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PubMed1993

Mapping of octopamine-immunoreactive neurons in the central nervous system of the lobster.

It has been suggested that serotonin and octopamine serve important roles in behavioral regulation in lobsters. In this paper the locations of octopamine-immunoreactive neurons were mapped in wholemount preparations of the ventral nerve cord of 4th stage lobster (Homarus americanus) larvae. Approximately 86 neurons were found, distributed as follows: brain, 12; circumesophageal ganglia, 2; subesophageal ganglion, 38; thoracic ganglia, 6 each; and 4th and 5th abdominal ganglia, 2 each. All the octopamine-immunoreactive neurons are paired and located along the midline. Of the 86 neurons, 28 were identified as neurosecretory, and 26 as intersegmental ascending thoracic, ascending abdominal, or descending interneurons. The neurosecretory system is arranged segmentally and located entirely within the thoracic and subesophageal neuromeres with extensive terminal fields of endings along 2nd thoracic and subesophageal nerve roots. This set of neurons shares the features of central and peripheral endings with 2 pairs of large serotonin-containing neurosecretory neurons found in the fifth thoracic and first abdominal ganglia. The intersegmental neurons include: (1) two cells in the brain and 2 pairs of cells in the 3rd and 4th neuromeres of the subesophageal ganglion, which project to the 6th abdominal ganglion; (2) a segmentally organized group of ascending interneurons found in the subesophageal and in all thoracic ganglia; and (3) pairs of ascending interneurons found in the 4th and 5th ganglia in the abdominal nerve cord. By means of a biochemical assay, the cell bodies of octopamine-immunoreactive neurosecretory cells in the thoracic segment of the nerve cord were found to contain 40-100 fmol of octopamine, while control neurons had none.

Animals↗
PubMed1986

Effects of octopamine, dopamine, and serotonin on production of flight motor output by thoracic ganglia of Manduca sexta.

Effects of biogenic amines on a centrally generated motor pattern in Manduca sexta were examined by pressure injecting nanomole to micromole amounts of octopamine, dopamine or serotonin into thoracic ganglia. Motor output was recorded extracellularly from a pair of antagonistic flight muscles and their motor neurons. The monoamines were found to alter production of a motor pattern that produces rhythmic wing flapping (10 Hz) and exhibits phase relationships similar to those in the flight pattern of intact moths. In mesothoracic ganglia with sensory nerves intact, octopamine (4 X 10(-9) mol) injected into lateral regions evoked regular firing of a single motor neuron, whereas a higher dose (4 X 10(-8) mol) often elicited the flight motor pattern. In the absence of sensory input, these doses of octopamine had little effect. Low doses (10(-10) mol) greatly enhanced motor responses to electrical stimulation of a wing sensory nerve. Dopamine (2 X 10(-10) mol) injected into the medial region of the mesothoracic ganglion elicited the flight motor pattern in the presence or absence of sensory input. Rhythmic output induced by dopamine (5 X 10(-10) mol) was suppressed by injecting serotonin (5 X 10(-10) mol) into the same region. These findings demonstrate that dopamine, octopamine, and serotonin have different effects on motor output in Manduca and suggest that these amines are involved in initiating, maintaining and terminating flight behavior, respectively. Octopamine may elicit flight production by enhancing the efficacy of sensory transmission thereby increasing excitability or arousal. Dopamine may act on interneurons involved in generating the flight motor pattern.

Animals↗
PubMed1986

Effects of octopamine on miniature excitatory junction potentials from developing and adult moth muscle.

Intracellular recordings of excitatory junction potentials (EJPs) and miniature EJPs (MEJPs) were made from the dorsal longitudinal muscle of Manduca sexta to determine the sites of action of octopamine. MEJPs increased in amplitude and frequency as the moth developed during the 3 days before eclosion. DL-Octopamine (5 X 10(-6) M) increased the amplitude of excitatory junction potentials in both immature moths (one day before eclosion) and adults. Octopamine (10(-5) M) also increased the amplitude and frequency of MEJPs from immature animals (one and two days before eclosion) but had the opposite effect on adults and pharate adults ready to eclose. Treatment with octopamine (10(-5) M) resulted in a decrease in input resistance and a hyperpolarization in both immature and adult muscle fibers. The results suggest that octopamine acts both presynaptically and postsynaptically but that the increase in the amplitude of the evoked response is due primarily to influences on presynaptic processes.

Age Factors↗
PubMed1989

Primary afferent responses of a crustacean mechanoreceptor are modulated by proctolin, octopamine, and serotonin.

Modulation of sensory responses recorded intracellularly in primary sensory afferents of a crustacean proprioceptor is described. The neuropeptide proctolin enhances the sensory response, whereas the bioamines octopamine and serotonin depress it. The lobster oval organ of the second maxilla, a simple stretch receptor lacking centrifugal control, provides a useful model for studies on nonsynaptic modulation at peripheral sensory loci. Its three large afferents, X, Y, and Z, were prepared for intracellular recording and tested under five experimental conditions: (1) when fully rested, (2) when adapted to maintained stretch and firing tonically, (3) when showing reduced responses after habituation to repetitive stimulation, (4) not stretched but depolarized with current injections, (5) after TTX blockade. The results, taken together, indicate that conductances contributing to the overall amplitude of the receptor potential are major targets for modulators. Thus proctolin increased receptor potential amplitudes with consequent augmentation of spiking, whereas serotonin and octopamine depressed the receptor potentials, often to subthreshold levels with loss of spiking. Octopamine was a less potent agent than serotonin and failed to act upon fibers under TTX blockade. Fibers Y and Z consistently showed sensitivity to the modulators tested. The largest fiber, X, typically was resistant to proctolin, octopamine, and serotonin. Threshold concentrations of 10(-10)-10(-11) M determined in vitro are well below the circulating levels for serotonin and octopamine found in vivo. Proctolin, however, is usually not detectable in the hemolymph, and it is suggested that a significant site of proctolin release may be the oval organ itself.

Action Potentials↗
PubMed1993

Molecular studies on insect octopamine receptors.

Octopamine receptors are widely distributed in the insect nervous system and carry out a range of functions equivalent to the adrenergic receptors of the vertebrate sympathetic nervous system. Molecular studies on insect octopamine receptors have concentrated upon molecular pharmacological approaches to identify the particular subtype of octopamine receptor mediating its effects in a particular tissue and on the modes of action of the receptors in a particular tissue. Molecular biological approaches are now being pursued to define the structure of the octopamine receptor. Recent findings in this area will be reviewed, along with promising approaches for future molecular studies on insect octopamine receptors.

Amino Acid Sequence↗
PubMed1988

Immunocytochemical demonstration of octopamine-immunoreactive cells in the nervous system of Locusta migratoria and Schistocerca gregaria.

The distribution of octopamine in the metathoracic ganglion, brain and corpus cardiacum of Locusta migratoria and Schistocerca gregaria was investigated by means of immunocytochemistry with an antiserum against octopamine. The dorsal unpaired median (DUM) cells of the metathoracic ganglion were found to be strongly octopamine-immunoreactive. In the rostroventral part of the protocerebrum a group of seven immunopositive cells was demonstrated. Stained nerve fibres of these cells run into three directions: circumoesophageal connectives, midbrain, and optic lobes. As far as the protocerebrum is concerned, immunoreactive fibres were found in the central body, the protocerebral bridge, and in other neuropile areas. In the optic lobe a dense plexus of immunopositive fibres was found in the lobula and in the medulla. In the brain one other immunopositive cell was demonstrated, situated at the lateral border of the tritocerebrum. Octopamine could not be shown to occur either in the globuli cells of the mushroom bodies or in the dorsolateral part of the protocerebrum, where the perikarya of the secretomotor neurones are located that innervate the glandular cells of the corpus cardiacum. In the nervi corporis cardiaci II, which contain the axons of the neurones that extend into the glandular part of the corpus cardiacum, and in the corpus cardiacum proper no specific octopamine immunoreactivity could be found.

Animals↗
PubMed2003

The effect of octopamine on behavioral responses of free-foraging bumblebees to a change in food source profitability.

The invertebrate neuromodulator octopamine is known to be involved in bees' associative learning, enhancing the responsiveness of a bee to a conditioned stimulus. In this study, we tested the effect of octopamine on the choice behavior of free-flying bumblebees using a two-phase experiment in an array of artificial flowers. During the first phase of the experiment, the bee was allowed to collect octopamine-laden sugar water from two types of equally rewarding flowers (yellow versus blue). In the second phase, one type of flower was set to be unrewarding. The behavior of the bee (proportion of visits to the unrewarding flowers) over the two phases was fitted to a sigmoid regression model. Our results show that octopamine had no significant effect on the bees' equilibrium choice or on the overall rate of the behavioral change in response to the change in reward. Rather, octopamine significantly affected the time interval between the change in reward status and the initiation of behavioral change in the bee.

Adrenergic alpha-Agonists↗
PubMed2003

To swim or not to swim: regional effects of serotonin, octopamine and amine mixtures in the medicinal leech.

Focally treating the head brain of the medicinal leech Hirudo medicinalis with various biogenic amines affected the initiation, termination and maintenance of fictive swimming (i.e., the neural correlate of swimming). Application of serotonin to saline surrounding only the head brain inhibited fictive swimming, whereas removing serotonin induced swimming. This contrasts sharply with previous observations that serotonin applied to the nerve cord induces swimming. Although application of octopamine to the brain activated swimming, a mixture of octopamine and serotonin inhibited swimming. Subsequent removal of this mixture from the brain activated robust swimming and was more potent for activating swimming than either the removal of serotonin or the application of octopamine. Swim episodes induced by brain-specific manipulations of octopamine had more swim bursts per episode than those induced by serotonin. These brain-specific effects of the amines on fictive swimming are probably due to the modulation of higher-order circuits that control locomotion in the leech. We observed that serotonin or a mixture of serotonin and octopamine hyperpolarized an identified descending brain interneuron known as Tr2. Removal of the mixture caused Tr2 to exhibit membrane potential depolarizations that correlated in time with the expression of swim episodes.

Amines↗
PubMed2001

Presynaptic effects of octopamine, serotonin, and cocktails of the two modulators on neuromuscular transmission in crustaceans.

The effect of the biogenic amines octopamine and serotonin, and of both amines combined (cocktails) on transmitter release at neuromuscular junctions of two crustaceans was studied. octopamine (10(-8) mol l(-1) to 10(-6) mol l(-1)) either enhanced or decreased evoked transmitter release through presynaptic effects. The results were identical for the slow and the fast excitor in the closer muscle of the crab, and for the excitor in the opener muscle of the crayfish. Application of serotonin always resulted in a strong increase of release. However, this potentiating effect of serotonin was reduced in strength by subsequent application of cocktails consisting of serotonin and octopamine. In all experiments, a cocktail of serotonin and octopamine was less effective than serotonin alone. The decrease in the mean quantal content m by octopamine was due to a reduction of the probability of release p. Since both amines are synthesized in the central nervous system and are released from neurohaemal organs into the haemolymph bathing the neuromuscular junctions, the results suggest that the two amines, when present together, modulate transmitter release in an antagonistic way, and that the level of the two determines synaptic efficacy.

Animals↗
PubMed1985

Behavioral depression after intraventricular infusion of octopamine in rats.

The behavioral and neurochemical effects of four intraventricular infusions of octopamine (3,200 micrograms), tryptophan (800 micrograms), and octopamine plus tryptophan delivered over 6 hours was studied in rats after performing a portacaval anastomosis or a sham operation. After each infusion, each animal was rated for neurologic depression with a 17 point test battery. Although overt coma was not induced, octopamine infusions severely depressed neurologic function. Concentrations of norepinephrine, dopamine, and serotonin in the brain were significantly decreased after the infusion of octopamine. Levels of norepinephrine in the brain were significantly correlated with neurologic status and greater depletion of norepinephrine was associated with greater neurologic depression. These studies demonstrate that infusing large amounts of the trace amine octopamine depresses behavior in the rat and this depression is most closely associated with depletion of stores of norepinephrine in the brain.

Animals↗
PubMed1990

Octopamine receptors in locust nervous tissue.

The octopamine binding site in the nervous tissue of the migratory locust Locusta migratoria is identified as an octopamine receptor of class 2. The binding of octopamine to the binding site is saturable, reversible, stereospecific and shows a pharmacological profile typical for octopamine receptors. Saturation analysis results in a single class of non-interacting binding sites (KD = 7.9 +/- 0.9 nM; Bmax = 160 fmol/mg). The pharmacological analysis shows that the phenyliminoimidazolidines NC7 and NC5 (Ki = 0.29 and 0.87 nM, respectively) are the most potent agonists, and that mianserin (Ki = 1.20 nM) is the most potent antagonist ever reported for octopamine receptors in direct binding studies.

Adrenergic Antagonists↗
PubMed1983

Brain octopamine and strain differences in avoidance behavior.

According to recent research, a significant relationship seems to exist between brain contents of p-octopamine and two-way avoidance responding in rats. Levels of this amine in hypothalamus and brainstem are higher in rats from the Roman High Avoidance (RHA) strain than in rats from the Roman Low Avoidance (RLA) strain. Intracerebroventricular administration of p-octopamine facilitates avoidance responding. The present paper reports the behavioral and neurochemical effects of p-octopamine administration on rats from the Roman strains. This treatment has no significant effect on cerebral levels of catecholamines, but it temporarily suppresses the strain differences in p-octopamine levels. In parallel, it also suppresses the strain differences in two-way avoidance conditioning, its facilitatory effect being much greater in RLA than in RHA rats. Avoidance behavior appears to be a useful model for the study of octopamine functions in the mammalian brain.

Animals↗
PubMed1993

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.

Animals↗
PubMed1976

Octopamine plasma levels and hepatic encephalopathy: a re-appraisal of the problem.

An investigation on the blood levels of octopamine was carried out on 70 adult individuals. There was a statistically significant correlation between the levels of octopamine and hepatic encephalopathy. Normal subjects had values below 1 ng/ml, while patients with grade 3 or grade 4 encephalopathy constantly showed values above 3.2 ng/ml. In these two groups the distribution was fairly homogeneous. Through the differences between cirrhotics without neurologic involvement and those with grade 1 or 2 hepatic encephalopathy displayed statistical significance, distribution of values in these groups was rather non-homogeneous. Octopamine levels paralleled variations in mental state in 3 out 4 cases. No difference was found between venous and arterial values. The reaction of transmethylation used in the assay of octopamine was constantly found to be inhibited by the presence of plasma. This inhibition is probably due to the presence of one or more beta-hydroxyphenylethanolamines other than octopamine.

Adult↗
PubMed1977

Octopamine and ammonia plasma levels in hepatic encephalopathy.

It has been recently proposed that hepatic encephalopathy could be due to the accumulation of octopamine acting as a false neurotransmitter, and the increase of ammonia might reflect this accumulation. The simultaneous determination of octopamine and ammonia was performed in 88 cases with or without encephalopathy. The correlation between the two substances appeared to be good (P less than 0.01; r = 0.5), except in shunted patients. All the cases with low octopamine and high ammonia were patients who had been submitted to surgical portal-systemic anastomosis. This finding does not seem to be coincidental; in this type of patients, the mechanism of hepatic encephalopathy could involve other beta-hydroxyphenylethanolamines in addition to octopamine. The presence of the inhibition of the reaction of transmethylation constantly observed during octopamine plasma assay is in favour of this hypothesis.

Ammonia↗
PubMed1985

Receptors for 3H-octopamine in the adult firefly light organ.

3H-Octopamine binds reversibly and with high affinity to sites on adult firefly light organ membranes. The binding is characterized by multiple affinities. Scatchard analysis supported a two site binding model with a tentative Kd value of about 1 nM for the high affinity component. The more abundant lower affinity site had a Kd value of about 60 nM. Guanyl nucleotides (Gpp(NH)p and GTP) greatly reduced the apparent number of octopamine binding sites. Competition studies with known octopaminergic agonists including the formamidine pesticides chlordimeform (CDM) and N-demethyl chlordimeform (DCDM) showed the following rank order of potencies in displacing octopamine: DCDM greater than octopamine = synephrine greater than naphazoline greater than clonidine greater than CDM. It was also observed that phentolamine was much more active than propranolol in antagonizing OA-binding. These relative activities are similar to the abilities of the same compounds to alter adenylate cyclase activity in light organ homogenates. Together with the effect of GTP on binding, these results suggest that the binding sites are functional octopamine receptors of the light organ.

Animals↗
PubMed1990

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.

Adenylyl Cyclase Inhibitors↗
PubMed1984

Neuropharmacological studies on the receptors mediating responses to carbachol, amino acids and octopamine on Limulus and Hirudo central neurons.

Intracellular recordings were made from central neurons of Limulus polyphemus and from Retizu cells of the leech, Hirudo medicinalis. The effects of carbachol, amino acids and octopamine were examined on these neurons. Octopamine was found to have a mainly inhibitory effect on a few Limulus neurons. The effects of octopamine were mimicked by clonidine and napthazoline but not by xylazine. Both compounds were slightly more potent than octopamine. Yohimbine, metoclopramide, chlorpromazine and chlordimeform failed to antagonize this octopamine response. The excitatory effect of carbachol was blocked by alpha-bungarotoxin, 10(-7)M. Neither this concentration nor higher concentrations of alpha-bungarotoxin had any effect on L-glutamate excitation. m-Carboxyphenyl derivatives of alanine and glycine acted differentially on Limulus neurons responding to L-glutamate. m- Carboxyphenylglycine only inhibited neurones which showed a biphasic response to L-glutamate while m- carboxyphenylalanine only excited these neurons. Both compounds excited leech Retzius cells, with m- carboxyphenylalanine being about 20 times more potent than m- carboxyphenylglycine . The actions of alpha- ketokainate and allo-alpha- ketokainate were compared to kainate, dihydrokainate and L-glutamate on leech Retzius cells. The equipotent molar ratios for kainate, dihydrokainate , alpha- ketokainate and allo-alpha- ketokainate were 0.0029 +/- 0.0004, 0.021 +/- 0.047, 0.029 +/- 0.005 and 0.14 +/- 0.0093 respectively with L-glutamate as one. All the analogues were more potent than L-glutamate. Quinolinic acid had no glutamate-like activity on either Limulus or Hirudo neurons. Methyltetrahydrofolate was inactive on Limulus neurons but excited leech Retzius cells, being slightly less potent than L-glutamate. Dibutyl cAMP terminated the excitatory actions of kainate on both Limulus and Hirudo neurons. Anisatin , a putative GABA antagonist, was a potent antagonist of GABA inhibition on Limulus neurons.

Amino Acids↗