Nociceptin/orphanin FQ prevents ethanol-induced gastric lesions in the rat

Nociceptin/orphanin FQ (N/OFQ), the endogenous ligand of the NOP receptor, exerts a variety of effects on the gastrointestinal tract. The present study was aimed at evaluating the possible implication of N/OFQ in the maintenance of gastric mucosal integrity. N/OFQ was given either centrally or peripherally 30 min prior to intragastric administration (i.g.) of 1 ml/rat of ethanol (either 25% or 50%, v/v), which produces macroscopically visible gastric lesions. Intracerebroventricular (i.c.v.) injection of 2 microg/rat of N/OFQ significantly reduced lesions caused by 50% ethanol, while 1 microg/rat was enough to significantly reduce lesions caused by 25% ethanol. Intracerebroventricular injection of 5 microg/rat of the selective NOP receptor antagonist, UFP-101, completely reversed the protective effect of N/OFQ, 1 or 4 microg/rat against 25% or 50% ethanol, respectively. The intraperitoneal (i.p.) injection of N/OFQ produced a significant reduction of lesions induced by 50% ethanol, the peak effect being observed at 10 microg/kg. Intraperitoneal pretreatment with UFP-101, 120 microg/kg, completely abolished the protective effect of peripherally injected N/OFQ. Therefore, N/OFQ acts both centrally and peripherally as a protective agent against ethanol-induced gastric lesions, and its effect is mediated by NOP receptors.     

Metabolic fate of nociceptin/orphanin FQ in the rat spinal cord and biological activity of its released fragment.

Metabolism of orphanin FQ/nociceptin (OFQ/N) was studied in the spinal cord of rats. The heptadecapeptide was efficiently cleaved by a neutral serine endopeptidase, thus releasing the major metabolite, OFQ/N(1-11), further truncated to the final product, OFQ/N(1-6). Biologic activity of this latter fragment was tested in vivo, after intracerebroventricular and intrathecal injections. Hexapeptide exhibited a bi-phasic effect, causing antinociception up to 10 min after injection, followed by a hyperalgesia. The analgesic effect was blocked by naloxone and hyperalgesia was inhibited by NMDA--and NMDA/glycine site antagonists. The results indicate that shorter nociceptin fragments still possess their biologic activity though possibly acting via receptors other than ORL1.     

Nociceptin/orphanin FQ stimulates human monocyte chemotaxis via NOP receptor activation

Nociceptin/orphanin FQ (N/OFQ) produces several biological actions by activating the N/OFQ peptide receptor (NOP). It has been previously shown that N/OFQ stimulates leukocyte chemotaxis both in vitro and in vivo. In the present study we investigated the ability of N/OFQ, in comparison with the proinflammatory peptide formyl-Met-Leu-Phe (fMLP), to stimulate human neutrophil and monocyte chemotaxis and the release of lysozyme and superoxide anion (O2-) production from neutrophils. fMLP stimulated all the leukocyte functions examined. N/OFQ stimulated monocyte (pEC50 12.15) but not neutrophil chemotaxis. The production of O2- from neutrophils was not affected by N/OFQ while the release of lysozyme was increased in a concentration dependent manner (pEC50 11.00) although the maximal effects evoked by N/OFQ were about half of those of fMLP. The NOP ligands [Arg14, Lys15]N/OFQ, N/OFQ(1-13)NH2, Ro 64-6198, UFP-101 and the opioid antagonist naloxone were used for pharmacologically characterizing the receptor involved in the monocyte chemoattractant action of N/OFQ. [Arg14, Lys15]N/OFQ, N/OFQ(1-13)NH2, and Ro 64-6198 mimicked the action of N/OFQ showing similar maximal effects and the following order of potency: [Arg14, Lys15]N/OFQ (pEC50 13.22)>Ro 64-6198 (pEC50 12.96)>N/OFQ(1-13)NH2 (pEC50 12.67)>N/OFQ (pEC50 12.15). Moreover, the monocyte chemoattractant action of N/OFQ was not modified by naloxone 1 microM while antagonized by UFP-101 10 microM (pA2 7.00). Thus, the order of potency of agonists and the antagonist selectivity demonstrated that N/OFQ stimulates human monocyte chemotaxis via NOP receptor activation.     

Antinociceptive effect of Nidularium procerum: a Bromeliaceae from the Brazilian coastal rain forest

Nidularium procerum, a common plant of the Brazilian flora, has not yet been studied for its pharmacological properties. We report here that extracts of N. procerum show both analgesic and anti-inflammatory properties. Oral (p.o.) or intraperitoneal (i.p.) administration of an aqueous crude extract from leaves of N. procerum (LAE) inhibited the writhing reaction induced by acetic acid (ED50 value = 0.2 mg/kg body weight, i.p.) in a dose-dependent manner. This analgesic property was confirmed in rats using two different models of bradykinin-induced hyperalgesia; there was 75% inhibition of pain in the modified Hargreaves assay, and 100% inhibition in the classical Hargreaves assay. This potent analgesic effect was not blocked by naloxone, nor was it observed in the hot plate model, indicating that the analgesic effect is not associated with the activation of opioid receptors in the central nervous system. By contrast, we found that LAE (0.02 microg/ml) selectively inhibited prostaglandin E2 production by cyclooxygenase (COX)-2, but not COX-1, which is a plausible mechanism for the analgesic effect. A crude methanol extract from the leaves also showed similar analgesic activity. An identical extract from the roots of N. procerum did not, however, block acetic acid-induced writhes, indicating that the analgesic compounds are concentrated in the leaves. Finally, we found that LAE inhibited an inflammatory reaction induced by lipopolysaccharide in the pleural cavity of mice.     

Orphanin FQ/nociceptin inhibits morphine withdrawal

The influence of orphanin FQ/nociceptin (OFQ/N) on the morphine-withdrawal symptom was investigated. Withdrawal syndrome was induced in the morphine-dependent rats by an intraperitoneal (i.p.) injection of 2 mg/kg naloxone hydrochloride--an opioid receptors antagonist. Wet-dog shakes were used as a measure of the abstinence syndrome. Intraventricular injections of OFQ/N (5-20 microg/animal) caused significant inhibition of the withdrawal signs at doses between 15-20 microg, in the morphine-dependent rats. OFQ/N alone did not change behavior of the morphine-dependent animals. The obtained results indicate that OFQ/N can inhibit the morphine withdrawal symptoms induced by naloxone.     

Reversal of morphine, methadone and heroin induced effects in mice by naloxone methiodide

Opioid overdose, which is commonly associated with opioid induced respiratory depression, is a problem with both therapeutic and illicit opioid use. While the central mechanisms involved in the effects of opioids are well described, it has also been suggested that a peripheral component may contribute to the effects observed. This study aimed to further characterise the effects of the peripherally acting naloxone methiodide on the respiratory, analgesic and withdrawal effects produced by various opioid agonists. A comparison of the respiratory and analgesic effects of morphine, methadone and heroin in male Swiss-Albino mice was conducted and respiratory depressive ED(80) doses of each opioid determined. These doses (morphine 9 mg/kg i.p., methadone 7 mg/kg i.p., and heroin 17 mg/kg i.p.) were then used to show that both naloxone (3 mg/kg i.p.) and naloxone methiodide (30-100 mg/kg i.p.) could reverse the respiratory and analgesic effects of these opioid agonists, but only naloxone precipitated withdrawal. Further investigation in female C57BL/6J mice using barometric plethysmography found that both opioid antagonists could reverse methadone induced decreases in respiratory rate and increases in tidal volume. Its effects do not appear to be strain or sex dependent. It was concluded that naloxone methiodide can reverse the respiratory and analgesic actions of a variety of opioid agonists, without inducing opioid withdrawal.     

Dimerization of morphine and orphanin FQ/nociceptin receptors: generation of a novel opioid receptor subtype

Although orphanin FQ/nociceptin (OFQ/N) receptors are a member of the opioid receptor family of receptors, they bind traditional opioids with very poor affinity. We now demonstrate that mu opioid receptors can physically associate with OFQ/N receptors, resulting in a complex with a unique binding selectivity profile. Immunoprecipitation of epitope-tagged OFQ/N receptors co-precipitates mu receptors. When the two receptors were co-expressed in CHO cells, [3H]OFQ/N retained its high binding affinity for its receptor. However, co-expression of the two receptors increased by up to 250-fold the affinity of a series of opioids in [3H]OFQ/N binding assays. This enhanced affinity was limited to agonists with high affinity for mu receptors. Selective kappa(1) and delta opioids did not lower binding. Despite the dramatic increase in affinity for the opioid agonists in co-expressing cells, the opioid antagonists naloxone and diprenorphine failed to compete [3H]OFQ/N binding.     

Nonpeptide/peptide chimeric ligands for the nociceptin/orphanin FQ receptor: design, synthesis and in vitro pharmacological activity.

Nociceptin/orphanin FQ (N/OFQ) is the endogenous ligand for the G-protein coupled receptor referred to as N/OFQ peptide (NOP) receptor. NOP receptor activation by N/OFQ modulates several biological functions both at central and peripheral level. Structure activity relationship (SAR) studies demonstrated that the N/OFQ sequence can be divided into a N-terminal tetrapeptide 'message' crucial for receptor activation and a C-terminal 'address' important for receptor binding. On the basis of this message/address concept we synthesized some chimeric compounds in which we substituted the natural message domain with the nonselective nonpeptide NOP ligand (8-Naphthalen-1-yl-methyl-4-oxo-1-phenyl-1,3,8-triaza-spiro[4,5]dec-3-yl)-aceticacid methyl ester (NNC 63-0532) and used as address domain the peptide sequences Thr-NH2, N/OFQ(5-9)-NH2, N/OFQ(5-13)-NH2 and N/OFQ(5-17)-NH2. All the compounds were pharmacologically evaluated in the electrically stimulated guinea-pig ileum. NNC 63-0532 produced a concentration-dependent inhibition of the electrically induced twitches showing, in comparison with N/OFQ, lower potency and higher maximal effects. In addition, contrary to N/OFQ, the effects of NNC 63-0532 were insensitive to the NOP selective antagonist [Nphe1, Arg14, Lys15]N/OFQ-NH2 (UFP-101) while prevented by naloxone. Similar results were obtained with NNC 63-0532/Thr-NH2 and NNC 63-0532/N/OFQ(1-9)-NH2. On the contrary, the inhibitory effects of NNC 63-0532/N/OFQ(5-13)-NH2 and NNC 63-0532/N/OFQ(5-17)-NH2 were slightly antagonized by UFP-101 while naloxone prevented the effects of the high but not of the low concentrations of the two ligands. These data indicate that it is possible to functionalize with the N/OFQ address sequence a nonpeptide NOP ligand for increasing its binding to the NOP receptor. Moreover, these results corroborate the idea that the 5-13 sequence represents the crucial core of the N/OFQ address domain.     

Nociceptin/orphanin FQ increases ANP secretion in neonatal cardiac myocytes

Nociceptin (N/OFQ) is a novel heptadecapeptide with an amino acid sequence similar to that of endogenous opioid peptide dynorphin A. Dynorphin have been reported to increase the secretion of atrial natriuretic peptide (ANP) via selective activation of kappa-opioid receptor in cultured atrial cardiocytes. The present study was designed to investigate the direct effect of N/OFQ on the ANP secretion in cultured neonatal rat cardiac myocytes via N/OFQ receptor (NOP) activation. The secretion of ANP from cultured neonatal cardiac myocytes was increased in terms of incubation time. N/OFQ, at a dose of 0.3, 1, 3, and 10 microM, caused increases in ANP secretion in a dose-dependent manner. The N/OFQ-induced ANP secretion was completely antagonized by antagonists of NOP, 1 microM each of [Phe1 (CH2-NH) Gly2] nociceptin (1-13)-NH2 ([FG]N/OFQ(1-13)NH2) or naloxone benzoylhydrazone. In contrast, naloxone (1 microM), the non-selective opioid receptor antagonist, did not alter ANP response to N/OFQ. N/OFQ at 3 microM inhibited basal and forskolin-stimulated cAMP production, which was partially antagonized with the pretreatment of [FG]N/OFQ(1-13)NH2. An increase in ANP secretion by N/OFQ was also partially blocked by the pretreatment of forskolin. Homologous competition studies in neonatal cardiomyocyte membranes revealed the presence of two distinct sites. The high affinity site (10.9 +/- 1.6 nM) was far less abundant than the low affinity site. Therefore, these results suggest that N/OFQ causes an increase in ANP secretion in cultured neonatal cardiac myocytes by decreasing cAMP through its binding sites.     

Nociceptin/orphanin FQ inhibits electrically induced contractions of the human bronchus via NOP receptor activation

Nociceptin/orphanin FQ (N/OFQ) has been reported to inhibit neurogenic contractions in various tissues, including guinea pig airways. In the present study, we investigated the ability of N/OFQ to affect cholinergic contractions of human bronchi elicited by electrical field stimulation (EFS). Tissues were obtained from 23 patients undergoing surgery for lung cancer. EFS (20 Hz, 320 mA, 1.5 ms, 10 s) was applied five times every 20 min. Contractions induced by EFS were abolished by either TTX (1 microM) or atropine (1 microM) and concentration-dependently (10 nM-1 microM) inhibited by N/OFQ (Emax, 11.5+/-1.8% inhibition). The inhibitory effects of N/OFQ were mimicked by the N/OFQ receptor (NOP) ligand [Arg14, Lys15]N/OFQ which displayed however, higher significant maximal effects (17.7+/-2.9% inhibition, P<0.05). The actions of N/OFQ and [Arg14, Lys15]N/OFQ were not affected by naloxone (1 microM) while prevented by the selective NOP receptor antagonist UFP-101 (10 microM). Moreover, the inhibitory effects of NOP agonists were no longer evident in tissues treated with tertiapin (10 microM), an inhibitor of inward-rectifier potassium channels. In conclusion, the present data demonstrate that N/OFQ inhibited acetylcholine (ACh) release in the human bronchi via NOP receptor activation. This effect may involve stimulation of potassium currents.     

Analgesic activity and selectivity of isothiocyanate derivatives of fentanyl analogs for opioid receptors

The analgesic activity and opioid receptor binding characteristics were studied for the isothiocyanate ohmefentanyl (OMFIT), and isothiocyanate carfentanil (CarFIT), isothiocyanate 4-methoxymethylfentanyl (MethoFIT), isothiocyanate 3-methylfentanyl (superFIT) and their amide analogs. Antinociceptive activity was evaluated using the mouse hot plate test; selectivity for opioid receptor was determined in bioassay and binding assay. SuperFIT, CarFIT, OMFIT and MethoFIT exhibited an analgesic ED50 lower than those of their parent compounds without isothiocyanate (SCN) group. Furthermore these compounds exhibited potent inhibitory actions on the electrically evoked contractions of mouse vas deferens, which could be antagonized by naloxone, but their actions were weaker than those of their parent compounds without SC N-group. The inhibitory actions of these compounds on binding of [3H]OMF to mouse brain membrane was weaker than those of their parent compounds without SCN-group. CarFIT and MethoFIT showed weaker inhibitory actions on the binding of [3H] DADLE than their parent compounds without SCN-group, but SuperFIT and OMFIT stronger than their parent compounds, 3-methylfentanyl and ohmefentanyl. The selectivity of these isothiocyanate derivatives for delta opioid receptors increased. In conclusion, introducing isothiocyanato-group into 1-position of phenyl ring of ohmefentanyl and other fentanyl analogs would enhance the selectivity of these compounds for delta-opioid receptors, but decrease their analgesic activity.     

Chain-lengthened and imidazoline analogues of nicotine

Analogues of nicotine (1) and azanicotine (3) were prepared with an additional methylene group inserted between the two rings (i.e., homonicotine and homoazanicotine; 6 and 5, respectively). Although 6 (Ki = 3110 nM) and 3 (Ki = 206 nM) bind at nACh receptors with > or = 100-fold lower affinity than nicotine (Ki = 2.1 nM), 5 displays high affinity (Ki = 7.8 nM). Like nicotine (ED50 = 12 microg/mouse), both 3 and 5 (ED50 = 21 and 19 microg/mouse, respectively) produced antinociceptive activity in the tail-flick assay following intrathecal administration. The antinociceptive actions of 3 and 5, unlike those of nicotine, were not antagonized by mecamylamine. Compounds 3 and 5 might represent novel analgesic agents that act via a non-nicotinic mechanism, or via a nicotinic mechanism that is distinct from that mediating the antinociceptive actions of nicotine.     

N-terminal modifications leading to peptide ORL1 partial agonists and antagonists.

Nociceptin/Orphanin FQ (N/OFQ) is a 17 amino acid peptide that is the endogenous ligand for the G protein-coupled receptor (opioid receptor like 1, ORL1), a member of the opioid receptor family. Although it is clear that this receptor system is involved in a variety of physiological functions, including analgesia, the precise actions of N/OFQ remain largely uncharacterized. One reason for this has been limited high affinity ligands to ORL1, and particularly the lack of availability of useful specific antagonists. Herein we describe the pharmacological activity of a series of N-terminally modified hexapeptides with high affinity for ORL1. These compounds were tested for binding affinity using [3H]N/OFQ binding to human ORL1 in CHO cells, and functional activity by measuring stimulation of [35S]GTPgammaS binding in CHO cell membranes. The N-terminal modifications have produced compounds that maintained very high receptor affinity, but led to significant changes in intrinsic activity. One compound, pentanoyl-RYYRWR-NH2, with barely measurable agonist activity was tested in vivo. It was found to possess modest analgesic activity, but it was unable to block the morphine modulatory activity of N/OFQ.     

Magnetic fields inhibit opioid-mediated ‘analgesic’ behaviours of the terrestrial snail,Cepaea nemoralis

1. The terrestrial snail, Cepaea nemoralis, when placed on a warmed surface (40 degrees C) displays a thermal avoidance behaviour that entails an elevation of the anterior portion of the fully extended foot. The latency of this nociceptive response was increased by the prototypical mu and specific kappa opiate agonists, morphine and U-50, 488H, respectively, in a manner indicative of anti-nociception and the induction of 'analgesia'. Pretreatment with the prototypical opiate antagonist, naloxone, blocked the morphine- and reduced the U-50, 488H-induced analgesia. Naloxone had no effects on the thermal response latencies of saline treated animals. 2. Exposure to either cold (7 degrees C) or warm (38 degrees C) temperature stress increased the nociceptive thresholds of Cepaea in a manner indicative of the induction of 'stress-induced analgesia'. The warm stress-induced analgesia was opioid mediated, being blocked by naloxone, whereas, the cold stress-induced analgesia was insensitive to naloxone. 3. Exposure for 15-30 min to 0.5 Hz weak rotating magnetic fields (1.5-8.0 G) significantly reduced the analgesic effects of the mu and kappa opiate agonists in a manner similar to that observed with naloxone. The magnetic stimuli also inhibited the endogenous opioid mediated warm stress-induced analgesia and significantly reduced the cold stress-induced analgesia. The magnetic stimuli had no evident effects on the nociceptive responses of saline-treated animals. The dihydropyridine (DHP) and non-DHP calcium channel antagonists diltiazem, verapamil. and nifedipine differentially and significantly reduced, while the DHP calcium channel agonist, BAY K8644, significantly enhanced the inhibitory effects of the magnetic fields on morphine-induced analgesia.     

A cellular mechanism for the bidirectional pain-modulating actions of orphanin FQ/nociceptin

Orphanin FQ/nociceptin (OFQ/N) and its receptor share substantial structural features and cellular actions with classic opioid peptides and receptors, but have distinct pharmacological profiles and behavioral effects. Currently there is an active debate about whether OFQ/N produces hyperalgesia or analgesia. Using a well-defined brainstem pain-modulating circuit, we show that OFQ/N can cause either an apparent hyperalgesia by antagonizing mu opioid-induced analgesia or a net analgesic effect by reducing the hyperalgesia during opioid abstinence. It presumably produces these two opposite actions by inhibiting two distinct groups of neurons whose activation mediates the two effects of opioid administration. OFQ/N antagonism of the hyperalgesia may have significance for the treatment of opioid withdrawal and sensitized pain.     

Changes in expression of nociceptin/orphanin FQ and its receptor in spinal dorsal horn during electroacupuncture treatment for peripheral inflammatory pain in rats

The neuropeptide nociceptin/orphanin FQ (N/OFQ), the endogenous agonist of the N/OFQ peptide receptor (NOP receptor), has been demonstrated to be involved in many physiological and pathological functions including pain modulation. It was reported that electroacupuncture (EA) had a potent analgesic effect on inflammatory pain by activating various endogenous transmitters such as the opioid peptides. In the present study, we investigated the effect of EA on peripheral inflammatory pain and the expression of N/OFQ and the NOP receptor in the spinal dorsal horn of rats, using a behavioral test, RT-PCR, immunohistochemistry and Western blot analysis techniques. The results showed: (1) EA had an accumulative analgesic effect on chronic inflammatory pain; (2) in the superficial layers of the spinal dorsal horn, the level of mRNA of the precursor protein for N/OFQ (preproN/OFQ, ppN/OFQ) was increased and the N/OFQ immunoreactivity was decreased after peripheral inflammation, and could be significantly increased by EA treatment; (3) both mRNA and protein levels of the NOP receptor in the spinal dorsal horn were significantly increased after chronic inflammatory pain and could be further enhanced by EA treatment. The present data demonstrated that EA could activate the endogenous N/OFQ-NOP receptor system, and this might underlie the effectiveness of EA in the treatment of inflammatory pain.     

In vitro and in vivo studies on UFP-112, a novel potent and long lasting agonist selective for the nociceptin/orphanin FQ receptor

[(pF)Phe(4)Aib(7)Arg(14)Lys(15)]N/OFQ-NH(2) (UFP-112) has been designed as a novel ligand for the nociceptin/orphanin FQ (N/OFQ) peptide receptor (NOP) by combining into the same peptide different chemical modifications reported to increase N/OFQ potency. In vitro data obtained in the electrically stimulated mouse vas deferens demonstrated that UFP-112 behaved as a high potency (pEC(50) 9.43) full agonist at the NOP receptor. UFP-112 effects were sensitive to the NOP antagonist UFP-101 but not to naloxone and no longer evident in tissues taken from NOP(-/-) mice. In vitro half life of UFP-112 in mouse plasma and brain homogenate was 2.6- and 3.5-fold higher than that of N/OFQ. In vivo, in the mouse tail withdrawal assay, UFP-112 (1-100pmol, i.c.v.) mimicked the actions of N/OFQ producing pronociceptive effects after i.c.v. administration and antinociceptive effects when given i.t.; in both cases, UFP-112 was approximately 100-fold more potent than the natural peptide and produced longer lasting effects. UFP-112 also mimicked the hyperphagic effect of N/OFQ producing a bell shaped dose response curve with the maximum reached at 10pmol. The hyperphagic effects of N/OFQ and UFP-112 were absent in NOP(-/-) mice. Equi-effective high doses of UFP-112 (0.1nmol) and N/OFQ (10nmol) were injected i.c.v. in mice and spontaneous locomotor activity recorded for 16h. N/OFQ produced a clear inhibitory effect which lasted for 60min while UFP-112 elicited longer lasting effects (>6h). In conscious rats, UFP-112 (0.1 and 10nmol/kg, i.v.) produced a marked and sustained decrease in heart rate, blood pressure, and urinary sodium excretion and a profound increase in urine flow. Collectively, these findings demonstrate that UFP-112 behaves in vitro and in vivo as a highly potent and selective ligand able to produce full and long lasting activation of NOP receptors.     

Gastrointestinal effects of intracerebroventricularly injected nociceptin/orphaninFQ in rats

Nociceptin/orphanin FQ/(N/OFQ), a novel heptadecapeptide recently isolated from porcine and rat brain, is the endogenous ligand of the N/OFQ peptide receptor (NOP, previously known as ORL-1). In this study we examined the effects of intracerebroventricularly (icv) injected N/OFQ on gastric emptying, gastrointestinal transit, colonic propulsion and gastric acid secretion in rats. N/OFQ (0.01-10 nmol/rat) significantly delayed gastric emptying of a phenol red meal, inhibited transit of a non-absorbable charcoal marker through the small intestine and increased the mean colonic bead expulsion time. These N/OFQ-motor effects were abolished by the NOP receptor selective antagonist [NPhe(1)]N/OFQ(1-13)-NH(2) (50 nmol/rat), but were unaltered by the classical opioid receptor antagonist, naloxone (9.2 micromol/kg). Icv injected N/OFQ (10 nmol/rat) decreased gastric acid secretion in 2-h pylorus ligated rats in a naloxone sensitive manner. [NPhe(1)]N/OFQ(1-13)-NH(2) (100 nmol/rat) icv administered alone stimulated gastric acid secretion. These results indicate that N/OFQ activates via NOP receptor stimulation a central inhibitory pathway modulating gastrointestinal propulsive activity and gastric acid secretion in rats.     

Analgesia induced by intrathecal injection of dynorphin B in the rat

A dose-dependent analgesic effect of intrathecally injected dynorphin B was observed in rats using the tail flick as nociceptive test. Intrathecal injection of 20 nmol of dynorphin B increased the tail flick latency by 90 +/- 23%, an effect that lasted about 90 min. For the same degree of analgesia, dynorphin B was 50% more potent than morphine on a molar basis. The analgesic effect of this dose of dynorphin B was partially blocked by 10 mg/kg, but not by 1 mg/kg, of subcutaneous naloxone, showing a relative resistance to naloxone reversal as compared with morphine analgesia. The analgesia produced by dynorphin B was unchanged in morphine-tolerant rats but was significantly decreased in rats tolerant to ethylketazocine. These results suggest that dynorphin B produces its potent analgesic effect by activation of kappa rather than mu opioid receptors in the rat spinal cord.     

UFP-101 antagonizes the spinal antinociceptive effects of nociceptin/orphanin FQ: behavioral and electrophysiological studies in mice

Nociceptin/orphanin FQ (N/OFQ) modulates various biological functions, including nociception, via selective stimulation of the N/OFQ peptide receptor (NOP). Here we used the NOP selective antagonist UFP-101 to characterize the receptor involved in the spinal antinociceptive effects of N/OFQ evaluated in the mouse tail withdrawal assay and to investigate the mechanism underlying this action by assessing excitatory postsynaptic currents (EPSC) in laminas I and II of the mouse spinal cord dorsal horn with patch-clamp techniques. Intrathecal (i.t.) injection of N/OFQ in the range of 0.1-10 nmol produced a dose dependent antinociceptive effect, which was prevented by UFP-101, but not by naloxone. In contrast the antinociceptive effect of the mu-opioid peptide receptor agonist endomorphin-1 was blocked by naloxone but not by UFP-101. Moreover, N/OFQ and endomorphin-1 induced a significant antinociceptive effect in wild type mice while in mice knockout for the NOP receptor gene only endomorphin-1 was found to be active. In mouse spinal cord slices 1 microM N/OFQ reduced EPSC to 60+/-4% of control values. This inhibitory effect was reversed in a concentration dependent manner by UFP-101 (pA2 value 6.44). The present results demonstrate that N/OFQ-induced spinal antinociception in vivo and inhibition of spinal excitatory transmission in vitro are mediated by receptors of the NOP type.