficient flies were leaner than controls, implying that the regulation of this phenotype is more complex than anticipated. Other phenotypes seen in tβh-deficient animals, such as the reduced ability to perform complex movements tasks can mainly be attributed to the octß2r. Tissue-specific RNAi experiments revealed a very complex interorgan communication leading to the different metabolic phenotypes observed in OA or OA and TA-deficient flies.

A Circuit Node that Integrates Convergent Input from Neuromodulatory and Social Behavior-Promoting Neurons to Control Aggression in Drosophila

Diffuse neuromodulatory systems such as norepinephrine (NE) control brain-wide states such as arousal, but whether they control complex social behaviors more specifically is not clear. Octopamine (OA), the insect homolog of NE, is known to promote both arousal and aggression. We have performed asystematic, unbiased screen to identify OA receptor-expressing neurons (OARNs) that control aggression in Drosophila. Our results uncover a tiny population of male-specific aSP2 neurons that mediate a specific influence of OA on aggression, independent of any effect on arousal. Unexpectedly, these neurons receive convergent input from OA neurons and P1 neurons, a population of FruM+ neurons that promotes male courtship behavior. Behavioral epistasis experiments suggest that aSP2 neurons may constitute an integration node at which OAergic neuromodulation can bias the output of P1 neurons to favor aggression over inter-male courtship. These results have potential implications for thinking aboutthe role of related neuromodulatory systems in mammals.

Methyl-CpG binding domain proteins inhibit interspecies courtship and promote aggression in Drosophila

Reproductive isolation and speciation are driven by the convergence of environmental and genetic variation. The integration of these variation sources is thought to occur through epigenetic marks including DNA methylation. Proteins containing a methyl-CpG-binding domain (MBD) bind methylated DNA and interpret epigenetic marks, providing a dynamic yet evolutionarily adapted cellular output. Here, we report the Drosophila MBD-containing proteins, dMBD-R2 and dMBD2/3, contribute to reproductive isolation and survival behavioral strategies. Drosophila melanogaster males with a reduction in dMBD-R2 specifically in octopamine (OA) neurons exhibit courtship toward divergent interspecies D. virilis and D. yakuba females and a decrease in conspecific mating success. Conspecific male-male courtship is increased between dMBD-R2-deficient males while aggression is reduced. These changes in adaptive behavior are separable as males with a hypermethylated OA neuronal genome exhibited a decrease in aggression without altering male-male courtship. These results suggest Drosophila MBD-containing proteins are required within the OA neural circuitry to inhibit interspecies and conspecific male-male courtship and indicate that the genetically hard-wired neural mechanisms enforcing behavioral reproductive isolation include the interpretation of the epigenome.

Biogenic Amines in Insect Antennae.

Insect antenna is a multisensory organ, each modality of which can be modulated by biogenic amines. Octopamine (OA) and its metabolic precursor tyramine (TA) affect activity of antennal olfactory receptor neurons. There is some evidence that dopamine (DA) modulates gustatory neurons. Serotonin can serve as a neurotransmitter in some afferent mechanosensory neurons and both as a neurotransmitter and neurohormone in efferent fibers targeted at the antennal vessel and mechanosensory organs. As a neurohormone, serotonin affects the generation of the transepithelial potential by sensillar accessory cells. Other possible targets of biogenic amines in insect antennae are hygro- and thermosensory neurons and epithelial cells. We suggest that the insect antenna is partially autonomous in the sense that biologically active substances entering its hemolymph may exert their effects and be cleared from this compartment without affecting other body parts.

Maximized complexity in miniaturized brains: morphology and distribution of octopaminergic, dopaminergic and serotonergic neurons in the parasitic wasp, Trichogramma evanescens

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.

Modulation of Low-Voltage-Activated Inward Current Permeable to Sodium and Calcium by DARPP-32 Drives Spontaneous Firing of Insect Octopaminergic Neurosecretory Cells.

Identification of the different intracellular pathways that control phosphorylation/dephosphorylation process of ionic channels represents an exciting alternative approach for studying the ionic mechanisms underlying neuronal pacemaker activity. In the central nervous system of the cockroach Periplaneta americana, octopaminergic neurons, called dorsal unpaired median (DUM; DUM neurons), generate spontaneous repetitive action potentials. Short-term cultured adult DUM neurons isolated from the terminal abdominal ganglion (TAG) of the nerve cord were used to study the regulation of a tetrodotoxin-sensitive low-voltage-activated (LVA) channel permeable to sodium and calcium (Na/Ca), under whole cell voltage- and current-clamp conditions. A bell-shaped curve illustrating the regulation of the amplitude of the maintained current vs. [ATP]i was observed. This suggested the existence of phosphorylation mechanisms. The protein kinase A (PKA) inhibitor, H89 and elevating [cyclic adenosine 3′, 5′ monophosphate, cAMP]i, increased and decreased the current amplitude, respectively. This indicated a regulation of the current via a cAMP/PKA cascade. Furthermore, intracellular application of PP2B inhibitors, cyclosporine A, FK506 and PP1/2A inhibitor, okadaic acid decreased the current amplitude. From these results and because octopamine (OA) regulates DUM neuron electrical activity via an elevation of [cAMP]i, we wanted to know if, like in vertebrate dopaminergic neurons, OA receptor (OAR) stimulation could indirectly affect the current via PKA-mediated phosphorylation of Dopamine- and cAMP-regulated Phosphoprotein-32 (DARPP-32) known to inhibit PP1/2A. Experiments were performed using intracellular application of phospho-DARPP-32 and non-phospho-DARPP-32. Phospho-DARPP-32 strongly reduced the current amplitude whereas non-phospho-DARPP-32 did not affect the current. All together, these results confirm that DARPP-32-mediated inhibition of PP1/2A regulates the maintained sodium/calcium current, which contributes to the development of the pre-depolarizing phase of the DUM neuron pacemaker activity.

Biochemical mechanisms of acaricidal activity of 2,4-di-tert-butylphenol and ethyl oleate against the carmine spider mite Tetranychus cinnabarinus

Tetranychus cinnabarinus (Boisduval) is one of the most economically important and highly polyphagous herbivorous pests in fields and greenhouses worldwide. We previously reported that 2,4-di-tert-butylphenol (DTBP) and ethyl oleate (EO) showed significantly acaricidal, repellent and oviposition deterrent properties against T. cinnabarinus via an unknown mechanism. In this study, the acaricidal activities of DTBP and EO and their biochemical mechanisms in controlling T. cinnabarinus were investigated at different time points by assessing the associated changes in toxic symptoms, potential target-related enzyme activities and seven neurotransmitters belonging to the biogenic amines (BAs). The results showed that the median lethal times (LT50) for DTBP and EO were 8 and 15 h after treatment, respectively. Using dynamic symptomatology observations, typical neurotoxic symptoms including excitation, convulsion and paralysis were observed in the mites treated with DTBP and EO. Furthermore, the two compounds exerted significant inhibitory activity on monoamine oxidase (MAO) in adult T. cinnabarinus females in vitro and in vivo and had little effect on acetylcholinesterase (AChE) activity. The content levels of the seven BAs analyzed by UPLC-3QMS were higher in the mites treated with DTBP and EO than in the controls, except for phenethylamine (PEA) (for DTBP and EO) and octopamine (OA) (for EO). These results demonstrate that both DTBP and EO exert effects on T. cinnabarinus that are possibly consequences of their preventive effects on the deamination of BAs in the nervous system, most likely through inhibitory effects on MAO or MAO-like enzymes and/or interactions with certain special biogenic amine G protein-coupled receptors.

Identification of multiple functional receptors for tyramine on an insect secretory epithelium

The biogenic amine tyramine (TA) regulates many aspects of invertebrate physiology and development. Although three TA receptor subtypes have been identified (TAR1-3), specific receptors have not been linked to physiological responses in native tissue. In the Malpighian (renal) tubule of Drosophila melanogaster, TA activates a transepithelial chloride conductance, resulting in diuresis and depolarization of the transepithelial potential. In the current work, mutation or RNAi-mediated knockdown in the stellate cells of the tubule of TAR2 (tyrR, CG7431) resulted in a dramatic reduction, but not elimination, of the TA-mediated depolarization. Mutation or knockdown of TAR3 (tyrRII, CG16766) had no effect. However, deletion of both genes, or knockdown of TAR3 on a TAR2 mutant background, eliminated the TA responses. Thus while TAR2 is responsible for the majority of the TA sensitivity of the tubule, TAR3 also contributes to the response. Knockdown or mutation of TAR2 also eliminated the response of tubules to the related amine octopamine (OA), indicating that OA can activate TAR2. This finding contrasts to reports that heterologously expressed TAR2 is highly selective for TA over OA. This is the first report of TA receptor function in a native tissue and indicates unexpected complexity in the physiology of the Malpighian tubule.

Cannabinoids Activate Monoaminergic Signaling to Modulate Key C. elegans Behaviors.

Cannabis sativa, or marijuana, a popular recreational drug, alters sensory perception and exerts a range of potential medicinal benefits. The present study demonstrates that the endogenous cannabinoid receptor agonists 2-arachidonoylglycerol (2-AG) and anandamide (AEA) activate a canonical cannabinoid receptor in Caenorhabditis elegans and also modulate monoaminergic signaling at multiple levels. 2-AG or AEA inhibit nociception and feeding through a pathway requiring the cannabinoid-like receptor NPR-19. 2-AG or AEA activate NPR-19 directly and cannabinoid-dependent inhibition can be rescued in npr-19-null animals by the expression of a human cannabinoid receptor, CB1, highlighting the orthology of the receptors. Cannabinoids also modulate nociception and locomotion through an NPR-19-independent pathway requiring an α2A-adrenergic-like octopamine (OA) receptor, OCTR-1, and a 5-HT1A-like serotonin (5-HT) receptor, SER-4, that involves a complex interaction among cannabinoid, octopaminergic, and serotonergic signaling. 2-AG activates OCTR-1 directly. In contrast, 2-AG does not activate SER-4 directly, but appears to enhance SER-4-dependent serotonergic signaling by increasing endogenous 5-HT. This study defines a conserved cannabinoid signaling system in C. elegans, demonstrates the cannabinoid-dependent activation of monoaminergic signaling, and highlights the advantages of studying cannabinoid signaling in a genetically tractable whole-animal model.SIGNIFICANCE STATEMENTCannabis sativa, or marijuana, causes euphoria and exerts a wide range of medicinal benefits. For years, cannabinoids have been studied at the cellular level using tissue explants with conflicting results. To better understand cannabinoid signaling, we have used the Caenorhabditis elegans model to examine the effects of cannabinoids on behavior. The present study demonstrates that mammalian cannabinoid receptor ligands activate a conserved cannabinoid signaling system in C. elegans and also modulate monoaminergic signaling, potentially affecting an array of disorders, including anxiety and depression. This study highlights the potential role of cannabinoids in modulating monoaminergic signaling and the advantages of studying cannabinoid signaling in a genetically tractable, whole-animal model.

Octopamine enhances oxidative stress resistance through the fasting-responsive transcription factor DAF-16/FOXO inC.elegans.

Dietary restriction regimens lead to enhanced stress resistance and extended life span in many species through the regulation of fasting and/or diet-responsive mechanisms. The fasting stimulus is perceived by sensory neurons and causes behavioral and metabolic adaptations. Octopamine (OA), one of the Caenorhabditis elegans neurotransmitters, is involved in behavioral adaptations, and its levels are increased under fasting conditions. However, it remains largely unknown how OA contributes to the fasting responses. In this study, we found that OA administration enhanced organismal resistance to oxidative stress. This enhanced resistance was suppressed by a mutation of the OA receptors, SER-3 and SER-6. Moreover, we found that OA administration promoted the nuclear translocation of DAF-16, the key transcription factor in fasting responses, and that the OA-induced enhancement of stress resistance required DAF-16. Altogether, our results suggest that OA signaling, which is triggered by the absence of food, shifts the organismal state to a more protective one to prepare for environmental stresses.

Molecular Characterization and Functional Analysis of a Putative Octopamine/Tyramine Receptor during the Developmental Stages of the Pacific Oyster, Crassostrea gigas.

Octopamine (OA) and its precursor, tyramine (TA), participate in invertebrate development such as growth, maturation, and reproduction by activating their corresponding G protein-coupled receptors (GPCRs). Although OA was first discovered in mollusks (octopus), subsequent studies on OA, TA and related receptors have primarily been conducted in Ecdysozoa, especially in insects. Accordingly, only limited reports on OA/TA receptors in mollusks are available and their physiological roles remain unclear. Here, a full-length cDNA encoding a putative 524 amino acid OA/TA receptor (CgGPR1) was isolated from the Pacific oyster Crassostrea gigas. CgGPR1 was most closely related to the Lymnaea stagnalis OA receptor OAR2 in sequence. Phylogenetic analysis showed that CgGPR1 belongs to a poorly studied subfamily of invertebrate OA/TA receptors. The spatio-temporal expression of CgGPR1 in C. gigas larvae was examined by quantitative real-time PCR and Western blot analysis. CgGPR1 was expressed during all developmental stages of C. gigas with higher levels at mid-developmental stages, indicating its potential role in embryogenesis and tissue differentiation. Immunoreactive fluorescence of CgGPR1 was mainly observed in the velum, foot, gill and mantle of C. gigas larvae. CgGPR1 transcripts were detected in all the tested organs of adult C. gigas, with highest level in the mantle. Pharmacological analysis showed that cAMP and Ca2+ concentrations remained unchanged in HEK293 cells expressing CgGPR1 upon addition of OA, TA or related amines, suggesting that CgGPR1 modulates other unknown molecules rather than cAMP and Ca2+. Our study sheds light on CgGPR1 function in oysters.

Octopamine controls starvation resistance, life span and metabolic traits in Drosophila.

The monoamines octopamine (OA) and tyramine (TA) modulate numerous behaviours and physiological processes in invertebrates. Nevertheless, it is not clear whether these invertebrate counterparts of norepinephrine are important regulators of metabolic and life history traits. We show that flies (Drosophila melanogaster) lacking OA are more resistant to starvation, while their overall life span is substantially reduced compared with control flies. In addition, these animals have increased body fat deposits, reduced physical activity and a reduced metabolic resting rate. Increasing the release of OA from internal stores induced the opposite effects. Flies devoid of both OA and TA had normal body fat and metabolic rates, suggesting that OA and TA act antagonistically. Moreover, OA-deficient flies show increased insulin release rates. We inferred that the OA-mediated control of insulin release accounts for a substantial proportion of the alterations observed in these flies. Apparently, OA levels control the balance between thrifty and expenditure metabolic modes. Thus, changes in OA levels in response to external and internal signals orchestrate behaviour and metabolic processes to meet physiological needs. Moreover, chronic deregulation of the corresponding signalling systems in humans may be associated with metabolic disorders, such as obesity or diabetes.

Octopamine cyclic release and its modulation of visual sensitivity in crayfish

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-hcycle. The peak value appeared about 2h 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 92nmol/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 100μM 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-hcycle 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.