Occurrence of crustacean cardioactive peptide (CCAP) in the nervous system of an insect,Locusta migratoria

Recent advances in neuropeptide signaling in Drosophila, from genes to physiology and behavior

This review focuses on neuropeptides and peptide hormones, the largest and most diverse class of neuroactive substances, known in Drosophila and other animals to play roles in almost all aspects of daily life, as w;1;ell as in developmental processes. We provide an update on novel neuropeptides and receptors identified in the last decade, and highlight progress in analysis of neuropeptide signaling in Drosophila. Especially exciting is the huge amount of work published on novel functions of neuropeptides and peptide hormones in Drosophila, largely due to the rapid developments of powerful genetic methods, imaging techniques and innovative assays. We critically discuss the roles of peptides in olfaction, taste, foraging, feeding, clock function/sleep, aggression, mating/reproduction, learning and other behaviors, as well as in regulation of development, growth, metabolic and water homeostasis, stress responses, fecundity, and lifespan. We furthermore provide novel information on neuropeptide distribution and organization of peptidergic systems, as well as the phylogenetic relations between Drosophila neuropeptides and those of other phyla, including mammals. As will be shown, neuropeptide signaling is phylogenetically ancient, and not only are the structures of the peptides, precursors and receptors conserved over evolution, but also many functions of neuropeptide signaling in physiology and behavior.

Ecdysis behaviors and circadian rhythm of ecdysis in the stick insect, Carausius morosus

Successful ecdysis in insects depends on proper timing and sequential activation of an elaborate series of motor programs driven by a relatively conserved network of neuropeptides. The behaviors must be activated at the appropriate times to ensure successful loosening and shedding of the old cuticle, and can be influenced by environmental cues in the form of immediate sensory feedback and by circadian rhythms. We assessed the behaviors, components of the neural network and the circadian basis of ecdysis in the stick insect, Carausius morosus. C. morosus showed many of the characteristic pre-ecdysis and ecdysis behaviors previously described in crickets and locusts. Ecdysis was described in three phases, namely the (i) preparatory or pre-ecdysis phase, (ii) the ecdysial phase, and (iii) the post-ecdysis or exuvial phase. The frequencies of push-ups and sways during the preparatory phase were quantified as well as durations of all the phases. The regulation of ecdysis appeared to act via elevation of cGMP, as described in many other insects, although eclosion hormone-like immunoreactivity was not noted using a lepidopteran antiserum. Finally, C. morosus showed a circadian rhythm to the onset of ecdysis, with ecdysis occurring just prior to or at lights on. Ecdysis could be induced precociously with mechanical stimulation.

Crustacean cardioactive peptide in the Chagas' disease vector, Rhodnius prolixus: presence, distribution and physiological effects

Crustacean cardioactive peptide (CCAP), a cyclic nonapeptide (PFCNAFTGCamide), has multifunctional roles in insects including stimulating visceral and cardiac muscle contraction, and regulating ecdysis. Previously, we have sequenced the cDNA for CCAP from Rhodnius prolixus central nervous system (CNS) and shown expression of the CCAP transcript in neurons of the CNS. In the present study, we have biochemically identified and sequenced CCAP from 5th instar R. prolixus CNS using matrix-assisted laser desorption ionization-time of flight-tandem mass spectrometry, and mapped CCAP-like immunoreactivity in the CNS and peripheral tissues of 5th instar R. prolixus. Physiologically, the hindgut of R. prolixus was found to be sensitive to CCAP, showing dose-dependent increases in contractions with threshold at 5 × 10(-9) M and maximum response at 10(-7) M CCAP. Also, CCAP was found to increase the frequency of the heartbeat in a reversible, dose-dependent manner, with threshold close to 10(-11) M and maximum response at 10(-10) M CCAP.

Transcriptome analysis of the desert locust central nervous system: production and annotation of a Schistocerca gregaria EST database

BACKGROUND

The desert locust (Schistocerca gregaria) displays a fascinating type of phenotypic plasticity, designated as 'phase polyphenism'. Depending on environmental conditions, one genome can be translated into two highly divergent phenotypes, termed the solitarious and gregarious (swarming) phase. Although many of the underlying molecular events remain elusive, the central nervous system (CNS) is expected to play a crucial role in the phase transition process. Locusts have also proven to be interesting model organisms in a physiological and neurobiological research context. However, molecular studies in locusts are hampered by the fact that genome/transcriptome sequence information available for this branch of insects is still limited.

METHODOLOGY

We have generated 34,672 raw expressed sequence tags (EST) from the CNS of desert locusts in both phases. These ESTs were assembled in 12,709 unique transcript sequences and nearly 4,000 sequences were functionally annotated. Moreover, the obtained S. gregaria EST information is highly complementary to the existing orthopteran transcriptomic data. Since many novel transcripts encode neuronal signaling and signal transduction components, this paper includes an overview of these sequences. Furthermore, several transcripts being differentially represented in solitarious and gregarious locusts were retrieved from this EST database. The findings highlight the involvement of the CNS in the phase transition process and indicate that this novel annotated database may also add to the emerging knowledge of concomitant neuronal signaling and neuroplasticity events.

CONCLUSIONS

In summary, we met the need for novel sequence data from desert locust CNS. To our knowledge, we hereby also present the first insect EST database that is derived from the complete CNS. The obtained S. gregaria EST data constitute an important new source of information that will be instrumental in further unraveling the molecular principles of phase polyphenism, in further establishing locusts as valuable research model organisms and in molecular evolutionary and comparative entomology.

Isolation, cloning and expression of the Crustacean Cardioactive Peptide gene in the Chagas' disease vector, Rhodnius prolixus

The blood-gorging bug, Rhodnius prolixus, is a major vector of Chagas' disease in Central and South America. We have cloned and characterized the crustacean cardioactive peptide (CCAP) gene in R. prolixus. The RhoprCCAP gene contains five exons and four introns, and encodes a 129 amino acid prepropeptide, which following post-translation processing, produces CCAP. The predicted RhoprCCAP amino acid sequence is identical to CCAP of crustaceans and other insects, i.e. it is highly conserved. RhoprCCAP mRNA is observed in the central nervous system (CNS) using reverse transcriptase (RT) PCR, but not in the gut and salivary glands. In situ hybridization reveals that the expression of CCAP mRNA is localized to a small number of dorsally situated bilaterally paired neurons within the CNS.

Neuropeptide physiology in insects

In a search for more environmentally benign alternatives to chemical pesticides, insect neuropeptides have been suggested as ideal candidates. Neuropeptides are neuromodulators and/or neurohormones that regulate most major physiological and behavioral processes in insects. The major neuropeptide structures have been identified through peptide purification in insects (peptidomics) and insect genome projects. Neuropeptide receptors have been identified and characterized in Drosophila and similar receptors are being targeted in other insects considered to be economically detrimental pests in agriculture and forestry. Defining neuropeptide action in different insect systems has been more challenging and as a consequence, identifying unique targets for potential pest control is also a challenge. In this chapter, neuropeptide biosynthesis as well as select physiological processes are examined with a view to pest control targets. The application of molecular techniques to transform insects with neuropeptide or neuropeptide receptor genes, or knockout genes to identify potential pest control targets, is a relatively new area that offers promise to insect control. Insect immune systems may also be manipulated through neuropeptides which may aid in compromising the insects ability to defend against foreign invasion.

Regulation of the crab heartbeat by crustacean cardioactive peptide (CCAP): central and peripheral actions

In regulating neurophysiological systems, neuromodulators exert multiple actions at multiple sites in such a way as to control the activity in an integrated manner. We are studying how this happens in a simple central pattern generator (CPG)-effector system, the heart of the blue crab Callinectes sapidus. The rhythmic contractions of this heart are neurogenic, driven by rhythmic motor patterns generated by the cardiac ganglion (CG). In this study, we used anatomical and physiological methods to examine the sources and actions on the system of crustacean cardioactive peptide (CCAP). Immunohistochemical localization revealed a plexus of CCAP-immunoreactive fibers in the pericardial organs (POs), neurohemal structures from which blood-borne neurohormones reach the heart. Combined backfill and immunohistochemical experiments indicated that the CCAP in the POs originated from a large contralateral neuron in each thoracic neuromere. In physiological experiments, we examined the actions of exogenous CCAP on the intact working heart, on the semi-intact heart in which we could record the motor patterns as well as the muscle contractions, and on the isolated CG. CCAP had strong positive inotropic and chronotropic effects. Dissection of these effects in terms of dose dependency, time course, and the preparation type in which they occurred suggested that they were produced by the interaction of three primary actions of CCAP exerted both on the heart muscle and on the CG. We conclude that CCAP released from the POs as a neurohormone regulates the crab heart by multiple actions on both the central and peripheral components of this model CPG-effector system.

Neuromodulation of the locust frontal ganglion during the moult: a novel role for insect ecdysis peptides

In insects, continuous growth requires the periodic replacement of the exoskeleton during the moult. A moulting insect displays a stereotypical set of behaviours that culminate in the shedding of the old cuticle at ecdysis. Moulting is an intricate process requiring tightly regulated physiological changes and behaviours to allow integration of environmental cues and to ensure the proper timing and sequence of its components. This is under complex hormonal regulation, and is an important point of interaction between endocrine and neural control. Here, we focus on the locust frontal ganglion (FG), an important player in moulting behaviour, as a previously unexplored target for ecdysis peptides. We show that application of 10(-7) mol l(-1) ecdysis-triggering hormone (ETH) or 10(-7) mol l(-1) and 10(-6) mol l(-1) Pre-ecdysis-triggering hormone (PETH) to an isolated FG preparation caused an increase in bursting frequency in the FG, whereas application of 10(-6) mol l(-1) eclosion hormone (EH) caused an instantaneous, though temporary, total inhibition of all FG rhythmic activity. Crustacean cardioactive peptide (CCAP), an important peptide believed to turn on ecdysis behaviour, caused a dose-dependent increase of FG burst frequency. Our results imply a novel role for this peptide in generating air-swallowing behaviour during the early stages of ecdysis. Furthermore, we show that the modulatory effects of CCAP on the FG motor circuits are dependent on behavioural state and physiological context. Thus, we report that pre-treatment with ETH caused CCAP-induced effects similar to those induced by CCAP alone during pre-ecdysis. Thus, the action of CCAP seems to depend on pre-exposure to ETH, which is thought to be released before CCAP in vivo.

The association of crustacean cardioactive peptide with the spermatheca of the African migratory locust, Locusta migratoria

Crustacean cardioactive peptide (CCAP)-like immunoreactivity was identified in neurons of the VIIIth abdominal ganglion and in axons in the nerves that project to the spermatheca of 3-4 week old adult female locusts. In addition, lightly stained CCAP-like immunoreactive processes were localized over the spermathecae. The amount of CCAP in the spermathecal tissue was quantified using an enzyme-linked immunosorbent assay (ELISA) performed on extracts of the whole spermatheca, and on its constituent parts, namely the sperm sac, coiled duct and straight duct. The spermatheca contains 920+/-273 fmol (mean+/-SE) of CCAP equivalents, with the majority localized in the coiled duct. There are age-related differences in the amount of CCAP present in the spermathecae with less content in spermathecae from 1 to 5 day old and greater content in spermathecae from 3 to 4 week old adults. There was also no difference in CCAP content of spermathecae in mated and virgin 3 to 4 week old adults. Reversed phase-high performance liquid chromatography (RP-HPLC) followed by ELISA further confirmed the presence of CCAP-like material in extracts of locust spermathecae. Physiological assays demonstrated that CCAP increased the basal tonus and frequency of spontaneous contractions of the spermatheca, with thresholds between 10(-10) and 10(-9)M and maxima at 10(-7)M CCAP. CCAP also increases the amplitude of neurally evoked contractions with a threshold less than 10(-11)M and a maximum of 10(-7)M CCAP. The present study suggests that CCAP acts as a neuromodulator/neurotransmitter at the spermathecal visceral tissue of female Locusta migratoria.

The presence and distribution of crustacean cardioactive peptide in the central and peripheral nervous system of the stick insect, Baculum extradentatum

Crustacean cardioactive peptide (CCAP)-like immunoreactivity was localized and quantified in the central and peripheral nervous system of the Vietnamese stick insect, Baculum extradentatum, using immunohistochemistry and enzyme-linked immunosorbent assay (ELISA). The brain, frontal ganglion, suboesophageal ganglion and ventral nerve cord displayed neurons and processes with CCAP-like immunoreactivity. The brain, in comparison to the other parts of the central nervous system, contained the greatest amount of CCAP (167 +/- 18 fmol), and showed CCAP-like staining in neurons, neuropil regions and the central complex. There were also CCAP-like varicosities and processes associated with the corpus cardiacum. The alimentary canal of B. extradentatum contained CCAP with the largest amount localized in the midgut (1110 +/- 274 fmol CCAP equivalents). The midgut contained numerous endocrine-like cells which stained positively for CCAP, whereas the foregut and hindgut revealed an extensive network of CCAP-like immunoreactive axons and varicosities. Based on physiological assays, the hindgut of the stick insect was found to be sensitive to CCAP, showing dose-dependent increases in contractions with threshold at 10(-10) M CCAP and maximal response at 5 x 10(-7) M CCAP. There were negligible quantities of CCAP in the oviducts and no CCAP-like immunoreactivity was associated with the oviducts. CCAP had no effect on spontaneous contractions of the oviducts. The presence of CCAP in the central nervous system, the stomatogastric nervous system, the corpus cardiacum and the alimentary canal, suggest broad ranging roles for CCAP in B. extradentatum.

Evidence for crustacean cardioactive peptide-like innervation of the gut in Locusta migratoria

Hindguts from female Vth instar larvae, young adults (1-2 days) and old adults (>10 days) are equally sensitive to the crustacean cardioactive peptide (CCAP), with changes in contraction occurring at a threshold concentration of 10(-9)M and maximal responses observed at concentrations ranging between 10(-7) and 5x10(-6)M. An immunohistochemical examination of the gut of Locusta migratoria with an antiserum raised against CCAP revealed an extensive network of CCAP-like immunoreactive processes on the hindgut and posterior midgut via the 11th sternal nerve arising from the terminal abdominal ganglion. Anterograde filling of the 11th sternal nerve with neurobiotin revealed extensive processes and terminals on the hindgut. Retrograde filling of the branch of the 11th sternal nerve which innervates the hindgut with neurobiotin revealed two bilaterally paired cells in the terminal abdominal ganglion which co-localized with CCAP-like immunoreactivity. Results suggest that a CCAP-like substance acts as a neurotransmitter/neuromodulator at the locust hindgut.

Neuropeptides in the nervous system of Drosophila and other insects: multiple roles as neuromodulators and neurohormones

Neuropeptides in insects act as neuromodulators in the central and peripheral nervous system and as regulatory hormones released into the circulation. The functional roles of insect neuropeptides encompass regulation of homeostasis, organization of behaviors, initiation and coordination of developmental processes and modulation of neuronal and muscular activity. With the completion of the sequencing of the Drosophila genome we have obtained a fairly good estimate of the total number of genes encoding neuropeptide precursors and thus the total number of neuropeptides in an insect. At present there are 23 identified genes that encode predicted neuropeptides and an additional seven encoding insulin-like peptides in Drosophila. Since the number of G-protein-coupled neuropeptide receptors in Drosophila is estimated to be around 40, the total number of neuropeptide genes in this insect will probably not exceed three dozen. The neuropeptides can be grouped into families, and it is suggested here that related peptides encoded on a Drosophila gene constitute a family and that peptides from related genes (orthologs) in other species belong to the same family. Some peptides are encoded as multiple related isoforms on a precursor and it is possible that many of these isoforms are functionally redundant. The distribution and possible functions of members of the 23 neuropeptide families and the insulin-like peptides are discussed. It is clear that each of the distinct neuropeptides are present in specific small sets of neurons and/or neurosecretory cells and in some cases in cells of the intestine or certain peripheral sites. The distribution patterns vary extensively between types of neuropeptides. Another feature emerging for many insect neuropeptides is that they appear to be multifunctional. One and the same peptide may act both in the CNS and as a circulating hormone and play different functional roles at different central and peripheral targets. A neuropeptide can, for instance, act as a coreleased signal that modulates the action of a classical transmitter and the peptide action depends on the cotransmitter and the specific circuit where it is released. Some peptides, however, may work as molecular switches and trigger specific global responses at a given time. Drosophila, in spite of its small size, is now emerging as a very favorable organism for the studies of neuropeptide function due to the arsenal of molecular genetics methods available.

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%.

Peptidomics of the pars intercerebralis-corpus cardiacum complex of the migratory locust, Locusta migratoria

The pars intercerebralis-corpora cardiaca system (PI-CC) of insects is the endocrinological equivalent of the hypothalamus-pituitary system of vertebrates. Peptide profiles of the pars intercerebralis and the corpora cardiaca were characterized using simple sampling protocols in combination with MALDI-TOF and electrospray ionization double quadrupole time of flight (ESI-Qq-TOF) mass spectrometric technologies. The results were compared with earlier results of conventional sequencing methods and immunocytochemical methods. In addition to many known peptides, several m/z signals corresponding to putative novel peptides were observed in the corpora cardiaca and/or pars intercerebralis. Furthermore, for a number of peptides evidence was provided about their localization and MALDI-TOF analysis of the released material from the corpora cardiaca yielded information on the hormonal status of particular brain peptides.

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.

Several isoforms of locustatachykinins may be involved in cyclic AMP-mediated release of adipokinetic hormones from the locust Corpora cardiaca

Four locustatachykinins (LomTK I-IV) were identified in about equal amounts in extracts of corpora cardiaca of locusts, using reverse-phase high-performance liquid chromatography and radioimmunoassay with synthetic LomTK I-IV as standards. Brain extracts also contained the four isoforms in roughly equimolar concentrations. Retrograde tracing of the nervi corporis cardiaci II (NCC II) in vitro with Lucifer yellow in combination with LomTK immunocytochemistry revealed that about half of the secretomotor neurons in the lateral part of the protocerebrum projecting into the glandular lobe of the corpora cardiaca (CCG) contain LomTK-immunoreactive material. Since the four LomTKs are present in the CCG, these four or five neurons in each hemisphere are likely to contain colocalized LomTK I-IV. The role of two of the LomTKs in the regulation of the release of adipokinetic hormones (AKHs) from the adipokinetic cells in the CCG in the locust was investigated. Experiments performed in vitro showed that LomTK I and II induced release of AKH in a dose-dependent manner. These peptides also rapidly and transiently elevated the cyclic AMP-content of the CCG. The peak level of cyclic AMP occurred about 45 seconds after stimulation with LomTK. These results support the proposal that LomTKs are involved in controlling the release of the adipokinetic hormones and suggest that all LomTK isoforms may participate in this cyclic AMP-mediated event.

Regulating the activity of a cardioacceleratory peptide

We measured the effect of crustacean cardioactive peptide on Drosophila heart rate in the animal and in a tissue preparation. Crustacean cardioactive peptide increased in vivo basal heart rate 1%, 6%, and 19% and increased in vitro basal heart rate 52%, 25%, and 35% in larvae, pupae, and adults, respectively. In the tissue preparation, the acceleratory period was followed by decreased in vitro heart rates of 42%, 16%, and 13% in larvae, pupae, and adults, respectively. The effects observed in the animal and tissue and in larvae, pupae, and adults suggest that Drosophila crustacean cardioactive peptide cardiac signaling is modulated and developmentally regulated.

Peptidergic control of the corpus cardiacum-corpora allata complex of locusts

The brain-corpora cardiaca-corpora allata complex of insects is the physiological equivalent of the brain-hypophysis axis of vertebrates. In locusts there is only one corpus cardiacum as a result of fusion, while most other insect species have a pair of such glands. Like the pituitary of vertebrates, the corpus cardiacum consists of a glandular lobe and a neurohemal lobe. The glandular lobe synthesizes and releases adipokinetic hormones. In the neurohemal part many peptide hormones, which are produced in neurosecretory cells in the brain, are released into the hemolymph. The corpora allata, which have no counterpart in vertebrates, synthesize and release juvenile hormones. The control of the locust corpus cardiacum-corpora allata complex appears to be very complex. Numerous brain factors have been reported to have an effect on biosynthesis and release of juvenile hormone or adipokinetic hormone. Many neuropeptides are present in nerves projecting from the brain into the corpora cardiaca-corpora allata complex, the most important ones being neuroparsins, ovary maturating parsin, insulin-related peptide, diuretic peptide, tachykinins, FLRFamides, FXPRLamides, accessory gland myotropin I, crustacean cardioactive peptide, and schistostatins. In this paper, the cellular distribution, posttranslational processing, peptide-receptor interaction, and inactivation of these peptides are reviewed. In addition, the signal transduction pathways in the release of adipokinetic hormone and juvenile hormone from, respectively, the corpora cardiaca and corpora allata are discussed.

Peptides in the locusts, Locusta migratoria and Schistocerca gregaria

The first peptide identified in locusts was adipokinetic hormone I (AKH-I), a neurohormone mobilizing lipids from the fat body. No other locusts peptides were isolated until 1985. From then on peptide identification started to boom at such a tremendously fast rate that even specialists in the field could hardly keep track. At this moment the total number of different insect neuropeptide sequences exceeds 100. Currently, the locusts Locusta migratoria and Schistocerca gregaria are the species from which the largest number of neuropeptides has been isolated and sequenced, namely 56. Myotropic bioassays have played a major role in the isolation and subsequent structural characterization of locust neuropeptides. They have been responsible for the discovery of locustamyotropins, locustapyrokinins, locustatachykinins, locustakinin, locusta accessory gland myotropins, locustasulfakinin, cardioactive peptide, and locustamyoinhibiting peptides. Members of the myotropin peptide families have been associated with a variety of physiological activities such as myotropic activities, pheromonotropic activities, diapause induction, stimulation of cuticular melanization, diuresis, pupariation, and allatostatic activities. Recently, we have identified in Schistocerca 10 peptides belonging to the allatostatin peptide family, which inhibit peristaltic movements of the oviduct. Some of the myotropins appear to be important neurotransmitters or modulators innervating the locust oviduct, the salivary glands, the male accessory glands, and the heart, whereas others are stored in neurohemal organs until release in the hemolymph. Some myotropic peptides have been found to be releasing factors of neurohormones from the corpora cardiaca. Several peptides isolated in locusts appear to be unique to insects or arthropods; others seem to be members of peptides families spanning across phyla: two vasopressin-like peptides, FMRFamide-related peptides, Locusta diuretic hormone (CRF-like), Locusta insulin-related peptide, locustatachykinins, locustasulfakinin (gastrin/CCK-like). In a systematic structural study of neuropeptides in Locusta, several novel peptides have been isolated from the corpora cardiaca and the pars intercerebralis. They include the neuroparsins, two 6-kDa dimeric peptides, and three proteinase inhibitors. Ovary maturating parsin is the first gonadotropin identified in insects. The isolation of a peptide from an ovary extract that inhibits ovary maturation in Schistocerca gregaria is currently underway in our lab. The proteinase inhibitors, recently found to be mainly transcribed in the fat body, are believed to play a role in defense reactions of insects. Finally, a locust ion transport peptide and a peptide stimulating salivation recently can be added to this extensive list of locust peptides.

Novel mouse IgG-like immunoreactivity expressed by neurons in the moth Manduca sexta: developmental regulation and colocalization with crustacean cardioactive peptide

Immunoglobulin-related molecules have been shown to play important roles in cell-cell recognition events during the development of both vertebrate and invertebrate nervous systems. In the moth, Manduca sexta, we report the presence of novel, mouse, immunoglobulin G (mIgG)-like immunoreactivity in a discrete population of identified neurosecretory neurons (the NS-Ls also known as the cell 27s) and interneurons (the IN-704s). A number of polyclonal anti-mIgG antibodies were used to immunostain these cells in wholemount. The mIgG-like-immunoreactive (IR) neurons were present during embryogenesis through the developing adult stages, but disappeared in the postemerged adult. Biochemical analysis of M. sexta ventral nerve cords revealed that the mIgG-like antigen is a membrane-associated 27-kDa protein which is likely responsible for the mIgG-like immunostaining observed. Unambiguous identification of the mIgG-like-IR neurons was based on neuronal morphology and our ability to demonstrate conclusively that these neurons expressed immunoreactivity to an antiserum against crustacean cardioactive peptide (CCAP). The NS-Ls and IN-704s were both shown to colocalize the CCAP and mIgG-like immunoreactivities. The mIgG-like and CCAP-IR neurons were identical to a subset of CCAP-IR neurons recently described by Davis et al. [(1993) J. Comp. Neurol., 338:612-627] in pupae. We found these CCAP-IR neurons, however, also to be present in larvae. The mIgG-like- and CCAP-IR neurons included the NS-L pair of the subesophageal maxillary neuromere, which projected anteriorly to the corpora cardiaca, and the NS-L of the labial neuromere whose axons projected out the dorsal nerve of the next posterior ganglion. The mIgG-like and CCAP-IR NS-Ls were also observed throughout the three thoracic ganglia, and all shared strikingly similar structural features. These cells exited out the dorsal nerve of the next posterior ganglion and eventually projected to the neurohemal release sites of the perivisceral organs. These neurons appear to be the homologues of the abdominal CCAP-IR NS-Ls, neurons that in the adult switch their neurotransmitter and release the neuropeptide bursicon. Our description of the distribution and developmental expression of this novel mIgG-like immunoreactivity may provide new insights into the regulation of neurotransmitter plasticity and/or recognition-signaling events involved in the embryonic and postembryonic assembly of the nervous system.

Immunocytochemical mapping of serotonin and neuropeptides in the accessory medulla of the locust, Schistocerca gregaria

Accumulating evidence suggests that pigment-dispersing hormone-immunoreactive neurons with ramifications in the accessory medulla of the insect brain are involved in circadian pacemaking functions. We have used immunocytochemical techniques to investigate the neurochemical organization of the accessory medulla in the locust Schistocerca gregaria. Local neurons with arborizations largely restricted to the accessory medulla are immunoreactive with antisera against serotonin, Manduca sexta allatotropin, and Diploptera punctata allatostatin 7. Projection neurons with arborizations in the accessory medulla and fibers to the lamina and/or several areas in the midbrain including the posterior optic tubercles, the inferior and the superior protocerebrum show Phe-Met-Arg-Phe (FMRF)amide-, gastrin/cholecystokinin-, crustacean cardioactive peptide-, and substance P immunoreactivities. A unique neuron with tangential ramifications in the medulla and lamina and varicose terminals in the accessory medulla contains a peptide related to locustatachykinin I/II. Double-label experiments show colocalization of pigment-dispersing hormone-immunoreactivity with substances related to gastrin/cholecystokinin, FMRFamide, substance P, or crustacean cardioactive peptide in certain projection neurons of the accessory medulla. The results suggest that neuropeptides and biogenic amines play major neuroactive roles in the accessory medulla of the locust. The abundance and extensive colocalization of neuropeptides in the locust accessory medulla is discussed with respect to the possible involvement of this brain area in circadian pacemaking functions.

Amino acid sequence of CAP2b, an insect cardioacceleratory peptide from the tobacco hawkmoth Manduca sexta

The primary structure of a novel insect neuropeptide, Cardioacceleratory Peptide 2b (CAP2b), from the tobacco hawkmoth Manduca sexta has been established using a combination of mass spectroscopy, Edman degradation microsequencing, amino acid analysis, and biological assays. The sequence of CAP2b, pyroGlu-Leu-Tyr-Ala-Phe-Pro-Arg-Val-amide, has a molecular weight of 974.6 and is blocked at both the amino and carboxyl ends. Examination of several national computer protein data bases failed to reveal other peptides or proteins with any sequence homology to CAP2b indicating that this is likely to be a novel insect neuropeptide. This peptide may be a general activator of insect viscera since it causes an increase in heart rate in Manduca and in Drosophila, and has also been implicated in the regulation of fluid secretion by the Malphigian tubules of Drosophila.

Characterization of crustacean cardioactive peptide-like immunoreactivity in the horseshoe crab, Limulus polyphemus

The localization of crustacean cardioactive peptide-like immunoreactivity in the horseshoe crab Limulus polyphemus was investigated with enzyme-linked immunosorbent assay and fluorescence microscopy. Immunoreactivity was quantified in the opisthosomal nervous system (67.7 +/- 11.4 ng/g), cardiac ganglion (45.0 +/- 10.3 ng/g), prosomal nervous system (28.5 +/- 6.6 ng/g), and midgut (24.6 +/- 6.7 ng/g). In the brain, immunoreactive somata were observed in ganglion cells of the central body, in the medullary group and within the ventral medial group. Clusters of immunoreactive cells were found in each of the circumesophageal, pedal ganglia, and in the opisthosomal, abdominal ganglia. In the periphery, immunoreactive varicose fibers were observed in branches of the intestinal nerves, and near longitudinal and circular muscle fibers of the midgut. Immunoreactivity was observed in the cardiac ganglion and myocardium of the neurogenic heart. Synthetic crustacean cardioactive peptide had slight excitatory effects on the cardiac rhythm at doses up to 10(-6) M. This peptide had excitatory effects on the midgut at nanomolar doses. Ventral nerve cord extracts were partially purified with reverse phase high performance liquid chromatography. Two regions of immunoreactivity were detected, one of which coeluted with the authentic peptide. The distribution of crustacean cardioactive peptide immunoreactivity is compared with other transmitter systems in the Limulus nervous system, and myotropic actions of this peptide are discussed with respect to peptidergic modulation of intestinal motility.

Occurrence of analogues of the myotropic neuropeptide orcokinin in the shore crab, Carcinus maenas: evidence for a novel neuropeptide family

By use of an enzyme immunoassay that was developed for the determination of orcokinin, a myotropic neuropeptide of the sequence NFDEIDRSGFGFN from the crayfish, Orconectes limosus, immunoreactive material was detected in extracts of thoracic ganglia from the shore crab, Carcinus maenas. Isolation of the immunoreactive material was achieved by the following steps: 1) prepurification by gel filtration, 2) immunoaffinity chromatography on an anti-orcokinin IgG protein-A sepharose column, and 3) reversed-phase HPLC. The HPLC profile after affinity purification revealed three main immunoreactive peptides that were rechromatographed. None of these peptides was identical to orcokinin in terms of retention time. Automated gas-phase sequencing revealed these peptides to be analogues of orcokinin differing in one amino acid residue. They were named [Ser9]-, [Ala13]- and [Val13]orcokinin (NFDEIDRSSFGFN, Mr 1549.3; NFDEIDRSGFGFA, Mr 1475.3; NFDEIDRSGFGFV, Mr 1503.9). Carboxypeptidase A treatment of the peptides indicated a free C-terminus. Complete characterization of the three peptides was achieved from approximately 230 thoracic ganglia of Carcinus maenas.

Comparative aspects of peptidergic signaling pathways in the nervous systems of arthropods

Comparative aspects of arthropod peptidergic systems--in principle--can be studied on the level of precursor sequences (genes, preprohormones), peptide sequences (peptide families), and peptide expression patterns within the nervous system. The number of known arthropod neuropeptide precursor sequences is as yet far too small to provide a reasonably large basis for extended comparative studies. Comparative studies of peptide sequences have shown that many peptides belong to families with homologous members in both invertebrates and vertebrates. Comparative research on peptide expression has to find out whether phylogenetic necessities lead to "hard wired" neurochemical identities, i.e., a more or less fixed "Bauplan" that not only determines the lineage and morphology of a neuron but also its transmitter(s), or whether these necessities demand greater flexibility (plasticity), and hence cause great variability that would complicate comparative studies. As will be shown here, both possibilities appear to exist. On the one hand, peptidergic neurons may exist in comparable form in different groups of arthropods. On the other hand, the neurochemical identity of cells may vary in segmented organisms when comparing serially homologous sets of nerve cells in different segments. As a further complication, identical or similar peptides may serve different functions, even in closely related species. In view of these functional aspects in particular, it appears that peptidergic signalling pathways represent rapidly evolving systems. This conclusion, although very interesting in itself, reduces the use of such systems for general comparisons. However, arthropod nervous systems represent excellent model systems for the study of homology. At least for morphological and ontogenetic aspects arthropods provide numerous opportunities to study homology on the level of the individually identified peptidergic nerve cell.

Common general morphological pattern of peptidergic neurons in the arachnid brain: crustacean cardioactive peptide-immunoreactive neurons in the protocerebrum of seven arachnid species

A polyclonal antiserum raised against crustacean cardioactive peptide labels 14 clusters of immunoreactive neurons in the protocerebrum of the spiders Tegenaria atrica and Nephila clavipes, and the harvestman (opilionid) Rilaena triangularis. In all species, these clusters possess the same number of neurons, and share similar structural and topological characteristics. Two sets of bilateral symmetrical neurons associated with the optic lobes and the arachnid "central body" were analysed in detail, comparing the harvestman R. triangularis and the spiders Brachypelma albopilosa (Theraphosidae), Cupiennius salei (Lycosidae), Tegenaria atrica (Agelenidae), Meta segmentata (Metidae) and Nephila clavipes (Araneidae). Sixteen neurons have been identified that display markedly similar axonal pathways and arborization patterns in all species. These neurons are considered homologues in the opilionid and the araneid brains. We presume that these putative phylogenetically persisting neurons represent part of the general morphological pattern of the arachnid brain.

Postembryonic development of corazonin-containing neurons and neurosecretory cells in the blowfly, Phormia terraenovae

An antiserum against the cockroach cardioactive peptide corazonin was used to investigate the distribution of immunoreactive neurons and neurosecretory cells in the nervous system of the blowfly, Phormia terraenovae, during postembryonic development. A small number of corazonin-immunoreactive neurons was found at larval, pupal, and adult stages. At all postembryonic stages two cell groups were found in the protocerebrum of the brain: 1) two lateral cell clusters and 2) two median cells. In the larva eight bilateral cell pairs were found in thoracic and abdominal neuromeres of the fused ventral ganglion. The lateral brain neurons are located in the lateral neurosecretory cell group and extend axons with branches in several components of the retrocerebral neuroendocrine complex, in the stomatogastric nervous system of larvae and adults, and additionally in muscles of the alimentary canal in the adult. The most prominent element of these peripheral processes is a large plexus of varicose fibers located in the wall of the aorta, the main site for the release of neurohormones produced in the brain of blowflies. The presence of corazonin-immunoreactive material in the aortic plexus suggests that this peptide functions as a neurohormone. During metamorphosis, the immunoreactive neurons found in the thoracic-abdominal ganglion of the larva disappear, and in the brain new immunoreactive neurons are added to those that persist from larval stages. The bulk of the corazonin-immunoreactive material extracted from adult brains and corpora cardiaca-aorta complexes was found to co-elute with synthetic corazonin in reversed-phase high-performance liquid chromatography as monitored with enzyme-linked immunosorbent assay.

Crustacean cardioactive peptide-immunoreactive neurons in the ventral nervous system of crayfish

Crustacean cardioactive peptide-immunoreactive neurons have been mapped in whole-mount preparations and sections of the ventral nervous system of the crayfish Astacus astacus and Orconectes limosus. Based on their morphology, projection patterns, and staining characteristics, two types of contralaterally projecting neurons are individually identifiable. In both species, these neurons occur in all neuromers as apparent serial homologs. In adult specimens, one type of cell has a small, densely stained dorsal lateral perikaryon, and a descending axon, and appears to be an interneuron. Each neuromer contains a single pair of these cells. Only in maxillary ganglia, these cells may have an additional ascending projection. The other type, a neurosecretory cell, has a larger, weakly stained perikaryon and a projection to the segmental third root of the next anterior neuromer. All neuromers contain a single pair of these neurons adjacent to the interneurons except for the abdominal neuromers, which contain two pairs of the neurosecretory cells. Central arborizations and varicose processes toward the surface of the third roots and within the perineural sheath of the ventral nerve cord arise from these neurons. Electron microscopy of granule-containing terminals substantiated that these newly discovered extensive neurohemal areas are release sites for the peptide. In young immature specimens, the perikarya of both neuron types do not differ in size. Additional weakly stained small perikarya occur in all neuromers of Astacus astacus. These two types of crayfish neurons and other comparable aminergic and peptidergic neurons of crayfish and lobster are differentially distributed in the ventral cord. Furthermore, comparison of similar neuron types in crab, locust, meal worm, and moth species indicates intra- and interphyletic structural homologies.

Crustacean cardioactive peptide-immunoreactive neurons in the hawkmoth Manduca sexta and changes in their immunoreactivity during postembryonic development

An antiserum against crustacean cardioactive peptide was used, in indirect immunocytochemistry on whole-mounts and Vibratome sections, to map immunoreactive neurons at various stages of postembryonic development of the hawkmoth Manduca sexta. About 90 immunoreactive neurons were identified. Many of these cells are immunoreactive at hatching and persist into the adult stage; others become immunoreactive late in postembryonic development. During adult development, transient immunoreactivity is expressed in several cells in the subesophageal and thoracic ganglia. Two sets of immunoreactive neurons are found in the protocerebrum of larvae, but only one of these sets persists into the adult stage. Paired lateral interneurons and neurosecretory neurons are segmentally repeated in the abdominal ganglia and are present from the first larval stage to the adult; the abdominal interneurons project contralaterally to arborizations in adjacent ganglia, and some ascend to tritocerebral arborizations. The abdominal neurosecretory cells, which correspond to a pair of cells reported to contain bursicon, project posteriorly to neurohemal release organs. Motor neurons of dorsal external oblique abdominal muscles become immunoreactive in the fourth larval stage. Paired median neurosecretory cells of abdominal ganglia become immunoreactive during the fifth larval stage. The immunoreactive median and lateral abdominal neurosecretory cells are a subset of a group of cells known to contain cardioactive peptides. Paired lateral neurosecretory cells of the subesophageal ganglion become immunoreactive during pupation and project to the corpora cardiaca and aorta of the adult. Many of the neurons identified here are comparable to crustacean cardioactive peptide-immunoreactive cells described previously in locusts and the mealworm beetle.

Isolation and identification of a cardioactive peptide from Tenebrio molitor and Spodoptera eridania

We isolated several cardioactive peptides from extracts of whole heads of the mealworm, Tenebrio molitor, and the southern armyworm, Spodoptera eridania, using a semi-isolated heart of Manduca sexta for bioassay. We have now isolated from each species the peptide with the strongest effect on rate of contraction of the heart. The peptides were identified using micro Edman sequencing and mass spectrometric methods. This cardioactive peptide has the same primary structure from both species: Pro-Phe-Cys-Asn-Ala-Phe-Thr-Gly-Cys-NH2, a cyclic nonapeptide which is identical to crustacean cardioactive peptide (CCAP) originally isolated from the shore crab, Carcinus maenas, and subsequently isolated from Locusta migratoria and Manduca sexta. This is additional evidence that CCAP has widespread occurrence in arthropoda.

The myotropic peptides of Locusta migratoria: structures, distribution, functions and receptors

The search for myotropic peptide molecules in the brain, corpora cardiaca, corpora allata suboesophageal ganglion complex of Locusta migratoria using a heterologous bioassay (the isolated hindgut of the cockroach, Leucophaea maderae) has been very rewarding. It has lead to the discovery of 21 novel biologically active neuropeptides. Six of the identified Locusta peptides show sequence homologies to vertebrate neuropeptides, such as gastrin/cholecystokinin and tachykinins. Some peptides, especially the ones belonging to the FXPRL amide family display pleiotropic effects. Many more myotropic peptides remain to be isolated and sequenced. Locusta migratoria has G-protein coupled receptors, which show homology to known mammalian receptors for amine and peptide neurotransmitters and/or hormones. Myotropic peptides are a diverse and widely distributed group of regulatory molecules in the animal kingdom. They are found in neuroendocrine systems of all animal groups investigated and can be recognized as important neurotransmitters and neuromodulators in the animal nervous system. Insects seem to make use of a large variety of peptides as neurotransmitters/neuromodulators in the central nervous system, in addition to the aminergic neurotransmitters. Furthermore quite a few of the myotropic peptides seem to have a function in peripheral neuromuscular synapses. The era in which insects were considered to be "lower animals" with a simple neuroendocrine system is definitely over. Neural tissues of insects contain a large number of biologically active peptides and these peptides may provide the specificity and complexity of intercellular communications in the nervous system.

Crustacean cardioactive peptide in the sphinx moth, Manduca sexta

The isolation, identification, and actions of crustacean cardiactive peptide (CCAP) have been examined in the sphinx moth Manduca sexta. A sensitive and specific enzyme-linked immunosorbent assay (ELISA) was used to quantify CCAP-like immunoreactivity in the nervous system. The CCAP-like immunoreactivity from the abdominal CNS was then purified, and its sequence was ascertained by amino acid analysis, mass spectral analysis, and HPLC. These studies showed that the nervous system of M. sexta contains a peptide with the sequence Pro-Phe-Cys-Asn-Ala-Phe-Thr-Gly-Cys-NH2, identical to CCAP originally isolated and sequenced from the shore crab Carcinus maenas. The actions of CCAP on the isolated heart of M. sexta and the extensor-tibia muscle of Schistocerca americana were tested. Crustacean cardioactive peptide had excitatory actions on both preparations: a dose-dependent increase in the rate of contractions was observed on the heart, and an increase in the rate of the myogenic rhythm was observed in the leg muscle. Moreover, purified and synthetic CCAP had identical effects on the isolated heart. We conclude that CCAP occurs in M. sexta and exerts potent neurotransmitter or neurohormonal actions on a variety of muscles.

Primary structure of a cardioactive neuropeptide from the tobacco hawkmoth, Manduca sexta

The amino acid sequence of the first of a family of insect cardioregulatory peptides from the tobacco hawkmoth, Manduca sexta, has been determined using a combination of Edman degradation microsequencing and mass spectroscopy. This peptide contains 9 amino acid residues and an observed mass for the monoisotopic protonated molecule of 956.4 Da. There are two cysteines at positions 3 and 9 forming a disulfide bridge and the carboxyl-terminus is amidated. The structure of this peptide, Pro-Phe-Cys-Asn-Ala-Phe-Thr-Gly-Cys-NH2, is identical to a peptide recently isolated from crabs called crustacean cardioactive peptide (CCAP) and we propose that this peptide be named Manduca CCAP.

Orcokinin: a novel myotropic peptide from the nervous system of the crayfish, Orconectes limosus

A myotropic peptide, named orcokinin, was isolated from approximately 1200 abdominal nerve cords of the crayfish, Orconectes limosus. Its amino acid sequence was determined as follows: Asn-Phe-Asp-Glu-Ile-Asp-Arg-Ser-Gly-Phe-Gly-Phe-Asn. This structure was confirmed by synthesis. There is no sequence similarity to any known neuropeptide. Orcokinin exhibits high potency on the crayfish hindgut, enhancing both frequency and amplitude of spontaneous contractions. The threshold of biological activity in vitro was determined to be approximately 5 x 10(-11) M.

Neurons in the cockroach nervous system reacting with antisera to the neuropeptide leucokinin I

Antisera were raised against the myotropic neuropeptide leucokinin I, originally isolated from head extracts of the cockroach Leucophaea maderae. Processes of leucokinin I immunoreactive (LKIR) neurons were distributed throughout the nervous system, but immunoreactive cell bodies were not found in all neuromeres. In the brain, about 160 LKIR cell bodies were distributed in the protocerebrum and optic lobes (no LKIR cell bodies were found in the deuto- and tritocerebrum). In the ventral ganglia, LKIR cell bodies were seen distributed as follows: eight (weakly immunoreactive) in the subesophageal ganglion; about six larger and bilateral clusters of 5 smaller in each of the three thoracic ganglia, and in each of the abdominal ganglia, two pairs of strongly immunoreactive cell bodies were resolved. Many of the LKIR neurons could be described in detail. In the optic lobes, immunoreactive neurons innervate the medulla and accessory medulla. In the brain, three pairs of bilateral LKIR neurons supply branches to distinct sets of nonglomerular neuropil, and two pairs of descending neurons connect the posterior protocerebrum to the antennal lobes and all the ventral ganglia. Other brain neurons innervate the central body, tritocerebrum, and nonglomerular neuropil in protocerebrum. LKIR neurons of the median and lateral neurosecretory cell groups send axons to the corpora cardiaca, frontal ganglion, and tritocerebrum. In the muscle layer of the foregut (crop), bi- and multipolar LKIR neurons with axons running to the retrocerebral complex were resolved. The LKIR neurons in the abdominal ganglia form efferent axons supplying the lateral cardiac nerves, spiracles, and the segmental perivisceral organs. The distribution of immunoreactivity indicates roles for leucokinins as neuromodulators or neurotransmitters in central interneurons arborizing in different portions of the brain, visual system, and ventral ganglia. Also, a function in circuits regulating feeding can be presumed. Furthermore, a role in regulation of heart and possibly respiration can be suggested, and probably leucokinins are released from corpora cardiaca as neurohormones. Leucokinins were isolated by their myotropic action on the Leucophaea hindgut, but no innervation of this portion of the gut could be demonstrated. The distribution of leucokinin immunoreactivity was compared to immunolabeling with antisera against vertebrate tachykinins and lysine vasopressin.

Crustacean neuropeptides: structures, functions and comparative aspects

In this article, an attempt is made to review the presently known, completely identified crustacean neuropeptides with regard to structure, function and distribution. Probably the most important progress has been made in the elucidation of a novel family of large peptides from the X-organ-sinus gland system which includes crustacean hyperglycemic hormone (CHH), putative molt-inhibiting hormone (MIH) and vitellogenesis (= gonad)-inhibiting hormone (VIH). These peptides have so far only been found in crustaceans. Renewed interest in the neurohemal pericardial organs has led to the identification of a number of cardioactive/myotropic neuropeptides, some of them unique to crustaceans. Important contributions have been made by immunocytochemical mapping of peptidergic neurons in the nervous system, which has provided evidence for a multiple role of several neuropeptides as neurohormones on the one hand and as local transmitters or modulators on the other. This has been corroborated by physiological studies. The long-known chromatophore-regulating hormones, red pigment concentrating hormone (RPCH) and pigment-dispending hormone (PDH), have been placed in a broader perspective by the demonstration of an additional role as local neuromodulators. The scope of crustacean neuropeptide research has thus been broadened considerably during the last years.