Localization of Lom-AG-myotropin I-like substances in the male reproductive and nervous tissue of the locust, Locusta migratoria

Molecular cloning and characterization of the allatotropin precursor and receptor in the desert locust, Schistocerca gregaria

Allatotropins (ATs) are pleiotropic neuropeptides initially isolated from the tobacco hornworm, Manduca sexta. In 2008, the first receptor for AT-like peptides (ATR) was characterized in Bombyx mori. Since then, ATRs have also been characterized in M. sexta, Tribolium castaneum, Aedes aegypti and Bombus terrestris. These receptors show sequence similarity to vertebrate orexin (ORX) receptors. When generating an EST-database of the desert locust (Schistocerca gregaria) central nervous system, we found cDNA sequences encoding the Schgr-AT precursor and a fragment of its putative receptor. This receptor cDNA has now been completed and functionally expressed in mammalian cell lines. Activation of this receptor, designated as Schgr-ATR, by Schgr-AT caused an increase in intracellular calcium ions, as well as cyclic AMP (cAMP), with an EC₅₀ value in the nanomolar range. In addition, the transcript distribution of both the Schgr-AT precursor and Schgr-ATR was investigated by means of quantitative real-time PCR. Moreover, we found more evidence for the myotropic and allatostimulatory actions of Schgr-AT in the desert locust. These data are discussed and situated in a broader context by comparison with literature data on AT and ATR in insects.

Characterisation of a functional allatotropin receptor in the bumblebee, Bombus terrestris (Hymenoptera, Apidae)

Allatotropins (ATs) are multifunctional neuropeptides initially isolated from the tobacco hornworm, Manduca sexta, where they were found to stimulate juvenile hormone synthesis and release from the corpora allata. ATs have been found in a wide range of insects, but appear to be absent in Drosophila. The first AT receptor (ATR) was characterised in 2008 in the lepidopteran Bombyx mori. Since then ATRs have been characterised in Coleoptera and Diptera and in 2012, an AT precursor gene was identified in hymenopteran species. ATRs show large sequence and structural similarity to vertebrate orexin receptors (OXR). Also, AT in insects and orexin in vertebrates show some overlap in functions, including modulation of feeding behaviour and reproduction. The goal of this study was to identify a functional ATR in a hymenopteran species. We used ATRs (insect sequences) and OXRs (vertebrate sequences) to search the genome of the bumblebee, Bombus terrestris. Two receptors (XP_003402490 and XP_003394933) with resemblance to ATRs and OXRs were found. Phylogenetic analysis provided the first indication that XP_003402490 was more closely related to ATRs than XP_003394933. We investigated the transcript level distribution of both receptors and the AT precursor gene by means of quantitative real-time reverse transcriptase PCR. XP_003402490 displayed a tissue distribution comparable with ATRs in other species, with high transcript levels in the male accessory glands. After pharmacological characterisation, it appeared that XP_003402490 is indeed a functional ATR. Activation of the receptor causes an increase in intracellular calcium and cyclic AMP levels with an EC50 value in the low nanomolar to picomolar range. XP_003394933 remains an orphan receptor.

Neuropeptides in insect mushroom bodies

Owing to their experimental amenability, insect nervous systems continue to be in the foreground of investigations into information processing in - ostensibly - simple neuronal networks. Among the cerebral neuropil regions that hold a particular fascination for neurobiologists are the paired mushroom bodies, which, despite their function in other behavioral contexts, are most renowned for their role in learning and memory. The quest to understand the processes that underlie these capacities has been furthered by research focusing on unraveling neuroanatomical connections of the mushroom bodies and identifying key players that characterize the molecular machinery of mushroom body neurons. However, on a cellular level, communication between intrinsic and extrinsic mushroom body neurons still remains elusive. The present account aims to provide an overview on the repertoire of neuropeptides expressed in and utilized by mushroom body neurons. Existing data for a number of insect representatives is compiled and some open gaps in the record are filled by presenting additional original data.

Characterization of an allatotropin-like peptide receptor in the red flour beetle, Tribolium castaneum

Following a reverse pharmacology approach, we identified an allatotropin-like peptide receptor in Tribolium castaneum. Allatotropins are multifunctional neuropeptides initially isolated from the tabacco hornworm, Manduca sexta. They have been shown to be myoactive, to be cardio-acceleratory, to inhibit active ion transport, to stimulate juvenile hormone production and release and to be involved in the photic entrainment of the circadian clock. A tissue distribution analysis of the T. castaneum allatotropin-like peptide receptor by means of qRT-PCR revealed a prominent sexual dimorphism, the transcript levels being significantly higher in the male fat body and reproductive system. The endogenous ligand of the receptor, Trica-ATL, is able to increase the frequency and tonus of contractions in the gut and in the reproductive tract of mature red flour beetles.

Sexual differentiation in adult insects: male-specific cuticular yellowing in Schistocerca gregaria as a model for reevaluating some current (neuro)endocrine concepts

Changes in the color of the cuticle, days after the completion of hardening, are rare in adult insects. Even more so when such changes are specific to one sexual form and coincide with sexual maturation. Adult males of the desert locust Schistocerca gregaria deposit a well characterized 'yellow protein' in their cuticle about 10 days after the adult molt, but only if they live under crowded (gregarious) conditions. Isolated-reared (solitarious) males do not turn yellow, neither do the females. Upon regrouping, yellowing is quickly induced, but again, only in the males. Juvenile hormone (JH) is involved, but its sex- and phase-specific effect suggests that other factors are also involved. We analyzed the recent and classical literature to find out what should be added or changed to the classical way of thinking on sex differentiation in insects so that a comprehensive conceptual framework could emerge. Undervalued and/or new data on male accessory glands as a possible second site of JH synthesis, on ecdysteroids as possible sex steroids, on the transcription factor fruitless in insects and on the evolutionarily highly conserved transcription factor Foxl2 that, when ablated in mice is responsible for the transdifferentiation of the ovaries into testes, are considered.

Peptidomic survey of the locust neuroendocrine system

Neuropeptides are important controlling agents in animal physiology. In order to understand their role and the ways in which neuropeptides behave and interact with one another, information on their time and sites of expression is required. We here used a combination of MALDI-TOF and ESI-Q-TOF mass spectrometry to make an inventory of the peptidome of different parts (ganglia and nerves) of the central nervous system from the desert locust Schistocerca gregaria and the African migratory locust Locusta migratoria. This way, we analysed the brain, suboesophageal ganglion, retrocerebral complex, stomatogastric nervous system, thoracic ganglia, abdominal ganglia and abdominal neurohemal organs. The result is an overview of the distribution of sixteen neuropeptide families, i.e. pyrokinins, pyrokinin-like peptides, periviscerokinins, tachykinins, allatotropin, accessory gland myotropin, FLRFamide, (short) neuropeptide F, allatostatins, insulin-related peptide co-peptide, ion-transport peptide co-peptide, corazonin, sulfakinin, orcokinin, hypertrehalosaemic hormone and adipokinetic hormones (joining peptides) throughout the locust neuroendocrine system.

Mas-allatotropin/Lom-AG-myotropin I immunostaining in the brain of the locust, Schistocerca gregaria

Mas-allatotropin (Mas-AT) and Lom-accessory gland-myotropin I (Lom-AG-MTI) are two members of a conserved family of insect neuropeptides, collectively termed allatotropins, which have diverse functions, ranging from stimulation of juvenile hormone secretion to myotropic effects on heart and hindgut. In addition, allatotropins appear to be abundant within the nervous system, suggesting neuroactive roles. To identify neurons in the insect brain suitable for a neurophysiological analysis of the roles of allatotropins, we used antisera against Mas-AT and Lom-AG-MTI to map allatotropin-immunoreactive neurons in the brain of a suitable insect, the locust Schistocerca gregaria. Both antisera revealed basically identical staining patterns throughout the locust brain with more than 12,500 immunostained interneurons per brain hemisphere. Neurosecretory cells were not labeled, and the retrocerebral complex was devoid of immunostaining. Prominent immunoreactive cell types include about 9,600 lamina monopolar neurons, medulla to lobula interneurons, local neurons of the antennal lobe, a giant interneuron of the mushroom body, projection neurons of the glomerular lobe to the mushroom body, and three systems of tangential neurons of the central complex. Several groups of neurons showed colocalization of Mas-AT- and gamma-aminobutyric acid immunostaining. Mass spectrometric analysis identified a peptide with a molecular mass identical to Lom-AG-MTI in all major parts of the locust brain but not in the retrocerebral complex. This study strongly suggests that Lom-AG-MTI is highly abundant in the locust brain, and is likely to play a neuroactive role in many brain circuits including all stages of sensory processing, learning and memory, and higher levels of motor control.

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.

Evidence for a role of GABA and Mas-allatotropin in photic entrainment of the circadian clock of the cockroach Leucophaea maderae

Accumulating evidence suggests that the accessory medulla is the location of the circadian pacemaker in the fruit fly Drosophila melanogasterand the cockroach Leucophaea maderae. γ-Aminobutyric acid(GABA) and Mas-allatotropin are two putative neurotransmitters, in the accessory medulla in the cockroach Leucophaea maderae. Neurons immunoreactive to the neuropeptide Mas-allatotropin are local neurons with arborizations in the noduli of the accessory medulla, while GABA-immunoreactive neurons connect the noduli of the accessory medulla to the medulla and to the lamina via processes in the distal tract. Injections of GABA and Mas-allatotropin into the vicinity of the accessory medulla resulted in stable phase-dependent resetting of the circadian locomotor activity of the cockroach. The resulting phase response curves closely matched light-dependent phase response curves, suggesting that both substances play a role in circuits relaying photic information from circadian photoreceptors to the central pacemaker.

Neurotransmitters and neuropeptides in the brain of the locust

As part of continuous research on the neurobiology of the locust, the distribution and functions of neurotransmitter candidates in the nervous system have been analyzed particularly well. In the locust brain, acetylcholine, glutamate, gamma-aminobutyric acid (GABA), and the biogenic amines serotonin, dopamine, octopamine, and histamine most likely serve a transmitter function. Increasing evidence, furthermore, supports a signalling function for the gaseous molecule nitric oxide, but a role for neuroptides is so far suggested only by immunocytochemistry. Acetylcholine, glutamate, and GABA appear to be present in large numbers of interneurons. As in other insects, antennal sensory afferents might be cholinergic, while glutamate is the transmitter candidate of antennal motoneurons. GABA is regarded as the principle inhibitory transmitter of the brain, which is supported by physiological studies in the antennal lobe. The cellular distribution of biogenic amines has been analyzed particularly well, in some cases down to physiologically characterized neurons. Amines are present in small numbers of interneurons, often with large branching patterns, suggesting neuromodulatory roles. Histamine, furthermore, is the transmitter of photoreceptor neurons. In addition to these "classical transmitter substances," more than 60 neuropeptides were identified in the locust. Many antisera against locust neuropeptides label characteristic patterns of neurosecretory neurons and interneurons, suggesting that these peptides have neuroactive functions in addition to hormonal roles. Physiological studies supporting a neuroactive role, however, are still lacking. Nitric oxide, the latest addition to the list of neurotransmitter candidates, appears to be involved in early stages of sensory processing in the visual and olfactory systems.

Flights of fancy: possible roles of allatostatin and allatotropin in migration and reproductive success of Pseudaletia unipuncta

Many invertebrate neuropeptides have recently been identified and there is evidence that the same compound may serve different roles in different species and/or multiple functions within a given species. However, until the relevant receptors or 'knock out' animals, lacking the neuropeptide of interest, become available it will be difficult to clarify the precise inter- and intraspecific functions of these neuropeptides. In the present paper, we argue that until these tools are available a more meaningful understanding of the roles of neuropeptides could be obtained by carrying out experiments within an ecological context. Furthermore, this approach would allow us to generate hypotheses that could be rigorously tested when more sophisticated techniques are developed. We discuss these ideas using our interdisciplinary research on the reproductive biology of the true armyworm, Pseudaletia unipuncta, as a case study.

Allatotropin-like neuropeptide in the cockroach abdominal nervous system: myotropic actions, sexually dimorphic distribution and colocalization with serotonin

Allatotropin (AT) was isolated from the moth Manduca sexta as a peptide stimulating biosynthesis of juvenile hormone in the corpora allata, but has also been shown to be cardioactive in the same species. Here, we have investigated the presence and biological activity of AT-like peptide in the cockroaches Leucophaea maderae and Periplaneta americana with focus on abdominal ganglia and their target tissues. An antiserum to M. sexta AT was used for immunocytochemical mapping of neurons in the abdominal ganglia. A small number of interneurons and efferent neurons were found AT-like immunoreactive (AT-LI) in each of the abdominal ganglia. A prominent sexual dimorphism was detected in the terminal abdominal ganglion: in L. maderae the male ganglion there are approximately 18 AT-LI neurons with cell bodies posteriorly and efferent axons in the genital nerves; in the female ganglion 4-5 AT-LI cell bodies (with efferent axons) were found in the same region. Correlated with the extra efferents in males, the male accessory glands are richly supplied by AT-LI fibers and in females a less prominent innervation was seen in oviduct muscle. A similar dimorphism was seen in abdominal ganglia of P. americana. A sexual dimorphism was also detected in the abdominal ganglia A4-A6 of L. maderae. In each of these ganglia, approximately 8-10 large AT-LI neuronal cell bodies were found along the midline; in females these neurons have significantly larger cell bodies than in males. In both sexes, and both cockroach species, two large dorsal midline neurons were detected in A-5 and 6, which seem to send axons to the hindgut: the rectal pads of the hindgut are supplied by arborizing AT-LI axons. In males and females of both species, efferent AT-LI axons from midline neurons in A3-A6 supply the lateral heart nerves and other neurohemal release sites with arborizations. The efferent midline neurons of females contain colocalized serotonin-immunoreactivity. We tested the in vitro actions of M. sexta AT on muscle contractions in the L. maderae hindgut and the abdominal heart of both species. The frequency of contractions in the hindgut increased dose dependently when applying AT at 5 x 10(-8) to 5 x 10(-6) M (maximal response at 5 x 10(-7) M). Also the frequency of contractions of the heart increased by application of AT (threshold response at 5 x 10(-9) M). This effect was more prominent in males of both species (maximal response was a 35-40% increase in males and 10-20% in females). In conclusion, an AT-like peptide is present in neurons and neurosecretory cells of cockroach abdominal ganglia and seems to play a role in control of contractions in the hindgut and heart and also to have some function in male accessory glands and oviduct.

Molecular characterization of a cDNA from the true armyworm Pseudaletia unipuncta encoding Manduca sexta allatotropin peptide(1)

Allatotropin (AT) is an insect neuropeptide isolated from the tobacco hornworm, Manduca sexta, stimulates juvenile hormone (JH) biosynthesis by the corpora allata. A cDNA isolated from the true armyworm, Pseudaletia unipuncta, encodes a 135 amino acid AT precursor peptide which contains the AT peptide, with processing sites necessary for its endoproteolytic cleavage and amidation, plus two additional peptides of unknown function. The encoded AT peptide is identical to that isolated from M. sexta and Agrius convolvuli. Southern blot analysis indicated that AT is a single copy gene per haploid genome and is present in two allelic forms. A single transcript of approximately 1.5 kilobases was detected by northern blot analysis. The expression of the AT gene was analyzed during development from sixth instar larvae to five day-old moths. Initial expression was observed in late pupae and this expression was maintained throughout the adult stages in both sexes. In one day-old moths, expression was at its lowest level of the stages that express AT mRNA but levels increased in day 3 and day 5 adults. This pattern of AT expression in adult P. unipuncta moths mirrors that of JH biosynthesis and supports the notion that AT may act in the adult stages. Immunohistochemistry and in situ hybridization revealed that AT expression was localized to numerous structures of the nervous system, suggesting that AT may have functions distinct from regulation of JH biosynthesis.

Multifactorial control of the release of hormones from the locust retrocerebral complex

The retrocerebral complex of locusts consists of the corpus cardiacum, the corpora allata, and the nerves that connect these glands with the central nervous system. Both corpus cardiacum and corpora allata are neuroendocrine organs and consist of a glandular part, which synthesizes adipokinetic hormones and juvenile hormone, respectively, and of a neurohemal part. The glandular adipokinetic cells in the corpus cardiacum appear to be subjected to a multitude of regulatory stimulating, inhibiting, and modulating substances. Neural influence comes from secretomotor cells in the lateral part of the protocerebrum. Up to now, only peptidergic factors have been established to be present in the neural fibres that make synaptic contact with the adipokinetic cells. Humoral factors that act on the adipokinetic cells via the hemolymph are of peptidergic and aminergic nature. In addition, high concentrations of trehalose inhibit the release of adipokinetic hormones. Although there is evidence that neurosecretory cells in the protocerebrum are involved in the control of JH biosynthesis, the nature of the factors involved remains to be resolved.

Neuropeptides in insect sensory neurones: tachykinin-, FMRFamide- and allatotropin-related peptides in terminals of locust thoracic sensory afferents

Sensory afferents in the thoracic ganglia of the locust Locusta migratoria were labelled with antisera to different neuropeptides: locustatachykinins, FMRFamide and allatotropin. The locustatachykinin-immunoreactive (LTKIR) sensory fibres were derived from the legs and entered the ventral sensory neuropil of each of the thoracic ganglia via nerve 5. In the thoracic neuropil, the LTKIR sensory fibres formed a distinct plexus of terminations ventrally in the ipsilateral hemisphere. The peripheral cell bodies of the sensory neurones could not be revealed, but lesion experiments indicated that origin of the LTKIR fibres was the tarsus of each leg. Possibly the thin fibres are from tarsal chemoreceptors. Double labelling immunocytochemistry revealed that all the LTKIR sensory fibres contained colocalized FMRFamide immunoreactivity. A larger population of sensory fibres reacted with antiserum to moth (Manduca sexta) allatotropin. By means of double labelling immunocytochemistry, we could show that the LTKIR fibres constituted a subpopulation of the larger set of allatotropin-like immunoreactive fibres. Thus some sensory fibres may contain colocalized peptides related to locustatachykinins, FMRFamide-related peptide(s) and allatotropin-like peptide. A separate non-overlapping small set of sensory fibres in nerve 5 reacted with an antiserum to serotonin. Sensory fibres of the other nerves of the ventral nerve cord, including the abdominal ganglia, did not react with the peptide antisera. Since acetylcholine is the likely primary neurotransmitter of insect sensory fibres, it is possible that the peptides and serotonin are colocalized with this transmitter and serve modulatory functions in a subset of the leg afferents.

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.

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.

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.

Immunocytochemical characterization of the accessory medulla in the cockroach Leucophaea maderae

Several lines of evidence suggest that pigment-dispersing hormone-immunoreactive neurons with ramifications in the accessory medulla are involved in the circadian system of insects. The present study provides a detailed analysis of the anatomical and neurochemical organization of the accessory medulla in the brain of the cockroach Leucophaea maderae. We show that the accessory medulla is compartmentalized into central dense nodular neuropil surrounded by a shell of coarse fibers. It is innervated by neurons immunoreactive to antisera against serotonin and the neuropeptides allatostatin 7, allatotropin, corazonin, gastrin/cholecystokinin, FMRFamide, leucokinin I, and pigment-dispersing hormone. Some of the immunostained neurons appear to be local neurons of the accessory medulla, whereas others connect this neuropil to various brain areas, including the lamina, the contralateral optic lobe, the posterior optic tubercles, and the superior protocerebrum. Double-label experiments show the colocalization of immunoreactivity against pigment-dispersing hormone with compounds related to FMRFamide, serotonin, and leucokinin I. The neuronal and neurochemical organization of the accessory medulla is consistent with the current hypothesis for a role of this brain area as a circadian pacemaking center in the insect brain.

Partial identification, synthesis and immunolocalization of locustamyoinhibin, the third myoinhibiting neuropeptide isolated from Locusta migratoria

A blocked neuropeptide that suppresses the motility of the cockroach hindgut has been isolated from an extract of 9000 brain-corpora cardiaca-corpora allata-suboesophageal ganglion complexes of Locusta migratoria. Biological activity was monitored during HPLC purification by observing the myoinhibiting activity of column fractions on the isolated hindgut of Leucophaea maderae. Due to the low amount of material left after deblocking, this myoinhibiting peptide--designated as locustamyoinhibin or Lom-MIH--could only be partially sequenced: pGlu-X-Tyr-X'-Lys-Gln-Ser-Ala-Phe-Asn-Ala-Val-Ser-NH2. Nevertheless, the carboxy-terminal nonamer sequence (Lom-MIH5-13) was synthesized and also displayed myoinhibiting activity, indicating that the biologically active core lies in the carboxy-terminal sequence. Lom-MIH shows no sequence similarities with other peptides from vertebrate or invertebrate sources and is the third myoinhibiting peptide identified in Locusta migratoria. A polyclonal antiserum was raised against Lom-MIH5-13 and used to investigate the distribution of immunoreactive peptide in the central nervous system and its associated neurohaemal structures. Two groups of neurons with somata in the optic lobes show locustamyoinhibin (Lom-MIH)-like immunoreactivity. These groups have somata at the dorsal and ventral edge of the lamina ganglionaris. The neurons have dense ramifications in the lamina, with processes extending into the first optic chiasma and into the accessory medulla. Four cell bodies were detected in the protocerebrum, and two cells were found at the externo-lateral edge of the tritocerebrum. No immunoreactive perikarya could be observed in the suboesophageal ganglion nor in the ganglia of the ventral nerve cord. Neither the corpora cardiaca nor the neurohaemal organs of the ventral nerve cord showed immunolabelling. Therefore, our findings provide anatomical evidence for a central neurotransmitter role of Lom-MIH.

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.

Insect myotropic peptides: differential distribution of locustatachykinin- and leucokinin-like immunoreactive neurons in the locust brain

Locustatachykinin I is one of four closely related myotropic neuropeptides isolated from brain and corpora-cardiaca complexes of the locust Locusta migratoria. Antiserum was raised against locustatachykinin I for use in immunocytochemistry. It was found that the antiserum recognizes also locustatachykinin II and hence probably also the other two locustatachykinins due to their similarities in primary structure. Locustatachykinin-like immunoreactive (LomTK-LI) neurons were mapped in the brain of the locust, L. migratoria. A total of approximately 800 LomTK-LI neurons were found with cell bodies distributed in the proto-, deuto- and tritocerebrum, in the optic lobes and in the frontal ganglion. Processes of these neurons innervate most of the synaptic neuropils of the brain and optic lobes, as well as the frontal ganglion and hypocerebral ganglion. The widespread distribution of LomTK-LI neurons in the locust brain indicates an important role of the locustatachykinins in signal transfer or regulation thereof. As a comparison neurons were mapped with an antiserum against the cockroach myotropic peptide leucokinin I. This antiserum, which probably recognizes the native peptide locustakinin, labels a population of about 140 neurons distinct from the LomTK-LI neurons (no colocalized immunoreactivity). These neurons have cell bodies that are distributed in the proto- and tritocerebrum and in the optic lobe. The processes of the leucokinin-like immunoreactive (LK-LI) neurons do not invade as large areas in neuropil as the LomTK-LI neurons do and some neuropils, e.g. the mushroom bodies, totally lack innervation by LK-LI fibers. In some regions, however, the processes of the LomTK-LI and LK-LI neurons are superimposed: most notably in the central body and optic lobes. A functional relation between the two types of neuropeptide in the locust brain can, however, not be inferred from the present findings.

Glial localization of interleukin-1 alpha in invertebrate ganglia

1. Mytilus pedal ganglion contains a small population of glial cells that are immunopositive for interleukin-1 alpha. Positively stained fibers can also be seen in the neuropil of these sections. 2. The marine worm Nereis diversicolor also exhibits positive neural immunostaining for interleukin-1 alpha. 3. Both organisms contain hemocytes that contain immunoactivity for interleukin-1 alpha. The study suggests interleukin-1 alpha to be an ancient cytokine given its presence in organisms that evolved significantly earlier than mammals.