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PubMed1995

Eight novel FMRFamide-like neuropeptides isolated from the nematode Ascaris suum.

Eight FMRFamide-like neuropeptides were isolated from an extract of heads and tails from the nematode Ascaris suum using seven steps of HPLC. The peptides ranged in size from 8 to 14 amino acid residues: AF3 (Ala-Val-Pro-Gly-Val-Leu-Arg-Phe-amide), AF4 (Gly-Asp-Val-Pro-Gly-Val-Leu-Arg-Phe-amide), AF5 (Ser-Gly-Lys-Pro-Thr-Phe-Ile-Arg-Phe-amide), AF7 (Ala-Gly-Pro-Arg-Phe-Ile-Arg-Phe-amide), AF9 (Gly-Leu-Gly-Pro-Arg-Pro-Leu-Arg-Phe-amide), AF10 (Gly-Phe-Gly-Asp-Glu-Met-Ser-Met-Pro-Gly-Val-Leu-Arg-Phe-amide), AF11 (Ser-Asp-Ile-Gly-Ile-Ser-Glu-Pro-Asn-Phe-Leu-Arg-Phe-amide), and AF12 (Phe-Gly-Asp-Glu-Met-Ser-Met-Pro-Gly-Val-Leu-Arg-Phe-amide). The effect of synthetic AF4 on muscle tension in a dorsal muscle strip preparation was a strong, long-lasting contraction. PF1, a peptide present in Panagrellus redivivus and Caenorhabditis elegans, relaxed the AF4-induced contraction.

Amino Acid Sequence↗
PubMed1994

Biological activity and receptor binding properties of some C-terminally modified analogues of FMRFamide.

The functional role of the C-terminal amide group (-CONH2) of the molluscan regulatory peptide FMRFamide has been examined in two sets of analogues based on FnLKFamide and FnLRFamide (nL = norleucine). In each series the amide group was replaced by -CONHCH3, -CON(CH3)2, -CONHNH2, -COOCH3, -CH2OH, and -COOH. The analogues were tested for their ability to bind to receptors in membranes from Helix aspersa circumoesophageal ganglia and for their biological effects on the isolated Helix heart. The results indicate i) that agonist activity, but not binding to the receptor, requires the presence of the amide carbonyl group; ii) the hydrogen atoms of the amide group are not essential either for binding or for agonist activity (the mono- and dimethylamides were more effective than the parent compounds on both counts); iii) the is more effective an agonist than is the amide in stimulating Helix heart.

Animals↗
PubMed1995

A single receptor transduces both inhibitory and stimulatory signals of FMRFamide-related peptides.

In the oviduct of Locusta migratoria, an inhibitory neuropeptide, PDVDHVFLRFamide (SchistoFLRFamide) has separate binding and activation regions. VFLRFamide is the minimum sequence required for binding, which is comparable to the parent peptide, whereas the His residue, which does not contribute to binding, is a critical amino acid for the inhibitory activity of the receptor. In this study, the His residue of HVFLRFamide was substituted by Tyr, Leu, Ile, or Val to yield a group of HVFLRFamide analogues. As revealed by bioassay, all of these hexapeptide analogues exert stimulatory effects on oviduct muscle contraction. However, results from three sets of binding experiments indicate that these stimulatory FMRFamide-related peptides (FaRPs) share the same binding site as PDVDHVFLRFamide and HVFLRFamide, the inhibitory FaRPs. First, unlabeled stimulatory FaRPs competitively displace bound [125I]YDVDHVFLRFamide. Second, two binding sites for the stimulatory peptide YVFLRFamide were identified and both of them have similar binding affinities and maximum binding capacities as the two binding sites for PDVDHVFLRFamide. Third, unlabeled PDVDHVFLRFamide and HVFLRFamide competitively displace the bound [125I]YVFLRFamide in the same manner as unlabeled YVFLRFamide. These findings suggest the presence of a novel ligand-receptor reaction system. In this system, inhibitory peptides and stimulatory peptides share a single receptor by having the same binding sequence VFLRFamide, but are able to produce opposite muscle responses due to differences in activation sites. Correspondingly, this single receptor could be coupled with two different intracellular signaling systems to mediate either inhibitory or stimulatory responses.

Animals↗
PubMed1991

FMRFamide-like immunoreactivity in cells and fibers of the holothurian nervous system.

Immunoreactivity to FMRFamide (FMRFa) was detected in several components of the nervous system of the sea cucumber, Holothuria glaberrima. Neurons and fibers expressing immunoreactivity to this peptide were found in the radial nerves, and in nerve plexuses of the esophagus, and large and small intestine. The neurons in the enteric nervous system were located in the serosal layer and immunoreactive fibers appeared to innervate the longitudinal muscle. Co-existence of immunoreactivities to FMRFa and cholecystokinin was detected in most of the enteric fibers. Therefore, in the holothurians, neurons expressing FMRFa and FMRFa/cholecystokinin might be involved in the physiology of the digestive tract.

Animals↗
PubMed1988

Light and electron microscopic immunocytochemistry of neurons in the blowfly optic lobe reacting with antisera to RFamide and FMRFamide.

Different antisera to the molluscan cardioexcitatory peptide FMRFamide, and its fragment, RFamide (Arg-Phe-NH2), label a distinct population of neurons in the optic lobe of the blowfly, Calliphora erythrocephala. Seven morphological types of RFamide/FMRFamide-like immunoreactive neurons could be distinguished in the optic lobes based on the locations of their cell bodies, their axonal projections and the distribution of their processes. Of these, two types could be resolved in their entire extent, the others were labeled only in their cell bodies and terminal processes or were partly obscured by other immunoreactive processes. The RF-like immunoreactive neurons in the optic lobes are of two main classes: (1) two types of large field projection neurons and (2) five types of local neurons. One type of projection neurons (five in each lobe) connects the entire projected retinal mosaic of the medulla and lobula in the optic lobe with protocerebral centres associated with the mushroom body calyx. The other type (2-3 invading each lobe) has cell bodies in the protocerebrum and contralateral processes invading optic lobes. Of the class of local neurons there are two amacrine RF-like immunoreactive neurons in each medulla. Each of these amacrines supplies the entire mosaic with fine processes. The remaining local RF-like immunoreactive neurons are present in relatively large numbers (one type in more than 2000 copies in each medulla) and-supply the medulla, lobula and lobula plate neuropils with fine varicose processes. In the medulla the RF-like immunoreactive processes are arranged in strict layers whereas in the lobula complex the distribution is diffuse. Electron microscopic immunocytochemistry, using both pre-embedding immuno peroxidase-antiperoxidase and post-embedding protein A-gold labeling, was employed for analysis of cytology and synaptic connections of RF-like immunoreactive neurons in the medulla. The varicosities of the processes of the large field projection neurons were not found to make chemical synapses with other neurons in the medulla. The spines of the RF-like immunoreactive processes of the large medulla amacrines, however, make pre- and postsynaptic contacts with other neural elements. Our findings indicate that an RFamide/FMRFamide-like substance may be used as a neurotransmitter or neuromodulator by optic lobe neurons of different types. The local and projection RF-like immunoreactive pathways probably play different roles in visual processing.

Animals↗
PubMed1992

The FMRFamide-related decapeptide of Mytilus contains a D-amino acid residue.

1. An FMRFamide-related decapeptide isolated from the anterior byssus retractor muscle (ABRM) of the bivalve mollusc, Mytilus edulis, was shown to have D-Leu as the second amino acid residue. 2. The excitatory effects of the peptide (Mytilus-FFRFamide) on the ABRM were not changed appreciably by substituting an L-Leu residue for the D-Leu residue.

Animals↗
PubMed2004

Extrabulbar olfactory system and nervus terminalis FMRFamide immunoreactive components in Xenopus laevis ontogenesis.

The extrabulbar olfactory system (EBOS) is a collection of nerve fibers which originate from primary olfactory receptor-like neurons and penetrate into the brain bypassing the olfactory bulbs. Our description is based upon the application of two neuronal tracers (biocytin, carbocyanine DiI) in the olfactory sac, at the cut end of the olfactory nerve and in the telencephalon of the developing clawed frog. The extrabulbar olfactory system was observed already at stage 45, which is the first developmental stage compatible with our techniques; at this stage, the extrabulbar olfactory system fibers terminated diffusely in the preoptic area. A little later in development, i.e. at stage 50, the extrabulbar olfactory system was maximally developed, extending as far caudally as the rhombencephalon. In the metamorphosing specimens, the extrabulbar olfactory system appeared reduced in extension; caudally, the fiber terminals did not extend beyond the diencephalon. While a substantial overlapping of biocytin/FMRFamide immunoreactivity was observed along the olfactory pathways as well as in the telencephalon, FMRFamide immunoreactivity was never observed to be colocalized in the same cellular or fiber components visualized by tracer molecules. The question whether the extrabulbar olfactory system and the nervus terminalis (NT) are separate anatomical entities or represent an integrated system is discussed.

Animals↗
PubMed2005

FMRFamide related peptide ligands activate the Caenorhabditis elegans orphan GPCR Y59H11AL.1.

G-protein coupled receptors (GPCRs) are ancient molecules that can sense environmental and physiological signals. Currently, the majority of the predicted Caenorhabditis elegans GPCRs are orphan. Here, we describe the characterization of such an orphan C. elegans GPCR, which is categorized in the tachykinin-like group of receptors. Since the C. elegans genome predicts only one tachykinin-like peptide (SFDRMGGTEFGLM), which could not activate the receptor, we hypothesized that one or some of the numerous FMRFamide related peptides (FaRPs) could be the cognate ligands for this receptor. This hypothesis was based on the suggestion that RFamides may be ancestral neuropeptides, from which a lot of the amidated neuropeptides, including tachykinins, derived. Indeed, we found that the orphan receptor encoded by the Y59H11AL.1 gene is activated by several C. elegans neuropeptides, including SPMERSAMVRFamide. These peptides activate the receptor in a concentration-dependent way.

Amino Acid Sequence↗
PubMed2004

FMRFamide tagging--how an ionotropic receptor can be used to measure peptide secretion.

In this chapter, we describe a technique, FMRFamide tagging, that in principle can be used to measure the release of any sequenced neuropeptide. The method relies upon the addition of an "electrophysiologically active" tag to the prohormone that encodes the neuropeptide of interest. Secretion of the electrophysiological tag (and thus the peptide of interest) is detected by activation of the ionotropic "tag receptor." Both the tagged prohormone and the tag receptor are expressed in the cell type under investigation. Since the tag and the neuropeptide of interest are on the same prohormone they are co-secreted and thus secretion of the tag reflects the co-secretion of the neuropeptide of interest. This method can be used to detect neuropeptide secretion on a millisecond timescale.

Animals↗
PubMed1994

FMRFamide and membrane stretch as activators of the Aplysia S-channel.

The long-standing distinction between channels and transporters is becoming blurred, with one pump protein even able to convert reversibly to a channel in response to osmotic shock. In this light, it is plausible that stretch channels, membrane proteins whose physiological roles have been elusive, may be transporters exhibiting channel-like properties in response to mechanical stress. We recently described a case, however, where this seems an unlikely explanation. An Aplysia K channel whose physiological pedigree is well established (it is an excitability-modulating conductance mechanism) was found able to be activated by stretch. Here we establish more firmly the identity of this Aplysia conductance, the S-channel, as a stretch channel. We show that the permeation and fast kinetic properties of the stretch-activated channel and of the FMRFamide-activated S-channel are indistinguishable. We have also made progress in extending the kinetic analysis of the stretch channel to situations of multiple channel activity. This analysis implements a novel renewal theory approach and is therefore explained in some detail.

Animals↗
PubMed1997

Distribution of presumptive chemosensory afferents with FMRFamide- or substance P-like immunoreactivity in decapod crustaceans.

In five species of decapod crustaceans--Cherax destructor (crayfish), Carcinus maenas (crab), Homarus americanus (clawed lobster), Eriocheir sinensis (crab), Macrobrachium rosenbergii (shrimp)--immunocytochemical stainings revealed the presence of sensory afferents with FMRFamide-like immunoreactivity in the central nervous system. These afferents were extremely thin, very numerous, and innervated all sensory neuropils except the optic and olfactory lobes. In their target neuropils they gave rise to condensed net- or ball-like terminal structures. Only in Homarus americanus but not in any other studied species immunocytochemistry revealed a separate, non-overlapping class of sensory afferents with substance P-like immunoreactivity. Also the afferents with substance P-like immunoreactivity were very thin and numerous, innervated all sensory neuropils except optic and olfactory lobes, and gave rise to condensed terminal structures. From their morphological characteristics it can be concluded that likely both classes of afferents are chemosensory. The substance P-like immunoreactivity suggests a link with the nociceptor afferents of vertebrates, with which both classes of afferents share several other morphological features.

Animals↗
PubMed2002

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.

Animals↗
PubMedDate not supplied

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.

Amino Acid Sequence↗
PubMed2001

Three more novel FMRFamide-like neuropeptide sequences from the eyestalk of the giant freshwater prawn Macrobrachium rosenbergii.

In addition to five FMRFamide-like peptides (FLPs) previously isolated from the eyestalk of the giant freshwater prawn Macrobrachium rosenbergii (16), three more new FLPs (Mar-FLP6-8) were identified from minor immunoreactive fractions of 5,000 eyestalk extracted in methanol/acetic acid/water: DGGRNFLRFamide, GYGDRNFLRFamide and VSHNNFLRFamide. These three peptides share 5-6 common residues at the C-terminus with Mar-FLP1,2 and 3. This evidence reveals that the structural diversity and complexity of the FLP family in M. rosenbergii are similar to that found in other invertebrate species.

Animals↗
PubMed1997

Actions of FMRFamide-related peptides on the gCa2+ of the C1 neuron in Helix aspersa.

The endogenous neuropeptides FMRFamide and FLRFamide (tetrapeptides) reversibly reduced a voltage-activated calcium current in the C1 neuron of Helix aspersa by an average of 20%. Two structurally related heptapeptides, pQDPFLRFamide and pQDPFLRIamide, both derived from another precursor protein in this species, did not reduce the current at all.

Animals↗
PubMed1997

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.

Amino Acid Sequence↗
PubMed1997

Structure-activity relationships of FMRFamide-related peptides contracting Schistosoma mansoni muscle.

This study reports the potent myoactivity of flatworm FMRFamide-related peptides (FaRPs) on isolated muscle fibers of the human blood fluke, Schistosoma mansoni. The turbellarian peptides YIRFamide (EC50 4 eta M), GYIRFamide (EC50 1 eta M), and RYIRFamide (EC50 7 eta M), all induced muscle contraction more potently than the cestode FaRP GNFFRFamide (EC50 500 eta M). Using a series of synthetic analogs of the flatworm peptides YIRFamide, GYIRFamide and RYIRFamide, the structure-activity relationships of the muscle FaRP receptor were examined. With a few exceptions, each residue in YIRFamide is important in the maintenance of its myoactivity. Alanine scans resulted in peptides that were inactive (Ala1, Ala2, Ala3 and Ala4 YIRFamide; Ala4 and Ala5 RYIRFamide) or had much reduced potencies (Ala1, Ala2 and Ala3 RYIRFamide). Substitution of the N-terminal (Tyr1) residue of YIRFamide with the non-aromatic residues Thr or Arg produced analogs with greatly reduced potency. Replacement of the N-terminal Tyr with aromatic amino acids resulted in myoactive peptides (FIRFamide, EC50 100 eta M; WIRFamide, EC50 0.5 eta M). The activity of YIRFamide analogs which possessed a Leu2, Phe2 or Met2 residue (EC50's 10, 1 and 3 eta M, respectively) instead of Ile2 was not significantly altered, whereas, YVRFamide had a greatly reduced (EC50 200 eta M) activity. Replacement of the Phe4 with a Tyr4 (YIRYamide) also greatly lowered potency. Truncated analogs were either inactive (FRFamide, YRFamide, HRFamide, RFamide, Famide) or had very low potency (IRFamide and MRFamide), with the exception of nLRFamide (EC50 20 eta M). YIRF free acid was inactive. In summary, these data show the general structural requirements of this schistosome muscle FaRP receptor to be similar, but not identical, to those of previously characterized molluscan FaRP receptors.

Amino Acid Sequence↗
PubMed1997

Action of FMRFamide-like peptides on porcine gastrointestinal motility in vitro.

Mechanical activity was recorded in circular and longitudinal smooth muscle preparations isolated from extensive regions of the porcine gastrointestinal tract in response to the FMRFamide-like neuropeptides F8Famide and A18Famide. In all preparations, the peptides were about equipotent in producing phasic contractions or enhancing spontaneous activity. The most prominent responses were observed in jejunal longitudinal strips which were on the average 91% (+/- 4% SEM, n = 15; 10(-6) M) of the histamine (10(-5) M) responses. The peptide-induced phasic activity was completely abolished by nifedipine but was unaffected by tetrodotoxin, atropine, phentolamine, yohimbine, phenoxybenzamine, propranolol, methysergide, cimetidine, indomethacin, levallorphane or naloxone. Both peptides enhanced acetylcholine-induced contractions. However, bovine ileum and guinea-pig taenia coli was not affected by these peptides. The results indicate that F8F- and A18F-amide contract porcine gastrointestinal smooth muscle by acting directly via non-opioid receptors on L-type calcium channels. In addition an increase of the sensitivity to cholinergic stimulation occurs.

Animals↗