Allatostatin-like immunoreactivity in the stomatogastric nervous system and the pericardial organs of the crabCancer pagurus, the lobster Homarus americanus, and the crayfishCherax destructor andProcambarus clarkii

Local olfactory interneurons provide the basis for neurochemical regionalization of olfactory glomeruli in crustaceans

The primary olfactory centers of metazoans as diverse as arthropods and mammals consist of an array of fields of dense synaptic neuropil, the olfactory glomeruli. However, the neurochemical structure of crustacean olfactory glomeruli is largely understudied when compared to the insects. We analyzed the glomerular architecture in selected species of hermit crabs using immunohistochemistry against presynaptic proteins, the neuropeptides orcokinin, RFamide and allatostatin, and the biogenic amine serotonin. Our study reveals an unexpected level of structural complexity, unmatched by what is found in the insect olfactory glomeruli. Peptidergic and aminergic interneurons provide the structural basis for a regionalization of the crustacean glomeruli into longitudinal and concentric compartments. Our data suggest that local olfactory interneurons take a central computational role in modulating the information transfer from olfactory sensory neurons to projection neurons within the glomeruli. Furthermore, we found yet unknown neuronal elements mediating lateral inhibitory interactions across the glomerular array that may play a central role in modulating the transfer of sensory input to the output neurons through presynaptic inhibition. Our study is another step in understanding the function of crustacean olfactory glomeruli as highly complex units of local olfactory processing.

Comparative analyses of olfactory systems in terrestrial crabs (Brachyura): evidence for aerial olfaction?

Adaptations to a terrestrial lifestyle occurred convergently multiple times during the evolution of the arthropods. This holds also true for the "true crabs" (Brachyura), a taxon that includes several lineages that invaded land independently. During an evolutionary transition from sea to land, animals have to develop a variety of physiological and anatomical adaptations to a terrestrial life style related to respiration, reproduction, development, circulation, ion and water balance. In addition, sensory systems that function in air instead of in water are essential for an animal's life on land. Besides vision and mechanosensory systems, on land, the chemical senses have to be modified substantially in comparison to their function in water. Among arthropods, insects are the most successful ones to evolve aerial olfaction. Various aspects of terrestrial adaptation have also been analyzed in those crustacean lineages that evolved terrestrial representatives including the taxa Anomala, Brachyura, Amphipoda, and Isopoda. We are interested in how the chemical senses of terrestrial crustaceans are modified to function in air. Therefore, in this study, we analyzed the brains and more specifically the structure of the olfactory system of representatives of brachyuran crabs that display different degrees of terrestriality, from exclusively marine to mainly terrestrial. The methods we used included immunohistochemistry, detection of autofluorescence- and confocal microscopy, as well as three-dimensional reconstruction and morphometry. Our comparative approach shows that both the peripheral and central olfactory pathways are reduced in terrestrial members in comparison to their marine relatives, suggesting a limited function of their olfactory system on land. We conclude that for arthropod lineages that invaded land, evolving aerial olfaction is no trivial task.

Consequences of acute and long-term removal of neuromodulatory input on the episodic gastric rhythm of the crab Cancer borealis

For decades, the episodic gastric rhythm of the crustacean stomatogastric nervous system (STNS) has served as an important model system for understanding the generation of rhythmic motor behaviors. Here we quantitatively describe many features of the gastric rhythm of the crab Cancer borealis under several conditions. First, we analyzed spontaneous gastric rhythms produced by freshly dissected preparations of the STNS, including the cycle frequency and phase relationships among gastric units. We find that phase is relatively conserved across frequency, similar to the pyloric rhythm. We also describe relationships between these two rhythms, including a significant gastric/pyloric frequency correlation. We then performed continuous, days-long extracellular recordings of gastric activity from preparations of the STNS in which neuromodulatory inputs to the stomatogastric ganglion were left intact and also from preparations in which these modulatory inputs were cut (decentralization). This allowed us to provide quantitative descriptions of variability and phase conservation within preparations across time. For intact preparations, gastric activity was more variable than pyloric activity but remained relatively stable across 4-6 days, and many significant correlations were found between phase and frequency within animals. Decentralized preparations displayed fewer episodes of gastric activity, with altered phase relationships, lower frequencies, and reduced coordination both among gastric units and between the gastric and pyloric rhythms. Together, these results provide insight into the role of neuromodulation in episodic pattern generation and the extent of animal-to-animal variability in features of spontaneously occurring gastric rhythms.

Neuropeptide complexity in the crustacean central olfactory pathway: immunolocalization of A-type allatostatins and RFamide-like peptides in the brain of a terrestrial hermit crab

BACKGROUND

In the olfactory system of malacostracan crustaceans, axonal input from olfactory receptor neurons associated with aesthetascs on the animal's first pair of antennae target primary processing centers in the median brain, the olfactory lobes. The olfactory lobes are divided into cone-shaped synaptic areas, the olfactory glomeruli where afferents interact with local olfactory interneurons and olfactory projection neurons. The local olfactory interneurons display a large diversity of neurotransmitter phenotypes including biogenic amines and neuropeptides. Furthermore, the malacostracan olfactory glomeruli are regionalized into cap, subcap, and base regions and these compartments are defined by the projection patterns of the afferent olfactory receptor neurons, the local olfactory interneurons, and the olfactory projection neurons. We wanted to know how neurons expressing A-type allatostatins (A-ASTs; synonym dip-allatostatins) integrate into this system, a large family of neuropeptides that share the C-terminal motif -YXFGLamide.

RESULTS

We used an antiserum that was raised against the A-type Diploptera punctata (Dip)-allatostatin I to analyse the distribution of this peptide in the brain of a terrestrial hermit crab, Coenobita clypeatus (Anomura, Coenobitidae). Allatostatin A-like immunoreactivity (ASTir) was widely distributed in the animal's brain, including the visual system, central complex and olfactory system. We focussed our analysis on the central olfactory pathway in which ASTir was abundant in the primary processing centers, the olfactory lobes, and also in the secondary centers, the hemiellipsoid bodies. In the olfactory lobes, we further explored the spatial relationship of olfactory interneurons with ASTir to interneurons that synthesize RFamide-like peptides. We found that these two peptides are present in distinct populations of local olfactory interneurons and that their synaptic fields within the olfactory glomeruli are also mostly distinct.

CONCLUSIONS

We discuss our findings against the background of the known neurotransmitter complexity in the crustacean olfactory pathway and summarize what is now about the neuronal connectivity in the olfactory glomeruli. A-type allatostatins, in addition to their localization in protocerebral brain areas, seem to be involved in modulating the olfactory signal at the level of the deutocerebrum. They contribute to the complex local circuits within the crustacean olfactory glomeruli the connectivity within which as yet is completely unclear. Because the glomeruli of C. clypeatus display a distinct pattern of regionalization, their olfactory systems form an ideal model to explore the functional relevance of glomerular compartments and diversity of local olfactory interneurons for olfactory processing in crustaceans.

Mass spectrometric elucidation of the neuropeptidome of a crustacean neuroendocrine organ

The blue crab Callinectes sapidus has been used as an experimental model organism for the study of regulation of cardiac activity and other physiological processes. Moreover, it is an economically and ecologically important crustacean species. However, there was no previous report on the characterization of its neuropeptidome. To fill in this gap, we employed multiple sample preparation methods including direct tissue profiling, crude tissue extraction and tissue extract fractionation by HPLC to obtain a complete description of the neuropeptidome of C. sapidus. Matrix-assisted laser desorption/ionization (MALDI)-Fourier transform mass spectrometry (FTMS) and MALDI-time-of-flight (TOF)/TOF were utilized initially to obtain a quick snapshot of the neuropeptide profile, and subsequently nanoflow liquid chromatography (nanoLC) coupled with electrospray ionization quadrupole time-of-flight (ESI-Q-TOF) tandem MS analysis of neuropeptide extracts was conducted for de novo sequencing. Simultaneously, the pericardial organ (PO) tissue extract was labeled by a novel N,N-dimethylated leucine (DiLeu) reagent, offering enhanced fragmentation efficiency of peptides. In total, 130 peptide sequences belonging to 11 known neuropeptide families including orcomyotropin, pyrokinin, allatostatin A (AST-A), allatostatin B (AST-B), FMRFamide-like peptides (FLPs), and orcokinin were identified. Among these 130 sequences, 44 are novel peptides and 86 are previously identified. Overall, our results lay the groundwork for future physiological studies of neuropeptides in C. sapidus and other crustaceans.

Distribution and physiological effects of B-type allatostatins (myoinhibitory peptides, MIPs) in the stomatogastric nervous system of the crab Cancer borealis

The crustacean stomatogastric ganglion (STG) is modulated by a large number of amines and neuropeptides that are found in descending pathways from anterior ganglia or reach the STG via the hemolymph. Among these are the allatostatin (AST) B types, also known as myoinhibitory peptides (MIPs). We used mass spectrometry to determine the sequences of nine members of the AST-B family of peptides that were found in the stomatogastric nervous system of the crab Cancer borealis. We raised an antibody against Cancer borealis allatostatin-B1 (CbAST-B1; VPNDWAHFRGSWa) and used it to map the distribution of CbAST-B1-like immunoreactivity (-LI) in the stomatogastric nervous system. CbAST-B1-LI was found in neurons and neuropil in the commissural ganglia (CoGs), in somata in the esophageal ganglion (OG), in fibers in the stomatogastric nerve (stn), and in neuropilar processes in the STG. CbAST-B1-LI was blocked by preincubation with 10(-6) M CbAST-B1 and was partially blocked by lower concentrations. Electrophysiological recordings of the effects of CbAST-B1, CbAST-B2, and CbAST-B3 on the pyloric rhythm of the STG showed that all three peptides inhibited the pyloric rhythm in a state-dependent manner. Specifically, all three peptides at 10(-8) M significantly decreased the frequency of the pyloric rhythm when the initial frequency of the pyloric rhythm was below 0.6 Hz. These data suggest important neuromodulatory roles for the CbAST-B family in the stomatogastric nervous system.

Crustacean neuropeptides

Crustaceans have long been used for peptide research. For example, the process of neurosecretion was first formally demonstrated in the crustacean X-organ-sinus gland system, and the first fully characterized invertebrate neuropeptide was from a shrimp. Moreover, the crustacean stomatogastric and cardiac nervous systems have long served as models for understanding the general principles governing neural circuit functioning, including modulation by peptides. Here, we review the basic biology of crustacean neuropeptides, discuss methodologies currently driving their discovery, provide an overview of the known families, and summarize recent data on their control of physiology and behavior.

Mass spectral analysis of neuropeptide expression and distribution in the nervous system of the lobster Homarus americanus

The lobster Homarus americanus has long served as an important animal model for electrophysiological and behavioral studies. Using this model, we performed a comprehensive investigation of the neuropeptide expression and their localization in the nervous system, which provides useful insights for further understanding of their biological functions. Using nanoLC ESI Q-TOF MS/MS and three types of MALDI instruments, we analyzed the neuropeptide complements in a major neuroendocrine structure, pericardial organ. A total of 57 putative neuropeptides were identified and 18 of them were de novo sequenced. Using direct tissue/extract analysis and bioinformatics software SpecPlot, we charted the global distribution of neuropeptides throughout the nervous system in H. americanus. Furthermore, we also mapped the localization of several neuropeptide families in the brain by high mass resolution and high mass accuracy mass spectrometric imaging (MSI) using a MALDI LTQ Orbitrap mass spectrometer. We have also compared the utility and instrument performance of multiple mass spectrometers for neuropeptide analysis in terms of peptidome coverage, sensitivity, mass spectral resolution and capability for de novo sequencing.

Mass spectrometric characterization and physiological actions of novel crustacean C-type allatostatins

The crustacean stomatogastric ganglion (STG) is modulated by numerous neuropeptides that are released locally in the neuropil or that reach the STG as neurohormones. Using 1,5-diaminonaphthalene (DAN) as a reductive screening matrix for matrix-assisted laser desorption/ionization (MALDI) mass spectrometric profiling of disulfide bond-containing C-type allatostatin peptides followed by electrospray ionization quadrupole time-of-flight (ESI-Q-TOF) tandem mass spectrometric (MS/MS) analysis, we identified and sequenced a novel C-type allatostatin peptide (CbAST-C1), pQIRYHQCYFNPISCF-COOH, present in the pericardial organs of the crab, Cancer borealis. Another C-type allatostatin (CbAST-C2), SYWKQCAFNAVSCFamide, was discovered using the expressed sequence tag (EST) database search strategy in both C. borealis and the lobster, Homarus americanus, and further confirmed with de novo sequencing using ESI-Q-TOF tandem MS. Electrophysiological experiments demonstrated that both CbAST-C1 and CbAST-C2 inhibited the frequency of the pyloric rhythm of the STG, in a state-dependent manner. At 10(-6)M, both peptides were only modestly effective when initial frequencies of the pyloric rhythm were >0.8Hz, but almost completely suppressed the pyloric rhythm when applied to preparations with starting frequencies <0.7Hz. Surprisingly, these state-dependent actions are similar to those of the structurally unrelated allatostatin A and allatostatin B families of peptides.

Mass spectral characterization of peptide transmitters/hormones in the nervous system and neuroendocrine organs of the American lobster Homarus americanus

The American lobster Homarus americanus is a decapod crustacean with both high economic and scientific importance. To facilitate physiological investigations of peptide transmitter/hormone function in this species, we have used matrix-assisted laser desorption/ionization Fourier transform mass spectrometry (MALDI-FTMS), matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and nanoscale liquid chromatography coupled to electrospray ionization quadrupole time-of-flight tandem mass spectrometry (nanoLC-ESI-Q-TOF MS/MS) to elucidate the peptidome present in its nervous system and neuroendocrine organs. In total, 84 peptides were identified, including 27 previously known H. americanus peptides (e.g., VYRKPPFNGSIFamide [Val(1)-SIFamide]), 23 peptides characterized previously from other decapods, but new to the American lobster (e.g., pQTFQYSRGWTNamide [Arg(7)-corazonin]), and 34 new peptides de novo sequenced/detected for the first time in this study. Of particular note are a novel B-type allatostatin (TNWNKFQGSWamide) and several novel FMRFamide-related peptides, including an unsulfated analog of sulfakinin (GGGEYDDYGHLRFamide), two myosuppressins (QDLDHVFLRFamide and pQDLDHVFLRFamide), and a collection of short neuropeptide F isoforms (e.g., DTSTPALRLRFamide and FEPSLRLRFamide). Our data also include the first detection of multiple tachykinin-related peptides in a non-brachyuran decapod, as well as the identification of potential individual-specific variants of orcokinin and orcomyotropin-related peptide. Taken collectively, our results not only expand greatly the number of known H. americanus neuropeptides, but also provide a framework for future studies on the physiological roles played by these molecules in this commercially and scientifically important species.

Mass spectral comparison of the neuropeptide complement of the stomatogastric ganglion and brain in the adult and embryonic lobster, Homarus americanus

Neuropeptides in the stomatogastric ganglion (STG) and the brain of adult and late embryonic Homarus americanus were compared using a multi-faceted mass spectral strategy. Overall, 29 neuropeptides from 10 families were identified in the brain and/or the STG of the lobster. Many of these neuropeptides are reported for the first time in the embryonic lobster. Neuropeptide extraction followed by liquid chromatography coupled to quadrupole-time-of-flight mass spectrometry enabled confident identification of 24 previously characterized peptides in the adult brain and 13 peptides in the embryonic brain. Two novel peptides (QDLDHVFLRFa and GPPSLRLRFa) were de novo sequenced. In addition, a comparison of adult to embryonic brains revealed the presence of an incompletely processed form of Cancer borealis tachykinin-related peptide 1a (CabTRP 1a, APSGFLGMRG) only in the embryonic brain. A comparison of adult to embryonic STGs revealed that QDLDHVFLRFa was present in the embryonic STG but absent in the adult STG, and CabTRP 1a exhibited the opposite trend. Relative quantification of neuropeptides in the STG revealed that three orcokinin family peptides (NFDEIDRSGFGF, NFDEIDRSGFGFV, and NFDEIDRSGFGFN), a B-type allatostatin (STNWSSLRSAWa), and an orcomyotropin-related peptide (FDAFTTGFGHS) exhibited higher signal intensities in the adult relative to the embryonic STG. RFamide (Arg-Phe-amide) family peptide (DTSTPALRLRFa), [Val(1)]SIFamide (VYRKPPFNGSIFa), and orcokinin-related peptide (VYGPRDIANLY) were more intense in the embryonic STG spectra than in the adult STG spectra. Collectively, this study expands our current knowledge of the H. americanus neuropeptidome and highlights some intriguing expression differences that occur during development.

Multiple modulators act on the cardiac ganglion of the crab, Cancer borealis

Neuromodulators can change the output of neural circuits. The crustacean cardiac ganglion (CG) drives the contractions of the heart. The CG is a direct target for neurohormones that are released from the pericardial organs and other neuroendocrine sites. In this study, we have characterized for the first time the physiological actions of the peptides red pigment concentrating hormone (RPCH), Cancer borealis tachykinin-related peptide Ia (CabTRP Ia) and allatostatin III type A (AST-3) on the isolated CG of the crab, Cancer borealis. RPCH and CabTRP Ia excited the CG while AST-3 strongly inhibited its motor output. We also studied the actions of other peptides and small molecule transmitters known to be present in C. borealis. Dopamine, serotonin, proctolin, crustacean cardioactive peptide (CCAP), a number of extended FLRFamide peptides, and cholinergic agonists increased the activity of the CG, GABA inhibited the CG, while other substances had little or no significant effect on the CG motor pattern. These results demonstrate, in one species, that the CG is multiply modulated. We suggest that multiple modulators may be important to regulate and coordinate the activity of the heart and other organs in response to external stimuli or the endogenous physiological state.

Imaging mass spectrometry of neuropeptides in decapod crustacean neuronal tissues

Imaging mass spectrometry (IMS) of neuropeptides in crustacean neuronal tissues was performed on a MALDI-TOF/TOF instrument. Sample preparation protocols were developed for the sensitive detection of these highly complex endogenous signaling molecules. The neuromodulatory complements of the pericardial organ (PO) and brain of the Jonah crab, Cancer borealis, were mapped. Distributions of peptide isoforms belonging to 10 neuropeptide families were investigated using the IMS technique. Often, neuropeptides of high sequence homology were similarly located. However, two RFamide-family peptides and a truncated orcokinin peptide were mapped to locations distinct from other members of their respective families. Over 30 previously sequenced neuropeptides were identified based on mass measurement. For increased confidence of identification, select peptides were fragmented by post-source decay (PSD) and collisional-induced dissociation (CID). Collectively, this organ-level IMS study elucidates the spatial relationships between multiple neuropeptide isoforms of the same family as well as the relative distributions of neuropeptide families.

Mass spectrometric characterization and physiological actions of VPNDWAHFRGSWamide, a novel B type allatostatin in the crab, Cancer borealis

The neural networks in the crustacean stomatogastric ganglion are modulated by neuroactive substances released locally into the neuropil of the stomatogastric ganglion and by circulating hormones released by neuroendocrine structures including the pericardial organs. Using nanoscale liquid chromatography coupled to electrospray ionization quadrupole-time-of-flight mass spectrometry, we have identified and sequenced a novel B type allatostatin (CbAST-B1), VPNDWAHFRGSWamide, present in the pericardial organs of the crabs, Cancer borealis, and Cancer productus. We describe the physiological actions of CbAST-B1 on the pyloric rhythm of the stomatogastric ganglion of the crab, Cancer borealis. CbAST-B1 reduces the pyloric network frequency in a dose-dependent manner. The effect of bath-applied CbAST-B1 depends on the preceding physiological state of the preparation. Surprisingly, despite marked amino-acid sequence dissimilarity between the novel CbAST-B1 and the A type allatostatin family of peptides (AST-A), the physiological effects of CbAST-B1 are similar to those of AST-A.

Neuronal morphology and neuropil structure in the stomatogastric ganglion of the lobster, Homarus americanus

The stomatogastric nervous system (STNS) has long been used as a model system for the study of central pattern generation, neuromodulation, and network dynamics. Anatomical studies of the crustacean stomatogastric ganglion (STG) in different species have mostly been restricted to subsets of neurons and/or general structural features. For the first time, we describe the morphology of all STG neurons belonging to the two circuits that produce the well-described pyloric and gastric rhythms in the lobster, Homarus americanus. Somata sit on the dorsal and lateral surface of the STG and send a single primary neurite into the core of the neuropil, which is mostly made up of larger lower order branches. The perimeter of the neuropil consists mostly of finer higher order branches. Immunohistochemical labeling for synaptic proteins is associated with the small diameter branches. Somata positions are not constant but show preferred locations across individuals. The number of copies is constant for all neuron types except the PY and GM neurons (PY neuron number ranges from 3 to 7, and GM neuron number ranges from 6 to 9). Branch structure is largely nondichotomous, and branches can deviate substantially from cylindrical shape. Diameter changes at branch points can be as large as 20-fold. Clearly, the morphology of a specific neuron type can be quite variable from animal to animal.

The role of allatostatins in juvenile hormone synthesis in insects and crustaceans

Allatostatins are pleiotropic neuropeptides for which one function in insects is the inhibition of juvenile hormone synthesis. Juvenile hormone, an important regulator of development and reproduction in insects, is produced by the corpora allata. Mandibular organs, the crustacean homologs of insect corpora allata, produce precursors of juvenile hormone with putatively similar functions. Three types of allatostatins in insects have been isolated: FGLamides, W(X)(6)Wamides, and PISCFs. All act rapidly and reversibly; however, although these types occur in all groups of insects studied, they act as inhibitors of juvenile hormone production in only some groups. Only the FGLamide-type peptides have been isolated in crustaceans, in which they may function to stimulate production of hormone by the mandibular glands, as occurs in early cockroach embryos. Much remains to be learned in order to understand the role of allatostatins in the modulation of hormone production.

Molecular cloning and characterization of FGLamide allatostatin gene from the prawn, Macrobrachium rosenbergii

Allatostatins are important regulatory neuropeptides that inhibit juvenile hormone (JH) biosynthesis by the corpora allata (CA) in insects. However, to date, the structure and expression of the gene encoding allatostatins have not been reported in any species other than insects. In this study, we used a combination of a semi-nested polymerase chain reaction (PCR) and screening of a central nervous system cDNA library of Macrobrachium rosenbergii to isolate and sequence a cDNA clone (2885 bp) encoding a 701 amino acid FGLamide allatostatin precursor polypeptide. This is the first reported allatostatin gene in crustacean. The deduced precursor was conceptually split into at least 35 FGLamide allatostatins at dibasic cleavage sites (Lys and Lys/Arg), far more than reported for any other known FGLamide allatostatin precursors from insects (13-14 allatostatins). Reverse transcription-polymerase chain reaction (RT-PCR) analysis demonstrated that the gene was expressed in the brain, gut, thoracic and abdominal ganglia, but not in the heart, muscle, ovary, gill, or hepatopancreas. Furthermore, developmentally-dependent expression of the gene was observed in the brain and thoracic ganglia of the prawn by using semi-quantitative RT-PCR analysis.

Expression and bioactivity of allatostatin-like neuropeptides in helminths

Allatostatins are the largest family of known arthropod neuropeptides. To date more than 150 different arthropod type-A allatostatins have been identified and are characterized by the C-terminal signature, (Y/F)XFG(L/I)amide. Using specific allatostatin antisera, positive immunoreactivity has been identified within the central and peripheral nervous systems of the flatworm (platyhelminth) Procerodes littoralis and the roundworm (nematode) Panagrellus redivivus. Comparative analyses of the allatostatin-like immunoreactivity and that of other known helminth neuropeptides (FMRFamide-like peptides [FLPs]) indicate differences in the distribution of these peptide families. Specific differences in neuropeptide distribution have been noted within the pharyngeal innervation of flatworms and in the cephalic papillary neurons of nematodes. In arthropods, type-A allatostatins have functions that include potent myoactivity. In this study, seven members of the allatostatin superfamily induced concentration-dependent contractions of flatworm muscle fibres. Pharmacological studies indicate that these peptides do not interact with muscle-based FLP receptors. The type-A allatostatins, therefore, represent the second family of neuropeptides that induce muscle contraction in flatworms. Although the majority of arthropod type-A allatostatins examined did not affect the somatic body wall muscle or the ovijector of the pig nematode, Ascaris suum, two type-A allatostatins (GDGRLYAFGLamide and DRLYSFGLamide) exhibited significant inhibitory effects on the A. suum ovijector at 10 microM. These data suggest that allatostatin-like peptides and receptors occur in helminths. Further, although arthropod type-A allatostatins display inter-phyla activities, their receptors are less compelling as potential targets for broad-spectrum parasiticides (endectocides) than FLP receptors.

Profiling of neuropeptides released at the stomatogastric ganglion of the crab, Cancer borealis with mass spectrometry

Studies of release under physiological conditions provide more direct data about the identity of neuromodulatory signaling molecules than studies of tissue localization that cannot distinguish between processing precursors and biologically active neuropeptides. We have identified neuropeptides released by electrical stimulation of nerves that contain the axons of the modulatory projection neurons to the stomatogastric ganglion of the crab, Cancer borealis. Preparations were bathed in saline containing a cocktail of peptidase inhibitors to minimize peptide degradation. Both electrical stimulation of projection nerves and depolarization with high K+ saline were used to evoke release. Releasates were desalted and then identified by mass using MALDI-TOF (matrix-assisted laser desorption/ionization-time-of-flight) mass spectrometry. Both previously known and novel peptides were detected. Subsequent to electrical stimulation proctolin, Cancer borealis tachykinin-related peptide (CabTRP), FVNSRYa, carcinustatin-8, allatostatin-3 (AST-3), red pigment concentrating hormone, NRNFLRFa, AST-5, SGFYANRYa, TNRNFLRFa, AST-9, orcomyotropin-related peptide, corazonin, Ala13-orcokinin, and Ser9-Val13-orcokinin were detected. Some of these were also detected after high K+ depolarization. Release was calcium dependent. In summary, we have shown release of the neuropeptides thought to play an important neuromodulatory role in the stomatogastric ganglion, as well as numerous other candidate neuromodulators that remain to be identified.

Regulation of methyl farnesoate production by mandibular organs in the crayfish, Procambarus clarkii: a possible role for allatostatins

Decapod crustaceans do not appear to produce juvenile hormone, but rather its immediate precursor, methyl farnesoate (MF). Both MF and its immediate precursor, farnesoic acid (FA) are produced by the mandibular organs (MO) in crustaceans. The MO are homologous to the insect corpora allata (CA), the site of juvenile hormone biosynthesis. However, the FGLamide allatostatin (ASTs) peptides, of which there are about 60 distinct forms reported from crustaceans, have previously been found to have no effect on MO activity in crustaceans. We have identified by immunocytochemistry the presence of FGLamide-like AST immunoreactivity in neurosecretory cells throughout the CNS as well as in neurohaemal structures such as the sinus gland and pericardial organs. The ASTs are likely delivered to the MO hormonally and/or by local neurohaemal release. Using MO from adult males, we have found wide variability between animals in the in vitro rates of MF and FA biosynthesis. Treatment with Dippu-ASTs has a statistically significant stimulatory effect on MF synthesis, but only in MO that are initially producing MF at lower rates. No effect on FA production was observed, suggesting that the FGLamide ASTs exert their effect on the o-methyl transferase, the enzyme responsible for the conversion of FA to MF.

Mass spectrometric investigation of the neuropeptide complement and release in the pericardial organs of the crab, Cancer borealis

The crustacean stomatogastric ganglion (STG) is modulated by both locally released neuroactive compounds and circulating hormones. This study presents mass spectrometric characterization of the complement of peptide hormones present in one of the major neurosecretory structures, the pericardial organs (POs), and the detection of neurohormones released from the POs. Direct peptide profiling of Cancer borealis PO tissues using matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry (MS) revealed many previously identified peptides, including proctolin, red pigment concentrating hormone (RPCH), crustacean cardioactive peptide (CCAP), several orcokinins, and SDRNFLRFamide. This technique also detected corazonin, a well-known insect hormone, in the POs for the first time. However, most mass spectral peaks did not correspond to previously known peptides. To characterize and identify these novel peptides, we performed MALDI postsource decay (PSD) and electrospray ionization (ESI) MS/MS de novo sequencing of peptides fractionated from PO extracts. We characterized a truncated form of previously identified TNRNFLRFamide, NRNFLRFamide. In addition, we sequenced five other novel peptides sharing a common C-terminus of RYamide from the PO tissue extracts. High K+ depolarization of isolated POs released many peptides present in this tissue, including several of the novel peptides sequenced in the current study.

Dopamine and histamine in the developing stomatogastric system of the lobster Homarus americanus

Dopamine and histamine are neuromodulators found in the adult stomatogastric nervous system (STNS) of several crustacean species. We used antibodies against tyrosine hydroxylase (TH) and histamine to map the distribution and developmental acquisition of the dopamine and histamine neurons in the STNS of the lobster, Homarus americanus. Embryos, larvae, juvenile and adult animals were studied. TH labeling was present in the STNS as early as E80-85 (80-85% of embryonic development). A subset of preparations in embryos, larvae, juveniles, and adults contained 1-5 labeled somata in the stomatogastric ganglion. Histamine staining appeared in the STNS as early as E50. The distribution of both TH and histamine staining remained relatively constant through development. Electrophysiological recordings demonstrated that receptors for both amines are present in the embryo. Bath application of dopamine increased the frequency of the pyloric rhythm in embryos, and evidence for dopaminergic activation of peripherally initiated spiking in motor axons was seen. In embryos and adults, histamine inhibited the motor patterns produced by the stomatogastric ganglion (STG). These data suggest that the dopaminergic and histaminergic systems in H. americanus appear relatively early in development and that the effects of each are largely maintained through development.

Neuropeptides in the crayfish stomatogastric nervous system

Neuropeptides are peptides with profound effects on the nervous system. The function of neuropeptides can be studied in detail in the stomatogastric nervous system (STNS). Neuropeptides are ubiquitously distributed in the STNS and it contains well-studied neural circuits that are strongly modulated by neuropeptides. The STNS controls the movements of the foregut in crustaceans and has been studied intensively in a variety of decapod crustaceans including crayfish. This article reviews our knowledge of neuropeptides in the crayfish STNS. Within crayfish, peptides reach the circuits of the STNS as neurohormones released by neurohaemal organs or by putative neurohemal zones located within the STNS. As transmitters, neuropeptides are present in identified motoneurons, interneurons, and sensory neurons (mainly shown by immunocytochemistry), indicating a multiple role of peptides in the plasticity of neural networks. Neuropeptides are not only present in varicosities within the neuropil of ganglia, but also in varicosities on muscles and within small neuropil patches along nerves. This suggests that the muscles of the stomach are under a more direct modulatory control than previously thought, and that information processing can also occur within nerves. In addition to anatomical studies, biochemical and electrophysiological methods were used. For example, MALDI-TOF MS (matrix-assisted laser desorption ionization time of flight mass spectrometry) revealed the presence of four different peptides of the orcokinin family within a single neuron, and electrophysiological experiments demonstrated that the networks of the STNS are not only under excitatory but also inhibitory peptidergic influence. Comparing the similarities and differences between the STNS of crayfish and that of other decapod crustaceans has already contributed to our knowledge about peptides and will further help to unravel peptide function in the plasticity of neural circuits. For example, the identified neurons in the STNS can be used to study co-transmission because neuropeptides are co-localized with classical transmitters, biogenic amines, or other peptides in these neurons.

Putative neurohemal release zones in the stomatogastric nervous system of decapod crustaceans

The stomatogastric nervous system (STNS) of decapod crustaceans has long been used to study the modulation of small neural circuits. Profiles in the sheath of the nerves and ganglia of the STNS, which contain only dense-core vesicles, have been described in electron microscopical studies (Friend [1976] Cell Tissue Res. 175:369-380; Kilman and Marder [1997] Soc Neurosci Abstr. 23:477; Skiebe and Ganeshina [2000] J Comp Neurol 420:373-397). These profiles resemble those found in neurohemal organs and suggest the presence of neurohemal release zones in the STNS. To map these putative neurohemal release zones, a combination of two antibodies was used in the present study. A synapsin antibody recognizing vesicle proteins of clear vesicles was combined with a synaptotagmin antibody recognizing vesicle proteins of clear and dense-core vesicles. Exclusive synaptotagmin-like staining, therefore, indicated the regions with only dense-core vesicles. Such a staining was found in a mesh in the perineural sheath of nerves in the STNS of all three species investigated. In the crayfish Cherax destructor and the lobster Homarus americanus, the stained mesh was located in the sheath of nerves connecting all four ganglia of the STNS, whereas in the crab Cancer pagurus it was found on different nerves, which are more directly exposed to the hemolymph in this species. Exclusive synaptotagmin-like staining was also found in a putative neurohemal release zone in the sheath of the circumoesophageal connectives and the postoesophageal commissure in C. destructor. These data suggest that an important source of modulation of the networks and the muscles of the stomach is a compartmentalized release of neurohormones from zones in the STNS.

Neuromodulatory complement of the pericardial organs in the embryonic lobster, Homarus americanus

The pericardial organs (POs) are a pair of neurosecretory organs that surround the crustacean heart and release neuromodulators into the hemolymph. In adult crustaceans, the POs are known to contain a wide array of peptide and amine modulators. However, little is known about the modulatory content of POs early in development. We characterize the morphology and modulatory content of pericardial organs in the embryonic lobster, Homarus americanus. The POs are well developed by midway through embryonic (E50) life and contain a wide array of neuromodulatory substances. Immunoreactivities to orcokinin, extended FLRFamide peptides, tyrosine hydroxylase, proctolin, allatostatin, serotonin, Cancer borealis tachykinin-related peptide, cholecystokinin, and crustacean cardioactive peptide are present in the POs by approximately midway through embryonic life. There are two classes of projection patterns to the POs. Immunoreactivities to orcokinin, extended FLRFamide peptides, and tyrosine hydroxylase project solely from the subesophageal ganglion (SEG), whereas the remaining modulators project from the SEG as well as from the thoracic ganglia. Double-labeling experiments with a subset of modulators did not reveal any colocalized peptides in the POs. These results suggest that the POs could be a major source of neuromodulators early in development.

Allatostatins of the tiger prawn, Penaeus monodon (Crustacea: Penaeidea)

More than 40 peptides belonging to the -Y/FXFGL-NH(2) allatostatin superfamily have been isolated and identified from the central nervous system (CNS) of the tiger prawn, Penaeus monodon (Crustacea: Penaeidea). The peptides can be arranged in seven sub-groups according to the variable post-tyrosyl residue represented by Ala, Gly, Ser, Thr, Asn, Asp, and Glu. Two of the residues (Thr and Glu) have not been observed in this position previously in either insects or crustaceans. Also reported for the first time for allatostatins, two of the peptides are N-terminally blocked by a pyroglutamic acid residue. The yields of certain peptides with similar amino acid sequences to each other were, in some instances, very different. As an example, the yield of ANQYTFGL-NH(2) was 2pmol, compared with ASQYTFGL-NH(2), with a yield of 156 pmol. There are several possibilities to account for this. If, as in all species so far investigated, there is a single allatostatin gene in P. monodon, then it would appear that different sub-populations have contributed mutant forms of particular peptides to the extract. Another, less likely possibility is that this species has more than one allatostatin gene, producing a variable array of peptides albeit in different molar ratios. Several peptides were present apparently as a result of the loss of one or more residues at the N-terminus of a larger form, either due to N-terminal degradation or specific post-translational processing. The number of peptides identified exceeds that for any other insect or crustacean species previously investigated. None is identical to any of the 60-70 insect allatostatins so far identified, and only three are common to other crustaceans. Immunohistochemical study of the CNS of P. monodon, with the same antisera as used to monitor the purification, confirms the widespread nature and complexity of allatostatinergic neural pathways in arthropods. Thus, all neuromeres of the brain, and all except one of the ventral cord ganglia, possess allatostatin neurons and extensive areas of allatostatin-innervated neuropile. In addition to the cytological evidence that the allatostatins act as neurotransmitters, associated with tissues as varied as eyes and legs, their presence in neurohemal areas such as the sinus gland and the perineural sheath of the thoracic ganglia suggests a neuroendocrine function. As well as posing a challenge to physiologists assigning specific functions to the allatostatins, their extensive intra-species multiplicity, linked to their inter-species variability, also presents a complex problem to geneticists and evolutionists.

Orcokinin peptides in developing and adult crustacean stomatogastric nervous systems and pericardial organs

The orcokinins are a family of neuropeptides recently isolated from several crustacean species. We found orcokinin-like immunoreactivity in the stomatogastric nervous systems and pericardial organs of three decapod crustacean species, Homarus americanus, Cancer borealis, and Panulirus interruptus. The neuropil of the stomatogastric ganglion was stained in adults of all three species as well as in embryonic and larval H. americanus. In H. americanus, the somata giving rise to this projection were found in the inferior ventricular nerve. Matrix-assisted laser desorption/ionization mass spectrometry mass profiling and sequencing with postsource decay led to the identification of six different orcokinin family peptides, including those previously described in other decapods and two novel shorter peptides. Application of exogenous [Ala(13)]orcokinin to the stomatogastric ganglion of H. americanus resulted in changes in the pyloric rhythm. Specifically, the number of lateral pyloric (LP) neuron spikes/burst decreased, and the phase of firing of the pyloric neurons was altered. Together, these data indicate that the orcokinins are likely to function as modulators of the crustacean stomatogastric ganglion.

Identification of orcokinins in single neurons in the stomatogastric nervous system of the crayfish, Cherax destructor

The orcokinins are a highly conserved family of crustacean peptides that enhance hindgut contractions in the crayfish Orconectes limosus (Stangier et al. [1992] Peptides 13:859-864). By combining immunocytochemical and mass spectrometrical analysis of the stomatogastric nervous system (STNS) in the crayfish Cherax destructor, we show that multiple orcokinins are synthesized in single neurons. Immunocytochemistry demonstrated orcokinin-like immunoreactivity in all four ganglia of the STNS and in the pericardial organs, a major neurohaemal organ. Identified neurons in the STNS were stained, including a pair of modulatory interneurons (inferior ventricular nerve neuron, IVN), a neuron with its cell body in the stomatogastric ganglion that innervates cardiac muscle c6 via the anterior median nerves (AM-c6), and a sensory neuron (anterior gastric receptor neuron). Five orcokinin-related peptides were identified by matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS) post source decay fragmentation in samples of either the stomatogastric ganglion or the pericardial organs. Four of these peptides are identical to peptides derived from the cloned Procambarus clarkii precursor (Yasuda-Kamatani and Yasuda [2000] Gen. Comp. Endocrinol. 118:161-172), including the original [Asn(13)]-orcokinin (NFDEIDRSGFGFN, [M+H](+) = 1,517.7 Da), [Val(13)]-orcokinin ([M+H](+) = 1,502.7 Da), [Thr(8)-His(13)]-orcokinin ([M+H](+) = 1,554.8 Da), and FDAFTTGFGHS ([M+H](+) = 1,186.5 Da). The fifth peptide is a hitherto unknown orcokinin variant: [Ala(8)-Ala(13)]-orcokinin ([M+H](+) = 1,458.7 Da). The masses of all five peptides were also detected in the inferior ventricular nerve of C. destructor, which contains the cell bodies and axons of the IVNs as well as the axons of two other orcokinin-like immunoreactive neurons. In the oesophageal nerve, in which all the orcokinin-like immunoreactivity derives from the IVNs, at least two of the orcokinins were detected, indicating that multiple orcokinins are synthesized in these neurons. Similarly, all four orcokinin masses were detected in the anterior median nerves, in which all the orcokinin-like immunoreactivity derives from the AM-c6 neuron. This study therefore lays the groundwork to investigate the function of the orcokinin peptide family using single identified neurons in a well-studied system.

Neuropeptides are ubiquitous chemical mediators: Using the stomatogastric nervous system as a model system

The stomatogastric nervous system (STNS) controls the movements of the foregut and the oesophagus of decapod crustaceans and is a good example for demonstrating that peptides are ubiquitously distributed chemical mediators in the nervous system. The stomatogastric ganglion (STG), one of the four ganglia of the STNS, contains the most intensively investigated neuronal circuits. The other ganglia, including the two commissural ganglia (CoGs) and the oesophageal ganglion (OG), are thought to be modulatory control centres. Peptides reach the STNS either as neurohormones or are released as transmitters. Peptide neurohormones can be released either from neurohaemal organs or from local neurohaemal release zones located on the surface of nerves and connectives. There were thought to be no peptidergic neurones with cell bodies in the STG itself. However, some have recently been described in adults of four species, in addition to a transient expression of peptides during development in two species. None of these peptidergic neurones has been investigated physiologically, in contrast to peptidergic neurones that project to the STG and have cell bodies in either the CoGs or the OG. It has been shown that neurones containing the same peptide elicit different motor patterns, that the peptide transmitter and the classical transmitter are not necessarily co-released and that the effect of a peptidergic neurone depends on its firing frequency and on which other modulatory neurones are co-active. The activity of modulatory projection neurones can be elicited by sensory neurones, and their activity can depend on the firing frequency of the sensory neurone. In addition to being found within the neuropile of ganglia, peptides are present in neuropile patches located within the nerves of the STNS, suggesting that these nerves can integrate as well as transfer information. Furthermore, sensory neurones and muscles exhibit peptide-like immunoreactivity and are modulated by peptides. Bath-applied peptides elicit peptide-specific motor patterns within the STG by targeting subsets of neurones. This divergence is contrasted by a convergence at the level of currents: five different peptides modulate a single current. Peptides not only induce motor patterns but can also switch the alliance of neurones from one network to another or are able to fuse different networks. In general, peptides are the most abundant group of modulators within the STNS; they are ubiquitously present, indicating that they play multiple roles in the plasticity of neural networks.

Crab stomach pyloric muscles display not only excitatory but inhibitory and neuromodulatory nerve terminals

Movements of the foregut in crustaceans are produced by striated muscles that are innervated by motor neurons in the stomatogastric ganglion (STG). Firing of the STG motor neurons generates excitatory junctional potentials (EJPs) in the stomach muscles. We now provide evidence for the existence of separate inhibitory and neuromodulatory innervations of some pyloric muscles in the foregut of several crabs, Callinectes sapidus, Cancer magister, and Cancer borealis. Electron microscopic examination of several pyloric muscles revealed three distinct types of nerve terminals. Excitatory terminals were readily identified by the spherical shape of their small, clear synaptic vesicles. These terminals also housed a few large dense core vesicles. Inhibitory nerve terminals were recognized by the elliptical shape of their small, clear synaptic vesicles, and contacted the muscles at well-defined synapses equipped with dense bar active zones. Bath application of GABA reduced the amplitudes of EJPs in a pyloric muscle of C. borealis, consistent with the presence of GABAergic inhibitory innervation. Neuromodulatory terminals were characterized by their predominant population of large dense and dense core vesicles. These terminals formed synapses with presynaptic dense bars on the muscle, as well as on the excitatory and inhibitory nerve terminals. The presence of the inhibitory and neuromodulatory terminals creates a functional context for previously described reports of neuromodulatory actions on stomach muscles and suggests that the transfer function from STG motor patterns to pyloric movement may be orchestrated by a complex innervation from sources outside of the STG itself.

A review of the role of neurosecretion in the control of juvenile hormone synthesis: a tribute to Berta Scharrer

In the 1950s, Berta Scharrer predicted that neurosecretions from the brain regulated corpus allatum activity based upon the observation of the change in localization of neurosecretory material in the brain and change in gland activity after severance of nerves between the brain and corpus allatum. Isolation and characterization of neuropeptide regulators of juvenile hormone production by the corpora allata in the late 1980s has confirmed this prediction. Both a stimulatory allatotropin and an inhibitory allatostatin have been isolated from moth brains. Two families of allatostatins, both quite different from each other and that of moths, have been isolated from cockroaches and crickets. The wide distribution of these peptides in the nervous system, in nerves to visceral muscle, in endocrine cells of the midgut and in blood cells, indicate multifunctions in the insects in which they are allatoregulatory. Some of these other functions have been demonstrated in these insects and in insects in which these neuropeptides occur but do not act as corpus allatum regulators. For the latter group, the neuropeptide regulators of the corpora allata have yet to be isolated. The families of neurosecretory regulators will continue to grow.

Allatostatins: a growing family of neuropeptides with structural and functional diversity

The high degree of conservation of the core sequence of the "cockroach-types" of AST and their widespread distribution suggest that they should be considered a ubiquitous family of peptides within the invertebrates, regulating a range of important physiological processes. These functional processes, by either neural or humoral routes of action, include the inhibition of endocrine function, interneuronal functions, neuromodulatory roles, myotropic and myoendocrine roles, and direct action on biosynthetic pathways. The myomodulatory function appears to be conserved through evolutionary time, whereas the JH inhibitory activity appears to be confined to specific orders. This suggests that the myomodulatory role was the more ancestral of these two particular functions. Certainly, further purification and gene cloning as a means to precursor identification and functional analysis will be a prerequisite to understanding the diverse functions of this peptide family.

Development of the peptidergic modulation of a rhythmic pattern generating network

The stomatogastric ganglion (STG) of adult lobsters and crabs receives dense aminergic and peptidergic projections. The neuropeptides are found in sensory neurons and in descending interneurons that modulate the output of the rhythmic central pattern generating networks in the STG. We describe the presence of these peptidergic projections in the adult Homarus americanus, and the effects of some of these neuropeptides on the motor patterns of the adult STG. We describe the developmental acquisition of these neuropeptides during embryonic and larval times and demonstrate that the immature STG networks are already sensitive to a variety of neuromodulators.

The evolution of neuronal circuits underlying species-specific behavior

The nervous system is evolutionarily conservative compared to the peripheral appendages that it controls. However, species-specific behaviors may have arisen from very small changes in neuronal circuits. In particular, changes in neuromodulatory systems may allow multifunctional circuits to produce different sets of behaviors in closely related species. Recently, it was demonstrated that even species differences in complex social behavior may be attributed to a change in the promoter region of a single gene regulating a neuromodulatory action.

Allatostatin modulates skeletal muscle performance in crustaceans through pre- and postsynaptic effects

Allatostatins, originally identified in insects as peptide inhibitors of juvenile hormone biosynthesis, are regarded as potent inhibitory regulators of intestinal muscles in insects and crustaceans. However, accumulating data indicate that allatostatins might also be involved in modulation of skeletal neuromuscular events. We show that most ganglia of two isopod crustaceans (Idotea baltica and I. emarginata) contain pairs of large, allatostatin-immunoreactive motor neurons which supply several segmental muscles. Among them are the dorsal extensor muscles, of which some fibres receive immunoreactive, varicose innervation. We demonstrate, on identified muscle fibres, that allatostatin exerts a twofold inhibitory effect: it reduces contractions of single voltage-clamped fibres, and it decreases the amplitude of evoked excitatory junctional currents recorded from individual release boutons. No change in excitation-contraction threshold or in passive membrane parameters was observed. As the amplitude of miniature currents generated by spontaneously released single transmitter quanta was not changed, the inhibitory effect of the peptide on junctional currents must be of presynaptic origin. Supportive results were obtained on leg muscles of the crab Eriphia spinifrons, where allatostatin decreased evoked synaptic currents by reducing the mean number of transmitter quanta released by presynaptic depolarization without affecting the amplitudes of currents generated by single quanta. This effect of allatostatin was similar for two functionally different neurons, the slow and the fast closer excitor. The data show that allatostatin occurs in identified motor neurons of Idotea and exerts complementary pre- and postsynaptic modulatory effects which reduce muscle responses. Thus, allatostatin counteracts the effects of another neuropeptide, proctolin, which is also present in Idotea and causes potentiating effects on the same muscle fibres.

Sequential developmental acquisition of cotransmitters in identified sensory neurons of the stomatogastric nervous system of the lobsters, Homarus americanus and Homarus gammarus

We studied the developmental acquisition of three of the cotransmitters found in the gastropyloric receptor (GPR) neurons of the stomatogastric nervous systems of the lobsters Homarus americanus and Homarus gammarus. By using wholemount immunocytochemistry and confocal microscopy, we examined the distribution of serotonin-like, allatostatin-like, and FLRF(NH2)-like immunoreactivities within the stomatogastric nervous system of embryonic, larval, juvenile, and adult animals. The GPR neurons are peripheral sensory neurons that send proprioceptive information to the stomatogastric and commissural ganglia. In H. americanus, GPR neurons of the adult contain serotonin-like, allatostatin-like, and Phe-Leu-Arg-Phe-amide (FLRF(NH2))-like immunoreactivities. In the stomatogastric ganglion (STG) of the adult H. americanus and H. gammarus, all of the serotonin-like and allatostatin-like immunoreactivity colocalizes in neuropil processes that are derived exclusively from ramifications of the GPR neurons. In both species, FLRF(NH2)-like immunoreactivity was detected in the STG neuropil by 50% of embryonic development (E50). Allatostatin-like immunoreactivity was visible first in the STG at approximately E70-E80. In contrast, serotonin staining was not clearly visible until larval stage I (LI) in H. gammarus and until LII or LIII in H. americanus. These data indicate that there is a sequential acquisition of the cotransmitters of the GPR neurons.

Structure, distribution, and biological activity of novel members of the allatostatin family in the crayfish Orconectes limosus

In the central and peripheral nervous system of the crayfish, Orconectes limosus, neuropeptides immunoreactive to an antiserum against allatostatin I (= Dipstatin 7) of the cockroach Diploptera punctata have been detected by immunocytochemistry and a sensitive enzyme immunoassay. Abundant immunoreactivity occurs throughout the central nervous system in distinct interneurons and neurosecretory cells. The latter have terminals in well-known neurohemal organs, such as the sinus gland, the pericardial organs, and the perineural sheath of the ventral nerve cord. Nervous tissue extracts were separated by reverse-phase high-performance liquid chromatography and fractions were monitored in the enzyme immunoassay. Three of several immunopositive fractions have been purified and identified by mass spectroscopy and microsequencing as AGPYAFGL-NH2, SAGPYAFGL-NH2, and PRVYGFGL-NH2. The first peptide is identical to carcinustatin 8 previously identified in the crab Carcinus maenas. The others are novel and are designated orcostatin I and orcostatin II, respectively. All three peptides exert dramatic inhibitory effects on contractions of the crayfish hindgut. Carcinustatin 8 also inhibits induced contractions of the cockroach hindgut. Furthermore, this peptide reduces the cycle frequency of the pyloric rhythms generated by the stomatogastric nervous system of two decapod species in vitro. These crayfish allatostatin-like peptides are the first native crustacean peptides with demonstrated inhibitory actions on hindgut muscles and the pyloric rhythm of the stomatogastric ganglion.