FMRFamide neuropeptides simultaneously increase and decrease K+ current in an identified neurone

Distribution and development of FMRFamide-like immunoreactive neuronal systems in the brain of the brown trout, Salmo trutta fario

The distribution of Phe-Met-Arg-Phe-amide (FMRFamide) peptide-immunoreactive (FMRF-ir) cells and fibers in the terminal nerve and central nervous system was investigated in developing stages and adults of the brown trout, Salmo trutta fario. The first FMRF-ir neurons appeared in the terminal nerve system of 8-mm embryos in and below the olfactory placode. In the brain, FMRF-ir neurons were first observed in the rostral hypothalamus, primordial hypothalamic lobe, mesencephalic laminar nucleus, and locus coeruleus of 12- to 13 -m embryos. After hatching, FMRF-ir cells appeared in the lateral part of the ventral telencephalic area and the anterior tuberal nucleus. In adult trout, FMRF-ir cells were observed in all these areas. The number of FMRF-ir neurons increased markedly in some of these populations during development. Dense innervation by FMRF-ir fibers was observed in the dorsal and lateral parts of the dorsal telencephalic area, and in the ventral telencephalic area, the lateral preoptic area, the medial hypothalamic and posterior tubercle regions, midbrain tegmentum and rhombencephalic reticular areas, the central gray, the superior raphe nucleus, the secondary visceral nucleus, the vagal nuclei, and the area postrema. Fairly rich FMRF-ir innervation was also observed in the optic tectum and some parts of the torus semicircularis. The saccus vasculosus and hypophysis received a moderate amount of FMRF-ir fibers. Innervation of most of these regions appeared either in late alevins or fry, although FMRF-ir fibers in the preoptic area, hypothalamus, and reticular areas appeared in embryos. Comparative analysis of the complex innervation pattern observed in the brain of trout suggests that FMRF is involved in a variety of functions, like the FMRF family of peptides in mammals.

Inhibition of Na/Ca exchange by Phe-Met-Arg-Phe-NH2 (FMRFa)-related peptides in intact rat pancreatic B-cells

Phe-Met-Arg-Phe-NH2 (FMRFa)-related peptides were recently shown to inhibit Na/Ca exchange in cardiac sarcolemmal vesicles. In the present study, we examined the effects of FMRFa-related peptides on Na/Ca exchange in intact (pancreatic B) cells. At 2.8 mM glucose, FMRFa-related peptides only weakly inhibited Na/Ca exchange although their effect was more marked under depolarizing conditions. The peptides blocked neither the Na/K-ATPase nor Ca2+ channels but slightly reduced membrane K+ permeability. Our data indicate that FMRFa-related peptides are weak and non-specific inhibitors of Na/Ca exchange in intact B cells. The data do not confirm the view that the peptides may exert some of their physiological modulatory role by inhibiting Na/Ca exchange.

Comparison of two Caenorhabditis genes encoding FMRFamide(Phe-Met-Arg-Phe-NH2)-like peptides

We have identified a gene encoding multiple FMRFamide-like peptides in the necromenic nematode Caenorhabditis vulgaris. This gene, Cv-flp-1, shares strong sequence homology in the coding regions with the flp-1 gene from the related free-living soil nematode C. elegans. The predicted neuropeptide precursor proteins differ by only four conservative amino acid changes, none of which affects sequences of the predicted neuropeptides. DNA sequences in the non-coding areas are less conserved, but areas of sequence homology are found in introns and in 3' and 5' non-translated regions, suggesting some functional significance for these conserved regions. In C. vulgaris, as was found in C. elegans, two transcripts are presumably produced as a result of use of an alternative 3' splice acceptor site. Lastly, an antibody specific for the RF-moiety of FMRFamide stains a similar subset of cells in C. elegans and C. vulgaris. These results indicate that the function and regulation of the peptides are likely to be conserved in both species.

Actions of Fusinus FMRFamide-related peptides on the identified central neurones of the snail, Helix aspersa

The actions of Fusinus FMRFamide-related peptides, that is FMRFamide, FLRFamide, GSLFRFamide, SSLFRFamide, the analogue, GSFFRFamide, and the fragments, LFRFamide and RFamide, were examined on the F1, F2 and F5 neurones of Helix aspersa. All Fusinus peptides exhibit an inhibitory effect on F1 and F5 neurone. On F2 neurone, FMRFamide and FLRFamide exhibit an excitatory effect but GSLFRFamide and SSLFRFamide exhibit an inhibition. The fragment, LFRFamide, is 10-times less potent than GSLFRFamide. GSFFRFamide and RFamide are inactive on F1, F2 and F5 neurone. This evidence indicates that the fragment, LFRFamide, is crucial for the biological activity of Fusinus hexapeptides. The inhibition induced by Fusinus hexapeptides had a reversal potential around -75/-80 mV. It was potentiated in K(+)-free saline, partially abolished either in 10 mM TEA or in 10 mM Co2+ saline and completely abolished in 500 microM 4-AP saline. This evidence indicates that there are multiple K+ channels which are activated by Fusinus hexapeptides and that the IA is more susceptible than IK and IKCa to these peptides.

FMRFamide-related peptides from the kidney of the snail, Helisoma trivolvis

Three FMRFamide-related peptides (FaRPs) were purified and characterized from the kidney of the snail, Helisoma trivolvis, by HPLC and detected using two radioimmunoassays (RIA) for FaRPs. Automated sequencing and mass spectrometry of the isolated peptides suggest the following sequences: Phe-Met-Arg-Phe-NH2 (FMRFamide), Phe-Leu-Arg-Phe-NH2 (FMRFamide), and Gly-Asp-Pro-Phe-Leu-Arg-Phe-NH2 (GDPFLRFamide). The FaRPs, predominantly the heptapeptides, were also detected by HPLC and RIA in other osmoregulatory tissues such as the skin, mantle, and the hemolymph. The level of FaRPs, detected by radioimmunoassay, appears to be lower in snails kept under hyposmotic stress than in snails kept under isosmotic stress. The FaRPs appear to be involved in osmoregulation in H. trivolvis.

G-protein mediating the slow depolarization induced by FMRFamide in the ganglion cells of Aplysia

Application of FMRFamide (Phe-Met-Arg-Phe-NH2) induced a slow depolarization in neurons of the Aplysia abdominal ganglion. In voltage-clamped cells, FMRFamide induced a slow inward current that increased when the membrane was depolarized beyond -85 mV, showing a negative slope conductance. However, this inward current never reversed to outward current when hyperpolarized beyond the equilibrium potential for K+. The FMRFamide-induced response was markedly augmented in Ca(2+)-free media, but depressed in Na(+)-free media. It was unaffected by a change in external potassium. Intracellular injection of guanosine 5'-O-(2-thiodiphosphate) (GDP beta S) significantly depressed the FMRFamide response in a dose-dependent way. Injection of cholera toxin (CTX) which did not cause any current response, selectively and irreversibly blocked the FMRFamide response. Neither 3'-deoxyadenosine, an inhibitor of adenylate cyclase, nor H-8, an inhibitor of cyclic adenosine 3',5'-monophosphate (cyclic AMP)-dependent kinase, depressed the FMRFamide response. 3-Isobutyl-1-methylxanthine (IBMX) did not augment the FMRFamide response appreciably. The FMRFamide response was not occluded at all by a relatively large injection of 8-bromo-cyclic AMP. It was concluded that the FMRFamide response is produced by the opening of the voltage-dependent Na(+)-channels via activation of a certain CTX-sensitive G-protein which is different from conventional "Gs" that activates adenylate cyclase.

FMRFamide-immunoreactive structures in the brain of the brown hagfish, Paramyxine atami: relationship with neuropeptide Y-immunoreactive structures

Localization of the molluscan cardioexcitatory tetrapeptide FMRFamide (Phe-Met-Arg-Phe-NH2) in the brain and hypophysis of the brown hagfish, Paramyxine atami, was examined by immunohistochemistry specially regarding a possible relationship with neuropeptide Y (NPY). FMRFamide-immunoreactive fibers were demonstrated in many regions of the brain, with the highest density in the diencephalon. However, no immunoreactivity was found in the hypophysis. Labeled cells were chiefly located in the nucleus hypothalamicus of the diencephalon, although a few cells were recognized in the ventrolateral area of the caudal tegmentum. Examination of adjacent sections immunostained alternatively with anti-NPY antiserum and anti-FMRFamide antiserum showed overlapping of the distributional patterns of the immunoreactive structures in the brain. Moreover, the same cells in the nucleus hypothalamicus were immunostained with both antisera. Cross-blocking experiments showed that the FMRF-amide-immunoreactivity is abolished by preabsorption of the antiserum with homologous antigen, but not eliminated completely by pretreatment with appropriate antigens (NPY, avian pancreatic polypeptide and methionine-enkephalin-Arg-Phe). In contrast, the NPY-immunoreactivity was blocked by pretreatment of the antiserum with NPY, pancreatic polypeptide or FMRFamide, although no blocking by enkephalin was observed. Accordingly, the present study shows that, in the brown hagfish, FMRFamide-immunoreactive structures in the brain can be recognized by anti-NPY antiserum.

Immunocytochemical distribution of FMRFamide-like substance in the brain of the cloudy dogfish, Scyliorhinus torazame

The distribution of the molluscan cardioexcitatory tetrapeptide FMRFamide (Phe-Met-Arg-Phe-NH2) in the brain of the cloudy dogfish, Scyliorhinus torazame, was examined by immunocytochemistry. FMRFamide-like immunoreactivity was demonstrated to occur extensively in various regions of the dogfish brain, except for the corpus cerebelli. Immunoreactive neuronal perikarya were located in the ganglion of the nervus terminalis, the preoptic area, and the hypothalamic periventricular gray matter consisting of the nucleus medius hypothalamicus, the nucleus lateralis tuberis, and the nucleus lobi lateralis. Some of the immunoreactive cells in the hypothalamus were identified as cerebrospinal fluid-contacting neurons. The bulk of the immunostained fibers in the nervus terminalis penetrated into the midventral portion of the telencephalon and ran dorsocaudally toward the basal telencephalon and hypothalamus, showing radial projections or ramifications. The labeled fibers were abundant in the midbasal part of the telencephalon and in the hypothalamus, where some fibers were found in loose networks around the cell bodies of the nucleus septi and hypothalamic periventricular nuclei. The fibers demonstrated in the hypothalamus terminated around the vascular wall of the primary capillary plexus of the median eminence or penetrated deeply into the pars intermedia of the hypophysis. These results suggest that, in the dogfish, an FMRFamide-like substance participates in the regulation of adenohypophysial function. This molecule may have a role as a neurotransmitter and/or neuromodulator in the central nervous system.

Interaction of opiate peptides with dopamine effects on prolactin secretion and membrane electrical properties in anterior pituitary cells from lactating rats

Abstract Met-enkephalin and beta-endorphin induced a partial reversion of the dopamine inhibition of prolactin release from pituitary cells of lactating rats in primary culture. This effect of opiate peptides was dose-dependent with an EC50 of 40 +/- 8 nM and 45 +/- 7 nM and maximal blockade of dopamine inhibition of 60% and 68% for Met-enkephalin and beta-endorphin, respectively. Naloxone antagonized the effect of Met-enkephalin with an EC50 of 22 +/- 12 nM. Furthermore, this Met-enkephalin effect on dopamine inhibition of prolactin secretion appeared non-competitive since it reduced maximal inhibition without affecting the apparent affinity of dopamine. Finally, it should be noted that the two opiate peptides had no effect on spontaneous prolactin release. In electrophysiological experiments, local ejection of dopamine on tested cells induced an hyperpolarization concomitant with an increase of the membrane conductance. Ejection of Met-enkephalin or beta-endorphin alone did not modify the electrical properties of the cells (resting potential, membrane conductance and excitability). In contrast, both peptides blocked in a reversible manner the dopamine-induced electrical responses. These effects were antagonized by naloxone. However, this interaction of opiatepeptides with dopamine electrical response was not observed on all cells tested. We conclude that the blocking effect of opiates on dopamine-induced hyperpolarization may account, at least in part, for the ability of these peptides to interact with dopamine inhibition of prolactin release.

Electrophysiological effects of FLFQPQRF amide, an endogenous brain morphine modulating peptide, on cultured mouse spinal-cord neurons

Intracellular recordings were made from dissociated fetal mouse spinal cord neurones in primary culture. Micropressure application of FLFQPQRFamide (10(-5) M in the delivery pipette), an endogenous mammalian brain morphine modulating peptide, onto the surface of spinal cord neurones induced, in a dose dependent manner, a transitory hyperpolarization followed by a long lasting depolarization of the membrane potential (n = 37). In contrast, no response was observed when the peptide was applied on dorsal root ganglia neurones (n = 30). The depolarizing phase of this response was underlied by an increase of the input resistance. Extrapolated reversal potential for the depolarizing phase was close to -80 mV while it was close to -40 mV for the hyperpolarizing phase. Increasing extracellular K+ concentration raised the reversal potential value of depolarizing phases to more positive values. The amplitude of the depolarizing phase was reduced by application of tetraethylammonium (50 mM) while it was enhanced by application of 4-aminopyridine (3 mM). CaCl2 application (3 mM) reversibly blocked the hyperpolarization and decreased the subsequent depolarization. In presence of Ba2+ the extrapollated reversal potential of the hyperpolarizing phase was dramatically shifted to a more positive value. Finally FLFQPQRFamide induced response can be partially mimicked by FMRFamide application. Our observations indicate that FLFQPQRFamide can have multiple effects on membrane conductance of mammalian spinal cord neurones by acting on a single class of receptor. These effects of FLFQPQRFamide were found to be mainly excitatory.

Characterization of rat spinal cord receptors to FLFQPQRFamide, a mammalian morphine modulating peptide: a binding study

An in vitro binding assay, using 125I-YLFQPQRFamide, a newly synthetized iodinated analog of FLFQPQRFamide, in which Phe1 (F) has been substituted by a Tyr (Y), was developed to demonstrate and characterize putative binding sites of this brain morphine modulating peptide. This radioligand bound in a time-dependent manner to rat spinal cord membrane preparation. This binding was dose-dependent, saturable and reversible. Both kinetic data and saturation measured at equilibrium lead to the existence of a homogenous population of high affinity binding sites with a Kd value of 0.09-0.1 nM and a maximal capacity Bmax of 14.5 +/- 2 fmol/mg protein. Results of competition experiments show that both FLFQPQRFamide and its analog YLFQPQRFamide had a similar capacity to inhibit the 125I-YLFQPQRFamide binding, suggesting that this radioiodinated analog is a good tool to study binding characteristics of FLFQPQRFamide receptors. The related octadecapeptide AGEGLSSPFWSLAAPQRFamide, another mammalian morphine modulating peptide competes for radioligand binding with similar potency. Our results also show that mu, delta and kappa opiate receptor agonists as well as the antagonist naloxone were not able to affect binding either in presence or in absence of 120 mM NaCl. Together, these data demonstrate that FLFQPQRFamide does not function as an endogenous opiate receptor antagonist and that is capacity to reduce opiate-induced analgesia is supported by specific binding sites.

The molluscan neuropeptide FMRFamide stimulates the release of [14C]acetylcholine from isolated ileal synaptosomal preparations of guinea-pig

FMRFamide stimulated, in a dose-dependent manner, the efflux of [14C]acetylcholine (ACh) from isolated synaptosomes of guinea-pig ileum preloaded with labelled choline. Participation of the cholinergic mechanism and/or substance P was ruled out by the finding that antagonists failed to affect the FMRFamide-induced release of ACh. The ACh-releasing action of FMRFamide was negated by the deletion of calcium ion from the bathing medium and it was also abolished by tetrodotoxin. The results obtained suggest that FMRFamide possesses the ability to induce the release of ACh from enteric synaptosomes of guinea-pig.

Further characterization of Helix FMRFamide receptors: kinetics, tissue distribution, and interactions with the endogenous heptapeptides

The biphasic binding of 125I-daYFnLRFamide to crude brain membranes of Helix aspersa is due to two discernible sites (high and low affinity) rather than different agonist-induced states. The tissues in the snail that show the greatest specific 125I-daYFnLRFamide binding are the brain, reproductive system, and digestive system. The heart shows moderate binding levels, whereas low values are obtained in the oviduct and retractor muscles. The N-terminal SAR of the Helix heptapeptides (X-DPFLRFamide) indicates that, although the substitution of Leu for Met accounts for some, the dipeptide X-Asp produces most of the loss in potency at FMRFamide receptors in Helix brain.

AF1, a sequenced bioactive neuropeptide isolated from the nematode Ascaris suum

An FMRFamide-like neuropeptide, named AF1, was isolated from head extracts of the nematode Ascaris suum using five steps of HPLC. AF1 is a heptapeptide with the amino acid sequence Lys-Asn-Glu-Phe-Ile-Arg-Phe-NH2. Synthetic AF1 (10(-9) to 10(-7) M) rapidly and reversibly abolished slow membrane potential oscillations of identified ventral and dorsal inhibitory motoneurons and selectively reduced their input resistances. Synaptic transmission was not blocked. In intact Ascaris, AF1 inhibited locomotory movements. This study indicates a potential physiological role for an endogenous neuropeptide in nematodes.

In vitro inhibition of methionine incorporation in the dorsal bodies of Helix aspersa by synthetic FMRFamide

1. In in vitro conditions, synthetic FMRFamide was shown to inhibit the uptake of labelled methionine by the dorsal bodies (DB)-containing connective tissue of Helix aspersa. 2. This effect occurred at physiological concentrations and in a dose-dependent manner. 3. Among the different cell types of the explants, the DB cells preferentially incorporated the radioactive precursor. 4. These results suggest that FMRFamide plays a biological role in controlling the DB activity (protein synthesis) of Helix aspersa.

The action of FMRFamide (Phe-Met-Arg-Phe-NH2) and related peptides on mammals

First purified 11 years ago from clam ganglia, FMRFamide (Phe-Met-Arg-Phe-NH2) was quickly demonstrated to be cardioactive in several molluscan species. Subsequent discovery that FMRFamide, or FMRFamide-related peptides (FaRPs), were present in mammalian central nervous system and gastrointestinal tract prompted investigations into the effect of FMRFamide on mammals. FMRFamide has now been shown to be cardioexcitatory in mammals, to inhibit morphine-induced antinociception, and to block morphine-, defeat-, and deprivation-induced feeding. It also inhibits colonic propulsive motility, induces behavioral effects when administered intrathecally, and has been reported to have amnesic effects in rodents. A proposal has arisen that a FMRFamide-like substance is an endogenous opioid antagonist and has stimulated a search for such a substance. However, FMRFamide has only weak affinity for opioid receptors and not all the actions of FMRFamide appear to be explained by actions at opioid receptors. Alternative mechanisms have been proposed which suggest that FMRFamide acts as a neuromodulator.

Dual inhibitory action of FMRFamide on neurosecretory cells controlling egg laying behavior in the pond snail

We describe here the electrophysiological characterization of a dual inhibitory action of FMRFamide (FMRFa, Phe-Met-Arg-Phe-NH2) on the caudodorsal cells (CDCs) of the pond snail Lymnaea stagnalis: (i) a transient hyperpolarizing response (H-response) and (ii) a suppression of the excitability of the cells, which lasted as long as the peptide was present. Both effects of FMRFa occurred in silent, excitable cells as well as discharging cells. The effects were reversible and dose-dependent in the range of 10(-9) to 10(-5) M. The H-response was not blocked by any of the antagonists to classical neurotransmitters that were tested. The reversal potential of the H-response was dependent on the [K+]o, which suggests that K+ is the major charge carrier in this response. 4-Aminopyridine (4-AP) blocked the H-response but did not affect the suppression of the excitability by FMRFa. This indicates that the effects of the peptide on these cells are independent. Experiments on the mechanism of the inhibition of the excitability indicated that FMRFa blocks the cAMP-dependent activation of the pacemaking mechanism of the CDCs. In experiments with isolated cells it was demonstrated that the actions of FMRFa are mediated directly through receptors on CDCs (H-response: ED50 = 10(-8) M). Finally, anti-FMRFa-positive varicosities and axons close to the somata, the axons and the neurohaemal endings of the CDCs were demonstrated immunocytochemically. The duality of the action of FMRFa on the neural activity of CDCs indicates its role of high priority in the regulation of egg laying behavior.

Isolation and characterization of a Drosophila gene that encodes multiple neuropeptides related to Phe-Met-Arg-Phe-NH2 (FMRFamide)

A Drosophila gene that encodes neuropeptides related to molluscan Phe-Met-Arg-Phe-NH2 (FMRFamide) was isolated by screening a genomic library with a fragment of an Aplysia Phe-Met-Arg-Phe-NH2 cDNA and with synthetic oligonucleotides. This gene was used to isolate a cDNA from a Drosophila adult head cDNA library. The cDNA was defined by sequence analysis to encode 13 peptides that have Phe-Met-Arg-Phe-NH2 or related sequences at their carboxyl termini. Other putative neuropeptides, including one that has homology to mammalian corticotropin-releasing factor, are present in the deduced approximately equal to 39-kDa precursor. Southern blot analysis suggested the presence of a single Phe-Met-Arg-Phe-NH2-like gene within the haploid genome. RNA blot analysis indicated the expression of at least two transcripts of approximately equal to 1.7 and approximately equal to 0.7 kilobases. Both transcripts are evident throughout larval, pupal, and adult developmental stages. In situ hybridization was used to localize this neuropeptide gene to band 46C on the right arm of the 2nd chromosome. These data provide the basis for utilizing the advanced genetics and molecular techniques of Drosophila to address complex aspects of neuropeptide expression and function.

Isolation and characterization of a Drosophila neuropeptide gene

We have purified a 9 amino acid amidated neuropeptide, DPKQDFMRFamide, from whole adult D. melanogaster. This peptide exhibits sequence homology to the molluscan bioactive tetrapeptide FMRFamide and is a novel member of the FMRFamide peptide family. The gene encoding DPKQDFMRFamide has been cloned and characterized. It is present in a single copy per haploid genome, is expressed as a unique 1.7 kb mRNA species, and cytologically maps to 46C on the right arm of chromosome 2. Characterization of a cDNA clone indicates that the precursor protein is 347 amino acids in length and contains 5 copies of DPKQDFMRFamide, as well as 10 additional amidated peptides exhibiting varying degrees of structural relatedness. The Drosophila DPKQDFMRFamide gene and the Aplysia FMRFamide gene are ancestrally related; however, peptides display a higher degree of homology within a species than between species, suggesting intragenic concerted evolution of these neuropeptides.

The effect of Phe-Met-Arg-Phe-NH2 (FMRFamide) on morphine-induced inhibition of colonic propulsive motility in mice

Morphine and the molluscan neuropeptide Phe-Met-Arg-Phe-NH2 (FMRFamide) were administered to mice alone or in combination intracerebroventricularly (i.c.v.) and the effect on colonic propulsive motility was measured. Both morphine (1.0 microgram, i.c.v.) and FMRFamide (10 and 50 micrograms, i.c.v.) delayed expulsion of a 3 mm glass bead placed in the distal colon of mice compared to vehicle-treated controls. The inhibitory effects of morphine and FMRFamide on expulsion time were additive at the doses used and individually blocked by naloxone. These data suggest that FMRFamide does not antagonize this nonanalgesic effect of morphine, but appears to have opioid agonist properties.

Purification and characterization of FMRFamidelike immunoreactive substances from the lobster nervous system: isolation and sequence analysis of two closely related peptides

In the preceding paper (Kobierski et al: J. Comp. Neurol. 266:1-15, '87) FMRFamidelike immunoreactivity (FLI) was localized to specific cells and processes in the nervous system of the lobster Homarus americanus. In an effort to establish a role for this material we have purified and characterized a variety of immunoreactive peptides that can be extracted from the secretory pericardial organs. By using gel-filtration chromatography and three different HPLC systems, it has been established that little or no authentic FMRFamide is present. Of the major immunoreactive components two peptides were purified in sufficient quantity for microsequence analysis and have been tentatively identified as the octapeptides Ser-Asp-Arg-Asn-Phe-Leu-Arg-Phe-amide (FLI 3) and Thr-Asn-Arg-Asn-Phe-Leu-Arg-Phe-amide (FLI 4). Both of these are novel neuropeptides with some sequence homology to the previously described FMRFamide family. The pericardial organs release FLI when depolarized with 100 mM K+ in the presence of calcium. Between 75 and 80% of this release is accounted for by FLI 3 and FLI 4. One of these peptides (FLI 4) has been synthesized and shown to cochromatograph with the endogenous immunoreactive material. Preliminary studies show that this peptide can act as a modulator of exoskeletal and cardiac neuromuscular junctions.

FMRFamidelike peptides of Homarus americanus: distribution, immunocytochemical mapping, and ultrastructural localization in terminal varicosities

The distribution of FMRFamidelike peptides was studied in the nervous system of the lobster Homarus americanus by using immunocytochemical and radioimmunological techniques. By radioimmunoassay FMRFamidelike immunoreactivity (FLI) was found in low levels (ca. 1 pmol/mg protein) throughout the ventral nerve cord and in much higher amounts (60-100 pmol/mg protein) in the neurosecretory pericardial organs. Immunocytochemical studies showed FLI in approximately 300-350 cell bodies, and in distinct neuropil regions, neuronal fiber tracts, and varicose endings. Specificity of the immunostaining was tested by preabsorbing the antiserum with FMRFamide, with peptides having similar carboxyl termini to FMRFamide (Met-enkephalin-Arg-Phe, Phe-Met-Arg-Tyr-amide), with several amidated peptides (alpha-melanocyte-stimulating hormone, substance P, oxytocin), and with proctolin, a peptide found widely distributed in the lobster nervous system. Of these substances, only FMRFamide blocked the staining. In addition to the pericardial organs, significant levels of FLI were found in neurosecretory regions associated with thoracic second roots and in the connective tissue sheath that surrounds the ventral nerve cord. In all three regions, immunocytochemical studies showed the FLI to be localized to fine fibers and associated terminal varicosities lying close to the surface of the tissue, with no obvious target in their immediate vicinity. When examined at the ultrastructural level, the immunoreactive varicosities of the thoracic second roots and of the ventral nerve cord sheaths were found a few microns from the surface of the tissue and contained electron-dense granules. In the immunoreactive nerve cord sheath endings, in addition to the large, dense granules, small, clear vesicles were found. The appearance and location of these terminals suggest a neurohormonal role for FMRFamidelike peptides in lobsters. The observation that low levels of FLI are found in the hemolymph supports this suggestion. In addition, the localization of FLI to particular neuronal somata, fiber tracts, and neuropil regions suggests possible functional roles for these peptides in (1) integration of visual and olfactory information, (2) function of the anterior and posterior gut, and (3) the control of exoskeletal muscles.

Identification of motor neurons that contain a FMRFamidelike peptide and the effects of FMRFamide on longitudinal muscle in the medicinal leech, Hirudo medicinalis

Excitatory motor neurons in the leech are cholinergic. By using a combination of intracellular Lucifer yellow injection and indirect immunofluorescence, we localized FMRFamidelike immunoreactivity to a number of the motor neurons innervating longitudinal and dorsoventral muscle in the leech. All excitatory motor neurons innervating longitudinal muscle (cells 3, 4, 5, 6, 8, L, 106, 107, 108) were labeled with an antiserum to FMRFamide, while the inhibitory motor neurons innervating longitudinal muscle (cells, 1, 2, 7, 9, 102) were not. The excitatory motor neuron innervating medial dorsoventral muscle (cell 117) was labeled, while the excitatory motor neuron innervating lateral dorsoventral muscle (cell 109) was not. The inhibitory motor neuron innervating dorsoventral muscle (cell 101) was also labeled. Nerve terminals along dorsoventral muscle were also labeled with the antiserum. FMRFamide was bath applied to strips of longitudinal muscle while recording tension, and the muscle's response was compared to its response to the previously identified neuromuscular transmitter ACh. Brief applications of FMRFamide caused a contraction approximately one-tenth as large as that caused by an equimolar amount of ACh. The muscle response to FMRFamide was unaffected by curare. During extended exposures, FMRFamide caused a maintained contraction in longitudinal muscle without any apparent desensitization of the FMRFamide receptors and occasionally triggered an irregular myogenic rhythm. This extended exposure to FMRFamide caused a post-exposure potentiation of the longitudinal muscle's response to ACh that shorter applications of FMRFamide did not. Thus FMRFamide may act as a transmitter or modulator in cholinergic motor neurons innervating longitudinal and dorsoventral muscles in the leech.

Amnesic action of FMRFamide in rats

The effects of FMRFamide on passive avoidance behaviour and electroshock-induced amnesia following intracerebroventricular administration were studied in rats. FMRFamide given immediately after the learning trial, or 20 min before the retention trial, attenuated the avoidance response, thereby impairing the consolidation and retrieval processes. Electroshock induced amnesia when applied immediately after the learning trial. Treatment with FMRFamide facilitated the amnesia of the passive avoidance response. The results indicate that FMRFamide peptide belongs in the class of neuropeptide which are amnesic.

Calcium channel blockers inhibit the antagonistic effects of Phe-Met-Arg-Phe-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 (Phe-Met-Arg-Phe-NH2) 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.

Modulation of potassium conductances by an endogenous neuropeptide in neurones of Aplysia californica

1. Macroscopic and single-channel currents were recorded from voltage-clamped neurones in the abdominal and pleural ganglia of Aplysia californica in order to investigate conductance changes elicited by application of the endogenous peptide FMRFamide (Phe-Met-Arg-Phe-NH2) and related neuropeptides to the cell surface. 2. The Ca-dependent K current, IK(Ca), when elicited at a constant voltage by intracellular injection of Ca2+, was insensitive to FMRFamide or its derivative YGG-FMRFamide (Tyr-Gly-Gly-Phe-Met-Arg-Phe-NH2). 3. Under steady voltage clamp, certain cells responded to a brief puff of FMRFamide or YGG-FMRFamide with a transient outward current lasting about 1 min. Unclamped cells responded with a corresponding hyperpolarization. These responses reversed at about -75 mV. Ion substitution indicated that the current is carried by K+. 4. FMRFamide and YGG-FMRFamide were equally effective in activating the outward current, whereas FMRF, met-enkephalin and leu-enkephalin were ineffective. 5. At voltages negative to -30 mV and, in the absence of extracellular Ca2+, also at more positive potentials, the FMRFamide-sensitive current showed no voltage dependence beyond that predicted from constant-field considerations. 6. The response to FMRFamide was relatively insensitive to extracellular tetraethylammonium (TEA, KD approximately 75 mM) and 4-aminopyridine (4-AP, KD approximately 6 mM). It was suppressed in Ba-containing solutions, but was unaffected by injection of the Ca chelating agent EGTA. The response was blocked by serotonin and other agents known to elevate intracellular adenosine 3',5'-phosphate (cyclic AMP) levels, and by direct injection of cyclic AMP into the cell. 7. In its pharmacological properties and lack of voltage dependence, the FMRFamide-activated current resembles the 'S' current, IK(S), a K current suppressed by application of serotonin in Aplysia neurones. 8. The similarity between the FMRFamide-sensitive current and the 'S' current was confirmed in cell-attached patch-clamp studies, in which activity of 'S' channels was found to be reduced by serotonin, and enhanced by FMRFamide. 9. Thus, FMRFamide may function in Aplysia to counteract the serotonergic modulation of 'S' channels, which has been proposed as a mechanism of presynaptic plasticity in this mollusc.

Comparison of the effects of FMRF-amide and pQDPFLRF-amide on identified Helix neurons

Intracellular recordings were made from a selection of identified neurons in the sub-oesophageal ganglia of Helix aspersa, and their responses to the molluscan neuropeptides FMRF-amide and pQDPFLRF-amide compared. While FMRF-amide excited certain neurons and inhibited others, pQDPFLRF-amide did not produce excitation in any of the cells tested. A few cells were unresponsive to pQDPFLRF-amide, but most were inhibited with varying potency. FMRF-amide was generally 10-100 times more potent than pQDPFLRF-amide, but one cell, E13 in the visceral ganglion, showed equal sensitivity to the two peptides. On most cells there was no clear evidence for cross desensitization between the two peptides, although it is possible that in some cases where both peptides are inhibitory they may be acting on a single receptor.

The cAMP cascade in the nervous system: molecular sites of action and possible relevance to neuronal plasticity

Many intercellular messages regulate the activity of their target cells by altering the intracellular level of cAMP and, as a consequence, the phosphorylation state of proteins which serve as substrates for cAMP-dependent protein kinase. Such regulation plays a crucial role in neuronal development, neuronal function, and neuronal plasticity (e.g., elementary learning mechanisms). Ample information has been accumulated in recent years on the enzymes that regulate the level of cAMP or respond to it, on the regulation of cAMP synthesis by neurohormones, neurotransmitters, ions, and toxins, on neuronal-specific substrate proteins that are phosphorylated by the cAMP-dependent kinase, and on the interaction of the cAMP-cascade with other second-messenger systems within neurons. Such data, obtained by a combination of molecular-biological, biochemical, and cellular approaches, shed light on the detailed mechanisms by which modulation of a ubiquitous molecular cascade leads to a great variety of short-term as well as long-term specific neuronal responses and alterations.

Multiple receptor sites for a molluscan peptide (FMRFamide) and related peptides of Helix

1. The membrane actions of some tetrapeptide amides and heptapeptide amides chemically related to the molluscan neuropeptides Phe-Met-Arg-Phe-NH2 (FMRFamide) and p-Glu-Asp-Pro-Phe-Leu-Arg-Phe-NH2 (pQDPFLRFamide) were tested and compared on identified neurones of Helix aspersa. 2. The C-terminal sequence -Phe-NH2 was an important requirement for each of the four different actions studied: slow increase in K conductance (gK), fast increase in gK, increase in Na conductance (gNa) and decrease in gK. 3. The response of some neurones involved a combination of such actions. 4. The tetrapeptide amides FMRFamide, Phe-Leu-Arg-Phe-NH2 (FLRFamide) and Phe-Ile-Arg-Phe-NH2 (FIRFamide) were more potent than the heptapeptide amides at producing the slow increase in gK and also produced the increase in gNa, not seen at all with the heptapeptide amides. 5. The heptapeptide amides induced the fast increase in gK which was not observed with the tetrapeptide amides. 6. Evidence is presented that each of the tetrapeptide amides tested acts on the same receptor type which mediates the increase in gNa and on which the heptapeptides were inactive. 7. The results are interpreted in terms of multiple receptors each of which however appears to require the C-terminal sequence Phe-Met(or Leu)-Arg-Phe-NH2, as has been shown for some molluscan muscle preparations which react to these peptide amides (Price & Greenberg, 1980).

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: an endogenous peptide with marked inhibitory effects on opioid-induced feeding behavior

The peptide FMRFamide (Phe-Met-Arg-Phe-NH2), which displays a broad phylogenetic distribution, is considered to have important regulatory influences on basic functions in invertebrates. Extensive FMRFamide-like immunoreactive neuropeptides have also been demonstrated in the mammalian central nervous system, suggesting a possible physiological role for these peptides in mammals. There is evidence that FMRFamide, and/or related neuropeptides, may modulate opioid-mediated responses. Intracerebroventricular (ICV) administrations of FMRFamide inhibit in a dose-dependent manner (0.01-10 micrograms) mu- (morphine) and kappa- (U-50,488H) opiate-induced feeding in the laboratory mouse. In deer mice, FMRFamide inhibits the display of exogenous opiate-induced components of natural feeding behavior, such as food hoarding and food ingestion. In addition, ICV administrations of FMRFamide also antagonize endogenous opioid-mediated, stress-induced feeding in mice. These observations suggest that FMRFamide, or FMRFamide-like peptides present in the mammalian brain, may have important roles in the control of opioid-mediated feeding.

Plasticity in the nervous system of adult hydra. I. The position-dependent expression of FMRFamide-like immunoreactivity

The plasticity of nerve cells expressing the neuropeptide FMRFamide was examined in adult hydra. Using a whole-mount technique with indirect immunofluorescence, the spatial pattern of neurons showing FMRFamide-like immunoreactivity (FLI) was visualized. These neurons were located in the tentacles, hypostome, and peduncle, but not in the body column or basal disc. Since every neuron in the nerve net is continuously displaced toward an extremity and eventually sloughed, the constant pattern of FLI+ neurons could arise in one of two ways. When displaced into the appropriate region, FLI- neurons are converted to FLI+ neurons, or FLI+ neurons arise by differentiation from interstitial cells. To distinguish between these two possibilities, interstitial cells, the multipotent precursors of the nerve cells, were eliminated by treatment with hydroxyurea or nitrogen mustard. Following head, or foot and peduncle, removal from these animals, the missing structures regenerated. The spatial pattern of FLI+ neurons reappeared in the newly regenerated head or peduncle. This shows FLI- neurons in the body column were converted to FLI+ when their position was changed to the head or the peduncle. When the peduncle was grafted into the body column, it was converted to basal disc or body column tissue, and FLI disappeared. The appearance and loss of FLI was always position dependent. These results indicate that the neurons in the mature nerve net can change their neuropeptide phenotype in response to changes in their position.

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.

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

The effects of i.c.v. administration 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 microgram) 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.

Intrathecal FMRFamide (Phe-Met-Arg-Phe-NH2) induces excessive grooming behavior in mice

The molluscan neuropeptide Phe-Met-Arg-Phe-NH2 (FMRFamide) was administered intrathecally (i.t.) to mice and their behavior was monitored for 30 min. FMRFamide induced a dramatic and dose-related (5-12 micrograms) increase in grooming-related activities compared to saline-treated controls. The grooming behavior produced by 8 micrograms FMRFamide was not blocked by simultaneous i.t. administration of 10 micrograms of the following antagonists: atropine, phentolamine, methysergide, naloxone or spantide; peripheral administration of naloxone (3.5 mg/kg, s.c.) also failed to antagonize FMRFamide grooming. These data constitute the first report that FMRFamide produces behavioral changes in mammals.

Distinct localization of FMRFamide- and bovine pancreatic polypeptide-like material in the brain, retrocerebral complex and suboesophageal ganglion of the cockroach Periplaneta americana L

One bovine pancreatic polypeptide (BPP) antiserum and two FMRFamide antisera were applied in the peroxidase-antiperoxidase (PAP) immunohistochemical technique on a complete series of sections of brains, suboesophageal ganglia (SOG), corpora cardiaca (CC) and corpora allata of Periplaneta americana L. Double immunohistochemical staining demonstrated that the same perikarya and processes were stained by both the BPP and FMRFamide antisera. This was caused by cross-reaction of the BPP and FMRFamide antisera with common antigenic determinants as was shown by a number of solid-phase absorptions. Application of a third FMRFamide antiserum, which was especially selected for its inability to react with bovine and avian pancreatic polypeptide, showed that more than half of the structures that were stained with the 'unspecific' BPP and FMRFamide antisera, contained material which was genuinely FMRFamide-like. This peptide material was located in cerebral neuronal structures, in the SOG, in the storage site of the CC and in numerous nerve fibres throughout the neuropile regions, which suggested a neurotransmitter/modulator as well as a neurohormonal role. The FMRFamide-like peptide was also found to be present in the same brain sites as an adipokinetic hormone-like peptide, but double labelling revealed that these two substances were never located in the same perikarya or fibres.

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.

FMRFamide suppresses kappa opiate induced feeding in the mouse

Intracerebroventricular administration of 0.01-1.0 micrograms of the peptide FMRFamide (Phe-Met-Arg-Phe-NH2) to mice suppressed feeding induced by the specific kappa opiate agonist, U-50, 488H. This suggests that FMRFamide, or FMRFamide-like neuropeptides, may have a role in the control of kappa opioid mediated feeding in the mouse.

Membrane responses and changes in cAMP levels in Aplysia sensory neurons produced by serotonin, tryptamine, FMRFamide and small cardioactive peptideB (SCPB)

While recent evidence indicates a role for serotonin (5-HT) in modulating the defensive tail-withdrawal reflex in Aplysia, little information exists concerning the specificity of these 5-HT effects. As a first-step in addressing this issue we have examined the dose-response relationship for one aspect of the 5-HT modulation (enhancement of cAMP levels in isolated clusters of sensory neurons) and compared the effects of 5-HT with three potential neurotransmitters: tryptamine, FMRFamide (Phe-Met-Arg-Phe-NH2) and small cardioactive peptideB (SCPB). Cyclic adenosine monophosphate (cAMP) levels were enhanced as a graded function of the concentration of 5-HT with an EC50 of 14 microM. At a concentration of 5 microM, both 5-HT and SCPB produced nearly identical increases in the cAMP content of sensory neurons. In contrast, 5 microM tryptamine or 5 microM FMRFamide had little or no effect on cAMP levels. We also examined the effects of these agents on membrane currents and membrane conductance. Both 5-HT and SCPB produced an inward current associated with a decrease in input conductance. Tryptamine had little or no effect, while FMRFamide produced a response opposite to that of 5-HT and SCPB; an outward current associated with an increase in membrane conductance.

The distribution of bovine pancreatic polypeptide/FMRFamide-like immunoreactivity in the ventral nervous system of the locust

The distribution of bovine pancreatic polypeptide (BPP) FMRFamide-like immunoreactivity is described in the ganglia of the ventral nerve cord and in the peripheral median nervous system of the locust, Schistocerca gregaria. Immunoreactive cell bodies occur in three regions of the thoracic ganglia: 1) two pairs of cells lie in the anterior of the ganglion ventral to the root of nerve 1 and the anterior ventral association centre; 2) a group of cells lies in the ventral midline at the level at which nerves 3 and 4 leave the ganglion; 3) and two bilaterally symmetrical, posterior lateral groups lie between nerves 5 and 6 at the edge of the ganglion. Immunoreactive cell bodies in the suboesophageal and abdominal ganglia are confined to the midline and are distributed along the anterior-posterior axis both dorsally and ventrally. The processes of the posterior lateral groups have been traced into the neurohaemal organs of the median nerve and beyond. In the periphery such processes innervate the salivary glands and various muscles. The nature of the endogenous antigen contained in the immunoreactive cells has been investigated with the use of antisera against other peptides of the pancreatic polypeptide family, namely avian pancreatic polypeptide, neuropeptide Y, and peptide YY. In addition, BPP antisera not specific for the C terminal hexapeptide have been tested. Liquid preabsorption experiments with BPP and FMRFamide (the molluscan cardioacceleratory peptide) suggest that the endogenous peptide antigen contained in the stained neurones may belong to the pancreatic polypeptide family or to the FMRFamide family.