Two FMRFamide-like peptides from the free-living nematode Panagrellus redivivus

Mass Spectrometry Quantification, Localization, and Discovery of Feeding-Related Neuropeptides in Cancer borealis

The crab Cancer borealis nervous system is an important model for understanding neural circuit dynamics and modulation, but the identity of neuromodulatory substances and their influence on circuit dynamics in this system remains incomplete, particularly with respect to behavioral state-dependent modulation. Therefore, we used a multifaceted mass spectrometry (MS) method to identify neuropeptides that differentiate the unfed and fed states. Duplex stable isotope labeling revealed that the abundance of 80 of 278 identified neuropeptides was distinct in ganglia and/or neurohemal tissue from fed vs unfed animals. MS imaging revealed that an additional 7 and 11 neuropeptides exhibited altered spatial distributions in the brain and the neuroendocrine pericardial organs (POs), respectively, during these two feeding states. Furthermore, de novo sequencing yielded 69 newly identified putative neuropeptides that may influence feeding state-related neuromodulation. Two of these latter neuropeptides were determined to be upregulated in PO tissue from fed crabs, and one of these two peptides influenced heartbeat in ex vivo preparations. Overall, the results presented here identify a cohort of neuropeptides that are poised to influence feeding-related behaviors, providing valuable opportunities for future functional studies.

The FMRFamide-Like Peptide Family in Nematodes

In the three decades since the FMRFamide peptide was isolated from the mollusk Macrocallista nimbosa, structurally similar peptides sharing a C-terminal RFamide motif have been identified across the animal kingdom. FMRFamide-like peptides (FLPs) represent the largest known family of neuropeptides in invertebrates. In the phylum Nematoda, at least 32 flp-genes are classified, making the FLP system of nematodes unusually complex. The diversity of the nematode FLP complement is most extensively mapped in Caenorhabditis elegans, where over 70 FLPs have been predicted. FLPs have shown to be expressed in the majority of the 302 C. elegans neurons including interneurons, sensory neurons, and motor neurons. The vast expression of FLPs is reflected in the broad functional repertoire of nematode FLP signaling, including neuroendocrine and neuromodulatory effects on locomotory activity, reproduction, feeding, and behavior. In contrast to the many identified nematode FLPs, only few peptides have been assigned a receptor and there is the need to clarify the pathway components and working mechanisms of the FLP signaling network. Here, we review the diversity, distribution, and functions of FLPs in nematodes.

Three independent techniques localize expression of transcript afp-11 and its bioactive peptide products to the paired AVK neurons in Ascaris suum: in situ hybridization, immunocytochemistry, and single cell mass spectrometry

We utilized three independent techniques, immunocytochemistry (ICC), single cell mass spectrometry (MS), and in situ hybridization (ISH), to localize neuropeptides and their transcripts in the nervous system of the nematode Ascaris suum . AF11 (SDIGISEPNFLRFa) is an endogenous peptide with potent paralytic effects on A. suum locomotory behavior. A highly specific antibody to AF11 showed robust immunostaining for AF11 in the paired AVK neurons in the ventral ganglion. We traced the processes from the AVK neurons into the ventral nerve cord and identified them as ventral cord interneurons. MS and MS/MS of single dissected AVKs detected AF11, two previously characterized peptides (AF25 and AF26), seven novel sequence-related peptides, including several sharing a PNFLRFamide C-terminus, and peptide NY, a peptide with an unrelated sequence. Also present in a subset of AVKs was AF2, a peptide encoded by the afp-4 transcript. By sequencing the afp-11 transcript, we discovered that it encodes AF11, all the AF11-related peptides detected by MS in AVK, and peptide NY. ISH detected the afp-11 transcript in AVK neurons, consistent with other techniques. ISH did not detect afp-11 in the ALA neuron, although both ICC and MS found AF11 in ca. 30% of ALAs. All 10 AF11-related peptides reduced acetylcholine-induced muscle contraction, but they differed in their rate of reversal of inhibition after removal of the peptide.

Neuropeptide gene families in Caenorhabditis elegans

Neuropeptides are short sequences ofamino acids that function in all multicellular organisms to communicate information between cells. The first sequence ofa neuropeptide was reported in 1970' and the number of identified neuropeptides remained relatively small until the 1990s when the DNA sequence of multiple genomes revealed treasure troves ofinformation. Byblasting away at the genome, gene families, the sizes ofwhich were previously unknown, could now be determined. This information has led to an exponential increase in the number of putative neuropeptides and their respective gene families. The molecular biology age greatly benefited the neuropeptide field in the nematode Caenorhabditis elegans. Its genome was among the first to be sequenced and this allowed us the opportunity to screen the genome for neuropeptide genes. Initially, the screeningwas slow, as the Genefinder and BLAST programs had difficulty identifying small genes and peptides. However, as the bioinformatics programs improved, the extent of the neuropeptide gene families in C. elegans gradually emerged.

Mapping neuropeptide expression by mass spectrometry in single dissected identified neurons from the dorsal ganglion of the nematode Ascaris suum

We have developed a method for dissecting single neurons from the nematode Ascaris suum, in order to determine their peptide content by mass spectrometry (MS). In this paper, we use MALDI-TOF MS and tandem MS to enumerate and sequence the peptides present in the two neurons, ALA and RID, that comprise the dorsal ganglion. We compare the peptide content determined by MS with the results of immunocytochemistry and in situ hybridization of previously isolated peptides AF2, AF8 and 6 peptides encoded by the afp-1 transcript. We find complete agreement between the three techniques, which validates single neuron MS as a method for peptide localization. We also discovered and sequenced 6 novel peptides in the ALA neuron. Cloning of cDNAs and database searching of Genomic Survey Sequences showed that transcript afp-12 encodes peptide AF36 (VPSAADMMIRFamide), and afp-13 encodes AF19 (AEGLSSPLIRFamide), AF34 (DSKLMDPLIRFamide), AF35 (DPQQRIVTDETVLRFamide), and 3 non-amidated peptides (PepTT, PepTL, and PepGE). We have found no similarities with reported peptide expression in the nematode Caenorhabditis elegans. This method promises to be ideally suited for determining the peptide content of each of the 298 neurons in the nervous system of this nematode.

A review of FMRFamide- and RFamide-like peptides in metazoa

Neuropeptides are a diverse class of signalling molecules that are widely employed as neurotransmitters and neuromodulators in animals, both invertebrate and vertebrate. However, despite their fundamental importance to animal physiology and behaviour, they are much less well understood than the small molecule neurotransmitters. The neuropeptides are classified into families according to similarities in their peptide sequence; and on this basis, the FMRFamide and RFamide-like peptides, first discovered in molluscs, are an example of a family that is conserved throughout the animal phyla. In this review, the literature on these neuropeptides has been consolidated with a particular emphasis on allowing a comparison between data sets in phyla as diverse as coelenterates and mammals. The intention is that this focus on the structure and functional aspects of FMRFamide and RFamide-like neuropeptides will inform understanding of conserved principles and distinct properties of signalling across the animal phyla.

Effects of SDPNFLRF-amide (PF1) on voltage-activated currents in Ascaris suum muscle

Helminth infections are of significant concern in veterinary and human medicine. The drugs available for chemotherapy are limited in number and the extensive use of these drugs has led to the development of resistance in parasites of animals and humans (Geerts and Gryseels, 2000; Kaplan, 2004; Osei-Atweneboana et al., 2007). The cyclooctadepsipeptide, emodepside, belongs to a new class of anthelmintic that has been released for animal use in recent years. Emodepside has been proposed to mimic the effects of the neuropeptide PF1 on membrane hyperpolarization and membrane conductance (Willson et al., 2003). We investigated the effects of PF1 on voltage-activated currents in Ascaris suum muscle cells. The whole cell voltage-clamp technique was employed to study these currents. Here we report two types of voltage-activated inward calcium currents: transient peak (I(peak)) and a steady-state (I(ss)). We found that 1microM PF1 inhibited the two calcium currents. The I(peak) decreased from -146nA to -99nA (P=0.0007) and the I(ss) decreased from -45nA to -12nA (P=0.002). We also found that PF1 in the presence of calcium increased the voltage-activated outward potassium current (from 521nA to 628nA (P=0.004)). The effect on the potassium current was abolished when calcium was removed and replaced with cobalt; it was also reduced at a higher concentration of PF1 (10microM). These studies demonstrate a mechanism by which PF1 decreases the excitability of the neuromuscular system by modulating calcium currents in nematodes. PF1 inhibits voltage-activated calcium currents and potentiates the voltage-activated calcium-dependent potassium current. The effect on a calcium-activated-potassium channel appears to be common to both PF1 and emodepside (Guest et al., 2007). It will be of interest to investigate the actions of emodepside on calcium currents to further elucidate the mechanism of action.

Neuropeptides

The role of neuropeptides in modulating behavior is slowly being elucidated. With the sequencing of the C. elegans genome, the extent of the neuropeptide genes in C. elegans can be determined. To date, 113 neuropeptide genes encoding over 250 distinct neuropeptides have been identified. Of these, 40 genes encode insulin-like peptides, 31 genes encode FMRFamide-related peptides, and 42 genes encode non-insulin, non-FMRFamide-related neuropeptides. As in other systems, C. elegans neuropeptides are derived from precursor molecules that must be post-translationally processed to yield the active peptides. These precursor molecules contain a single peptide, multiple copies of a single peptide, multiple distinct peptides, or any combination thereof. The neuropeptide genes are expressed extensively throughout the nervous system, including in sensory, motor, and interneurons. In addition, some of the genes are also expressed in non-neuronal tissues, such as the somatic gonad, intestine, and vulval hypodermis. To address the effects of neuropeptides on C. elegans behavior, animals in which the different neuropeptide genes are inactivated or overexpressed are being isolated. In a complementary approach the receptors to which the neuropeptides bind are also being identified and examined. Among the knockout animals analyzed thus far, defects in locomotion, dauer formation, egg laying, ethanol response, and social behavior have been reported. These data suggest that neuropeptides have a modulatory role in many, if not all, behaviors in C. elegans.

Stage-specific gene expression in Teladorsagia circumcincta (Nematoda: Strongylida) infective larvae and early parasitic stages

Suppression subtractive hybridisation was used to enrich genes expressed in a stage-specific manner in infective, exsheathed L3s (xL3) versus early L4s of the ovine nematode, Teladorsagia circumcincta prior to gene expression profiling by microarray. The 769 cDNA sequences obtained from the xL3-enriched library contained 361 unique sequences, with 292 expressed sequence tags (ESTs) being represented once ("singletons") and 69 sequences which were represented more than once (overlapping and non-overlapping "contigs"). The L4-enriched EST dataset contained 472 unique sequences, with 314 singletons and 158 contigs. Of these 833 sequences, 85% of the xL3 sequences and 86% of the L4 sequences exhibited homology to known genes or ESTs derived from other species of nematode. Quantitative differential expression (P<0.05) was demonstrated for 563 (68%) of the ESTs by microarray. Within the L3-specific dataset, more than 30% of the transcripts represented the enzyme, guanosine-5'-triphosphate (GTP)-cyclohydrolase, which is the first and rate-limiting enzyme of the tetrahydrobiopterin synthesis pathway and may be involved in critical elements of larval development. In L4s, proteolytic enzymes were highly up-regulated, as were collagens and a number of previously characterised secretory proteins, reflecting the rapid growth of these larvae in abomasal glands. Nucleotide sequence data reported in this paper are available in the EMBL, GenBank and DDJB databases under accession numbers AM 743198-AM 744942.

Inter-phyla studies on neuropeptides: the potential for broad-spectrum anthelmintic and/or endectocide discovery

Flatworm, nematode and arthropod parasites have proven their ability to develop resistance to currently available chemotherapeutics. The heavy reliance on chemotherapy and the ability of target species to develop resistance has prompted the search for novel drug targets. In view of its importance to parasite/pest survival, the neuromusculature of parasitic helminths and pest arthropod species remains an attractive target for the discovery of novel endectocide targets. Exploitation of the neuropeptidergic system in helminths and arthropods has been hampered by a limited understanding of the functional roles of individual peptides and the structure of endogenous targets, such as receptors. Basic research into these systems has the potential to facilitate target characterization and its offshoots (screen development and drug identification). Of particular interest to parasitologists is the fact that selected neuropeptide families are common to metazoan pest species (nematodes, platyhelminths and arthropods) and fulfil specific roles in the modulation of muscle function in each of the three phyla. This article reviews the inter-phyla activity of two peptide families, the FMRFamide-like peptides and allatostatins, on motor function in helminths and arthropods and discusses the potential of neuropeptide signalling as a target system that could uncover novel endectocidal agents.

The ever-expanding neuropeptide gene families in the nematode Caenorhabditis elegans

Neuropeptides act as chemical signals in the nervous system to modulate behaviour. With the ongoing EST projects and DNA sequence determination of different genomes, the identification of neuropeptide genes has been made easier. Despite the relatively 'simple' repertoire of behaviours in the nematode Caenorhabditis elegans, this worm contains a surprisingly large and diverse set of neuropeptide genes. At least 109 genes encoding over 250 potential neuropeptides have been identified in C. elegans; all genes are likely to be expressed and many, if not all, of the predicted peptides are produced. The predicted peptides include: 38 insulin-like peptides, several of which are involved in development and reproductive growth, and over 70 FMRFamide-related peptides, some of which are involved in locomotion, reproduction, and social behaviour. Many of the C. elegans peptides are identical or highly similar to those isolated or predicted in parasitic nematodes, such as Ascaris suum, Haemonchus contortus, Ancylostoma caninum, Heterodera glycines and Meloidogyne arenaria, suggesting that the function of these peptides is similar across species. The challenge for the future is to determine the function of all the genes and individual peptides and to identify the receptors through which the peptides signal.

Role of a FMRFamide-like family of neuropeptides in the pharyngeal nervous system of Caenorhabditis elegans

The nervous system of C. elegans has a remarkable abundance of flp genes encoding FMRFamide-like (FLP) neuropeptides. To provide insight into the physiological relevance of this neuropeptide diversity, we have tested more than 30 FLPs (encoded by 23 flps) for bioactivity on C. elegans pharynx. Eleven flp genes encode peptides that inhibit pharyngeal activity, while eight flp genes encode peptides that are excitatory. Three potent peptides (inhibitory, FLP-13A, APEASPFIRFamide; excitatory, FLP-17A, KSAFVRFamide; excitatory, FLP-17B, KSQYIRFamide) are encoded by flp genes, which, according to reporter gene constructs, are expressed in pharyngeal motoneurons. Thus, they may act through receptors localized on the pharyngeal muscle. The two other potent peptides, FLP-8 (excitatory AF1, KNEFIRFamide,) and FLP-11A (inhibitory, AMRNALVRFamide), appear to be expressed in extrapharyngeal neurons and are therefore likely to act either indirectly or as neurohormones. Intriguingly, a single neuron can express peptides that have potent but opposing biological activity in the pharynx. Only five flp genes encode neuropeptides that have no observable effect on the pharynx, but none of these have shown reporter gene expression in the pharyngeal nervous system. To examine the roles of multiple peptides produced from single precursors, a comparison was made between the bioactivity of different neuropeptides for five flp genes (flp-3, flp-13, flp-14, flp-17, and flp-18). For all but one gene (flp-14), the effects of peptides encoded by the same gene were similar. Overall, this study demonstrates the impressive neurochemical complexity of the simple circuit that regulates feeding in the nematode, C. elegans.

Changes in FaRP-like peptide levels during development of eggs from the plant-parasitic cyst nematode, Heterodera glycines

The plant-parasitic cyst nematode Heterodera glycines requires a host plant to complete its life cycle, which involves hatching of infective juveniles that parasitize through root entry. A laboratory population of H. glycines grown on soybean, Glycine max, undergoes a sharp increase in maturity between 5 and 6 weeks in culture, as measured by the proportion of eggs containing well developed pre-hatch juveniles (late development eggs) versus eggs without visible juveniles (early development eggs). The median percent of eggs classified as late development, representing all samples taken from 4 to 7 weeks in culture, was 61%. For all samples taken up to 5 weeks, 80% scored below the median. In samples taken after 5 weeks, 15% scored below the median. This shift in population maturity was accompanied by a significant increase (P < 0.01) in the number of hatched juveniles present in each sample. There was also a significant increase (P < 0.02) in amount of FaRP-like peptide detected by specific ELISA. Total FaRP levels increased from 0.18 +/- 0.07 fMol FLRFamide equivalents per ng protein in early development eggs to 0.40 +/- 0.17 in late development eggs. The level remained high in hatched juveniles. HPLC/ELISA detected as many as nine potential FaRPs in H. glycines, two of which were specifically increased (P < 0.005) in hatched juveniles. The association of FaRPs with maturing eggs and the possible involvement of these neuropeptides with juvenile hatching and motility are discussed.

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.

Discovering neuropeptides in Caenorhabditis elegans by two dimensional liquid chromatography and mass spectrometry

Completion of the Caenorhabditis elegans genome sequencing project in 1998 has provided more insight into the complexity of nematode neuropeptide signaling. Several C. elegans neuropeptide precursor genes, coding for approximately 250 peptides, have been predicted from the genomic database. One can, however, not deduce whether all these peptides are actually expressed, nor is it possible to predict all post-translational modifications. Using two dimensional nanoscale liquid chromatography combined with tandem mass spectrometry and database mining, we analyzed a mixed stage C. elegans extract. This peptidomic setup yielded 21 peptides derived from formerly predicted neuropeptide-like protein (NLP) precursors and 28 predicted FMRFamide-related peptides. In addition, we were able to sequence 11 entirely novel peptides derived from nine peptide precursors that were not predicted or identified in any way previously. Some of the identified peptides display profound sequence similarities with neuropeptides from other invertebrates, indicating that these peptides have a long evolutionary history.

Nematode neuropeptides: Localization, isolation and functions

Historically, peptidergic substances (in the form of neurosecretions) were linked to moulting in nematodes. More recently, there has been a renewal of interest in nematode neurobiology, initially triggered by studies demonstrating the localization of peptide immunoreactivities to the nervous system. Here, David Brownlee, Ian Fairweather, Lindy Holden-Dye and Robert Walker will review progress on the isolation of nematode neuropeptides and efforts to unravel their physiological actions and inactivation mechanisms. Future avenues for research are suggested and the potential exploitation of peptidergic pathways in future therapeutic strategies highlighted.

Expression and regulation of an FMRFamide-related neuropeptide gene family in Caenorhabditis elegans

FMRFamide (Phe-Met-Arg-Phe-NH2) and related peptides (FaRPs) have been found throughout the animal kingdom, where they are involved in many behaviors. We previously identified 22 genes comprising the flp gene family that encodes FaRPs in Caenorhabditis elegans; in this paper we report the identification of another flp gene, flp-23. As a first step toward determining their functional roles in C. elegans, we examined the cell-specific expression pattern of the flp gene family. Of the 19 flp genes examined, each gene is expressed in a distinct set of cells; these cells include interneurons, motor neurons, and sensory neurons that are involved in multiple behaviors, as well as supporting cells, muscle cells, and epidermal cells. Several flp genes show sex-specific expression patterns. Furthermore, we find that expression of two flp genes changes in response to the developmental state of the animal. Many neurons express multiple flp genes. To investigate how flp genes are regulated in different neuronal subtypes, we examined flp expression in a small, well-defined subset of neurons, the mechanosensory neurons. Mutations in the unc-86 and mec-3 genes, which are necessary for the production and differentiation of the mechanosensory neurons, result in the complete loss of flp-4, flp-8, and flp-20 expression in mechanosensory neurons. Collectively, these data indicate that members of the flp gene family are likely to influence multiple behaviors and that their regulation can be dependent on the developmental state of the organism.

The ovijector of Ascaris suum: multiple response types revealed by Caenorhabditis elegans FMRFamide-related peptides

Caenorhabditis elegans possesses 22 FMRFamide-like peptide (flp) genes predicted to encode 60 different FMRFamide-related peptides with a range of C-terminal signatures. Peptides from five flp genes (1, 6, 8, 9 and 14) are known to modulate the ovijector of Ascaris suum in vitro. This study examines the physiological effects of peptides from the remaining 17 flp genes such that the variety of FMRFamide-related peptide-induced ovijector response types can be delineated. Five categories of response were identified according to the pattern of changes in contractile behaviour and baseline tension. Peptides encoded on 16 flp genes (1, 2, 3, 4, 6, 7, 9, 10, 11, 12, 13, 14, 15, 16, 17 and 20) had qualitatively similar inhibitory (response type 1) actions, with the lowest activity thresholds (1 nM) recorded for peptides with FIRFamide or FLRFamide C-terminal signatures. Peptides encoded on four flp genes (2, 18, 19 and 21), and on the A. suum afp-1 gene, had excitatory actions on the ovijector (response type 2), with PGVLRFamides having the lowest activity threshold (1 nM). An flp-2 peptide (LRGEPIRFamide) induced a transient contraction of the ovijector (activity threshold, 10nM) that was designated response type 3. Response type 4 comprised a transient contraction followed by an extended period of inactivity and was observed with peptides encoded on flp-5 (AGAKFIRFamide, APKPKFIRFamide), flp-8 (KNEFIRFamide) and flp-22 (SPSAKWMRFamide). SPSAKWMRFamide was the most potent peptide tested with an activity threshold of 0.1 nM. A single peptide (AMRNALVRFamide; activity threshold 0.1 microM), encoded on flp-11, induced response type 5, a shortening of the ovijector coupled with an increase in contraction frequency. Although most flp genes encode structurally related peptides that trigger one of the five ovijector response types, flp-2 and flp-11 co-encode FMRFamide-related peptides that induce distinct responses. Within the ovijector of A. suum FaRPs play a complex role involving at least five receptor subtypes or signalling pathways.

Structure-activity relationships of an inhibitory nematode FMRFamide-related peptide, SDPNFLRFamide (PF1), on Ascaris suum muscle

FMRFamide-related peptides are widespread among the Nematoda. Among them is a family of extended PNFLRFamide peptides encoded on the flp-1 peptide precursor gene in Caenorhabditis elegans. The most studied peptide from this series is SDPNFLRFamide (PF1). Each residue in this peptide was sequentially substituted with either alanine or the corresponding d-isomer of the native amino acid in order to define structure-function relationships in this peptide using an Ascaris suum muscle tension assay. In general, substitutions in the N-terminal tetrapeptide had only minor consequences for efficacy, while substitutions in the C-terminal tetrapeptide caused more dramatic changes. Such substitutions typically markedly diminished efficacy, but d-isomer substitution at either position 5 (Phe) or 6 (Leu) converted the inhibitory activity of the prototype into excitation. In addition, it has been evident that KPNFLRFamide and SDPNFLRFamide, though encoded on flp-1 and sharing a PNFLRFamide hexapeptide, act through different receptors. KPNFLRFamide directly gates a chloride channel in A. suum muscle cells, while SDPNFLRFamide acts through nitric oxide synthase to open K+ channels in the same tissue. The use of K+ channel blockers and nitric oxide synthase inhibitors in electrophysiological experiments employing A. suum muscle membranes allowed the unambiguous conclusion that the N-terminal lysine is absolutely required for activation of the chloride channel and excludes interaction with the SDPNFLRFamide receptor.

Isolation, characterization, and distribution of a novel neuropeptide, Rana RFamide (R-RFa), in the brain of the European green frog Rana esculenta

A novel neuropeptide of the RFamide peptide family was isolated in pure form from a frog (Rana esculenta) brain extract by using reversed-phase high performance liquid chromatography in combination with a radioimmunoassay for mammalian neuropeptide FF (NPFF). The primary structure of the peptide was established as Ser-Leu-Lys- Pro-Ala-Ala-Asn-Leu-Pro-Leu- Arg-Phe-NH(2). The sequence of this neuropeptide, designated Rana RFamide (R-RFa), exhibits substantial similarities with those of avian LPLRFamide, gonadotropin-inhibitory hormone, and human RFRP-1. The distribution of R-RFa was investigated in the frog central nervous system by using an antiserum directed against bovine NPFF. In the brain, immunoreactive cell bodies were primarily located in the hypothalamus, i.e., the anterior preoptic area, the suprachiasmatic nucleus, and the dorsal and ventral hypothalamic nuclei. The most abundant population of R-RFa-containing neurons was found in the periependymal region of the suprachiasmatic nucleus. R-RFa- containing fibers were widely distributed throughout the brain from the olfactory bulb to the brainstem, and were particularly abundant in the external layer of the median eminence. In the spinal cord, scattered immunoreactive neurons were found in the gray matter. R-RFa-positive processes were found in all regions of the spinal cord, but they were more abundant in the dorsal horn. This study provides the first characterization of a member of the RFamide peptide family in amphibians. The occurrence of this novel neuropeptide in the hypothalamus and median eminence and in the dorsal region of the spinal cord suggests that, in frog, R-RFa may exert neuroendocrine activities and/or may be involved in the transmission of nociceptive stimuli.

Isolation and preliminary biological assessment of AADGAPLIRFamide and SVPGVLRFamide from Caenorhabditis elegans

To date, 9 FMRFamide-related peptides (FaRPs) have been structurally characterised from Caenorhabditis elegans. Radioimmunometrical screening of an ethanolic extract of C. elegans revealed the presence of two additional FaRPs that were purified by reverse-phase HPLC and subjected to Edman degradation analysis and gas-phase sequencing. Unequivocal primary structures for the two FaRPs were determined as Ala-Ala-Asp-Gly-Ala-Pro-Leu-Ile-Arg-Phe-NH(2) and Ser-Val-Pro-Gly-Val-Leu-Arg-Phe-NH(2). Using MALDI-TOF mass spectrometry, the molecular masses of the peptides were found to be 1032 Da (MH) and 875 Da (MH)(+), respectively. Two copies of AADGAPLIRFamide are predicted to be encoded on the precursor gene termed flp-13, while one copy of SVPGVLRFamide is located on flp-18. Synthetic replicates of the peptides were tested on Ascaris suum somatic muscle to assess bioactivity. ADDGAPLIRFamide had inhibitory effects on A. suum muscle strips, which occurred over a range of concentrations from a threshold for activity of 10 nM to 10 microM. SVPGVLRFamide was excitatory on A. suum somatic musculature from a threshold concentration for activity of 1 nM to 10 microM. The inhibitory and excitatory effects of AADGAPLIRFamide and SVPGVLRFamide, respectively, were the same for dorsal and ventral muscle strips as well as innervated and denervated preparations, suggesting that these physiological effects are not nerve cord dependent. Addition of ADDGAPLIRFamide (10 microM) to muscle strips preincubated in high-K(+) and -Ca(2+)-free medium resulted in a normal inhibitory response. Peptide addition to muscle strips preincubated in Cl(-)-free medium showed no inhibitory response, suggesting that the inhibitory response of the peptide may be chloride mediated. A normal excitatory response was noted following the addition of 10 microM SVPGVLRFamide to muscle strips preincubated in high-K(+), Ca(2+)- and Cl(-)-free media.

The range and biological activity of FMRFamide-related peptides and classical neurotransmitters in nematodes

Nematodes include both major parasites of humans, livestock and plants in addition to free-living species such as Caenorhabditis elegans. The nematode nervous system (especially in C. elegans) is exceptionally well defined in terms of the number, location and projections of the small number of neurons in the nervous system and their integration into circuits involved in regulatory behaviours vital to their survival. This review will summarize what is known about the biological activity of neurotransmitters in nematodes: the biosynthetic pathways and genes involved, their receptors, inactivation mechanisms and secondary messenger signalling systems. It will cover the 'classical' transmitters, such as acetylcholine (ACh), GABA, glutamate, serotonin, dopamine, octopamine, noradrenaline and nitric oxide. The localization of peptides throughout the nematode nervous system is summarized, in addition to the isolation of nematode neuropeptides by both traditional biochemical techniques and more modern genetic means. The major contribution of the completion of the C. elegans genome-sequencing program is highlighted throughout. Efforts to unravel neurotransmitter action in various physiological actions such as locomotion, feeding and reproduction are detailed as well as the various inactivation mechanisms for the current complement of nematode transmitters.

Pharmacology of FMRFamide-related peptides in helminths

Nervous systems of helminths are highly peptidergic. Species in the phylum Nematoda (roundworms) possess at least 50 FMRFamide-related peptides (FaRPs), with more yet to be identified. To date, few non-FaRP neuropeptides have been identified in these organisms, though evidence suggests that other families are present. FaRPergic systems have important functions in nematode neuromuscular control. In contrast, species in the phylum Platyhelminthes (flatworms) apparently utilize fewer FaRPs than do nematodes; those species examined possess one or two FaRPs. Other neuropeptides, such as neuropeptide F (NPF), play key roles in flatworm physiology. Although progress has been made in the characterization of FaRP pharmacology in helminths, much remains to be learned. Most studies on nematodes have been done with Ascaris suum because of its large size. However, thanks to the Caenorhabditis elegans genome project, we know most about the FaRP complement of this free-living animal. That essentially all C. elegans FaRPs are active on at least one A. suum neuromuscular system argues for conservation of ligand-receptor recognition features among the Nematoda. Structure-activity studies on nematode FaRPs have revealed that structure-activity relationship (SAR) "rules" differ considerably among the FaRPs. Second messenger studies, along with experiments on ionic dependence and anatomical requirements for activity, reveal that FaRPs act through many different mechanisms. Platyhelminth FaRPs are myoexcitatory, and no evidence exists of multiple FaRP receptors in flatworms. Interestingly, there are examples of cross-phylum activity, with some nematode FaRPs being active on flatworm muscle. The extent to which other invertebrate FaRPs show cross-phylum activity remains to be determined. How FaRPergic nerves contribute to the control of behavior in helminths, and are integrated with non-neuropeptidergic systems, also remains to be elucidated.

FMRFamide-related neuropeptide gene family in Caenorhabditis elegans

Neuropeptides are used as signaling molecules in the nervous system of most organisms, including mammals. The family of FMRFamide (Phe-Met-Arg-Phe-NH2)-like neuropeptides (FaRPs) all share an RFamide sequence at their C-termini and have been shown to have diverse functions in the central and peripheral nervous systems. In the nematode Caenorhabditis elegans, FMRFamide-like peptides (FaRPs) are expressed in at least 10% of the neurons, including motor, sensory, and interneurons that are involved in movement, feeding, defecation, and reproduction. Twenty-two genes, designated flp-1 through flp-22, encode FaRPs in C. elegans, although there are likely to be additional flp genes to be identified. Each flp gene encodes a different set of FaRPs, yielding a predicted total of 59 distinct FaRPs; a few of the genes may also encode non-FaRPs. Inactivation of some of the flp genes indicates that at least one flp gene has unique functions, while at least two flp genes appear to have overlapping functions with other flp genes. These results suggest that a complex family of FaRPs have varied roles through all stages of development and in adulthood in C. elegans.

Structural characterisation and pharmacology of KHEYLRFamide (AF2) and KSAYMRFamide (PF3/AF8) from Haemonchus contortus

The FMRFamide-related peptides (FaRPs), KHEYLRFamide (AF2) and KSAYMRFamide (PF3) were structurally characterised from the parasitic nematode of sheep, Haemonchus contortus (MH isolate). Both peptides were sequenced in a single gas-phase sequencing run and their structure confirmed by mass spectrometry which identified peptides of 920 Da (C-terminally amidated AF2) and 902/918 Da (C-terminally amidated non-oxidised/oxidised PF3, respectively). AF2 had inhibitory effects on H. contortus muscle and inhibited acetylcholine (ACh, 10 microM)-induced contractions, with a threshold for activity of 1 microM. PF3 induced concentration-dependent contractions of H. contortus (activity threshold, 10 nM) and enhanced ACh contractions. Compared with the MH isolate, an isolate of H. contortus which has reduced sensitivity to cholinergic drugs (Lawes isolate) was less sensitive to the effects of PF3. The concentration-response curves for the cholinergic compounds ACh and levamisole (LEV), and PF3, but not a control, KPNFIRFamide (PF4), showed a statistically similar shift. This study implicates PF3 in the modulation of cholinergic function in H. contortus.

Isolation, pharmacology and gene organization of KPSFVRFamide: a neuropeptide from Caenorhabditis elegans

To date, 53 peptides with C-terminal RFamides have been identified by the genome sequencing project in the nematode, Caenorhabditis elegans. In this study the FMRFamide-related peptide (FaRP) KPSFVRFamide (879.90 Da [MH]+) was structurally characterized from extracts of the nematode, Caenorhabditis elegans. Two copies of KPSFVRFamide are encoded by a gene designated flp-9. RT-PCR identified a single cDNA product which was confirmed as flp-9 by sequence determination. Flp-9 cDNA was isolated from larval stages of C. elegans but was not detected in adult worms, indicating that its expression is may be developmentally regulated. KPSFVRFamide displays sequence homology to the nematode peptide, KPNFIRFamide (PF4). The physiological effects of KPSFVRFamide, PF4 and the chimeras, KPNFVRFamide and KPSFIRFamide, were measured on body wall muscle and the vagina vera of the parasitic nematode, Ascaris suum. KPNFVRFamide and KPNFIRFamide had Cl--dependent inhibitory activity on innervated and denervated muscle-preparations, whereas KPSFVRFamide and KPSFIRFamide did not elicit a detectable physiological effect. Although all 4 peptides had inhibitory effects on the vagina vera, KPSFVRFamide and KPSFIRFamide (threshold, >/=0.1 microM) were less potent than KPNFVRFamide and KPNFIRFamide (threshold, >/=10 nM).

Exploring the neurotransmitter labyrinth in nematodes

Nematodes include both free-living species such as Caenorhabditis elegans and major parasites of humans, livestock and plants. The apparent simplicity and uniformity of their nervous system belies a rich diversity of putative signalling molecules, particularly neuropeptides. This new appreciation stems largely from the genome-sequencing project with C. elegans, which is due to be completed by the end of 1998. The project has provided additional insights into other aspects of nematode neurobiology, as have studies on the mechanism of action of anthelmintics. Here, progress on the identification, localization, synthesis and physiological actions of transmitters identified in nematodes is explored.

Parasitic peptides! The structure and function of neuropeptides in parasitic worms

Parasitic worms come from two very different phyla-Platyhelminthes (flatworms) and Nematoda (roundworms). Although both phyla possess nervous systems with highly developed peptidergic components, there are key differences in the structure and action of native neuropeptides in the two groups. For example, the most abundant neuropeptide known in platyhelminths is the pancreatic polypeptide-like neuropeptide F, whereas the most prevalent neuropeptides in nematodes are FMRFamide-related peptides (FaRPs), which are also present in platyhelminths. With respect to neuropeptide diversity, platyhelminth species possess only one or two distinct FaRPs, whereas nematodes have upwards of 50 unique FaRPs. FaRP bioactivity in platyhelminths appears to be restricted to myoexcitation, whereas both excitatory and inhibitory effects have been reported in nematodes. Recently interest has focused on the peptidergic signaling systems of both phyla because elucidation of these systems will do much to clarify the basic biology of the worms and because the peptidergic systems hold the promise of yielding novel targets for a new generation of antiparasitic drugs.

KSAYMRFamide (PF3/AF8) is present in the free-living nematode, Caenorhabditis elegans

To date, seven FMRFamide-related peptides (FaRPs) have been structurally characterized from C. elegans, of which one is structurally identical to the parasitic nematode peptide AF2 (KHEYLRFamide). The other six FaRPs have so far been identified in free-living forms only. In the present study an additional FaRP was isolated and structurally characterized from an ethanolic extract of C. elegans. The extract was screened using a C-terminally directed FaRP antiserum, and the FMRFamide-immunoreactive peptide purified to homogeneity using HPLC. Approximately 80 pmol of the peptide was subjected to Edman degradation and the unequivocal primary structure of the K7-amide, KSAYMRFamide (PF3/AF8) was determined following a single gas-phase sequencing run. The molecular mass of the peptide was determined using a MALDI-TOF mass spectrometer and was found to be 919 (MH+), which is in agreement with the theoretical mass of C-terminally amidated PF3. A new flp-gene, designated flp-6, has recently been identified which encodes six copies of KSAYMRFamide (PF3/AF8).

FMRFamide-related gene family in the nematode, Caenorhabditis elegans

Many organisms, including mammals, use short peptides as neurotransmitters. The family of FMRFamide (Phe-Met-Arg-Phe-NH2)-like neuropeptides, which all share an -RFamide sequence at their C-termini, has been shown to have diverse functions, including neuromodulation and stimulation or inhibition of muscle contraction. In the nematode, Caenorhabditis elegans, FMRFamide-like peptides (FaRPs) are expressed in approximately 10% of the neurons, including motor, sensory, and interneurons that are involved in movement, feeding, defecation, and reproduction. At least 14 genes, designated flp-1 through flp-14, encode FaRPs in C. elegans. Here, we present data that all 14 flp genes are transcribed in C. elegans, and several of these genes are alternatively spliced. Each flp gene encodes a different set of FaRPs, yielding a predicted total of 44 distinct FaRPs. Using staged RNA for reverse-transcription/polymerase chain reactions (RT/PCR), we determined that most flp genes are expressed throughout development. These results suggest that a complex family of FaRPs have varied roles through all stages of development and in adulthood in C. elegans.

The effects of the peptide KPNFIRFamide (PF4) on the somatic muscle cells of the parasitic nematode Ascaris suum

1. Commonly used anthelmintic agents act on the muscle cells of parasitic nematodes to cause paralysis of the parasite and its expulsion from the host. 2. The motonervous system of nematodes contains neuropeptides, many of which are myoactive and elicit prolonged worm paralysis. Here we describe the actions of a novel peptide, KPNFIRFamide (Lys-Pro-Asn-Phe-Ileu-Arg-Phe-amide; PF4), which mediates relaxation of the somatic muscle of the parasitic nematode Ascaris suum. Its mechanism of action is compared to that of the inhibitory neuromuscular junction transmitter, gamma-aminobutyric acid (GABA), which gates a chloride channel on Ascaris muscle. 3. Both PF4 and GABA hyperpolarized the muscle cells (EC50 values 98 nM and 59 microM, respectively; n = 6) and this was accompanied by an increase in input conductance. 4. The increase in input conductance elicited by PF4 and a supramaximal concentration of GABA were additive (10 microM PF4, 7.78 +/- 1.88 microS; 10 mM GABA, 4.68 +/- 1.39 microS; 10 mM GABA and 10 microM PF4 12.05 +/- 2.6 microS, n = 6, P < 0.02 with respect to PF4 alone; P < 0.01 with respect to GABA alone). 5. The membrane potential response to 10 microM PF4 initially consisted of a fast hyperpolarization that occurred within 1 min of PF4 application. The reversal potential for this early response to PF4 (PF4-early) was determined at different extracellular chloride concentrations. Linear regression analysis of the natural logarithm of the extracellular chloride concentration against the reversal potential for PF4-early yielded a straight line with a slope of -29.6 +/- 2.4 (-34.4 to -24.9, 95% confidence limits; r2 = 0.82). This is close to the slope of -26.5 for a chloride-dependent event, as predicted by the Nernst equation. There was a significant correlation between the reversal potential for this event and the reversal potential for GABA (r = 0.94; P < 0.001; n = 12). 6. The late response to PF4 (PF4-late) appeared after 1 min and consisted of a slow reduction in the hyperpolarization to a plateau level, before the return of the membrane potential to the resting value. PF4-late is not likely to be a chloride-dependent event as during the hyperpolarization caused by a supramaximal concentration of GABA the muscle cells depolarized when a supramaximal concentration of PF4 was added to the perfusate. The membrane potential in the presence of 1 mM GABA was -61.8 +/- 4.8 mV and in the presence of 1 mM GABA with 10 microM PF4 was -47.5 +/- 1.5 mV (P < 0.02; n = 6). 7. The conductance increase elicited by 30 microM GABA was blocked by 10 microM ivermectin (before ivermectin 0.97 +/- 0.2 microS, after ivermectin 0.33 +/- 0.12 microS; n = 5; P < 0.05; Student's paired t test) but the conductance increase elicited by 1 microM PF4 was not (before ivermectin 0.96 +/- 0.14 microS, after ivermectin 1.07 +/- 0.19 microS; n = 0.34; Student's paired t test). 8. These data indicate that PF4 elicits a potent, inhibition of Ascaris muscle cells which is partially mediated by chloride and which is independent of the inhibitory GABA receptor.

afp-1: a gene encoding multiple transcripts of a new class of FMRFamide-like neuropeptides in the nematode Ascaris suum

We have identified a gene, afp-1, that encodes a new subfamily of six FMRFamide-like neuropeptides in the nematode Ascaris suum. The predicted peptides share the C-terminal sequence PGVLRF-NH2 but have different N-terminal extensions. We discuss possible functional roles of these different peptides based upon experiments with Ascaris as well as results from other organisms. Three of the peptides were previously isolated from extracts of A. suum (4) and three other are novel sequences. The translated product of afp-1 is a precursor protein containing two main halves: a C-terminal region containing a series of putative peptides separated by characteristic processing sites and a relatively hydrophobic N-terminal region with no obvious peptides. Although the overall structure of the translated product of afp-1 is similar to flp-1 from C. elegans (18), there is little evidence for homology between the two nematode neuropeptide genes. At least four different transcripts of afp-1 have been identified. These transcripts differ in their 3' and 5' untranslated regions, and one of the transcripts predicts a truncated precursor protein which contains only the C-terminal peptide-containing region.

The Pharmacology of Nematode FMRFamide-related Peptides

FMRFamide-related peptides (FaRPs) are the largest known family of invertebrate neuropeptides. Immunocytochemical screens of nematode tissues using antisera raised to these peptides have localized extensive FaRP-immunostaining to their nervous systems. Although 21 FaRPs have been isolated and sequenced from extracts of free-living and parasitic nematodes, available evidence indicates that other FaRPs await discovery. While our knowledge of the pharmacology of these native nematode neuropeptides is extremely limited, reports on their physiological activity in nematodes are ever increasing. All the nematode FaRPs examined so far have been found to have potent and varied actions on nematode neuromuscular activity. It is only through the extensive pharmacological and physiological assessment of the tissue, cell and receptor interactions of these peptidic messengers that an understanding of their activity on nematode neuromusculature will be possible. In this review, Aaron Maule and colleagues examine the current understanding of the pharmacology of nematode FaRPs.

Nematode FMRFamide-related peptide (FaRP)-systems: occurrence, distribution and physiology

The application of rational (mechanism-based) approaches to anthelmintic discovery requires information about target proteins which are pharmacologically distinguishable from their vertebrate homologs. In helminths, several such targets (e.g., beta-tubulin, ATP-generating enzymes, cholinergic receptors, CI- channels) have been characterized only after the discovery, through empirical screening, of compounds that interfere with their function. From the perspective of anthelmintic discovery, the utility of these targets is diminishing due to the emergence of drug-resistant strains of parasites. This has motivated the search for compounds with novel modes-of-action. Recent basic research in helminth physiology and biochemistry has identified several potential targets for rational anthelmintic discovery, including receptors for FMRFamide-related peptides (FaRPs). To date, over 20 different nematode FaRPs have been identified and these peptides, which are broadly distributed in helminths, have been localized to all of the major neuronal subtypes in nematodes. The FaRPs that have been examined have been found profoundly to affect somatic muscle function in gastrointestinal nematodes. In this respect, complex inhibitory and excitatory actions have been identified for a number of these peptides. Although the transduction pathways for any of these peptides remain to be elucidated, the available evidence indicates that nematode FaRPs have numerous mechanisms of action. The employment of nematode neuropeptide receptors in mechanism-based screens has immense potential in the identification of novel anthelmintics.

The motornervous system of Ascaris: electrophysiology and anatomy of the neurons and their control by neuromodulators

Analysis of the electrical properties of neurons in the motornervous system of Ascaris sutom suggests that it is largely an analogue system. The motorneurons do not conduct action potentials and they release transmitter tonically at their normal resting potential; transmitter release is increased or decreased as a continuous function of membrane potential. Despite extensive physiological descriptions of the electrical properties of the neurons and their synapses, as well as morphological descriptions of the synaptic circuitry of the system, the predicted activities of the neurons in the circuit differ from those observed by direct recording in semi-intact behaving animals. We conclude that the description of the circuit is incomplete. There are several possibilities for the missing elements, including chemical, proprioceptive, and additional neuronal components. Recently, attention has been focussed most heavily on the intercellular chemical signalling systems; in addition to those mediated by classical neurotransmitters, a surprisingly complex array of neuropeptides has been identified. One family of these peptides, the AF peptides, has been analyzed in detail. It comprises at least 20 peptides, and they fall into sequence-related subfamilies. One of these subfamilies, containing 6 peptides, is encoded by a single transcript, suggesting that the AF peptides are under multiple genetic control. All AF peptides tested have potent activity on the motornervous system and/or on muscle. There are multiple physiological activities, and cellular localization studies show multiple patterns of cellular expression. Studies on Panagrellus and Caenorhabditis emphasize the diversity of this family and its genetic control.

Neuropeptides and their evolution

Neuropeptides are ubiquitous signalling molecules in all metazoans possessing nervous systems, from the simple nerve nets of the cnidarians to the immensely complex systems of mammals. While the discipline of peptide neuroendocrinology was born through the study of higher vertebrates, there now exists a plethora of information regarding neuropeptides and peptidic regulatory factors in invertebrates. Such phylogenetic studies have revealed that peptidic neurotransmission is of early evolutionary origin and that, while invertebrates have nervous systems which are simpler in terms of nerve cell number and organisation when compared with vertebrates, the complexity of the peptidic 'vocabulary' of invertebrate neurones is of a similar order of magnitude. Most research on invertebrate neuropeptides has been directed towards representative members of groups such as the insects and molluscs and it is only in recent years that efforts have been focused on the helminths (platyhelminths and nematodes). Here, the putative origins of peptidic transmitters is discussed and the current state of knowledge on helminth neuropeptides is reviewed. In order to place the study of helminth neuropeptides in an historical and conceptual perspective, methodological development and conceptual modifications in the disciplines of vertebrate and higher invertebrate peptide neuroendocrinology have been summarised.

FMRFamide-related peptides (FaRPs) in nematodes: occurrence and neuromuscular physiology

The occurrence of classical neurotransmitter molecules and numerous peptidic messenger molecules in nematode nervous systems indicate that although structurally simple, nematode nervous systems are chemically complex. Thus far, studies on one nematode neuropeptide family, namely the FMRFamide-related peptides (FaRPs), have revealed an unexpected variety of neuropeptide structures in both free-living and parasitic species. To date 23 nematode FaRPs have been structurally characterized including 12 from Ascaris suum, 8 from Caenorhabditis elegans, 5 from Panagrellus redivivus and 1 from Haemonchus contortus. Ten FaRP-encoding genes have been identified in Caenorhabditis elegans. However, the full complement of nematode neuronal messengers has yet to be described and unidentified nematode FaRPs await detection. Preliminary characterization of the actions of nematode neuropeptides on the somatic musculature and neurones of A, suum has revealed that these peptidic messengers have potent and complex effects. Identified complexities include the biphasic effects of KNEFIRFamide/KHEYLRFamide (AF1/2; relaxation of tone followed by oscillatory contractile activity) and KPNFIRFamide (PF4; rapid relaxation of tone followed by an increase in tone), the diverse actions of KSAYMRFamide (AF8 or PF3; relaxes dorsal muscles and contracts ventral muscles) and the apparent coupling of the relaxatory effects of SDPNFLRFamide/SADPNFLRFamide (PF1/PF2) to nitric oxide release. Indeed, all of the nematode FaRPs which have been tested on somatic muscle strips of A. suum have actions which are clearly physiologically distinguishable. Although we are a very long way from understanding how the actions of these peptides are co-ordinated, not only with those of each other but also with those of the classical transmitter molecules, to control nematode behaviour, their abundance coupled with their diversity of structure and function indicates a hitherto unidentified sophistication to nematode neuromuscular intergration.

NADPH diaphorase activity in peptidergic neurones of the parasitic nematode, Ascaris suum

The histochemical marker for nitric oxide synthase, NADPH diaphorase, is known to co-localize in mammalian neurones with various classical neurotransmitters and neuropeptides. The nervous system of the parasitic nematode Ascaris suum has previously been shown to contain both NADPH diaphorase activity and neuropeptide immunoreactivity. This study examined the possibility that NADPH diaphorase and neuropeptide immunoreactivity may co-exist in the same neurones. Two antisera were used, one raised to KYSALMFamide, a C-terminal synthetic analogue of SALMFamide 1 (GFNSALMFamide), and another that recognizes calcitonin-gene-related peptide (CGRP). We provide evidence that in a distinct subset of neurones in the ventral, dorsal and lateral ganglia NADPH diaphorase staining and SALMFamide-like immunoreactivity are co-localized, suggesting a possible role for nitric oxide in modulating neuropeptide activity in these regions. CGRP-like immunoreactivity was less widely distributed, and was not consistently co-localized with NADPH diaphorase.

Electrophysiology of Ascaris muscle and anti-nematodal drug action

Three groups of anthelmintic drugs act directly and selectively on muscle membrane receptors of parasitic nematodes. These groups of anthelmintics are: (1) The Nicotinic Agonists (levamisole, pyrantel, morantel and oxantel) that act on acetylcholine receptors of nematode somatic muscle; (2) The GABA Agonist, piperazine, that acts on nematode muscle GABA receptors; and (3) The Avermectins that open glutamate gated Cl- channels on nematode pharyngeal muscle. The electrophysiology and pharmacology of muscle and neuromuscular transmission the nematode parasite, Ascaris suum, is outlined and effects of anthelmintics that interfere with transmission described. Resistance to anthelmintics has appeared in some parasitic nematodes but the mechanisms of this resistance remain to be determined.

Inhibitory effects of nematode FMRFamide-related peptides (FaRPs) on muscle strips from Ascaris suum

A large number of FMRFamide-related peptides (FaRPs) are found in nematodes, and some of these are known to influence tension and contractility of neuromuscular strips isolated from Ascaris suum body wall. Relaxation of these strips has been noted with five nematode FaRPs. The inhibitory actions of SDPNFLRFamide (PF1) and SADPNFLRFamide (PF2) appear to be mediated by nitric oxide, as previously demonstrated with inhibitors of nitric oxide synthase (NOS). This present study showed that the effects of PF1 were also depended on external Ca++ and were reduced by the Ca(++)-channel blocker verapamil, observations consistent with the finding that nematode NOS is Ca(++)-dependent. KSAYMRFamide (PF3), KNIRFamide (PF4) and KNAFIRFamide (an alanine substituted analog of KNEFIRFamide, AF1, termed A3AF1) also relaxed A. suum muscle strips, but these responses were not affected by NOS inhibitors. PF3 inhibited the activity of strips prepared from the dorsal side of the worm, but contracted ventral strips. Both effects were dependent on the presence of ventral/dorsal nerve cords (unlike PF1/PF2) and were attenuated in medium which contained high K+ or low Ca++. PF4-induced muscle relaxation and hyperpolarization were independent of nerve cords, but were reversed in Cl-free medium, unlike PF1 or PF3. The PF4 effect physiologically desensitized muscle strips to subsequent treatment with PF4 and/or GABA. However, PF4 and GABA were not synergistic in this preparation. The effects of GABA, but not PF4, were reduced in muscle strips treated with the GABA antagonist, NCS 281-93. Following PF4 (or GABA) relaxation, subsequent treatment with higher doses of PF4 caused muscle strip contraction. A3AF1 was found to relax muscle strips and hyperpolarize muscle cells independently of the ventral and dorsal nerve cords, K+, Ca++, and Cl-, and mimicked the inhibitory phase associated with the exposure of these strips to AF1. On the basis of anatomical and ionic dependence, these data have delineated at least four distinct inhibitory activities attributable to nematode FaRPs. Clearly, a remarkably complex set of inhibitory mechanisms operate in the nematode neuromuscular system.

The pharmacology of FMRFamide-related neuropeptides in nematodes: new opportunities for rational anthelmintic discovery?

The chemotherapeutic control of helminth parasites is compromised by the limited number of classes of anthelmintic drugs. Discovery of novel anthelmintics is impeded by the lack of novel screening technologies that overcome the difficulties inherent in screens based on whole organism toxicity. The development and implementation of mechanism-based screens for new anthelmintics offers great promise for the revitalization of antiparasitic drug discovery. However, mechanism-based screens must be based on a thorough understanding of the proteins or processes that offer the best chance for selective chemotherapeutic intervention. Basic research on the characterization of nematode FMRFamide-related peptides (FaRPs) has revealed that these peptides are ubiquitously distributed in helminths. Chemical identification of a number of nematode FaRPs has been achieved, and these peptides have potent and profound effects on the nematode neuromuscular system. Physiological processes mediated by nematode FaRPs (and other helminth neuropeptides) offer potential targets for the discovery of novel anthelmintics.

The FMRFamide-like neuropeptide AF2 is present in the parasitic nematode Haemonchus contortus

Peptides belonging to the FMRFamide family are widely distributed amongst invertebrates. We report here on the isolation of the FMRFamide neuropeptide AF2 (Lys-His-Glu-Tyr-Leu-Arg-Phe-NH2) from the parasitic nematode Haemonchus contortus. Immunocytochemical techniques showed that FMRFamide-like material was distributed in several regions of these organisms including nerve cords and cell bodies of the central nervous system. AF2 was isolated using a method that employed 6 steps of reverse-phase HPLC. The concentration of AF2 in this organism was approximately 30 pmol/g of nematode.

The action of serotonin and the nematode neuropeptide KSAYMRFamide on the pharyngeal muscle of the parasitic nematode, Ascaris suum

The pharyngeal component of the enteric nervous system of the parasitic nematode, Ascaris suum exhibits immunoreactivity for serotonin (5-hydroxytryptamine or 5-HT) and for FMRFamide-like peptides. This paper describes the application of an in vitro pharmacological approach to investigate the functional role of 5-HT and FMRFamide-like peptides. The pharyngeal pumping behaviour of Ascaris suum was monitored using a modified pressure transducer system which measures pharyngeal pressure changes and therefore pumping. The pharynx did not contract spontaneously; however, 5-HT (10-1000 microM) stimulated pumping at a frequency of 0.5 Hz. FMRFamide had no apparent effect on pharyngeal pumping. The native nematode FMRFamide-related peptide (FaRP), KSAYMRFamide inhibited the pumping elicited by 5-HT. The duration of inhibition was dose-dependent (0.1-1000 nM) with a threshold of 0.1 nM. In 4 preparations, the inhibition of the pharyngeal muscle was preceded by an initial excitation and increase in the amplitude of pharyngeal pressure changes. The pharynx is involved in various nematode processes, including feeding, regulation of hydrostatic pressure and excretion. The role of 5-HT and KSAYMRFamide in the pharyngeal function of nematodes is discussed.

The effect of the nematode peptides SDPNFLRFamide (PF1) and SADPNFLRFamide (PF2) on synaptic transmission in the parasitic nematode Ascaris suum

The action of two peptides isolated from the nematode Panagrellus redivivus, PF1 (SDPNFLRFamide) and PF2 (SADPNFLRFamide) have been studied on synaptic transmission in the motornervous system of the parasitic nematode Ascaris suum. Intracellular recordings were made from Ascaris somatic muscle cells and excitatory junction potentials (EJPs) elicited by stimulation of the ventral nerve cord. The EJPs were cholinergic as they were blocked by the Ascaris nicotinic receptor antagonist, benzoquinonium. PF1 caused a slow hyperpolarization, similar to the action of this peptide first reported by Bowman, Geary & Thompson (1990) and further characterized by Franks et al. (1994). The hyperpolarization was accompanied by a marked decrease in the amplitude of the EJPs with an EC50 of 311 +/- 30 nM (n = 5). This inhibition is unlikely to be due to a post-synaptic site of action of the peptide as the muscle cell input conductance was not significantly altered by PF1 and furthermore the response to bath-applied acetylcholine was not inhibited by PF1 at concentrations up to 10 microM (n = 6). PF2 also inhibited the EJPs in a similar manner to PF1. These studies indicate that both of the peptides isolated from the free-living nematode Panagrellus redivivus have biological activity in the parasitic nematode Ascaris suum. PF1 and PF2 have inhibitory actions in contrast to the predominantly excitatory actions of the Ascaris endogenous peptides AF1 (KNEFIRFamide) and AF2 (KHEYLRFamide). The potent actions of the Panagrellus neuropeptides PF1 and PF2 in Ascaris suggest that peptides with a similar or identical sequence may also occur in Ascaris and have an inhibitory role in the motornervous system.

The effects of the nematode peptide, KHEYLRFamide (AF2), on the somatic musculature of the parasitic nematode Ascaris suum

AF2 is an endogenous RFamide-like peptide from the parasitic nematode Ascaris suum. The potent stimulatory effects of this peptide on the somatic musculature of Ascaris strongly suggest that it may have an important role in the motornervous system. Here we have investigated the possibility that AF2 may elicit a stimulatory action on Ascaris muscle by potentiating the actions of the excitatory cholinergic motonervous system either pre-synaptically, post-synaptically or both. In in vitro pharmacological experiments AF2 produced a dose-dependent increase in the frequency and amplitude of spontaneous contractions of Ascaris muscle strip which lasted for more than 1 h after a 3 min application of AF2 (10 nM-10 microM; N = 7). In addition, AF2 (100 nM) potentiated the contraction elicited by ACh by 43 +/- 9% (P < 0.01; N = 8). In electrophysiological recordings from muscle cells, AF2 (10-100 nM; N = 10) potentiated the amplitude of EJPs (excitatory junction potentials). For 100 nM AF2, the potentiation of the EJP was 218 +/- 48% (N = 7; P < 0.01). This effect reversed after a wash of 10 min. AF2 did not potentiate the depolarization of the muscle cell elicited by bath applied ACh. These latter two observations are consistent with a presynpatic action of AF2. AF2 (10-100 nM) generated spontaneous muscle cell action potentials in previously quiescent cells. This effect took more than 1 h to wash out. These observations are discussed in terms of the paralysis of Ascaris that is elicited by AF2.

Isolation and preliminary biological characterization of KPNFIRFamide, a novel FMRFamide-related peptide from the free-living nematode, Panagrellus redivivus

A novel FMRFamide-related heptapeptide, Lys-Pro-Asn-Phe-Ile-Arg-Phe-NH2 (KPNFIRFamide), was isolated and characterized from acid ethanol extracts of the free-living nematode, Panagrellus redivivus. Whole-worm extracts contained > or = 9 pmol KPNFIRFamide/g wet weight. A synthetic replicate of this peptide induced a rapid relaxation of tone and inhibited spontaneous contractility in isolated innervated and denervated body-wall muscle strips of the parasitic nematode, Ascaris suum. KPNFIRFamide (0.1 nM) induced measurable relaxations in 50% of the muscle preparations examined. Concentrations > or = 0.3 nM induced relaxation in 100% of muscle preparations examined. The relaxation was short-lived at concentrations of peptide > or = 1 microM and displayed a profile typical of receptor desensitization. These data suggest the occurrence of a closely related peptide in A. suum and add further evidence to the concept of primary structural conservation of FaRPs within the nematodes.