Biogenic amines modulate pulse rate in the dorsal blood vessel of Lumbriculus variegatus

The biogenic amines are widespread regulators of physiological processes, and play an important role in regulating heart rate in diverse organisms. Here, we present the first pharmacological evidence for a role of the biogenic amines in the regulation of dorsal blood vessel pulse rate in an aquatic oligochaete, Lumbriculus variegatus (Müller, 1774). Bath application of octopamine to intact worms resulted in an acceleration of pulse rate, but not when co-applied with the adenylyl cyclase inhibitor MDL-12,330a. The phosphodiesterase inhibitor theophylline mimicked the effects of OA, but the polar adenosine receptor antagonist 8(p-sulphophenyl)theophylline was significantly less potent than theophylline. Pharmacologically blocking synaptic reuptake of the biogenic amines using the selective 5-HT reuptake blocker fluoxetine or various tricyclic antidepressants also accelerated heart rate. Depletion of the biogenic amines by treatment with the monoamine vesicular transporter blocker reserpine dramatically depressed pulse rate. Pulse rate was partially restored in amine-depleted worms after treatment with octopamine or dopamine, but fully restored following treatment with serotonin. This effect of 5-HT was weakly mimicked by 5-methoxytryptamine, but not by alpha-methylserotonin; it was completely blocked by clozapine and partially blocked by cyproheptadine. Because they are known to orchestrate a variety of adaptive behaviors in invertebrates, the biogenic amines may coordinate blood flow with behavioral state in L.variegatus.

Octopamine and experience-dependent modulation of aggression in crickets

Intraspecific aggression is influenced in numerous animal groups by the previous behavioral experiences of the competitors. The underlying mechanisms are, however, mostly obscure. We present evidence that a form of experience-dependent plasticity of aggression in crickets is mediated by octopamine, the invertebrate counterpart of noradrenaline. In a forced-fight paradigm, the experience of flying maximized the aggressiveness of crickets at their first encounter and accelerated the subsequent recovery of aggressiveness of the normally submissive losers, without enhancing general excitability as evaluated from the animals' startle responses to wind stimulation. This effect is transitory and concurrent with the activation of the octopaminergic system that accompanies flight. Hemocoel injections of the octopamine agonist chlordimeform (CDM) had similar effects on aggression but also enhanced startle responses. Serotonin depletion, achieved using alpha-methyl-tryptophan, enhanced startle responses without influencing aggression, indicating that the effect of CDM on aggression is not attributable to increased general excitation. Contrasting this, aggressiveness was depressed, and the effect of flying was essentially abolished, in crickets depleted of octopamine and dopamine using alpha-methyl-p-tyrosine (AMT). CDM restored aggressiveness in AMT-treated crickets, indicating that their depressed aggressiveness is attributable to octopamine depletion rather than to dopamine depletion or nonspecific defects. Finally, the flight effect was blocked in crickets treated with the octopamine receptor antagonist epinastine, or with the alpha-adrenoceptor and octopamine receptor antagonist phentolamine, but not with the beta-adrenoceptor antagonist propranolol. The idea that activity-specific induction of the octopaminergic system underlies other forms of experience-dependent plasticity of aggressive motivation in insects is discussed.

Comparative receptor surface analysis of octopaminergic antagonists for the locust neuronal octopamine receptor

In drug discovery, it is common to have measured activity data for a set of compounds acting upon a particular protein but not to have knowledge of the three-dimensional structure of the protein active site. In the absence of such three-dimensional information, one can attempt to build a hypothetical model of the receptor site that can provide insight about receptor site characteristics. Such a model is known as a comparative receptor surface analysis (CoRSA) model, which provides compact and quantitative descriptors which capture three-dimensional information about a putative receptor site. The quantitative structure-activity relationship (QSAR) of a set of 20 antagonists for octopamine (OA) receptor 3 in locust nervous tissue, was analyzed using CoRSA. Three-dimensional energetics descriptors were calculated from receptor surface model (RSM)-ligand interaction and these three-dimensional descriptors were used in QSAR analysis. The predictive character of the QSAR was further assessed using 24 agonists for OA receptor as test molecules. An RSM was generated using some subset of the most active structures and the results provided useful information in the characterization and differentiation of OA receptor.

Hygienic behavior in the honey bee (Apis mellifera L.) and the modulatory role of octopamine

Honey bees, Apis mellifera, which perform hygienic behavior, quickly detect, uncap and remove diseased brood from the nest. This behavior, performed by bees 15-20 days old and prior to foraging, is likely mediated by olfactory cues. Because the neuromodulator octopamine (OA) plays a pivotal role in olfactory-based behaviors of honey bees, we examined whether bees bred for hygienic and nonhygienic behavior differed with regard to their OA expression and physiology. We compared the staining intensity of octopamine-immunoreactive (OA-ir) neurons in the deutocerebral region of the brain, medial to the antennal lobes, between hygienic and nonhygienic bees (based on genotype and phenotype). We also tested how the olfactory responses of the two lines, based on electroantennograms (EAGs), were affected by oral administration of OA and of epinastine, a highly specific OA antagonist. Our results revealed that bees expressing hygienic behavior (irrespective of genotype) possessed OA-ir neurons that exhibited more intense labeling than same-aged bees not performing the behavior. In bees bred for nonhygienic behavior, OA significantly increased the EAG response to low concentrations of diseased brood odor. Conversely, in bees bred for hygienic behavior, epinastine significantly reduced the magnitude of the EAG response, a reduction not observed in nonhygienic bees. Our results provide two lines of evidence that OA has the potential to facilitate the detection and response of honey bees to diseased brood. We discuss the contributions of OA for behavioral shaping and its ability to bias the nervous system to express one form of behavior over another.

B96Bom encodes a Bombyx mori tyramine receptor negatively coupled to adenylate cyclase

A cDNA encoding a biogenic amine receptor (B96Bom) was isolated from silkworm (Bombyx mori) larvae, and the ligand response of the receptor stably expressed in HEK-293 cells was examined. Tyramine (TA) at 0.1-100 micro m reduced forskolin (10 micro m)-stimulated intracellular cAMP levels by approximately 40%. The inhibitory effect of TA at 1 micro m was abolished by yohimbine and chlorpromazine (each 10 micro m). Although octopamine (OA) also reduced the cAMP levels, the potency was at least two orders of magnitude lower than that of TA. Furthermore, unlabelled TA (IC50 = 5.2 nm) inhibited specific [3H]TA binding to the membranes of B96Bom-transfected HEK-293 cells more potently than did OA (IC50 = 1.4 micro m) and dopamine (IC50 = 1.7 micro m). Taken together with the result of phylogenetic analysis, these findings indicate that the B96Bom receptor is a B. mori TA receptor, which is negatively coupled to adenylate cyclase. The use of this expression system should facilitate physiological studies of TA receptors as well as structure-activity studies of TA receptor ligands.

Octopamine modulates spermathecal muscle contractions in Locusta migratoria

Octopamine was identified in the spermathecal tissue of Locusta migratoria using HPLC and immunohistochemical techniques. Octopamine-like immunoreactive unpaired median neurons were identified in the VIIth and VIIIth (terminal) abdominal ganglia and octopamine-like immunoreactive axons were present in the ventral ovipositor nerve (branches from this nerve innervate the spermatheca). Stimulatory actions of octopamine on myogenic and neurogenic contractions were observed. Dose-dependent increases in the frequency of myogenic contractions and the amplitude of neurogenic contractions were elicited by the application of octopamine to the spermathecal muscle. Non-sustained basal tension increases were noted in some preparations, although these were not found to be dose-dependent. SchistoFLRFamide (PDVDHVFLRFamide) inhibited octopamine-induced contractions by a maximum of about 30%. In the presence of 3-isobutyl-1 -methylxanthine, octopamine increased cAMP levels in all regions of the spermathecal. The largest increase in cAMP content was found in the spermathecal sac, followed by the straight duct and coil duct. Phentolamine blocked octopamine-induced increases in cAMP levels and abolished the actions of octopamine on myogenic contractions.

Inhibitors of calling behavior of Plodia interpunctella

Some octopamine agonists were found to suppress the calling behavior of the stored product Indian meal moth, Plodia interpunctella. Compounds were screened using a calling behavior bioassay using female P. interpunctella. Four active derivatives, with inhibitory activity at the nanomolar range, were identified in order of decreasing activity: 2-(1-phenylethylamino)-2-oxazoline > 2-(2-ethyl,6-methylanilino)oxazolidine > 2-(2-methyl benzylamino)-2-thiazoline > 2-(2,6-diethylanilino)thiazolidine. Three-dimensional pharmacophore hypotheses were built from a set of 15 compounds. Among the ten common-featured models generated by the program Catalyst/HipHop, a hypothesis including a hydrogen-bond acceptor lipid, a hydrophobic aromatic and two hydrophobic aliphatic features was considered to be essential for inhibitory activity in the calling behavior. Active compounds mapped well onto all the hydrogen-bond acceptor lipid, hydrophobic aromatic and hydrophobic aliphatic features of the hypothesis. On the other hand, less active compounds were shown not to achieve the energetically favorable conformation that is found in the active molecules in order to fit the 3D common-feature pharmacophore models. The present studies demonstrate that inhibition of calling behavior is via an octopamine receptor.

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

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

Octopamine reverses the isolation-induced increase in trophallaxis in the carpenter ant Camponotus fellah

Social deprivation is an unusual situation for ants that normally maintain continuous contact with their nestmates. When a worker was experimentally isolated for 5 days and then reunited with a nestmate, she engaged in prolonged trophallaxis. It is suggested that trophallaxis allows her to restore a social bond with her nestmates and to re-integrate into the colony, particularly via the exchange of colony-specific hydrocarbons. Octopamine reduced trophallaxis in these workers as well as hydrocarbon transfer between nestmates, but not hydrocarbon biosynthesis. Administration of serotonin to such 5-day-isolated ants had no effect on the percentage of trophallaxis. Administration of phentolamine alone, an octopamine antagonist, had no effect, but when co-administrated with octopamine it reduced the effect of octopamine alone and restored trophallaxis to control levels. Moreover, the observed effect of octopamine was not due to a non-specific effect on locomotor activity. Therefore, we hypothesise that octopamine mediates behaviour patterns linked to social bonding, such as trophallaxis. On the basis of an analogy with the role of norepinephrine in vertebrates, we suggest that the levels of octopamine in the brain of socially deprived ants may decrease, together with a concomitant increase in their urge to perform trophallaxis and to experience social contacts. Octopamine administration may reduce this social deprivation effect, and octopamine could therefore be regarded as being partly responsible for the social cohesion between nestmates in ant colonies.

Quantitative structure-activity studies of octopaminergic agonists and antagonists against Locusta migratoria using similarity indexes

The quantitative structure-activity relationship of 39 octopamine (OA) agonists and 12 antagonists against the thoracic nerve cord of the migratory locust, Locusta migratoria L. was analyzed using atom based rigid fit method or flexible fitting offered by PowerFit 1.0 from MicroSimulation. For OA agonists, the more similar to reference compound NC (24) the structure of test compound, the higher the activity, whereas for OA antagonists it was not the case. Antagonists may not interact with the same part of the membrane with which the agonists interact. Taken the part of the membrane with which the agonist interacts as the true receptor, the antagonist may well interact with an area surrounding the receptor including the ionophore.

Effect of octopamine on the activity of juvenile-hormone esterase in the silkworm Bombyx mori and the red flour beetle Tribolium freemani

This study focuses on the effect of octopamine (OA) on metamorphosis of the silkworm Bombyx mori and the red flour beetle Tribolium freemani Hinton. Titers of OA and juvenile-hormone esterase (JHE) were measured at various larval and pupal stadia of both insects. Effects of OA, OA agonists, and antagonists on metamorphosis and JHE activity were also examined. At day 2, peaks of OA and JHE activity were observed in third instars, and at day 3, a sharp peak of OA was observed, followed by a large peak of JHE activity at day 4 in last instars of B. mori. However, no peaks of OA and JHE activity were observed in fourth instars. A high titer of OA appeared at days 2-4, followed by a peak of JHE activity at day 7 and the second OA peak at day 9 after the start of assay of T. freemani. At pupation, a small peak of OA and the highest activity of JHE were observed. The effects of OA on JHE activity were examined in vitro, because the relationship could be responsible for triggering pupation in B. mori and T. freemani larvae. Exogeneous OA (0.1-10 mM) stimulated the JHE activity of final instars (day 2) of B. mori in vitro. Similarly, the presence of OA (10 mM) activated the JHE activity of newly ecdysed T. freemani pupae in vitro. OA antagonists chlorpromazine and gramine delayed the start of spinning and reduced the JHE activity of B. mori, when applied in diet at 10-100 ppm. Some OA agonists stimulated the pupation and JHE activity of T. freemani larvae reared under crowded conditions, when topically applied. Thus, OA may contribute to activation of the events preparatory to a pupal molt, i.e., the secretion of OA increases JHE activity followed by stimulation of pupation.

Quantitative structure-activity studies of octopaminergic agonists and antagonists against nervous system of Locusta migratoria

The quantitative structure activity relationship (QSAR) of octopaminergic agonists and antagonists against the thoracic nerve cord of the migratory locust, Locusta migratoria L., was analyzed using physicochemical parameters and regression analysis. The hydrophobic effect, dipole moment, and shape index were important in terms of Ki: the more hydrophobic, the greater dipole moment, and the smaller shape index of the molecules, the greater the activity. A receptor surface model (RSM) was generated using some subset of the most active structures. Three-dimensional energetics descriptors were calculated from RSM/ligand interaction and these three-dimensional descriptors were used in QSAR analysis. This data set was studied further using molecular shape analysis.

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.

Differential effects of angiotensin II and eledoisin on monoamine oxidase A and B activities in rat brain

Intracerebroventricular injections of angiotensin II caused 108, 62, and 54% increases in monoamine oxidase A activities in rat hippocampus, hypothalamus, and striatum, respectively. These activatory effects were abolished by simultaneous injections of eledoisin. No significant changes of monoamine oxidase B activities were found under the same experimental conditions. Neither angiotensin II nor elodoisin changed substrate/inhibitor affinities of both isoenzymes. These data indicate that angiotensin II and tachykinin transmitter systems may exert opposite, long-term regulatory effects on monoaminergic neurons in rat brain.

Taurine inhibits octopamine-stimulated cAMP production in cockroach haemocytes

Taurine and the taurine analogue guanidinoethanesulfonic acid interact with octopamine receptors of cockroach hemocytes to decrease octopamine-stimulated cAMP production. Dopamine-, synephrine- and tyramine-stimulated cAMP production in the haemocytes are also inhibited by taurine.

Octopaminergic modulation of the membrane potential of the Schwann cell of the squid giant nerve fibre

The actions of octopamine on the Schwann cells of the giant nerve fibre of the tropical squid are described. The pharmacology of the receptors mediating the actions of octopamine has been investigated in terms of stereospecificity, amine specificity and interactions with a range of agonists and antagonists. The receptors are maximally activated by D(−)-octopamine and share many of the characteristics of OCTOPAMINE2 class receptors in other preparations. The octopamine receptors appear to mediate their actions by increasing the intracellular levels of cyclic AMP in the Schwann cells. Low concentrations of octopamine potentiate the actions of the nicotinic cholinergic activation system of the Schwann cells. The results are discussed in terms of the possible physiological role of octopamine in the modulation of Schwann cell activity during stressful conditions when the giant axon system is likely to be used at a high frequency to facilitate the escape response of the squid.

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.

Pharmacodynamic differentiation of chronotropic and inotropic beta-adrenergic receptors in rabbit heart

Isolated, perfused rabbit hearts were used to identify substituted phenylethylamines selective for either chronotropic or inotropic stimulation relative to norepinephrine. Heart rate and dF/dtmax were measured; the difference in their normalized values was used as an index of selectivity. p-Octopamine (OA) showed chronotropic preference, while phenylephrine (PE) showed a significant inotropic preference. Their effects were not prevented by reserpine pretreatment, cocaine, butoxamine, or phenoxybenzamine, but were antagonized by propranolol, which suggests that OA and PE exert their selective actions directly at beta 1-receptors. These findings provide further evidence for the existence of separate chronotropic and inotropic beta-adrenergic receptors in the heart.

Multiple receptor types for octopamine in the locust

1. Three different pharmacological classes of octopamine receptor mediate the actions of octopamine on the locust extensor-tibiae neuromuscular preparation. A receptor classification scheme is proposed based on the results of detailed studies with agonists and antagonists. 2. Octopamine1 class receptors mediate the slowing of a myogenic rhythm found in a specialized proximal bundle of muscle fibres. Octopamine2A class receptors mediate the increase in amplitude of slow motoneurone twitch tension and octopamine2B class receptors mediate the increase in relaxation rate of twitch tension induced by firing either the fast or the slow motoneurones. 3. Octopamine1 receptors can be distinguished from the 2A and 2B classes since chlorpromazine (and yohimbine) are much better blocking agents than metoclopramide at the former receptors, whereas the converse is true for the latter class. Also clonidine is a more effective agonist than naphazoline for the former receptors and the converse is true for the latter class. 4. Octopamine 2A can be distinguished for octopamine 2B receptors since metoclopramide, mianserin and cyproheptadine show a strong preference for blocking the former class. Also naphazoline is a much better agonist than tolazoline at the former receptors and tolazoline is a much better agonist than clonidine at a latter. 5. The results are discussed in terms of the location of the various classes of octopamine receptors, their possible relationship to vertebrate alpha-adrenoreceptors, and the significance of the results for studies on octopamine receptors in the vertebrate central nervous system.

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.

Pharmacologic analysis of positive chronotropic and inotropic responses to octopamine

Effects of octopamine on sinus rate and atrial contractility were investigated using the isolated atrium preparation of the dog which perfused with heparinized arterial blood led from a support dog. When octopamine, dopamine or norepinephrine was administered into the cannulated sinus node artery, positive chronotropic and inotropic responses were dose-relatedly induced from 0.1 mug, 0.1 mug or 0.01 mug, respectively. The D.R.50 values (dose ratio at 50% maximum response) of octopamine, dopamine and norepinephrine are roughly 30-100: 30:1, respectively. The duration of action of octopamine was longest. Effects induced by octopamine were blocked by an adrenergic beta-blocking agent, alprenolol. Desmethyl-imipramine treatment significantly suppressed octopamine-induced effects but rather enhanced norepinephrine-induced ones. Octopamine-induced effects were not influenced by tetrodotoxin which blocked those induced by nicotine. From these results, it is concluded that positive chronotropic and inotropic responses to octopamine are mainly due to a tyramine-like action.

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.

The effects of changes in ionic environment and modification of adrenergic function on the vascular responses to sympathomimetic amines

The responses to each of four sympathomimetic amines: noradrenaline 200 ng, octopamine 50 μg, metaraminol 20 μg and tyramine 100 μg were studied in the perfused rat mesentery preparation. Perfusion with Ca2+- and Mg2+-free solutions potentiated the responses to all four amines compared with control responses obtained during normal Krebs perfusion. Under perfusion conditions using either normal or Ca2+- and Mg2+-free Krebs solution, nialamide and reserpine retained their characteristic effects on the responses to each amine. Cocaine and desipramine abolished the responses to tyramine but potentiated those to noradrenaline and metaraminol under all perfusion conditions. The responses to each of the amines were only antagonized by ouabain when Ca2+ ions were present in the perfusion solution. It is concluded that perfusion with Ca2+- and Mg2+-free solution interferes with the normal uptake mechanisms occurring in the adrenergic neuron.

Octopamine-sensitive adenylate cyclse: evidence for a biological role of octopamine in nervous tissue

An adenylate cyclase that is activated specifically by very low concentrations of octopamine has been identified both in homogenates and in intact cells of the thoracic ganglia of an insect nervous system. This enzyme appears to be distinct from two other adenylate cyclases present in the same tissue, which are activated by dopamine and by 5-hydroxytryptamine, respectively. The data raise the possibility of a role of octopamine-sensitive adenylate cyclase in the physiology of synaptic transmission.