The effect of biogenic amines and their analogs on carbohydrate metabolism in the fat body of the cockroach Blaberus discoidalis

Octopaminergic descending neurons in Drosophila: Connectivity, tonic activity and relation to locomotion

Projection neurons that communicate between different brain regions and local neurons that shape computation within a brain region form the majority of all neurons in the brain. Another important class of neurons is neuromodulatory neurons; these neurons are in much smaller numbers than projection/local neurons but have a large influence on computations in the brain. Neuromodulatory neurons are classified by the neurotransmitters they carry, such as dopamine and serotonin. Much of our knowledge of the effect of neuromodulators comes from experiments in which either a large population of neuromodulatory neurons or the entire population is perturbed. Alternatively, a given neuromodulator is exogenously applied. While these experiments are informative of the general role of the neurotransmitter, one limitation of these experiments is that the role of individual neuromodulatory neurons remains unknown. In this study, we investigate the role of a class of octopaminergic (octopamine is the invertebrate equivalent of norepinephrine) neurons in Drosophila or fruit fly. Neuromodulation in Drosophila work along similar principles as humans; and the smaller number of neuromodulatory neurons allow us to assess the role of individual neurons. This study focuses on a subpopulation of octopaminergic descending neurons (OA-DNs) whose cell bodies are in the brain and project to the thoracic ganglia. Using in-vivo whole-cell patch-clamp recordings and anatomical analyses that allow us to compare light microscopy data to the electron microscopic volumes available in the fly, we find that neurons within each cluster have similar physiological properties, including their relation to locomotion. However, neurons in the same cluster with similar anatomy have very different connectivity. Our data is consistent with the hypothesis that each OA-DN is recruited individually and has a unique function within the fly's brain.

Age-Dependent Honey Bee Appetite Regulation Is Mediated by Trehalose and Octopamine Baseline Levels

Simple Summary

Appetite regulation is an important function necessary to maintain energetic balance, but how honey bees accomplish this could vary as they age because they go through a number of behavioral and physiological changes during development. Here, we determine if the amount of trehalose, which is a sugar found in the hemolymph of honey bees, influences appetite levels and if this interacts with the octopamine neurotransmitter in the bee brain. To accomplish this, we decreased trehalose levels in the hemolymph by injecting an inhibitor of trehalose synthesis. In addition, we increased octopamine levels in the brain by injecting it with a syringe. We found that octopamine and trehalose interact to increase appetite in the two older age classes of bees, beyond just treating the bees with octopamine. The youngest age class did not respond to either treatment. Our results suggest that older honey bees may have an alternative pathway for regulating appetite that uses sugar levels in their hemolymph to communicate to the brain how hungry they are and that octopamine is responsible for elevating appetite levels when the bee is hungry. This pathway is different from how vertebrates regulate their appetite levels based on glucose levels in the blood.

Abstract

There are multiple feedback mechanisms involved in appetite regulation, which is an integral part of maintaining energetic homeostasis. Older forager honey bees, in comparison to newly emerged bees and nurse bees, are known to have highly fluctuating hemolymph trehalose levels, higher appetite changes due to starvation, and higher octopamine levels in the brain. What remains unknown is if the hemolymph trehalose and octopamine levels interact with one another and how this varies as the bee ages. We manipulated trehalose and octopamine levels across age using physiological injections and found that nurse and forager bees increase their appetite levels due to increased octopamine levels in the brain. This is further enhanced by lower trehalose levels in the hemolymph. Moreover, nurse bees with high octopamine levels in the brain and low trehalose levels had the same appetite levels as untreated forager bees. Our findings suggest that the naturally higher levels of octopamine as the bee ages may result in higher sensitivity to fluctuating trehalose levels in the hemolymph that results in a more direct way of assessing the energetic state of the individual. Consequently, forager bees have a mechanism for more precise regulation of appetite in comparison to newly emerged and nurse bees.

She's got nerve: roles of octopamine in insect female reproduction

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.

The control of metabolic traits by octopamine and tyramine in invertebrates

Octopamine (OA) and tyramine (TA) are closely related biogenic monoamines that act as signalling compounds in invertebrates, where they fulfil the roles played by adrenaline and noradrenaline in vertebrates. Just like adrenaline and noradrenaline, OA and TA are extremely pleiotropic substances that regulate a wide variety of processes, including metabolic pathways. However, the role of OA and TA in metabolism has been largely neglected. The principal aim of this Review is to discuss the roles of OA and TA in the control of metabolic processes in invertebrate species. OA and TA regulate essential aspects of invertebrate energy homeostasis by having substantial effects on both energy uptake and energy expenditure. These two monoamines regulate several different factors, such as metabolic rate, physical activity, feeding rate or food choice that have a considerable influence on effective energy intake and all the principal contributors to energy consumption. Thereby, OA and TA regulate both metabolic rate and physical activity. These effects should not be seen as isolated actions of these neuroactive compounds but as part of a comprehensive regulatory system that allows the organism to switch from one physiological state to another.

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).

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.

Sequential Proton Loss Electron Transfer in Deactivation of Iron(IV) Binding Protein by Tyrosine Based Food Components

The iron(IV) binding protein ferrylmyoglobin, MbFe(IV)═O, was found to be reduced by tyrosine based food components in aqueous solution through a sequential proton loss electron transfer reaction mechanism without binding to the protein as confirmed by isothermal titration calorimetry. Dopamine and epinephrine are the most efficient food components reducing ferrylmyoglobin to oxymyoglobin, MbFe(II)O₂, and metmyoglobin, MbFe(III), as revealed by multivariate curve resolution alternating least-squares with second order rate constants of 33.6 ± 2.3 L/mol/s (ΔH^⧧ of 19 ± 5 kJ/mol, ΔS^⧧ of -136 ± 18 J/mol K) and 228.9 ± 13.3 L/mol/s (ΔH^⧧ of 110 ± 7 kJ/mol, ΔS^⧧ of 131 ± 25 J/mol K), respectively, at pH 7.4 and 25 °C. The other tyrosine based food components were found to reduce ferrylmyoglobin to metmyoglobin with similar reduction rates at pH 7.4 and 25 °C. These reduction reactions were enhanced by protonation of ferrylmyoglobin and facilitated proton transfer at acidic conditions. Enthalpy-entropy compensation effects were observed for the activation parameters (ΔH^⧧ and ΔS^⧧), indicating the common reaction mechanism. Moreover, principal component analysis combined with heat map were performed to understand the relationship between density functional theory calculated molecular descriptors and kinetic data, which was further modeled by partial least squares for quantitative structure-activity relationship analysis. In addition, a three tyrosine residue containing protein, lysozyme, was also found to be able to reduce ferrylmyoglobin with a second order rate constant of 66 ± 28 L/mol/s as determined by a competitive kinetic method.

Physiological functions and pharmacological and toxicological effects of p-octopamine

p-Octopamine occurs naturally in plants, invertebrates and animals with diverse functions and effects. This review summarizes the chemistry, metabolism, receptor binding characteristics, known physiological functions, and pharmacological and toxicological effects of p-octopamine. Databases used included PubMed and Google Scholar Advanced. p-Octopamine binds to neuroreceptors in insects that are not present in humans, while exhibiting poor binding to α-1, α-2, β-1, and β-2 adrenergic receptors in mammalian systems. p-Octopamine modestly binds to β-3 adrenergic receptors and may therefore promote lipolysis and weight loss. p-Octopamine is produced in brain and nerve tissues of mammals and is present and can be measured in the blood of normal human subjects. p-Octopamine is considered to be a CNS stimulant in spite of the fact that it binds poorly to adrenergic receptors. Variations occur in blood levels in association with neurological and hepatic diseases. Its precise role in normal neurophysiology is unclear. No human studies have been reported that demonstrate adverse cardiovascular effects following oral administration. No human studies have examined the effects of p-octopamine on athletic performance or weight loss and weight management. A need exists for both animal and human safety and efficacy studies involving oral administration of p-octopamine.

Adrenergic metabolic and hemodynamic effects of octopamine in the liver

The fruit extracts of Citrus aurantium (bitter orange) are traditionally used as weight-loss products and as appetite suppressants. A component of these extracts is octopamine, which is an adrenergic agent. Weight-loss and adrenergic actions are always related to metabolic changes and this work was designed to investigate a possible action of octopamine on liver metabolism. The isolated perfused rat liver was used to measure catabolic and anabolic pathways and hemodynamics. Octopamine increased glycogenolysis, glycolysis, oxygen uptake, gluconeogenesis and the portal perfusion pressure. Octopamine also accelerated the oxidation of exogenous fatty acids (octanoate and oleate), as revealed by the increase in ¹⁴CO₂ production derived from ¹⁴C labeled precursors. The changes in glycogenolysis, oxygen uptake and perfusion pressure were almost completely abolished by α₁-adrenergic antagonists. The same changes were partly sensitive to the β-adrenergic antagonist propranolol. It can be concluded that octopamine accelerates both catabolic and anabolic processes in the liver via adrenergic stimulation. Acceleration of oxygen uptake under substrate-free perfusion conditions also means acceleration of the oxidation of endogenous fatty acids, which are derived from lipolysis. All these effects are compatible with an overall stimulating effect of octopamine on metabolism, which is compatible with its reported weight-loss effects in experimental animals.

A review of the receptor-binding properties of p-synephrine as related to its pharmacological effects

Bitter orange (Citrus aurantium) extract and its primary protoalkaloid p-synephrine are used widely in weight loss/weight management and sports performance products. Because of structural similarities, the pharmacological effects of p-synephrine are widely assumed to be similar to those of ephedrine, m-synephrine (phenylephrine), and endogenous amine neurotransmitters as norepinephrine and epinephrine. However, small structural changes result in the receptor binding characteristics of these amines that are markedly different, providing a plausible explanation for the paucity of adverse effects associated with the wide-spread consumption of p-synephrine in the form of dietary supplements as well as in various Citrus foods and juices. This paper summarizes the adrenoreceptor binding characteristics of p-synephrine relative to m-synephrine, norepinephrine, and other amines as related to the observed pharmacological effects.

Boric acid-induced effects on protein profiles of Galleria mellonella hemolymph and fat body

The dietary effects of boric acid (BA) on the protein profiles of greater wax moth, Galleria mellonella (L.), were investigated in hemolymph and fat body of final instar (VIIth) and pupae. The insects were reared from first-instar larvae on an artificial diets containing 156, 620, 1250 or 2500 ppm of BA. We detected many undetermined protein fractions (6.5-260 kDa) in addition to well-defined protein fractions such as lipophorins and storage proteins in the tissues by using sodium dodecyl-sulphate polyacrylamide gradient gel electrophoresis. A marked quantitative change in the 45 kDa protein fraction of the hemolymph was observed in the VIIth instar larvae reared on 2500 ppm dietary BA.

Determination of bitter orange alkaloids in dietary supplement Standard Reference Materials by liquid chromatography with atmospheric-pressure ionization mass spectrometry

A liquid chromatographic atmospheric-pressure ionization electrospray mass spectrometry (LC-API-ES-MS) method has been developed for the determination of five bitter orange alkaloids (synephrine, octopamine, n-methyltyramine, tyramine, and hordenine) in bitter orange-containing dietary supplement standard reference materials (SRMs). The materials represent a variety of natural, extracted, and processed sample matrices. Two extraction techniques were evaluated: pressurized-fluid extraction (PFE) and sonication extraction. The influence of different solvents, extraction temperatures, and pH were investigated for a plant material and a processed sample. The LC method uses a new approach for the separation of highly polar alkaloids. A fluorinated, silica-based stationary phase separated the five alkaloids and the internal standard terbutaline in less than 20 min. This method enabled the determination of the dominant alkaloid synephrine and other minor alkaloids in a variety of dietary supplement SRMs.

Chemiluminescence of synephrine based on the cerium(IV)–rhodamine B system

A new chemiluminescence (CL) method is described for the determination of synephrine. It is based on the reaction between synephrine and Ce(IV) in a nitric acid medium and measurement of the CL intensity produced by rhodamine B used as a luminophore, similar to luminol or lucigenin in basic media, instead of as a sensitizer. In the optimum conditions, the increase of CL intensity was correlated with synephrine concentration over the range 5.0 x 10(-9)-1.0 x 10(-6) g/mL with a detection limit of 1.0 x 10(-9) g/mL. The relative standard deviation (RSD) was 2.9% for 1.0 x 10(-7) g/mL synephrine (n = 11). The method was applied to the determination of a drug in herbal products, citrus fruit and biological samples, with satisfactory results. The results given by the proposed method are in good agreement with those given by HPLC-UV and UV spectrophotometry.

A rapid and simple procedure for the determination of synephrine in dietary supplements by gas chromatography-mass spectrometry

A simple and rapid procedure based on gas chromatography-mass spectrometry (GC-MS) is described for determination of synephrine, active principle of Citrus aurantium plant, in solid and liquid dietary supplements. After the addition of 3,4-methylenedioxypropylamphetamine as internal standard (I.S.), a liquid-liquid extraction procedure in alkaline conditions with chloroform/isopropanol (9:1, v/v) was applied to the samples prior to analysis. Chromatography was performed on a fused capillary column and synephrine and I.S., derivatized with pentafluoropropionic anhydride, were determined in the selected-ion-monitoring (SIM) mode. The method was validated in the range 0.1-50 microg/mg or microg/mL synephrine. Mean recovery ranged between 89.3% and 90.5% in both solid and liquid dietary supplements. The quantification limit was 0.1 microg/mg or microg/ml. The method was applied to analysis of various dietary supplements promoted for aiding weight control containing, among other constituents such as ephedrine alkaloids and methylxanthines, Citrus aurantium. Amount of synephrine present in such products ranged from 3.1 microg/mg solid product to 480.2 microg/mL liquid product.

Sensitive determination of synephrine by flow-injection chemiluminescence

It was found that light emission produced by the oxidation of luminol by potassium ferricyanide in basic medium was enhanced by synephrine, an anti-obesity drug. The optimum conditions for this chemiluminescent reaction were studied in detail in a flow injection system and employed in a new, simple and rapid method for the determination of synephrine. A mechanism for this reaction is proposed, based on the chemiluminescence reaction spectra. In the optimum conditions, CL intensity is proportional to concentration of synephrine in the 0.008-1 microg/mL range. The limit of detection is 1.6 ng/mL for synephrine (3sigma), and the relative standard deviation (n = 11) is 2.6% for 0.5 microg/mL synephrine. The method was applied to the determination of synephrine in herbal products, citrus fruit and biological fluids. The recoveries were satisfactory (90-102%). The results given by the proposed method are in good agreement with those given by HPLC-UV.

AKH-producing neuroendocrine cell ablation decreases trehalose and induces behavioral changes in Drosophila

Adipokinetic hormone (AKH) is a metabolic neuropeptide principally known for its mobilization of energy substrates, notably lipid and trehalose during energy-requiring activities, such as flight and locomotion. Drosophila melanogaster AKH cell localization in corpora cardiaca, as in other insect species, was confirmed by immunoreactivity and by a genetic approach using the UAS/GAL4 system. To assess AKH general physiological rules, we ablated AKH endocrine cells by specifically driving the expression of apoptosis transgenes in AKH cells. Trehalose levels were decreased in larvae and starved adults, when the stimulation by AKH of the production of trehalose from fat body glycogen is no longer possible. Moreover, we show that these adults without AKH cells become progressively hypoactive. Finally, under starvation conditions, those hypoactive AKH-knockout cell flies survived approximately 50% longer than control wild-type flies, suggesting that the slower rate at which AKH-ablated flies mobilize their energy resources extends their survival.

Characterization of a tyramine receptor from Caenorhabditis elegans

Octopamine (OA) plays an important role in the regulation of a number of key processes in nematodes, including pharyngeal pumping, locomotion and egg-laying. However, while putative OA receptors can be tentatively identified in the Caenorhabditis elegans database, no OA receptors have been functionally characterized from any nematode. We have isolated two cDNAs, ser-2 and ser-2a, encoding putative C.elegans serotonin/OA receptors (C02D4.2, ser-2). The sequences of these cDNAs differ from that predicted by GeneFinder and lack 42 bp of exon 2. In addition, ser-2a appears to be alternatively spliced and lacks a predicted 23 amino acids in the third intracellular loop. COS-7 cells expressing SER-2 bind [3H]LSD in the low nM range and exhibit Kis for tyramine, octopamine and serotonin of 0.07, 2, and 13.7 micro m, respectively. Significantly, tyramine reduces forskolin-stimulated cAMP levels in HEK293 cells stably expressing SER-2 with an IC50 of about 360 nm, suggesting that SER-2 is a tyramine receptor.

Determination of adrenergic agonists from extracts and herbal products of Citrus aurantium L. var. amara by LC

The purpose of this study was to set up a HPLC method to separate adrenergic amines (dl-octopamine, dl-synephrine and tyramine) and to determine their content in fruits, extracts and herbal products of Citrus aurantium L. var. amara. A rapid method for the quantitative analysis of these amines is described, based on their separation by RP-HPLC technique with UV detection. The analysis were conducted on a Lichrospher RP-18 column at room temperature, using a mobile phase consisting of 0.02 M citric acid-0.02 M NaH2PO4 (7:3 v/v) and adjusted to a final pH of 3. The detection was at 220 nm. Since some of these amines are chiral compounds and their enantiomers showed different pharmacological activity, the direct separation of synephrine enantiomers was carried out with HPLC on a beta-cyclodextrin stationary phase. The mobile phase consisted of methanol-NaH2PO4 25 mM pH 3.5 (20:80 v/v) and tetrabutylammonium hydrogen sulfate 10 mM in ratio of 30:70 v/v in isocratic condition and the detection was at 220 nm. The two proposed methods were applied to the analysis of fruits, extracts and herbal products of C. aurantium L. var. amara. Taking into account that some authors have reported that l-synephrine may be converted into its d-form by high temperature, this optical isomerization was monitored by the same HPLC method used for the separation of enantiomers.

Inositol trisphosphate mediates the action of hypertrehalosemic hormone on fat body of the American cockroach, Periplaneta americana

The rate of synthesis of inositol trisphosphate (InsP(3)) in trophocytes derived from disaggregated cockroach (Periplaneta americana) fat body increases following treatment of the cells with hypertrehalosemic hormone I or II (HTH-I, -II) in vitro. Trophocytes preloaded with [3H]inositol display a significant increase in InsP(3) synthesis as early as 15 s after addition of the hormone. When the trophocytes are pre-incubated with LiCl and subsequently incubated with HTH the [3H] content of the InsP(3) fraction is greater than that found with HTH alone. This is taken as evidence that inositol monophosphate phosphatase is part of the mechanism for clearing InsP(3) from the cytosol. In contrast to HTH, octopamine, which is also capable of exerting a hypertrehalosemic effect in the cockroach, does not increase the synthesis of InsP(3). 1-Octadecyl-2-methyl-rac-glycero-3-phosphocholine (ET-18-OCH(3)), a potent and selective inhibitor of phosphatidylinositol phospholipase C, blocks the activation of phosphorylase by HTH-I as well as the hypertrehalosemic effect induced by the hormone.