Octopamine and some related noncatecholic amines in invertebrate nervous systems

Electromagnetic field exposure affects the calling song, phonotaxis, and level of biogenic amines in crickets

The electromagnetic field (EMF) is ubiquitous in the environment, constituting a well-known but poorly understood stressor. Few studies have been conducted on insect responses to EMF, although they are an excellent experimental model and are of great ecological importance. In our work, we tested the effects of EMF (50 Hz, 7 mT) on the cricket Gryllus bimaculatus: the male calling song pattern, female mate choice, and levels of biogenic amines in the brain. Exposure of males to EMF increased the number and shortened the period of chips in their calling song (by 2.7% and 5% relative to the control song, respectively), but not the sound frequency. Aged (3-week-old) females were attracted to both natural and EMF-modified male signals, whereas young (1-week-old, virgin) females responded only to the modified signal, suggesting its higher attractance. Stress response of males to EMF may be responsible for the change in the calling song, as suggested by the changes in the amine levels in their brains: an increase in dopamine (by 50% relative to the control value), tyramine (65%), and serotonin (25%) concentration and a decrease in octopamine level (by 25%). These findings indicate that G. bimaculatus responds to EMF, like stressful conditions, which may change the condition and fitness of exposed individuals, disrupt mate selection, and, in consequence, affect the species' existence.

Exploring the Intestinal Microbiota and Metabolome Profiles Associated With Feed Efficiency in Pacific Abalone (Haliotis discus hannai)

Feed efficiency (FE) is critical to the economic and environmental benefits of aquaculture. Both the intestines and intestinal microbiota play a key role in energy acquisition and influence FE. In the current research, intestinal microbiota, metabolome, and key digestive enzyme activities were compared between abalones with high [Residual feed intake (RFI) = -0.029] and low FE (RFI = 0.022). The FE of group A were significantly higher than these of group B. There were significant differences in intestinal microbiota structures between high- and low-FE groups, while higher microbiota diversity was observed in the high-FE group. Differences in FE were also strongly correlated to variations in intestinal digestive enzyme activity that may be caused by Pseudoalteromonas and Cobetia. In addition, Saprospira, Rhodanobacteraceae, Llumatobacteraceae, and Gaiellales may potentially be utilized as biomarkers to distinguish high- from low-FE abalones. Significantly different microorganisms (uncultured beta proteobacterium, BD1_7_clade, and Lautropia) were found to be highly correlated to significantly different metabolites [DL-methionine sulfoxide Arg-Gln, L-pyroglutamic acid, dopamine, tyramine, phosphatidyl cholines (PC) (16:0/16:0), and indoleacetic acid] in the high- and low-FE groups, and intestinal trypsin activity also significantly differed between the two groups. We propose that interactions occur among intestinal microbiota, intestinal metabolites, and enzyme activity, which improve abalone FE by enhancing amino acid metabolism, immune response, and signal transduction pathways. The present study not only elucidates mechanisms of variations in abalone FE, but it also provides important basic knowledge for improving abalone FE by modulating intestinal microbiota.

Differences in Small Molecule Neurotransmitter Profiles From the Crown-of-Thorns Seastar Radial Nerve Revealed Between Sexes and Following Food-Deprivation

Neurotransmitters serve as chemical mediators of cell communication, and are known to have important roles in regulating numerous physiological and metabolic events in eumetazoans. The Crown-of-Thorns Seastar (COTS) is an asteroid echinoderm that has been the focus of numerous ecological studies due to its negative impact on coral reefs when in large numbers. Research devoted to its neural signaling, from basic anatomy to the key small neurotransmitters, would expand our current understanding of neural-driven biological processes, such as growth and reproduction, and offers a new approach to exploring the propensity for COTS population explosions and subsequent collapse. In this study we investigated the metabolomic profiles of small molecule neurotransmitters in the COTS radial nerve cord. Multivariate analysis shows differential abundance of small molecule neurotransmitters in male and female COTS, and in food-deprived individuals with significant differences between sexes in gamma-aminobutyric acid (GABA), histamine and serotonin, and significant differences in histamine and serotonin between satiation states. Annotation established that the majority of biosynthesis enzyme genes are present in the COTS genome. The spatial distribution of GABA, histamine and serotonin in the radial nerve cord was subsequently confirmed by immunolocalization; serotonin is most prominent within the ectoneural regions, including unique neural bulbs, while GABA and histamine localize primarily within neuropil fibers. Glutamic acid, which was also found in high relative abundance and is a precursor of GABA, is known as a spawning inhibitor in seastars, and as such was tested for inhibition of ovulation ex-vivo which resulted in complete inhibition of oocyte maturation and ovulation induced by 1-Methyladenine. These findings not only advance our knowledge of echinoderm neural signaling processes but also identify potential targets for developing novel approaches for COTS biocontrol.

Trace Amines and the Trace Amine-Associated Receptor 1: Pharmacology, Neurochemistry, and Clinical Implications

Biogenic amines are a collection of endogenous molecules that play pivotal roles as neurotransmitters and hormones. In addition to the "classical" biogenic amines resulting from decarboxylation of aromatic acids, including dopamine (DA), norepinephrine, epinephrine, serotonin (5-HT), and histamine, other biogenic amines, present at much lower concentrations in the central nervous system (CNS), and hence referred to as "trace" amines (TAs), are now recognized to play significant neurophysiological and behavioral functions. At the turn of the century, the discovery of the trace amine-associated receptor 1 (TAAR1), a phylogenetically conserved G protein-coupled receptor that is responsive to both TAs, such as β-phenylethylamine, octopamine, and tyramine, and structurally-related amphetamines, unveiled mechanisms of action for TAs other than interference with aminergic pathways, laying the foundations for deciphering the functional significance of TAs and its mammalian CNS receptor, TAAR1. Although, its molecular interactions and downstream targets have not been fully elucidated, TAAR1 activation triggers accumulation of intracellular cAMP, modulates PKA and PKC signaling and interferes with the β-arrestin2-dependent pathway via G protein-independent mechanisms. TAAR1 is uniquely positioned to exert direct control over DA and 5-HT neuronal firing and release, which has profound implications for understanding the pathophysiology of, and therefore designing more efficacious therapeutic interventions for, a range of neuropsychiatric disorders that involve aminergic dysregulation, including Parkinson's disease, schizophrenia, mood disorders, and addiction. Indeed, the recent development of novel pharmacological tools targeting TAAR1 has uncovered the remarkable potential of TAAR1-based medications as new generation pharmacotherapies in neuropsychiatry. This review summarizes recent developments in the study of TAs and TAAR1, their intricate neurochemistry and pharmacology, and their relevance for neurodegenerative and neuropsychiatric disease.

Octopamine promotes rhythmicity but not synchrony in a bilateral pair of bursting motor neurons in the feeding circuit of Aplysia

Octopamine-like immunoreactivity was localized to a limited number (<40) of neurons in the Aplysia central nervous system, including three neurons in the paired buccal ganglia (BG) that control feeding movements. Application of octopamine (OA) to the BG circuit produced concentration-dependent (10(-8)-10(-4) mol l(-1)) modulatory actions on the spontaneous burst activity of the bilaterally paired B67 pharyngeal motor neurons (MNs). OA increased B67's burst duration and the number of impulses per burst. These effects reflected actions of OA on the intrinsic tetrodotoxin-resistant driver potential (DP) that underlies B67 bursting. In addition to its effects on B67's burst parameters, OA also increased the rate and regularity of burst timing. Although the bilaterally paired B67 MNs both exhibited rhythmic bursting in the presence of OA, they did not become synchronized. In this respect, the response to OA differed from that of dopamine, another modulator of the feeding motor network, which produces both rhythmicity and synchrony of bursting in the paired B67 neurons. It is proposed that modulators can regulate burst synchrony of MNs by exerting a dual control over their intrinsic rhythmicity and their reciprocal capacity to generate membrane potential perturbations. In this simple system, dopaminergic and octopaminergic modulation could influence whether pharyngeal contractions occur in a bilaterally synchronous or asynchronous fashion.

Effect of tyramine and stress on sex-pheromone production in the pre- and post-mating silkworm moth, Bombyx mori

Tyramine (TA) increased significantly after mating, whereas there were no significant differences in octopamine (OA) and dopamine (DA) levels in the brain-suboesophageal ganglion (SOG) complexes between virgin and mated females. The effects of various biogenic amines were tested on pheromone production of virgin and mated females of the silkworm moth, Bombyx mori. After 8h a significant reduction by TA (46%) was observed. Meanwhile, when OA or DA was injected, a significant increase of pheromone titer was observed in both virgin and mated females. This study also presents evidence for an increase in levels of OA and DA in the brain-SOG complexes in response to mechanical stress in B. mori female. TA suppressed pheromone production in an in vitro pheromone gland (PG) homogenate preparation, thus suggesting that the target of TA is the PG. TA inhibited pheromone production in vitro in a dose-dependent manner and DA had a lower inhibitory activity than TA, whereas OA had no effect, suggesting that TA is a candidate for regulating pheromone production in the PG, although other factors could be responsible for the pheromonostatic function.

Trace amine-associated receptor 1-Family archetype or iconoclast?

Interest has recently been rekindled in receptors that are activated by low molecular weight, noncatecholic, biogenic amines that are typically found as trace constituents of various vertebrate and invertebrate tissues and fluids. The timing of this resurgent focus on receptors activated by the "trace amines" (TA) beta-phenylethylamine (PEA), tyramine (TYR), octopamine (OCT), synephrine (SYN), and tryptamine (TRYP) is the direct result of 2 publications that appeared in 2001 describing the cloning of a novel G protein-coupled receptor (GPCR) referred to by their discoverers Borowsky et al. as TA1 and Bunzow et al. as TA receptor 1 (TAR1). When heterologously expressed in Xenopus laevis oocytes and various eukaryotic cell lines, recombinant rodent and human TAR dose-dependently couple to the stimulation of adenosine 3',5'-monophosphate (cAMP) production. Structure-activity profiling based on this functional response has revealed that in addition to the TA, other biologically active compounds containing a 2-carbon aliphatic side chain linking an amino group to at least 1 benzene ring are potent and efficacious TA receptor agonists with amphetamine (AMPH), methamphetamine, 3-iodothyronamine, thyronamine, and dopamine (DA) among the most notable. Almost 100 years after the search for TAR began, numerous TA1/TAR1-related sequences, now called TA-associated receptors (TAAR), have been identified in the genome of every species of vertebrate examined to date. Consequently, even though heterologously expressed TAAR1 fits the pharmacological criteria established for a bona fide TAR, a major challenge for those working in the field is to discern the in vivo pharmacology and physiology of each purported member of this extended family of GPCR. Only then will it be possible to establish whether TAAR1 is the family archetype or an iconoclast.

Anxiety from a phylogenetic perspective: is there a qualitative difference between human and animal anxiety?

A phylogenetic approach to anxiety is proposed. The different facets of human anxiety and their presence at different levels of the phylum are examined. All organisms, including unicellular such as protozoan, can display a specific reaction to danger. The mechanisms enabling the appraisal of harmful stimuli are fully present in insects. In higher invertebrates, fear is associated with a specific physiological response. In mammals, anxiety is accompanied by specific cognitive responses. The expression of emotions diversifies in higher vertebrates, only primates displaying facial expressions. Finally, autonoetic consciousness, a feature essential for human anxiety, appears only in great apes. This evolutive feature parallels the progress in the complexity of the logistic systems supporting it (e.g., the vegetative and central nervous systems). The ability to assess one's coping potential, the diversification of the anxiety responses, and autonoetic consciousness seem relevant markers in a phylogenetic perspective.

Molecular and pharmacological analysis of an octopamine receptor from American cockroach and fruit fly in response to plant essential oils

Octopamine receptors from American cockroach, Periplaneta americana (Pa oa1), and fruit fly, Drosophila melanogaster (OAMB), were cloned and permanently expressed in HEK-293 cells, and found to activate adenylate cyclase activity and increase [Ca2+]i levels through G-protein coupled receptor signaling pathways. Sequencing information (GenBank accession number AY333178) and functional data of Pa oa1 were recently published. Saturation binding analysis with 3H-yohimbine was performed with Pa oa(1) and OAMB expressed in COS-7 cells. The K(d) values were determined to be 28.4 and 43.0 nM, respectively. B(max) was determined to be 11.8 and 8.04 pmol receptor/mg protein, respectively. Competitive binding data using cell membranes expressing either OAMB or Pa oa1 demonstrated significantly decreased binding activity in binding assays performed in the presence of plant essential oils, eugenol, cinnamic alcohol, and trans-anethole. Eugenol decreased cAMP level in HEK-293 cells expressing Pa oa1, but trans-anethole increased cAMP in HEK-293 cells expressing OAMB. All three chemicals increased [Ca2+]i level in both cell models. Toxicity data against fruit flies and American cockroaches demonstrated species differences in response to treatment with tested plant essential oils. The toxicity of tested chemicals against wild type and octopamine mutant (iav) fly strains suggested that an octopamine receptor mediates the toxicity of cinnamic alcohol, eugenol, trans-antehole, and 2-phenethyl propionate against fruit flies. Collectively, the data suggest a correlation between cellular changes induced by tested plant essential oils and their toxicity against fruit fly and American cockroach.

Molecular response of Drosophila melanogaster tyramine receptor cascade to plant essential oils

This paper reports the role of the tyramine (TA) receptor cascade in the insecticidal activity of plant essential oils. A TA receptor cDNA encoding a putative seven transmembrane domain G-protein coupled receptor was amplified from Drosophila melanogaster head cDNA phage library. The encoded protein contains 601 amino acids and has a sequence similar to other biogenic amine receptors. This protein was expressed in Drosophila S2 cells for radioligand binding studies with the ligand 3H-TA. Competitive binding studies comparing biogenic amines that could potentially function as endogenous ligands have demonstrated that this receptor had the highest affinity for TA (Ki=1.27 microM) followed by DL-octopamine, dopamine, serotonin and histamine. TA decreased the forskolin-increased cAMP levels (IC50=5.802 microM) and increased [Ca2+]i through the receptor expressed in S2 cells. The toxicity rank order of the tested plant essential oils against wild type D. melanogaster fly demonstrated a pattern similar to their effect on receptor binding activity and changes in cAMP level and [Ca2+]i. The toxicity of two of these chemicals was eliminated when tested against the TA receptor mutant (TyrRneo30) Drosophila strain. Therefore, the data indicates a correlation between cellular changes and insecticidal activity of tested plant essential oils, and suggests that the toxicity of at least two of these chemicals is mediated through the TA receptor.

The Pheromone Production of FemalePlodia interpunctella Is Inhibited by Tyraminergic Antagonists

Several compounds were found to suppress the calling behavior and in vitro pheromone biosynthesis of the Indian meal moth, Plodia interpunctella. The compounds were screened by means of a calling-behavior bioassay with female P. interpunctella. Five derivatives with activities in the nanomolar range were identified, in order of decreasing pheromonostatic activity: 4-hydroxybenzaldehyde semicarbazone (42) > 5-(4-methoxyphenyl)-1,3-oxazole (38) > 5-[4-(tert-butyl)phenyl]-1,3-oxazole (40) > 5-(3-methoxyphenyl)-1,3-oxazole (35) > 5-(4-cyanophenyl)-1,3-oxazole (36). These compounds also showed in vitro inhibitory activity in intracellular de novo pheromone biosynthesis, as determined with isolated pheromone-gland preparations that incorporated [1-(14)C]sodium acetate in the presence of the so-called pheromone-biosynthesis-activating neuropeptide (PBAN). The non-additive effect of the inhibitor with antagonist (yohimbine) for the tyramine (TA) receptor suggests that it could be a tyraminergic antagonist. Three-dimensional (3D) computer models were built from a set of compounds. Among the common-featured models generated by the program Catalyst/HipHop, aromatic-ring (AR) and H-bond-acceptor-lipophilic (HBAl) features were considered to be essential for inhibitory activity in the calling behavior and in vitro pheromone biosynthesis. Active compounds, including yohimbine, mapped well onto all the AR and HBAl features of the hypothesis. Less-active compounds were shown to be unable to achieve an energetically favorable conformation, consistent with our 3D common-feature pharmacophore models. The present hypothesis demonstrates that calling behavior and PBAN-stimulated incorporation of radioactivity are inhibited by tyraminergic antagonists.

Three-dimensional pharmacophore hypotheses of octopamine/tyramine agonists which inhibit [1-14C]acetate incorporation in Plodia interpunctella

Three-dimensional pharmacophore hypotheses were built from a set of 36 octopamine (OA)/tyramine (TA) agonists responsible for the inhibition of sex-pheromone production in Plodia interpunctella. Among the ten chemical-featured models generated by a program Catalyst/Hypo, hypotheses including hydrogen-bond acceptor (HBA), hydrogen-bond acceptor aliphatic (HBAl), hydrophobic (Hp), hydrophobic aromatic (HpAr) and hydrophobic aliphatic (HpAl) features were considered to be important and predictive in evaluating OA/TA agonists. Active agonists mapped well onto all the features of the hypothesis such as HBA, HBAl, Hp, HpAr and HpAl features. On the other hand, inactive compounds were shown to be poorly capable of achieving an energetically favorable conformation shared by the active molecules in order to fit the 3-D chemical-feature pharmacophore models. Those hypotheses are considered to be used in designing new leads for hopefully more active compounds. Further research on the comparison of models from the agonists may help elucidate the mechanisms of OA/TA receptor-ligand interactions.

A trace amine, tyramine, functions as a neuromodulator in Drosophila melanogaster

The tyramine receptor (TyrR) is a G protein-coupled receptor for trace amines, cloned in Drosophila melanogaster, and claimed to be either an octopamine receptor or a tyramine receptor. We previously reported that in the larval neuromuscular junctions, the modulatory effect on the excitatory junction potentials of tyramine is distinctly different from that of octopamine. The effect of tyramine but not of octopamine was selectively abolished in the TyrR mutant hono, suggesting that this gene encodes a receptor for tyramine, and not for octopamine. We examined whether there was a gene-dosage effect of this tyramine modulation using combinations of hono, deficiency (Df) and wild-type alleles. The tyramine effect was observed in hono heterozygotes (+/hono), which showed intermediate levels of response, but was not seen in +/Df or hono/Df hemizygotes. While these further suggest that tyramine is the true ligand, it is possible that the gene-dosage effect is only evident above some threshold of gene expression levels. Immunohistochemical staining using an anti-tyramine antibody identified tyramine-containing neurons in the larval central nervous system, some of which were distinct from the octopamine-containing neurons. Taken together, these results strongly suggest that tyramine functions as a neuromodulator.

Intracerebroventricular administration of octopamine stimulates food intake of chicks through alpha(2)-adrenoceptor

Octopamine, known to be an important neurotransmitter in invertebrates, has been noted to have several similarities to noradrenaline (NA) in mammals. The present study was done to elucidate whether central injection of octopamine enhances the feeding behavior of chicks and to investigate the interaction of octopamine with both alpha(1)- and alpha(2)-adrenoceptors. We found that the intracerebroventricular injection of octopamine significantly stimulated food intake of neonatal chicks during 30 min postinjection, but not thereafter. Moreover, this octopamine-induced eating response was attenuated by the alpha(2)-antagonist yohimbine, but not by the alpha(1)-antagonist prazosin. These results suggest that the action of octopamine on the feeding behavior of the neonatal chick is similar to that of NA, since octopamine regulates food intake through the alpha(2)-adrenoceptor.

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.

Identification of novel inhibitors of calling and in vitro [14C]acetate incorporation by pheromone glands of Plodia interpunctella

Some octopamine agonists were found to suppress in vitro biosynthesis of the calling pheromone of the Indian meal moth, Plodia interpunctella. Isolated pheromone-gland preparations incorporated sodium [14C]acetate at a linear rate for 3 h when incubated with the pheromone biosynthesis activating neuropeptide (PBAN). This incorporation was dependent on the dose of PBAN (up to 0.5 microM). Thin-layer chromatography of a pheromone-gland extract revealed quantitative incorporation of radioactivity into a product exhibiting the same mobility as (Z,E)-9,12-tetradecadienyl acetate, the main component of the calling pheromone of P interpunctella. Twenty-seven octopamine agonists were initially screened using a calling behaviour bioassay of female P interpunctella. Four derivatives with activity in the nanomolar range were identified which were, in order of decreasing pheromonostatic activity: 2-(2,6-diethylphenylimino)thiazolidine > 2-(2,6-diethylphenylimino)oxazolidine > 2-(2,6-dimethylphenylimino)thiazolidine > 2-(2-ethylphenylimino)oxazolidine. These compounds also showed in vitro inhibitory activity in intracellular de novo pheromone biosynthesis. The results of the present study indicate that these derivatives could provide useful information in the characterization and differentiation of octopaminergic receptor types and subtypes.

Titres of biogenic amines and ecdysteroids: effect of octopamine on the production of ecdysteroids in the silkworm Bombyx mori

At day two, a sharp peak of octopamine (OA) was observed in last instar female Bombyx mori larvae. This peak also appeared in male larvae a day later than in females at day three. An OA peak was also observed before the 3rd ecdysis. However, no OA peaks were observed in 4th instar larvae. At day eight and nine of the 5th instar, another OA peak was observed for male and female, respectively. A peak of tyramine (TA) was found at day one followed by a peak of OA at day two in 3rd instar larvae. At day two, a day before OA peak, a peak of TA was observed for male insects and before the 2nd peak of OA, TA titre was also high in 5th instar larvae. Immediately after 3rd ecdysis, a high titre of DL-beta-(3,4-dihydroxyphenyl)alanine (DOPA) was observed, followed by a peak of dopamine (DA) at day five. A peak of DOPA was found at day one followed by a peak of DA at day two in 3rd instar larvae. Similarly, a small peak of DOPA was observed at day two, followed by an increase of DA at days eight and nine after the 4th ecdysis. Ecdysteroid peaks were observed just before the 3rd and 4th ecdysis and an ecdysteroid titre increased after the start of spinning. The effects of OA and JH on production of ecdysteroids by prothoracic glands (PGs) were examined in order to identify neuromediators responsible for triggering pupation in B. mori larvae. Exogeneous OA (10-100 mM) reduced and 10 &mgr;M OA stimulated the production of ecdysteroids in the presence and absence of brain extracts by PGs in the final instar (day five) of B. mori in vitro. Meanwhile, exogeneous JHI (10 &mgr;g/ml) stimulated and at 5 &mgr;g/ml it reduced production of ecdysteroids in the presence of brain extracts. Gramine, an OA antagonist, delayed pupation when applied in the diet. Thus, OA may produce some biological effects on the programming of larval-pupal development.

Octopamine: a new feeding modulator in Lymnaea

The role of octopamine (OA) in the feeding system of the pond snail,Lymnaea stagnalis, was studied by applying behavioural tests on intact animals, and a combination of electrophysiological analysis and morphological labelling in the isolated central nervous system. OA antagonists phentolamine, demethylchlordimeform (DCDM) and 2–chloro–4–methyl–2–(phenylimino)–imidazolidine (NC–7) were injected into intact snails and the sucrose–induced feeding response of animals was monitored. Snails that received 25–50 mg kg-1phentolamine did not start feeding in sucrose, and the same dose of NC–7 reduced the number of feeding animals by 80–90% 1–3 hours after injection. DCDM treatment reduced feeding by 20–60%. In addition, both phentolamine and NC–7 significantly decreased the feeding rate of those animals that still accepted food after 1–6 hours of injection. In the central nervous system a pair of buccal neurons was identified by electrophysiological and morphological criteria. After double labelling (intracellular staining with Lucifer yellow followed by OA–immunocytochemistry) these neurons were shown to be OA immunoreactive, and electrophysiological experiments confirmed that they are members of the buccal feeding system. Therefore the newly identified buccal neurons were called OC neurons (putative OA containing neurons or OAergic cells). Synchronous intracellular recordings demonstrated that the OC neurons share a common rhythm with feeding neurons either appearing spontaneously or evoked by intracellularly stimulated feeding interneurons. OC neurons also have synaptic connections with identified members of the feeding network: electrical coupling was demonstrated between OC neurons and members of the B4 cluster motoneurons, furthermore, chemically transmitted synaptic responses were recorded both on feeding motoneurons (B1, B2 cells) and the SO modulatory interneuron after the stimulation of OC neurons. However, elementary synaptic potentials could not be recorded on the follower cells of OC neurons. Prolonged (20 to 30 s) intracellular stimulation of OC cells activated the buccal feeding neurons leading to rhythmic activity pattern (fictive feeding) in a way similar to OA applied by perfusion onto isolated central nervous system (CNS) preparations. Our results suggest that OA acts as a modulatory substance in the feeding system ofLymnaea stagnalisand the newly identified pair of OC neurons belongs to the buccal feeding network.

Cloning of biogenic amine receptors from moths (Bombyx mori and Heliothis virescens)

Based on the similarity of genes which code for guanine-nucleotide binding protein- (G-protein-) coupled receptors, cDNA clones encoding new members of the receptor family have been isolated from Bombyx mori and Heliothis virescens. The deduced protein structures exhibit highest similarity to tyramine/octopamine and serotonin receptors of Drosophila. One of the receptor clones (K50Hel) was permanently expressed in the mammalian cell line LLC-PK1. In stimulation experiments its responded to octopamine leading to an inhibition of adenylate cyclase activity in a dose-dependent manner. Pharmacological studies revealed a higher affinity for mianserin than for yohimbine suggesting, that the K50Hel clone encoded a neuronal type 3 octopamine receptor. As revealed by in situ hybridization, this receptor type is expressed in the central nervous system and antennae of moth.

Characterization of tyramine and octopamine receptors in the insect (Locusta migratoria migratorioides) brain

The kinetic and pharmacological properties of [3H]tyramine and [3H]octopamine binding to membrane preparations of locust (Locusta migratoria migratorioides) brain were studied to characterize the tyramine and octopamine receptors. [3H]Tyramine and [3H]octopamine bind specifically and reversibly to the locust brain membrane with equilibrium achieved after 20 min. The dissociation of [3H]tyramine is monophasic while that of the [3H]octopamine shows a biphasic tendency. Scatchard analysis of the saturation curves reveals a single high affinity binding site for each of tyramine and octopamine. The mean (+/- S.E.M.) values of Kd and Bmax are 6.11 +/- 0.71 nM and 21.45 +/- 3.0 fmol/mg tissue for tyramine and 5.65 +/- 0.91 nM and 15.0 +/- 2.4 fmol/mg tissue for octopamine, respectively. Pharmacological analysis of the binding suggests the presence of both tyramine and octopamine receptors in the locust brain. alpha-Adrenergic agonists and antagonists have a high affinity to the octopamine but not the tyramine receptor whereas dopaminergic drugs have a higher affinity to the tyramine receptor than the octopamine receptor. No highly effective inhibitors of tyramine binding were identified. The serotonergic blockers, mianserin, LSD, BOL are effective blockers for both tyramine and octopamine receptors, whereas the serotonergic antagonist gramine is more active against the octopamine than the serotonin receptor. The results suggest that a G-protein binding mechanism is involved in the expression of both the tyramine and octopamine effects.

Inhibitory effect of octopamine on the release of endogenous acetylcholine from isolated myenteric synaptosomes of guinea-pig

1. The effect of octopamine on the release of endogenous acetylcholine (ACh) from isolated ileal synaptosomal preparations of guinea-pigs was examined using high pressure liquid chromatography with electrochemical detection. Release of ACh was induced by substance P or by depolarization with high potassium (50 mmol/L) in medium containing atropine, propranolol and naloxone. 2. Octopamine produced a dose-dependent inhibition of substance P-induced ACh release. A similar inhibitory action of octopamine was found in the samples depolarized by high potassium as a reference. 3. The action of octopamine was not reversed by the dopamine receptor antagonists either for the DA-2 subtype, domperidone, or for the DA-1 subtype, SCH23390, or by haloperidol. However, idazoxan and yohimbine antagonized this octopamine-induced inhibition at concentrations sufficient to abolish the action of clonidine. 4. Failure of guanethidine or nomifensine to inhibit octopamine ruled out mediation by noradrenergic neurotransmitters. 5. Octopamine decreased the influx of [45Ca] stimulated by substance P into synaptosomal preparations and this was reversed by idazoxan or yohimbine at concentrations sufficient to block the action of clonidine. 6. Pertussis toxin abolished the inhibitory action of octopamine at a dose high enough to block the action of clonidine. 7. These results indicate that octopamine suppresses the influx of calcium ions into cholinergic nerve terminals of ileal synaptosomes of guinea-pigs via an activation of alpha 2-adrenoceptors coupled with a pertussis toxin-sensitive GTP-binding protein which results in a decrease of ACh release.

Taurine-like immunoreactivity in octopaminergic neurones of the cockroach, Periplaneta americana (L.)

Taurine (2-aminoethanesulphonic acid) is reported to interact with the octopaminergic system. The distribution of taurine-like immunoreactivity (-LIR) in relation to octopamine-like immunoreactive dorsal unpaired median (DUM) neurones was investigated with the aim of revealing possible colocalization of these two neuromediators. The specificity of the anti-taurine serum used was demonstrated by dot blot immunoassay and by use of preabsorption controls. There was no crossreactivity with octopamine. The specificity of the octopamine antiserum employed has been described elsewhere. Taurine-LIR could be demonstrated in large dorso-median cells in the suboesophageal and the mesothoracic ganglion as well as in the abdominal ganglia. In addition taurine-LIR is distributed in numerous other regions of the ganglia. A comparison of the immunostaining for taurine and octopamine indicates that several of the taurine-like immunoreactive (-LI) neurones are probably members of the octopamine-immunoreactive DUM cell population. These taurine-LI neurones resemble octopamine-LI DUM cells in soma position and size as well as in the projections of their primary neurites. Colocalization of octopamine-LIR and taurine-LIR within the same neuronal element could be shown by alternate immunostaining of consecutive sections. It is probable that all octopamine-LI DUM neurones also exhibit taurine-LIR, and the possible physiological significance of this coexistence is discussed.

Small sets of putative interneurons are octopamine-immunoreactive in the central nervous system of the pond snail, Lymnaea stagnalis

An antibody raised against conjugated octopamine was applied to map octopamine-containing neurons in the central nervous system of the pond snail Lymnaea stagnalis. A small number of octopamine-like immunoreactive neurones occurs in all ganglia, but the pleural ones. The neurons are located either in small clusters or occur individually. Major concentrations of octopamine-immunoreactive neurons can first of all be found in the buccal, cerebral and pedal ganglia. Varicose arborizations were observed in the neuropiles, but peripheral projections of labelled elements could not be traced. We suggest that a set of octopaminergic interneurons would exist in the Lymnaea brain. Mapping of octopamine-immunoreactive neurons given may also facilitate physiological investigations on octopaminergic neurotransmission in the gastropod nervous system.

The effects of m-octopamine on salivary flow rates and protein secretion by rat submandibular glands

1. m-Octopamine given i.v. or i.p. was a potent sialogogue for rat salivary glands. 2. Salivation in response to i.v. m-octopamine was completely abolished by prazosin and phenoxybenzamine. 3. The alpha-type of proteins were secreted in response to all doses of i.v. and i.p. m-octopamine and these were converted into the beta-type with prazosin, but not with yohimbine. 4. m-Octopamine stimulated both alpha- and beta-adrenoceptors and was a much more selective alpha 1-agonist than was the p-isomer.

Determination of gamma-glutamyl conjugates of monoamines by means of high-performance liquid chromatography with electrochemical detection and application to gastropod tissues

Catabolism of aminergic neurotransmitters in gastropods appears to be primarily by means of gamma-glutamyl conjugation rather than by oxidative deamination as is typical of vertebrates. High-performance liquid chromatography with electrochemical detection was used to develop a method for the routine measurement of gamma-glutamyl conjugates of dopamine and 5-hydroxytryptamine in gastropod tissues.

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.

Indolamines in the cockroach Blaberus craniifer Burm. nervous system--I. Fed and crowded young females

1. Indolamine levels were determined in the cerebral ganglion, the thoraco-abdominal nerve cord (except the last ganglion), and the 6th abdominal ganglion of females of Blaberus craniifer. 2. Measurements were made at the imaginal molt and on fed and crowded imagos at 10, 20 and 30 post-imaginal days. 3. Indolamines were found in the nervous system of young females, but 5-hydroxytryptophan was only detected in the thoraco-abdominal nerve cord. 4. Amine levels were related to the age of the cockroach, particularly during this period, to post-ecdysis events and ootheca formation.

Inhibitory effect of octopamine on dopamine D-1 receptor in striatal homogenates of the rat

In the striatal homogenates of rats, octopamine produced a dose-dependent inhibition of dopamine D-1 receptor both in the receptor binding of [3H]Sch-23390 and the formation of cyclic adenosine 3',5'-monophosphate (cyclic AMP) stimulated by dopamine in the presence of sulpiride. Failure of octopamine in the displacement of binding with [3H]N-0437, one of the radioligands for the dopamine D-2 receptor, indicated the specific selectivity of octopamine to dopamine D-1 receptor sites. Lack of effect on forskolin-stimulated formation of cyclic AMP ruled out the possible direct effect of octopamine on adenylate cyclase. These results suggest that octopamine possesses the ability to bind to striatal dopamine D-1 receptors of rats.

Gene expression of tyrosine hydroxylase in the developing fetal brain

Tyrosine hydroxylase, aromatic L-amino-acid decarboxylase, and dopamine beta-hydroxylase activities were studied in the developing fetal rat brain. A delay of 2-3 days between the detection of the tyrosine hydroxylase and the aromatic L-amino-acid decarboxylase and dopamine beta-hydroxylase activities was observed. For this reason, the expression of tyrosine hydroxylase mRNA was studied. Tyrosine hydroxylase mRNA was visualized in the whole brain from 13 days of gestation, but the largest increase of the expression was observed in the hypothalamus. These results are discussed in terms of the relative gene expressions of the three enzymes involved in the biosynthesis of catecholamines and phenolamines in nervous tissues.

Dopamine and octopamine in whole body extracts of the bulb mite

Using high performance liquid chromatography with electrochemical detection, whole body extracts of the bulb mite, Rhizoglyphus echinopus (Fumouze and Robin), were found to contain the biogenic amines dopamine and octopamine at concentrations of 4.3 +/- 0.6 and 2.3 +/- 1.4 ng g-1 wet weight, respectively. Adrenaline, noradrenaline, tyramine, N-methyldopamine, N-acetyldopamine, and 5-hydroxytryptamine, if present, were below the limits of detectability. This is the initial demonstration of the presence of octopamine in a mite species.

Octopamine uptake and metabolism in the insect nervous system

Several insect tissues were examined for their ability to take up octopamine in the presence and absence of sodium ions. The cockroach Malpighian tubules, ovary, and ventral nerve cord showed the highest level of sodium-dependent uptake. The adult firefly lantern exhibited substantial sodium-independent uptake. Some of these tissues were also examined for their ability to metabolize octopamine by N-acetylation. Measurable N-acetyltransferase activity was present in the cockroach ventral nerve cord, tobacco hornworm CNS, and firefly light organ. N-Acetylation is proposed to be the major metabolic pathway for octopamine in the cockroach (Periplaneta americana) nervous system. Several classes of compounds, including octopamine receptor agonists, tricyclic antidepressants, amphetamines, chloroethylbenzylamines, and some experimental insecticides, were tested for their ability to inhibit octopamine uptake and metabolism. The sodium-insensitive component of uptake was not inhibited by most compounds tested, but the sodium-sensitive component was strongly inhibited by xylamine, N-ethyl-N-chloroethyl-o-bromobenzylamine, and their aziridinium ions (60-100%). These compounds also effectively inhibited N-acetyl-transferase (IC50 values at or below 1 microM). Other good inhibitors of N-acetyltransferase included desipramine, synephrine, and an experimental insecticide, CGA 132427. Formamidine pesticides had limited effect on both processes, and neither action seems likely to be involved in their octopaminergic actions in vivo. Cocaine was unique in stimulating N-acetyltransferase activity. When inhibition of sodium-sensitive uptake is compared with inhibition of N-acetyltransferase in the cockroach ventral nerve cord, two groups of inhibitors are discernible. Type 1 compounds inhibit uptake without an effect on N-acetyltransferase, whereas type 2 compounds inhibit both processes. These results suggest a functional linkage between the uptake and acetylation of octopamine.

M-octopamine injected into the paraventricular nucleus induces eating in rats: a comparison with noradrenaline-induced eating

1. The effects on food intake in rats of injection of m- and p-octopamine into the paraventricular nucleus (PVN) of the hypothalamus were examined, and compared to the effects of noradrenaline (NA). 2. m-Octopamine injected into the PVN induced a dose-dependent increase in food intake, with the maximal effect occurring at a dose of 25 nmol. p-Octopamine did not elicit eating unless it was administered to animals pretreated with the monoamine oxidase inhibitor, pargyline. 3. The effects of pretreatment with various adrenoceptor antagonists, injected into the PVN, on the eating responses induced by 25 nmol m-octopamine and NA were examined. The alpha 1-adrenoceptor antagonist, corynanthine, and the beta-adrenoceptor antagonist, propranolol, failed to alter the eating induced by m-octopamine or NA. The effects of these two amines were susceptible to blockade of alpha 2-adrenoceptors. Idazoxan reversed the eating induced by m-octopamine and noradrenaline. However, yohimbine was effective only against the eating induced by m-octopamine. Thus, both m-octopamine and NA appear to act via alpha 2, but not alpha 1 or beta-adrenoceptors. 4. Injection of alpha-methyl-p-tyrosine into the PVN attenuated the effect of m-octopamine, but not of NA. This result suggests that m-octopamine elicits eating, at least in part, by releasing endogenous NA. 5. The NA and octopamine uptake inhibitor, desipramine, significantly potentiated the eating induced by a low dose of m-octopamine. This effect may occur because desipramine would prolong the synaptic activity of released NA. 6. The results indicate that m-octopamine elicits a marked and reliable eating response which is mediated largely by a release of endogenous NA, which acts at alpha 2-receptors. These results are consistent with the view that octopamine may function as a modulator of NA activity in the central nervous system.

Distribution of biogenic amines in the cricket central nervous system

The distribution of biogenic amines, their precursors, and metabolites in the central nervous system (CNS) of the cricket was determined using HPLC with electrochemical detection. Three biogenic amines, octopamine (OA), dopamine (DA), and 5-hydroxytryptamine (5-HT); two precursors, tyramine and tryptophan; and two metabolites, synephrine and 5-hydroxyindole-3-acetic acid, were detected in all ganglia. In the brain, 5-HT occurred in the largest quantities followed by OA, while in other ganglia OA occurred in the largest quantities followed by 5-HT and DA. In all ganglia, the amount of OA was two to nine times greater than that of DA. The results are discussed in comparison with different insect species.

A study of cyclic AMP-dependent protein phosphorylation in Schistocerca gregaria CNS: a comparison to that in mammalian CNS

1. The effect of cyclic AMP (10 microM) on the incorporation of 32P into protein was studied in cell-free preparations of Schistocerca gregaria cerebral ganglia. 2. Cyclic AMP-dependent phosphorylation of total protein was maximal after 60 sec, had a pH optimum of 7 to 8, was not affected by temperature (22-37 degrees C) and had a Km of 77 microM ATP. 3. Cyclic AMP increased the phosphorylation of total and specific protein in soluble fractions greater than synaptosomal greater than microsomal greater than crude membrane fractions. 4. In a direct comparison of locust brain to rat cerebral cortex, cyclic AMP stimulated the increased phosphorylation of only three protein bands, whereas in identical fractions of locust brain the phosphorylation of at least 12 protein bands was observed.