in insect nervous tissue

N-beta-Alanyldopamine: Major Role in Insect Cuticle Tanning

N-beta-Alanyldopamine is the major tyrosine metabolite in the hemolymph and cuticle during pupal tanning in the tobacco hornworm, Manduca sexta L. Its concentration in hemolymph increases over 800-fold above larval levels by the start of tanning and decreases as the pupal cuticle darkens and hardens. It is a major catechol in species representing several insect orders and is the preferred substrate for pupal cuticular o-diphenol oxidase. In insects, N-beta-alanyldopamine appears to be the main precursor for tanning chemicals at certain developmental stages.

Electrochemical oxidation of N-acyldopamines and regioselective reactions of their quinones with N-acetylcysteine and thiourea

The metabolism of catechols often involves their oxidation to quinones and subsequent nucleophilic addition reactions with sulfur-containing compounds. Adducts formed during these reactions may play important roles in many biological systems. We have studied the electrochemical oxidation of N-acetyldopamine (NADA) and N-beta-alanyldopamine (NBAD) in the presence of two sulfur-centered nucleophiles, N-acetylcysteine (NACySH) and thiourea (TU), and have characterized the adducts and reaction pathways. NADA and NBAD react similarly, but their adducts with NACySH and TU were formed regioselectively. NACySH yields mainly 5-adducts and TU only 6-adducts. The NACySH adducts are oxidized more easily than the parent N-acyldopamine, and their oxidations are chemically reversible. However, the TU adducts are more difficult to oxidize, and their oxidation products undergo further chemical reactions. An intramolecular base catalysis mechanism for adduct formation with NACySH is proposed, which facilitates removal of the proton from the sulfhydryl group of NACySH and directs formation of the 5-adduct via a 1,6-Michael addition reaction. The absence of a proton on the thioureylene sulfur atom leads to formation of the 6-thioureylene adduct via a 1,4-Michael addition reaction of TU. This mechanism is consistent with the formation of other sulfur-centered adducts of catechols previously reported in the literature.

Characterization of two high molecular weight catechol-containing glycoproteins from pharate pupal cuticle of the tobacco hornworm, Manduca sexta

Two high molecular weight cuticular proteins (MSCP120 and MSCP246) were extracted in acidic guanidine hydrochloride solution from tanning abdominal cuticle of Manduca sexta pharate pupae and purified by size exclusion high performance liquid chromatography. The apparent molecular weights were ca. 120 and 246 kDa as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Both proteins contained high levels of glutamate/glutamine, glycine, serine, alanine and aspartate/asparagine. MSCP120 was enriched in histidine relative to MSCP246, but the reverse was true for valine and proline. Small quantities of beta-alanine and 3,4-dihydroxyphenylalanine (DOPA), as well as other catechols and carbohydrates, also were detected in the hydrolysates. The proteins became radiolabeled when [1-14C]-beta-alanine was injected into pharate pupae, presumably by the formation of adducts with N-beta-alanyldopamine metabolites during sclerotization. Mild acid hydrolysis released N-beta-alanylnorepinephrine and 3,4-dihydroxyphenylketoethanol from both proteins. Strong acid hydrolysis yielded predominantly 3,4-dihydroxyphenylketoethylamine (arterenone), but also DOPA and dopamine. The N-terminal amino acid sequences of the two cuticular proteins were dissimilar, and that of MSCP246 was more hydrophobic than MSCP120. Both of these proteins were glycosylated with glucose, N-acetylglucosamine and traces of N-acetylgalactosamine, and MSCP246 also contained galactose. These structural glycoproteins, which occur in cuticle undergoing sclerotization, apparently react post-translationally with quinonoid tanning agents to yield catecholamine-protein adducts. Small amounts of peptidyl DOPA probably are formed by hydroxylation of tyrosyl residues. Results from this study are consistent with the hypothesis that these catechol-containing glycoproteins participate in cross-linking reactions in M. sexta pupal cuticle during sclerotization.

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.

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.

Biogenic amines: their occurrence, biosynthesis and metabolism in the locust, Schistocerca gregaria, by gas chromatography-negative-ion chemical ionisation mass spectrometry

Extraction-derivatisation techniques have been developed for the unambiguous identification of biogenic amines, and their putative amino acid precursors and metabolites (both major and minor), in single ventral thoracic nerve cords of the locust. Schistocerca gregaria, by the use of gas chromatography-negative-ion chemical ionisation mass spectrometry with selected ion monitoring. In addition the configuration of that enantiomer of p-octopamine present in the thoracid nervous system of the locust was established as R using the chiral derivatisation reagent, (-)-heptafluorobutyrylphenylalanyl chloride.

Biogenic amines in newly-ecdysed cockroaches

1. Simultaneous quantification (HPLC and electrochemical detection) of biological extracts have shown dopamine, N-acetyl dopamine, tryptophan, 5-hydroxytryptamine, a 5-hydroxyindolacetic acid-like substance in nervous tissue and hemolymph of Blaberus craniifer and Periplaneta americana. 2. 5-Hydroxytryptophan was only detected in head and thoraco-abdominal nerve cord. 3. Octopamine, but not N-acetyl-5-HT was quantified in the hemolymph.

Serotonin, dopamine, noradrenaline and their metabolites: levels in the brain of the house cricket (Acheta domesticus L.) during a 24-hour period and after administration of quipazine--a 5-HT2 receptor agonist

1. The levels of 5-HT, DA, NA and DA metabolites (NADA, DOPAC) measured by HPLC (with electrochemical detection) in the brain of the house cricket did not change over a 24-hr period. The level of 5-HIAA, a 5-HT metabolite, was below the limit of detection. 2. The 5-HT and DOPAC levels decreased and NADA increased after quipazine injection but DA and NA levels did not change after it. 3. [3H]Ketanserin was used to identify serotonin receptors bound to sites in the house cricket brain with a KD of 5 nM and a concentration of Bmax 180 fmol/mg protein.

Identification and quantitation of N-acetyl metabolites of biogenic amines in the thoracic nervous system of the locust, Schistocerca gregaria, by gas chromatography-negative-ion chemical ionisation mass spectrometry

The N-acetylated metabolites of p-tyramine, p-octopamine and dopamine were identified unambiguously and quantitatively determined in a single ventral thoracic nerve cord of the locust, Schistocerca gregaria, by gas chromatography-negative-ion chemical ionisation mass spectrometry (GC-NICIMS). Deuterium-labelled analogues of each compound were added to a single ventral thoracic nerve cord in acetonitrile: the tissue was homogenised and the suspension centrifuged. The solvent was removed from the supernatant and the resultant residue was derivatised with trifluoroacetic anhydride. Under negative-ion chemical ionisation conditions, the trifluoroacetyl derivatives produced ions which were sufficiently abundant to be suitable for selected-ion monitoring. This method is highly specific and gave a limit of detection below the picogram levels. N-Acetyl-5-hydroxytryptamine was determined using a previously published GC-NICIMS technique [S.P. Markey, R.W. Colburn and J.N. Johannessen, Biomed. Mass Spectrom., 7 (1981) 301]. The concentrations of N-acetyltyramine, N-acetyloctopamine, N-acetyldopamine and N-acetyl-5-hydroxytryptamine in locust thoracic nerve cords were, respectively, 1.86 +/- 0.71, 1.13 +/- 0.34, 6.77 +/- 8.48 and 0.07 +/- 0.02 ng per tissue.

Selective depletion of dopamine, octopamine, and 5-hydroxytryptamine in the nervous tissue of the cockroach (Periplaneta americana)

High-performance liquid chromatography with electrochemical detection was used to measure the concentrations of 3,4-dihydroxyphenylethylamine (dopamine), 5-hydroxytryptamine (5-HT), p-hydroxyphenylethanolamine (octopamine), alpha-methyl-p-tyrosine, and tryptophan in the cerebral ganglia of cockroaches (Periplaneta americana) after peripheral administration of alpha-methyl-p-tyrosine and alpha-methyltryptophan. In addition, the levels of dopamine, 5-HT, octopamine, alpha-methyl-p-tyrosine, and tryptophan were determined after injection of alpha-methyl-p-tyrosine, 6-hydroxydopamine, or 5,7-dihydroxytryptamine directly into the cerebral ganglia by means of microinjection needles. Peripheral administration of alpha-methyl-p-tyrosine (400-1,600 micrograms/insect) caused a reduction in dopamine and 5-HT concentrations in cockroach cerebral ganglia, although the reduction in dopamine concentrations was more pronounced. Peripheral injections of alpha-methyl-p-tyrosine also reduced octopamine levels in the cerebral ganglia. Peripheral injection of alpha-methyltryptophan (400-1,600 micrograms/insect) caused a marked reduction in 5-HT and tryptophan concentrations in cockroach cerebral ganglia without altering dopamine or octopamine concentrations. Central injections of alpha-methyl-p-tyrosine (80 micrograms/insect) reduced dopamine concentrations in the cerebral ganglia. However, neither 6-hydroxydopamine (20 micrograms/insect) nor 5,7-dihydroxytryptamine (20 micrograms/insect) caused reductions in amine levels when applied near or directly into the cerebral ganglia. The results suggest that specific lesions of aminergic neurons in insects by either 6-hydroxydopamine or 5,7-dihydroxytryptamine are impractical. The specific, long-lasting depletion of 5-HT by alpha-methyltryptophan suggests that this chemical may be useful in elucidating the functions of 5-HT in insects.

Sclerotization of mosquito cuticle

The mode of sclerotization of Aedes aegypti pupal and adult cuticle was examined by employing biochemical and radioactive techniques. During larval-pupal metamorphosis, tyrosine is converted to tanning precursors and is incorporated into aryl-amino adducts and beta-crosslinks. The major hydrolysis product of beta-crosslinks in pupal cases is identified to be arterenone. Examination of tanning modes in five different mosquito species shows that the ratio of quinone to beta-sclerotization not only differs within the life stages of the insects, but also differs between species.

Distribution of serotonin-containing neurons and their pathways in the supraoesophageal ganglion of the cockroach Periplaneta americana (L.) as revealed by immunocytochemistry

The distribution of serotonin (5-HT)-containing neurons in the supraoesophageal (cerebral) ganglion of the cockroach Periplaneta americana was studied using immunocytochemistry and the formaldehyde histofluorescence method ( Klemm , '83). In this material immunocytochemistry was more sensitive than the formaldehyde histofluorescence procedure. A relatively small number of 5-HT-immunoreactive cell bodies (220-280) were found. For the first time, their processes could be followed. They highly arborize and innervate many brain regions. Three patterns of monoamine innervation have been demonstrated: (1) 5-HT and catecholamine fibres ( Klemm , '83) occurring in the same region (e.g., outer lateral protocerebral neuropil, stratum caudale , mushroom body, fan-shaped body, olfactory lobe), but having certain differences with respect to the organization of their projection fields; (2) 5-HT fibres innervating a region lacking catecholamine-containing fibres (pons); and (3) catecholamine neurons innervating a region lacking 5-HT fibres (ellipsoid body). In the mushroom body only the extrinsic neurons contain 5-HT immunoreactivity. They form a commissural fibre system linking the left- and right-hand mushroom bodies and other brain regions. The pons is part of a 5-HT-neuron fibre system innervating many areas including the mushroom bodies. The present study demonstrates novel, complex, and widely distributed connections within the insect brain.

Distribution of 5-hydroxytryptamine and indolealkylamine metabolites in the American cockroach, Periplaneta americana L

A procedure is described for simultaneous estimation of tryptophan (TP), 5-hydroxytryptophan (5-OHTP), 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), N-acetyl 5-hydroxytryptamine (NA5-HT) and N-acetyldopamine (NADA) using high performance liquid chromatography with coulometric electrochemical detection. The procedure has been used to determine the distribution of these compounds in the central nervous system of the American cockroach, Periplaneta americana. The ratio of TP:5-HT is greatest in the cerebral ganglia (6.5) with lesser ratios evident in the thoracic ganglia (15.5-18.9) and abdominal ganglia (9.6-11.2). Relatively low concentrations of 5-OHTP and NA5-HT were observed in the cerebral ganglia whereas 5-HIAA was not detected. Incubation of ganglia resulted in increased concentrations of NA5-HT. Reserpine reduced levels of 5-HT and NADA whereas probenecid caused a marked reduction in TP and slight elevation of NADA levels. No MAO activity was detected in the central nervous system.

Catecholamines in honey bee (Apis mellifera L.) and various vespid (Hymenoptera) venoms

Liquid chromatography with electrochemical detection was used to separate, identify and quantitate the levels of dopamine (DA) and noradrenaline (NA) present in the venoms of honey bees of known ages and of DA and 5-hydroxytryptamine (5-HT) in various species of vespid wasps. Fluorescence histochemistry corroborated the presence of amines in honey bee venom glands and reservoirs and supported the quantitative results. The results show: (i) There is an age dependent variation in DA and NA levels in honey bee venom and there may be a similar variation in DA and 5-HT in the venom of queen Dolichovespula arenaria. (ii) There appears to be a seasonal variation in the quantities of DA and NA present in honey bee venom. Such a seasonal variation may be one of the factors involved in the variation in the levels of amine components present in the various vespid wasp venom samples. (iii) 5-HT is present in much greater quantities than DA in vespid venoms. Low levels of NA and DOPA are present in vespid venoms.