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PubMed1985

Regional differences in responsiveness to octopamine within a locust skeletal muscle.

Regional differences in the physiological and biochemical responses to octopamine have been investigated in the extensor tibiae muscle of the hind leg of the locust. Octopamine increases the rate of relaxation of twitch tension generated by the slow motoneurone by different amounts in different regions of the muscle. It also increases the amplitude of twitch tension by the same amount in different regions of the muscle. The relaxation rate of fast twitch tension is increased by the same amount in all regions of the muscle innervated by the fast motoneurone. Octopamine also increases cyclic AMP levels by different amounts in different regions of both the extensor muscle and its antagonistic muscle, the flexor tibiae. In both muscles the maximal responses are obtained in the regions of the muscles containing the highest proportions of slow and intermediate muscle fibres as characterized by their contractile and ultrastructural properties. The results are discussed in terms of their functional significance and compared with examples of differential responses of different muscle fibre types in other invertebrate and vertebrate skeletal muscles.

2-Hydroxyphenethylamine↗

PubMed1997

Molecular cloning and pharmacological characterization of a molluscan octopamine receptor.

We describe the cloning and functional expression of a cDNA encoding a novel G protein-coupled receptor, which was isolated from the central nervous system of the pond snail Lymnaea stagnalis. The amino acid sequence predicted by this cDNA shows highest similarity with the sequence of the Locusta tyramine receptor, the Drosophila tyramine/octopamine receptor, and the mammalian alpha-adrenergic receptors. On expression in mammalian cells, [3H]rauwolscine, an alpha2-adrenergic receptor antagonist, binds with high affinity (K(D) = 2.9 x 10(-9) M) to the receptor. Of several tested neurotransmitters, octopamine (which is considered to be the invertebrate counterpart of norepinephrine) showed the highest affinity (1.9 x 10(-6) M) for the receptor. Therefore, we consider this receptor to be the first true octopamine receptor to be cloned. The ligand binding properties of the novel receptor, designated Lym oa1, seem to be distinct from any of the binding profiles described for octopamine receptors in tissue preparations. Although the pharmacological profile of Lym oa1 shows some similarity with that of Tyr/Oct-Dro and Tyr-Loc, there are also clear differences. In particular, phentolamine, chlorpromazine, and mianserine display markedly higher affinities for Lym oa1 than for the insect receptors. As far as the vertebrate adrenergic receptors are concerned, the ligand binding properties of Lym oa1 resemble alpha2-adrenergic receptors more than they do alpha- or beta-adrenergic receptors. Octopaminergic stimulation of Lym oa1 induces an increase in both inositol phosphates and cAMP (EC50 = 9.1 x 10(-7) M and 5.1 x 10(-6) M, respectively). This is in contrast to the signal transduction pathways described for the related tyramine- and alpha2-adrenergic receptors, which couple in an inhibitory way to adenylyl cyclase.

Amino Acid Sequence↗

PubMed1979

Octopamine receptors, adenosine 3',5'-monophosphate, and neural control of firefly flashing.

An adenylate cyclase activated as much as 25-fold by low concentrations of octopamine has been identified in the firefly lantern. The relative potency of octopamine and various other amines in stimulating this enzyme, and effects of antagonists in blocking octopamine activation, correlate well with the known effects of these agents in affecting light production. In addition to suggesting a role for adenosine 3',5'-monophosphate (or pyrophosphate) in the neural control of firefly flashing, identification of this potent enzyme should facilitate the characterization of phenylethylamine receptors in excitable tissue.

Adenylyl Cyclases↗

PubMed1982

Efferent fibers to Limulus eyes synthesize and release octopamine.

Octopamine synthesized in vitro from tyramine by Limulus lateral and ventral eyes was located by light microscopic and electron microscopic autoradiography in efferent fibers which innervate ventral photoreceptors and lateral eye ommatidia. Newly synthesized octopamine was released from efferent fibers in response to depolarization in high concentrations of potassium. We propose that octopamine is a neurotransmitter of efferent fibers that may modulate basic retinal processes such as photoreceptor sensitivity, photomechanical movements, and photoreceptive membrane turnover.

Animals↗

PubMed1982

Serotonin and octopamine in the nematode Caenorhabditis elegans.

The biogenic amines serotonin and octopamine are present in the nematode Caenorhabditis elegans. Serotonin, detected histochemically in whole mounts, is localized in two pharyngeal neurons that appear to be neurosecretory. Octopamine, identified radioenzymatically in crude extracts, probably is also localized in a few neurons. Exogenous serotonin and octopamine elicit specific and opposite behavioral responses in Caenorhabditis elegans, suggesting that these compounds function physiologically as antagonists.

Age Factors↗

PubMedDate not supplied

Categorical and prolonged potentials are evoked when brief, intermediate-intensity flashes stimulate horseshoe crab lateral eye photoreceptors during octopamine neuromodulation.

Octopamine, a major efferent neurotransmitter in the lateral eye of the horseshoe crab (Limulus polyphemus), has previously been shown to modulate photoreceptor responses evoked by long flashes. Quantification of these data indicates that this modulation produced a genuine increase in sensitivity to light which cannot be entirely due to an increase in optical efficiency consequent on an anatomical alteration. Other previous studies demonstrated that extrinsic current can modulate Limulus lateral eye photoreceptor cells by inducing a bistable membrane potential with two distinct states. The present study was therefore undertaken to find out if octopamine could modulate visual responses by inducing prolonged and bistable polarization shifts similar to those demonstrated in several other neural systems. Intracellular microelectrodes were used to execute an electrophysiological study of the receptor potentials evoked in the lateral eye of Limulus when brief (20-ms) flashes were delivered while 50 microM octopamine perfused dark-adapted photoreceptors. The combined chemical and optical stimuli prolonged photoreceptor responses to light to the degree that they often exceeded the duration of the brief stimulus by hundreds of milliseconds. Moreover, these prolonged potentials were clearly bistable because they were categorical--either a prolongation was perceptually clear-cut and present or it was not, with no intermediate patterns being observed. During seawater control perfusions, such prolongations were absent. This appears to be the first demonstration of such categorical and prolonged potentials in a photoreceptor neuron. This finding particularly suggests that efferent-driven neuromodulation can enable the development of a persisting short-term representation of a brief stimulus, with this representation being retained at the most distal possible neural site.

Animals↗

PubMed1975

Pharmacological effects of alpha-methyldopa, alpha-methylnorepinephrine, and octopamine on rat arteriolar, arterial, and terminal vascular smooth.

Experiments on rat mesenteric arterioles, metarterioles, and aortae demonstrate that although alpha-methylnorepinephrine is much less potent in inducing contraction than epinephrine on all three blood vessel types, it is either equivalent or only one and a half to two times less potent than the natural postganglionic neurotransmitter, norepinephrine, on these blood vessels. Furthermore, alpha-methylnorepinephrine is equivalent to norepinephrine in its ability to induce maximal contractile responses on rat arterioles, metarterioles, and aortae. Systemic administration of alpha-methyldopa to rats for 15 days shifted the log dose-response curves for all three catecholamines, but not vasopressin or potassium chloride, to the right of all three blood vessel types; the maximal contractile responses to these amines were, however, not affected by chronic treatment with alpha-methyldopa. In addition, acute, intra-arterial administration of 500 mg/kg of alpha-methyldopa was found not only to induce mesenteric arteriolar vasodilatation gradually but also to depress arteriolar reponsiveness to catecholamines. In view of these direct findings, it is difficult to accept the hypothesis that alpha-methyldopa induces hypotension via formation of a "false" postganglionic neurotransmitter substance, namely, alpha-methylnorepinephrine. The present findings suggest that alpha-methyldopa may exert some of its anti-hypertensive action, at least in the rat, by (1) depressing arteriolar responsiveness to circulating and released catecholamines and (2) some unknown direct action on peripheral vascular muscle. In addition, the present study indicates that octopamine is (1) between 60 and 15,000 times less potent than norepinephrine on rat arterioles and metarterioles and (2) incapable of eliciting more than a 40% occlusion of these terminal vessels. It is suggested that such data support the concept that octopamine, in contrast to alpha-methylnorepinephrine, could serve as a false adrenergic neurotransmitter agent and thus account for part or all of the hypotensive action of monoamine oxidase inhibitors like pargyline. The use of complete dose-response curves, several different adrenergic compounds (i.e., epinephrine, norepinephrine, alpha-methylnorepinephrine, octopamine, phenylephrine, and dopamine), and different rat blood vessels supports the concept that adrenergic molecules containing a catecholamine nucleus and a beta-hydroxyl group elicit the most potent constrictor responses from peripheral blood vessels. In addition, the data suggest that the structure-activity relationships for catecholamines and their analogs on terminal vascular smooth muscle are probably different from those for arterial smooth muscle.

Administration, Topical↗

PubMed1984

Studies on the mode of action of octopamine, 5-hydroxytryptamine and proctolin on a myogenic rhythm in the locust.

The modes of action of the modulatory compounds octopamine, 5-hydroxytryptamine (5-HT) and proctolin on the frequency of the myogenic rhythm of the extensor-tibiae muscle of the hindleg of the locust, Schistocerca americana gregaria, have been investigated. 5-HT and proctolin increase the frequency of the myogenic rhythm and the results of the present study suggest that they may mediate their effects by increasing the levels of cyclic AMP in the pacemaker of the myogenic bundle. In contrast, octopamine reduces the frequency of the myogenic rhythm and appears to mediate its effects by a mechanism that does not involve an elevation of cyclic AMP. A number of other possible mechanisms for the action of octopamine are discussed.

1-Methyl-3-isobutylxanthine↗

PubMed2004

Octopamine modulates the axons of modulatory projection neurons.

Octopamine increases the cycle frequency of the pyloric rhythm in the crab Cancer borealis by acting at multiple sites within the stomatogastric nervous system. The junction between the stomatogastric nerve (stn) and the superior esophageal nerve (son) shows synaptic structures. When applied only to the stn-son junction, octopamine induced action potentials in the axons of the modulatory commissural neuron 5 (MCN5) that project from the commissural ganglia to the stomatogastric ganglion (STG). The activation of the MCN5 neurons was correlated with an increase in the pyloric rhythm frequency. Additionally, octopamine had direct effects on the STG, including the activation of the pyloric dilator and pyloric neurons, an increase in the pyloric frequency, and a change in the phase relationships of the pyloric neurons. Thus, the same modulator can influence the pyloric rhythm by acting at multiple sites, including the axons of identified modulatory neurons that project to the STG. These data demonstrate that axonal propagation may be influenced locally by neuromodulators acting on axonal receptors, therefore altering the conduction of information from different command and integrating centers.

Action Potentials↗

PubMedDate not supplied

A selective radioenzymatic assay for the determination of octopamine and phenylethanolamine in plasma and cerebrospinal fluid. Preliminary results in human and experimental hepatic encephalopathy.

A sensitive radioenzymatic assay for the simultaneous determination of phenylethanolamine and octopamine in biological fluids is described. It is derived from the radioenzymatic assay originally described by Molinoff et al. (1969) and subsequently modified by Saavedra (1974). The enzymatic reaction is based upon the methylation of phenylethanolamine and octopamine by phenylethanolamine-N-methyl transferase using 14C-S-adenosylmethionine as the methyl donor. The N-methyl derivatives of the two amines are separately extracted and estimated. Selectivity is increased by optimization of extraction and evaporation and by subsequent extraction of the two compounds. Phenylethanolamine and octopamine levels were determined in plasma of human subjects and in plasma and CSF of dogs. The levels were found significantly elevated both in human and experimental hepatic encephalopathy.

2-Hydroxyphenethylamine↗

PubMed1983

Serotonin and octopamine have opposite modulatory effects on the crayfish's lateral giant escape reaction.

Serotonin and octopamine have opposite effects on a simple behavioral response, the crayfish's lateral giant escape reaction. Specifically, serotonin depresses the lateral giants' responsiveness, whereas octopamine enhances it. Both effects are largely confined to the disynaptic pathway from the sensory afferents to the lateral giants, although, occasionally, small effects are also seen in the monosynaptic pathway to the lateral giants. One specific locus of the octopaminergic effect is the synapse between the afferents and the largest of the sensory interneurons in the disynaptic pathway, interneuron A. Serotonin, however, does not have a consistent effect at this synapse. Although serotonin and octopamine modulate the excitability of the escape response, neither monoamine appears to significantly alter the rate at which this response habituates.

Animals↗

PubMedDate not supplied

Interactions between agents stimulating and inhibiting the central dopamine receptors and octopamine.

Octopamine administered to rats in doses of 50, 100 and 250 microgram into the cerebral ventricles exerted a stimulating effect on the dopaminergic structures in the rat brain as evidenced by the potentiation of amphetamine and apomorphine induced hyperactivity, and potentiation of stereotypy caused by these agents. Octopamine hyperactivity was abolished by spiroperidol (0.1 mg/kg intraperitoneally). In doses of 100 and 250 microgram octopamine also had an anticataleptic effect.

Amphetamines↗

PubMed2005

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.

Adenylyl Cyclases↗

PubMed2004

Octopamine receptors in the honeybee (Apis mellifera) brain and their disruption by RNA-mediated interference.

Octopamine plays important neuromodulatory roles in the honeybee brain. Accordingly, mRNA from a recently identified honeybee octopamine receptor (AmOA1) is distributed throughout the brain. We have evaluated the occurrence of AmOA1 in the antennal lobe (AL) as well as rest of the brain (RB) by western blotting using an antiserum raised against a peptide selected from AmOA1 sequence. In addition to an expected band (78 kDa in the AL), one additional band (72 kDa) was identified from the AL and four bands (48, 60, 72 and 78 kDa) were observed in the RB. These bands were also recognized with antiserum against a different peptide segment from an octopamine receptor ortholog from the fruitfly (OAMB). Significant sequence identity with the peptide segment used to generate the antiserum was only found with OAMB and its splice variants in fruitfly; it was less conserved in other biogenic amine receptors from honeybee and other insects. Furthermore, western blot analysis performed on brains with dsRNA-treated antennal lobes showed a decrease in the intensity of all four bands. This suggests that AmOA1 antiserum specifically recognizes one or more types of AmOA1 receptors in the honeybee brain. We extend our earlier study of RNAi to quantify the rate of spread of dsRNA from a localized injection to other neuropils.

Amino Acid Sequence↗

PubMed1999

Cultured insect mushroom body neurons express functional receptors for acetylcholine, GABA, glutamate, octopamine, and dopamine.

Fluorescence calcium imaging with fura-2 and whole cell, patch-clamp electrophysiology was applied to cultured Kenyon cells (interneurons) isolated from the mushroom bodies of adult crickets (Acheta domesticus) to demonstrate the presence of functional neurotransmitter receptors. In all cells investigated, 5 microM acetylcholine (ACh, n = 52) evoked an increase in intracellular free calcium ([Ca2+]i). Similar effects were observed in response to 10 microM nicotine. The ACh response was insensitive to atropine (50 microM) but was reduced by mecamylamine (50 microM) and alpha-bungarotoxin (alpha-bgt, 10 microM). ACh-induced inward ion currents (n = 28, EACh approximately 0 mV) were also blocked by 1 microM mecamylamine and by 1 microM alpha-bgt. Nicotine-induced inward currents desensitized more rapidly than ACh responses. Thus functional alpha-bgt-sensitive nicotinic ACh receptors are abundant on all Kenyon cells tested, and their activation leads to an increase in [Ca2+]i. gamma-Aminobutyric acid (GABA, 100 microM) triggered a sustained decrease in [Ca2+]i. Similar responses were seen with a GABAA agonist, muscimol (100 microM), and a GABAB agonist, 3-APPA (1 mM), suggesting that more than one type of GABA receptor can affect [Ca2+]i. This action of GABA was not observed when the extracellular KCl concentration was lowered. All cells tested (n = 26) with patch-clamp electrophysiology showed picrotoxinin (PTX)-sensitive, GABA-induced (30-100 microM) currents with a chloride-sensitive reversal potential. Thus, an ionotropic PTX-sensitive GABA receptor was found on all Kenyon cells tested. Most (61%) of the 54 cells studied responded to -glutamate (100 microM) application either with a biphasic increase in [Ca2+]i or with a single, delayed, sustained [Ca2+]i increase. Nearly all cells tested (95%, n = 19) responded to (100 microM) -glutamate with rapidly desensitizing, inward currents that reversed at approximately -30 mV. Dopamine (100 microM) elicited either a rapid or a delayed increase in [Ca2+]i in 63% of the 26 cells tested. The time course of these responses varied greatly among cells. Dopamine failed to elicit currents in patch-clamped cells (n = 4). A brief decrease in [Ca2+]i was induced by octopamine (100 microM) in approximately 54% of the cells tested (n = 35). However, when extracellular CaCl2 was lowered, octopamine triggered a substantial increase in [Ca2+]i in 35% of the cells tested (n = 26). No octopamine-elicited currents were detected in patched-clamped cells (n = 10).

Animals↗

PubMed1997

Correlation between changes in host behaviour and octopamine levels in the tobacco hornworm Manduca sexta parasitized by the gregarious braconid parasitoid wasp Cotesia congregata

The parasitoid wasp Cotesia congregata lays its eggs within the body of its host, the larval form of the tobacco hornworm Manduca sexta. Host behaviour appeared normal until approximately 8 h prior to the emergence of the parasitoids from their host at which time M. sexta feeding and locomotion declined irreversibly. This change in host behaviour may be to the advantage of the wasp since unparasitized M. sexta presented with wasp pupae ate them. Despite the decline in feeding and locomotion, hosts with emerged parasitoids had normal reflexes and showed no other signs of debilitation. Concomitant with the change in host behaviour, octopamine concentration measured using high-performance liquid chromatography with electrochemical detection (HPLC-ED) increased from 22.2±2.1 pg µl-1 to 143.7±7.8 pg µl-1 in the haemolymph of the host. In unparasitized M. sexta, however, increased octopamine levels were correlated with increased activity. We discuss possible explanations for the co-occurrence of high haemolymph octopamine levels and low behavioural arousal in parasitized M. sexta.

Journal Article↗

PubMed2002

Immunoreactivity against choline acetyltransferase, gamma-aminobutyric acid, histamine, octopamine, and serotonin in the larval chemosensory system of Dosophila melanogaster.

We have studied the distribution of choline acetyltransferase (ChAT), gamma-aminobutyric acid (GABA), histamine, octopamine and serotonin in the larval chemosensory system of Drosophila melanogaster. Colocalization at the confocal level with green fluorescent protein (GFP) or Tau-GFP reporters, expressed in selected P[GAL4] enhancer trap lines, was used to identify the cells making up these neurotransmitters. As in the adult fly, larval olfactory afferents project into the (larval) antennal lobe (LAL), where they synapse onto local interneurons and projection neurons, whereas gustatory afferents terminate essentially in the tritocerebral-subesophageal (TR-SOG) region. We demonstrate that the neuropils of the LAL and the TR-SOG are immunoreactive to ChAT and GABA. In addition, serotonin- and octopamine-immunoreactive fibers are present in the LAL. ChAT immunostaining is localized in subsets of olfactory and gustatory afferents and in many of the projection neurons. In contrast, GABA is expressed in most, and perhaps all, of the local interneurons. Serotonin immunoreactivity in the LAL derives from a single neuron that is situated close to the LAL and projects to additional neuropil regions. Taken together, these findings resemble the situation in the adult fly. Hence, given the highly reduced numbers of odorant receptor neurons in the larva, as shown in a previous study (Python and Stocker [2002] J. Comp. Neurol. 445:374-387), the larval system may become an attractive model system for studying the roles of neurotransmitters in olfactory processing.

Animals↗

PubMed1994

Octopamine-like immunoreactivity in the brain and subesophageal ganglion of the honeybee.

The organization of putative octopaminergic pathways in the brain and subesophageal ganglion of the honeybee was investigated with a well-defined polyclonal antiserum against octopamine. Five prominent groups of just over 100 immunoreactive (IR) somata were found in the cerebral ganglion: Neurosecretory cells in the pars intercerebralis innervating the corpora cardiaca via NCC I, one cluster mediodorsal to the antennal lobe, one scattered on both sides of the midline of the protocerebrum, one between the lateral protocerebral lobes and the dorsal lobes, and a single soma on either side of the central body. With the exception of the pedunculi and beta-lobes of the mushroom bodies, varicose immunoreactive fibers penetrate all parts of the cerebral ganglion. Strong labelling was found in the central complex and the protocerebral bridge. Fine networks of labelled processes invade the antennal lobes, the calyces and a small part of the alpha-lobes of the mushroom bodies, the protocerebrum, and all three optic ganglia. In the subesophageal ganglion, one labelled cell body was found in the lateral soma layer of the mandibular segment. Each of the three neuromeres contains a group of six to ten somata in the ventral median parts. Most of the ventral median cells send their neurites dorsally through the midline tracts, whereas the neurites of a few cells follow the ventral cell body neurite tracts. Octopamine-IR was demonstrated in all neuropils that contain pathways for proboscis extension learning in honeybees. Because octopaminergic mechanisms seem to be involved in the behavioral plasticity of the proboscis extension reflex, our study provides anatomical data on the neurochemical organization of an appetitive learning paradigm.

Animals↗