Octopamine drives honeybee thermogenesis

In times of environmental change species have two options to survive: they either relocate to a new habitat or they adapt to the altered environment. Adaptation requires physiological plasticity and provides a selection benefit. In this regard, the Western honeybee (Apis mellifera) protrudes with its thermoregulatory capabilities, which enables a nearly worldwide distribution. Especially in the cold, shivering thermogenesis enables foraging as well as proper brood development and thus survival. In this study, we present octopamine signaling as a neurochemical prerequisite for honeybee thermogenesis: we were able to induce hypothermia by depleting octopamine in the flight muscles. Additionally, we could restore the ability to increase body temperature by administering octopamine. Thus we conclude, that octopamine is necessary and sufficient for thermogenesis. Moreover, we show that these effects are mediated by β octopamine receptors. The significance of our results is highlighted by the fact the respective receptor genes underlie enormous selective pressure due to adaptation to cold climates. Finally, octopamine signaling in the service of thermogenesis might be a key strategy to survive in a changing environment.

An octopamine receptor confers selective toxicity of amitraz on honeybees and Varroa mites

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 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.

Knockdown of a β-Adrenergic-Like Octopamine Receptor Affects Locomotion and Reproduction of Tribolium castaneum

The neurohormone octopamine regulates many crucial physiological processes in insects and exerts its activity via typical G-protein coupled receptors. The roles of octopamine receptors in regulating behavior and physiology in Coleoptera (beetles) need better understanding. We used the red flour beetle, Tribolium castaneum, as a model species to study the contribution of the octopamine receptor to behavior and physiology. We cloned the cDNA of a β-adrenergic-like octopamine receptor (TcOctβ2R). This was heterologously expressed in human embryonic kidney (HEK) 293 cells and was demonstrated to be functional using an in vitro cyclic AMP assay. In an RNAi assay, injection of dsRNA demonstrated that TcOctβ2R modulates beetle locomotion, mating duration, and fertility. These data present some roles of the octopaminergic signaling system in T. castaneum. Our findings will also help to elucidate the potential functions of individual octopamine receptors in other insects.

Effect of Aerobic Training and Octopamine Supplementation on the Expression of Octopamine Receptors in the Visceral Adipose Tissue of Rats Exposed to Deep Fried Oils

Background: The use of deep fried oils (DFOs) to cook foods is associated with numerous diseases. Although the role of physical activity and some supplements on fat lipolysis has been established, the effect of aerobic training (AT) and octopamine (Oct) on octopamine receptor-dependent lipolysis pathway is not well understood. Objectives: The present study aimed to investigate the effect of AT and Oct supplementation on the expression of Oct receptors in the visceral adipose tissue of DFO-exposed rats. Methods: In this experimental study, 30 male Wistar rats were divided into (1) healthy control (C), (2) DFO, (3) DFO + Oct, (4) DFO + AT, and (5) DFO + Oct + AT groups. Aerobic training was performed for four weeks, five sessions per week at an intensity of 16 - 26 m/min and equivalent to 50% - 65% VO2max, and Otc supplement was interperitoneally injected at 81 µmol/kg five days a week. Results: Aerobic training and Oct supplementation increased tyramin-R and hormone-sensitive lipase (HSL) (P ≤ 0.05), while Oct significantly decreased G protein-coupled receptors (GPCR) (P ≤ 0.05). Also, the interaction of AT and Oct on GPCR reduction was significant (P ≤ 0.05). Conclusions: It seems that AT and Otc alone improve octopamine receptors and lipolysis markers in the visceral adipose tissue of DFO-treated rats, but these two factors have no interactive effects on this pathway.

Ion channels and G protein-coupled receptors as targets for invertebrate pest control: from past challenges to practical insecticides

In the late 1970s, we discovered that toxic bicyclic phosphates inhibit the generation of miniature inhibitory junction potentials, implying their antagonism of γ-aminobutyric acid (GABA) receptors (GABARs; GABA-gated chloride channels). This unique mode of action provided a strong incentive for our research on GABARs in later years. Furthermore, minor structural changes conferred insect GABAR selectivity to this class of compounds, convincing us of the possibility of GABARs as targets for insecticides. Forty years later, third-generation insecticides acting as allosteric modulator antagonists at a distinctive site of action in insect GABARs were developed. G protein-coupled receptors (GPCRs) are also promising targets for pest control. We characterized phenolamine receptors functionally and pharmacologically. Of the tested receptors, β-adrenergic-like octopamine receptors were revealed to be the most sensitive to the acaricide/insecticide amitraz. Given the presence of multiple sites of action, ion channels and GPCRs remain potential targets for invertebrate pest control.

Appetitive learning relies on octopamine and dopamine in ants

Associative learning relies on the detection of coincidence between a stimulus and a reward or punishment. In the insect brain, this process is thought to be carried out in the mushroom bodies under control of octopaminergic and dopaminergic neurons. It was assumed that appetitive learning is governed by octopaminergic neurons, while dopamine is required for aversive learning. This view has been recently challenged: Both neurotransmitters seem to be involved in both types of memory in bees and flies. Here, we test which neurotransmitters are required for appetitive learning in ants. We trained Lasius niger ant workers to discriminate two mixtures of linear hydrocarbons and associate one of them with a sucrose reward. We analysed the behaviour of the trained ants using machine learning and found that they preferred the rewarded odour over the other, a preference that was stable for at least 24 hours. We then treated the ants before learning with either epinastine, an octopamine receptor blocker, or with flupentixol, a dopamine receptor blocker. Ants with blocked octopamine receptors did not remember the rewarded odour. Octopamine signalling is thus necessary for the formation of appetitive memory. In contrast, ants with blocked dopamine receptors initially learned the rewarded odour but failed to retrieve this memory 24 hours later. Dopamine is thus required for long-term memory consolidation during appetitive conditioning, independent of short-term memory formation. Our results show that appetitive learning depends on both octopamine and dopamine signalling in ants.

AmOctα2R: Functional Characterization of a Honeybee Octopamine Receptor Inhibiting Adenylyl Cyclase Activity

The catecholamines norepinephrine and epinephrine are important regulators of vertebrate physiology. Insects such as honeybees do not synthesize these neuroactive substances. Instead, they use the phenolamines tyramine and octopamine for similar physiological functions. These biogenic amines activate specific members of the large protein family of G protein-coupled receptors (GPCRs). Based on molecular and pharmacological data, insect octopamine receptors were classified as either α- or β-adrenergic-like octopamine receptors. Currently, one α- and four β-receptors have been molecularly and pharmacologically characterized in the honeybee. Recently, an α2-adrenergic-like octopamine receptor was identified in Drosophila melanogaster (DmOctα2R). This receptor is activated by octopamine and other biogenic amines and causes a decrease in intracellular cAMP ([cAMP]i). Here, we show that the orthologous receptor of the honeybee (AmOctα2R), phylogenetically groups in a clade closely related to human α2-adrenergic receptors. When heterologously expressed in an eukaryotic cell line, AmOctα2R causes a decrease in [cAMP]i. The receptor displays a pronounced preference for octopamine over tyramine. In contrast to DmOctα2R, the honeybee receptor is not activated by serotonin. Its activity can be blocked efficiently by 5-carboxamidotryptamine and phentolamine. The functional characterization of AmOctα2R now adds a sixth member to this subfamily of monoaminergic receptors in the honeybee and is an important step towards understanding the actions of octopamine in honeybee behavior and physiology.

Menthol Increases Bendiocarb Efficacy Through Activation of Octopamine Receptors and Protein Kinase A

Great effort is put into seeking a new and effective strategies to control insect pests. One of them is to combine natural products with chemical insecticides to increase their effectiveness. In the study presented, menthol which is an essential oil component was evaluated on its ability to increase the efficiency of bendiocarb, carbamate insecticide. A multi-approach study was conducted using biochemical method (to measure acetylcholinesterase enzyme activity), electrophysiological technique (microelectrode recordings in DUM neurons in situ), and confocal microscopy (for calcium imaging). In the electrophysiological experiments, menthol caused hyperpolarization, which was blocked by an octopamine receptor antagonist (phentolamine) and an inhibitor of protein kinase A (H-89). It also raised the intracellular calcium level. The effect of bendiocarb was potentiated by menthol and this phenomenon was abolished by phentolamine and H-89 but not by protein kinase C inhibitor (bisindolylmaleimide IX). The results indicate that menthol increases carbamate insecticide efficiency by acting on octopamine receptors and triggering protein kinase A phosphorylation pathway.