Octopamine Metabolism Research Articles

Genotype of Wolbachia pipientis Endosymbiont Affects Octopamine Metabolism in Drosophila melanogaster Females

The effect of the genotype of the endosymbiont Wolbachia pipientis on the metabolism of octopamine (one of the main biogenic amines in insects) was studied in young Drosophila melanogaster females. The activity of tyrosine decarboxylase (key octopamine synthesis enzyme) and the activity of octopamine-dependent N-acetyltransferase (the enzyme of its degradation) were measured. It was demonstrated that the activity of both studied enzymes is increased under normal conditions in females infected with bacteria of the pathogenic wMelPop strain and decreased in those infected with bacteria of the wMelCS genotype, while it does not differ from those in uninfected flies in females infected with the wMel genotype. It was also found that the intensity of tyrosine decarboxylase response to heat stress is decreased in all females infected with Wolbachia. Thus, the effect of Wolbachia on octopamine metabolism was for the first time demonstrated in the Drosophila females, and it was shown that the nature of this effect is determined by the symbiont genotype.

Acute Exposure to Worst-Case Concentrations of Amitraz Does Not Affect Honey Bee Learning, Short-Term Memory, or Hemolymph Octopamine Levels.

Amitraz, an acaricide used to treat Varroa destructor Anderson & Trueman, is one of the most commonly detected pesticides in honey bee (Apis mellifera L.) hives. Acaricides sometimes negatively impact honey bee cognition, but potential effects of amitraz on honey bee learning have been rarely studied. We topically exposed foragers to 95th percentile field-relevant levels of amitraz and, 24 h later, tested the ability of bees to associate a sucrose reward with a conditioned odor (learning response) using the proboscis extension response (PER). We then tested the ability of the bees to retain this memory 1 h and 2 h post-conditioning. Because amitraz is thought to affect octopamine metabolism in honey bees, and because octopamine is directly related to honey bee learning and memory, we also examined effects of exposure to amitraz on octopamine levels in honey bee hemolymph. We found that acute exposure to 95th percentile doses of amitraz had no impact on honey bee learning or short-term memory as measured by PER. Concentrations of octopamine in hemolymph from our low amitraz treatment were 1.4-fold higher than control levels, but other treatments had no effect. Our results from worst-case acute exposure experiments with worker bees in the laboratory suggest that typical field-relevant (within hive) exposures to amitraz probably have little effect on honey bee learning and memory.

The impact of FOXO on dopamine and octopamine metabolism in Drosophila under normal and heat stress conditions.

ABSTRACTThe forkhead boxO transcription factor (FOXO) is a component of the insulin signalling pathway and plays a role in responding to adverse conditions, such as oxidative stress and starvation. In stressful conditions, FOXO moves from the cytosol to the nucleus where it activates gene expression programmes. Here, we show that FOXO in Drosophila melanogaster responds to heat stress as it does to other stressors. The catecholamine signalling pathway is another component of the stress response. In Drosophila, dopamine and octopamine levels rise steeply under heat, nutrition and mechanical stresses, which are followed by a decrease in the activity of synthesis enzymes. We demonstrate that the nearly twofold decline of FOXO expression in foxoBG01018 mutants results in dramatic changes in the metabolism of dopamine and octopamine and the overall response to stress. The absence of FOXO increases tyrosine decarboxylase activity, the first enzyme in octopamine synthesis, and decreases the enzymatic activity of enzymes in dopamine synthesis, alkaline phosphatase and tyrosine hydroxylase, in young Drosophila females. We identified the juvenile hormone as a mediator of FOXO regulation of catecholamine metabolism. Our findings suggest that FOXO is a possible trigger for endocrinological stress reactions.

Insulin‐like receptor substrate gene chico regulates octopamine metabolism in Drosophila melanogaster

AbstractOctopamine, one of the main insect biogenic amines, plays an important role in the control of fitness in Drosophila melanogaster Meigen. The present study examines the effects of a null mutation of the gene of the insulin‐like receptor substrate (chico), in the heterozygous state, on octopamine metabolism, heat stress resistance and fecundity of D. melanogaster. A rise in the activity of one of the key enzymes of octopamine synthesis, tyrosine decarboxylase, as well as that of an enzyme of its degradation, octopamine‐dependent N‐acetyl transferase, is observed in chico1/+ females. It is also found that the resistance to heat stress is decreased and fecundity is reduced dramatically in chico1/+ flies. Such changes in these parameters in D. melanogaster females result from a rise in octopamine titre, which suggests that chico affects the octopamine level by regulating the activity of tyrosine decarboxylase.

Gene dilp6 regulates octopamine metabolism in Drosophila melanogaster

The effect of strong hypomorphic mutation of the insulin-like protein gene (dilp6) on metabolism of octopamine (one of the main biogenic amines in insects) was studied in Drosophila melanogaster males and females. The activity of tyrosine decarboxylase (the key enzyme of octopamine synthesis) and the activity of octopamine-dependent N-acetyltransferase (the enzyme of its degradation) were measured. It was demonstrated that the activity of both studied enzymes is decreased under normal conditions in the dilp6 41 mutants (as we previously demonstrated, this is correlated with an increased level of octopamine). It was also found that hypomorphic mutation of the dilp6 gene decreases the intensity of tyrosine decarboxylase response to heat stress. Thus, it was demonstrated for the first time that insulin-like DILP6 protein in drosophila influences the level of octopamine (regulating the activity of the enzyme degrading octopamine).

InR gene expression and octopamine metabolism in Drosophila melanogaster females

The influence of suppression of the expression of the Drosophila insulin-like receptor gene (InR) in corpus allatum (the gland-synthesizing juvenile hormone) on octopamine and juvenile hormone metabolism and on the development of the stress-reaction in Drosophila melanogaster females was studied. It was demonstrated that the suppression of InR gene expression in corpus allatum induces in D. melanogaster females an increase in the activity of the enzyme that limits the rate of octopamine synthesis (tyrosine decarboxylase), as well as in the level of juvenile hormone degradation and the intensity of the response of octopamine and juvenile hormone metabolism systems to heat stress. It was mentioned that a decrease in InR gene expression in corpus allatum does not influence the activity of OA-dependent N-acetyltransferase (the enzyme that degrades octopamine). It was established that the influence of suppression of the InR gene expression in corpus allatum on octopamine metabolism is mediated by juvenile hormone, since the processing of flies by exogenous juvenile hormone restores the activity oftyrosine decarboxylase in flies with decreased InR expression in corpus allatum up to the normal level.

Decrease in juvenile hormone level as a result of genetic ablation of the Corpusallatum cells affects the synthesis and metabolism of stress related hormones in Drosophila

Previous studies have shown that juvenile hormone (JH) regulates dopamine (DA) and octopamine (OA) content in Drosophila, and we have shown the influence of an increase in JH level on DA and OA metabolism in young females of Drosophila virilis and Drosophila melanogaster. Here we investigate the effects of genetic ablation of a subset of cells in the Corpusallatum (CA, endocrine gland synthesizing JH) on the DA levels and activities of alkaline phosphatase (ALP), tyrosine hydroxylase (TH), DA-dependent arylalkylamine N-acetyltransferase (DAT) and tyrosine decarboxylase (TDC) in young D. melanogaster females under normal conditions and upon heat stress (38°С). We show that ablation of СА cells causes: (1) a decrease in ALP, TH and DAT activities, (2) an increase in DA level and (3) an increase in TDC activity in young females. The CA ablation was also found to modulate ALP, TH and TDC responses to heat stress. Mechanisms of regulation of DA and OA levels by JH in Drosophila females are discussed.

Effects of 20‐hydroxyecdysone and juvenile hormone on octopamine metabolism in females of Drosophila

The effect of exogenous 20-hydroxyecdysone (20E) and juvenile hormone (JH) on the activities of the tyrosine decarboxylase (TDC), the first enzyme in octopamine (OA) synthesis, has been studied in young females of wild type D. virilis and D. melanogaster under normal and heat stress (38 degrees C) conditions. Flies fed 20E expressed increased TDC activity in both species. JH application decreased TDC activity in both species. A rise in JH and 20E levels did not prevent a TDC response to heat stress, but changed the response intensity. A long-term increase in JH titre had no effect on the activity of main OA catabolyzing enzyme, arylalkylamine N-acetyltransferase, in females of both species. A possible mechanism of regulation of OA levels by 20E and JH in Drosophila females is discussed.

Adaptive Value of Genes Controlling the Level of Biogenic Amines in Drosophila

The effects of mutations that change the level of biogenic amines (octopamine and dopamine) on stress-reactivity and fitness of Drosophila imagoes are considered. It has been shown that (1) the biogenic amines represent an important but not triggering factor of the development of stress reaction; (2) under normal conditions, reproduction is regulated by genes that control dopamine metabolic pathways (indirectly via regulation of the juvenile hormone level). Under unfavorable conditions, reproduction is regulated by genes that control octopamine metabolism; (3) heat-stress adaptation depends on expression of genes controlling the background level of dopamine.

Prolonged negative selection of Drosophila melanogaster for a character of adaptive significance disturbs stress reactivity

The metabolism of juvenile hormone by JH-esterase and JH-epoxide hydrolase, and octopamine by tyrosine decarboxylase were studied under normal and stress conditions in flies of two related lines of D. melanogaster. One was selected for high (HA line) and another for low (LA line) male sexual activity for more than 700 generations. It was demonstrated that prolonged selection for low male sexual activity results in considerable changes in both systems. Tyrosine decarboxylase activity in males and females of the LA line was sharply reduced as compared with those of the HA and controle Canton-S lines; JH-esterase and JH-epoxide hydrolase activities were decreased in females, and not in males, of the LA line. It was demonstrated that the response of both metabolic systems to heat stress is impaired in individuals of the LA line: the system of juvenile hormone metabolism does not respond to stress, and that of octopamine metabolism is decelerated. The role of juvenile hormone metabolism in male reproductive function is discussed.

Octapamine N-acetyltransferase activity from the cattle tick, Boophilus microplus

The metabolism of octopamine in the tick, Boophilus microplus, was studied by incubating synganglia, excised from adult females, with [ 3H]octopamine. The major metabolite co-chromatographed with N-acetyloctopamine and was predominantly found outside the nervous tissue in the surrounding saline. The N-acetyltransferase (NAT) activity was measured in enzyme preparations from adult synganglia using [ 3H]octopamine as the substrate and acetyl CoA as a co-factor. Under the assay conditions employed, the V max was 7 nmol/h/mg of protein and the apparent K m for octopamine was 4 μM. The N-acetylation of octopamine was inhibited by divalent cations (Zn 2+ and Cu 2+), β-carbolines, imipramine and a number of biogenic amines. NAT activity towards octopamine was also found in enzyme preparations from larvae of B. microplus and this enzyme had similar K m and V max values (4 μM and 10 nmol/h/mg of protein, respectively) to the neural enzyme and was inhibited both by β-carbolines and biogenic amines. These results suggest that N-acetylation is a key reaction in the metabolism of octopamine in the nervous system of the tick and may also play an important role in the metabolism of octopamine and other biogenic amines in larval stages of this acarine.

The effects of imipramine and iprindole on the metabolism of octopamine in the rat

Acute injections of imipramine and iprindole in rats produced significant decreases in the concentration of p-hydroxyphenylglycol (pHPG), a neutral metabolite of octopamine in brain at 6 and 24 hr after the administration of drugs. The 24-hr urinary levels of both free and total pHPG were reduced to 25–29% of control with acute administration of imipramine, while iprindole produced a 30% decrease in free pHPG. With chronic administration of imipramine, concentrations of pHPG in brain returned to normal, while the 24-hr urinary levels were still decreased (to 24%). Octopamine in brain was unaltered after both single and repeated injections of imipramine. Thus, these data suggest that the turnover of octopamine in brain is reduced after acute administration of imipramine and iprindole, while after chronic treatment with imipramine, turnover of octopamine in brain has returned to control levels.

Effects of drugs interfering with the metabolism of octopamine on blood pressure of rats

1. p-Octopamine injected in lateral ventricle of conscious spontaneously hypertensive rats d decreased systolic blood pressure (SBP). 2. Precursors of octopamine—tyrosine, tyramine and phenylethanolamine (PEA)—had the same effect. The administration of pargyline, a MAO inhibitor, which increased brain octopamine, resulted in a reduction of systolic blood pressure; and this decrease was greater after administration of octopamine precursors and PEA. 3. Similarly, drugs known to inhibit activity of phenylethanolamine N-methyl-transferase (PNMT) and to increase brain octopamine level such as SKF 64139 and DCMB decreased SBP. 4. p-Octopamine hypotension was not antagonized by piperoxan, yohimbine and prazosin, a relatively selective antagonist of post-synaptic α adrenoceptors. 5. These results suggest that octopamine may be involved in central blood pressure regulation, and the receptors sensitive to octapamine appeared to be distinct from those receptive to the catecholamines.

Octopamine in leeches—II. Synthesis, release and reuptake of octopamine by the ventral nerve cord of Erpobdella octoculata

1. Octopamine was synthesized by the ventral nerve cords of E. octuculata during in vitro incubation in radiolabelled tyrosine and tyramine. Trace amounts of dopamine were also synthesized from tyrosine and tyramine. 2. In vitro uptake of 3H-octopamine revealed the presence of a sodium sensitive and a sodium insensitive component which was linear up to 10.54 μM. The sodium sensitive component showed at least one component that was fully saturated at 1.54 μM octopamine, possessed a K m of approximately 4 × 10 −7 M and a V max of 15.5 mM/10 ventral nerve cord ganglia/min. 3. Release of preloaded 3H-octopamine from ventral nerve cords was by a calcium-dependent process. A high-potassium-induced calcium-dependent release was also demonstrated. 4. Hydroxymandelic acid production was decreased in the presence of iproniazid phosphate suggesting the presence of a monoamine oxidase. 5. The synthesis, release, reuptake and metabolism of octopamine are discussed in the light of octopamine as a central transmitter in the leech.

Metabolism of octopamine in vitro by monoamine oxidase in some rat tissues

The deamination in vitro of DL-octopamine by MAO in rat brain, heart, kidney, liver and vas deferens has been studied by a radiochemical method. Kinetic constants for octopamine metabolism, as well as its sensitivity to inhibition by the irreversible MAO inhibitor clorgyline are described for each tissue. On the basis of the inhibition data, it was concluded that octopamine is metabolized preferentially by type A MAO in heart, kidney and vas deferens. However, in brain and liver, type B MAO is also responsible for a significant proportion of total octopamine metabolism. These studies are discussed in relation to current ideas about the regulation of octopamine concentrations in animal tissues, and the possible importance of this amine in mammalian physiology.

Platelet Uptake of Octopamine and Norepinephrine in Hepatic Encephalopathy

To explore platelets as a model of intracellular amine metabolism in liver disease, we studied platelet uptake of octopamine (OA) in controls and patients with hepatic encephalopathy (HE) and the influence of OA and plasma from patients with HE on platelet norepinephrine uptake. Normal platelets incubated at 37°C actively accumulate OA. A high ratio of platelet OA concentration to plasma concentration (30:1) and inhibition of platelet OA uptake at reduced temperature suggests uptake by an active process. More than 90% of OA accumulated by platelets is recovered intact after 1 hr. Thrombin released 40% of platelet OA, suggesting sequestration within amine storage granules. OA inhibits the uptake of [3H]norepinephrine by platelets, suggesting that these substances share the same transfer system. Platelets of patients with HE demonstrated decreased uptake of OA and norepinephrine. Inhibition of platelet OA uptake was proportional to the clinical stage of HE. Plasma from patients with HE inhibited norepinephrine uptake by normal platelets. These findings suggest that plasma OA and/or other amines are taken up by platelets where they are protected from degradation. The reduced uptake of OA and norepinephrine by platelets from patients with HE could result from uptake blockade by intraplatelet amines and/or inhibition of platelet amine uptake by plasma amines. The demonstration of altered platelet OA and norepinephrine metabolism in patients with encephalopathy suggest that this model may be useful for the study of intracellular amines in liver disease.

Octopamine metabolism in invertebrates (Locusta, Astacus, Helix): Evidence for N-acetylation in arthropod tissues

1. 1. Various tissues of adult Locusta migratoria, Astacus leptodactylus, Mytilus edulis and Helix pomatia were analyzed for monoamine oxidase (MAO) and N-acetyltransferase activity directed against octopamine. 2. 2. MAO activity against octopamine was detectable in Mytilus muscle and Locusta Malpighian tubules. No activity was found in any other tissue of the species studied ( Astacus not investigated). 3. 3. Low MAO activity against 5-hydroxytryptamine (5-HT) and dopamine (DA) was present in Helix tissues (about 1% of that found in rabbit tissues). 4. 4. N-Acetylation of octopamine, 5-HT and DA was prominent in Locusta nerve tissue and Malpighian tubules, and high in other locust tissues and in Astacus nerve tissue. Relatively low activity was found in skeletal muscle of these species. 5. 5. N-Acetylation of octopamine was enhanced by the addition of acetyl CoA. With 14C-labelled acetyl CoA, the label appeared in the acetylated product, which was identified as N-acetyl-octopamine. 6. 6. Addition of acetylcholine and eserine enhanced N-acetylation of octopamine in locust nerve tissue (by inhibiting cholin-acetylase which competes for acetyl CoA), but not in other locust tissues and in crayfish tissues. 7. 7. No N-acetylase activity was found in Helix and Mytilus. 8. 8. It is concluded that N-acetylation is the predominant mechanism of octopamine metabolism in arthropod tissues, particularly in the nervous system.

A solid silver clip for induction of predictable levels of renal hypertension in the rat.

A solid silver clip for induction of predictable levels of renal hypertension in the rat.