FMRFamide, a putative endogenous opiate antagonist: Evidence from suppression of defeat-induced analgesia and feeding in mice

Social conflict and defeat in mice leads to an activation of endogenous opiate systems. The effects of intracerebroventricular administration of the peptide FMRFamide (Phe-Met-Arg-Phe-NH2) and the opiate antagonist naloxone, on aggressive encounters, defeat-induced analgesia and defeat-induced feeding were examined in male mice. Both substances reduced the number of bites required to cause defeat in subordinate mice during aggressive encounters, as well as suppressing the subsequent defeat-induced analgesia. Administration of FMRFamide or naloxone also reduced defeat-induced feeding. These results indicate that FMRFamide (or FMRFamide-like neuropeptides) may function as endogenous opioid antagonists.     

PLG and FMRFamide — Endogenous peptides with marked inhibitory effects on opioid-induced feeding

1. Social conflict and defeat in mice leads to an activation of endogenous opiate systems and the display of marked feeding behavior.

2. Intraperitoneal administrations of prolyl-leucyl-glycinamide (PLG 0.01–10 mg/kg) leads to a dose-dependent inhibition of defeat-induced feeding that is analogous to that obtained after treatment with either the endogenous peptide FMRFamide (Phe-Met-Arg-Phe-NH₂), or the prototypic opiate antagonist, naloxone.

3. These results suggest that PLG, and FMRFamide, or related small peptides may function as endogenous antagonists of opioid-induced feeding.     

Inhibitory influences of FMRFamide and PLG on stress-induced opioid analgesia and activity

The effects of i.c.v. administrations of the peptide FMRFamide (Phe-Met-Arg-Phe-NH₂), as well as i.p. injections of PLG (Pro-Leu-Gly-NH₂) and the opiate antagonist, naloxone, on immobilization-induced analgesia and locomotor activity were examined in CF-1 and C57BL strains of mice. Both naloxone (1.0 mg/kg) and FMRFamide (0.10–1.0 μg) blocked the experimentally induced analgesia and activity, whereas PLG (0.10–10 mg/kg) suppressed only analgesia. These results indicate that FMRFamide (or FMRFamide-like neuropeptides) and PLG may function as differential antagonists of the behavioral and physiological consequences of endogenous opioid activation.     

Calcium channel blockers inhibit the antagonistic effects of PheMetArgPhe-amide (FMRFamide) on morphine- and stress-induced analgesia in mice

Determinations were made of the effects of the calcium channel blockers, nifedipine and verapamil, on the antagonistic effects of FMRFamide (PheMetArgPheNH₂) and naloxone on morphine- and immobilization-induced opioid analgesia in mice. Intraperitoneal (i.p.) administrations of the calcium channel antagonists significantly reduced the inhibitory effects of intracerebroventricular (i.c.v.) FMRFamide, but had no effects on i.p. or i.c.v. naloxone-mediated inhibition of either morphine- or immobilization-induced analgesia. These results suggest that the antagonistic effects of FMRFamide, (or other endogenous FMRFamide-like peptides) on both opiate- and opioid-mediated analgesia in mice may involve alterations in the functioning of calcium channels.     

Neuropeptides myomodulin,small cardioactive peptide,and buccalin in the central nervous system of Lymnaea stagnalis: Purification,immunoreactivity, and artifacts

The neuropeptides myomodulin, small cardioactive peptide (SCP), and buccalin are widely distributed in the phylum Mollusca and have important physiological functions. Here, we describe the detailed distribution of each class of peptide in the central nervous system (CNS) of the snail Lymnaea stagnalis by the use of immunocytochemical techniques combined with dye-marking of electrophysiologically identified neurons. We report the isolation and structural characterization of a Lymnaea myomodulin, PMSMLRLamide, identical to myomodulin A of Aplysia californica. Myomodulin immunoreactivity was localized in all 11 ganglia, in their connectives, and in peripheral nerves. In many cases, myomodulin immunoreactivity appeared localized in neuronal clusters expressing FMRFamide-like peptides, but also in a large number of additional neurons. Double-labelling experiments demonstrated myomodulin immunoreactivity in the visceral white interneuron, involved in regulation of cardiorespiration. SCP-like immunoreactivity also appeared in all ganglia, and double-labelling experiments revealed that in many locations it was specifically associated with clusters expressing distinct exons of the FMRFamide gene that are differentially expressed in the CNS. Characterization of the two types of SCP-antisera used in this study, however, suggested that they cross-reacted with both FMRFamide and N-terminally extended FMRFamide-like peptides. Selective preadsorption with these cross-reacting peptides resulted in elimination of the widespread staining and retention of bona fide SCP immunoreactivity in the buccal and pedal ganglia only. Buccalin immunoreactivity was limited to the buccal and pedal ganglia. It did not coincide with the distribution of either myomodulin or SCP. Most immunoreactive clusters were found in the pedal ganglia. © 1994 Wiley-Liss, Inc.     

FMRFamide-like immunoreactivity in rat brain: Development of a radioimmunoassay and its application in studies of distribution and chromatographic properties

A radioimmunoassay is described for the molluscan neuropeptide, Phe-Met-Arg-Phe-NH2 (FMRFamide). The antibody used is C-terminal-specific and shows slight but significant (1-2%) cross-reactivity with chicken pancreatic polypeptide (APP). The assay has been used to identify in rat brain extracts a pair of molecules that may represent mammalian counterparts of FMRFamide. Their concentrations were highest in spinal cord and hypothalamus (greater than 10 pmol . g-1) and lowest in cerebellum and striatum (less than 3.5 pmol . g-1). The two immunoreactive peptides were separated on CM ion-exchange chromatography where they appeared to be less basic than FMRFamide. On Sephadex G50 gel filtration one eluted in a similar position of FMRFamide and the other slightly earlier suggesting it may be of higher molecular weight. The rat immunoreactive components do not correspond to previously described neuropeptides or hormones, and may be members of a new group of mammalian neuropeptides with transmitter or modulatory functions.     

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.     

The regulation of circadian rhythms in the fly's visual system: involvement of FMRFamide-like neuropeptides and their relationship to pigment dispersing factor in Musca domestica and Drosophila melanogaster

The cross-sectional area of axon profiles in two classes of interneuron, L1 and L2, in the fly's lamina, exhibits a circadian rhythm of swelling and shrinking; axon caliber also changes after microinjecting putative lamina neurotransmitters. Among these, the neuropeptide pigment-dispersing factor, PDF, is proposed to transmit circadian information from the housefly's (Musca domestica) clock to L1 and L2, increasing axon caliber during the day. Testing whether other neurotransmitters may modulate this effect we have: (1) examined optic lobe cell immunoreactivity to FMRFamide peptides and its co-immunolocalization to PDF in M. domestica and Drosophila melanogaster, and to the product of the circadian clock gene PER in D. melanogaster; and (2) made microinjections of FMRFamide and related neuropeptides into the second neuropil, or medulla. In M. domestica, nine groups of optic lobe cells, several cells in the lateral and dorsal protocerebrum, and in the subesophageal ganglion, together contribute dense FMRFamide immunoreactive arborizations in almost all central brain and optic lobe neuropils. In D. melanogaster a similar pattern of labeling arises from fewer cells. Daytime microinjections show that another neuropeptide, similar to molluscan FMRFamide, shrinks M. domestica's L1 and L2 axons, thus opposing the action of PDF. We discuss evidence for a medulla site of action for a released FMRFamide-like peptide, either from: MeRF2 cells, acting directly on L1 and L2's medulla terminals; or MeRF1 cells, acting indirectly via medulla centrifugal cells C2 and C3.     

FMRFamide-like substances in the leech. III. Biochemical characterization and physiological effects

FMRFamide-like immunoreactivity has been previously localized to identified neurons in the CNS of the leech, Hirudo medicinalis (Kuhlman et al., 1985a). These leech antigens have been characterized biochemically by reverse-phase high-pressure liquid chromatography (HPLC) followed by radioimmunoassay (RIA). The majority of the FMRFamide-like immunoreactivity recovered by HPLC from extracts of leech nerve cords coelutes with authentic FMRFamide. We have tentatively identified this major leech peptide as authentic FMRFamide. Two neurons that control heartbeat in the leech, the HE motor and HA modulatory neurons, and their neural processes on the heart are FMRFamide-like immunoreactive (Kuhlman et al., 1985a). Single individually dissected HE and HA cells were analyzed by HPLC and RIA. Only 1 FMRFamide-like peptide was found in extracts of HA cells; this peptide was chromatographically indistinguishable from authentic FMRFamide. The FMRFamide-like peptide in HE cells could not be isolated by experimental procedures used. Most of the FMRFamide-like immunoreactivity contained within the neural processes on the heart also coeluted with authentic FMRFamide. HE motor neurons, which are believed to be cholinergic (Wallace, 1981a, b; Maranto and Calabrese, 1984a, b), were examined for their FMRFamide-like effects on the heart. The presence of curare in the bathing medium did not block the ability of FMRFamide to induce myogenic activity in heart muscle, suggesting that FMRFamide and ACh act at different receptor sites on the heart. Prolonged firing in HE cells in the presence of curare also induced myogenic activity in heart muscle. This FMRFamide-like action of the HE motor neurons may be normally masked by their cholinergic actions.     

Processing of the FMRFamide Precursor Protein in the Snail Lymnaea stagnalis: Characterization and Neuronal Localization of a Novel Peptide, 'SEEPLY'

In the pulmonate snail Lymnaea stagnalis , FMRFamide-like neuropeptides are encoded by a multi-exon genomic locus which is subject to regulation at the level of mRNA splicing. We aim to understand the post-translational processing of one resulting protein precursor encoding the tetrapeptide FMRFamide and a number of other putative peptides, and determine the distribution of the final peptide products in the central nervous system (CNS) and periphery of Lymnaea. We focused on two previously unknown peptide sequences predicted by molecular cloning to be encoded in the tetrapeptide protein precursor consecutively, separated by the tetrabasic cleavage site RKRR. Here we report the isolation and structural characterization of a novel non-FMRFamide-like peptide, the 22 amino acid peptide SEQPDVDDYLRDWLQSEEPLY. The novel peptide is colocalized with FMRFamide in the CNS in a number of identified neuronal systems and their peripheral motor targets, as determined by in situ hybridization and immunocytochemistry. Its detection in heart excitatory motoneurons and in nerve fibres of the heart indicated that the novel peptide may play a role, together with FMRFamide, in heart regulation in the snail. The second predicted peptide, STEAGGQSEEMTHRTA (16 amino acids), was at very low abundance in the CNS and was only occasionally detected. Our current findings, suggestive of a distinct pattern of post-translational processing, allowed the reassessment of a previously proposed hypothesis that the two equivalent sequences in the Aplysia FMRFamide gene constitute a molluscan homologue of vertebrate corticotrophin releasing factor-like peptides.     

Fast axonal transport of modulatory neuropeptides from central ganglia to components of the feeding system in Aplysia

The transport of neuropeptides from central ganglia to components of the feeding system was studied in Aplysia. Peptide transport was determined by incubating buccal or cerebral ganglia with 35S-methionine and measuring the appearance of labeled peptides by high-pressure liquid chromatography (HPLC) of extracts of target tissues. Selected nerves were left intact and passed through a Vaseline diffusion barrier separating the ganglia and their targets. Five major labeled peptides were observed to be transported from the buccal ganglia to feeding muscles. They were buccalin, FMRFamide, myomodulin, and 2 small cardioactive peptides. Each of these peptides has been shown to modulate the responses of these muscles to their motor neurons. The peptides were transported by fast axonal transport, as judged by the distance transported and the sensitivity to colchicine. When normalized to correct for differences in total incorporation, the patterns of peptide transport were reproducible between animals. The nature and amount of the peptides transported were different for different muscles. The nature of peptide transport also varied for different nerve groups. These results support the proposition that these 5 peptides act as modulatory transmitters at feeding muscles. No transport of neuropeptides from the cerebral ganglia to feeding muscles was observed, although myomodulin was specifically transported to the buccal ganglia. This suggests that this peptide may play an important role in the previously observed regulation of buccal ganglia activity by neurons in the cerebral ganglia.     

FMRFamide peptides in Helisoma: identification and physiological actions at a peripheral synapse

Previous reports have demonstrated powerful neuromodulatory actions of the molluscan tetrapeptide FMRFamide in both the central and peripheral nervous systems of the freshwater snail Helisoma. The present study was designed to examine both the nature of the FMRFamide-like peptides in Helisoma and to define their physiological actions at a peripheral synapse. We report that, as determined by HPLC/RIA and mass spectrometry, Helisoma contains both FMRFamide and 2 of its analogs, FLRFamide and GDPFLRFamide. Whereas whole animals contain about 100 pmol/gm of these peptides, they were enriched in the nervous system (3000 pmol/gm) and in a peripheral target organ, the salivary glands (500 pmol/gm). For histochemical and physiological studies we examined the salivary glands, which are known to be innervated by neuron 4 of the buccal ganglion. We confirmed the presence of FMRFamide-like fibers on the salivary gland by immunohistochemistry using a polyclonal antiserum. These fibers appear to be largely derived from somata located in the central ring ganglia. For physiological tests we examined the neuron 4-gland synapse, at which presynaptic action potentials normally evoke a suprathreshold EPSP in gland cells. Bath application of FMRFamide, FLRFamide, or GDPFLRFamide at micromolar concentration to a buccal ganglia/salivary gland preparation completely suppressed spontaneous rhythmic activity. The sites of action of these peptides were examined by iontophoretic application of FMRFamide to neuron 4 or the salivary gland. Application of the peptide to the soma of neuron 4 caused a hyperpolarization that suppressed spontaneously generated action potentials. When applied to the salivary gland, FMRFamide caused a hyperpolarization that reduced the EPSPs evoked by neuron 4 to below spike threshold. The latter observation implies a postsynaptic locus of action for FMRFamide, and this possibility was tested by direct depolarization of the gland with iontophoresis of ACh (the putative transmitter of neuron 4). Such depolarizations were also reduced by FMRFamide. We conclude that Helisoma contains FMRFamide and 2 of its analogs, these peptides being enriched in the nervous system and salivary glands. Furthermore, these peptides can suppress activation of the salivary glands by actions both directly on gland cells and on the effector neuron.     

Low affinity inhibition of opioid receptor binding by FMRFamide

The ability of the molluscan neuropeptide Phe-Met-Arg-Phe-NH2 (FMRFamide) to inhibit the binding of opioid-receptor radioligands to mammalian neural tissue was examined. Rabbit brain membrane preparations were exposed to tritiated dihydromorphine and ethylketocyclazocine in the presence of various concentrations of FMRFamide. FMRFamide inhibited the specific binding of both ligands in a dose-related manner, suggesting that the neuropeptide can inhibit binding to at least two subtypes of opioid receptors (mu and kappa). These data are consistent with the recent proposal that FMRFamide, or the immunoreactive FMRFamide-like material in mammalian brain, spinal cord, and gastrointestinal tract, can act as an endogenous opioid antagonist. However, the low binding affinity of FMRFamide might suggest an alternative mechanism for FMRFamide antagonism of opioid action in vivo.     

SCPB- and FMRFamide-like immunoreactivities in lobster neurons: Colocalization of distinct peptides or colabeling of the same peptide(s)?

Virtually all of the SCPB-like immunoreactive neurons (ca. 60 cells) in the lobster Homarus americanus also contain FMRFamide-like immunoreactivity. Control experiments reveal that SCPB-and FMRFamide-like immunoreactivities are successfully preadsorbed with their specific antigens, while the normal staining pattern is retained following preadsorption of each antibody with the alternate peptide. These experiments potentially lead to the conclusion that the anti-SCPB and anti-FMRFamide antibodies are labeling distinct compounds that are colocalized in lobster neurons. The lobster nervous system does not, however, contain authentic FMRFamide, but rather several FMRFamide-like compounds (Trimmer et al., J. Comp. Neurol. 266:16-26, 1987). The most abundant of these is the octapeptide TNRNFLRFamide. Experiments demonstrate that SCPB-like immunoreactivity is completely preadsorbed with synthetic TNRNFLRFamide, while there is a significant or complete loss of staining after preadsorption of the FMRFamide antibody with this molecule. Met-enkephalin-Arg-Phe-amide (YGGFMRFamide), an extended opioid peptide containing the FMRFamide sequence, also preadsorbs SCPB- and FMRFamide-like immunoreactivities, while Met-enkephalin-Arg-Phe (YGGFMRF) has no effect on the staining properties of these antibodies. These results suggest that the SCPB antibody can bind to extended forms of FMRFamide-like molecules, and that anti-SCPB and anti-FMRFamide antibodies may be colabeling one or more FMRFamide-like molecules in lobster neurons.     

Interspecific comparison of a Drosophila gene encoding FMRFamide-related neuropeptides

In order to identify functionally important regions of a neuropeptide gene in Drosophila melanogaster, we have studied its occurrence in related species and have characterized the structure of a homologous gene in Drosophila virilis. The melanogaster gene encodes a precursor that contains 13 neuropeptides related to the molluscan tetrapeptide FMRFamide (Nambu et al., 1988; Schneider and Taghert, 1988). Using the melanogaster gene as a probe in Southern blot analysis, related sequences were detected in DNA from each of 7 species tested. D. virilis, which is estimated to have diverged from D. melanogaster between 60 and 80 million years ago (Throckmorton, 1975), was chosen for more detailed study. Immunocytochemical staining using an antibody to authentic FMRFamide revealed a similar set of immunoreactive neurons in the CNS of larvae from the 2 Drosophila species. Using a melanogaster gene probe, overlapping clones were isolated from a virilis genomic library; DNA sequence analysis indicated the presence of a homologous gene. Comparisons of the genes and deduced proteins between the 2 species revealed the following points. (1) Both genes are divided into 2 exons: in D. melanogaster the exons are 106 and 1352 bp long; in D. virilis, they are 169 and at least 1232 bp long; in both species, the intron is approximately 2.5 kb long. (2) The sequence of exon I has largely diverged, and in neither species are exon I sequences translated. In this vicinity of the gene, sequence conservation is limited to a 67 bp region that spans the TATA box and the RNA start site. (3) The deduced neuropeptide precursors have very similar sizes (347 vs 339 amino acids) and the presumed signal sequences are perfectly conserved. (4) While the melanogaster precursor contains 13 FMRFamide-related peptides, the virilis precursor contains only 10. (5) The sequences of some but not all of the FMRFamide-like peptides are perfectly conserved. (6) In the rest of the precursor, significant sequence conservation is found only in the N-terminal portion; immediately downstream of the final FMRFamide-like peptide, the protein sequences are highly divergent. (7) 5' to the RNA start sites (1.2 kb of melanogaster DNA and 1.8 kb of virilis DNA), 17 small (9-52 base pairs) regions are evolutionarily conserved (greater than 80% sequence conservation). We discuss neuropeptide biosynthesis, the functions and evolution of FMRFamide-like neuropeptides in insects, and the cell-specific regulation of neuropeptide gene expression in the contexts of these results.     

Interganglionic axonal transport of neuropeptides in Aplysia

The transport of neuropeptides between central ganglia was studied in Aplysia. Peptide transport was determined by incubating ganglia with 35S-methionine and measuring the appearance of labeled peptides in connected ganglia. Selected interganglionic connectives were left intact and passed through a diffusion barrier separating the ganglia. Labeled peptides transported between ganglia included FMRFamide, myomodulin, and pedal peptide. Each of these peptides has been shown to be physiologically active in Aplysia. In addition to these previously characterized neuropeptides, a number of other as yet uncharacterized labeled peptides were also transported. All the peptides were transported by fast axonal transport as judged by the distance transported and/or the sensitivity to colchicine. Overall, FMRFamide and several unidentified peptides were the predominant transported peptides. However, the nature and amount of the peptides transported differed for each ganglia. These results support the proposition that the labeled peptides have transmitterlike actions and suggest that there are a number of neuropeptides that are likely to have central actions that have not yet been characterized in Aplysia.     

Biochemical and immunocytological localization of the neuropeptides FMRFamide, SCPA, SCPB, to neurons involved in the regulation of feeding in Aplysia

The localization of the neuropeptide FMRFamide in the buccal ganglia and buccal muscles of Aplysia was studied by immunocytology and high-pressure liquid chromatography (HPLC) combined with either a sensitive bioassay or 35S-methionine labeling. Immunocytology with an antiserum directed to FMRFamide stained a large number of fibers, varicosities, and neuronal somata. Two groups of stained neurons were of particular interest. One was the S cells, a group comprised of many small neurons, the majority of which were stained. HPLC of pooled labeled S cells confirmed that at least some of these neurons synthesize FMRFamide. The other group of stained neurons were in the ventral cluster, a group comprised of a small number of large neurons, many of which are motor neurons that innervate the buccal muscles involved in producing biting and swallowing movements. Several of the ventral neurons were previously shown to contain 2 other neuropeptides, the small cardioactive peptides SCPA and SCPB. These neurons are sufficiently large to permit HPLC analyses of the neuropeptides synthesized by individual neurons. This procedure confirmed that individual ventral neurons synthesized FMRFamide, or the SCPs, or all 3 peptides. The coexistence of FMRFamide and the SCPs in the same neuron was confirmed by simultaneous staining of sections from the buccal ganglia with a monoclonal antibody to the SCPs and an antiserum to FMRFamide. The coexistence of the 3 peptides in the same neuron was surprising in light of the observations that these peptides often have opposite biological activity. The ventral neurons are large and potentially identifiable as individuals. Thus, these neurons may be particularly useful for studying the physiological and behavioral roles of neuropeptides in generating complex behaviors.     

Gonadotropin-releasing hormone (GnRF), Molluscan cardioexcitatory peptide (FMRFamide), enkephalin and related neuropeptides affect goldfish retinal ganglion cell activity

Recently gonadotropin-releasing hormone (GnRF)-like and molluscan cardioexcitatory peptide (FMRFamide)-like compounds have been colocalized immunocytochemically to the terminal nerve, a presumed olfactoretinal efferent system in goldfish. In the present study these and related neuropeptides were shown to affect ganglion cell activity, recorded extracellularly, when applied to the isolated superfused goldfish retina. GnRF was usually excitatory. Salmon GnRF (sGnRF) was 10-30x more potent than chicken or mammalian GnRF. FMRFamide and enkephalin also were often excitatory but caused more varied responses than sGnRF. Met5-enkephalin-Arg6-Phe7-NH2 (YGGFMRFamide), which contains both enkephalin and FMRFamide sequences, tended to act like both of these peptides but with mainly enkephalin-like properties. Neuropeptide Y and the C-terminal hexapeptide of pancreatic polypeptides, whose C-terminus (-Arg-Tyr-NH2) is closely related to that of FMRFamide (-Arg-Phe-NH2), gave no consistent responses. Threshold doses were equivalent to: 0.1 microM for sGnRF; 0.5 microM for YGGFMRFamide; 1.5 microM for FMRFamide and enkephalin. Rapid, complete and irreversible desensitization was induced by single, 10-20x threshold doses of sGnRF; but desensitization was infrequent and limited with the other peptides. In general, all peptides tested affected the spatially and chromatically antagonistic receptive field components similarly, but selective actions were seen in a few cases with FMRFamide and with the opioid antagonist, naloxone. Responses, especially to sGnRF and FMRFamide, tended to be most frequently obtained and pronounced in winter and spring, suggesting a correlation with seasonally regulated sexual and reproductive activity. Our observations provide further evidence for transmitter-like roles of neuropeptides related to sGnRF and FMRFamide in the teleostean terminal nerve. The actions of agonists and antagonists, singly and in combination, imply strongly that there are distinctive postsynaptic receptors and/or neural pathways for GnRF-, FMRFamide- and enkephalin-like peptides in the goldfish retina.     

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.     

Peptidergic modulation of a neuromuscular junction inAplysia: bioactivity and immunocytochemistry

Three endogenous peptides were assayed for bioactivity at an Aplysia neuromuscular junction. Evoked contractions were enhanced by Phe-Met-Arg-Phe-NH2 (FMRFamide) and suppressed by arginine vasotocin; small cardioactive peptide B (SCPB) also enhanced contractions at low concentrations, but caused suppression at higher doses. In accordance with their putative roles as neuromodulators, immunocytochemistry revealed FMRFamide-like and SCPB-like fibers on the muscle surface.