Pharmacological profile of octopamine and 5HT receptors on the lateral oviducts of the cockroach,Periplaneta americana

The effects of the amines 5HT and octopamine on the myogenic activity of Periplaneta americana (L.) oviducts and the pharmacological profile of octopamine and 5HT receptors on the lateral oviducts have been determined. Application of 5HT to the oviducts resulted in a dose-dependent increase in basal tonus and amplitude of contractions. Antagonist studies revealed that the 5HT receptor on the cockroach oviduct most resembles the mammalian 5HT₂ receptor. Application of octopamine resulted in a decrease in basal tonus and had a biphasic effect on the amplitude of contractions, being stimulatory at low doses and inhibitory at higher ones. The inhibitory effects of octopamine appear to be mediated via cAMP and are blocked by antagonists which indicate that the octopamine receptor is of the octopamine-2 type. © 1995 Wiley-Liss, Inc.     

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.     

Crustacean cardioactive peptide is a modulator of oviduct contractions in Locusta migratoria

Crustacean cardioactive peptide (CCAP) stimulates the contractions of locust oviducts. CCAP increased the basal tonus and increased the frequency and amplitude of phasic contractions, as well as the amplitude of neurally-evoked oviduct contractions in a dose-dependent manner. Oviducts from Vth instar larvae and adult locusts aged 10 days or less, were more sensitive to CCAP than oviducts from adult locusts aged 12 days or more. This may be indicative of a differential expression of number or subtypes of CCAP receptors on the oviducts at different ages, and may be related to reproductive functions or to functions of CCAP on the oviducts during ecdysis. The oviducts appear more sensitive to CCAP when compared with previously published reports of CCAP actions on the hindgut. CCAP actions on the amplitude of neurally-evoked contractions of the oviducts are similar to those of proctolin, however, the oviducts are more sensitive to CCAP. No CCAP-like immunoreactive structures were discovered in the nerves innervating the oviducts, or on the oviducts themselves, confirming the previously published suggestion (Dircksen et al., 1991) that CCAP acts as a neurohormone at the oviducts. Cells showing CCAP-like immunoreactivity were discovered in the fat body associated with the oviducts and represent a potential source of CCAP, along with CCAP released from the transverse nerve and perivisceral organs.     

The modulation of skeletal muscle contraction by FMRFamide-related peptides of the locust

The external ventral protractor muscle of the VIIth abdominal segment, M234, is a skeletal muscle that possesses receptors that recognize a range of FMRFamide-related peptides and application of these peptides results in an increase in the amplitude of neurally evoked contractions with little or no effect on basal tonus. FLRFamide itself has the same biologic activity as the extended peptides, whereas truncation to LRFamide or RFamide results in a peptide with no biologic activity. The receptors recognizing these extended FLRFamides, which include SchistoFLRFamide, seem to be different from the SchistoFLRFamide receptors found on locust oviduct visceral muscle. SchistoFLRFamide and the non-peptide mimetic, benzethonium chloride (Bztc), increase the frequency and amplitude of miniature endplate potentials, increase the amplitude of neurally evoked excitatory junction potentials, and result in a hyperpolarisation of resting membrane potential. Bztc, however, also abolishes the active membrane response that may explain its ability to decrease neurally evoked contractions.     

Some pharmacological properties of neuromuscular transmission in the oviduct of the locust,Locusta migratoria

The effects of various pharmacological agents on neurally evoked contractions of the visceral muscles of the oviduct of Locusta migratoria have been examined. The pentapeptide, proctolin, at low concentrations (10^?11 M?10^?10 M), induced an increase in the amplitude of neurally evoked contractions and basal tonus, and induced the appearance and increased the frequency of myogenic contractions. Glutamate, at 10^?4 M, produced a small transient contraction which in some preparations was accompanied by a reduction in amplitude of neurally evoked contractions. Octopamine, at 10^?6 M, reduced the amplitude of neurally evoked contractions and also resulted in a relaxation of the muscles. The octopaminergic effects were inhibited by the α-aminergic antagonist phentolamine. Neurally evoked contractions were unaffected by dopamine, 5-HT or the acetylcholine receptor antagonists atropine and hexamethonium. Acetylcholine increased the amplitude of neurally evoked contractions, but only at the high concentration of 10^?3 M. The possible role of proctolin and glutamate as excitatory neuro-transmitters and the inhibitory action of octopamine is discussed.     

Evidence for octopaminergic modulation of an insect visceral muscle

Two dorsal unpaired median neurons (DUMOV1 and DUMOV2) lying in the posterior region of the VIIth abdominal ganglion of Locusta migratoria have axons which project to the muscles of the oviducts. This study reports the presence of octopamine within isolated DUMOV cell bodies, as well as in the oviducal nerve and innervated oviducal muscle. Individual cell bodies were pooled and found to contain about 0.34 pmol of octopamine per cell body giving an approximate value of 1.27 mM octopamine. Octopamine is concentrated within the area of oviducal muscle which receives DUMOV axons. Pharmacological studies reveal that the amplitude of neurally-evoked contractions of the oviducal muscle is reduced in a dose-dependent manner by octopamine, with threshold lying between 5 X 10(-10) M and 7 X 10(-9) M. The receptors for this response show a specificity for octopamine and synephrine, with an order of potency being octopamine = synephrine greater than metanephrine greater than tyramine greater than dopamine. The presence of octopamine throughout this neural pathway, coupled with the demonstration of octopaminergic modulation of muscular contraction, supports the hypothesis that octopamine serves a physiological role in this visceral system.     

Proctolin's role in neurally evoked contractions of the locust oviducts

The effects of proctolin (RYLPT) on neurally evoked contractions of locust oviduct muscle were studied to examine the role of proctolin as a cotransmitter. Increasing the number of stimuli in a burst (from one to 30 stimuli) resulted in an increase in amplitude of contraction of locust oviduct muscle. Proctolin was capable of increasing the amplitude of neurally evoked contractions at lower-stimulus regimes (one- and two-stimulus bursts) but did not do so at higher-stimulus regimes (five- and 10-stimulus bursts). The effects of proctolin were dose dependent within the one- and two-stimulus regimes, with thresholds at 10⁻⁹ M and maxima at 2.5 × 10⁻⁸ M. Addition of proctolin increased the basal tonus and size of a postcontraction relaxation of the oviduct muscle in a dose-dependent manner during all stimulus regimes. However, the effect of proctolin on basal tonus and the postcontraction relaxation was much less at the higher stimulus regimes. Previously, several proctolin analogues have been tested for their ability to antagonize proctolin-induced contractions of the oviduct muscle. Since proctolin is proposed to be a cotransmitter at this neuromuscular junction, one of these analogues, cycloproctolin, was used to antagonize proctolin's effects on neurally evoked contractions. In the presence of the antagonist, the maximum amplitude induced by application of proctolin was decreased by 22.7%, while the proctolin-induced increase in basal tonus was decreased by 45.8%. Finally, the maximum increase in the size of the postcontraction relaxation caused by proctolin was lowered by 32.0%. The results of the present study show that exogenously applied proctolin is an excitant of the oviduct muscle at lower, rather than higher, stimulus regimes, and this latter inaction may be due to the corelease of endogenous proctolin during increased neural stimulation. © 1997 John Wiley & Sons, Inc. J Neurobiol 33: 139–150, 1997     

Evidence for the association of FMRFamide-related peptides with the spermatheca of Locusta migratoria

The association of FMRFamide-related peptides (FaRPs) with the spermatheca of Locusta migratoria was demonstrated using radioimmunoassay and immunohistochemical techniques. The physiological effects of various FaRPs on the neurally evoked contractions of the spermatheca were also examined. FMRFamide-like immunoreactivity (FLI) was demonstrated in processes and cell bodies situated in the VIIIth (terminal) abdominal ganglion. These included an anterior, central and posterior pair of ventral cell bodies positioned near the midline of the ganglion, in addition to two bilaterally paired dorsal cell bodies in the posterior region of the VIIIth abdominal ganglion. Two axons displaying FLI proceed down the ventral ovipositor nerve (VON) and into the receptaculum seminis nerve which innervates the anterior regions of the spermatheca. FLI was also noted in processes on the spermathecal muscle with the highest density occurring on the spermathecal sac and coil duct. FaRPs applied to the spermathecal muscle included GQERNFLRFamide, NFIRFamide, ADDRNFIRFamide, YGGFMRFamide, FMRFamide, ADVGHVFLRFamide and SchistoFLRFamide (PDVDHVFLRFamide). Dose-dependent physiological effects were only noted for FMRFamide, ADVGHVFLRFamide and SchistoFLRFamide. FMRFamide led to a dose-dependent increase in the amplitude of neurally evoked contractions with a threshold of approximately 5 x 10(-7) M. SchistoFLRFamide, and ADVGHVFLRFamide, had an inhibitory effect, decreasing the amplitude of neurally evoked spermathecal contractions.     

Octopamine modulates a central pattern generator associated with egg-laying in the locust,Locusta migratoria

Egg-laying in Locusta migratoria involves the control of a variety of complex behavioural patterns including those that regulate digging of the oviposition hole and retention of eggs during digging. These two behavioural patterns are under the control of central pattern generators (CPGs). The digging and egg-retention CPGs are coordinated and integrated with overlapping locations of neural substrate within the VIIth and VIIIth abdominal ganglia of the central nervous system (CNS). In fact, the egg-retention CPG of the VIIth abdominal ganglion is involved in both egg-retention and protraction of the abdomen during digging. The biogenic amine, octopamine, has peripheral effects on oviduct muscle, relaxing basal tension of the lateral and upper common oviduct and enabling egg passage. Here we show that octopamine also modulates the pattern of the egg-retention CPG by altering the motor pattern that controls the external ventral protractor of the VIIth abdominal segment. There is no change in the motor pattern that goes to the oviducts. Octopamine decreased the frequency of the largest amplitude action potential and decreased burst duration while leading to an increase in cycle duration and interburst interval. The effects of octopamine were greatly reduced in the presence of the α-adrenergic blocker, phentolamine, indicating that the action of octopamine was via a receptor. Thus, octopamine orchestrates events that can lead to oviposition, centrally inhibiting the digging behavior and peripherally relaxing the lateral and common oviducts to enable egg-laying.     

Proctolin and octopamine actions on the contractile systems of insect leg muscles

1. The pentapeptide proctolin produced contractions of the coxal depressor muscle of the cockroach, Periplaneta americana.2. The contraction was dependent upon extracellular calcium and the contraction was completely blocked by a Ca-free EGTA saline.3. Caffeine elicited transient contractions which were unaffected by manganese treatment.4. When the muscle was pre-treated with the conditioning solution with different K⁺ concentrations (1–100 mM), the amplitude of proctolin-induced contractions was reduced in the low K⁺ saline as well as in the high K⁺ saline.5. The results suggest that voltage sensitive calcium channels account for the proctolin-induced contractions.6. Octopamine (OA) reduced the contractions resulting from brief applications of elevated K⁺ concentration and of caffeine.7. The effect of OA on the response to elevated K⁺ concentrations was blocked by the α-adrenergic blocker, phentolamine.     

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^?8M, while for proctolin it was 3 × 10^?9M. 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^?7M, 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.     

Mode of action of proctolin on locust visceral muscle

Proctolin increases the frequency and amplitude of myogenic contractions and results in a sustained contraction of the oviducts of Locusta migratoria. The possible mode of action of proctolin receptors on this visceral muscle has been investigated. Calcium-free saline, containing either 20 mM magnesium ions or 100 μM EGTA, inhibited myogenic contractions, lowered basal tension, and abolished all the effects of proctolin following a 20 min incubation. These effects were reversible upon washing with normal saline. Similar results were obtained with normal saline containing 10 mM cobalt ions. Nifedipine at 50 μM lowered basal tension, abolished myogenic contractions, and reduced the proctolin-induced sustained contraction by 42-62% at 0.5 nM proctolin and by 33-37% at 5 nM proctolin. Similar results were obtained with 100 μM verapamil. Proctolin was still capable of eliciting considerable contractions (25-67% of controls) in preparations depolarized with 100 mM potassium saline. The removal of calcium from the high-potassium saline reversibly abolished the potassium-induced contraction and reversibly blocked the action of proctolin. Nifedipine was ineffective in blocking the action of proctolin in high-potassium saline. Neither cyclic AMP levels nor cyclic GMP levels of the lateral oviducts were elevated by proctolin in the presence of a phosphodiesterase inhibitor. The results indicate that proctolin mediates its effects via an influx of external calcium ions. This calcium appears to enter through two channels, a voltage-dependent channel and a receptor-operated channel. Cyclic nucleotides do not appear to be involved in the action of proctolin in this visceral muscle.     

Octopamine action on the spontaneous contractions of the isolated nerve cord of Lumbricus terrestris

Octopamine and synephrine were observed to effect the spontaneous rhythmic contractions displayed by the isolated ventral nerve cord of the earthworm, Lumbricus terrestris. octopamine and synephrine produced dose-dependent significant changes in the frequency, amplitude and basal tonus of the spontaneous contractions. Application of adrenergic receptor antagonists suggested the octopamine receptors to have some similarity to vertebrate alpha 1-adrenergic receptors. The spontaneous contractions were not abolished by tetrodotoxin (TTX) which suggested a myogenic origin for the contraction of the ventral nerve cord sheath muscles. Octopamine, in the presence of TTX, increased the basal tonus and maximum force of the spontaneous contractions.     

Evidence for a possible neurotransmitter/neuromodulator role of tyramine on the locust oviducts

Visualization of the tyraminergic innervation of the oviducts was demonstrated by immunohistochemistry, and the presence of tyramine was confirmed using high-performance liquid chromatography coupled to electrochemical detection. Oviducts incubated in high-potassium saline released tyramine in a calcium-dependent manner. Stimulation of the oviducal nerves also resulted in tyramine release, suggesting that tyramine might function as a neurotransmitter/neuromodulator at the locust oviducts. Tyramine decreased the basal tension, and also attenuated proctolin-induced contractions in a dose-dependent manner over a range of doses between 10(-7) and 10(-4) M. Low concentrations of tyramine attenuated forskolin-stimulated cyclic AMP levels in a dose-dependent manner. This effect was not blocked by yohimbine. High concentrations of tyramine increased basal cyclic AMP levels of locust oviducts in a dose-dependent manner; however, the increases in cyclic AMP were only evident at the highest concentrations tested, 5 x 10(-5) and 10(-4) M tyramine. The tyramine-induced increase in cyclic AMP shared a similar pharmacological profile with the octopamine-induced increase in cyclic AMP. Tyramine increased the amplitude of excitatory junction potentials at low concentrations while hyperpolarizing the membrane potential by 2-5 mV. A further increase in the amplitude of the excitatory junction potentials and the occurrence of an active response was seen upon washing tyramine from the preparation. These results suggest that tyramine can activate at least three different endogenous receptors on the locust oviducts a putative tyramine receptor at low concentrations, a different tyramine receptor to inhibit muscle contraction, and an octopamine receptor at high concentrations.     

The effects of crustacean cardioactive peptide on locust oviducts are calcium-dependent

The role of calcium as a second messenger in the crustacean cardioactive peptide (CCAP)-induced contractions of the locust oviducts was investigated. Incubation of the oviducts in a calcium-free saline containing, a preferential calcium cation chelator, or an extracellular calcium channel blocker, abolished CCAP-induced contractions, indicating that the effects of CCAP on the oviducts are calcium-dependent. In contrast, sodium free saline did not affect CCAP-induced contractions. Co-application of CCAP to the oviducts with preferential L-type voltage-dependent calcium channel blockers reduced CCAP-induced contractions by 32-54%. Two preferential T-type voltage-dependent calcium channel blockers both inhibited CCAP-induced oviduct contractions although affecting different components of the contractions. Amiloride decreased the tonic component of CCAP-induced contractions by 40-55% and flunarizine dihydrochloride decreased the frequency of CCAP-induced phasic contractions by as much as 65%, without affecting tonus. Flunarizine dihydrochloride did not alter the proctolin-induced contractions of the oviducts. Results suggest that the actions of CCAP are partially mediated by voltage-dependent calcium channels similar to vertebrate L-type and T-type channels. High-potassium saline does not abolish CCAP-induced contractions indicating the presence of receptor-operated calcium channels that mediate the actions of CCAP on the oviducts. The involvement of calcium from intracellular stores in CCAP-induced contractions of the oviducts is likely since, an intracellular calcium antagonist decreased CCAP-induced contractions by 30-35%.     

Tyramine as a possible neurotransmitter/neuromodulator at the spermatheca of the African migratory locust, Locusta migratoria

Tyramine-like immunoreactivity was identified in neurons of the VIIIth abdominal ganglion and in axons projecting to the spermatheca of adult females of Locusta migratoria. Tyramine-like immunoreactive processes were also found throughout all regions of the spermatheca and tyramine-like immunoreactive bipolar or multipolar neurons were present on the spermathecal sac. HPLC coupled with electrochemical detection revealed more tyramine than octopamine present in spermathecal tissue. Electrical stimulation of the ventral ovipositor nerve resulted in a significant increase in calcium-dependent release of tyramine from the spermatheca. Both tyramine and octopamine increase the frequency and basal tonus of spermathecal contractions in a dose-dependent manner, with octopamine having a lower threshold. When tyramine is applied along with a half maximal octopamine dose, there is an additive effect on contractions of the spermatheca with slight synergistic effects at lower doses of tyramine. High concentrations of tyramine (10(-4)M) stimulated increases in cyclic AMP levels of the spermatheca; an effect blocked by phentolamine. Phentolamine has a higher affinity (and thus a lower IC(50) value congruent with5.6x10(-8)M) than yohimbine (IC(50) congruent with1.1x10(-4)M) in reducing tyramine-induced spermathecal contractions. Taken together, these results suggest that tyramine may be a co-transmitter with octopamine at the spermatheca, with both neuroactive chemicals acting on an octopamine receptor.     

Evidence for postsynaptic modulation of muscle contraction by a Drosophila neuropeptide

DPKQDFMRFamide, the most abundant FMRFamide-like peptide in Drosophila melanogaster, has been shown previously to enhance contractions of larval body wall muscles elicited by nerve stimulation and to increase excitatory junction potentials (EJPs). The present work investigated the possibility that this peptide can also stimulate muscle contraction by a direct action on muscle fibers. DPKQDFMRFamide induced slow contractions and increased tonus in body wall muscles of Drosophila larvae from which the central nervous system had been removed. The threshold for this effect was approximately 10(-8)M. The increase in tonus persisted in the presence of 7x10(-3)M glutamate, which desensitized postsynaptic glutamate receptors. Thus, the effect on tonus could not be explained by enhanced release of glutamate from synaptic terminals and, thus, may represent a postsynaptic effect. The effect on tonus was abolished in calcium-free saline and by treatment with L-type calcium channel blockers, nifedipine and nicardipine, but not by T-type blockers, amiloride and flunarizine. The present results provide evidence that this Drosophila peptide can act postsynaptically in addition to its apparent presynaptic effects, and that the postsynaptic effect requires influx through L-type calcium channels.     

Octopamine modulates spermathecal muscle contractions in <Emphasis Type="Italic">Locusta migratoria</Emphasis>

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.     

The effects of octopamine on juvenile hormone biosynthesis,electrophysiology, and cAMP content of the corpora allata of the cockroach Diploptera punctata

Summary 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 5·10^-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.Abbreviations 4-AP 4-aminopyridine - CA corpora allata - CC corpora cardiaca - cAMP cyclic adenosine monophosphate - cGMP cyclic guanosine monophosphate - EDTA ethylenediamine tetraacetic acid - HEPES N-2-hydroxyethylpiperazine-N2-ethanesulfonic acid - HPLC high pressure liquid chromatography - IBMX 3-isobutyl-1-methylxanthine - JH juvenile hormone - ms millisecond - nA nanoampere - NCA I nervi corporis allati I - OCT octopamine - TEA tetraethyl ammonium     

Isolation and characterization of Locusta migratoria accessory gland myotropin I (Lom-AG-MT-I) from the brain of the Colorado potato beetle,Leptinotarsa decemlineata

A novel myotropic Colorado potato beetle peptide, active in the Locusta oviduct motility assay, was isolated from a methanolic extract of 9,000 brain complexes of adult Leptinotarsa decemlineata by means of HPLC. Its sequence is Gly-Phe-Lys-Asn-Val-Ala-Leu-Ser-Thr-Ala-Arg-Gly-Phe-NH₂. This peptide is identical to Lom-AG-MT-I, a myotropin previously isolated from the male accessory glands of Locusta migratoria, using the L. migratoria oviduct motility bioassay as a monitoring system. It strongly stimulated the frequency, amplitude, and tonus of the myogenic oviduct contractions, even at low concentrations. © 1996 Wiley-Liss, Inc.