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PubMed2002

Is Na(+) required for the binding of dopamine, amphetamine, tyramine, and octopamine to the human dopamine transporter?

The role of Na(+) in the recognition of blockers by the dopamine transporter is accomodated by a model with a cation site that overlaps with the blocker binding domain, and a distal Na(+) site that interacts with this cation site and perhaps with the blocker binding domain itself. The present study addresses the application of this model to the recognition of substrates by the dopamine transporter, focusing on conditions that should reveal a stimulatory effect, if present, of Na(+) on substrate binding. Recognition was studied via the inhibition of binding of [(3)H]WIN 35,428 (2beta-carbomethoxy-3beta-(4-fluorophenyl) [(3)H]tropane), a cocaine analog, to the human dopamine transporter in human embryonic kidney 293 cells. Little or no changes in binding were noted for dopamine, d-amphetamine, p-tyramine, or dl-octopamine by increasing [Na(+)] from 2 mM to 20 mM with co-varying Br(-), both at pH 7.4 and 7.0. In 74-mM Tris-HBr or -HCl, only dopamine and d-amphetamine showed binding increases upon raising Na(+), leveling off with NO(3)(-) or SO(4)(2-) but not Br(-) as anion at approximately 60 mM Na(+), consonant with a partly stimulatory action of Br(-). An Na(+) free, low 5-mM Tris-HEPES buffer was used for studying Na(+) curves truly starting at 0 mM, and, with SO(4)(2-) as the anion, no stimulation of binding by Na(+) was observed. This suggested that the stimulations observed in high (74 mM) Tris(+) buffer by Na(+) were not a direct effect of Na(+) but rather a disinhibitory effect of Na(+) in removing Tris(+) inhibition that depended upon substrate. Tris(+) IC(50) values in Na(+) free buffer were not lower for dopamine and d-amphetamine than p-tyramine and dl-octopamine. No evidence was found for a stronger inhibitory effect of Na(+) for dopamine and dl-octopamine potentially offsetting Tris(+) disinhibition. All results together support the existence of a substrate domain overlapping with a cation site that also binds Tris(+); a distal Na(+) site interacts with this cation site and with the substrate domain by negative allosterism and is additionally impacted by Cl(-). Importantly, interactions between sites vary with the type of substrate, and, in membrane preparations, Na(+) is not required for, or stimulatory to, the binding of any of the four substrates studied unlike the binding of the cocaine analog WIN 35,428.

Amphetamine↗

PubMed2002

Octopamine enhances moth olfactory responses to pheromones, but not those to general odorants.

Effects of octopamine on responses of olfactory receptor neurons of Bombyx mori males and females, specialized to the reception of pheromone components and general odorants, respectively, were compared. Injections of octopamine had no effect on the transepithelial potential of antennal sensilla trichodea in both sexes. In males, octopamine increased significantly the amplitude of receptor potentials and nerve impulse responses elicited by the pheromone components bombykol and bombykal. However, the responses of homologous female general odorant-sensitive neurons to linalool and benzoic acid were not affected. In control experiments, injection of physiological saline did not increase the responses in any neuron type.

Action Potentials↗

PubMed2004

Octopamine-containing (OC) interneurons enhance central pattern generator activity in sucrose-induced feeding in the snail Lymnaea.

In the pond snail Lymnaea stagnalis octopamine-containing (OC) interneurons trigger and reconfigure the feeding pattern in isolated CNS by excitation of the central pattern generator. In semi-intact (lip-mouth-CNS) preparations, this central pattern generator is activated by chemosensory inputs. We now test if sucrose application to the lips activates the OC neurons independently of the rest of the feeding central pattern generator, or if the OC interneuron is activated by inputs from the feeding network. In 66% of experiments, sucrose stimulated feeding rhythms and OC interneurons received regular synaptic inputs. Only rarely (14%) did the OC interneuron fire action potentials, proving that firing of OC interneurons is not necessary for the sucrose-induced feeding. Prestimulation of OC neurons increased the intensity and duration of the feeding rhythm evoked by subsequent sucrose presentations. One micromolar octopamine in the CNS bath mimicked the effect of OC interneuron stimulation, enhancing the feeding response when sucrose is applied to the lips. We conclude that the modulatory OC neurons are not independently excited by chemosensory inputs to the lips, but rather from the buccal central pattern generator network. However, when OC neurons fire, they release modulatory octopamine, which provides a positive feedback to the network to enhance the sucrose-activated central pattern generator rhythm.

Animals↗

PubMed2006

Octopamine boosts snail locomotion: behavioural and cellular analysis.

We measured the reduction in locomotion of unrestrained pond snails, Lymnaea stagnalis, subsequent to transdermal application of two selective octopamine antagonists, epinastine and phentolamine. After 3 h in fresh standard snail water following treatment with 4 mM epinastine or 3.5 mM phentolamine, the snails' speed was reduced to 25 and 56% of the controls (P < 0.001 and P = 0.02, respectively). The snails' speed decreased as the drug concentration increased. In the isolated CNS, 0.5 mM octopamine increased the firing rate of the pedal A cluster motoneurons, which innervate the cilia of the foot. In normal saline the increase was 26% and in a high magnesium/low calcium saline 22% (P < 0.05 and 0.01, respectively). We conclude that octopamine is likely to modulate snail locomotion, partially through effects on pedal motoneurons.

Adrenergic alpha-Agonists↗

PubMed1992

Octopamine selectively modifies the slow component of sensory adaptation in an insect mechanoreceptor.

The effects of octopamine were studied on the dynamic behavior of the sensory neuron in the cockroach femoral tactile spine. The neuron is a rapidly adapting mechanoreceptor in which adaptation occurs by elevation of the threshold for action potential encoding. The threshold follows increases or decreases of membrane potential, with a delay that involves two separate exponential components. Previous evidence has associated the slow component with sodium pumping and the fast component with sodium channel inactivation. Octopamine reversibly raised the resting threshold and increased but slowed the slow component. These data indicate that octopamine has specific effects on membrane-ionic processes in insect sensory neurons.

Action Potentials↗

PubMed1993

Octopamine immunoreactive neurons in the fused central nervous system of spiders.

Using antisera directed against octopamine (OA), we identified and mapped octopamine-immunoreactive (OA-ir) neurons and their projections in the fused, central ganglion complex of wandering spiders, Cupiennius salei. Labeled cell bodies are concentrated in the subesophageal ganglion complex (SEG) where they are arranged serially in ventral, midline clusters. OA-ir processes from these cells project dorsally. Some neurites end close to segmental septa; others merge into longitudinal tracts connecting the neuromeres. Labeled collaterals leaving these tracts project into peripheral neuropil. In the brain, OA-ir somata were found only in the two cheliceral hemiganglia, where a cluster of 4-5 relatively large cells (soma diameter 25 microns) lies next to a group of small somata (diameter < 10 microns). Neurites originating from the large somata descend into the SEG and merge into longitudinal tracts. The central body of the brain contains profuse ascending projections. Except for fine varicosities that are confined to the roots of nerves, we found no OA-ir fibers leaving the central nervous system (CNS). Within the CNS, however, OA-ir varicosities are concentrated in neuropil and near hemolymph spaces. This distribution suggests that OA acts as a neurotransmitter and/or local neuromodulator at central synapses, while it is also released into the hemolymph and presumably acts hormonally at peripheral sites. Using high-pressure liquid chromatography measurements, the hemolymph was in fact found to contain 12-40 nM of free octopamine.

Animals↗

PubMedDate not supplied

Propranolol and somatostatin interactions with the hyperglycemic effects of glucagon, octopamine, noradrenaline and cAMP in worker honeybees in vivo.

The hyperglycemic effects of vertebrate glucagon, octopamine and noradrenaline, are depressed when propranolol or somatostatin is simultaneously injected into emerging adult worker bees. The inhibitory action of the peptidic antagonist (somatostatin) is more marked against the peptidic agonist (glucagon) and the action of the aminergic antagonist (propranolol) is more marked against the aminergic agonist (octopamine). Somatostatin seems to be inactive against the hyperglycemic effects of cyclic AMP itself. Lastly, octopamine and cAMP might share a common stimulatory activity towards the honeybee's hemolymph trehalases.

Animals↗

PubMed1984

Influence of octopamine on trehalase activity in muscle and hemolymph of the American cockroach, Periplaneta americana L.

Injection of adult male cockroaches (Periplaneta americana) with 10 microliter 1 microM octopamine causes elevated activity of trehalase (alpha, alpha-trehalose glucohydrolase; EC 3.2.1.28) in hemolymph and muscle but not in gut. Tyramine, dopamine and glutamate, at the same concentration, failed to elicit any effect on trehalase activity. Determination of some kinetic parameters for muscle and hemolymph trehalases reveal that octopamine causes an increase in Vmax without any significant alteration in the Km of the enzyme for trehalose. The results are discussed in terms of the physiological significance of octopamine-mediated activation of tissue trehalases.

Animals↗

PubMed1995

Octopamine and Leydig cell stimulation depress the afterhyperpolarization in touch sensory neurons of the leech.

In touch sensory neurons of the leech, a train of spikes evoked by intracellular electrical stimulation leads to an afterhyperpolarization, mainly due to the activation of the Na+/K+ electrogenic pump and partly to a Ca(2+)-activated K+ conductance. It has been found that serotonin is able to reduce the afterhyperpolarization through the inhibition of the Na+/K+ electrogenic pump. We have investigated the possible modulation of the afterhyperpolarization by other endogenous neurotransmitters and we have found that octopamine is also able to reduce its amplitude. The electrical stimulation of the octopaminergic Leydig neurons mimics this effect. We have compared the actions of the two amines and found that the effect of serotonin is blocked by methysergide but not by high [Mg2+] or by phentolamine, and it is still present in touch cells isolated in culture. On the contrary, the octopamine modulation of the afterhyperpolarization does not occur in single touch cells in culture and it is blocked by all these treatments. These data suggest that while serotonin should act monosynaptically, octopamine should act through a serotonergic pathway.

Animals↗

PubMed1984

Effect of intracerebroventricularly administered octopamines and synephrines on angiotensin II-induced water intake in rats.

Recent studies from this laboratory showed that l-m-synephrine (phenylephrine), a metabolite of l-m-octapamine, inhibited the drinking response of rats to peripherally administered angiotensin II. The objective of this investigation was to determine whether the isomers of both octapamine and synephrine could inhibit angiotensin II-induced dipsogenesis in the rat. Of the isomers tested, only d,l-m-octopamine and l-m-synephrine blocked the dipsogenic response to administration of angiotensin II (200 micrograms/kg, SC). The antidipsogenic effect of both d,l-m-octopamine and l-m-synephrine could be blocked by concurrent administration of yohimbine (300 micrograms/kg, IP), an alpha 2-adrenoceptor antagonist. The results indicate that m-octopamine and m-synephrine exert their antidipsogenic effect via alpha 2-adrenoceptors. These studies add to a growing body of data suggesting that activation of alpha 2-adrenoceptors inhibits, while blockade of these receptors enhances, angiotensin II-induced drinking.

2-Hydroxyphenethylamine↗

PubMed1990

[11C]octopamine synthesis using [11C]cyanide: chemical and enzymatic approaches for the [11C]cyanohydrin synthesis.

[11C]-p- and m-octopamine hydrochloride were synthesized from [11C]HCN in a two-step sequence. Chemical and enzymatic approaches were used for the formation of the [11C]cyanohydrin intermediates as the key step. Isolated radiochemical yields of 0.7-2.3% at the end-of-synthesis were obtained with an overall preparation time of 40-60 min. The enantiomeric purity of the [11C]-p-octopamine obtained through the enzymatic process was 92% e.e. in the (S)-enantiomer, whereas that of the [11C]-m-octopamine was 42% e.e. in the (R)-enantiomer, as determined by HPLC without any derivatization.

Carbon Radioisotopes↗

PubMed1990

Cloning, localization, and permanent expression of a Drosophila octopamine receptor.

A cDNA for a member of the G protein-coupled receptor family was isolated from Drosophila using a probe derived from a human beta 2-adrenergic receptor cDNA. This Drosophila receptor gene is localized at 99A10-B1 on the right arm of chromosome 3 and is preferentially expressed in Drosophila heads. The insect octopamine receptor has been permanently expressed in mammalian cells, where it mediates the attenuation of adenylate cyclase activity and exhibits a pharmacological profile consistent with an octopamine type 1 receptor. Sequence and pharmacological comparisons indicate that the octopamine receptor is unique but closely related to mammalian adrenergic receptors, perhaps as an evolutionary precursor.

Amino Acid Sequence↗

PubMed2003

Octopamine receptor OAMB is required for ovulation in Drosophila melanogaster.

Octopamine is a major monoamine in invertebrates and affects many physiological processes ranging from energy metabolism to complex behaviors. Octopamine binds to receptors located on various cell types and activates distinct signal transduction pathways to produce these diverse effects. We previously identified one of the Drosophila octopamine receptors named OAMB that produces increases in cAMP and intracellular Ca2+ upon ligand binding. It is expressed at high levels in the brain. To explore OAMB's physiological roles, we generated deletions in the OAMB locus. The resultant oamb mutants were viable without gross anatomical defects. The oamb females displayed normal courtship and copulation; however, they were impaired in ovulation with many mature eggs retained in their ovaries. RT-PCR, in situ hybridization, and expression of a reporter gene revealed that OAMB was also expressed in the thoracicoabdominal ganglion, the female reproductive system, and mature eggs in the ovary. Moreover, analysis of various alleles pinpointed the requirement for OAMB in the body, but not in the brain, for female fecundity. The novel expression pattern of OAMB and its genetic resource described in this study will help advance our understanding on how the neuromodulatory or endocrine system controls reproductive physiology and behavior.

Animals↗

PubMed1999

Octopamine in invertebrates.

Octopamine (OA), a biogenic monoamine structurally related to noradrenaline, acts as a neurohormone, a neuromodulator and a neurotransmitter in invertebrates. It is present in relatively high concentrations in neuronal as well as in non-neuronal tissues of most invertebrate species studied. It functions as a model for the study of modulation in general. OA modulates almost every physiological process in invertebrates studied so far. Among the targets are peripheral organs, sense organs, and processes within the central nervous system. The known actions of OA in the central nervous system include desensitization of sensory inputs, influence on learning and memory, or regulation of the 'mood' of the animal. Together with tyramine, OA it is the only neuroactive non-peptide transmitter whose physiological role is restricted to invertebrates. This focussed the interest on the corresponding OA receptors. They are believed to be good targets for highly specific insecticides as they are not found in vertebrates. All octopamine receptors belong to the family of G-protein coupled receptors. Four of them could be distinguished using pharmacological tools. They show different coupling to second messenger systems including activation and inhibition of adenylyl cyclase, activation of phospholipase C and coupling to a chloride channel. Recently, octopamine receptors from molluscs and insects have been cloned. Further studies of all aspects of octopaminergic neurotransmission should give deeper insights into modulation of peripheral and sense organs and within the central nervous system in general.

Animals↗

PubMed1999

Isolation of a cDNA for an octopamine-like, G-protein coupled receptor from the cattle tick, Boophilus microplus.

Octopamine is a biogenic amine neurotransmitter of invertebrates that binds to a G-protein coupled receptor that has seven transmembrane domains. Formamidine pesticides like amitraz are highly specific agonists of the octopamine receptor. Amitraz is used extensively to control the cattle tick, Boophilus microplus, and many other ticks but now there are strains of ticks that are resistant to amitraz. We have isolated a cDNA from the cattle tick, B. microplus, that belongs to the biogenic amine family of receptors. The predicted amino acid sequence from this cDNA is most similar to octopamine receptors from insects. The nucleotide sequence of this gene from amitraz-resistant and amitraz-susceptible cattle ticks was identical. Thus, a point mutation/s did not confer resistance to amitraz in the strains we studied. Alternative explanations for resistance to amitraz in B. microplus are discussed.

Amino Acid Sequence↗

PubMed1974

Octopamine- and serotonin-stimulated phosphorylation of specific protein in the abdominal ganglion of Aplysia californica.

Phosphorylation of a protein (or proteins) of molecular weight 120,000 in the Aplysia abdominal ganglion, as measured by incorporation of [(32)P] or [(33)P]sodium phosphate in vitro followed by separation of the phosphoproteins on sodium dodecyl sulfate-polyacrylamide gels, was specifically stimulated by incubation in the presence of the putative neurotransmitters octopamine or serotonin. The stimulatory effect of octopamine and serotonin was inhibited by phentolamine and methysergide, respectively, and was mimicked by incubation in the presence of dibutyryl cyclic AMP. Label-chase experiments indicated that the difference between control and octopamine-treated ganglia persists for several hours after removal of the drug from the incubation medium. This result suggests that neurotransmitters may produce relatively long-lasting changes in a phosphoprotein in the ganglion, perhaps in postsynaptic cells.

Animals↗

PubMed1995

Pharmacology of the octopamine receptor from locust central nervous tissue (OAR3).

1. The present study characterized highly effective agonists from different classes of compounds for the neuronal octopamine receptor (OAR3) of the migratory locust (Locusta migratoria L.). Biogenic amines and phenyliminoimidazolidines (PIIs) were employed for the study of structure-activity relationships. 2. The highest affinity PIIs were predominantly those with substitutions at the positions 2 and 4 of the phenolic ring (e.g. NC 7, KI = 0.3 nM, NC 8, KI = 0.81 nM). Substitutions at these positions always had positive effects on the affinity of the respective agonists. 3. Substitutions at the positions 3, 5 and 6, however, always had negative effects on the affinity. At the position one of the phenolic ring, heterocyclic substituents are preferred. 4. Some PIIs had a more than 30 times higher affinity for OARs than for alpha-adrenoceptors which are the vertebrate homologues of the insect octopamine receptors. 5. The only non-PII with subnanomolar affinity was the aminooxazoline derivative AC 6 (KI = 0.92 nM). 6. A variety of substances with known insecticidal activity such as chlordimeform, demethylchlor-dimeform, amitraz or AC 6 had high affinity for the locust neuronal octopamine receptor.

Animals↗

PubMed1985

Effect of 6-hydroxydopamine on the metabolism of endogenous octopamines and catecholamines.

The daily excretion in rat urine of o-(OHMA) (0.2), m-(MHMA) (0.9), p-(PHMA) hydroxymandelic acid (78), vanillylmandelic acid (VMA) (3.5) and homovanillic acid (30 micrograms day-1), terminal metabolites of the isomeric octopamines and catecholamines, has been determined by gas chromatography-mass spectrometry. Chemical sympathectomy with 6-hydroxydopamine (i.p.) caused the daily output of each acid (except OHMA) to drop by 50% and that of PHMA was restored to normal the most rapidly after cessation of treatment. These results indicate that m- and p- (but not o-) octopamine coexist with catecholamines in sympathetic nerve terminals, are subject to the same compensatory biosynthetic mechanism following chemical sympathectomy and that p-octopamine has the highest turnover rate of these biogenic amines in the rat.

Animals↗