Octopamine is involved in TRP-induced thermopreference responses in American cockroach.

Insects' thermoregulatory processes depend on thermosensation and further processing of thermal information in the nervous system. It is commonly known that thermosensation involves thermoreceptors, including members of the TRP receptor family, but the involvement of neurotransmitters in thermoregulatory pathways remains unstudied. We conducted test to determine whether octopamine, a biogenic amine that acts as a neurotransmitter and neurohormone in insects, is involved in TRP-induced thermoregulatory responses in Periplaneta americana. We used capsaicin, an activator of the heat-sensitive TRP channel, Painless, to induce thermoregulatory response in cockroaches. Then, we evaluated the behavioural (thermal preferences and grooming), physiological (heart rate) and biochemical responses of insects to capsaicin, octopamine and phentolamine - octopaminergic receptor blocker. Capsaicin, similar to octopamine, increased cockroaches' grooming activity and heart rate. Moreover, octopamine level and protein kinase A (PKA) activity significantly increased after capsaicin treatment. Blocking octopaminergic receptors with phentolamine diminished cockroaches' response to capsaicin - thermoregulatory behaviour, grooming and heart rate were abolished. The results indicate that octopamine is a neurotransmitter secreted in insects after the activation of heat receptors.

Octopamine Rescues Endurance and Climbing Speed in Drosophila Clkout Mutants with Circadian Rhythm Disruption.

Circadian rhythm disturbances are associated with various negative health outcomes, including an increasing incidence of chronic diseases with high societal costs. While exercise can protect against the negative effects of rhythm disruption, it is not available to all those impacted by sleep disruptions, in part because sleep disruption itself reduces exercise capacity. Thus, there is a need for therapeutics that bring the benefits of exercise to this population. Here, we investigate the relationship between exercise and circadian disturbances using a well-established Drosophila model of circadian rhythm loss, the Clkout mutant. We find that Clkout causes reduced exercise capacity, measured as post-training endurance, flight performance, and climbing speed, and these phenotypes are not rescued by chronic exercise training. However, exogenous administration of a molecule known to mediate the effects of chronic exercise, octopamine (OA), was able to effectively rescue mutant exercise performance, including the upregulation of other known exercise-mediating transcripts, without restoring the circadian rhythms of mutants. This work points the way toward the discovery of novel therapeutics that can restore exercise capacity in patients with rhythm disruption.

Bite force, body size, and octopamine mediate mating interactions in the house cricket (Acheta domesticus).

Mating interactions are rife with conflict because the evolutionary interests of males and females seldom coincide. Intersexual conflict affects sexual selection, yet the proximate factors underlying male coercive ability and female resistance are poorly understood. Male combat outcomes are often influenced by bite force, with superior biters being more likely to achieve victory over poorer biters in a range of species, including crickets. If good performers also achieve mating success through sexual coercion, then bite force might play a role in intersexual conflict as well. We tested the capacity of bite force to influence mating interactions in house crickets both directly by measuring bite forces of males and females and by altering male bite capacity through neuropharmacological manipulation. In addition, the invertebrate neurotransmitter octopamine both mediates aggression and underlies motivation to bite in male house crickets. By blocking octopamine receptors through the application of an antagonist, epinastine, we tested the effects of reduced bite force on male mating success. Our results show that male bite capacity, in combination with body size, influences both the likelihood and the outcomes of mating interactions, whereas treatment of males with epinastine eliminates motivation to mate. Our results suggest a functional role for bite force in affecting both sexual conflict and sexual selection and expand our knowledge of the influence of biogenic amines on reproductive behaviour.

Target identification and acaricidal activity difference of amitraz and its metabolite DPMF in Tetranychus cinnabarinus (Boisduval).

BACKGROUND: Amitraz is a broad-spectrum formamidine acaricide proven to be effective against mites in all development stages. Under acidic conditions, amitraz is hydrolyzed to N2 -(2,4-dimethylphenyl)-N1 -methyformamidine (DPMF), an active metabolite for mite control. Octopamine and tyramine receptors are well known targets of amitraz. Until now, no research has been conducted about the amitraz target in Tetranychus cinnabarinus. This study aimed to identify the target genes of amitraz in T. cinnabarinus and reveal the mechanisms behind the differential acaricidal activities of amitraz and DPMF. RESULTS: Analysis of the toxicity, stress expression, target sensitivity and binding site of amitraz against T. cinnabarinus showed that TcOctß2R was the main target gene of amitraz. DPMF had more potent acaricidal activity against T. cinnabarinus and was more effective at activating TcOctß2R than amitraz. Furthermore, the three synergists had no significant effect on amitraz and DPMF, indicating that the detoxification metabolism was not related to the difference in acaricidal activity. CONCLUSION: In this study, TcOctß2R was identified as the main target gene of amitraz against T. cinnabarinus. The divergence of target binding was responsible for the difference in acaricidal activity between amitraz and DPMF. The results also revealed the physiological and pharmacological functions of octopamine receptors (OARs) in T. cinnabarinus and could provide a basis for the design of new acaricides, with OARs as a special target. © 2023 Society of Chemical Industry.

Molecular and Pharmacological Characterization of ß-Adrenergic-like Octopamine Receptors in the Endoparasitoid Cotesia chilonis (Hymenoptera: Braconidae).

Octopamine (OA) is structurally and functionally similar to adrenaline/noradrenaline in vertebrates, and OA modulates diverse physiological and behavioral processes in invertebrates. OA exerts its actions by binding to specific octopamine receptors (OARs). Functional and pharmacological characterization of OARs have been investigated in several insects. However, the literature on OARs is scarce for parasitoids. Here we cloned three ß-adrenergic-like OARs (CcOctßRs) from Cotesia chilonis. CcOctßRs share high similarity with their own orthologous receptors. The transcript levels of CcOctßRs were varied in different tissues. When heterologously expressed in CHO-K1 cells, CcOctßRs induced cAMP production, and were dose-dependently activated by OA, TA and putative octopaminergic agonists. Their activities were inhibited by potential antagonists and were most efficiently blocked by epinastine. Our study offers important information about the molecular and pharmacological properties of ß-adrenergic-like OARs from C. chilonis that will provide the basis to reveal the contribution of individual receptors to the physiological processes and behaviors in parasitoids.

Behavioral roles of biogenic amines in bumble bee males.

To compare the behavioral roles of biogenic amines in the males of primitive and advanced eusocial bees, we determined the levels of dopamine- and octopamine-related substances in the brain, and the behavioral effects of these monoamines by drug injection in the primitive eusocial bumble bee, Bombus ignitus. The levels of dopamine and its precursors in the brain peaked at the late pupal stage, but the dopamine peak extended to adult emergence. The tyramine and octopamine levels increased from the mid-pupal to adult stages. The locomotor and flight activities, and light preference increased with age. Injection of octopamine and its receptor antagonist had significant effects on the locomotor and flight activities, whereas dopamine injection did not, indicating that these activities can be regulated by the octopaminergic system. We also determined the dynamics of dopamine-related substances in honey bee (Apis mellifera) drones. The changes in the dopamine level in the brains of honey bee drones exhibited two peaks from the pupal to adult stages, whereas the bumble bee males had only one peak. These are consistent with the behavioral functions of dopamine in honey bee drones and ineffectiveness of dopamine injection at the adult stage in bumble bee males.

Octopamine modulates insect mating and Oviposition.

The neuro-mechanisms that regulate insect reproduction are not fully understood. Biogenic amines, including octopamine, are neuromodulators that have been shown to modulate insect reproduction in various ways, e.g., promote or inhibit insect mating or oviposition. In this study, we examined the role of octopamine in regulating the reproduction behaviors of a devastating underground insect pest, the dark black chafer (Holotrichia parallela). We first measured the abundance of octopamine in different neural tissues of the adult chafer pre- and post-mating, demonstrating that octopamine decreased in the abdominal ganglia of females but increased in males post-mating. We then fed the adult H. parallela with a concentration gradient of octopamine to test the effects on insect reproductive behaviors. Compared with its antagonist mianserin, octopamine at the concentration of 2 µg/mL resulted in the highest increase in males' preference for sex pheromone and females' oviposition, whereas the mianserin-treatment increased the survival rate and prolonged the lifespan of H. parallela. In addition, we did not observe significant differences in egg hatchability between octopamine and mianserin-treated H. parallela. Our results demonstrated that octopamine promotes H. parallela mating and oviposition with a clear low dosage effect, illustrated how neural substrates modulate insect behaviors, and provided insights for applying octopamine in pest management.

Octopamine affects courtship call structure in male Acheta domesticus crickets.

Secondary sexual displays vary considerably in both type and structure both within and across animal species. Although such variation is of keen interest to evolutionary biologists, the functional factors driving variation in male displays are poorly understood. In crickets, acoustic calls are produced by muscular contractions via stridulation of file and scraper wing components. We tested the effect of varying octopamine, an important biogenic amine neurohormone in invertebrates, on call production in male Acheta domesticus house crickets by blocking the octopamine receptors that influence skeletal muscle function with epinastine, a synthetic octopamine antagonist. We then measured male courtship calls and analyzed the call structure to quantify the differences in call structure based on the changes in carrier frequency, and whether chirps or ticks are a more prevalently expressed frequency in treated vs untreated males. Males treated with epinastine exhibited clear differences in call structure compared to untreated controls, such that epinastine-treated males were more likely to produce simpler calls and to exhibit their carrier frequencies as ticks rather than chirps. Thus, we were able to directly modify male courtship calling performance during mating interactions by altering the neuropharmacological milieu, demonstrating the potential role of biogenic amines in contributing to the diversity of call types in nature.

Biological functions of α2-adrenergic-like octopamine receptor in Drosophila melanogaster.

Octopamine regulates various physiological phenomena including memory, sleep, grooming and aggression in insects. In Drosophila, four types of octopamine receptors have been identified: Oamb, Oct/TyrR, OctßR and Octα2R. Among these receptors, Octα2R was recently discovered and pharmacologically characterized. However, the effects of the receptor on biological functions are still unknown. Here, we showed that Octα2R regulated several behaviors related to octopamine signaling. Octα2R hypomorphic mutant flies showed a significant decrease in locomotor activity. We found that Octα2R expressed in the pars intercerebralis, which is a brain region projected by octopaminergic neurons, is involved in control of the locomotor activity. Besides, Octα2R hypomorphic mutants increased time and frequency of grooming and inhibited starvation-induced hyperactivity. These results indicated that Octα2R expressed in the central nervous system is responsible for the involvement in physiological functions.

Maintenance of quiescent oocytes by noradrenergic signals.

All females adopt an evolutionary conserved reproduction strategy; under unfavorable conditions such as scarcity of food or mates, oocytes remain quiescent. However, the signals to maintain oocyte quiescence are largely unknown. Here, we report that in four different species - Caenorhabditis elegans, Caenorhabditis remanei, Drosophila melanogaster, and Danio rerio - octopamine and norepinephrine play an essential role in maintaining oocyte quiescence. In the absence of mates, the oocytes of Caenorhabditis mutants lacking octopamine signaling fail to remain quiescent, but continue to divide and become polyploid. Upon starvation, the egg chambers of D. melanogaster mutants lacking octopamine signaling fail to remain at the previtellogenic stage, but grow to full-grown egg chambers. Upon starvation, D. rerio lacking norepinephrine fails to maintain a quiescent primordial follicle and activates an excessive number of primordial follicles. Our study reveals an evolutionarily conserved function of the noradrenergic signal in maintaining quiescent oocytes.

Opposing Actions of Octopamine and Tyramine on Honeybee Vision.

The biogenic amines octopamine and tyramine are important neurotransmitters in insects and other protostomes. They play a pivotal role in the sensory responses, learning and memory and social organisation of honeybees. Generally, octopamine and tyramine are believed to fulfil similar roles as their deuterostome counterparts epinephrine and norepinephrine. In some cases opposing functions of both amines have been observed. In this study, we examined the functions of tyramine and octopamine in honeybee responses to light. As a first step, electroretinography was used to analyse the effect of both amines on sensory sensitivity at the photoreceptor level. Here, the maximum receptor response was increased by octopamine and decreased by tyramine. As a second step, phototaxis experiments were performed to quantify the behavioural responses to light following treatment with either amine. Octopamine increased the walking speed towards different light sources while tyramine decreased it. This was independent of locomotor activity. Our results indicate that tyramine and octopamine act as functional opposites in processing responses to light.

N-trans-Feruloyloctopamine Wakes Up BBC3, DDIT3, CDKN1A, and NOXA Signals to Accelerate HCC Cell Apoptosis.

N-trans-Feruloyloctopamine (FO), a natural compound, was reported in our previous study to inhibit a tumor cell malignant phenotype by AKT- and EMT-related signals and might be used as a promising drug for HCC treatment. However, the specific targets and detailed mechanisms still need to be clarified. Screening with RNA-Seq in Huh7 cells treated with FO revealed that 317 genes were modulated, of which 188 genes were upregulated and 129 genes were downregulated. Real-time cell analyzer and flow cytometry data reveal that tumor cell proliferation and apoptosis were impacted by FO. DAVID bioinformatic data showed that most of the biological process GO terms are related to proliferation and apoptosis. KEGG enrichment analysis showed that FO mainly regulates PI3K-AKT- and apoptosis-related signals, in which BBC3, DDIT3, NOXA, and CDKN1A on the surface serve as the novel targets of FO inducing HCC cell apoptosis. The result implied that FO might exacerbate HCC cell apoptosis by regulating BBC3, DDIT3, CDKN1A, and NOXA signals. The obstacle effect of FO can provide new targets and new credibility for the treatment of liver cancer.

Opposing effects of dopamine on agonistic behaviour in crayfish.

The effects of dopamine on the agonistic behaviour of crayfish were analysed. When dopamine concentrations of 1 µmol l-1 were injected into large crayfish, individuals were beaten by smaller opponents, despite their physical advantage. Injection of 10 µmol l-1 dopamine into small animals increased their rate of winning against larger opponents. Injection of a D1 receptor antagonist prohibited the onset of a 'loser' effect in subordinate animals, suggesting that the inhibitory effect of dopamine on larger animals is mediated by D1 receptors. Similarly, injection of a D2 receptor antagonist prohibited the onset of a 'winner' effect in dominant animals, suggesting that the facilitating effect of dopamine on small animals is mediated by D2 receptors. Since the inhibitory effect of 1 µmol l-1 dopamine was similar to that seen with 1 µmol l-1 octopamine and the facilitating effect of 10 µmol l-1 dopamine was similar to that of 1 µmol l-1 serotonin, functional interactions among dopamine, octopamine and serotonin were analyzed by co-injection of amines with their receptor antagonists in various combinations. The inhibitory effect of 1 µmol l-1 dopamine disappeared when administered with D1 receptor antagonist, but remained when combined with octopamine receptor antagonist. Octopamine effects disappeared when administered with either D1 receptor antagonist or octopamine receptor antagonist, suggesting that the dopamine system is downstream of octopamine. The facilitating effect of 10 µmol l-1 dopamine disappeared when combined with serotonin 5HT1 receptor antagonist or D2 receptor antagonist. Serotonin effects also disappeared when combined with D2 receptor antagonist, suggesting that dopamine and serotonin activate each other through parallel pathways.

Renal artery responses to trace amines: Multiple and differential mechanisms of action.

PURPOSE: The rise in consumption of dietary supplements containing the trace amines p-tyramine, p-synephrine and p-octopamine has been associated with cardiovascular side effects. Since renal blood flow plays an important role in blood pressure regulation, this study investigated the mechanisms of action of these trace amines on isolated porcine renal arteries. MAIN METHODS: Contractile responses to amines were investigated in noradrenaline-depleted rings of porcine main renal arteries in the absence and presence of the α1-adrenoceptor antagonist, prazosin (1 µM), ß-adrenoceptor antagonist, propranolol (1 µM), or the trace amine-associated receptor (TAAR-1) antagonist, EPPTB (RO-5212773; 100 nM or 100 µM). KEY FINDINGS: All three amines induced constrictor responses of similar magnitude and potency. However, their mechanisms of action on the renal artery appeared to differ. Depleting endogenous noradrenaline stores significantly reduced maximum responses to tyramine and synephrine, but less for octopamine. When direct responses were examined after depleting tissues of noradrenaline, responses to synephrine and octopamine, but not tyramine, were reduced in the presence of prazosin(1 µM) and potentiated in the presence of propranolol (1 µM) or L-NNA (100 µM). Generally, vasoconstrictor responses remaining after noradrenaline-depletion and α-adrenoceptor blockade were not affected by the TAAR-1 antagonist EPPTB (0.1-100 µM), although responses to low concentration of synephrine and octopamine were enhanced by this antagonist. SIGNIFICANCE: Tyramine appears to mediate constriction of the renal artery mainly via an indirect sympathomimetic mechanism, whereas synephrine and octopamine exert additional direct effects on α1-adrenoceptors and possibly contractile TAAR (not TAAR-1). The two amines also activate simultaneous inhibitory responses via ß-adrenoceptors, TAAR-1 and nitric oxide release.

Enhancement of synaptic responses in ascending interneurones following acquisition of social dominance in crayfish.

When crayfish have attained dominant status after agonistic bouts, their avoidance reaction to mechanical stimulation of the tailfan changes from a dart to a turn response. Ascending interneurones originating in the terminal ganglion receive sensory inputs from the tailfan and they affect spike activity of both uropod and abdominal postural motor neurones, which coordinates the uropod and abdominal postural movements. Despite the varying output effects of ascending interneurones, the synaptic responses of all interneurones to sensory stimulation were enhanced when they acquired a dominant state. The number of spikes increased as did a sustained membrane depolarizations. Regardless of social status, the output effects on the uropod motor neurones of all interneurones except VE-1 remained unchanged. VE-1 mainly inhibited the uropod opener motor neurones in naive animals, but tended to excite them in dominant animals. Synaptic enhancement of the sensory response of ascending interneurones was also observed in naive animals treated with bath-applied serotonin. However, subordinate animals or naive animals treated with octopamine had no noticeable effect on the synaptic response of their ascending interneurones to sensory stimulation. Thus, enhancement of the synaptic response is a specific neural event that occurs when crayfish attain social dominance and it is mediated by serotonin.

Visuo-Motor Feedback Modulates Neural Activities in the Medulla of the Honeybee, Apis mellifera.

Behavioral and internal-state modulation of sensory processing has been described in several organisms. In insects, visual neurons in the optic lobe are modulated by locomotion, but the degree to which visual-motor feedback modulates these neurons remains unclear. Moreover, it also remains unknown whether self-generated and externally generated visual motion are processed differently. Here, we implemented a virtual reality system that allowed fine-scale control over visual stimulation in relation to animal motion, in combination with multichannel recording of neural activity in the medulla of a female honeybee (Apis mellifera). We found that this activity was modulated by locomotion, although, in most cases, only when the bee had behavioral control over the visual stimulus (i.e., in a closed-loop system). Moreover, closed-loop control modulated a third of the recorded neurons, and the application of octopamine (OA) evoked similar changes in neural responses that were observed in a closed loop. Additionally, in a subset of modulated neurons, fixation on a visual stimulus was preceded by an increase in firing rate. To further explore the relationship between neuromodulation and adaptive control of the visual environment of the bee, we modified motor gain sensitivity while locally injecting an OA receptor antagonist into the medulla. Whereas female honeybees were tuned to a motor gain of -2 to 2 (between the heading of the bee and its visual feedback), local disruption of the OA pathway in the medulla abolished this tuning, resulting in similar low levels of response across levels of motor gain. Our results show that behavioral control modulates neural activity in the medulla and ultimately impacts behavior.SIGNIFICANCE STATEMENT When moving, an animal generates the motion of the visual scene over its retina. We asked whether self-generated and externally generated optic flow are processed differently in the insect medulla. Our results show that closed-loop control of the visual stimulus modulates neural activity as early as the medulla and ultimately impacts behavior. Moreover, blocking octopaminergic modulation further disrupted object-tracking responses. Our results suggest that the medulla is an important site for context-dependent processing of visual information and that placing the animal in a closed-loop environment may be essential to understanding its visual cognition and processing.

Epigenetic regulator Stuxnet modulates octopamine effect on sleep through a Stuxnet-Polycomb-Octß2R cascade.

Sleep homeostasis is crucial for sleep regulation. The role of epigenetic regulation in sleep homeostasis is unestablished. Previous studies showed that octopamine is important for sleep homeostasis. However, the regulatory mechanism of octopamine reception in sleep is unknown. In this study, we identify an epigenetic regulatory cascade (Stuxnet-Polycomb-Octß2R) that modulates the octopamine receptor in Drosophila. We demonstrate that stuxnet positively regulates Octß2R through repression of Polycomb in the ellipsoid body of the adult fly brain and that Octß2R is one of the major receptors mediating octopamine function in sleep homeostasis. In response to octopamine, Octß2R transcription is inhibited as a result of stuxnet downregulation. This feedback through the Stuxnet-Polycomb-Octß2R cascade is crucial for sleep homeostasis regulation. This study demonstrates a Stuxnet-Polycomb-Octß2R-mediated epigenetic regulatory mechanism for octopamine reception, thus providing an example of epigenetic regulation of sleep homeostasis.

Variation in mobility and exercise adaptations between Drosophila species.

Locomotion and mobility have been studied extensively in Drosophila melanogaster but less is known about the locomotor capacity of other Drosophila species, while the response to chronic exercise in other species has yet to be examined. We have shown that adult male D. melanogaster adapt to exercise training with improved running endurance, climbing speed, and flight ability compared to unexercised flies. Here, we examine baseline mobility of D. sechellia, D. simulans, and D. virilis, and their response to chronic exercise training. We found significant interspecific differences in mobility and in the response to exercise. Although there is a significant sex difference in exercise adaptations in D. melanogaster, intraspecific analysis reveals few sex differences in other Drosophila species. As octopamine has been shown to be important for exercise adaptations in D. melanogaster, we also asked if any observed differences could be attributed to baseline octopamine levels. We find that octopamine and tyramine levels have the same rank order as baseline climbing speed and endurance in males, but do not predict the response to chronic exercise in males or females. Future research should focus on determining the mechanisms responsible for the inter- and intraspecific differences in mobility and the response to exercise.

Pre-adult aggression and its long-term behavioural consequences in crickets.

Social experience, particularly aggression, is considered a major determinant of consistent inter-individual behavioural differences between animals of the same species and sex. We investigated the influence of pre-adult aggressive experience on future behaviour in male, last instar nymphs of the cricket Gryllus bimaculatus. We found that aggressive interactions between male nymphs are far less fierce than for adults in terms of duration and escalation. This appears to reflect immaturity of the sensory apparatus for releasing aggression, rather than the motor system controlling it. First, a comparison of the behavioural responses of nymphs and adults to mechanical antennal stimulation using freshly excised, untreated and hexane-washed antennae taken from nymphs and adults, indicate that nymphs neither respond to nor produce sex-specific cuticular semiochemicals important for releasing aggressive behaviour in adults. Second, treatment with the octopamine agonist chlordimeform could at least partially compensate for this deficit. In further contrast to adults, which become hyper-aggressive after victory, but submissive after defeat, such winner and loser effects are not apparent in nymphs. Aggressive competition between nymphs thus appears to have no consequence for future behaviour in crickets. Male nymphs are often attacked by adult males, but not by adult females. Furthermore, observations of nymphs raised in the presence, or absence of adult males, revealed that social subjugation by adult males leads to reduced aggressiveness and depressed exploratory behaviour when the nymphs become adult. We conclude that social subjugation by adults during pre-adult development of nymphs is a major determinant of consistent inter-individual behavioural differences in adult crickets.

p-Synephrine, ephedrine, p-octopamine and m-synephrine: Comparative mechanistic, physiological and pharmacological properties.

Confusion and misunderstanding exist regarding the lack of cardiovascular and other adverse health effects of p-synephrine and p-octopamine relative to ephedrine and m-synephrine (phenylephrine) which are known for their effects on the cardiovascular system. These four molecules have some structural similarities. However, the structural and stereochemical differences of p-synephrine and p-octopamine as related to ephedrine and m-synephrine result in markedly different adrenergic receptor binding characteristics as well as other mechanistic differences which are reviewed. p-Synephrine and p-octopamine exhibit little binding to α-1, α-2, ß-1 and ß-2 adrenergic receptors, nor are they known to exhibit indirect actions leading to an increase in available levels of endogenous norepinephrine and epinephrine at commonly used doses. The relative absence of these mechanistic actions provides an explanation for their lack of production of cardiovascular effects at commonly used oral doses as compared to ephedrine and m-synephrine. As a consequence, the effects of ephedrine and m-synephrine cannot be directly extrapolated to p-synephrine and p-octopamine which exhibit significantly different pharmacokinetic, and physiological/pharmacological properties. These conclusions are supported by human, animal and in vitro studies that are discussed.