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PubMed1996

Immunoreactive Phe-Met-Arg-Phe-NH2-like peptides in the brain of the antarctic icefish, Chionodraco hamatus.

The distribution of Phe-Met-Arg-Phe-NH2 (FMRFamide)-like immunoreactive peptides was investigated in the brain of the antarctic icefish, Chionodraco hamatus, using the indirect immunofluorescence technique. Three main groups of immunoreactive perikarya were respectively localized in the nucleus entopeduncularis of the telencephalon, the nucleus preopticus periventricularis of the hypothalamus, and within the nucleus oculomotorius of the mesencephalon. Delicate FMRFamide positive nerve fibers were distributed in several brain regions of the forebrain and brainstem. In particular, these fibers densely innervated the caudal part of the dorsomedial pallium, the hypothalamus, the thalamus, the mesencephalic tegmentum and the optic tectum. The distribution pattern of the FMRFamide-like immunoreactivity was compared with that reported in previous studies in other teleost species. The anatomical organization of the FMRFamide-like immunoreactive peptidergic system in the brain of Chionodraco hamatus suggests that a FMRFamide-like peptide may play a role as a neuromodulator in fish adapted to the extreme Antarctic environment.

Animals↗
PubMed1996

Modulatory mechanisms in the isolated internally perfused ventricle of the whelk Busycon canaliculatum.

1. Isolated cannulated ventricles commenced spontaneous beating on application of perfusion pressure of 10 cm water. Complete hearts showed a fast patterned cyclical rhythm, whereas ventricles devoid of atrial material showed a continuous slow rhythm. 2. Perfused ventricles were inhibited by ACh with a threshold at 10(-8) mol l-1 and arrested at 10(-7) mol l-1, and ventricles under stimulation by 5HT could be arrested by ACh at this concentration. 3. Perfused ventricles were stimulated by 5HT, with threshold at 10(-9) mol l-1 and maximum at 10(-5) mol l-1. Metoclopramide was without affect on 5HT responses, but metitipine and methysergide did inhibit such responses suggesting that the 5HT receptor present possessed mixed properties of the vertebrate 5-HT1 and 5-HT2 receptor subtypes. 4. Ventricles were very sensitive to the excitatory actions of FMRFamide in the 10(-9) to 10(-5) mol l-1 range. Preparations were insensitive to GAPFLRFamide, but SCP-B was modestly excitatory (threshold 10(-7) mol l-1). 5. Preparations were not significantly affected by adenosine, ATP, and guanosine, but GTP was strongly excitatory at 10(-7) mol l-1. 6. 5HT and FMRFamide responses were additive. Preparations responded strongly to the adenylate cyclase activator forskolin and dibutyryl cAMP enhanced spontaneous contractions and 5HT responses, suggesting that the 5HT receptor may operate via a cAMP secondary mechanism. 7. The IP3 inhibitor lithium (10 mmol l-1), caused slight inhibition of FMRFamide responses, suggesting that the receptor to this peptide may operate via IP3 as a second messenger. 8. Neuromodulation in this preparation would appear to involve ACh as inhibitor, 5HT and FMRFamide as upregulators, with no clear roles for FMRFamide-related peptides and GTP.

Acetylcholine↗
PubMed1994

Pre- and postsynaptic changes mediated by two second messengers contribute to expression of Aplysia long-term heterosynaptic inhibition.

FMRFamide evokes long-term inhibition of the sensorimotor connection of Aplysia that includes structural alterations in the presynaptic sensory cell. FMRFamide also evokes a down-regulation of the adhesion molecule apCAM from the surface of the postsynaptic motor cell L7. We examined the second messenger pathways mediating the long-term actions of FMRFamide on both the pre- and postsynaptic cells and determined whether the activation of each pathway is required for the expression of long-term functional and structural plasticity. Inhibition of the lipoxygenase pathway of arachidonic acid metabolism, but not the cyclooxygenase pathway, blocks the long-term changes in the presynaptic sensory cell evoked by FMRFamide. The down-regulation of apCAM in L7 appears to be mediated by cAMP-dependent activation of protein kinase A. Blocking the cAMP-dependent changes also blocks FMRFamide-induced long-term functional and structural changes. These results suggest that the expression of long-term heterosynaptic inhibition in Aplysia may require concomitant presynaptic and postsynaptic changes, each transduced by specific second messenger systems.

Animals↗
PubMed2004

Immunohistochemical localization of cardio-active neuropeptides in the heart of a living fossil, Nautilus pompilius L. (Cephalopoda, Tetrabranchiata).

Neuropeptides play an important role in modulating the effects of neurotransmitters such as acetylcholine and noradrenaline in the heart and the vascular system of vertebrates and invertebrates. Various neuropeptides, including substance P (SP), vasoactive intestinal polypeptide (VIP) and FMRFamide, have been localized in the brain in cephalopods and the neurosecretory system of the vena cava. Previous studies involving cephalopods have mainly focussed on the modern, coleoid cephalopods, whereas little attention was paid to the living fossil Nautilus. In this study, the distributions of the peptides related to tachykinins (TKs) and the high affinity receptor for the best characterized TK substance P (tachykinin NK-1), VIP, as well as FMRFamide were investigated in the heart of Nautilus pompilius L. by immunohistochemistry. TK-like immunoreactivity (TK-LI) was seen associated to a sub-population of hemocytes, VIP-LI glial cells in larger nerves entering the heart, whereas FMRFamide immunoreactivity was distributed throughout the entire heart, including the semilunar atrioventricular valves. The pattern of FMRFamide immunoreactivity matched that of Bodian silver staining for nervous tissue. The NK-1-LI receptor was located on endothelial cells, which were also positive for endothelial nitric oxide synthase-LI (eNOS). The results indicate that neuropeptides may be involved in the regulation of the Nautilus heart via different mechanisms, (1) by direct interaction with myocardial receptors (FMRFamide), (2) by interacting with the nervus cardiacus (VIP-related peptides) and (3) indirectly by stimulating eNOS in the endothelium throughout the heart (TK-related peptides).

Animals↗
PubMed1992

Low concentrations of neuroactive peptides modulate cholinergic transmission and cyclic AMP levels in Helix aspersa.

1. FMRFamide and the Catch relaxing peptide (CARP) at 0.01-0.1 nM modulate acetylcholine (ACh) induced currents of identified neurons of Helix aspersa, but have no direct effect on membrane current and conductivity. 2. Both FMRFamide and CARP noncompetitively inhibit ACh Cl- responses while having either no effect or increasing ACh Na+/K+ response. 3. The inhibitory effect of FMRFamide and CARP on the ACh Cl- response was eliminated following pretreatment with forskolin (20 microM), an activator of adenylate cyclase. 4. Ascaris peptide (ASC) and a synthetic CARP analogue NORL-CARP, in which the amino acid methionine is replaced by either leucine or norleucine, at 1-10 microM, showed no effect on responses to ACh. 5. FMRFamide and CARP, at 10 nM, increased cAMP levels to 240% and 148% respectively above resting basal cAMP levels, while ASC and NORL-CARP had no significant effective. 6. Our results suggest that FMRFamide and CARP, in low concentrations, modulate ACh responses of Helix neurons, possibly through changes in cAMP levels. They also indicate the importance of the presence of methionine in these neuroactive peptides.

Acetylcholine↗
PubMed1993

Neuropeptide FF receptors: structure-activity relationship and effect of morphine.

Neuropeptide FF (FLFQPQRFamide, NPFF) is an octapeptide implicated in morphine analgesia, tolerance and dependence. Many of the behavioral effects of NPFF have also been observed with the invertebrate neuropeptide Phe-Met-Arg-Phe-amide (FMRFamide), which binds to NPFF receptors because of its low homology to the C-terminal portion of NPFF. A competitive ligand binding assay was used to characterize NPFF receptors in rat spinal cord and a strong requirement was found for the C-terminal Arg-Phe-amide. It was found that FMRFamide (Ki = 1.8 nM) bound with lower affinity than NPFF (0.26 nM) but it was about 7-fold more potent than PQRFamide (12 nM). This finding explains the similar bioactivities of NPFF and FMRFamide. The Gln2 appeared to be the cause of the relatively low potency of PQRFamide, based on the binding specificity of NPFF receptors for a series of FMRFamide analogs. In contrast to the Arg-Phe-amide, substitutions at the first and second positions of FMRFamide were generally tolerated, with the most potent analogs being PMRFamide (Ki = 0.54 nM), FFRFamide (0.25 nM) and FWRFamide (0.42 nM). Among the most potent ligands was a pentapeptide containing a photoreactive Phe analog, D-Tyr-(p-benzoyl-Phe)-norLeu-Arg-Phe-amide (Ki = 0.23 nM). It was found that dansyl-PQRFamide and dansyl-RFamide also bound to NPFF receptors with Ki values of 6.1 and 73 nM, respectively. The radioligand binding and G-protein coupling of NPFF receptors were not altered by chronic morphine treatment.

Amino Acid Sequence↗
PubMed1996

Differential distribution of functional receptors for neuromodulators evoking short-term heterosynaptic plasticity in Aplysia sensory neurons.

Synaptic transmission and excitability in Aplysia sensory neurons (SNs) are bidirectionally modulated by 5-HT and FMRFamide. To explore the regional distribution of different functional receptors that modulate SN properties, we examined changes in synaptic efficacy and excitability with brief focal applications of the neuromodulators to different regions of SNs that have established connections with motor cell L7 in culture. Short-term changes in synaptic efficacy were evoked only when 5-HT or FMRFamide was applied to regions with SN varicosities along the surface of L7 axons. Applications to adjacent SN neurites with few varicosities in contact with L7 axons failed to evoke a significant change in synaptic efficacy. The distribution of functional receptors mediating changes in excitability differed for 5-HT and FMRFamide. Whereas excitability increases were evoked only when 5-HT was applied to SN cell bodies, excitability decreases in SNs were evoked only when FMRFamide was applied to regions along the L7 axon with SN varicosities. Without the target cell, cell bodies of SNs expressed both 5-HT and FMRFamide receptors that modulate excitability. These results indicate that functional G-protein-coupled receptors for two neuromodulators are distributed differentially along the surface of a presynaptic neuron that forms chemical connections in vitro. This differential distribution of receptors on the presynaptic neuron is regulated by a target and does not require the physical presence of neurons that release the neuromodulators.

Animals↗
PubMed1995

Peptidergic innervation of leg muscles of the cockroach, Periplaneta americana (L.), and a possible role in modulation of muscle contraction.

FMRFamide-related peptides of insects are particularly important because of their possible function as neurohormones and neuromodulators on a wide variety of tissues. Part of this study was an investigation of the immunofluorescent staining of motor nerves which arise in the metathoracic ganglion, examined in wholemount using an antiserum that recognizes extended -RFamide peptides (generally recognized to be of the FMRFamide family). This antiserum revealed immunochemical staining of numerous cell bodies in the metathoracic ganglion and of axons in peripheral nerve 5, a large nerve which contains both motor and sensory fibres. Axons staining positive for FMRFamide-related peptides were traced in nerve 5 as far as the femur-tibia joint, and into the first (sensory-motor) and third (motor only) ramus of nerve 5. Reverse-phase HPLC with radioimmunoassay revealed a peak of FMRFamide-related peptide activity in nerve 5 that was coincident with a peak found when thoracic ganglia were processed in the same fashion. A physiological assay was devised to test the ability of various non-native peptides to alter the characteristics of contraction of skeletal muscles of the legs. Using neurally evoked contractions of coxal depressor muscles of the metathoracic leg it was determined that several non-native peptides could potentiate muscle contractions. The results of this study suggest that muscles of the legs receive innervation by identifiable, FMRFamide-related peptide-containing neurons and that the release of peptide(s) at the muscle may be yet another method of modulating the mechanics of muscle contraction.

Animals↗
PubMed2005

Molecular identification of a myosuppressin receptor from the malaria mosquito Anopheles gambiae.

The insect myosuppressins (X1DVX2HX3FLRFamide) are neuropeptides that generally block insect muscle activities. We have used the genomic sequence information from the malaria mosquito Anopheles gambiae Genome Project to clone a G protein-coupled receptor that was closely related to the two previously cloned and characterized myosuppressin receptors from Drosophila [Proc. Natl. Acad. Sci. USA 100 (2003) 9808]. The mosquito receptor cDNA was expressed in Chinese hamster ovary cells and was found to be activated by low concentrations of Anopheles myosuppressin (TDVDHVFLRFamide; EC50, 1.6 x 10(-8)M). The receptor was not activated by a library of 35 other insect neuropeptides and monoamines, including neuropeptides that resembled myosuppressin in their C-terminal moiety, such as PDRNFLRFamide (Anopheles FMRFamide-3), other Anopheles FMRFamide peptides, or neuropeptide F-like peptides, showing that the receptor was quite selective for myosuppressin. These results also showed that the myosuppressin receptor needs a much larger portion than the C-terminal FLRFamide sequence for its activation. The insect myosuppressins are often grouped together with the insect FMRFamides under the name FaRPs (FMRFamide-related peptides). However, this is not justified anymore, because the insect myosuppressin receptor/ligand couple is both functionally and evolutionarily fully unrelated to the insect FMRFamide receptor/ligand couple. To our knowledge, this is the first report on the molecular identification of a mosquito neuropeptide receptor.

Amino Acid Sequence↗
PubMed1998

The effects of SchistoFLRFamide on contractions of locust midgut.

The midgut of insects has recently been shown to contain numerous endocrine-like cells and the midgut is now considered one of the largest endocrine organs in the insect. Using immunohistochemistry, radioimmunoassay, and muscle bioassay techniques, the midgut of the adult locust, Locusta migratoria, has been investigated for the distribution and possible function of FMRFamide-related peptides contained within these endocrine-like cells and innervation. Endocrine-like cells containing RFamide-like immunoreactivity were observed to be unequally distributed throughout the midgut. RFamide-like immunoreactivity was also seen in the ingluvial ganglion and in the nerves projecting posteriorly to the midgut. These axonal tracts resulted in extensive arborizations over the posterior midgut which were RFamide-like immunoreactive. Radioimmunoassay indicated larger amounts of FMRFamide equivalents in female locust midgut as compared to males with an unequal distribution of FMRFamide-like immunoreactivity in the gastric caeca and in the anterior and posterior parts of the midgut. Circular muscle contraction of the midgut was monitored using a ring-type preparation. Structure/activity studies have shown that the only FMRFamide-related peptides tested that alter circular muscle contraction of the midgut are those that belong to the subfamily referred to as myosuppressins. SchistoFLRFamide, leucomyosuppressin, and ManducaFLRFamide were each capable of lowering basal tonus and inhibiting spontaneous and proctolin-induced contractions of midgut muscle. Further structure/activity studies indicated that HVFLRFamide is the minimum sequence required to achieve inhibition comparable to the parent compound. This work suggests that a possible function for the FMRFamide-related peptides contained within the endocrine cells and innervation of the midgut of the locust may be in modulating midgut contraction and thereby playing a role in digestion.

Animals↗
PubMed1998

In situ hybridization analysis of leucomyosuppressin mRNA expression in the cockroach, Diploptera punctata.

In the cockroach Diploptera punctata, sequencing of the cDNA for the insect myoinhibitory neuropeptide, leucomyosuppressin (LMS), has demonstrated that LMS is the only Phe-Met-Arg-Phe-amide (NH2) (FMRFamide)-related peptide to be encoded by this gene (Donly et al. [1996] Insect Biochem. Mol. Biol. 26:627-637). However, in the present study, high performance liquid chromatography analysis of brain extracts showed six discrete FMRFamide-like immunoreactive fractions, one of which co-eluted with LMS. This study compared the distribution of FMRFamide-related peptides visualized by immunohistochemistry with LMS mRNA expression demonstrated by in situ hybridization in D. punctata. Immunohistochemistry with a polyclonal antiserum generated against FMRFamide, but which recognizes extended RFamide peptides, demonstrated numerous RFamide-like immunoreactive cells and processes in both nervous and nonnervous tissues. RFamide-like immunoreactivity was found in cells and processes of the brain and optic lobes, the stomatogastric nervous system, including the frontal and ingluvial ganglia, and the suboesophageal ganglion. Immunoreactivity was also present in all ganglia of the ventral nerve cord and in the alimentary canal. Within the alimentary canal, positively stained processes were found in the crop, midgut, and hindgut, and immunoreactive endocrinelike cells were located in the midgut. In situ hybridization with a digoxigenin-labeled RNA probe spanning the entire LMS coding region showed cell bodies containing LMS mRNA in all ganglia studied, other than the ingluvial ganglion. Expression was most abundant in the brain and optic lobes and in the frontal and suboesophageal ganglia. LMS mRNA was also apparent, although less intensely, in all other ganglia of the ventral nerve cord. Within the alimentary canal, LMS mRNA-positive cells were only visible in the anterior portion of the midgut, in the endocrinelike cells. The appearance of LMS mRNA in the central nervous system, stomatogastric nervous system, and midgut suggests that LMS may play a central role in Diploptera and may be associated with feeding and digestion.

Animals↗
PubMed1990

Immunohistochemical subpopulations of retinopetal neurons in the nucleus olfactoretinalis in a teleost, the whitespotted greenling (Hexagrammos stelleri).

Two subpopulations of retinopetal neurons in the nucleus olfactoretinalis (NOR) were revealed by means of general histological, tract tracing, and immunohistochemical methods in a marine teleost, the whitespotted greenling (Hexagrammos stelleri). Two types of cells in the NOR (M cell, L cell) were morphologically distinguishable from one another. The cell bodies of M cells were medium-size and fusiform, while those of L cells were large and ellipsoidal or irregular. M cells were located at the ventralmost region of the junction between the olfactory bulb and telencephalon, while L cells were scattered more rostrally along the ventromedial surface of the olfactory bulb. Following applications of HRP or Fluoro-Gold to the optic nerve, almost all M cells and about half of the L cells were labeled in the contralateral NOR. L cells showed strong immunoreactivities to gonadotropin releasing hormone (GnRH) and Phe-Met-Arg-Phe-NH2 (FMRFamide), whereas M cells showed only weak GnRH-immunoreactivity and no FMRFamide-immunoreactivity. Axons of L cells were detected in the optic nerve by means of GnRH- and FMRFamide-immunohistochemistry. The axons were concentrated in the myelinated edge (the oldest area) of the "ribbon" optic nerve. GnRH- and FMRFamide-immunoreactive fibers constituted a plexus at the junction between the inner nuclear layer and inner plexiform layer. The existence of two structurally separate classes of NOR cells suggests two functionally separate channels from the NOR to the retina.

Animals↗
PubMed1990

Electron microscopic study of immunocytochemically labeled centrifugal fibers in the goldfish retina.

The centrifugal fibers innervating the goldfish retina were studied quantitatively by light and electron microscopy. These fibers originating from cell bodies in the olfactory bulb were labeled by antiserum to the tetrapeptide Phe-Met-Arg-Phe-NH2 (FMRFamide). The number of FMRFamide-immunoreactive (ir) centrifugal fibers in each eye of the adult goldfish (body length: 12-15 cm) was 65 +/- 14 (mean +/- S.D., n = 7). All of these fibers in the optic nerve and the retina were unmyelinated. Each FMRFamide-ir centrifugal fiber runs along the optic fiber layer and gives several terminal arborizations in the outermost layer (layer 1) of the inner plexiform layer. Layer 1 is, therefore, densely covered by a plexus of terminal arborizations. Along these terminal arborizations, we found output synapses characterized by a cluster of small clear vesicles (40 nm in diameter) at the presynaptic site and a thickened membrane in the apposed retinal cell processes. In a sample area of 2,000 microns 2, such synapses occurred at a density of one per 105 microns 2, or about 13,000 per centrifugal fiber. Thus, the FMRFamide-ir centrifugal fibers are likely to modulate retinal cell activity through an estimated total of 840,000 output synapses per retina.

Animals↗
PubMed2001

Activity modes and modulation of the peptide-gated Na(+) channel of Helix neurones.

Unitary currents activated by steady-state applications of FMRFamide analogues have been recorded in outside-out patches from the C2 and F2 neurones of Helix aspersa. The bimodal conductance distribution ranged from 4 pS to 6 pS in patches in each neurone. Application of up to 10 microM cytochalasin B or D to 12 of the 41 inside-out patches tested stimulated activity of the larger conductance events and/or increased the amplitude of smaller conductance events, indicating a cytoskeletal influence on the channels. FMRFamide-gated currents were blocked by external Ca(2+) and Mg(2+), both with an IC(50) of about 1 mM. During continuous application of FMRFamide, clustering of events and/or the appearance of a mode of activity with a lower probability of being open (P(open)) suggested two different types of desensitization. More rarely, exceptionally high P(open) activity with low FMRFamide concentrations was seen. In some cases, there were long periods of high activity during which the channels gated normally with regular short sojourns in the fully closed state. In others, isolated long openings were seen which interrupted the normal gating pattern of the channels. Amiloride and its analogue 5-(N-ethyl- N-isopropyl) amiloride (EIPA) consistently caused channel block, but in some patches with a low background activity an increased P(open) was also observed in the presence of each drug.

Amiloride↗
PubMed2005

Domain near TM1 influences agonist and antagonist responses of peptide-gated Na+ channels.

A molecular biological approach was used to analyse the importance of different amino acids for ligand activation and for determining the action of amiloride on peptide- (Phe-Met-Arg-Phe-NH(2), FMRFamide)-gated Na(+) channels, members of the degenerin/epithelial Na channel (DEG/ENaC) family. Amiloride is a low-affinity blocker of most DEG/ENa channels, but has an unusual enhancing effect on responses of some of them. Chimeras were expressed in Xenopus oocytes and studied electrophysiologically. Differences in properties of channels from Helix aspersa and Helisoma trivolvis highlighted a sequence of 50 residues of the extracellular domain, near the first transmembrane segment (TM1), that affected sensitivity to FMRFamide, and whether amiloride blocked or enhanced the response to FMRFamide. Comparisons of chimeras prepared from H. aspersa and the extracellular domains of two other species, Aplysia californica and Lymnaea stagnalis and the preparation of further constructs, showed that amino acids 128-134 in the H. aspersa sequence are important in determining the predominant effect of amiloride and influencing the EC(50) of FMRFamide. The results also showed that amino acids in this region are influenced by amino acids in other regions of the extracellular domain so as to affect not only the magnitude of responses, but also their time course and desensitisation.

Amiloride↗
PubMed1997

Convergence of multiple G-protein-coupled receptors onto a single type of potassium channel.

The light green cells (LGCs) in the central nervous system of the pond snail Lymnaea stagnalis form a homogeneous group of neuroendocrine cells that are involved in the control of growth and metabolism. These cells are inhibited by dopamine and the neuropeptides APGWamide, FMRFamide and GGSLFRFamide. Thus, the LGCs form an endogenous system in which processing and integration of different inputs into a physiological response can be studied. In this study we characterize the current(s) that are responsible for the inhibition of the LGCs by dopamine, APGWamide, FMRFamide and GGSLFRFamide. The responses are G-protein dependent, as follows from experiments with GTP-gamma-S. Several experiments indicate that the four agonists activate a single type of potassium channel. First, the currents evoked by the agonists have the same ion selectivity and voltage dependence. Potassium is the predominant charge carrier and the responses are weakly voltage sensitive, with conductance decreasing at potentials below approximately - 100 mV. Second, the currents activated by the four agonists display similar sensitivity towards several blockers. Internal and external TEA (10 mM), and extracellular Ba2+ (1 mM) cause a block of approximately 60-90%. External 4AP (1 mM) causes approximately 30% block and external Cs+ (1 mM) causes a voltage sensitive block. There is no sensitivity towards apamine and glibenclamide. Third, there is no summation of the responses to dopamine, APGWamide and GGSLFRFamide with maximal FMRFamide responses. Together, these data indicate that the responses induced by dopamine, APGWamide, FMRFamide and GGSLFRFamide are G-protein mediated and converge onto a single type of potassium channel in the LGCs of Lymnaea stagnalis.

Animals↗
PubMed1998

The effect of FMRF-amide-like peptides on electrical activity in isolated mammalian spinal cord.

FMRFamide and seven FMRFamide-like peptides were manually synthesized on solid phase and their effects tested upon the amplitude of the dorsal root-ventral root monosynaptic reflex (MSR) and dorsal horn field potentials (FP) in an isolated preparation of rat spinal cord. FLFQPQRFamide (NPFF) and AGEGLSSPFWSLAAPQRFamide (NPAF) both depressed a fast component of the FP with similar potencies. FMRFamide also inhibited the FP but its potency was much lower. NPFF and NPAF potentiated the amplitude of the MSR while FMRFamide had no effect. PQRFamide, PFRFamide, FFRFamide, DPQRFamide and Fmoc-FLFQPQRFamide were also examined on the MSR. PQRFamide and PFRFamide potentiated the MSR whereas FFRFamide and DPQRFamide caused a small depression at high concentrations. The increase in amplitude of the MSR induced by NPFF was completely abolished when the N-terminal was left protected with an Fmoc-group. The results suggest that PFRFamide and PQRFamide may act as agonists of NPFF and NPAF whereas the other peptides did not show such activity.

Amino Acid Sequence↗
PubMed1997

Modulation by APGW-amide, an Achatina endogenous inhibitory tetrapeptide, of currents induced by neuroactive compounds on Achatina neurons: peptides.

1. Modulatory effects of APGW-amide (Ala-Pro-Gly-Trp-NH2), proposed as an inhibitory neurotransmitter of Achatina neurons, perfused at 3 x 10(-6) M on the currents induced by neuroactive peptides, ejected by brief pressure, were examined by using Achatina giant neuron types, v-RCDN (ventral-right cerebral distinct neuron) and PON (periodically oscillating neuron), under voltage clamp. 2. Outward current (Iout) caused by FMRFamide (Phe-Met-Arg-Phe-NH2) on v-RCDN, which was probably K+ dependent, was inhibited with membrane conductance (g) increase by APGW-amide. From the dose (pressure duration)-response curves of FMRFamide and a Lineweaver-Burk plot of these data, the inhibition caused by APGW-amide was mainly in an uncompetitive manner. 3. Iout caused by APGW-amide on v-RCDN, which was probably K+ dependent, was inhibited with g increase by APGW-amide. The inhibition caused by APGW-amide was partly in a competitive manner and partly in a noncompetitive manner. 4. Iout caused by [Ser2]-Mytilus inhibitory peptide, [Ser2]-MIP (Gly-Ser-Pro-Met-Phe-Val-NH2) on v-RCDN, which was probably K+ dependent, was inhibited with g increase by APGW-amide. Because the modulation of this current was not so marked, a dose-response study of this compound was not carried out. Iin induced by oxytocin on PON was not affected by APGW-amide. 5. From the dose-response curves of APGW-amide, perfused consecutively, the inhibitory effects of APGW-amide on the Iout caused by APGW-amide were stronger than those on the Iout caused by FMRFamide. 6. The inhibition of the APGW-amide-induced Iout on v-RCDN by APGW-amide was partly due to the competition in the receptor sites and partly to the g increase. The inhibition by APGW-amide on the Iout induced by FMRFamide and [Ser2]-MIP would be partly due to the g increase. In addition, we consider that APGW-amide affects intracellular signal transduction systems or ionic channels, thus modulating these currents. 7. The currents modulated by APGW-amide were different from those modulated by achatin-1, another Achatina endogenous neuroexcitatory peptide. We consider that the mechanisms underlying the modulatory effects of APGW-amide are different from those of achatin-I.

Animals↗