Feeding state influences the content of FMRFamide- and tachykinin-related peptides in endocrine-like cells of the midgut of Locusta migratoria

Differential expression of neuropeptide F in the digestive organs of female freshwater prawn, Macrobrachium rosenbergii, during the ovarian cycle

Neuropeptide F is a key hormone that controls feeding in invertebrates, including decapod crustaceans. We investigated the differential expression of Macrobrachium rosenbergii neuropeptide F (MrNPF) in the digestive organs of female prawns, M. rosenbergii, during the ovarian cycle. By using RT-qPCR, the expression of MrNPF mRNA in the esophagus (ESO), cardia (CD), and pylorus (PY) of the foregut (FG) gradually increased from stage II and peaked at stage III. In the midgut (MG), hindgut (HG), and hepatopancreas (HP), MrNPF mRNA increased from stage I, reaching a maximal level at stage II, and declined by about half at stages III and IV (P < 0.05). In the ESO, CD, and PY, strong MrNPF-immunoreactivities were seen in the epithelium, muscle, and lamina propria. Intense MrNPF-ir was found in the MG cells and the muscular layer. In the HG, MrNPF-ir was detected in the epithelium of the villi and gland regions, while MrNPF-ir was also more intense in the F-, R-, and B-cells in the HP. However, we found little colocalization between the MrNPF and PGP9.5/ChAT in digestive tissues, implying that most of the positive cells might not be neurons but could be digestive tract-associated endocrine cells that produce and secrete MrNPF to control digestive organ functions in feeding and utilizing feed. Taken together, our first findings indicated that MrNPF was differentially expressed in digestive organs in correlation with the ovarian cycle, suggesting an important link between MrNPF, the physiology of various digestive organs in feeding, and possibly ovarian maturation in female M. rosenbergii.

Investigating postsynaptic effects of a Drosophila neuropeptide on muscle contraction

The Drosophila neuropeptide, DPKQDFMRFamide, was previously shown to enhance excitatory junctional potentials (EJPs) and muscle contraction by both presynaptic and postsynaptic actions. Since the peptide acts on both sides of the synaptic cleft, it has been difficult to examine postsynaptic modulatory mechanisms, particularly when contractions are elicited by nerve stimulation. Here, postsynaptic actions are examined in 3rd instar larvae by applying peptide and the excitatory neurotransmitter, l-glutamate, in the bathing solution to elicit contractions after silencing motor output by removing the central nervous system (CNS). DPKQDFMRFamide enhanced glutamate-evoked contractions at low concentrations (EC50 1.3 nM), consistent with its role as a neurohormone, and the combined effect of both substances was supra-additive. Glutamate-evoked contractions were also enhanced when transmitter release was blocked in temperature-sensitive (Shibire) mutants, confirming the peptide's postsynaptic action. The peptide increased membrane depolarization in muscle when co-applied with glutamate, and its effects were blocked by nifedipine, an L-type channel blocker, indicating effects at the plasma membrane involving calcium influx. DPKQDFMRFamide also enhanced contractions induced by caffeine in the absence of extracellular calcium, suggesting increased calcium release from the sarcoplasmic reticulum (SR) or effects downstream of calcium release from the SR. The peptide's effects do not appear to involve calcium/calmodulin-dependent protein kinase II (CaMKII), previously shown to mediate presynaptic effects. The approach used here might be useful for examining postsynaptic effects of neurohormones and cotransmitters in other systems.NEW & NOTEWORTHY Distinguishing presynaptic and postsynaptic effects of neurohormones is a long-standing challenge in many model organisms. Here, postsynaptic actions of DPKQDFMRFamide are demonstrated by assessing its ability to potentiate contractions elicited by direct application of the neurotransmitter, glutamate, when axons are silent and when transmitter release is blocked. The peptide acts at multiple sites to increase contraction, increasing glutamate-induced depolarization at the cell membrane, acting on L-type channels, and acting downstream of calcium release from the sarcoplasmic reticulum.

Modulation of neuromuscular synapses and contraction in Drosophila 3rd instar larvae

Over the past four decades, Drosophila melanogaster has become an increasingly important model system for studying the modulation of chemical synapses and muscle contraction by cotransmitters and neurohormones. This review describes how advantages provided by Drosophila have been utilized to investigate synaptic modulation, and it discusses key findings from investigations of cotransmitters and neurohormones that act on body wall muscles of 3rd instar Drosophila larvae. These studies have contributed much to our understanding of how neuromuscular systems are modulated by neuropeptides and biogenic amines, but there are still gaps in relating these peripheral modulatory effects to behavior.

Glucose, some amino acids and a plant secondary metabolite, chlorogenic acid induce the secretion of a regulatory hormone, tachykinin-related peptide, from the silkworm midgut

Enteroendocrine cells in the insect midgut are thought to secrete peptide hormones in response to the nutritional state. However, the role of dietary compounds in inducing peptide hormone secretion from enteroendocrine cells in insects remains unknown. In the present study, we demonstrated that several dietary compounds from mulberry leaves, including glucose, amino acids, and the secondary metabolite chlorogenic acid, induced significant secretion of tachykinin-related peptides from isolated silkworm midguts at the luminal concentrations measured in fed larvae. This study provides evidence that the insect midgut senses a non-nutritious secondary metabolite in addition to nutrient metabolites to monitor luminal food status and secretes a feeding regulatory hormone, suggesting that a unique dietary sensory system modulates insect feeding via enteroendocrine control.

PHARMACOLOGICAL REGULATION OF DIGESTION IN THE ANAUTOGENOUS FLESH FLY, Sarcophaga crassipalpis, BY SIMPLE INJECTION OF 6-HYDROXYDOPAMINE

Female anautogenous Sarcophaga flesh flies need a protein meal to start large-scale yolk polypeptides (YPs) production and oocyte maturation. Protein meal rapidly elicits a brain-dependent increase in midgut proteolytic activity. Trypsin and chymotrypsin together represent over 80% of protease activity in liver-fed flies. Abdominal injection of 6-hydroxydopamine (6-OHDA) dose-dependently prohibits this increase in proteolytic activity at translational level in a similar way as post liver feeding decapitation. Delayed injection of 6-OHDA later than 6 h post liver meal has no effect. In flesh flies, chemical decapitation by 6-OHDA, by interrupting the brain-gut dopaminergic signaling, can be used as tool for the controlled inhibition of midgut proteolytic activity and subsequent ovarial development. Inhibition of ovarial development is probably indirect due to a deficit in circulating amino acids needed for YPs synthesis.

Chemical identity, function and regulation of enteroendocrine peptides in insects

How animals allocate energy and metabolic decisions are coordinated is a fundamental physiological question. Metabolic research is strongly driven by an increasing obesity rate in humans. For insects-which contain many pest species and disease vectors-the control of feeding is of agroeconomical and medical importance. Regulatory peptides have since long been in focus of metabolic research. In insects, major advances have been made recently, mostly due to research in the genetically tractable Drosophila melanogaster with focus on the central nervous system as a source of neuropeptides. Research on peptides produced by enteroendocrine cells remained peripheral, but this situation is about to change. This review highlights current knowledge and advances on the identity and role of enteroendocrine insect peptides.

Differential peptidomics highlights adipokinetic hormone as key player in regulating digestion in anautogenous flesh fly, Sarcophaga crassipalpis

Females of anautogenous flesh flies, Sarcophaga crassipalpis, need a protein meal in order to produce their first batch of eggs. This protein meal elicits an increase in midgut proteolytic activity that is under neuropeptidergic regulation. Time series of decapitation and rescue experiments of liver fed flies evidenced the need of a peptide factor released by corpora cardiaca (CC) within 4h post protein feeding in order to assure complete protein digestion. Q-Exactive quantitative differential peptidomics analysis on CC of sugar fed flies and flies 5h post protein feeding respectively, showed a unique consistent decrease in the stored amount of adipokinetic hormone (AKH) ranging between 16% up to 63%. Injection of AKH into liver fed decapitated flies as well as sugar fed intact flies resulted in dose dependent enhanced midgut proteolytic activity up to the level of intact protein fed flies. This suggests a key role of AKH in food depended reproduction.

Regulation of feeding by Neuropeptide F in the desert locust, Schistocerca gregaria

Our knowledge on the physiological function of the insect Neuropeptide F (NPF) mostly comes from studies in the fruit fly, Drosophila melanogaster, where NPF was shown to regulate diverse processes, such as feeding, learning and responding to stress. In the desert locust, Schistocerca gregaria, only a truncated form of the "full-length" NPF (the biologically active "trNPF") has been isolated. In this study, we investigated whether this peptide is involved in the regulation of feeding in this orthopteran species. In the S. gregaria EST-database, an NPF-precursor encoding transcript was found. Alignment with other insect NPF-precursors showed relatively highest sequence conservation within the trNPF region (and the flanking dibasic cleavage site), as compared to other regions of the NPF-precursor. Quantitative real-time RT-PCR revealed that the Schgr-NPF-precursor encoding transcript occurs throughout the central nervous system with relatively high transcript levels in the brain, optic lobes and suboesophageal ganglion. It was also detected at relatively high levels in the midgut, which suggests that the encoded peptide also functions in the digestive system. Moreover, Schgr-NPF-transcript levels were notably higher in starved animals than in animals fed ad libitum, while transcript levels were also shown to be regulated after the consumption of a meal. Injection of locust trNPF in adults stimulated food intake, while RNAi knockdown reduced food intake. Furthermore, injection of trNPF in adults stimulated weight increase, while RNAi knockdown reduced weight gain. This effect of trNPF on body weight gain may result from its stimulatory effect on food intake. Taken together, we provide clear evidence for an important role of trNPF in the regulation of feeding in the desert locust, S. gregaria.

Transcriptomic analysis of neuropeptides and peptide hormones in the barnacle Balanus amphitrite: evidence of roles in larval settlement

The barnacle Balanus amphitrite is a globally distributed marine crustacean and has been used as a model species for intertidal ecology and biofouling studies. Its life cycle consists of seven planktonic larval stages followed by a sessile juvenile/adult stage. The transitional processes between larval stages and juveniles are crucial for barnacle development and recruitment. Although some studies have been conducted on the neuroanatomy and neuroactive substances of the barnacle, a comprehensive understanding of neuropeptides and peptide hormones remains lacking. To better characterize barnacle neuropeptidome and its potential roles in larval settlement, an in silico identification of putative transcripts encoding neuropeptides/peptide hormones was performed, based on transcriptome of the barnacle B. amphitrite that has been recently sequenced. Potential cleavage sites andstructure of mature peptides were predicted through homology search of known arthropod peptides. In total, 16 neuropeptide families/subfamilies were predicted from the barnacle transcriptome, and 14 of them were confirmed as genuine neuropeptides by Rapid Amplification of cDNA Ends. Analysis of peptide precursor structures and mature sequences showed that some neuropeptides of B. amphitrite are novel isoforms and shared similar characteristics with their homologs from insects. The expression profiling of predicted neuropeptide genes revealed that pigment dispersing hormone, SIFamide, calcitonin, and B-type allatostatin had the highest expression level in cypris stage, while tachykinin-related peptide was down regulated in both cyprids and juveniles. Furthermore, an inhibitor of proprotein convertase related to peptide maturation effectively delayed larval metamorphosis. Combination of real-time PCR results and bioassay indicated that certain neuropeptides may play an important role in cypris settlement. Overall, new insight into neuropeptides/peptide hormones characterized in this study shall provide a platform for unraveling peptidergic control of barnacle larval behavior and settlement process.

An unusual myosuppressin from the blood-feeding bug Rhodnius prolixus

The myosuppressin (MS) gene was cloned from a central nervous system (CNS) cDNA library of the hematophagous insect Rhodnius prolixus and is predicted to contain two introns and three exons. The mRNA transcribed from the myosuppressin gene encodes an 88 amino acid prepropeptide, which results in a mature decapeptide after post-translational modification. When compared with the myosuppressins isolated from other insects, the R. prolixus myosuppressin has a unique amino acid sequence (pQDIDHVFMRFamide), with isoleucine (I) in position 3 and methionine (M) in position 8. Reverse transcriptase (RT)-PCR shows that Rhopr-MS is expressed in the CNS and posterior midgut in R. prolixus and immunohistochemistry suggests that an RFamide-like peptide is present in endocrine-like cells in the midgut. Physiological assays using Rhopr-MS indicate that, despite the unusual M at position 8, it still retains myoinhibitory activity, inhibiting the frequency and reducing the amplitude of contractions in the anterior midgut and hindgut, and decreasing heart rate.

Insulin-producing cells and their regulation in physiology and behavior ofDrosophila1This review is part of a virtual symposium on recent advances in understanding a variety of complex regulatory processes in insect physiology and endocrinology, including development, metabolism, cold hardiness, food intake and digestion, and diuresis, through the use of omics technologies in the postgenomic era

Insulin-like peptide signaling regulates development, growth, reproduction, metabolism, stress resistance, and life span in a wide spectrum of animals. Not only the peptides, but also their tyrosine kinase receptors and the downstream signaling pathways are conserved over evolution. This review summarizes roles of insulin-like peptides (DILPs) in physiology and behavior of Drosophila melanogaster Meigen, 1830. Seven DILPs (DILP1–7) and one receptor (dInR) have been identified in Drosophila. These DILPs display cell and stage specific expression patterns. In the adult, DILP2, 3, and 5 are expressed in insulin-producing cells (IPCs) among the median neurosecretory cells of the brain, DILP7 in 20 neurons of the abdominal ganglion, and DILP6 in the fat body. The DILPs of the IPCs regulate starvation resistance, responses to oxidative and temperature stress, and carbohydrate and lipid metabolism. Furthermore, the IPCs seem to regulate feeding, locomotor activity, sleep and ethanol sensitivity, but the mechanisms are not elucidated. Insulin also alters the sensitivity in the olfactory system that affects food search behavior, and regulates peptidergic neurons that control aspects of feeding behavior. Finally, the control of insulin production and release by humoral and neuronal factors is discussed. This includes a fat body derived factor and the neurotransmitters GABA, serotonin, octopamine, and two neuropeptides.

Insulin production and signaling in renal tubules of Drosophila is under control of tachykinin-related peptide and regulates stress resistance

The insulin-signaling pathway is evolutionarily conserved in animals and regulates growth, reproduction, metabolic homeostasis, stress resistance and life span. In Drosophila seven insulin-like peptides (DILP1-7) are known, some of which are produced in the brain, others in fat body or intestine. Here we show that DILP5 is expressed in principal cells of the renal tubules of Drosophila and affects survival at stress. Renal (Malpighian) tubules regulate water and ion homeostasis, but also play roles in immune responses and oxidative stress. We investigated the control of DILP5 signaling in the renal tubules by Drosophila tachykinin peptide (DTK) and its receptor DTKR during desiccative, nutritional and oxidative stress. The DILP5 levels in principal cells of the tubules are affected by stress and manipulations of DTKR expression in the same cells. Targeted knockdown of DTKR, DILP5 and the insulin receptor dInR in principal cells or mutation of Dilp5 resulted in increased survival at either stress, whereas over-expression of these components produced the opposite phenotype. Thus, stress seems to induce hormonal release of DTK that acts on the renal tubules to regulate DILP5 signaling. Manipulations of S6 kinase and superoxide dismutase (SOD2) in principal cells also affect survival at stress, suggesting that DILP5 acts locally on tubules, possibly in oxidative stress regulation. Our findings are the first to demonstrate DILP signaling originating in the renal tubules and that this signaling is under control of stress-induced release of peptide hormone.

Neuropeptide F and the corn earworm, Helicoverpa zea: a midgut peptide revisited

The neuropeptide Y family of peptides is implicated in the regulation of feeding across a broad range of animals, including insects. Among vertebrates, neuropeptide Y exerts its actions mainly centrally, whereas peptide YY and pancreatic polypeptide arise from digestive tissues. Among invertebrates, neuropeptide F (NPF) is the sole counterpart of the NPY family. Shared features of NPF sequences derived for Lepidoptera indicate that the midgut peptide (Hez-MP-I) of the corn earworm, Helicoverpa zea, characterized more than a decade ago, is a carboxyl fragment of a full-length NPF. An antibody to Hez-MP-I was used to characterize the peptide's distribution in tissues of larvae, pupae, and adults. Immunostaining demonstrated NPF-related material both in nervous tissues and in abundant endocrine cells of the midgut. Radioimmunoassay of Hez-MP-I in the head, midgut and hemolymph of fifth instar larvae revealed concentration changes corresponding to development and feeding state. As with the vertebrate homologs, NPF may arise both centrally and peripherally to modulate the physiology of feeding and digestion of Lepidoptera.

Neural substrate and allatostatin-like innervation of the gut of Locusta migratoria

Allatostatin-like immunoreactivity (ALI) is widely distributed in processes and varicosities on the fore-, mid-, and hindgut of the locust, and within midgut open-type endocrine-like cells. ALI is also observed in cells and processes in all ganglia of the central nervous system (CNS) and the stomatogastric nervous system (SNS). Ventral unpaired median neurons (VUMs) contained ALI within abdominal ganglia IV-VII. Neurobiotin retrograde fills of the branches of the 11th sternal nerve that innervate the hindgut revealed 2-4 VUMs in abdominal ganglia IV-VIIth, which also contain ALI. The VIIIth abdominal ganglion contained three ventral medial groups of neurons that filled with neurobiotin and contained ALI. The co-localization of ALI in the identified neurons suggests that these cells are the source of ALI on the hindgut. A retrograde fill of the nerves of the ingluvial ganglia that innervate the foregut revealed numerous neurons within the frontal ganglion and an extensive neuropile in the hypocerebral ganglion, but there seems to be no apparent co-localization of neurobiotin and ALI in these neurons, indicating the source of ALI on the foregut comes via the brain, through the SNS.

Metabolic stress responses in Drosophila are modulated by brain neurosecretory cells that produce multiple neuropeptides

In Drosophila, neurosecretory cells that release peptide hormones play a prominent role in the regulation of development, growth, metabolism, and reproduction. Several types of peptidergic neurosecretory cells have been identified in the brain of Drosophila with release sites in the corpora cardiaca and anterior aorta. We show here that in adult flies the products of three neuropeptide precursors are colocalized in five pairs of large protocerebral neurosecretory cells in two clusters (designated ipc-1 and ipc-2a): Drosophila tachykinin (DTK), short neuropeptide F (sNPF) and ion transport peptide (ITP). These peptides were detected by immunocytochemistry in combination with GFP expression driven by the enhancer trap Gal4 lines c929 and Kurs-6, both of which are expressed in ipc-1 and 2a cells. This mix of colocalized peptides with seemingly unrelated functions is intriguing and prompted us to initiate analysis of the function of the ten neurosecretory cells. We investigated the role of peptide signaling from large ipc-1 and 2a cells in stress responses by monitoring the effect of starvation and desiccation in flies with levels of DTK or sNPF diminished by RNA interference. Using the Gal4-UAS system we targeted the peptide knockdown specifically to ipc-1 and 2a cells with the c929 and Kurs-6 drivers. Flies with reduced DTK or sNPF levels in these cells displayed decreased survival time at desiccation and starvation, as well as increased water loss at desiccation. Our data suggest that homeostasis during metabolic stress requires intact peptide signaling by ipc-1 and 2a neurosecretory cells.

FMRFamide-like immunoreactivity in the central nervous system and alimentary tract of the non-hematophagous blow fly, Phormia regina, and the hematophagous horse fly, Tabanus nigrovittatus

FMRFamide-related peptides (FaRPs) are a diverse and physiologically important class of neuropepeptides in the metazoa. In insects, FaRPs function as brain-gut neuropeptides and have been immunolocalized throughout the nervous system and alimentary tract where they have been shown to affect feeding behavior. The occurrence of FMRFamide-like immunoreactivity (FLI) was examined in the central nervous system and alimentary tract of non-hematophagous blow fly, Phormia regina Meigen (Diptera: Calliphoridae), and the hematophagous horse fly, Tabanus nigrovittatus Macquart (Diptera:Tabanidae). Although the central nervous system and alimentary anatomy differ between these two dipteran species, many aspects of FLI remain similar. FLI was observed throughout the central and stomatogastric nervous systems, foregut, and midgut in both flies. In the central nervous system, cells and processes with FLI occurred in the brain, subesophageal ganglion, and ventral nerve cord. FLI was associated with neurohemal areas of the brain and ventral nerve cord. A neurohemal plexus of fibers with FLI was present on the dorsal region of the thoracic central nervous system in both species. In the gut, processes with FLI innervated the crop duct, crop and anterior midgut. Endocrine cells with FLI were present in the posterior midgut. The distribution of FLI in these two flies, in spite of their different feeding habits, further supports the role of FaRPs as important components of the braingut neurochemical axis in these insects and implicates FaRPs as regulators of insect feeding physiology among divergent insect taxa.

Isolation and sequencing of two FMRFamide-related peptides from the gut of Locusta migratoria L

Two FMRFamide-related peptides (FaRPs) have been isolated and sequenced from the whole gut of Locusta migratoria L. Peptides were extracted from 500 locust whole guts and separated using reversed-phase high performance liquid chromatography (RP-HPLC). Fractions containing FMRFamide-like immunoreactive (FLI) material were identified using radioimmunoassay (RIA). Sequencing of fractions, using tandem mass spectrometry (MALDI-TOF MS/MS), revealed the myosuppressin previously isolated from the locust CNS, SchistoFLRFamide (PDVDHVFLRFamide), and a novel extended RFamide (LWENLRFamide). The isolation of SchistoFLRFamide from midgut tissue supports the hypothesis that this myosuppressin is released locally from FLI processes over the gut and/or from endocrine-like midgut cells to play a role in the regulation of digestion.

Identification, physiological actions, and distribution of TPSGFLGMRamide: a novel tachykinin-related peptide from the midgut and stomatogastric nervous system of Cancer crabs

In most invertebrates, multiple species-specific isoforms of tachykinin-related peptide (TRP) are common. In contrast, only a single conserved TRP isoform, APSGFLGMRamide, has been documented in decapod crustaceans, leading to the hypothesis that it is the sole TRP present in this arthropod order. Previous studies of crustacean TRPs have focused on neuronal tissue, but the recent demonstration of TRPs in midgut epithelial cells in Cancer species led us to question whether other TRPs are present in the gut, as is the case in insects. Using direct tissue matrix assisted laser desorption/ionization Fourier transform mass spectrometry, in combination with sustained off-resonance irradiation collision-induced dissociation, we found that at least one additional TRP is present in Cancer irroratus, Cancer borealis, Cancer magister, and Cancer productus. The novel TRP isoform, TPSGFLGMRamide, was present not only in the midgut, but also in the stomatogastric nervous system (STNS). In addition, we identified an unprocessed TRP precursor APSGFLGMRG, which was detected in midgut tissues only. TRP immunohistochemistry, in combination with preadsorption studies, suggests that APSGFLGMRamide and TPSGFLGMRamide are co-localized in the stomatogastric ganglion (STG), which is contained within the STNS. Exogenous application of TPSGFLGMRamide to the STG elicited a pyloric motor pattern that was identical to that elicited by APSGFLGMRamide, whereas APSGFLGMRG did not alter the pyloric motor pattern.

Proctolin-like immunoreactivity in the central and peripheral nervous systems of the locust, Locusta migratoria

Proctolin-like immunoreactivity (PLI) was widely distributed in the locust, Locusta migratoria, within the central, peripheral and stomatogastric nervous systems, as well as the digestive system and retrocerebral complex. Proctolin-like immunoreactivity was observed in cells and processes of the brain and all ganglia of the ventral nerve cord. Of interest, PLI was found in the lateral neurosecretory cells, which send axons within the paired nervi corporis cardiaci II (NCC II) to the corpus cardiacum (CC). The CC contained extensive processes displaying PLI, which continued on within the paired nervi corporis allata (NCA) to the paired corpora allata (CA) where the axons entered and branched therein. The frontal and hypocerebral ganglia of the stomatogastric nervous system contained PLI within processes, resulting in a brightly staining neuropile. Each region of the gut contained PLI in axons and processes of varying patterns and densities. The paired ingluvial ganglia contained PLI, including an extensively stained neuropile and immunoreactive axons projecting through the nerves to the foregut. The hindgut contained PLI within longitudinal tracts, with lateral projections originating from the 8th abdominal ganglion via the proctodeal nerve. The midgut contained PLI in a regular latticework pattern with many varicosities and blebs. No difference in PLI in cells and processes of the central nervous system (CNS) was found between males and females.

The distribution and activity of tachykinin-related peptides in the blood-feeding bug, Rhodnius prolixus

The invertebrate tachykinin-related peptides (TRPs) with the conserved C-terminal sequence FX1GX2Ramide shows sequence similarity to the vertebrate tachykinins after which they are named, and are hypothesized to be ancestrally related. In this study a polyclonal antiserum generated against a locust tachykinin (LomTK I), was used to demonstrate the presence and describe the distribution of LomTK-like immnoreactivity in the CNS and gut of Rhodnius prolixus. Reverse phase high performance liquid chromatography (RP-HPLC) was used in combination with a sensitive radioimmunoassay (RIA) to demonstrate picomolar amounts of immunoreactive material in the CNS, and femptomolar amounts associated with the hindgut. Furthermore, the results from CNS extracts separated by RP-HPLC, suggest that at least two tachykinin isoforms exist in R. prolixus. A hindgut contraction assay was developed to quantify the myotropic effects of selected LomTKs on R. prolixus hindgut contraction. Both LomTK I and II caused an increase in the frequency of hindgut contractions with EC50 values of 3.6x10(-8)M and 3.8x10(-8)M for LomTK I and II, respectively.

In vitro analysis of the digestive enzymes amylase and alpha-glucosidase in the midguts of Locusta migratoria L. in response to the myosuppressin, SchistoFLRFamide

We have investigated the effect of the locust myosuppressin, SchistoFLRFamide, on the activity of amylase and alpha-glucosidase in the midgut of 2-week old male locusts. Total enzyme activity in the lumen contents and tissue extracts of midguts responds to SchistoFLRFamide in a dose-dependent manner that appears to vary with the feeding state of the locust and duration of exposure to the peptide. Starvation for 24h prior to assessment alters the distribution of enzyme activity between the midgut lumen contents and tissue extracts in response to SchistoFLRFamide when compared with fed locusts. Duration of exposure to SchistoFLRFamide also alters the distribution of total amylase and alpha-glucosidase activity; as duration of exposure increases, lower concentrations of SchistoFLRFamide increase total enzyme activity in the lumen contents while decreasing total enzyme activity in the tissue extracts. We suggest that the minimum amino acid sequence in SchistoFLRFamide necessary to increase both amylase and alpha-glucosidase activity is DHVFLRFamide. We have determined that two other peptides endogenous to the locust, AFIRFamide and GQERNFLRFamide, increase amylase and alpha-glucosidase activity in midgut lumen contents.

The influence of diet and feeding state on FMRFamide-related peptides in the gut of Locusta migratoria L

Gut tissues of 2-week post-ecdysis female Locusta migratoria L. were assayed for FMRFamide-like immunoreactivity (FLI) during various feeding states using both radioimmunoassay and immunohistochemistry. The feeding states investigated were: (a) 48- and 24-h starved; (b) 5-, 30-, or 60-min post-feeding initiation; and (c) a diet of wheat grass, carrots, or apples. We determined: (1) the feeding state of a locust influences FLI in all gut tissues; (2) variations in diet appear to influence FLI in all gut tissues; (3) more than one FMRFamide-related peptide (FaRP) responds to differences in diet and state of starvation in the gut tissues; and (4) the protein poor diets (carrot and apple), in conjunction with the assertion that protein to carbohydrate ratio in the diet is the key component for nutrient balancing, suggests that FaRPs may play a role in maintaining balanced nutrient content in the locust.

Diuretic action of the peptide locustatachykinin I: cellular localisation and effects on fluid secretion in Malpighian tubules of locusts

In insects primary urine is produced by the Malpighian tubules under hormonal control. Here we have analysed the effects of the peptide locustatachykinin I (Lom-TK-I) on secretion in isolated Malphigian tubules. We also mapped the distribution of Lom-TK immunoreactivity in the gut in comparison with Locusta diuretic hormone (Lom-DH) and serotonin, two other factors that are active on locust tubules. Lom-TK-I produces an immediate, potent and long-lasting stimulation of fluid secretion. Furthermore, we show that Lom-TK-I acts synergistically with Lom-DH on fluid secretion and demonstrate that Lom-TKs are co-localised with Lom-DH in endocrine cells of the midgut ampullae. Thus, the two peptides might be released together to act synergistically on fluid secretion. Also serotonin and Lom-DH act synergistically and we can demonstrate a plexus of serotonin-containing axon processes over the midgut.

FMRFamide-related peptides in the gut of Locusta migratoria L.: a comprehensive map and developmental profile

The gut tissues and associated nervous system of the African migratory locust, Locusta migratoria, were found to contain FMRFamide-like immunoreactive (FLI) material throughout the five larval instars and 2 weeks into the adult stage in both males and females. FMRFamide-like immunoreactivity associated with the locust gut was described using camera lucida techniques. FMRFamide-like immunoreactivity is observed in the frontal connectives, recurrent nerve, and oesophageal nerves; projections from the ingluvial ganglion onto the anterior midgut, and from the proctodeal nerve onto the hindgut and posterior midgut; in the neuropils of the frontal ganglion, hypocerebral ganglion and ingluvial ganglia; 30 cell bodies in the frontal ganglion; multipolar sensory cells on the foregut; and endocrine-like cells in the gastric caecae and midgut. Radioimmunoassay (RIA) was used to determine the quantities of FLI material in foreguts, gastric caecae, anterior and posterior midguts, and hindgut of first-fifth instar larvae, 1-3- and 14-17-day male and female adult locusts. As expected, as the tissue size (assessed by total protein content) increases, so does the amount of FLI material in each tissue. Normalizing for tissue size reveals significant differences in FLI content among the stages for each tissue tested. Reversed phase-high pressure liquid chromatography (RP-HPLC) followed by RIA has identified four groups of FLI fractions present in the gut, and different members of these groups are present in the various gut tissues.

In vitro release of digestive enzymes by FMRF amide related neuropeptides and analogues in the lepidopteran insect Opisina arenosella (Walk.)

The insect neuropeptides FMRF amide, leucomyosupressin (LMS) and neuropeptide analogues leucosulfakinins (FLSK and LSK II Ser (SO(3)H)), perisulfakinin (PSK), proleucosulfakinin (PLSK), 14A[phi1]WP-I, 542phi1, and 378A[5b]WP-I were assayed for their effects on the release of amylase and protease from the midgut tissue of larvae of Opisina arenosella. In the bioassay, empty midgut tubes ligated at both ends using hair were incubated with insect saline containing neuropeptides/analogues in a bioassay apparatus at 37 degrees C for 30 min. After incubation the contents of the midgut preparations were analyzed for amylase and protease activity. In control experiments, the midgut preparations were incubated in insect saline without neuropeptides. The results of the study reveal that for stimulating amylase release from midgut tissue, the peptides require an FXRF amide (X may be methionine or leucine) sequence at the C-terminal. The presence of HMRF amide at C-terminal of peptides may inhibit the release of amylase. Meanwhile, peptides with both FMRF and HMRF amide sequence at the C-terminal are found to be effective in stimulating protease release. The tetrapeptide segment at the C-terminal probably represent the active core of the neuropeptide.

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.

FMRFamide-like midgut endocrine cells during the metamorphosis in Melipona quadrifasciata anthidioides (Hymenoptera, Apidae)

The FMRFamide, gastrin and cholecystokinin (CCK) occurrence in endocrine cells of insects has been described by several authors, although their functions are still not well defined for this group of animals. In the present study, the occurrence of endocrine cells producing FMRFamide, gastrin 1 and CCK-8 in the midgut (ventriculus) of Melipona quadrifasciata anthidioides (Hymenoptera, Apidae), before, during and after the metamorphosis, were investigated by means of pre-embedding immunofluorescence techniques. FMRFamide reactivity was found in the endocrine cells as well as in the nervous fibers and neurons of the intestine of these bees. 'Open' and 'closed' types of FMRFamide-like cells were observed in last instar larvae. In the black eyed pupae the producing cells of FMRFamide seemed to be immature, and, in the workers, where the FMRFamide producing cells were more abundant, the production of this substance seemed to occur only in the open cells. Reactivity of the nervous fibers and neurons were observed, during the prepupae, white eyed pupae, and pink eyed pupae. The same did not occur with the midgut endocrine cells. There were no immunoreactivity observations for gastrin 1 and for CCK-8. The FMRFamide-like cells were present in the midgut of these insects during or close to the period that they were eating, which indicates that the FMRFamide may be involved in the control of the digestive process.