fmrfamide and Pain

The endogenous neuropeptide FF (NPFF) and its two cognate G protein-coupled receptors, Neuropeptide FF Receptors 1 and 2 (NPFFR1 and NPFFR2), represent a relatively new target system for many therapeutic applications including pain regulation, modulation of opioid side effects, drug reward, anxiety, cardiovascular conditions, and other peripheral effects. Since the cloning of NPFFR1 and NPFFR2 in 2000, significant progress has been made to understand their pharmacological roles and interactions with other receptor systems, notably the opioid receptors. A variety of NPFFR ligands with different mechanisms of action (agonists or antagonists) have been discovered although with limited subtype selectivities. Differential pharmacological effects have been observed for many of these NPFFR ligands, depending on assays/models employed and routes of administration. In this Perspective, we highlight the therapeutic potentials, current knowledge gaps, and latest updates of the development of peptidic and small molecule NPFFR ligands as tool compounds and therapeutic candidates.

Topics: Analgesics, Opioid; Animals; Anxiety; Humans; Ligands; Mice; Oligopeptides; Pain; Peptidomimetics; Rats; Receptors, Neuropeptide; Small Molecule Libraries

Our previous study showed that a chimeric peptide of Met-enkephalin and FMRFamide, YFa (YGGFMKKKFMRFa) not only caused antinociception and potentiated morphine analgesia but also blocked the development of tolerance and physical dependence. In the continuation of that study three chimeric analogues of YFa, [Ser5]YFa, [O-Glu-Ser5]YFa and [O-Gal-Ser5]YFa, were synthesized. To increase the bioavailability and penetration of blood brain barrier (BBB), glycosylated analogues, [O-Glu-Ser5]YFa and [O-Gal-Ser5]YFa, have been synthesized by solid phase peptide synthesis by building block method using anomeric acetate activation method. Circular dichroism studies showed that all the three chimeric peptides are stable and have a propensity for adopting helical conformation in the presence of membrane mimicking solvent. In comparison of parent chimeric peptide YFa, helicity of [Ser5]YFa, [O-Glu-Ser5]YFa and [O-Gal-Ser5]YFa has decreased. Pharmacological studies using tail-flick latency in mice showed that [O-Glu-Ser5]YFa have increased analgesia and bioavailability in comparison of [O-Gal-Ser5]YFa and non-glycosylated analogue [Ser5]YFa. Exhibition of enhanced analgesia by [O-Glu-Ser5]YFa as compared to [O-Gal-Ser5]YFa seems to be due to preference of GLUT-1 transporter system for glucose.

Topics: Animals; Blood-Brain Barrier; Dose-Response Relationship, Drug; Drug Design; Drug Interactions; Enkephalin, Methionine; FMRFamide; Glycopeptides; Glycosylation; Mass Spectrometry; Mice; Oligopeptides; Pain; Pain Measurement; Protein Conformation; Reaction Time; Time Factors

In our previous study YFa (YGGFMKKKFMRFa), a chimeric peptide of met-enkephalin and FMRFa, not only produced analgesia but also did not let the tolerance develop. In the continuation of the same study, Phe4 is chlorinated so as to assess the effect of chlorination on the conformation, lipophilicity and analgesia of chimeric peptide [p-Cl Phe(4)] YFa. Not only does the chlorination increase the lipophilicity but also enhances the propensity of [p-Cl Phe(4)] YFa to form alpha helix in comparison of YFa in presence of membrane mimicking solvent trifluoroethanol (TFE). This increase in lipophilicity and helix-forming ability results in more bioavailability and naloxone-reversible analgesia by [p-Cl Phe(4)] YFa. Though analgesia produced by [p-Cl Phe(4)] YFa is more than YFa at all doses, there is sudden decrease in analgesia at 45 and 60 min at 60 mg/kg. This sudden decrease of analgesia seems to be due to desensitization of opioid receptors.

Topics: Analgesia; Analgesics, Opioid; Animals; Circular Dichroism; Enkephalin, Methionine; FMRFamide; Male; Mice; Octanols; Oligopeptides; Pain; Protein Structure, Secondary; Solubility; Water

An enzymatically stable analog of YGGFMKKKFMRFamide (YFa), a chimeric peptide of metenkephalin and FMRFa, was synthesised. The antinociceptive effects of intracerebroventricular injections of this analog-[D-Ala2)]YAGFMKKKFMRFamide ([D-Ala2]YFa)-was then investigated using the mouse radiant-heat tail-flick test. [D-Ala2]YFa produced modest to good antinociception at 1, 2, and 5 microg/mouse (0.64, 1.28, and 3.22 nmol, respectively). This antinociceptive effect was completely reversed by the opioid receptor antagonist naloxone (1.5 microg/mouse: 4.12 nmol, intracerebroventricular [i.c.v.]), administered 5 min prior. Pretreatment (5 min) with either neuropeptides FF (1 microg/mouse: 0.92 nmol, i.c.v.) or FMRFa (1 microg/mouse: 1.69 nmol, i.c.v.) significantly attenuated the antinociceptive effects induced by [D-Ala2]YFa (1 microg/mouse, i.c.v.). Intracerebroventricular administration of [D-Ala2]YFa at 1 microg/mouse dose with morphine (2 microg/mouse: 5.86 nmol, i.c.v.) produced an additive antinociceptive effect, suggesting that [D-Ala2]YFa may have a modulatory effect on opioid (morphine) analgesia. These results provide further support for a role of such amphiactive sequences in antinociception and its modulation.

Topics: Analgesics, Opioid; Animals; Brain; Drug Interactions; Enkephalin, Methionine; FMRFamide; Injections, Intraventricular; Mice; Mice, Inbred Strains; Morphine; Naloxone; Narcotic Antagonists; Neurons; Nociceptors; Oligopeptides; Pain; Pain Measurement; Recombinant Fusion Proteins

The ability of Phe-Met-Arg-Phe-NH2 (FMRFamide) or [D-Met2]-FMRFamide to produce antinociception in mice, or to block morphine-induced antinociception, was examined using the tail-flick and tail-immersion (55 degrees C) tests. [D-Met2]-FMRFamide dose-dependently produced antinociception following intracerebroventricular (i.c.v.) administration with ED50 values (95% confidence limits) of 5.0 (2.2-7.2) and 12.8 (8.1-19.9) micrograms in the tail-flick and tail-immersion tests, respectively. FMRFamide did not produce a maximal effect in the tail-flick test. Naloxone (administered s.c. 20 min prior to the i.c.v. administration of [D-Met2]-FMRFamide) dose-dependently attenuated [D-Met2]-FMRFamide-induced antinociception. The shift in the [D-Met2]-FMRFamide dose-response curve was parallel and a pA2 value for naloxone of 6.3 +/- 0.3 was determined from a Schild plot analysis. Mice made tolerant to the antinociceptive effect of morphine were cross-tolerant to the antinociceptive effect of [D-Met2]-FMRFamide. FMRFamide and [D-Met2]-FMRFamide both produced rightward, parallel shifts of the morphine antinociceptive dose-response curve. The findings that [D-Met2]-FMRFamide both elicited naloxone-sensitive antinociception and attenuated morphine-induced antinociception are consistent with the view that FMRFamide-related peptides (FaRPs) are weak agonists at opioid receptors and, further, appear to reconcile the apparently chimeric agonist and antagonist properties of these peptides observed in vivo.

Topics: Amino Acid Sequence; Analgesics; Animals; FMRFamide; Hot Temperature; Injections, Intraventricular; Male; Mice; Molecular Sequence Data; Morphine; Naloxone; Neuropeptides; Pain; Pain Measurement; Perception; Pressure; Receptors, Opioid; Tail

The gill- and siphon-withdrawal reflex of Aplysia undergoes transient inhibition following noxious stimuli such as tail shock. This behavioral inhibition appears to be due in part to transient presynaptic inhibition of the siphon sensory cells, which can be mimicked by application of the peptide FMRFamide. Although FMRFamide is widespread in the Aplysia nervous system, an FMRFamide-containing inhibitory neuron has not previously been identified. We have searched for such a neuron by combining FMRFamide immunofluorescence with fluorescent dye backfilling from the abdominal ganglion, the location of the siphon sensory cells. These methods localized a neuron in the left pleural ganglion, which we have named LPL16. LPL16 is FMRFamide immunoreactive; it is excited by tail shock; and stimulation of LPL16 produces inhibition of siphon sensory cell-to-motor cell postsynaptic potentials and narrowing of action potentials in the sensory cells in tetraethylammonium solution. These results indicate that LPL16 participates in the inhibitory effects of tail shock, and support the idea that FMRFamide plays a physiological role in the inhibition.

Topics: Animals; Aplysia; Electroshock; Fluorescent Antibody Technique; FMRFamide; Ganglia; Motor Neurons; Neural Inhibition; Neurons; Neurons, Afferent; Neuropeptides; Neurotransmitter Agents; Pain; Physical Stimulation; Pleura; Skin Physiological Phenomena; Synapses

Previous studies suggest that neuropeptide FF (NPFF) plays a role in opiate dependence and subsequent abstinence syndrome. The present study assessed the role of NPFF in opiate tolerance. Third ventricular injection of IgG from NPFF antiserum restored the analgesic response to i.c.v. morphine in morphine-tolerant rats (radiant heat tail flick test). IgG from control serum failed to produce this effect. In opiate-naive rats, however, the same treatment with IgG from NPFF antiserum did not affect the analgesic response to i.c.v. morphine. Thus, immunoneutralization of NPFF appears to selectively restore morphine sensitivity in opiate-tolerant animals. These results support the hypothesis that endogenous NPFF contributes to opiate tolerance.

Topics: Amino Acid Sequence; Analgesia; Animals; Cross Reactions; Drug Tolerance; FMRFamide; Immunoglobulin G; Male; Molecular Sequence Data; Morphine; Neuropeptides; Oligopeptides; Pain; Rabbits; Rats; Rats, Inbred Strains

The effects of two endogenous mammalian FMRFamide (Phe-Met-Arg-Phe-NH2)-related peptides, an octapeptide F8Fa (Phe-Leu-Phe-Gln-Pro-Gln-Arg-Phe-NH2) and an octadecapeptide A18Fa (Ala-Gly-Glu-Gly-Leu-Ser-Ser-Pro-Phe-Trp-Ser-Leu-Ala-Ala-Pro-Gln-Arg-Phe -NH2) on morphine- and restraint stress-induced analgesia and basal nociceptive sensitivity, as measured by the latency of a foot-lifting response to a warmed surface, were examined in male mice. Intracerebroventricular (i.c.v.) administrations of F8Fa and A18Fa (0.10-10 micrograms) during the day-time significantly reduced morphine (10 mg/kg) and restraint-induced analgesia at 30 min after administration, with F8Fa having a greater inhibitory effect than A18Fa. At night during the dark period i.c.v. F8Fa also significantly reduced the elevated nocturnal thermal response latency, while not affecting the shorter day-time nociceptive responses. Peripheral administrations of the prototypic opiate antagonist, naloxone (1.0 mg/kg), had similar inhibitory effects on morphine- and stress-induced analgesia, and the day-night rhythm of nociceptive sensitivity. These results indicate that F8Fa and A18Fa are involved in the modulation of opioid analgesia and suggest that these endogenous FMRFamide-related peptides may be associated with the expression of the day-night rhythm of opioid-mediated nociceptive sensitivity.

Topics: Amino Acid Sequence; Analgesia; Animals; Circadian Rhythm; Endorphins; FMRFamide; Injections, Intraventricular; Male; Mice; Molecular Sequence Data; Morphine; Neuropeptides; Oligopeptides; Pain; Restraint, Physical; Stress, Psychological

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.

Topics: Animals; Calcium; Drug Interactions; FMRFamide; Ion Channels; Mice; Morphine; Nervous System; Neuropeptides; Nifedipine; Pain; Stress, Physiological; Verapamil

Cholecystokinin octapeptide (CCK 8) produced significant antinociception in the tail immersion test in the rat, paw pressure test in the rat and acetylcholine-induced writhing test in the mouse after subcutaneous (s.c.) administration. In the hot plate test, CCK 8 (s.c.) showed antinociceptive activity if the latency to lick was used as the end point but if the latency to jump was recorded the antinociceptive effects were not evident. Cholecystokinin tetrapeptide (CCK 4) was shown to be antinociceptive in the writhing but not in the hot plate test after subcutaneous administration and appeared to be less potent than CCK 8 when tested under the same conditions. Antinociception induced by CCK 8 in the hot plate test (lick) could also be demonstrated after direct intracerebroventricular (i.c.v.) injection and this observation was also made with the CCK-related peptide FMRF amide. Antinociception induced by CCK 8 (which did not appear to be associated with reduced locomotor activity) was evident 5 min after intraventricular injection and was maximal at 10 min, the effect lasting over a 30-45 min period. The antinociceptive effect of CCK 8 was antagonised by naloxone and was potentiated by simultaneous administration of the peptidase inhibitors bestatin, thiorphan and captopril.

Topics: Animals; Captopril; FMRFamide; Gastrins; Leucine; Male; Mice; Naloxone; Neuropeptides; Pain; Protease Inhibitors; Rats; Rats, Inbred Strains; Reaction Time; Sincalide; Tetragastrin; Thiorphan; Tiopronin

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.

Topics: Animals; Brain; Endorphins; FMRFamide; Mice; Mice, Inbred C57BL; Motor Activity; MSH Release-Inhibiting Hormone; Oligopeptides; Pain; Restraint, Physical; Stress, Physiological

Phe-Met-Arg-Phe-NH2 (FMRF-NH2) was initially isolated from the macrocallista nimbosa clam and subsequently existence of FMRF-NH2-like immunoreactivity (FMRF-NH2-IR) was detected in mammalian CNS. Due to the structural similarity between FMRF-NH2 and the C-terminal extended form of met5-enkephalin, met5-enkephalin-arg6-phe7 (YGGFMRF), a possible interaction between these two peptides was explored. FMRF-NH2 injected intrathecally decreases the antinociceptive action of YGGFMRF or morphine. However, the FMRF-NH2-IR present in rat and bovine brains differs from FMRF-NH2. Intrathecally injected FMRF-NH2-IR partially purified from bovine brain reduces YGGFMRF antinociception. The antagonism elicited by FMRF-NH2 can be reversed by proglumide, which was reported to act as a CCK antagonist. In order to characterize the biological profile of FMRF-NH2-IR, the effect of proglumide and of the FMRF-NH2 antibody on morphine analgesia was tested. Both the IgG isolated from FMRF-NH2 antiserum and proglumide were found to potentiate the morphine analgesia. The results taken together suggest that endogenous FMRF-NH2-IR modulates opioid antinociception; perhaps by acting as an endogenous naloxone.

Topics: Animals; Bivalvia; Brain Chemistry; Cattle; FMRFamide; Immunoenzyme Techniques; Male; Medulla Oblongata; Morphine; Nociceptors; Oligopeptides; Pain; Proglumide; Rats; Rats, Inbred Strains; Spinal Cord

In rats the antinociceptive actions of morphine (injected intraventricularly) or of [Met5]enkephalin-Arg6-Phe7 (YGGFMRF) (injected intrathecally) were attenuated by a pretreatment with 10 microliter of artificial cerebral spinal fluid containing 1 microM captopril/1 microM bestatin/2.5 microM Phe-Met-Arg-Phe-NH2 (FMRF-NH2) given 5 min earlier by the same route. A high molecular weight form of FMRF-NH2 purified from bovine brain attenuated the antinociceptive action of YGGFMRF. IgG, prepared from a specific FMRF-NH2 antiserum, elicited a moderate antinociception reversible by naloxone; in contrast, IgG prepared from control serum failed to change tail-flick latencies. In rats receiving morphine every 2 hr and anti-FMRF-NH2 IgG every 4 hr, the antinociceptive action was still evident after eight successive injections; in rats receiving only morphine, the antinociceptive action had disappeared after six successive injections. Morphine (1 microM) added to the perfusion fluid of the subarachnoidal spaces of rat spinal cord releases FMRF-NH2-like peptides in the perfusate.

Topics: Animals; Drug Tolerance; Enkephalin, Methionine; FMRFamide; Male; Morphine; Oligopeptides; Pain; Rats; Spinal Cord