Injection Of Octopamine Research Articles

Effect of octopamine on the frequency tuning of the auditory system in <i>Culex pipiens pipiens</i> mosquito (Diptera, Culicidae)

We aimed at demonstrating the direct physiological effects of octopamine on the auditory responses of the Johnston’s organ sensory neurons in Culex pipiens pipiens mosquitoes. Responses to acoustic stimulation were measured as the frequency-threshold curves and as an instantly recorded autoexcitation frequency before and after the injection of octopamine (or chlordimeform, an agonist of octopamine receptors). The autoexcitation frequency was assessed by including the auditory neurons into a positive feedback loop, when the amplified neuronal response was used to drive the stimulating loudspeaker. Our results indicate that: octopamine affects the properties of the auditory system both in male and female mosquitoes; in female mosquitoes, octopamine significantly reduces the sensitivity of auditory neurons below 90 Hz and produces little effect in the high-frequency range (100 Hz and above); in male mosquitoes, octopamine significantly raises the tuning frequency of the auditory system (ratio of tuning frequencies before and after the injection 1.32–1.55). There is a strong sexual dimorphism in the octopaminergic modulation of the mosquito auditory system. The observed physiological effects of octopamine, both in male and female mosquitoes, cannot be fully explained by the modulation of mechanical stiffness of the antenna and must include the changes in frequency tuning of the auditory neurons.

Effects of octopamine on memory retention under chemical stress: a behavioral study on honey bees

Honey bees may experience the adverse effects of environmental contaminants when exposed during foraging trips, or something to that effect. We hypothesized that octopamine (OA), with important functions in reward signaling and learning, can improve the behavior of honey bees under chemical stress. Memory retention and sucrose responsiveness were evaluated using the proboscis extension reflex (PER) assay. The one-day-old bees were exposed separately to diazinon, imidacloprid, paraquat, manganese, and thymol at concentrations of 0.22, 29.04, 55.69, 106.19, and 0.91 ppm, respectively. On the 21st day of exposure, the bees’ responses to memory retention and sucrose responsiveness experiments were recorded after the training trial. In addition, PERs were recorded after OA injection. During the intervals, honey bees were exposed to the toxins topically. The expression levels of OA receptor genes, AmoctαR1 and AmoctβR4, were measured. The sucrose responsiveness tests showed no significant differences between the bees stimulated with the control solutions or toxins. Moreover, our results indicated that memory retention significantly declined in honey bees exposed to toxins compared to the controls (P ≤ 0.05). According to the findings, OA improved the memory retention of honey bees exposed to toxins (P ≤ 0.05). The expression levels of AmoctαR1 and AmoctβR4 genes significantly increased in the treated honey bees, especially those exposed to paraquat and manganese, after 30 min post-OA injection. It can be concluded that under chemical stress, OA administration encouraged honey bees to respond to a stimulus. Therefore, it can be added to a nutrient-enriched diet.

Behavioral roles of biogenic amines in bumble bee males

To compare the behavioral roles of biogenic amines in the males of primitive and advanced eusocial bees, we determined the levels of dopamine- and octopamine-related substances in the brain, and the behavioral effects of these monoamines by drug injection in the primitive eusocial bumble bee, Bombus ignitus. The levels of dopamine and its precursors in the brain peaked at the late pupal stage, but the dopamine peak extended to adult emergence. The tyramine and octopamine levels increased from the mid-pupal to adult stages. The locomotor and flight activities, and light preference increased with age. Injection of octopamine and its receptor antagonist had significant effects on the locomotor and flight activities, whereas dopamine injection did not, indicating that these activities can be regulated by the octopaminergic system. We also determined the dynamics of dopamine-related substances in honey bee (Apis mellifera) drones. The changes in the dopamine level in the brains of honey bee drones exhibited two peaks from the pupal to adult stages, whereas the bumble bee males had only one peak. These are consistent with the behavioral functions of dopamine in honey bee drones and ineffectiveness of dopamine injection at the adult stage in bumble bee males.

The intracellular signaling pathway of octopamine upregulating immune resistance functions in Penaeus monodon

Octopamine (OA), a biogenic monoamine, is known to mediate several immune responses. This study analyzed the effects of OA on immunological regulation in the tiger shrimp Penaeus monodon. The immune parameters including total haemocyte count, differential haemocyte count, phenoloxidase activity, respiratory bursts, superoxide dismutase activity, and phagocytic activity and clearance efficiency in response to the pathogen, Photobacterium damselae, were determined when shrimp were individually injected with saline or OA at 100 or 1000 pmol shrimp−1. In addition, the intracellular second messengers in haemocyte such as Ca2+ and adenosine 3′,5′-cyclic monophosphate (cAMP) were examined in shrimp receiving saline or OA at 1 or 10 nmol shrimp−1. Results showed that all of the immune parameters significantly increased at 2–4 h in OA-injected shrimp except hyaline cells in 100 pmol shrimp−1-injected shrimp at 4 h, but phenoloxidase activity per granulocyte significantly decreased at 2–4 h. However, these had returned to saline control levels after receiving OA for 8 h except differential haemocyte count and phenoloxidase activity per granulocyte for 16 h. An injection of OA also significantly increased the survival rate of shrimp challenged with Pho. damselae. Shrimp receiving OA at 1 and 10 nmol shrimp−1 significantly increased the intracellular Ca2+ concentration ([Ca2+]i) at 30–60 min and 30 min, and cAMP concentration [cAMP]i) at 5–15 min and 15 min, respectively. However, [Ca2+]i at 50–60 min, and [cAMP]i at 30–60 min returned to saline control when the shrimp received OA at 10 nmol shrimp−1, and at 1 and 10 nmol shrimp−1, respectively. These results suggest that OA administration by injection at ≤1000 pmol shrimp−1 mediates transient upregulation of immunity together with the increased resistance of P. monodon to Pho. damselae, which are modulated through intracellular Ca2+ and cAMP second messenger pathways.

Transient enhancement of immune resistance functions in Litopenaeus vannamei through a low-dose octopamine injection

Octopamine (OA) is known to play an important role in regulating invertebrate immune responses. In this study, we determined the effects of OA on immunity and physiological regulation in the white shrimp Litopenaeus vannamei. The total haemocyte count (THC), differential haemocyte count (DHC), phenoloxidase (PO) activity, respiratory bursts (RBs), superoxide dismutase (SOD) activity, and lysozyme, glucose, and lactate levels in plasma, and phagocytic activity and clearance efficiency in response to the pathogen, Vibrio alginolyticus, were measured when shrimp (11.1–13.0 g) were individually injected with saline or OA at 100 and 1000 pmol shrimp−1. Results showed significant increases in THC, semigranular cells (SGCs), and PO activity per 50 μL of haemolymph at 0.5–4 h; granular cells at 0.5–2 h; respiratory bursts (RBs) at 0.5–1 h; phagocytic activity at 2–4 h; and clearance efficiency at 2–8 h, but PO activity per granulocyte at 0.5–2 h significantly decreased after the OA injection. All of the immune parameters had returned to control values by 8 h after receiving OA except granular cells at 4 h, RBs at 2 h, clearance efficiency at 16 h, and PO activity per granulocyte at 4 h. However, no significant differences were observed in hyaline cells, RBs per haemocyte, lysozyme and SOD activities, glucose, or lactate during the experimental period. An injection of OA also significantly decreased the mortality of shrimp challenged with V. alginolyticus. In another experiment, the immune-related genes of transglutaminase-I, lipopolysaccharide- and β-1,3-glucan-binding protein, prophenoloxidase-II, and peroxidase of shrimp that received 1000 pmol OA shrimp−1 for 1 h were significantly higher than those of shrimp that received the saline control. These results suggest that OA administration at ≤1000 pmol shrimp−1 mediates transient upregulation of immunity, which in turn promotes the resistance of L. vannamei to V. alginolyticus.

Altered immunity in crowded Mythimna separata is mediated by octopamine and dopamine

Similar to pathogenic infection, high population density alters insects’ prophylactic immunity. Density-dependent prophylaxis has been reported in many polyphenic insects, but the regulatory mechanism underlying this phenomenon remains unclear. The biogenic monoamines are known to play critical roles in mediating insect immune responses. In the current study, the immune capacity and the levels of three biogenic monoamines were investigated in the polyphenic larvae of Mythimna separata, reared at the densities of 1, 2, 5, 10, and 30 larvae per 650-mL jar. Concomitant with the increased phenoloxidase (PO) activity and total haemocyte count in the larvae at high densities (5, 10, 30 larvae/jar), the octopamine level was also increased. In contrast, the dopamine level was decreased, and the 5-hydroxytryptamine level was not significantly affected. Injection of octopamine induced significant increases in the total haemocyte count and PO activity. Conversely, epinastine, a specific antagonist of octopamine, decreased the total haemocyte count and PO activity. Another octopamine antagonist, phentolamine, inhibited the activity of PO and lysozymes. In addition, injection of dopamine induced a significant increase in PO activity and decreased the total haemocyte count and lysozyme activity. These results suggested that both octopamine and dopamine mediate the increases in total haemocyte count and PO activity in the crowded larvae.

Octopamine enhances the immune responses of freshwater giant prawn, Macrobrachium rosenbergii, via octopamine receptors

Octopamine (OA) is known to play an important role in regulating insect immune responses. In Macrobrachium rosenbergii (18.0 ± 1.7 g), OA at 25.0 and 250.0 pmol/prawn significantly increased THC, semigranular cells (SGCs) and PO activity in hemocytes per 50 μL hemolymph, hyaline cells, granular cells (GCs) and RBs in hemocytes per 10 μL hemolymph, and RBs per hemocyte, and however, significantly decreased PO activity per granulocyte (GC + SGC), which returned to control levels after 4 h of injection. The significantly increased phagocytic activity and clearance efficiency of prawn received OA for 8 h returned to control levels after 16 h of injection. In addition, the significantly increased glucose and decreased lactate were observed within 1 h of OA injection. In the susceptibility test, prawn received OA at 25.0 or 250.0 pmol/prawn for 2 h then challenged with Lactococcus garvieae at 105 colony-forming units/prawn significantly increased the resistance of prawns by 23.3% and 30.0%, respectively, compared to the saline-challenged control after 144 h of challenge. In addition, the changes on immunocompetence induced by OA were observed to be blocked by adrenoceptors antagonists. These results suggest that OA administration at 250.0 pmol/prawn or less causes the mediate a transient up-regulation in immune and physiologic responses to promote the resistance of M. rosenbergii to L. garvieae, which are thought to be mediated by α- and β-adrenergic-like octopamine receptors.

The behavioural effects of predator-induced stress responses in the cricket (Gryllus texensis): the upside of the stress response

Predator-induced stress responses are thought to reduce an animal's risk of being eaten. Therefore, these stress responses should enhance anti-predator behaviour. We found that individual insects (the cricket Gryllus texensis) show reliable behavioural responses (i.e. behavioural types) in a plus-shaped maze. An individual's behaviour in the plus maze remained consistent for at least 1/2 of its adult life. However, after exposure to a model predator, both male and female crickets showed a reduced period of immobility and an increased amount of time spent under shelter compared with controls. These changes could be mimicked by injections of the insect stress neurohormone octopamine. These behavioural changes probably aid crickets in evading predators. Exposure to a model predator increased the ability of crickets to escape a live predator (a bearded dragon, Pogona vitticeps). An injection of octopamine had the same effect, showing that stress hormones can reduce predation. Using crickets to study the fitness consequences of predator-induced stress responses will help integrate ecological and biomedical concepts of 'stress'.

Aminergic Control of Social Status in Crayfish Agonistic Encounters

Using pairings of male crayfish Procambarus clarkii with a 3–7% difference in size, we confirmed that physically larger crayfish were more likely to win encounters (winning probability of over 80%). Despite a physical disadvantage, small winners of the first pairings were more likely to win their subsequent conflicts with larger naive animals (winning probability was about 70%). By contrast, the losers of the first pairings rarely won their subsequent conflicts with smaller naive animals (winning probability of 6%). These winner and loser effects were mimicked by injection of serotonin and octopamine. Serotonin-injected naive small crayfish were more likely to win in pairings with untreated larger naive crayfish (winning probability of over 60%), while octopamine-injected naive large animals were beaten by untreated smaller naive animals (winning probability of 20%). Furthermore, the winner effects of dominant crayfish were cancelled by the injection of mianserin, an antagonist of serotonin receptors and were reinforced by the injection of fluoxetin, serotonin reuptake inhibitor, just after the establishment of social order of the first pairings. Injection of octopamine channel blockers, phentolamine and epinastine, by contrast, cancelled the loser effects. These results strongly suggested that serotonin and octopamine were responsible for winner and loser effects, respectively.

Central pattern generation underlying Limulus rhythmic behavior patterns

Abstract Many behavioral activities of the horseshoe crab Limulus are rhythmic, and most of these are produced in large part by central pattern generators within the CNS. The chain of opisthosomal ('abdominal') ganglia controls gill movements of ventilation and gill cleaning, and the prosomal ring of fused ganglia (brain and segmental 'thoracic' ganglia) controls generation of feeding and locomotor movements of the legs. Both the opisthosomal CNS and the prosomal CNS can generate behaviorally appropriate patterns of motor output in isolation, without movements or sensory input. Preparations of the isolated opisthosomal CNS generate rhythmic output patterns of motor activity characterized as fictive ventilatory and gill cleaning rhythms. Moreover, CNS preparations also express longer-term patterns, such as intermittent ventilation or sequential bouts of ventilation and gill cleaning. Such longer-term patterns are commonly observed in intact animals. The isolated prosomal CNS does not spontaneously generate the activity patterns characteristic of walking, swimming, and feeding. However, perfusion of octopamine in the isolated prosomal CNS activates central pattern generators underlying rhythmic chewing movements, and injection of octopamine into intact Limulus promotes the chewing pattern of feeding, whether or not food is presented. Our understanding of the ability of neuromodulators such as octopamine to elicit or alter central motor programs may help to clarify the central neural circuits of pattern generation that produce and coordinate these rhythmic behaviors.

Mating-induced transient inhibition of responses to sex pheromone in a male moth is not mediated by octopamine or serotonin

In the male moth, Agrotis ipsilon, mating induces a transient inhibition of behavioural and central nervous responses to sex pheromone. Newly mated males are not attracted to sex pheromone, and the sensitivity of their antennal lobe (AL) neurons is lower than in virgin males. This rapid transient olfactory inhibition prevents them from re-mating unsuccessfully until they have refilled their sex glands. We hypothesized that this olfactory 'switch off' might be controlled by neuromodulators such as biogenic amines. To test our hypothesis, we studied the effects of octopamine (OA) and serotonin (5-hydroxytryptamine, 5-HT) on the coding properties of pheromone-sensitive AL neurons in virgin and newly mated males. We show that AL neuron sensitivity increased in newly mated males after injection of OA or 5-HT, but only OA treatment affected certain response characteristics of AL neurons in virgin males. Whereas all measured AL neuron response characteristics were different between virgin and newly mated males, amine treatment in newly mated males restored only the latency and spike frequency, but not the duration of excitatory and inhibitory phases, which were initially found in virgin males. Additionally, we investigated the behavioural effects of OA and 5-HT treatments in virgin and mated males. Although OA and 5-HT enhanced the general flight activity of newly mated males, amine treatments did not restore the behavioural pheromone response of mated moths. Altogether, these results show that, although biogenic amines modulate the olfactory system in moths, OA and 5-HT are probably not involved in the post-mating inhibition of responses to sex pheromone in A. ipsilon males.

Reduced female mating receptivity and activation of oviposition in two Callosobruchus species due to injection of biogenic amines

Analyses of proximate mechanisms that control mating and oviposition behaviours in insects are important because they link behavioural ecology and physiology. Recently, seed beetles have been used as models to study evolution of female multiple mating and cost of reproduction including mating. In the present study, we investigated the effects of biogenic amines into the abdomens of females of two Callosobruchus species, Callosobruchus chinensis and Callosobruchus maculatus, on mating receptivity and oviposition behaviour. In C. chinensis, injection of octopamine and tyramine reduced receptivity to mating and tyramine and serotonin increased the number of eggs laid. Similarly, injection of tyramine reduced the receptivity of females and increased the number of eggs laid by females of C. maculatus. These results show the possibility that biogenic amines control mating receptivity and oviposition behaviour in females of two Callosobruchus species.

Why should an immune response activate the stress response? Insights from the insects (the cricket Gryllus texensis)

Mediators of the stress response (e.g. glucocorticoids and norepinephrine) can be immunosuppressive. Nevertheless, immune challenge leads to the release of these compounds in vertebrates. To resolve this paradox, it has been suggested that stress hormones help restore immune homeostasis, preventing self-damage. A comparative approach may provide additional hypotheses as to why an immune challenge induces the release of stress hormones/neurohormones. Octopamine, a neurohormonal mediator of the stress response in the cricket Gryllus texensis, increased in concentration in the hemolymph during an immune challenge. Therefore, the release of stress hormones during an immune response occurs in animals across phyla. Octopamine induced an increase in lipid concentration in the hemolymph. After an acute stress (flying or running) the total number of hemocytes in the hemolymph increased. Injections of octopamine had the same effect, suggesting that it may enhance hemocyte-dependent immune functions. On the other hand, octopamine decreased lysozyme-like activity in vitro, suggesting that it inhibits some immune functions. However, lysozyme-like activity was increased by the presence of heat-killed bacteria in vitro and this increase was significantly augmented by the presence of octopamine. Therefore, the effect of octopamine on immune function differed depending on the presence of pathogens. Stress hormones may help shift immune function into the most optimal configuration depending on the physiological context.

Contrasting Role of Octopamine in Appetitive and Aversive Learning in the Crab Chasmagnathus

BackgroundBiogenic amines are implicated in reinforcing associative learning. Octopamine (OA) is considered the invertebrate counterpart of noradrenaline and several studies in insects converge on the idea that OA mediates the reward in appetitive conditioning. However, it is possible to assume that OA could have a different role in an aversive conditioning.Methodology/Principal FindingsHere we pharmacologically studied the participation of OA in two learning processes in the crab Chasmagnathus granulatus, one appetitive and one aversive. It is shown that the aversive memory is impaired by an OA injection applied immediately or 30 minutes after the last training trial. By contrast, the appetitive memory is blocked by OA antagonists epinastine and mianserine, but enhanced by OA when injected together with the supply of a minimum amount of reinforcement. Finally, double-learning experiments in which crabs are given the aversive and the appetitive learning either successively or simultaneously allow us to study the interaction between both types of learning and analyze the presumed action of OA. We found that the appetitive training offered immediately, but not one hour, after an aversive training has an amnesic effect on the aversive memory, mimicking the effect and the kinetic of an OA injection.Conclusions/SignificanceOur results demonstrate that the role of OA is divergent in two memory processes of opposite signs: on the one hand it would mediate the reinforcement in appetitive learning, and on the other hand it has a deleterious effect over aversive memory consolidation.

The emergency life-history stage and immunity in the cricket, Gryllus texensis

Both vertebrates and molluscs (e.g. oysters) become more susceptible to disease after exposure to a stressor. Indirect evidence suggested that insects may become less susceptible to disease when exposed to stress. If true, this would force us to reconsider our hypotheses about the possible adaptive significance of stress-induced immunosuppression. We tested the effect of crowding, physical exercise, restraint, flight, heat, cold, agonistic behaviour and elevated levels of the flight-or-fight neurohormone octopamine on immune function and disease resistance (i.e. resistance to the bacterium Serratia marcescens) in the cricket Gryllus texensis. Crowding did not induce increased disease resistance (density-dependent prophylaxis); however, this result is difficult to interpret because mortality was higher for crowded crickets than it was for isolated crickets. Physical exercise, restraint, flight, heat and agonistic behaviour induced a decline in disease resistance. Restraint and heat also induced a decline in inducible lysozyme-like activity, suggesting a reduction in this immune function. Injections of octopamine resulted in a decrease in disease resistance, suggesting that it may affect immunosuppression after flight-or-fight activity. We have no evidence that stress induces a redistribution of immune resources resulting in enhanced wound surveillance. Following physical restraint, crickets were more susceptible to bacterial infection after wounding than were controls. The widespread occurrence of stress-induced immunosuppression suggests that it serves an important function.

Interactions between the endocrine and immune systems in locusts

Abstract. The prophenoloxidase cascade in the haemolymph of mature adult Locusta migratoria migratorioides (R & F) is activated in response to injection of laminarin, a β‐1,3 glucan. Co‐injection of adipokinetic hormone‐I (Lom‐AKH‐I) and laminarin prolongs the activation of the enzyme in a dose‐dependent manner. However, injections of bacterial lipopolysaccharide (LPS) do not activate prophenoloxidase unless AKH is co‐injected, when there is a dose‐dependent increase in the level of phenoloxidase that persists in the haemolymph for several hours. Even when AKH is co‐injected, the highest levels of phenoloxidase activity are always greater after injection of laminarin than after LPS, and these two immunogens must activate the prophenoloxidase cascade by quite distinct pathways. In the present study, interactions between the endocrine and immune systems were examined with respect to activation of prophenoloxidase and the formation of nodules: injection of LPS induces nodule formation in adult locusts. With LPS from Pseudomonas aeruginosa, nodules form exclusively in dense accumulations in the anterior portion of the abdomen on either side of the dorsal blood vessel associated with the dorsal diaphragm. However, with LPS from Escherichia coli, fewer nodules are formed but with a similar distribution, except that occasionally some nodules are aligned additionally on either side of the ventral nerve cord. Co‐injection of Lom‐AKH‐I with LPS from either bacteria stimulates greater numbers of nodules to be formed. This effect of coinjection of AKH on nodule formation is seen at low doses of hormone with only 0.3 or 0.4 pmol of Lom‐AKH‐1, respectively, increasing the number of nodules by 50%. Injections of octopamine or 5‐hydroxytryptamine do not mimic either of the actions of Lom‐AKH‐I described here. Co‐injection of an angiotensin‐converting enzyme inhibitor, captopril, reduces nodule formation in response to injections of LPS but has no effect on the activation of phenoloxidase. Co‐injection of an inhibitor of eicosanoid synthesis, dexamethasone, with LPS influences nodule formation (with or without AKH) in different ways according to the dose of dexamethasone used, but does not affect activation of prophenoloxidase. Eicosanoid synthesis is important for nodule formation, but not for the activation of the prophenoloxidase cascade in locust haemolymph.

Intracerebroventricular administration of octopamine stimulates food intake of chicks through α 2-adorenoceptor

Octopamine, known to be an important neurotransmitter in invertebrates, has been noted to have several similarities to noradrenaline (NA) in mammals. The present study was done to elucidate whether central injection of octopamine enhances the feeding behavior of chicks and to investigate the interaction of octopamine with both α 1- and α 2-adorenoceptors. We found that the intracerebroventricular injection of octopamine significantly stimulated food intake of neonatal chicks during 30 min postinjection, but not thereafter. Moreover, this octopamine-induced eating response was attenuated by the α 2-antagonist yohimbine, but not by the α 1-antagonist prazosin. These results suggest that the action of octopamine on the feeding behavior of the neonatal chick is similar to that of NA, since octopamine regulates food intake through the α 2-adorenoceptor.

Apolipophorin-III in the greater wax moth, Galleria mellonella (Lepidoptera: Pyralidae).

The level of apolipophorin-III reached a maximum in the haemolymph of Galleria mellonella at the end of the feeding phase of the seventh larval instar and declined to a plateau value in the pupal and the adult stages. Apolipophorin-III was detected immunologically in fat body tissue, haemocyte lysates, and plasma. In its native state, apolipophorin-III may be associated with another protein with an apparent molecular mass of 77 kDa, possibly apolipophorin-II. Injections of octopamine did not cause lipid loading of high density lipophorin.

Modulation of claw-closing behavior in the crayfishProcambarus clarkiiby extrinsic factors and biogenic amines

Claw closure in the crayfish can be elicited by tactile stimulation of the closer-field sensory hairs located along the biting surfaces of the apposed dactyl and propodite. The possibility that this simple behavior can be extrinsically modulated was examined by stimulating closer-field hairs in specimens of the crayfish Procambarus clarkii while the animals were either unrestrained, restrained, or bathed in chemical feeding stimulants. Restraint increases both the probability of closure and the average angular velocity of the dactyl during closure compared with responses in unrestrained specimens. Chemical feeding stimulants increase the probability, but not the average angular velocity, of closure compared with the unrestrained condition. Injection of octopamine into unrestrained animals produces effects on claw closure that resemble those accompanying restraint. Injection of serotonin, however, is followed by decreases in both the probability and the average angular velocity of closure. It is argued that extrinsic factors modulate claw-closure behavior in ways appropriate to current circumstances, and that biogenic amines are implicated as "gain-setters" in this process.

Biogenic amines modulate olfactory receptor neurons firing activity in Mamestra brassicae.

The modulatory effects of the biogenic amines octopamine and serotonin on pheromonal receptor neurons of Mamestra brassicae were investigated. The responses to sex pheromone components of two cells types (A and B) in single male long sensilla trichodea were monitored. Cell types A and B do not respond to the same compound. The response of type A to a pulse of the major sex pheromone component increased 5 min after octopamine injection. Responses of type B to other odorants increased after 30 min. In the absence of any pheromone stimulation the background firing activity of type A increased following octopamine injection. This background activity was used to evaluate the kinetics of octopamine and other biogenic amine effects on olfactory receptor neurons. Octopamine increased this background activity in a concentration- and time-dependent manner. Clonidine, an octopamine agonist, was shown to be more powerful in increasing the background activity of olfactory receptor neurons. The effects of octopamine and clonidine were hypothesized to arise from specific receptor activation as chlorpromazine (an octopamine antagonist) was shown to block the effect of octopamine. Serotonin, a known neuromodulator in most animal species, induced a reversible inhibition of spike firing. Altogether, these results indicate that biogenic amines can modulate the sensitivity of olfactory receptor neurons of moths either directly or by an action on adaptation.