Octopamine uptake and metabolism in the insect nervous system

Drosophila development, physiology, behavior, and lifespan are influenced by altered dietary composition

Diet profoundly influences the behavior of animals across many phyla. Despite this, most laboratories using model organisms, such as Drosophila, use multiple, different, commercial or custom-made media for rearing their animals. In addition to measuring growth, fecundity and longevity, we used several behavioral and physiological assays to determine if and how altering food media influence wild-type (Canton S) Drosophila melanogaster, at larval, pupal, and adult stages. Comparing 2 commonly used commercial food media we observed several key developmental and morphological differences. Third-instar larvae and pupae developmental timing, body weight and size, and even lifespan significantly differed between the 2 diets, and some of these differences persisted into adulthood. Diet was also found to produce significantly different thermal preference, locomotory capacity for geotaxis, feeding rates, and lower muscle response to hormonal stimulation. There were no differences, however, in adult thermal preferences, in the number or viability of eggs laid, or in olfactory learning and memory between the diets. We characterized the composition of the 2 diets and found particularly significant differences in cholesterol and (phospho)lipids between them. Notably, diacylglycerol (DAG) concentrations vary substantially between the 2 diets, and may contribute to key phenotypic differences, including lifespan. Overall, the data confirm that 2 different diets can profoundly influence the behavior, physiology, morphology and development of wild-type Drosophila, with greater behavioral and physiologic differences occurring during the larval stages.

Action of octopamine and tyramine on muscles of Drosophila melanogaster larvae

Octopamine (OA) and tyramine (TA) play important roles in homeostatic mechanisms, behavior, and modulation of neuromuscular junctions in arthropods. However, direct actions of these amines on muscle force production that are distinct from effects at the neuromuscular synapse have not been well studied. We utilize the technical benefits of the Drosophila larval preparation to distinguish the effects of OA and TA on the neuromuscular synapse from their effects on contractility of muscle cells. In contrast to the slight and often insignificant effects of TA, the action of OA was profound across all metrics assessed. We demonstrate that exogenous OA application decreases the input resistance of larval muscle fibers, increases the amplitude of excitatory junction potentials (EJPs), augments contraction force and duration, and at higher concentrations (10−5 and 10−4 M) affects muscle cells 12 and 13 more than muscle cells 6 and 7. Similarly, OA increases the force of synaptically driven contractions in a cell-specific manner. Moreover, such augmentation of contractile force persisted during direct muscle depolarization concurrent with synaptic block. OA elicited an even more profound effect on basal tonus. Application of 10−5 M OA increased synaptically driven contractions by ∼1.1 mN but gave rise to a 28-mN increase in basal tonus in the absence of synaptic activation. Augmentation of basal tonus exceeded any physiological stimulation paradigm and can potentially be explained by changes in intramuscular protein mechanics. Thus we provide evidence for independent but complementary effects of OA on chemical synapses and muscle contractility.

Decrease in juvenile hormone level as a result of genetic ablation of the corpus allatum 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.

Mechanisms of age-specific regulation of dopamine metabolism by juvenile hormone and 20-hydroxyecdysone in Drosophila females

20-hydroxyecdysone (20E) and the juvenile hormone (JH) have an age-specific effect on total dopamine (DA) content in Drosophila (Gruntenko and Rauschenbach 2008). Earlier we studied the mechanism of influence of 20E and JH on DA metabolism in young females (Rauschenbach et al. in J Insect Physiol 53:587-591, 2007a: Arch Insect Biochem Physiol 65:95-102, 2008a; Gruntenko et al. in Arch Insect Biochem Physiol 72:263-269, 2009). Here we investigate the effects of 20E and JH on the activities of the alkaline phosphatase (ALP), tyrosine hydroxylase (TH) and DA-dependent arylalkylamine N-acetyltransferase (AANAT) in mature females of wild type D. virilis under normal conditions and under heat stress (38°C). 20E feeding of the flies led to a substantial decrease in ALP and TH activities and to an increase in AANAT activity in mature females. JH application resulted in an increasing of ALP and TH activities, but did not influence AANAT activity in mature females. A rise in JH and 20E levels was found to change ALP and TH stress reactivities. Mechanisms of age-specific regulation of DA level by 20E and JH in Drosophila females are discussed.

Biogenic amines modulate pulse rate in the dorsal blood vessel of Lumbriculus variegatus

The biogenic amines are widespread regulators of physiological processes, and play an important role in regulating heart rate in diverse organisms. Here, we present the first pharmacological evidence for a role of the biogenic amines in the regulation of dorsal blood vessel pulse rate in an aquatic oligochaete, Lumbriculus variegatus (Müller, 1774). Bath application of octopamine to intact worms resulted in an acceleration of pulse rate, but not when co-applied with the adenylyl cyclase inhibitor MDL-12,330a. The phosphodiesterase inhibitor theophylline mimicked the effects of OA, but the polar adenosine receptor antagonist 8(p-sulphophenyl)theophylline was significantly less potent than theophylline. Pharmacologically blocking synaptic reuptake of the biogenic amines using the selective 5-HT reuptake blocker fluoxetine or various tricyclic antidepressants also accelerated heart rate. Depletion of the biogenic amines by treatment with the monoamine vesicular transporter blocker reserpine dramatically depressed pulse rate. Pulse rate was partially restored in amine-depleted worms after treatment with octopamine or dopamine, but fully restored following treatment with serotonin. This effect of 5-HT was weakly mimicked by 5-methoxytryptamine, but not by alpha-methylserotonin; it was completely blocked by clozapine and partially blocked by cyproheptadine. Because they are known to orchestrate a variety of adaptive behaviors in invertebrates, the biogenic amines may coordinate blood flow with behavioral state in L.variegatus.

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.

The PM1 neurons, movement sensitive centrifugal visual brain neurons in the locust: anatomy, physiology, and modulation by identified octopaminergic neurons

The locust's optic lobe contains a system of wide-field, multimodal, centrifugal neurons. Two of these cells, the protocerebrum-medulla-neurons PM4a and b, are octopaminergic. This paper describes a second pair of large centrifugal neurons (the protocerebrum-medulla-neurons PM1a and PM1b) from the brain of Locusta migratoria based on intracellular cobalt fills, electrophysiology, and immunocytochemistry. They originate and arborise in the central brain and send processes into the medulla of the optic lobe. Double intracellular recording from the same cell suggests input in the central brain and output in the optic lobe. The neurons show immunoreactivity to gamma-amino-butyric acid and its synthesising enzyme, glutamate decarboxylase. The PM1 cells are movement sensitive and show habituation to repeated visual stimulation. Bath application of octopamine causes the response to dishabituate. A very similar effect is produced by electrical stimulation of one of an octopaminergic PM4 neuron. This effect can be blocked by application of the octopamine antagonists, mianserin and phentolamine. This readily accessible system of four wide-field neurons provides a system suitable for the investigation of octopaminergic effects on the visual system at the cellular level.

Role of arylalkylamine N-acetyltransferase in regulation of biogenic amines levels by gonadotropins in Drosophila

The effect of 20-hydroxyecdysone (20E) and the juvenile hormone (JH) on the activity of the arylalkylamine N-acetyltransferase (AANAT) was studied in young females of wild-type D. virilis and D. melanogaster. 20E feeding of the flies led to a decrease in AANAT activity in both species when dopamine (DA) was used as substrate, but did not affect the enzyme activity when octopamine (OA) was used as substrate. JH application increased AANAT activity with DA as substrate in both species, but did not change it with OA as substrate. AANAT activity was also measured in young females of a JH-deficient strain of D. melanogaster, apterous ( 56f ). A decrease in the enzyme activity was observed in the mutant females as compared to wild-type. Mechanisms of regulation of DA level by gonadotropins in Drosophila are discussed.

Are Caenorhabditis elegans receptors useful targets for drug discovery: pharmacological comparison of tyramine receptors with high identity from C. elegans (TYRA-2) and Brugia malayi (Bm4)

The biogenic amine, tyramine (TA), modulates a number of key processes in nematodes and a number of TA-specific receptors have been identified. In the present study, we have identified a putative TA receptor (Bm4) in the recently completed Brugia malayi genome and compared its pharmacology to its putative Caenorhabditis elegans orthologue, TYRA-2, under identical expression and assay conditions. TYRA-2 and Bm4 are the most closely related C. elegans and B. malayi BA receptors and differ by only 14aa in the TM regions directly involved in ligand binding. Membranes from HEK-293 cells stably expressing Bm4 exhibited specific, saturable, high affinity, [(3)H]LSD and [(3)H]TA binding with K(d)s of 18.1+/-0.93 and 15.1+/-0.2 nM, respectively. More importantly, both TYRA-2 and Bm4 TA exhibited similar rank orders of potencies for a number of potential tyraminergic ligands. However, some significant differences were noted. For example, chloropromazine exhibited an order of magnitude higher affinity for Bm4 than TYRA-2 (pK(i)s of 7.6+/-0.2 and 6.49+/-0.1, respectively). In contrast, TYRA-2 had significantly higher affinity for phentolamine than Bm4. These results highlight the utility of the nearly completed B. malayi genome and the importance of using receptors from individual parasitic nematodes for drug discovery.

Functionally distinct dopamine and octopamine transporters in the CNS of the cabbage looper moth

A cDNA was cloned from the cabbage looper Trichoplusia ni based on similarity to other cloned dopamine transporters (DATs). The total nucleotide sequence is 3.8 kb in length and contains an open reading frame for a protein of 612 amino acids. The predicted moth DAT protein (TrnDAT) has greatest amino acid sequence identity with Drosophila melanogasterDAT (73%) and Caenorhabditis elegansDAT (51%). TrnDAT shares only 45% amino acid sequence identity with an octopamine transporter (TrnOAT) cloned recently from this moth. The functional properties of TrnDAT and TrnOAT were compared through transient heterologous expression in Sf9 cells. Both transporters have similar transport affinities for DA (Km 2.43 and 2.16 micro m, respectively). However, the competitive substrates octopamine and tyramine are more potent blockers of [3H]dopamine (DA) uptake by TrnOAT than by TrnDAT. D-Amphetamine is a strong inhibitor and l-norepinephrine a weak inhibitor of both transporters. TrnDAT-mediated DA uptake is approximately 100-fold more sensitive to selective blockers of vertebrate transporters of dopamine and norepinephrine, such as nisoxetine, nomifensine and dibenzazepine antidepressants, than TrnOAT-mediated DA uptake. TrnOAT is 10-fold less sensitive to cocaine than TrnDAT. None of the 15 monoamine uptake blockers tested was TrnOAT-selective. In situ hybridization shows that TrnDAT and TrnOAT transcripts are expressed by different sets of neurons in caterpillar brain and ventral nerve cord. These results show that the caterpillar CNS contains both a phenolamine transporter and a catecholamine transporter whereas in the three invertebrates whose genomes have been completely sequenced only a dopamine-selective transporter is found.

Characterization and purification of polymorphic arylalkylamine N-acetyltransferase from the American cockroach, Periplaneta americana

We separated two forms of arylalkylamine N-acetyltransferase (AANAT) from various organs of the American cockroach, Periplaneta americana. Both forms of the enzyme had an equivalent molecular mass of 28 kDa. One form isolated from the testicular accessory glands had high enzyme activity at acidic pHs. The isoelectric point was 5-6 and the substrate specificity was wider than the other type. The other isolated form from female midguts had a higher level of enzyme activity at basic pHs. These findings suggested that P. americana contains polymorphic AANAT, as is the case in Drosophila melanogaster. These forms differed not only in pH specificity, and substrate specificity but in chromatographic behavior and kinetic properties. Most of the organs we examined contained a mixture of the two forms since two types of AANAT activity were separated in different chromatographic fractions when two pH conditions were used for activity measurement.

Insecticidal activity of essential oils: octopaminergic sites of action

A study was conducted to determine the insecticidal activity and mechanism of action of three essential oils (eugenol, alpha-terpineol and cinnamic alcohol) and an equal part mixture (3-blend) against American cockroaches (Periplaneta americana). To address species differences in response to treatment with the test oils, Carpenter ants (Camponotus pennsylvanicus De Geer), and German cockroaches (Blattella germanica) were included in this study. Exposed American cockroaches demonstrated hyperactivity followed by hyperextension of the legs and abdomen, then fast knockdown or quick immobilization followed by death. Ants and German cockroaches showed fast immobilization/knockdown followed by mortality. The 1:1:1 mixture (3-blend) was substantially effective against all test insects. One of the most remarkable observations was the increased frequency of heartbeats of American cockroaches in response to topical application of test oils. The changes in the pattern of cAMP level was biphasic. A significant increase in the cAMP level was found in response to 1 nmol/ml of eugenol, or 3-blend or 10 nmol/ml of alpha-terpineol. At higher concentrations a significant decrease in cAMP level was found. Blockage of octopamine receptors binding sites was also illustrated at lower concentrations of the test chemicals as judged by the decreased binding activity of [3H]octopamine to its receptors.

IN CONCLUSION

(1) test oils are neuro-insecticides and their insecticidal activity is species-dependent; (2) a synergistic effect of the three oils was found when they were equally mixed (3-blend); and (3) the octpaminergic system mediates the insecticidal activity of eugenol, alpha-terpienol and the 3-blend.

Characterization and developmental regulation of tyramine-beta-hydroxylase in the CNS of the moth, Manduca sexta

Octopamine (OA) is present in insect nervous tissue, but little is known about its biosynthesis. In the CNS of Manduca sexta, OA levels increase markedly during postembryonic adult development. To study this increase, we developed an assay for tyramine-beta-hydroxylase, the putatively rate-limiting enzyme for OA biosynthesis. Tyramine-beta-hydroxylase activity in extracts of M. sexta CNS tissue: (1) was time- and protein-dependent, and with protein concentrations up to 2 microg/microl, was linear for 20 min; (2) had a pH optimum of 7.0 for conversion of tyramine to OA; (3) required ascorbate, copper, and catalase; and (4) had an apparent K(M, tyramine) of 0.22+/-0.04 mM. These characteristics resemble those of the mammalian enzyme dopamine-beta-hydroxylase, suggesting that these two enzymes are functionally related. During adult development, tyramine-beta-hydroxylase activity increased 11-fold in the brain and 9-fold in the abdominal ganglia, paralleling increases in OA levels in those CNS structures during metamorphosis. The apparent kinetic constants of tyramine-beta-hydroxylase suggested that the amount of this enzyme present in the tissues increases. The increase in OA levels during adult development thus appears to be due to an increase in the level of enzyme available for OA synthesis and may reflect an increase in the number of octopaminergic neurons.

Membrane lipid metabolism and phospholipase activity in insect Spodoptera frugiperda 9 ovarian cells

Although there is increasing use of insect ovarian Sf9 cells for the production of recombinant proteins, namely, via the baculovirus vector expression system, little is known about the lipids in the cell membrane and whether endogenous phospholipases are present for regulation of the cell membrane lipids. In this study, analysis of membrane lipids of Sf9 cells indicated the presence of phosphatidylethanolamine (PE) (diacyl type) and phosphatidylcholine as major phospholipids, followed by phosphatidylserine and phosphatidylinositol (PI), and only trace amounts of ethanolamine plasmalogen. These phospholipids contain high proportions of monoenoic fatty acids, e.g., 16:1 and 18:1, which comprise more than 70% of the total fatty acids although small amounts of polyunsaturated fatty acids such as 18:2 and 20:4 are also present. When Sf9 cells were incubated in a culture medium containing [14C]oleic acid and [14C]arachidonic acid, a large portion of the labels were incorporated into membrane phospholipids. Using [14C]arachidonoyl-phospholipids as substrates for incubation with cell homogenate and subcellular fractions, results indicate the presence of a ca(2+)-independent phospholipase A (PLA2) in the Sf9 cell cytosol fraction. This PLA2 shows a high preference for hydrolysis of PE and is active at a pH range of 7-9. Unlike the brain cells which contain active phospholipase C (PLC) specific for phosphatidylinositol, only limited amount of diacylglycerol (DAG) was released from [14C]arachidonoyl-PE in the Sf9 cells. Taken together, this study demonstrates active metabolism of membrane phospholipids in Sf9 cells, most likely mediated by acyltransferases and PLA2. Furthermore, despite the absence of PLC for PI, limited amount of DAG could be generated through hydrolysis of PE.

Insect neurotransmission: neurotransmitters and their receptors

The roles of acetylcholine, dopamine, octopamine, tyramine, 5-hydroxytryptamine, histamine, glutamate, 4-aminobutanoic acid (gamma-aminobutyric acid) and a range of peptides as insect neurotransmitters are evaluated in terms of the criteria used to identify transmitters. Of the biogenic amines considered, there is good evidence that acetylcholine, dopamine, octopamine, 5-hydroxytryptamine, and histamine should be considered to be neurotransmitters, but the case for tyramine is less convincing at the moment. The evidence supporting neurotransmitter roles for glutamate and gamma-aminobutyric acid at specific insect synapses is overwhelming, but much work remains to be undertaken before the full significance of these molecules in the insect nervous system is appreciated. Attempts to characterise biogenic amine and amino acid receptors using pharmacological and molecular biological techniques have revealed considerable differences between mammalian and insect receptors. The number of insect neuropeptides isolated and identified has increased spectacularly in recent years, but genuine physiological or biochemical functions can be assigned to very few of these molecules. Of these, only proctolin fulfills the criteria expected of a neurotransmitter, and the recent discovery of proctolin receptor antagonists should enable the biology of this pentapeptide to be explored fully.

Monoamine uptake in insect synaptosomal preparations

Biochemical studies of mammalian synaptosomal nerve fractions indicate the existence of multiple transporter proteins important for the termination of synaptic transmission by each of several monoamines. In insects, however, data on monoamine uptake has been limited to the study of whole tissue preparations, making it unclear whether neuronal (as opposed to glial) uptake is a significant mechanism in the insect. The present experiments elucidate the difficulties that have limited the use of insect synaptosomal preparations for characterizing amine reuptake. Key procedural improvements, including the utilization of carrier protein for tracer separation and the use of receptor antagonists to decrease non-specific membrane binding are described. With these and other modifications, reproducible sodium-dependent and cocaine-inhibitable dopamine and octopamine uptake are described in synaptosomal-containing preparations from insect brain and ganglia. These studies therefore support the existence of specific Na(+)-dependent uptake mechanisms in insect neurons.

Cloning, expression, and localization of a chloride-facilitated, cocaine-sensitive serotonin transporter from Drosophila melanogaster

We report here on the isolation and characterization of a serotonin (5HT) transporter from Drosophila melanogaster. A 3.1-kb complementary DNA clone (dSERT) was found to encode a protein of 622 amino acid residues with a predicted molecular mass of approximately 69 kDa and a putative transmembrane topology characteristic of cloned members of the mammalian Na+/Cl- neurotransmitter cotransporter gene family. dSERT displays highest overall amino acid sequence identity with the mammalian 5HT (51%), norepinephrine (47%), and dopamine (47%) transporters and shares with all transporters 104 absolutely conserved amino acid residues. Upon transient expression in HeLa cells, dSERT exhibited saturable, high-affinity, and sodium-dependent [3H]5HT uptake with estimated Km and Vmax values of approximately 500 nM and 5.2 x 10(-18) mol per cell per min, respectively. In marked contrast to the human SERT (hSERT), 5HT-mediated transport by dSERT was not absolutely dependent on extracellular Cl-, while the sodium-dependent uptake of 5HT was facilitated by increased extracellular Cl- concentrations. dSERT displays a pharmacological profile and rank order of potency consistent with, but not identical to, mammalian 5HT transporters. Comparison of the affinities of various compounds for the inhibition of 5HT transport by both dSERT and hSERT revealed that antidepressants were 3- to 300-fold less potent on dSERT than on hSERT, while mazindol displayed approximately 30-fold greater potency for dSERT. Both cocaine and RTI-55 inhibited 5HT uptake by dSERT with estimated inhibition constants of approximately 500 nM, while high concentrations (> 10 microM) of dopamine, norepinephrine, octopamine, tyramine, and histamine failed to inhibit transport. In situ hybridization reveals the selective expression of dSERT mRNA to specific cell bodies in the ventral ganglion of the embryonic and larval Drosophila nervous system with a distribution pattern virtually identical to that of 5HT-containing neurons. The dSERT gene was mapped to position 60C on chromosome 2. The availability of the gene encoding the unique ion dependence and pharmacological characteristics of dSERT may allow for identification of those amino acid residues and structural motifs that confer the pharmacologic specificity and genetic regulation of the 5HT transport process.

Acetyl CoA generation and N-acetylation of serotonin (5HT) in the mosquito, Aedes togoi

Acetyl CoA synthetase (ACS; EC 6.2.1.1) was studied in the mosquito, Aedes togoi, by a novel assay which coupled the acetyl-CoA generated to p-aminosalicylic acid (ASA). The N-acetylated product was determined by an HPLC-fluorimetric procedure. High ACS activity was observed in the newly-pupated pupae of both sexes and in the adult male mosquito whose activity was five times that of the female. Acetyl CoA-dependent N-acetyltransferase (NAT; EC 2.3.1.5) activity toward serotonin (5HT) was also studied using HPLC-electrochemical detection (HPLC-ECD). A progressive increase in the 5HT-NAT activity was observed from the fourth-instar larvae to the adult mosquito with the latter showing 6-fold higher activity in the head compared to the abdomen-thorax region. Kinetic studies on the pupal enzyme extracts showed that the apparent Km values for 5HT and acetyl CoA were 63 and 66 microM respectively. Tryptamine inhibited 5HT-NAT non-competitively with a Ki value of 8 microM.

A cocaine-sensitive Drosophila serotonin transporter: cloning, expression, and electrophysiological characterization

A cocaine-sensitive, high-affinity Drosophila serotonin (5-hydroxytryptamine; 5HT) transporter cDNA, denoted dSERT1, was isolated and characterized in oocytes. dSERT1 shows little transport of other monoamines and is Na+ and Cl- dependent. Sequence analysis indicates 12 putative transmembrane domains and strong homologies (approximately 50%) among dSERT1 and mammalian 5HT, norepinephrine, and dopamine transporters. Interestingly, the pharmacological properties of dSERT1, including sensitivity to antidepressants, are more similar to those of mammalian catecholamine transporters than to mammalian 5HT transporters. Two-electrode voltage-clamp analysis demonstrated 5HT-induced, voltage-dependent currents. Cloning and characterization of dSERT1 adds significantly to our knowledge of the diversity of 5HT transporters with regard to primary sequence, pharmacological profile, and permeation properties.

Properties of an arylalkylamine N-acetyltransferase from the nematode, Ascaridia galli

1. An arylalkylamine N-acetyltransferase (NAT) of the parasitic nematode, Ascaridia galli was studied using either [14C]serotonin (5-HT) or [14C]octopamine (OA) as substrates and with acetyl-CoA as the donor of the acetate group. 2. The NAT activity towards 5-HT and OA co-eluted from a size-exclusion column and appeared to have an M(r) of around 30,000. The enzyme had apparent Km values of 540 +/- 100 microM (+/- SEM) and 33 +/- 4 microM (+/- SEM) for 5-HT and octopamine, respectively, when assayed in the presence of 1 mM acetyl-CoA. 3. High levels of NAT were found in the gonads of male and female worms and the muscle/body wall. 4. N-acetylation was strongly inhibited by Cu2+ but not by other divalent metal ions and the effect of a number of compounds including biogenic amines, formamidines, hydrazines, and beta-carbolines on the arylalkylamine N-acetyltransferase activity was studied.

Cocaine as a naturally occurring insecticide

Although cocaine has a fascinating and complex medicinal history in man, its natural function in plants is unknown. The present studies demonstrate that cocaine exerts insecticidal effects at concentrations which occur naturally in coca leaves. Unlike its known action on dopamine reuptake in mammals, cocaine's pesticidal effects are shown to result from a potentiation of insect octopaminergic neurotransmission. Amine-reuptake blockers of other structural classes also exert pesticidal activity with a rank order of potency distinct from that known to affect vertebrate amine transporters. These findings suggest that cocaine functions in plants as a natural insecticide and that octopamine transporters may be useful sites for targeting pesticides with selectivity toward invertebrates.

Sulphate conjugation of serotonin and N-acetylserotonin in the mosquito, Aedes togoi

The sulphate conjugation of serotonin and N-acetylserotonin (NAS) was studied in the mosquito, Aedes togoi, using a high-pressure liquid chromatography-radioisotopic procedure. This involved the transfer of the sulphate group from 3'-phosphoadenosine-5'-phosphosulphate (PAP35S) to serotonin or NAS by phenolsulphotransferase (PST). NAS, the acetylated product, is less polar than serotonin but it is a better substrate of PST. Its removal would conceivably be facilitated by sulphate conjugation which renders it more water-soluble. This sequential two-step reaction, comprising N-acetylation of serotonin and sulphate conjugation of the acetylated product (NAS) was also demonstrated in vitro. The developmental profile of PST activity using NAS as substrate showed that peak activity occurred at pupation and increased progressively for a few days after emergence of the adult. Based on the selective inhibition of the "P" form of PST by 2,6-dichloro-4-nitrophenol (DCNP), the sulphate conjugation of NAS appeared to be catalysed by the "M" form of PST.

Analysis of the biogenic amines in the central nervous system of the tobacco hornworm by high-performance liquid chromatography with 16-sensor electrochemical detection

A method was developed to analyze biogenic amines in extracts of the central nervous system of the tobacco hornworm, Manduca sexta by high-performance liquid chromatography with 16-sensor electrochemical detection (n-EC-HPLC). The amines, precursors, and metabolites were separated in two dimensions. The first dimension involves separation based upon retention time by reversed-phase HPLC, while the second dimension involves separation based upon the characteristic oxidation potentials achieved by n-EC. Biogenic amine identification was based upon maximum oxidation potential and peak height ratios in addition to retention time. The improved resolving power of this method allows for a simplified sample preparation procedure and simultaneous determination of a wide range of compounds, including phenylethylamine, catecholamines, indoleamines, and some of their precursors and metabolites.

A dopamine- and octopamine-sensitive adenylate cyclase in the nervous system of Octopus vulgaris

1. Adenylate cyclase activity was assayed in the optic lobe of Octopus vulgaris. 2. Both octopamine and dopamine stimulate the octopus adenylate cyclase, apparently by competing with the same receptor site. 3. (+/-)-2-Amino-6,7-dihydroxy-1,2,3,4-tetrahydronaphthalene-HBr (6,7-ADTN) and a number of phenylethanolamine derivatives stimulate the octopus adenylate cyclase activity. 4. The dopamine D-1 antagonists R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl- 2,3,4,5-tetrahydro-1H-3-benzazepine-HCl (SCH-23390) and (+/-)-7-bromo-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H- 3-benzazepine-HCl (SKF-83566) are unable to antagonize the effects of dopamine and octopamine, and similarly ineffective is the agonist (+/-)-1-phenyl-2,3,4,5-tetrahydro-1H-3- benzazepine-7,8-diol-HCl (SKF-38393). 5. No detectable binding of labelled SCH-23390 occurs on membrane preparations from octopus optic lobe.