Octopamine as the transmitter at the firefly lantern: presence of an octopamine-sensitive and a dopamine-sensitive adenylate cyclase.
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Adenylyl Cyclases↗
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m-Octopamine, p-octopamine and phenylethanolamine in rat brain: a sensitive, specific assay and the effects of some drugs.
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Animals↗
Effects of denervation of the levels of p-octopamine m-octopamine (norphenylephrine) and phenylethanolamine in rat salivary gland.
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2-Hydroxyphenethylamine↗
Activities of octopamine and synephrine stereoisomers on octopaminergic receptor subtypes in locust skeletal muscle.
The activities of the (-) and (+)- forms of p-, m- and o-octopamine and p- and m-synephrine have been compared on the different subtypes of octopamine receptor present in the extensor-tibiae neuromuscular preparation from the locust hindleg. The rank order of potency of the (-)-forms on the OCTOPAMINE2A receptors was p-synephrine greater than p-octopamine greater than m-octopamine greater than o-octopamine greater than m-synephrine whilst the rank order of the (+)-forms was p-synephrine greater than p-octopamine greater than m-octopamine. (+)-m-Synephrine and (+)-o-octopamine had no effect on this class of receptor when tested up to a concentration of 10(-3) M. The rank order of potency of the (-)-forms on the OCTOPAMINE2B receptors was p-synephrine greater than p-octopamine greater than m-synephrine greater than m-octopamine greater than o-octopamine whilst the rank order of the (+)-forms was p-octopamine greater than p-synephrine greater than m-octopamine greater than o-octopamine. (+)-m-Synephrine again had no effect up to a concentration of 10(-3) M. The rank order of potency of the (-)-forms on the OCTOPAMINE1 receptors was p-synephrine greater than p-octopamine greater than m-synephrine greater than m-octopamine greater than o-octopamine, whilst the rank order of the (+)-forms was p-synephrine greater than p-octopamine greater than o-octopamine greater than m-synephrine greater than m-octopamine.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Distribution and developmental expression of octopamine-immunoreactive neurons in the central nervous system of the leech.
Octopamine, a biogenic amine analogous to norepinephrine, plays an important role in the orchestration and modulation of invertebrate behavior. In the leech, the behavioral actions of octopamine have been demonstrated; however, identification of octopaminergic neurons had not been determined by using immunohistochemical techniques. Thus, we used an antibody highly specific to octopamine to examine the distribution of octopamine-immunoreactive neurons in the segmental ganglia of American and European medicinal leeches (Macrobdella decora and Hirudo medicinalis). One pair of octopamine-immunoreactive neurons was located in the dorsolateral ganglionic region of anterior ganglia 1-6 and posterior ganglia 15-21. No corresponding octopamine-immunoreactive neurons were found in midbody ganglia 7-14. Using Neutral Red staining in combination with intracellular Neurobiotin injections and octopamine immunostaining, we determined the identity of the dorsolateral octopamine-immunoreactive cells. The dorsolateral octopamine-immunoreactive neuron (the DLO) was not cell 21, the only previously reported Neutral Red staining neuron in the dorsolateral position. We also determined that the Leydig neuron was not octopamine immunoreactive in either of the two medicinal leech species. Octopamine immunostaining in the sex ganglia revealed hundreds of immunoreactive neurons in sexually mature leeches. Such neurons were not observed in juvenile leeches. The developmental time course of octopamine immunoreactivity in the dorsolateral octopamine-immunoreactive neurons was also investigated by staining embryonic Hirudo medicinalis. Octopamine expression occurred relatively late as compared with the detectable onset of serotonin expression. Octopamine expression in the dorsolateral octopamine-immunoreactive cells was not detectable at early to mid-embryonic stages, and must commence during late embryonic to early juvenile stages. The identification of octopamine-immunoreactive cells now sets the stage for further investigations into the functional role of octopamine in leech behavior and the development of behavior.
Animals↗
Activities of octopamine and synephrine stereoisomers on alpha-adrenoceptors.
1. The activities of the (-)- and (+)-forms of m- and p-octopamine and m- and p-synephrine on alpha 1-adrenoceptors from rat aorta and anococcygeus and alpha 2-adrenoceptors from rabbit saphenous vein were compared with those of noradrenaline (NA). 2. The rank order of potency of the (-)-forms on alpha 1-adrenoceptors from rat aorta and alpha 2-adrenoceptors was NA greater than m-octopamine = m-synephrine greater than p-octopamine = p-synephrine. The two m-compounds were 6 fold less active than NA on alpha 1-adrenoceptors from rat aorta and 150 fold less active on alpha 2-adrenoceptors. The two p- compounds were 1,000 fold less active than NA on both alpha 1-adrenoceptors from rat aorta and alpha 2-adrenoceptors. The rank order of potency of the (-)- forms on alpha 1-adrenoceptors from rat anococcygeus was NA = m-synephrine greater than m-octopamine greater than p-octopamine = p-synephrine. m-Octopamine was 4 fold less active than NA and (-)-m-synephrine. The two p- compounds were 30 fold less active than NA. 3. The rank order of potency of the (+)- forms was NA greater than m-octopamine greater than m-synephrine greater than p-octopamine greater than p-synephrine on both alpha 1- and alpha 2-adrenoceptors. The potency of each (+)- form was 1-2 orders of magnitude less than that of the (-) counterpart, the differences being greater for the stereoisomers of synephrine than for those of octopamine on both alpha 1- and alpha 2-adrenoceptors. 4. The yohimbine diastereoisomer antagonists, rauwolscine and corynanthine, were tested against (-)-NA and (-)-m-octopamine-induced contractions in both preparations. Based upon the known selectivities of these isomers for alpha-adrenoceptor subtypes, it is concluded that the rat aorta contains only alpha 1-adrenoceptors while the rabbit saphenous vein possesses predominantly alpha 2-adrenoceptors. 5. Ligand binding data for the octopamine and synephrine stereoisomers at alpha 1- and alpha 2-binding sites from rat cerebral cortex was also obtained. (-)-Forms were more active than (+)-forms. The rank order of affinity of the (-)-forms for both alpha 1- and alpha 2-binding sites was NA greater than m-octopamine = m-synephrine greater than p-synephrine greater than p-octopamine. The relative affinities of the members of the series against alpha 1-binding sites were very similar to their relative functional activities on rat aorta. However, the affinities of both m- and p-compounds relative to that of ( -)-NA were much greater at the x2-binding sites than were the relative activities in rabbit saphenous vein, possibly suggesting low intrinsic efficacy. Functional antagonist responses to NA by the (-)-octopamine and synephrines could not, however, be demonstrated on rat aorta or rabbit saphenous vein. 6. The activities of m-octopamine and m-synephrine were not significantly different from each other on either a,-adrenoceptors from rat aorta or x2-adrenoceptors; however, m-synephrine is more active than m-octopamine on a,-adrenoceptors from rat anococcygeus. Both m-octopamine and msynephrine can be considered to be naturally occurring x,-selective amines. However, if m- and poctopamine are co-released with NA in amounts proportional to their concentration, it is concluded that their activities on m,- and x2-adrenoceptors are too low to be physiologically significant.
2-Hydroxyphenethylamine↗
A role for octopamine in honey bee division of labor.
Efficient division of labor is one of the main reasons for the success of the social insects. In honey bees the division of labor is principally achieved by workers changing tasks as they age. Typically, young adult bees perform a series of tasks within the colony before ultimately making the transition to foraging outside the hive for resources. This lifelong behavioral development is a well-characterized example of naturally occurring behavioral plasticity, but its neural bases are not well understood. Two techniques were used to assess the role of biogenic amines in the transition from in-hive work to foraging, which is the most dramatic and obvious transition in honey bee behavioral development. First, associations between amines and tasks were determined by measuring the levels of amines in dissected regions of individual bee brains using HPLC analysis. Second, colonies were orally treated with biogenic amines and effects on the onset of foraging were observed. Octopamine concentration in the antennal lobes of the bee brain was most reliably associated with task: high in foragers and low in nurses regardless of age. In contrast, octopamine in the mushroom bodies, a neighboring neuropil, was associated with age and not behavior, indicating independent modulation of octopamine in these two brain regions. Treating colonies with octopamine resulted in an earlier onset of foraging in young bees. In addition, octopamine levels were not elevated by non-foraging flight, but were already high on return from the first successful foraging trip and subsequently remained high, showing no further change with foraging experience. This observation suggests that octopamine becomes elevated in the antennal lobes in anticipation of foraging and is involved in the release and maintenance of the foraging state. Foraging itself, however, does not modulate octopamine levels. Behaviorally related changes in octopamine are modulated by juvenile hormone, which has also been implicated in the control of honey bee division of labor. Treatment with the juvenile hormone analog methoprene elevated octopamine and octopamine treatment 'rescued' the delay in behavioral development caused by experimentally depleting juvenile hormone in bees. Although the pathways linking juvenile hormone and octopamine are presently unknown, it is clear that octopamine acts 'downstream' of juvenile hormone to influence behavior and that juvenile hormone modulates brain octopamine levels. A working hypothesis is that octopamine acts as an activator of foraging by modulating responsiveness to foraging-related stimuli. This is supported by the finding that octopamine treatment increased the response of bees to brood pheromone, a stimulator of foraging activity. Establishing a role for octopamine in honey bee behavioral development is a first step in understanding the neural bases of this example of naturally occurring, socially mediated, behavioral plasticity. The next level of analysis will be to determine precisely where and how octopamine acts in the nervous system to coordinate this complex social behavior.
Animals↗
Effects of octopamine on lipolysis, glucose transport and amine oxidation in mammalian fat cells.
Octopamine is known to exert adrenergic effects in mammals although specific octopamine receptors have been cloned only in invertebrates. It has been shown that octopamine can stimulate alpha(2)-adrenoceptors (ARs) in Chinese hamster ovary cells transfected with human alpha(2)-ARs. More recently, we reported that octopamine stimulates lipolysis through beta(3)-rather than beta(1)-or beta(2)-AR activation in white adipocytes from different mammalian species. The present study was thus undertaken to further characterize the adrenergic properties of octopamine. For this purpose, several biological processes known to be regulated by adrenergic stimulation were studied in response to octopamine, noradrenaline, adrenaline and tyramine in white adipocytes from different mammals. First, octopamine was fully lipolytic in garden dormouse and Siberian hamster while tyramine was ineffective. Although being around one hundred-fold less potent that noradrenaline, octopamine was slightly more potent in these hibernators known for their high sensitivity to beta(3)-AR agonists than in rat and chiefly more active than in human adipocytes known for their limited responses to beta(3)-AR agonists. Second, octopamine reduced insulin-dependent glucose transport in rat fat cells, a response also observed with noradrenaline and selective beta(3)-AR agonists but not with beta(1)-or beta(2)-agonists. Third, human adipocytes, which endogenously express a high level of alpha(2)-ARs, exhibited a clear alpha(2)-adrenergic antilipolytic response to adrenaline but not to octopamine. Moreover, octopamine exhibited only a very weak affinity for the alpha(2A)-ARs labeled by [3H]RX821002 in human adipocyte membranes. In Syrian hamster adipocytes, which also possess alpha(2)-ARs, octopamine induced only a weak antilipolysis. Finally, octopamine was a substrate of fat cell amine oxidases, with an apparent affinity similar to that of noradrenaline. All these results demonstrate that octopamine, tyramine noradrenaline and adrenaline can be degraded by adipocyte amine oxidases. However these biogenic amines interact differently with adipocyte adrenoceptors: tyramine is inactive, adrenaline and noradrenaline activate both beta- and alpha(2)-ARs while octopamine activates only beta(3)-ARs and is devoid of alpha(2)-adrenergic agonism. Thus, octopamine could be considered as an endogenous selective beta(3)-AR agonist.
Adipocytes↗
Interaction between octopamine and proctolin on the oviducts of Locusta migratoria.
The biogenic amine octopamine and the pentapeptide proctolin are two important neuroactive chemicals that control contraction of the oviducts of the African locust Locusta migratoria. The physiological responses and signal transduction pathways used by octopamine and proctolin have been well characterized in the locust oviducts and this therefore provides the opportunity to examine the interaction between these two pathways. Octopamine, via the intracellular messenger adenosine 3',5'-cyclic monophosphate (cyclic AMP), inhibits contraction of the oviducts, while proctolin, via the phosphoinositol pathway, stimulates contraction. We have examined the physiological response of the oviducts to combinations of octopamine and proctolin and also looked at how combinations of these affect one of the main intracellular mediators of the octopamine response, namely cyclic AMP. It was found that application of octopamine to the oviducts led to a dose-dependent reduction in tonus of the muscle and also a decrease in the amplitude and frequency of spontaneous phasic contractions. Octopamine-induced relaxation was enhanced in the presence of the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX). Octopamine was also able to inhibit proctolin-induced contractions of the oviducts in a dose-dependent manner. A 10(-9) M proctolin-induced contraction was inhibited by 83% in the presence of 10(-5) M octopamine, and was completely inhibited in the presence of 10(-5) M octopamine plus 5x10(-4) M IBMX. Octopamine led to a dose-dependent increase in cyclic AMP content as measured by radioimmunoassay. In the presence of 10(-9) M proctolin, this octopamine-induced increase in cyclic AMP was reduced by as much as 60%. Proctolin also caused a dose-dependent decrease in the cyclic AMP elevation produced by 5x10(-6) M octopamine. These results indicate that octopamine and proctolin can antagonize each other's physiological response when added in combination, and that proctolin is able to modulate the response of the oviducts to octopamine by influencing cyclic AMP levels.
Journal Article↗
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.
Animals↗
Octopamine enhances neuromuscular transmission in developing and adult moths, Manduca sexta.
The effect of octopamine on neuromuscular transmission was examined in developing and adult Manduca sexta. Intracellular recordings were made from the dorsal longitudinal muscle (DLM), superfused with solutions containing DL-octopamine or other amines. In untreated adult moths and pharate adults nearly ready to enclose (stage Day 19), stimulation of the motor nerve evokes a large excitatory junction potential (EJP), an active membrane response, and a twitch. In adults and Day 19 animals DL-octopamine (10(-7) to 10(-4)M) has no effect on the amplitude and rise-time of the electrical response in normal saline, but 10(-6) to 10(-4) M DL-octopamine increases the amplitude of the excitatory junction potential recorded in saline containing one-third the normal calcium concentration. Immature (Day 16) muscle, which normally produces only small EJPs following stimulation of its motor nerve, responds to 10(-6) to 10(-4) M DL-octopamine by an increase in the EJP above threshold for an active membrane response and a contraction. When the muscle has developed sufficiently to spike and contract in response to nerve stimulation in the absence of exogenous octopamine (Days 17 and 18), application of DL-octopamine increases the maximum rate at which the muscle contracts in response to each stimulus in a train (designated the maximum following frequency, MFF). The threshold dose for an effect on the MFF of Day 18 immature moths is less than 10(-10) M. At this stage 10(-8) M DL-octopamine increases the MFF four-fold. The effect on the MFF is dose-dependent over the range 10(-10) M to 10(-6) M. The biogenic amines DL-epinephrine, DL-norepinephrine, tyramine, DL-phenylethanolamine, 2-phenylethylamine, and dopamine, applied at concentrations of 10(-8) or 10(-4) M, do not change the MFF. Both DL-synephrine (10(-8) M) and serotonin (10(-7) M) mimic the action of 10(-10) M DL-octopamine on the MFF. The action of DL-octopamine (10(-7) M) is blocked by phentolamine (10(-4)M) but not by propranolol (10(-4)M). The octopamine content of hemolymph was determined with a radioenzymtic assay. The concentration of octopamine in the hemolymph increases 3.6-fold, from 5 X 10(-8) M on Day 18 (duration of adult development is 19 days) to 1.85 X 10(-7) M one day following eclosion.(ABSTRACT TRUNCATED AT 400 WORDS)
Animals↗
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.
Adrenergic alpha-Agonists↗
Octopamine induces steady-state reflex reversal in crayfish thoracic ganglia.
1. This paper investigates the effect of octopamine on spontaneous and reflex motor output of crayfish leg motor neurons. Octopamine modulated spontaneous activity, both rhythmic and tonic, and dramatically modulated the pattern of reflex motor output elicited by stimulating identified proprioceptors of the basal limb. 2. Spontaneous reciprocal motor patterns, involving alternating bursts of promotor and remotor motor neuron activity, were reversibly abolished by octopamine. The threshold concentration for this effect was approximately 1 microM. 3. At concentrations greater than approximately 10 microM octopamine inhibited spontaneous promotor nerve activity in both bursting and nonbursting preparations. In some experiments promotor inhibition was correlated with the induction of tonic remotor nerve activity. The EC50 for complete inhibition of promotor nerve activity by octopamine was 20-30 microM. 4. Reflexes mediated by two basal limb proprioceptors, the thoracocoxal muscle receptor organ (TCMRO; which signals leg promotion) and the thoracocoxal chordotonal organ (TCCO; which signals leg remotion) were analyzed in a number of promotor and remotor motor neurons. In both cases assistance reflexes (excitation of promotors by the TCCO and remotors by the TCMRO) were restricted to subgroups of the motor pool. Among remotor motor neurons, the first two units recruited during bursts of spontaneous activity were members of the assistance reflex group (group 1). A third unit, sometimes recruited during more intense spontaneous bursts, was excited by TCCO stimulation and was therefore a member of the resistance reflex group (group 2). Other resistance group remotors were also excited by the TCCO, but this input normally remained subthreshold. 5. Stimulation of the TCCO afferent nerve elicited excitatory postsynaptic potentials (EPSPs) in group 2 (resistance group) remotor motor neurons at a latency compatible with a monosynaptic connection. The same stimulation excited group 1 (assistance group) promotor motor neurons, but at a greater and more variable latency. Thus the remotor resistance reflex from the TCCO is probably monosynaptic, but the promotor assistance reflex, also elicited by TCCO stimulation, is likely to be di- or polysynaptic. Assistance group (group 1) remotor motor neurons are inhibited by mechanical stimulation of the TCCO, or electrical stimulation of its nerve. 6. Octopamine had selective effects on individual remotor units. First, assistance group remotor motor neurons were affected in two ways. One unit was inhibited, so that reflex spiking in response to TCMRO stimulation was abolished. A second unit was not inhibited, but its reflex response mode changed, so that instead of responding to TCMRO input with an assistance reflex, it responded to TCCO input with a resistance reflex. Second, among motor neurons that normally respond to TCCO input with resistance reflexes, these responses were enhanced by octopamine. 7. Promotor motor neurons were inhibited by octopamine and reflex responses were also affected selectively. Responses to TCCO input (assistance reflexes) were abolished; whereas, responses to TCMRO input (resistance reflexes) were relatively less affected. 8. Intracellular recordings revealed that the majority of remotor motor neurons depolarized in the presence of octopamine. In preparations where these could be classified on the basis of TCMRO/ TCCO inputs, all were identified as group 2 (resistance group). A minority of remotor motor neurons were hyperpolarized by octopamine. All of these were identified as group 1 (assistance group), with strong TCMRO input. 9. The majority of promotor motor neurons were depolarized by octopamine. This depolarization was nevertheless inhibitory since it reversed slightly positive to rest and was associated with a substantial fall in inp
Animals↗
Development of a photoaffinity ligand for octopamine receptors.
Octapamine receptors are widely distributed in invertebrate species, yet little is known about their biochemical structure or tissue localization, in part because there exist no high affinity or irreversible ligands for these receptors. This paper characterizes 2-(2,6-diethyl-4-azidophenylimino)imidazolidine (NC-5Z), a new, high affinity octopamine receptor probe that binds reversibly and, under photolyzing conditions, irreversibly to membrane-associated octopamine receptors. Under reversible conditions NC-5Z is a full agonist, 50-100 times more potent than octopamine in activating the highly enriched and specific octopamine-sensitive adenylate cyclase of the firefly light organ. NC-5Z shows a similar potency in cockroach muscle and thoracic ganglia and in tobacco hornworm nerve cord. Activation of light organ adenylate cyclase by NC-5Z is nonadditive to that caused by octopamine and can be blocked by antagonists, including mainserin (Ki = 0.9 microM), cyproheptadine (Ki = 5 microM), phentolamine (Ki = 20 microM), and propranolol (Ki = 75 microM). These constants agree well with those for the same antagonists in inhibiting stimulation due to octopamine. In physiological studies, NC-5Z mimics the action of, but is more potent than, octopamine in stimulating light emission in intact firefly tails and in disrupting motor behavior and feeding of tobacco hornworms. Under reversible conditions, [3H]NC-5Z, the tritiated derivative of NC-5Z, binds to light organ membranes with an apparent affinity (0.59-0.7 microM) similar to that (0.35-0.7 microM) for NC-5Z in activating adenylate cyclase. Under photolyzing conditions, NC-5Z irreversibly activates light organ adenylate cyclase, and this can be blocked by an excess of octopamine. Under similar conditions, [3H]NC-5Z binds irreversibly to light organ membranes and to membranes from tobacco hornworm nerve ganglia, fat body, and gut. This binding is reduced by prior incubation with octopamine agonists, including octopamine, demethyl-chlordimeform, and 2-(phenylimino)imidazolidines, but not by norepinephrine, dopamine, serotonin, or histamine. Irreversible binding is also reduced by prior incubation with antagonists, most effectively (55% of total binding) by mianserin. The apparent affinity of [3H]NC-5Z for membrane binding, as reflected by its ability to be displaced by mianserin, is altered by GTP. In autoradiographic studies of whole tissue, [3H]NC-5Z shows irreversible, mianserin-displaceable labeling of intact firefly light organs. Taken together, these data indicate that NC-5Z and [3H]NC-5Z are potent and selective agonists of octopamine receptors in a variety of tissues.(ABSTRACT TRUNCATED AT 400 WORDS)
Adenylyl Cyclases↗
Octopamine enhances phagocytosis in cockroach hemocytes: involvement of inositol trisphosphate.
Octopamine and 5-hydroxytryptamine (5-HT) were previously shown to affect phagocytosis in cockroach hemocytes through unidentified receptor-mediated events. In the present study, we examined the ability of 5-HT and octopamine to enhance inositol trisphosphate (IP3) production using hemocyte membranes of the American cockroach, Periplaneta americana. Octopamine enhanced IP3 production with a maximal peak at 100 nM. Similarly, 5-HT enhanced IP3 production with a maximal effect at 10 nM. The effects of 5-HT and octopamine are not additive, suggesting that both are working through the same receptor. Phentolamine, a general octopamine antagonist, blocked the effects of octopamine and 5-HT, while a mammalian 5-HT2 antagonist that blocks 5-HT-sensitive receptors in insect peripheral tissue, ketanserin, did not. A pharmacological profile indicates that the receptor is similar to an octopamine1-type. Octopamine at 1 microM increased phagocytosis in cockroach hemocytes exposed to Staphylococcus aureus in vitro, and this effect was mimicked by IP3 (10 microM). The octopamine-treated hemocytes were shown to increase IP3 production in the latter stage of phagocytosis. Adult cockroaches exposed to an LD50 dose of S. aureus in conjunction with either 0.1 mM octopamine or the octopamine1 agonist, clonidine, had higher survival rates compared to saline-treated cockroaches. Correspondingly, the octopamine1 antagonist, chlorpromazine, partially blocked the octopamine-mediated increase in cockroach survival.
Analysis of Variance↗
Neuromuscular modulation in Limulus by both octopamine and proctolin.
Both octopamine and proctolin potentiate nerve-evoked skeletal muscle contractions in the horseshoe crab, Limulus. The threshold concentration for octopamine was 10(-9) to 10(-8)M, while for proctolin it was 3 X 10(-9)M. Norepinephrine and dopamine produced effects similar to octopamine but at higher thresholds; tyramine and serotonin were ineffective. Octopamine caused significant increases in amplitudes of excitatory postsynaptic potentials (epsps) of muscle fibers, but had little effect on muscle fiber input resistance or membrane potential. Also, octopamine did not affect depolarization of muscle fibers and subsequent contraction due to the direct action of exogenously applied glutamate. These results suggest that octopamine potentiates nerve-evoked contractions primarily by facilitating release of neuromuscular transmitter. At concentrations above 10(-7)M, however, octopamine sometimes caused muscle spikes in response to motoneuron stimulation, a finding that suggests that octopamine may also have some postsynaptic action. Proctolin potentiated the muscle contractions evoked by glutamate but had little effect on glutamate-evoked muscle fiber depolarization, muscle fiber input resistance, or membrane potential. Thus, proctolin appears to act directly on skeletal muscle to enhance contractility. The proctolin-induced potentiations of contraction were sometimes accompanied by modest increases in epsp amplitude, so that unlike lobster skeletal and Limulus cardiac neuromuscular preparations, proctolin may have a secondary direct synaptic effect. Both octopamine and proctolin have been found in Limulus cardiac ganglion. This potential access to the hemolymph and the relatively low threshold concentrations needed for physiological action suggest that octopamine and proctolin could function as hormonal modulators of neuromuscular function in Limulus.
Animals↗
Juvenile hormone and octopamine in the regulation of division of labor in honey bee colonies.
Forager honey bees have high circulating levels of juvenile hormone (JH) and high brain levels of octopamine, especially in the antennal lobes, and treatment with either of these compounds induces foraging. Experiments were performed to determine whether octopamine acts more proximally than JH to affect the initiation of foraging behavior. Bees treated with octopamine became foragers more rapidly than bees treated with the JH analog methoprene. Bees treated with methoprene showed an increase in antennal lobe levels of octopamine, especially after 12 days. Bees with no circulating JH (corpora allata glands removed) treated with octopamine became foragers in similar numbers to bees with intact corpora allata. These results suggest that JH affects the initiation of foraging at least in part by increasing brain levels of octopamine, but octopamine can act independently of JH. Effects of JH that are not related to octopamine also are possible, as bees treated with both octopamine and methoprene were more likely to become foragers than bees treated with only octopamine or methoprene.
Animals↗
The effects of octopamine on juvenile hormone biosynthesis, electrophysiology, and cAMP content of the corpora allata of the cockroach Diploptera punctata.
Juvenile hormone production by the corpora allata of the adult female cockroach, Diploptera punctata, can be modulated by treatment with the biogenic amine, octopamine. Endogenous octopamine has been identified within the CA, using HPLC and electrochemical detection. Treatment with octopamine results in a sinusoidal, dose-dependent inhibition of JH biosynthesis by CA from day 2 virgin females, with maximal inhibition occurring at 10(-10) M and 10(-4 M. In day 4 and day 8 mated female corpora allata octopamine inhibited JH biosynthesis at 5 x 10(-5) M. Although the elevation of either cAMP or cGMP within the CA is known to be associated with an inhibition of JH biosynthesis, treatment with high concentrations of octopamine results in an increase in the level of cAMP but not cGMP. This effect is both dose- and time-dependent. Octopamine treatment also initiates changes in the passive membrane responses of the CA. Superfusion of CA with octopamine results in a pronounced hyperpolarization of CA cells and an increase in the electrotonic potential (indicative of the degree of electrical coupling between CA cells). This effect could be blocked by the octopamine receptor blocker phentolamine. Treatment with octopamine or phentolamine also blocked the hyperpolarization of CA cells normally associated with electrical stimulation of the axon tracts innervating the CA. We hypothesize that octopamine may be a natural neuromodulator of JH production by CA, regulating ion channels in CA cells themselves as well as release of the inhibitory neuropeptide, allatostatin, from the terminals within the CA.
Animals↗