Products of biogenic amine metabolism in the lobster: sulfate conjugates

Induced thermal stress on serotonin levels in the blue swimmer crab, Portunus pelagicus

The temperature of habitat water has a drastic influence on the behavioral, physiological and biochemical mechanisms of crustaceans. Hyperglycemia is a typical response of many aquatic animals to harmful physical and chemical environmental changes. In crustaceans increased circulating crustacean hyperglycemic hormone (CHH) and hyperglycemia are reported to occur following exposure to several environmental stress. The biogenic amine, serotonin has been found to modulate the CHH levels and oxidation of serotonin into its metabolites is catalysed by monoamine oxidase. The blue swimmer crab, Portunus pelagicus is a dominant intertidal species utilized throughout the indo-pacific region and is a particularly important species of Palk bay. It has high nutritional value and delicious taste and hence their requirements of capture and cultivation of this species are constantly increasing. This species experiences varying and increasing temperature levels as it resides in an higher intertidal zone of Thondi coast. The present study examines the effect of thermal stress on the levels of serotonin and crustacean hyperglycemic hormone in the hemolymph of P. pelagicus and analyzes the effect of the monoamine oxidase inhibitor, pargyline on serotonin and CHH level after thermal stress. The results showed increased levels of glucose, CHH and serotonin on exposure to 26 °C in control animals. Pargyline injected crabs showed highly significant increase in the levels of CHH and serotonin on every 2 °C increase or decrease in temperature. A greater CHH level of 268.86±2.87 fmol/ml and a greater serotonin level of 177.69±10.10 ng/ml was observed at 24 °C. This could be due to the effect of in maintaining the level of serotonin in the hemolymph and preventing its oxidation, which in turn induces hyperglycemia by releasing CHH into hemolymph. Thus, the study demonstrates the effect of thermal stress on the hemolymph metabolites studied and the role of pargyline in elevating the levels of serotonin and CHH on thermal stress in the blue swimmer crab, P. pelagicus.

Serotonin catabolism depends upon location of release: characterization of sulfated and gamma-glutamylated serotonin metabolites in Aplysia californica

Serotonin is a vital neurotransmitter for the functioning of the nervous system in species throughout the animal phyla. Despite its ubiquitous nature, the metabolism of this molecule has yet to be completely elucidated in even the most basic of organisms. Two novel serotonin catabolites, serotonin-O-sulfate and gamma-glu-serotonin-O-sulfate, are chemically characterized using capillary electrophoresis with wavelength-resolved fluorescence detection and electrospray mass spectrometry, and the formation of gamma-glu-serotonin in Aplysia californica is confirmed. These novel compounds appear to be synthesized enzymatically, and known mammalian enzymes exist for all serotonin transformations observed here. The pathway of serotonin inactivation depends upon the type of neuronal tissue subjected to neurotransmitter incubation, with assorted serotonin products observed in distinct locations. Initially demonstrated to be in the metacerebral cell (MCC) soma, the new serotonin metabolite serotonin-O-sulfate may contribute to important functions in the serotonergic system beyond simple serotonin inactivation.

Chronic alterations in serotonin function: dynamic neurochemical properties in agonistic behavior of the crayfish, Orconectes rusticus

The biogenic amine serotonin [5-hydroxytryptamine (5-HT)] has received considerable attention for its role in behavioral phenomena throughout a broad range of invertebrate and vertebrate taxa. Acute 5-HT infusion decreases the likelihood of crayfish to retreat from dominant opponents. The present study reports the biochemical and behavioral effects resulting from chronic treatment with 5-HT-modifying compounds delivered for up to 5 weeks via silastic tube implants. High performance liquid chromatography with electrochemical detection (HPLC-ED) confirmed that 5,7-dihydroxytryptamine (5,7-DHT) effectively reduced 5-HT in all central nervous system (CNS) areas, except brain, while a concurrent accumulation of the compound was observed in all tissues analyzed. Unexpectedly, two different rates of chronic 5-HT treatment did not increase levels of the amine in the CNS. Behaviorally, 5,7-DHT treated crayfish exhibited no significant differences in measures of aggression. Although treatment with 5-HT did not elevate 5-HT content in the CNS, infusion at a slow rate caused animals to escalate more quickly while 5-HT treatment at a faster rate resulted in slower escalation. 5,7-DHT is commonly used in behavioral pharmacology and the present findings suggest its biochemical properties should be more thoroughly examined. Moreover, the apparent presence of powerful compensatory mechanisms indicates our need to adopt an increasingly dynamic view of the serotonergic bases of behavior like crayfish aggression.

Effects of aggression and wing removal on brain serotonin levels in male crickets, Gryllus bimaculatus

When pairs of adult male crickets (Gryllus bimaculatus) that had been housed individually for 7 days were placed together, they fought, and dominant-subordinate relationships were formed within 1min. Aggressive behavior by the dominant male was repeated during the period in which the two males were kept together. Immediately after 10min of aggressive interaction, brain serotonin (5-hydroxytryptamine, 5-HT) levels were unchanged in dominant males and significantly reduced in subordinate males. The emission of aggressive song by dominant males is known to be abolished by removal of the wings. All wings were thus removed from male crickets. After 7 days of isolation, pairs of wingless males were placed together. The wingless males fought and formed dominant-subordinate relationships within 1min. The wingless, dominant males displayed aggressive behavior. Brain 5-HT levels in the wingless males were reduced immediately after 10min of aggressive interaction, and no significant differences in brain 5-HT levels were detected between the dominant and subordinate males, unlike the case for intact males. These data indicate a difference in brain serotonergic activity between dominant and subordinate male crickets during aggressive interaction, and suggest that aggressive behavior by dominant male crickets rapidly reduce brain 5-HT levels in subordinate ones. Furthermore, the data suggest that aggressive song is responsible for the change in brain 5-HT levels.

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.

Purification of toxic compounds from larvae of the gray fleshfly: the identification of paralysins

Larval haemolymph of Neobellieria bullata (Insecta, Diptera) is highly toxic to adults of the same species: injection causes instant paralysis to death. Referring to their dramatic effect in adult insects the responsible compounds were designated paralysins. Two paralysins, soluble in organic solvents and heat stable, were chromatographically purified to homogeneity. They were identified by use of mass spectrometry and nuclear magnetic resonance respectively as beta-alanine-tyrosine (beta-Ala-Tyr) and as 3-hydroxy-kynurenine (3-HK). The quantities of beta-Ala-Tyr and 3-HK in the insect appear to increase steadily during larval development, with peak values prior to the pupal stage. These findings may contribute to a better understanding of some aspects of the process of insect metamorphosis. Orienting experiments in mammals suggest that both compounds, when injected intraspinally, are also neurotoxic to rats. In addition, cytotoxicity tests revealed that 3-HK, but not beta-Ala-Tyr is toxic to human neuroblastoma cells, rat primary cortex neurons as well as to rat glial cells.

Catabolism of dopamine and 5-hydroxytryptamine by monoamine oxidase in the ixodid tick, Amblyomma hebraeum

The purpose of this study was to assess biogenic amine catabolism in Amblyomma hebraeum Koch (an African cattle tick). We assayed haemolymph and saliva for a variety of biogenic amines (usually following injection of substrate into the haemolymph) in partially fed females using HPLC coupled to electrochemical detection. Dopamine (DA) and 5-hydroxytryptamine (5-HT) were rapidly converted to dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindoleacetic acid (5-HIAA) respectively, indicating that monoamine oxidase (MAO) constitutes a major catabolic pathway for biogenic amines in this species. We could not detect N-acetylated or gamma-glutamyl conjugated metabolites of these important neurotransmitters. [In a few samples we looked for but could not detect homovanillic acid or 3-methoxytyramine (O-methylated metabolites of DOPAC and DA respectively).] Deprenyl was about 44-72 times more potent an inhibitor of MAO than clorgyline when either DA or 5-HT was offered as substrate, suggesting that this MAO is of the MAOB type. Conversion of DA to DOPAC was also detected in several tissues incubated with DA in vitro; in descending order of MAO activity (pmol mg-1 h-1 at about 18 degrees C) tissues tested were: skeletal muscle (approximately 100), Malpighian tubule (approximately 50), ovary (approximately 45), salivary gland (approximately 30), midgut (approximately 20), and haemolymph (approximately 4-5). This study suggests that ticks differ considerably from insects in utilizing MAO as an important metabolic pathway for biogenic amines.

gamma-Glutamyl conjugation of 5-hydroxytryptamine (serotonin) in the earthworm (Lumbricus terrestris)

The conversion of 5-hydroxytryptamine to several potential metabolites was examined in the annelid earthworm (Lumbricus terrestris). 5-hydroxytryptamine and some related amines were found to be present in several tissues of the earthworm. Injection of 5-hydroxytryptamine into the body cavity of the earthworm resulted in the production of a gamma-glutamyl conjugate of 5-hydroxytryptamine. Incubations of the anterior nerve cord of the earthworm resulted in the accumulation of considerable amounts of 5-hydroxytryptamine and gamma-glutamyl 5-hydroxytryptamine in the incubation medium. The earthworm did not produce any N-acetyl 5-hydroxytryptamine and only very little 5-hydroxyindoleacetic acid. Experiments involving the injection of radiolabeled 5-hydroxytryptamine or coinjection of radiolabeled glutamic acid with unlabeled 5-hydroxytryptamine into the earthworm resulted in the production of radiolabeled gamma-glutamyl 5-hydroxytryptamine. This work demonstrates that the enzymatic conversion of 5-HT in the earthworm is markedly different from that of vertebrates and insects.

Identification and function of octopamine and tyramine conjugates in the Limulus visual system

Major metabolites of octopamine and tyramine in the Limulus nervous system are identified here as gamma-glutamyl octopamine and gamma-glutamyl tyramine. We show that these conjugates are normal products of amine metabolism in Limulus, and that they are normally present in octopamine-rich Limulus tissues. The synthesis of these conjugates is not restricted to nervous tissue, but the highest activity of gamma-glutamyl amine synthetase was measured in the CNS. Our interest in these molecules stems from our previous observations which showed that they were synthesized and stored in, and released from, the efferent fibers to Limulus eyes which modulate the sensitivity of the eyes to light. Here we provide direct evidence for the release of the conjugates from Limulus eyes in response to depolarization, and that gamma-glutamyl octopamine can increase the sensitivity of the lateral eye to light. Our observations lend support to the hypothesis that gamma-glutamyl octopamine may serve as an intercellular messenger in the Limulus visual system.

Preparation of dopamine 3-O-sulphate and dopamine 4-O-sulphate as reference substances and high-performance liquid chromatographic trace determination

Simple syntheses of the biologically important but hitherto difficult to obtain dopamine sulpho conjugates dopamine 3-O-sulphate (I) and dopamine 4-O-sulphate (II), as analytical reference substances, starting from dopamine hydrochloride are described. A method for the determination of I and II with reversed-phase high-performance liquid chromatographic separation and coulometric detection in human urine together with calibration and current-voltage curves are presented. Detection limits of approximately 100 pg of I or II and unequivocal substance identifications even in very complex substrates such as human urine are reported.

Changes in serotonin concentration in a living neurone: a study by on-line intracellular voltammetry

Intraneuronal concentration of serotonin (5-HT) and its changes were measured in live serotonergic metacerebral cells of Aplysia for several hours following neuronal stimulation, after intracellular injection of 5-HT or extracellular application of L-tryptophan, reserpine, or p-chlorophenylalanine. This was achieved by an on-line intracellular differential pulse voltammetric method using a new, needle-tipped and glass-insulated, platinum microelectrode sensitive to 5-HT.

[Demonstration of carcinine synthetase, a new enzyme catalysing the metabolism of histamine in the central nervous system of Carcinus maenas]

Carcinine biosynthesis was induced in vitro from its two components, beta-alanine and histamine. The reaction was catalyzed by muscle, heart, and CNS extracts from Carcinus maenas. The specific activity of the enzyme, carcinine synthetase, was 15 times higher in CNS than in other organs. Only CNS extracts induced biosynthesis of carcinine from histidine, and only in the presence of pyridoxal-5'-phosphate. Hence the seat of carcinine biosynthesis seems to be the CNS. It is highly probable that in the CNS, histidine is transformed into histamine, which is then catabolized into carcinine. The latter would then be transported and accumulated in the cardiac tissue. Thus histamine--the metabolism of which takes place totally within the CNS--would be implicated as a participant in the neuronal activity of Carcinus maenas. Carcinine synthetase is a soluble enzyme that requires the presence of ATP, beta-alanine, and histamine. Mg2+ and dithiothreitol are also essential for activity. Optimum pH is approximately 7.6. Carcinine synthetase differs from carnosine synthetase and gamma-glutamylhistamine synthetase in that it does not catalyze synthesis of beta-alanylhistidine or gamma-glutamylhistamine.

[Biosynthesis and metabolism of histamine in the central nervous system of Carcinus maenas]

The central nervous system of Carcinus maenas synthesizes radioactive histamine when incubated in the presence of [14C] histidine and pyridoxal-5' phosphate. This biosynthesis increases linearly as a function of the amount of enzyme and the incubation time. It is not effected by heart, muscle or hepatopancreas extracts nor by haemolymph. Thus histamine appears to be synthesized mainly in the nervous system. The latter is also the seat of carcinine (beta-alanylhistamine) biosynthesis. Since carcinine seems to be a product of histamine neutralization, histamine metabolism should take place in its entirety in the nervous system. Thus histamine appears to be implicated in the neuronal activity of Carcinus. Different areas of the crustacean central nervous system: brain, eyestalks and thoracic ganglionic mass biosynthesize and metabolize histamine. Thus they all could contain sites of action for histamine. The nervous systems of two other Decapodes, Cancer and Astacus also effect histamine biosynthesis but don't metabolize it into carcinine.

Veratridine-stimulated release of amine conjugates from centrifugal fibers in the Limulus peripheral visual system

Centrifugal fibers that originate in the brain and project to the Limulus peripheral visual system synthesize and store octopamine and conjugates of octopamine and tyramine. In a previous study we showed that depolarization, induced by elevating extracellular K+, stimulated a preferential release of octopamine from these fibers. Here we show that veratridine-induced depolarization stimulates a rapid, transient release of octopamine and a delayed, sustained release of amine conjugates. Veratridine-stimulated release of both octopamine and amine conjugates depends on the influx of extracellular Ca2+ and is blocked by tetrodotoxin or the absence of extracellular Na+. The depolarization-stimulated release of amine conjugates raises the possibility that these molecules serve as intercellular messengers in the Limulus peripheral visual system.

Synthesis of gamma-glutamyldopamine and other peptidoamines in the nervous system of Aplysia californica

The synthesis of a series of gamma-glutamyl amines (gamma-Glu-amines), including gamma-Glu-dopamine, gamma-Glu-5-hydroxytryptamine, gamma-Glu-octopamine, gamma-Glu-tryptamine, gamma-Glu-tyramine, and gamma-Glu-phenylethylamine, by nervous tissue of the marine mollusc Aplysia californica is described. After ganglia were incubated in vitro with 14C-amines, the unchanged amine and a new 14C-labeled product, identified as the gamma-Glu conjugate of the amine, were isolated from the tissue extracts. Identification was made by comparing the chromatographic properties (HPLC, TLC, and LC) of the isolated conjugates with chemically synthesized gamma-Glu-amines before and after acid hydrolysis.

Sulfate conjugation of dopamine in rat brain: regional distribution of activity and evidence for neuronal localization

Brain tissue contains at least two forms of phenolsulfotransferase that are involved in the sulfate conjugation of biogenic amines and their metabolites. Two apparent Km values were obtained for p-nitrophenol at pH 7.4 (0.6 microM and 0.3 mM) but only one enzyme had the capacity to conjugate dopamine (Km = 130 microM). Dopamine sulfotransferase activity was found to vary 17-fold in different brain regions, with the highest levels in diencephalon, hippocampus, and striatum. To determine the cellular localization of the enzymes, phenolsulfotransferase activity was measured in striatum following selective destruction of striatal neurons by stereotaxic injection of 2 micrograms kainic acid. Fourteen days after injection the catecholamine sulfotransferase activity in the lesioned striatum was reduced to approximately 40-50% of that in the control contralateral striatum. There was a statistically significant correlation between the ratio of lesioned to control activity for the sulfotransferase and the neuronal marker enzymes glutamate decarboxylase and neuron-specific enolase. p-Nitrophenol sulfotransferase activity was also decreased in the lesioned striatum. These results suggest that PST activity is present within the kainic acid-sensitive neurons of the striatum. The regional variation in activity, together with the results of the kainic acid studies, suggest that sulfate conjugation of biogenic amines and their metabolites in brain may take place within specific types of neurons.

Octopamine release from centrifugal fibers of the Limulus peripheral visual system

Octopamine, a biogenic amine, is synthesized and stored within centrifugal (efferent) fibers that project from the brain to the lateral and ventral eyes of the horseshoe crab, Limulus polyphemus. The experiments described here show that depolarization of Limulus lateral and ventral eyes, produced by elevating the concentration of extracellular K+, causes the selective release of newly synthesized octopamine from centrifugal fibers in a manner that requires the influx of extracellular Ca2+. Conjugates of octopamine and tyramine that are also stored within centrifugal fibers are not released in response to K+-induced depolarization. These findings add further support to the hypothesis that octopamine is a neurotransmitter synthesized by and released from centrifugal fibers in Limulus eyes. This amine may be responsible for many of the alterations in lateral eye structure and function that are mediated by centrifugal innervation.

A neurochemical description of the dopaminergic innervation of the stomatogastric ganglion of the spiny lobster

The spiny lobster stomatogastric ganglion has been shown to be innervated by catecholaminergic processes which derive from cells of large central ganglia (Kushner and Maynard, 1977). Biochemical evidence had indicated that the stomatogastric system synthesizes dopamine and not norepinephrine from tritiated tyrosine (Barker, Kushner, and Hooper, 1979). Studies reported here document that the stomatogastric ganglion itself contains dopamine, as measured with a sensitive endogenous assay. Moreover, the ganglion can synthesize dopamine from tritiated tyrosine or DOPA. Additionally, when incubated in tritiated dopamine, the ganglion takes up dopamine and protects it from degradation; this process is inhibited by cocaine. When incubated with 3H-tyrosine, small but measurable amounts of tritiated dopamine were detected in the medium surrounding the ganglion.

An in vitro characterization of gamma-glutamylhistamine synthetase: a novel enzyme catalyzing histamine metabolism in the central nervous system of the marine mollusk, Aplysia californica

The properties of the histamine metabolizing enzyme, gamma-glutamylhistamine synthetase (gamma-GHA synthetase) were studied in Aplysia ganglia in vitro. This enzyme catalyzes the incorporation of histamine into peptide linkage with L-glutamate to form a peptidoamine, gamma-glutamylhistamine (gamma-GHA). gamma-GHA synthetase is a soluble enzyme with an apparent Km of 653 microM for histamine and 10.6 mM for L-glutamate. Synthesis of gamma-GHA is energy-dependent, having an absolute requirement for ATP. Magnesium ions and dithiothreitol are also essential for activity. Of a variety of gamma-glutamyl compounds and glutamate analogs tested, only L-glutamate was effectively incorporated into peptide linkage with histamine. Similarly, the enzyme has a higher affinity for histamine than for numerous imidazole analogs. In addition, 3,4-dihydroxyphenylethylamine (dopamine), 5-hydroxytryptamine, octopamine, and several other amines tested are effective inhibitors of gamma-GHA synthesis. Ganglia, nerve trunks, and the capsule surrounding the ganglion had the highest synthetase activity. The specific activity of the enzyme in muscle, heart, and hemolymph was less than 10% of that in ganglia. Differences in substrate specificity and effect of inhibitors distinguish gamma-GHA synthetase from gamma-glutamyl transpeptidase, glutamine synthetase, and carnosine synthetase.

Biochemistry and ultrastructure of serotonergic nerve endings in the lobster: serotonin and octopamine are contained in different nerve endings

In this article we report that the distribution of serotonin in the lobster nervous system parallels the distribution of octopamine and that the same tissues that contain endogenous serotonin can synthesize it from tryptophan. Octopamine and serotonin are highly concentrated in a neurosecretory region of the second thoracic roots in association with a group of neurosecretory cells. The roots possess separate high-affinity uptake systems for both serotonin and tryptophan. Radioactive serotonin, accumulated in tissues during incubations with either tritiated serotonin or tritiated tryptophan, can be released, in a calcium-dependent manner, by depolarization with potassium. A detailed morphological examination of the second thoracic roots shows four distinct categories of nerve endings in the vicinity of the neurosecretory cells. Octopamine is synthesized in one of these types of endings and serotonin in another. The high-affinity uptake systems for serotonin and tryptophan are found only in association with the endings that make serotonin. These endings and all the biochemical parameters of serotonin metabolism in the roots are selectively destroyed by previous injection of animals with the neurotoxin 5,7-dihydroxytryptamine.

Neurotransmitter synthesis in Limulus ventral nerve photoreceptors

Radiochemical precursor compounds for neurotransmitters were incubated with Limulus ventral nerve photoreceptor preparations. Octopamine was preferentially synthesized by a photoreceptor rich fraction of the nerve, acetylcholine was made by a photoreceptor poor fraction, and gamma-aminobutyric acid was made about equally well in both fractions. The possibility that the ventral nerve photoreceptor cells serve a neurosecretory function in the adult Limulus is discussed.

Synthesis of dopamine and octopamine in the crustacean stomatogastric nervous system

The spiny lobster stomatogastric nervous system synthesizes dopamine and octopamine in vitro from exogenous [3H]tyrosine. Each amine accumulates with a specific distribution among 9 separately analyzed regions within the system. Synthesis of other catecholamines was not observed. [3H]Dopamine is found in nerves, ganglia, and identified commissural ganglion cell bodies in which catecholamine histofluorescence has been demonstrated. The biosynthetic and histochemical data together indicate that dopaminergic cells send axons from the commissural ganglia to the stomatogastric ganglion neuropil along the same pathway followed by fibers that activate the pylroic motor network. The results support the hypothesis that dopamine mediates activation of the pyloric system in vivo, as observed in vitro. [3H]Octopamine accumulates primarily in the commissural and stomatogastric ganglia, where it may modulate neuronal activity, but octopaminergic cells and release sites within the stomatogastric system have not been identified.