Opioid Receptor-like Receptor Research Articles

The ORL-1 Receptor System: Are There Opportunities for Antagonists in Pain Therapy?

Following the cloning of the classical opioid receptors (mu, delta and kappa), the opioid receptor like-1 (ORL-1) was identified as a G-protein coupled receptor (GPCR) with 65% structure homology to the other members of the opioid family. Its endogenous ligand nociception/orphanin FQ (N/OFQ) was discovered shortly thereafter, becoming the subject of investigation in numerous studies. Since activation of the ORL-1 receptor by N/OFQ leads to G alpha(i)-coupling and signal transduction similar to that of opioid receptors, N/OFQ was thought to have a role in pain modulation, similar to that of the endogenous opioids. Surprisingly, studies characterizing N/OFQ's effects on pain transmission yielded conflicting results, attributing to N/OFQ both pronociceptive and antinociceptive actions, depending on doses and routes of administration as well as species and sex of the subjects. With the development of selective and potent ORL-1 antagonists, many scientists believed these contradicting actions would be elucidated. Here we review the recent literature reporting the use of novel ORL-1 antagonists, both peptide and non-peptide, in different models of pain and discuss their use as research tools or potential drug candidates.

Nociceptin/Orphanin FQ Peptide Receptor as a Therapeutic Target for Obesity

Nociceptin/orphanin FQ (N/OFQ) peptide (NOP) receptor is a candidate target for novel therapeutics for a range of conditions, including obesity. This article reviews recent advances in understanding of N/OFQ's involvement in the regulation of food intake and appraises current developments in the rational design of antagonists aimed at the NOP receptor.

The role of the opioid receptor-like (ORL1) receptor in motor stimulatory and rewarding actions of buprenorphine and morphine

We have previously shown that the ability of buprenorphine to activate the opioid receptor-like (ORL1) receptor compromises its antinociceptive effect. Furthermore, morphine has been shown to alter the level of orphanin FQ/nociceptin (OFQ/N), the endogenous ligand of the ORL1 receptor, raising the possibility that the endogenous OFQ/N/ORL1 receptor system may be involved in the actions of these opioids. Thus, using mice lacking the ORL1 receptor and their wild-type littermates, the present study assessed the role of the ORL1 receptor in psychomotor stimulant and rewarding actions of buprenorphine and morphine. Morphine (5, 10 mg/kg) dose-dependently increased motor activity and induced conditioned place preference. However, the magnitude of each response was comparable for the mutant mice and their wild-type littermates. In contrast, buprenorphine (1 mg/kg) induced greater motor stimulation in ORL1 receptor knockout mice as compared with their wild-type littermates. Further, single conditioning with buprenorphine (3 mg/kg) induced place preference in mutant mice but not in their wild-type littermates. The results of binding assay showed that buprenorphine concentration-dependently (0–1000 nM) displaced specific binding of [ 3H]-OFQ/N in brain membrane of wild-type mice. Together, the present results suggest that the ability of buprenorphine to interact with the ORL1 receptor modulates its acute motor stimulatory and rewarding effects.

Involvement of ORL1 receptor and ERK kinase in the orphanin FQ-induced nociception in the nucleus accumbens of rats

Nociceptin/orphanin FQ (N/OFQ) is a heptadecapeptide, which has been identified as an endogenous ligand of the opioid receptor-like (ORL1) receptor. The present study investigated the nociceptive effect of intra-nucleus accumbens (intra-NAc) injection of OFQ, and the involvement of ERK pathway in such effect. Intra-NAc injection of OFQ (0.1, 0.5, 1 nmol) dose-dependently decreased the nociceptive thresholds on the hindpaw withdrawal response to thermal and mechanical stimulation in rats. Moreover, the intra-NAc injection of OFQ-induced decreases in HWLs were antagonized by intra-NAc injection of (Nphe 1)nociceptin(1–13)NH 2, an antagonist of ORL1 receptor, in a dose-dependent way. Furthermore, the OFQ-induced nociception could be attenuated by pretreatment with the mitogen-activated protein kinase/ERK kinase (MEK) inhibitor 1,4-diamino-2,3-dicyano-1,4-bis(2-aminopheylthio)butadiene (U0126). Our results demonstrate that OFQ induces nociceptive effects in NAc. The effect was blocked by the antagonist (Nphe 1)nociceptin(1–13)NH 2 and attenuated by U0126, suggesting that the activation of ERK pathways is involved in the OFQ-induced nociceptive effect in the NAc of rats.

A Novel Class of Cycloalkano[b]pyridines as Potent and Orally Active Opioid Receptor-like 1 Antagonists with Minimal Binding Affinity to the hERG K+Channel

A series of compounds based on 7-{[4-(2-methylphenyl)piperidin-1-yl]methyl}-6,7,8,9-tetrahydro-5 H-cyclohepta[ b]pyridine-9-ol ( (-)-8b), a potent and selective opioid receptor-like 1 (ORL1) antagonist, was prepared and evaluated using structure-activity relationship studies with the aim of removing its affinity to human ether-a-go-go related gene (hERG) K (+) channel. From these studies, 10l was identified as an optimized structure with respect to ORL1 antagonist activity, and affinity to the hERG K (+)channel. Furthermore, 10l showed good in vivo antagonism with a wide therapeutic index in regards to adverse cardiovascular effects.

Alterations in the level of OFQ/N-IR in rat brain regions by cocaine

We have previously shown that administration of orphanin FQ/nociceptin (OFQ/N), the endogenous ligand of the opioid receptor-like (ORL-1) receptor, into the lateral ventricles or VTA blocked cocaine sensitization. In the present study, we determined the effect of acute and chronic cocaine treatment on the level of endogenous OFQ/N in rat brain regions. Male Sprague Dawley rats were tested for motor activity in response to saline or cocaine (20 mg/kg) injection once daily for three consecutive days. To determine the effect of single or repeated cocaine administration on the level of OFQ/N, rats were sacrificed 1 h following saline or cocaine injection either on day 1 or 3, respectively. Additional groups of rats were treated similarly with saline or cocaine on days 1–3 and sacrificed or tested for locomotor sensitization on day 8. Consistent with previous studies, repeated cocaine administration induced locomotor sensitization to a challenge dose of cocaine (7.5 mg/kg) given on day 8. Measurements of tissue content of OFQ/N-IR using radioimmunoassay indicated that the rat hypothalamus and striatum, respectively, contained the highest and lowest levels of the peptide among the brain regions tested. Acute cocaine decreased the level of OFQ-IR in the rat midbrain and to a lesser extent in the striatum. On the other hand, the level of OFQ/N was higher in rats treated with cocaine on days 1–3 and sacrificed on day 8. These findings suggest that endogenous OFQ/N may be involved in the actions of cocaine and possibly in cocaine-induced motor stimulation and locomotor sensitization.

Designed modification of partial agonist of ORL1 nociceptin receptor for conversion into highly potent antagonist

Nociceptin is an endogenous agonist ligand of the ORL1 (opioid receptor-like 1) receptor, and its antagonist is a potential target of therapeutics for analgesic and antineuropathy drugs. Ac-RYYRIK-NH 2 is a hexapeptide isolated from the peptide library as an antagonist that inhibits the nociceptin activities mediated through ORL1. However, the structural elements required for this antagonist activity are still indeterminate. In the present study, we evaluated the importance of the acetyl-methyl group in receptor binding and activation, examining the peptides acyl-RYYRIK-NH 2, where acyl (R-CO) possesses a series of alkyl groups, R = C n H 2 n+1 ( n = 0–5). The isovaleryl derivative with the C 4H 9 (=(CH 3) 2CHCH 2–) group was found to reveal a high receptor-binding affinity and a strong antagonist nature. This peptide achieved a primary goal of eliminating the agonist activity of Ac-RYYRIK-NH 2 and producing pure antagonist activity.

The endogenous OFQ/N/ORL-1 receptor system regulates the rewarding effects of acute cocaine

Previous studies have shown that orphanin FQ/nociceptin (OFQ/N), the endogenous ligand of the opioid receptor-like (ORL-1) receptor, reduces the rewarding and addictive properties of cocaine and other drugs of abuse. In the present study, using the conditioned place preference (CPP) paradigm, as an animal model of drug reward, we assessed whether the rewarding action of acute cocaine would be altered in mice lacking the ORL-1 receptor or in wild type mice treated with J-113397, an ORL-1 receptor antagonist, relative to their saline-treated controls. On day 1, mice were tested for their baseline place preferences, in which each mouse was placed in the neutral chamber of a three-chambered CPP apparatus, allowed to freely explore all the chambers and the amount of time that a mouse spent in each conditioning chamber was recorded for 15 min. On days 2–3, mice received once daily alternate-day saline/cocaine (15 or 30 mg/kg) conditioning for 30 min. On day 4, mice were tested for their postconditioning preferences, as described for day 1. In a subsequent study, the effect of J-113397 (3 mg/kg) on the rewarding action of acute cocaine (15 mg/kg) was also examined in wild type mice. Our results showed that mice lacking the ORL-1 receptor expressed greater CPP than their wild type littermates. Furthermore, the rewarding action of cocaine was enhanced in the presence of J-113397 in wild type mice. Together, the present results suggest that the endogenous OFQ/N/ORL-1 receptor system is involved in the rewarding action of acute cocaine.

Suppression of CCL2/MCP-1 and CCL5/RANTES Expression by Nociceptin in Human Monocytes

The receptor designated Opioid Receptor-Like 1 (ORL1) is abundantly expressed in the central nervous system (CNS) as well as by cells of the immune system. While much is known about the function of ORL1 in the CNS, there is little information in the literature about the role of ORL1 in the immune response. There have been numerous reports documenting the effects of GPCR activation on the expression of chemokines crucial in mediating inflammatory events in biological systems. The aim of the present work was to examine the effect of nociceptin administration on the pro-inflammatory chemokine expression of human monocytes. We report here that human CD14(+) monocytes expresses the mRNA for ORL1. Our results also demonstrate that nociceptin can suppress the production of CCL2/MCP-1 and CCL5/RANTES chemokine protein in both primary CD14(+) human monocytes and monocyte-like cell lines. However, nociceptin does not appear to regulate the expression of these chemokines at the level of transcription, as CCL2/MCP-1 and CCL5/RANTES mRNA levels following nociceptin treatment of monocytes were essentially normal. Although the mechanism of chemokine regulation by nociceptin is as yet unknown, it is evident that the ORL1/nociceptin system plays a role in regulating chemotactic responses of leukocytes through chemokine suppression. Finally, these data may provide the initial basis for the development of ORL1 agonists and antagonists for therapeutic treatment of inflammatory disease.

Opioid receptor‐like 1 (ORL1) receptor binding and the biological properties of Ac‐Arg‐Tyr‐Tyr‐Arg‐Ile‐Arg‐NH2 and its analogs

Hexapeptides such as Ac-Arg-Tyr-Tyr-Arg-Ile-Lys-NH(2) and Ac-Arg-Tyr-Tyr-Arg-Trp-Arg-NH(2) have been isolated from a combinatorial peptide library as small peptide ligands for the opioid peptide-like 1 (ORL1) receptor. To investigate the detailed structural requirements of hexapeptides, 25 analogs of these hexapeptides, based on the novel analog Ac-Arg-Tyr-Tyr-Arg-Ile-Arg-NH(2) (1), were synthesized and tested for their ORL1 receptor affinity and agonist/antagonist activity on mouse vas deferens (MVD) tissues. Analog 1 and its Cit(6)-analog (10) were found to possess high affinity to the ORL1 receptor, comparable to that of nociceptin/orphanin FQ, and exhibited potent antagonist activity (pA(2) values of 7.77 for 1 and 7.51 for 10, which are higher than that of [NPhe(1)]nociceptin(1-13)-NH(2) (6.90) on MVD assay. It was also found that the amino acid residue in position 5 plays a key role in agonist/antagonist activity, i.e. an L-configuration aliphatic amino acid is required for potent antagonist activity, while a nonchiral or D-configuration residue produces potent agonist activity. These lines of evidence may provide insight into the mechanisms controlling agonist/antagonist switching in the ORL1 receptor, and may also serve to help developing more potent ORL1 agonists and antagonists.

Role of hypothalamus nociceptin/orphanin FQ in pre-ovulatory luteinizing hormone surge of estrogen and progesterone-primed, ovariectomized rats

To investigate the role of hypothalamus nociceptin/orphanin FQ (OFQ) and its endogenous receptor, the opioid receptor-like1 receptor (ORL1 receptor) in the estrus cycle of female rats. Radioimmunoassay was used to detect the effect of the intracerebroventricular (icv) administration of OFQ and/or the ORL1 receptor antagonist [Nphe1]Nociceptin(1-13)NH2, that is, NC13 on luteinizing hormone (LH) levels of estrogen- and progesterone (EBP)-primed, ovariectomized (OVX) rats (EBP-primed OVX rats). RT-PCR, Western blotting, and immunohistochemistry techniques were adopted to observe the changes of OFQ and the ORL1 receptor in the pre-optic area (POA) and the medial basal hypothalamus (MBH) of the estrus cycle of female rat. Pre-ovulatory LH surges in EBP-primed, OVX rats were significantly reduced by icv administration of 20 and 200 nmol OFQ (P<0.05), and the effect of 20 nmol OFQ could be abolished by pretreatment with 20 nmol NC13. The OFQ mRNA level in the POA on pro-estrus was lowered markedly compared to diestrus and estrus (P<0.05), while the mRNA and protein levels of the ORL1 receptor showed no significant changes in the POA and MBH across the estrus cycle. Meanwhile, the number of OFQ-immunoreactive neurons in the medial POA, ventromedial hypothalamus, and the arcuate nucleus on pro-estrus was significantly decreased compared to diestrus and estrus (P<0.05). The inhibitory effect of OFQ on the LH surge of EBP-primed, OVX rats and its downregulation in POA and MBH on pro-estrus suggests that it might play a negative modulatory role in the estrus cycle.

Nociceptin/orphanin FQ decreases serotonin efflux in the rat brain but in contrast to a κ-opioid has no antagonistic effect on μ-opioid-induced increases in serotonin efflux

Similar to κ-opioids, nociceptin/orphanin FQ (OFQ) exerts anti-μ-opioid actions. This may involve interactions within the circuitry controlling 5-HT neurons in the dorsal raphe nucleus (DRN) that project to the nucleus accumbens (NAcc). To test this hypothesis, we compared the effects of OFQ and κ-opioids on 5-HT efflux in the CNS of freely behaving rats. First, OFQ (30–300 μM) infused into the DRN for 120 min dose-dependently decreased 5-HT efflux in the DRN. The opioid receptor-like 1 (ORL-1) antagonist [Nphe1]nociceptin(1–13)NH2 blocked this effect. Using dual-probe microdialysis we observed that OFQ (300 μM) infused into the DRN for 120 min produced parallel decreases in 5-HT efflux in the DRN and NAcc, suggesting that ORL-1 receptors in the DRN inhibit serotonergic neurons projecting to the NAcc. Also, 5-HT efflux in the NAcc was dose-dependently decreased during OFQ (30–300 μM) infusion into the NAcc. This suggests that OFQ can reduce 5-HT efflux in the NAcc both by inhibiting serotonergic neurons in the DRN and by stimulating ORL-1 receptors in the NAcc. Similar to OFQ, the κ-opioids U-50,488 (300 μM) and dynorphin A(1–13) (300 μM) infused into the DRN for 120 min decreased 5-HT efflux in the DRN. This effect was blocked only by the κ-opioid receptor antagonist nor-BNI. Lastly, we compared the ability of OFQ and U-50,488 to block μ-opioid-induced increases in 5-HT. The κ-opioid U-50,488 (1000 μM) attenuated the increase in 5-HT induced by the μ-opioid agonist endomorphin-1 (300 μM) in the DRN. In contrast, OFQ (300–1000 μM) did not alter μ-opioid-induced increases in 5-HT efflux. In summary, κ-opioids and OFQ both decreased 5-HT efflux in the CNS. However, in contrast to κ-opioids, which reversed μ-opioid-induced increases in 5-HT efflux, the anti-μ-opioid effects of OFQ apparently do not involve changes in 5-HT transmission under our experimental conditions.

Activation of the nociceptin opioid system in rat sensory neurons produces antinociceptive effects in inflammatory pain: Involvement of inflammatory mediators

Despite a large body of literature on the nociceptin (NC) opioid system in pain modulation, the mechanism of action of NC remains largely unexplored. Here, we investigated the role and mode of action of the spinal NC system in inflammatory pain. Preemptive intrathecal administration of NC attenuated thermal hyperalgesia and mechanical allodynia in rats with intraplantar complete Freund's adjuvant (CFA) injection. By using immunohistochemistry in L4 dorsal root ganglion (DRG) neurons, a marked increase of NC and ORL1 receptor immunoreactivity was detected following CFA. Intrathecal administration of NC attenuated the CFA-induced increases of calcitonin gene-related peptide, transient receptor potential vanilloid-1, and tumor necrosis factor-alpha in DRG neurons. Real-time reverse transcription-polymerase chain reaction showed that NC reduced the up-regulation of inducible nitric oxide synthase mRNA but not that of neuronal nitric oxide synthase mRNA in spinal cord segments after CFA. Furthermore, [Nphe1]NC(1-13)NH2, a selective opioid receptor-like 1 (ORL1) receptor antagonist, significantly antagonized the effects of NC on pain modulation and on the expression of inflammatory mediators, indicating a specific NC action through the ORL1 receptor. Together, these findings reveal novel mechanisms by which the NC system produces analgesia.

Effects of PKC on inhibition of delayed rectifier potassium currents by N/OFQ

Nociceptin/orphanin FQ (N/OFQ) is the endogenous ligand for the opioid receptor-like-1 (ORL-1) orphan receptor, which is responsible for inhibition of delayed rectifier potassium current ( I K). But its mechanism of N/OFQ acting on I K is not clear and whether PKC is involved in the modulation of this processing is still unknown. Whole-cell patch–clamp recordings were performed in acutely dissociated rat parietal cortical neurons. Bath application of N/OFQ (10 nM–10 μM) resulted in a dose-dependent depression of I K with partially recovery on washout. Furthermore, we investigated the role of PKC in the inhibition of I K by N/OFQ. Chelerythrine, an inhibitor of PKC, attenuated the inhibition of N/OFQ on I K. On the contrary, PDBu, an activator of PKC, augmented N/OFQ-evoked responses. The present study suggested that N/OFQ inhibited I K and PKC was involved in N/OFQ-evoked response in acutely dissociated rat cerebral parietal cortical neurons.

Nocistatin and its derivatives antagonize the impairment of short-term acquisition induced by nociceptin

We studied the effects of human nocistatin, a mature form of human nocistatin of 17 amino acid length (nocistatin17), and the amide derivative of nocistain17 (nocistatin amide), and nociceptin/orphanin FQ on short-term acquisition in mice using a multi trial passive avoidance protocol. Nociceptin 1 nmol administered by i.c.v. injection 15 min beforehand increased the number of trials required to achieve the learning objective and decreased the step through latency times in the first, second and third test trials. Nocistatin and nocistatin17 on their own did not affect acquisition, but were able at doses of 4 nmol to antagonize the impairment caused by nociceptin 1 nmol. Nocistatin amide on its own also did not impair acquisition and at a lower dose of 1 nmol was able to completely antagonize nociceptin. [N-Phe 1]-nociceptin (1–13) amide, a selective opioid receptor-like 1 (ORL1) receptor antagonist, could also antagonize the effect of nociceptin, confirming that nociceptin's effect is induced via the ORL1 receptor. The results support suggestions that both nocistatin and nociceptin have roles in learning and memory, with nocistatin working as a functional antagonist of nociceptin. The shorter mature human nocistatin peptide had similar activity to the larger peptide, and its amide derivative may be more potent.

The Hypnotic, Electroencephalographic, and Antinociceptive Properties of Nonpeptide ORL1 Receptor Agonists After Intravenous Injection in Rodents

Agonists at the opioid receptor-like receptor 1 (ORL1) induce motor impairment, sedation, and loss of righting reflex (LRR) in rodents. This receptor may provide a novel target in the field of anesthesia. We examined the hypnotic, electroencephalographic (EEG), and antinociceptive effects of two IV administered nonpeptide ORL1 agonists, (Ro 65-6570 and Org 26383), using LRR in mice and rats, percent EEG burst suppression in rats, and formalin paw test in mice. In mice, Ro 65-6570 and Org 26383 produced LRR (hypnotic dose 0.6 and 3.7 micromol/kg for Ro 65-6570 and Org 26383, respectively). Naloxone had no significant effect on sleep times produced by both compounds. In rats, Ro 65-6570 (0.6-2.4 micromol/kg) and Org 26383 (4-8 micromol/kg) produced LRR and burst suppression activity in the EEG. Both sleep times and burst suppression activity were significantly reduced with a selective ORL1 antagonist. In mice, dose-dependent inhibition of formalin-induced nociceptive behaviors occurred (Phase 1 ED50 0.4 and 1.8 micromol/kg and Phase 2 ED50 0.4 and 4.2 micromol/kg for Ro 65-6570 and Org 26383, respectively). These results show that Ro 65-6570 and Org 26383 (probably via the ORL1 receptor) behave as IV hypnotics and analgesics in mice and rats, and that the hypnotic and antinociceptive doses are similar.

Possible involvement of endogenous nociceptin/orphanin FQ in the pain-related behavioral responses induced by its own metabolite, nociceptin/orphanin FQ(14–17)

Nociceptin/orphanin FQ(14–17) (N/OFQ(14–17)) is one of the major fragments that are released from N/OFQ, an endogenous ligand for the opioid receptor like-1 (ORL-1) receptor by endopeptidase 24.11. In the present study, we determined the pharmacological profiles of N/OFQ(14–17) on pain-related behavioral responses in the mouse. Intrathecal (i.t.) administration of N/OFQ(14–17) (5–160 pmol) evoked pain-related behaviors, and these behavioral responses were reduced by i.t. co-administration of an ORL-1 receptor antagonist, [Nphe 1]N/OFQ(1–13)NH 2 (4 pmol). However, in the ligand-binding receptor assay, N/OFQ(14–17) had no affinity for the ORL-1 receptor. Furthermore, i.t. pretreatment with an antiserum against N/OFQ (1:50) diminished the N/OFQ(14–17)-induced pain-related behaviors, suggesting that endogenous N/OFQ is involved in their expression. Therefore, N/OFQ(14–17)-induced pain-related behaviors may be mediated through the release of endogenous N/OFQ in the mouse spinal cord.

Effects of ORL1 Receptor Agonists and Antagonists in Nociception

Nociceptin/orphanin FQ (N/OFQ), a 17-amino acid neuropeptide structurally similar to opioid peptides, selectively binds to opioid receptor-like (ORL1) receptor, which has the structure related to classical opioid receptors, but it does not bind opioid ligands. The functions of the N/OFQ system are still under active investigation. The N/OFQ, similarly to traditional opioids, produces membrane hyperpolarization through the opening of potassium channels and activation the ORL1 receptor inhibits adenylyl cyclase activity. In the central nervous system, N/OFQ affects feeding, anxiolytic activity, memory and locomotion but particularly influences sensory perception. In the periphery, N/OFQ inhibits neurogenic contractions in various tissues and affects the function of the cardiovascular and renal systems. N/OFQ is localized in the central nervous system in structures related to nociceptive processes and plays a role in peptidergic signaling of the primary afferent neurons which may be particularly relevant to pain control. Many studies have shown that exogenous application of N/OFQ into the central and peripheral nervous system of rats and mice induces both pro- and antinociceptive effects depending on the drug dose, route of administration, pain stimulus or animal species. The aim of the present review was to demonstrate contribution of both central and peripheral ORL1 receptors as well as various ORL1 ligands to the acute nociceptive stimulation and in chronic pain processes, e.g., inflammation and neuropathy. Moreover, intensive search for both agonists and antagonists of ORL1 receptor opened new experimental and therapeutic possibilities. The novel ligands of ORL1 receptor with high potency and selectivity corroborated a well-documented contribution of this receptor to pain perception, and their potential use in clinical practice has been postulated.

Daily Intravesical Instillation of 1 mg Nociceptin/Orphanin FQ for the Control of Neurogenic Detrusor Overactivity: A Multicenter, Placebo Controlled, Randomized Exploratory Study

We studied the feasibility, safety and efficacy of daily intravesical instillation of 1 mg of the endogenous peptide nociceptin/orphanin FQ in a selected group of patients who perform clean intermittent self-catheterization for neurogenic detrusor overactivity incontinence. A total of 18 patients with neurogenic detrusor overactivity incontinence and on clean intermittent self-catheterization were prospectively randomized to receive 1 mg nociceptin/orphanin FQ in 10 cc saline (9) or placebo (saline) solution (9) at the first morning catheterization for 10 days. All patients completed a voiding diary using a frequency/volume chart according to International Continence Society guidelines, and reported daily incontinence frequency. Mean changes in incontinence episode frequency and voiding diary mean bladder capacity from baseline throughout treatment were the primary outcome variables. Urodynamic parameters (cystomanometric bladder capacity, maximum bladder pressure) were also recorded at baseline and during the study. The 2 groups were well balanced and all patients completed the study. The urodynamic parameters recorded during the study showed an increase in cystomanometric bladder capacity and a decrease in maximum bladder pressure compared to baseline only in patients assigned to the nociceptin/orphanin FQ group. Mean daily urine leakage episodes during nociceptin/orphanin FQ treatment were 0.94 vs a pretreatment baseline of 2.18 (p < 0.05), while no significant changes were reported in the placebo group (2.06 vs 2.43 baseline). The total mean voiding diary bladder capacity increased from 171 +/- 70 to 294 +/- 107 ml in patients receiving nociceptin/orphanin FQ, while voiding diary mean bladder capacity remained unchanged in patients receiving placebo (from 182 +/- 55 to 178 +/- 23 ml). No significant problems related to feasibility of the procedure as well as significant side effects were reported by patients. This study showed that intravesical nociceptin/orphanin FQ but not placebo inhibited the micturition reflex in patients with neurogenic detrusor overactivity incontinence, and demonstrated the clinical efficacy of nociceptin/orphanin FQ during 10 days of treatment. These findings support the use of nociceptin/orphanin FQ peptide receptor agonists as an innovative therapeutic approach for controlling detrusor overactivity incontinence.

Nociceptin Levels in the Cerebrospinal Fluid of Chronic Pain Patients With or Without Intrathecal Administration of Morphine

The neuropeptide nociceptin/orphanin FQ (N/OFQ) is the endogenous ligand for the opioid-like receptor ORL-1 and is thought to be involved in pain transmission and modulation. Human studies have not yet defined its role in pain patients. The aims of this study were 1) to verify the presence of N/OFQ in the cerebrospinal fluid (CSF) of human controls and patients with chronic noncancer pain, including those treated with intrathecally administered morphine, and 2) to determine whether pain or treatment with long-term intrathecal morphine influences its levels. The CSF of 27 patients (nine controls and 18 with chronic noncancer pain, of whom 12 were treated chronically with intrathecally administered morphine and six were opioid naïve) was analyzed, blindly, with radioimmunoassay methods. N/OFQ was detected in all patients. Mean CSF concentrations were lowest in the morphine-treated group and highest in the untreated chronic pain patients (12.06 ± 1.19 and 57.41 ± 10.06 fmol/ml, respectively), and the difference between the morphine-treated group and controls was statistically significant (44.72 ± 13.56 fmol/ml, P < 0.05). The presence of N/OFQ peptide in human CSF may correlate with biological activities that are influenced by different pain states and long-term intrathecal-morphine treatment. Further studies should verify whether the determination of this peptide CSF level may provide information on opioid treatment efficacy and on the presence of opioid tolerance.