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Sample records for opioid receptor modulation

  1. Role of the mu opioid receptor in opioid modulation of immune function

    PubMed Central

    Ninković, Jana; Roy, Sabita

    2014-01-01

    SUMMARY Endogenous opioids are synthesized in vivo in order to modulate pain mechanisms and inflammatory pathways. Endogenous and exogenous opioids mediate analgesia in response to painful stimuli by binding to opioid receptors on neuronal cells. However, wide distribution of opioid receptors on tissues and organ systems outside the CNS, such as the cells of the immune system, indicate that opioids are capable of exerting additional effects in the periphery, such as immunomodulation. The increased prevalence of infections in opioid abusers based epidemiological studies further highlights the immunosuppressive effects of opioids. In spite of their many debilitating side effects, prescription opioids remain a gold standard for treatment of chronic pain. Therefore, given the prevalence of opioid use and abuse, opioid mediated immune suppression presents a serious concern in our society today. It is imperative to understand the mechanisms by which exogenous opioids modulate immune processes. In this review we will discuss the role of opioid receptors and their ligands in mediating immune suppressive functions. We will summarize recent studies on direct and indirect opioid modulation of the cells of the immune system as well as the role of opioids in exacerbation of certain disease states. PMID:22170499

  2. Ignavine: a novel allosteric modulator of the μ opioid receptor

    PubMed Central

    Ohbuchi, Katsuya; Miyagi, Chika; Suzuki, Yasuyuki; Mizuhara, Yasuharu; Mizuno, Keita; Omiya, Yuji; Yamamoto, Masahiro; Warabi, Eiji; Sudo, Yuka; Yokoyama, Akinobu; Miyano, Kanako; Hirokawa, Takatsugu; Uezono, Yasuhito

    2016-01-01

    Processed Aconiti tuber (PAT) is used to treat pain associated with various disorders. Although it has been demonstrated that the κ opioid receptor (KOR) signaling pathway is a mediator of the analgesic effect of PAT, active components affecting opioid signaling have not yet been identified. In this study, we explored candidate components of PAT by pharmacokinetic analysis and identified ignavine, which is a different structure from aconitine alkaloids. A receptor binding assay of opioid receptors showed that ignavine specifically binds the μ opioid receptor (MOR), not the KOR. Receptor internalization assay in MOR-expressing cell lines revealed that ignavine augmented the responses produced by D-Ala(2)-N-Me-Phe(4)-Gly-ol(5)-enkephalin (DAMGO), a representative MOR agonist, at a low concentration and inhibited it at a higher concentration. Ignavine also exerted positive modulatory activity for DAMGO, endomorphin-1 and morphine in cAMP assay. Additionally, ignavine alone showed an analgesic effect in vivo. In silico simulation analysis suggested that ignavine would induce a unique structural change distinguished from those induced by a representative MOR agonist and antagonist. These data collectively suggest the possibility that ignavine could be a novel allosteric modulator of the MOR. The present results may open the way for the development of a novel pain management strategy. PMID:27530869

  3. Opioid Receptors.

    PubMed

    Stein, Christoph

    2016-01-01

    Opioids are the oldest and most potent drugs for the treatment of severe pain. Their clinical application is undisputed in acute (e.g., postoperative) and cancer pain, but their long-term use in chronic pain has met increasing scrutiny. This article reviews mechanisms underlying opioid analgesia and other opioid actions. It discusses the structure, function, and plasticity of opioid receptors; the central and peripheral sites of analgesic actions and side effects; endogenous and exogenous opioid receptor ligands; and conventional and novel opioid compounds. Challenging clinical situations, such as the tension between chronic pain and addiction, are also illustrated.

  4. The mu (μ) and delta (δ) opioid receptors modulate boar sperm motility.

    PubMed

    Vicente-Carrillo, Alejandro; Álvarez-Rodríguez, Manuel; Rodríguez-Martínez, Heriberto

    2016-08-01

    Endogenous and exogenous opioids modulate reproductive functions in target cells via opioid receptors (μ, δ, and κ). Sperm motility is a metric of gamete functionality, and serves as a suitable parameter for in vitro drug-induced toxicity assays. This study identifies the presence and location of opioid receptors in pig spermatozoa as well as their functional response after in vitro challenge with known agonists (morphine [μ]; [D-Pen 2,5]-enkephanile [δ]; and U 50488 [κ]) and antagonists (naloxone [μ]; naltrindole [δ]; and nor-binaltrorphimine [κ]). Only the μ- and δ-opioid receptors were present in the boar sperm plasma membrane, overlying the acrosome, neck, and principal piece. Challenge experiments with agonists and antagonists identified both μ- and δ-opioid receptors as regulators of sperm kinematics, wherein μ maintains or increases sperm movement whereas δ decreases sperm motility over time. Mol. Reprod. Dev. 83: 724-734, 2016 © 2016 Wiley Periodicals, Inc.

  5. Opioid modulation of immunocompetence: Receptor characterization and second messenger involvement

    SciTech Connect

    Hemmick, L.M.

    1989-01-01

    The purpose of this thesis was to examine the effects of opioids on several indices of immunocompetence, determined the receptor specificity of these effects, and ascertain whether the actions of opioids on lymphocytes could be correlated with activation of second messenger systems. By measuring {sup 45}Ca{sup 2+} uptake into lymphocytes, it was demonstrated that {beta}-endorphin 1-31 ({beta}-END 1-31) enhanced rat thymocyte Ca{sup 2+} uptake in response to concanavalin A (Con A) but not phytohemagglutinin (PHA). Related opioid peptides and alkaloids were unable to mimic the effect, and naloxone did not block it, suggesting that {beta}-END 1-31 acted by binding to specific, non-opioid receptors on the thymocytes. Rat splenocyte Con A-stimulated Ca{sup 2+} uptake was not affected by {beta}-END 1-31. {beta}-END 1-31 did not affect basal Ca{sup 2+} uptake by either cell type. Using ({sup 3}H)thymidine uptake as an index of lymphocyte proliferation, {beta}-END 1-31 and several related opioid peptides reversed prostaglandin E{sub 1} (PGE{sub 1}) suppression of rat lymph node cell Con A- and PHA-stimulated proliferation. Naloxone did not block the reversal. {beta}-END 1-31 was unable to reverse forskolin and cholera toxin suppression of proliferation, indicating that the lowering of cyclic AMP levels was not the mechanism involved. Verapamil inhibition of proliferation was also not reversed by {beta}-END 1-31, suggesting that promotion of Ca{sup 2+} influx was not a major mechanism involved.

  6. Proposed Mode of Binding and Action of Positive Allosteric Modulators at Opioid Receptors

    PubMed Central

    2016-01-01

    Available crystal structures of opioid receptors provide a high-resolution picture of ligand binding at the primary (“orthosteric”) site, that is, the site targeted by endogenous ligands. Recently, positive allosteric modulators of opioid receptors have also been discovered, but their modes of binding and action remain unknown. Here, we use a metadynamics-based strategy to efficiently sample the binding process of a recently discovered positive allosteric modulator of the δ-opioid receptor, BMS-986187, in the presence of the orthosteric agonist SNC-80, and with the receptor embedded in an explicit lipid–water environment. The dynamics of BMS-986187 were enhanced by biasing the potential acting on the ligand–receptor distance and ligand–receptor interaction contacts. Representative lowest-energy structures from the reconstructed free-energy landscape revealed two alternative ligand binding poses at an allosteric site delineated by transmembrane (TM) helices TM1, TM2, and TM7, with some participation of TM6. Mutations of amino acid residues at these proposed allosteric sites were found to either affect the binding of BMS-986187 or its ability to modulate the affinity and/or efficacy of SNC-80. Taken together, these combined experimental and computational studies provide the first atomic-level insight into the modulation of opioid receptor binding and signaling by allosteric modulators. PMID:26841170

  7. Positive allosteric modulators of the μ-opioid receptor: a novel approach for future pain medications

    PubMed Central

    Burford, N T; Traynor, J R; Alt, A

    2015-01-01

    Morphine and other agonists of the μ-opioid receptor are used clinically for acute and chronic pain relief and are considered to be the gold standard for pain medication. However, these opioids also have significant side effects, which are also mediated via activation of the μ-opioid receptor. Since the latter half of the twentieth century, researchers have sought to tease apart the mechanisms underlying analgesia, tolerance and dependence, with the hope of designing drugs with fewer side effects. These efforts have revolved around the design of orthosteric agonists with differing pharmacokinetic properties and/or selectivity profiles for the different opioid receptor types. Recently, μ-opioid receptor-positive allosteric modulators (μ-PAMs) were identified, which bind to a (allosteric) site on the μ-opioid receptor separate from the orthosteric site that binds an endogenous agonist. These allosteric modulators have little or no detectable functional activity when bound to the receptor in the absence of orthosteric agonist, but can potentiate the activity of bound orthosteric agonist, seen as an increase in apparent potency and/or efficacy of the orthosteric agonist. In this review, we describe the potential advantages that a μ-PAM approach might bring to the design of novel therapeutics for pain that may lack the side effects currently associated with opioid therapy. LINKED ARTICLES This article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-2 PMID:24460691

  8. Modulation of Opioid Receptor Ligand Affinity and Efficacy Using Active and Inactive State Receptor Models

    PubMed Central

    Anand, Jessica P.; Purington, Lauren C.; Pogozheva, Irina D.; Traynor, John R.; Mosberg, Henry I.

    2012-01-01

    Mu opioid receptor (MOR) agonists are widely used for the treatment of pain; however chronic use results in the development of tolerance and dependence. It has been demonstrated that co-administration of a MOR agonist with a delta opioid receptor (DOR) antagonist maintains the analgesia associated with MOR agonists, but with reduced negative side effects. Using our newly refined opioid receptor models for structure-based ligand design, we have synthesized several pentapeptides with tailored affinity and efficacy profiles. In particular, we have obtained pentapeptides 8, Tyr-c(S-S)[DCys-1Nal-Nle-Cys]NH2, and 12, Tyr-c(S-S)[DCys-1Nal-Nle-Cys]OH, which demonstrates high affinity and full agonist behavior at MOR, high affinity but very low efficacy for DOR, and minimal affinity for the kappa opioid receptor (KOR). Functional properties of these peptides as MOR agonists/DOR antagonists lacking undesired KOR activity make them promising candidates for future in vivo studies of MOR/DOR interactions. Subtle structural variation of 12, by substituting D-Cys5 for L-Cys5, generated analog 13 which maintains low nanomolar MOR and DOR affinity, but which displays no efficacy at either receptor. These results demonstrate the power and utility of accurate receptor models for structure-based ligand design, as well as the profound sensitivity of ligand function on its structure. PMID:22882801

  9. Nanoconjugated NAP as a Potent and Periphery Selective Mu Opioid Receptor Modulator To Treat Opioid-Induced Constipation.

    PubMed

    Xu, Guoyan G; Zolotarskaya, Olga Yu; Williams, Dwight A; Yuan, Yunyun; Selley, Dana E; Dewey, William L; Akbarali, Hamid I; Yang, Hu; Zhang, Yan

    2017-01-12

    Opioids are the mainstay for cancer and noncancer pain management. However, their use is often associated with multiple adverse effects. Among them, the most common and persistent one is probably opioid-induced constipation (OIC). Periphery selective opioid antagonists may alleviate the symptoms of OIC without compromising the analgesic effects of opioids. Recently our laboratories have identified one novel lead compound, 17-cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6β-[(4'-pyridyl)acetamido]morphinan (NAP), as a peripherally selective mu opioid receptor ligand carrying subnanomolar affinity to the mu opioid receptor and over 100-folds of selectivity over both the delta and kappa opioid receptors, with reasonable oral availability and half-life, and potential to treat OIC. Nanoparticle-based drug delivery systems are now widely considered due to their technological advantages such as good stability, high carrier capacity, low therapeutic side effects, etc. Herein we report nanoparticle supported NAP as a potential candidate for OIC treatment with improved peripheral selectivity over the original lead compound NAP.

  10. Modulation of peripheral μ-opioid analgesia by σ1 receptors.

    PubMed

    Sánchez-Fernández, Cristina; Montilla-García, Ángeles; González-Cano, Rafael; Nieto, Francisco Rafael; Romero, Lucía; Artacho-Cordón, Antonia; Montes, Rosa; Fernández-Pastor, Begoña; Merlos, Manuel; Baeyens, José Manuel; Entrena, José Manuel; Cobos, Enrique José

    2014-01-01

    We evaluated the effects of σ1-receptor inhibition on μ-opioid-induced mechanical antinociception and constipation. σ1-Knockout mice exhibited marked mechanical antinociception in response to several μ-opioid analgesics (fentanyl, oxycodone, morphine, buprenorphine, and tramadol) at systemic (subcutaneous) doses that were inactive in wild-type mice and even unmasked the antinociceptive effects of the peripheral μ-opioid agonist loperamide. Likewise, systemic (subcutaneous) or local (intraplantar) treatment of wild-type mice with the selective σ1 antagonists BD-1063 [1-[2-(3,4-dichlorophenyl)ethyl]-4-methylpiperazine dihydrochloride] or S1RA [4-[2-[[5-methyl-1-(2-naphthalenyl)1H-pyrazol-3-yl]oxy]ethyl] morpholine hydrochloride] potentiated μ-opioid antinociception; these effects were fully reversed by the σ1 agonist PRE-084 [2-(4-morpholinethyl)1-phenylcyclohexanecarboxylate) hydrochloride], showing the selectivity of the pharmacological approach. The μ-opioid antinociception potentiated by σ1 inhibition (by σ1-receptor knockout or σ1-pharmacological antagonism) was more sensitive to the peripherally restricted opioid antagonist naloxone methiodide than opioid antinociception under normal conditions, indicating a key role for peripheral opioid receptors in the enhanced antinociception. Direct interaction between the opioid drugs and σ1 receptor cannot account for our results, since the former lacked affinity for σ1 receptors (labeled with [(3)H](+)-pentazocine). A peripheral role for σ1 receptors was also supported by their higher density (Western blot results) in peripheral nervous tissue (dorsal root ganglia) than in several central areas involved in opioid antinociception (dorsal spinal cord, basolateral amygdala, periaqueductal gray, and rostroventral medulla). In contrast to its effects on nociception, σ1-receptor inhibition did not alter fentanyl- or loperamide-induced constipation, a peripherally mediated nonanalgesic opioid effect. Therefore

  11. Structural and functional interactions between six-transmembrane μ-opioid receptors and β2-adrenoreceptors modulate opioid signaling.

    PubMed

    Samoshkin, Alexander; Convertino, Marino; Viet, Chi T; Wieskopf, Jeffrey S; Kambur, Oleg; Marcovitz, Jaclyn; Patel, Pinkal; Stone, Laura S; Kalso, Eija; Mogil, Jeffrey S; Schmidt, Brian L; Maixner, William; Dokholyan, Nikolay V; Diatchenko, Luda

    2015-12-11

    The primary molecular target for clinically used opioids is the μ-opioid receptor (MOR). Besides the major seven-transmembrane (7TM) receptors, the MOR gene codes for alternatively spliced six-transmembrane (6TM) isoforms, the biological and clinical significance of which remains unclear. Here, we show that the otherwise exclusively intracellular localized 6TM-MOR translocates to the plasma membrane upon coexpression with β2-adrenergic receptors (β2-ARs) through an interaction with the fifth and sixth helices of β2-AR. Coexpression of the two receptors in BE(2)-C neuroblastoma cells potentiates calcium responses to a 6TM-MOR ligand, and this calcium response is completely blocked by a selective β2-antagonist in BE(2)-C cells, and in trigeminal and dorsal root ganglia. Co-administration of 6TM-MOR and β2-AR ligands leads to substantial analgesic synergy and completely reverses opioid-induced hyperalgesia in rodent behavioral models. Together, our results provide evidence that the heterodimerization of 6TM-MOR with β2-AR underlies a molecular mechanism for 6TM cellular signaling, presenting a unique functional responses to opioids. This signaling pathway may contribute to the hyperalgesic effects of opioids that can be efficiently blocked by β2-AR antagonists, providing a new avenue for opioid therapy.

  12. Structural and functional interactions between six-transmembrane μ-opioid receptors and β2-adrenoreceptors modulate opioid signaling

    PubMed Central

    Samoshkin, Alexander; Convertino, Marino; Viet, Chi T.; Wieskopf, Jeffrey S.; Kambur, Oleg; Marcovitz, Jaclyn; Patel, Pinkal; Stone, Laura S.; Kalso, Eija; Mogil, Jeffrey S.; Schmidt, Brian L.; Maixner, William; Dokholyan, Nikolay V.; Diatchenko, Luda

    2015-01-01

    The primary molecular target for clinically used opioids is the μ-opioid receptor (MOR). Besides the major seven-transmembrane (7TM) receptors, the MOR gene codes for alternatively spliced six-transmembrane (6TM) isoforms, the biological and clinical significance of which remains unclear. Here, we show that the otherwise exclusively intracellular localized 6TM-MOR translocates to the plasma membrane upon coexpression with β2-adrenergic receptors (β2-ARs) through an interaction with the fifth and sixth helices of β2-AR. Coexpression of the two receptors in BE(2)-C neuroblastoma cells potentiates calcium responses to a 6TM-MOR ligand, and this calcium response is completely blocked by a selective β2-antagonist in BE(2)-C cells, and in trigeminal and dorsal root ganglia. Co-administration of 6TM-MOR and β2-AR ligands leads to substantial analgesic synergy and completely reverses opioid-induced hyperalgesia in rodent behavioral models. Together, our results provide evidence that the heterodimerization of 6TM-MOR with β2-AR underlies a molecular mechanism for 6TM cellular signaling, presenting a unique functional responses to opioids. This signaling pathway may contribute to the hyperalgesic effects of opioids that can be efficiently blocked by β2-AR antagonists, providing a new avenue for opioid therapy. PMID:26657998

  13. Discovery, synthesis, and molecular pharmacology of selective positive allosteric modulators of the δ-opioid receptor.

    PubMed

    Burford, Neil T; Livingston, Kathryn E; Canals, Meritxell; Ryan, Molly R; Budenholzer, Lauren M L; Han, Ying; Shang, Yi; Herbst, John J; O'Connell, Jonathan; Banks, Martyn; Zhang, Litao; Filizola, Marta; Bassoni, Daniel L; Wehrman, Tom S; Christopoulos, Arthur; Traynor, John R; Gerritz, Samuel W; Alt, Andrew

    2015-05-28

    Allosteric modulators of G protein-coupled receptors (GPCRs) have a number of potential advantages compared to agonists or antagonists that bind to the orthosteric site of the receptor. These include the potential for receptor selectivity, maintenance of the temporal and spatial fidelity of signaling in vivo, the ceiling effect of the allosteric cooperativity which may prevent overdose issues, and engendering bias by differentially modulating distinct signaling pathways. Here we describe the discovery, synthesis, and molecular pharmacology of δ-opioid receptor-selective positive allosteric modulators (δ PAMs). These δ PAMs increase the affinity and/or efficacy of the orthosteric agonists leu-enkephalin, SNC80 and TAN67, as measured by receptor binding, G protein activation, β-arrestin recruitment, adenylyl cyclase inhibition, and extracellular signal-regulated kinases (ERK) activation. As such, these compounds are useful pharmacological tools to probe the molecular pharmacology of the δ receptor and to explore the therapeutic potential of δ PAMs in diseases such as chronic pain and depression.

  14. Modulation of serotonin transporter function by kappa-opioid receptor ligands.

    PubMed

    Sundaramurthy, Santhanalakshmi; Annamalai, Balasubramaniam; Samuvel, Devadoss J; Shippenberg, Toni S; Jayanthi, Lankupalle D; Ramamoorthy, Sammanda

    2017-02-01

    Kappa opioid receptor (KOR) agonists produce dysphoria and psychotomimesis. While KOR agonists produce pro-depressant-like effects, KOR antagonists produce anti-depressant-like effects in rodent models. The cellular mechanisms and downstream effector(s) by which KOR ligands produce these effects are not clear. KOR agonists modulate serotonin (5-HT) transmission in the brain regions implicated in mood and motivation regulation. Presynaptic serotonin transporter (SERT) activity is critical in the modulation of synaptic 5-HT and, subsequently, in mood disorders. Detailing the molecular events of KOR-linked SERT regulation is important for examining the postulated role of this protein in mood disorders. In this study, we used heterologous expression systems and native tissue preparations to determine the cellular signaling cascades linked to KOR-mediated SERT regulation. KOR agonists U69,593 and U50,488 produced a time and concentration dependent KOR antagonist-reversible decrease in SERT function. KOR-mediated functional down-regulation of SERT is sensitive to CaMKII and Akt inhibition. The U69,593-evoked decrease in SERT activity is associated with a decreased transport Vmax, reduced SERT cell surface expression, and increased SERT phosphorylation. Furthermore, KOR activation enhanced SERT internalization and decreased SERT delivery to the membrane. These data demonstrate that KOR activation decreases 5-HT uptake by altering SERT trafficking mechanisms and phosphorylation status to reduce the functional availability of surface SERT.

  15. Individual differences in orexin-I receptor modulation of motivation for the opioid remifentanil.

    PubMed

    Porter-Stransky, Kirsten A; Bentzley, Brandon S; Aston-Jones, Gary

    2017-03-01

    Orexin-1 receptors (Ox1Rs) have been implicated in the motivation for drugs of abuse. Here, we utilized a within-session behavioral-economics threshold procedure to screen for individual differences in economic demand for the ultra-short-acting opioid remifentanil and to test whether antagonism of Ox1Rs reduces remifentanil demand. The behavioral-economics procedure revealed robust individual differences in free consumption of remifentanil (Q0 parameter; hedonic set point). Rats with low baseline Q0 (low takers) displayed high demand elasticity (α parameter; reduced responding as drug price increased indicating low motivation for drug), whereas subjects with a higher Q0 (high takers) exhibit low demand elasticity (low α) by continuing to self-administer remifentanil despite increased cost (reflecting higher motivation for drug). In a punished responding paradigm utilizing footshock, subjects that were classified as high takers at baseline withstood twice as much shock as low takers to continue self-administering remifentanil. Interestingly, Ox1R antagonism with SB-334867 reduced Q0 and increased α in low takers but not in high takers. Similarly, the Ox1R antagonist attenuated cue-induced, but not drug-induced, reinstatement of remifentanil seeking in low takers but had no significant effect on reinstatement of drug seeking in high takers. Together, these data reveal a novel role of orexins in demand for remifentanil: Ox1Rs modulate demand in low takers but not in individuals that exhibit addictive-like behaviors (high takers). Finally, the behavioral assays in this study can serve as a novel laboratory model for studying individual differences in opioid use disorders.

  16. Ligand-Based Discovery of a New Scaffold for Allosteric Modulation of the μ-Opioid Receptor.

    PubMed

    Bisignano, Paola; Burford, Neil T; Shang, Yi; Marlow, Brennica; Livingston, Kathryn E; Fenton, Abigail M; Rockwell, Kristin; Budenholzer, Lauren; Traynor, John R; Gerritz, Samuel W; Alt, Andrew; Filizola, Marta

    2015-09-28

    With the hope of discovering effective analgesics with fewer side effects, attention has recently shifted to allosteric modulators of the opioid receptors. In the past two years, the first chemotypes of positive or silent allosteric modulators (PAMs or SAMs, respectively) of μ- and δ-opioid receptor types have been reported in the literature. During a structure-guided lead optimization campaign with μ-PAMs BMS-986121 and BMS-986122 as starting compounds, we discovered a new chemotype that was confirmed to display μ-PAM or μ-SAM activity depending on the specific substitutions as assessed by endomorphin-1-stimulated β-arrestin2 recruitment assays in Chinese Hamster Ovary (CHO)-μ PathHunter cells. The most active μ-PAM of this series was analyzed further in competition binding and G-protein activation assays to understand its effects on ligand binding and to investigate the nature of its probe dependence.

  17. Regulator of G protein signaling proteins differentially modulate signaling of μ and δ opioid receptors

    PubMed Central

    Xie, Zhihua; Li, Zhisong; Guo, Lei; Ye, Caiying; Li, Juan; Yu, Xiaoli; Yang, Huifen; Wang, Yulin; Chen, Chongguang; Zhang, Dechang; Liu-Chen, Lee-Yuan

    2009-01-01

    Effects of regulator of G protein signaling (RGS) proteins on μ and δ opioid receptors were investigated in HEK293 cells. Co-expression of RGS1, RGS2, RGS4, RGS9, RGS10 or RGS19 (Gα-interacting protein (GAIP)) significantly reduced [Tyr-D-Ala-Gly-N-methyl-Phe-Gly-ol]-Enkephalin (DAMGO)-induced inhibition of adenylyl cyclase (AC) mediated by μ opioid receptor, but only RGS9 decreased the effects of [Tyr-D-Pen-Gly-p-Chloro-Phe-D-Pen]-Enkephalin (DPDPE) mediated by δ opioid receptor. When C-tails of the receptors were exchanged (μ/δC and δ/μC chimeras), RGS proteins decreased δ/μC-mediated AC inhibition, but none had significant effects on that via μ/δC receptor. Thus, the C-terminal domains of the receptors are critical for the differential effects of RGS proteins, which may be due to differences in receptor - G protein - RGS protein interactions in signaling complexes. PMID:17433292

  18. Chronic Kappa opioid receptor activation modulates NR2B: Implication in treatment resistant depression

    PubMed Central

    Dogra, Shalini; Kumar, Ajeet; Umrao, Deepmala; Sahasrabuddhe, Amogh A.; Yadav, Prem N.

    2016-01-01

    Psychotomimetic and prodepressive effect by kappa opioid receptor (KOR) activation in rodents and human is widely known. Significantly, recent clinical investigations demonstrated the salutary effects of KOR antagonists in patients with treatment resistant depression, indicating essential role of KOR signaling in refractory depression. This study was undertaken to reveal the molecular determinant of KOR mediated depression and antidepressant response of KOR antagonist. We observed that chronic KOR activation by U50488, a selective KOR agonist, significantly increased depression like symptoms (behavioral despair, anhedonia and sociability) in C57BL/6J mice, which were blocked by KOR antagonist norBNI and antidepressant imipramine, but not by fluoxetine or citalopram. Further, chronic KOR activation increased phosphorylation of NR2B subunit of NMDA at tyrosine 1472 (pNR2B NMDA) in the hippocampus, but not in the cortex. Similar to behavioral effects norBNI and imipramine, but not SSRIs, blocked NR2B phosphorylation. Moreover, KOR induced depression like behaviors were reversed by NR2B selective inhibitor Ro 25-6981. Mechanistic studies in primary cultured neurons and brain tissues using genetic and pharmacological approaches revealed that stimulation of KOR modulates several molecular correlates of depression. Thus, these findings elucidate molecular mechanism of KOR signaling in treatment resistant depression like behaviors in mice. PMID:27634008

  19. Current Research on Opioid Receptor Function

    PubMed Central

    Feng, Yuan; He, Xiaozhou; Yang, Yilin; Chao, Dongman; Lazarus, Lawrence H.; Xia, Ying

    2012-01-01

    The use of opioid analgesics has a long history in clinical settings, although the comprehensive action of opioid receptors is still less understood. Nonetheless, recent studies have generated fresh insights into opioid receptor-mediated functions and their underlying mechanisms. Three major opioid receptors (μ-opioid receptor, MOR; δ-opioid receptor, DOR; and κ-opioid receptor, KOR) have been cloned in many species. Each opioid receptor is functionally sub-classified into several pharmacological subtypes, although, specific gene corresponding each of these receptor subtypes is still unidentified as only a single gene has been isolated for each opioid receptor. In addition to pain modulation and addiction, opioid receptors are widely involved in various physiological and pathophysiological activities, including the regulation of membrane ionic homeostasis, cell proliferation, emotional response, epileptic seizures, immune function, feeding, obesity, respiratory and cardiovascular control as well as some neurodegenerative disorders. In some species, they play an essential role in hibernation. One of the most exciting findings of the past decade is the opioid-receptor, especially DOR, mediated neuroprotection and cardioprotection. The up-regulation of DOR expression and DOR activation increase the neuronal tolerance to hypoxic/ischemic stress. The DOR signal triggers (depending on stress duration and severity) different mechanisms at multiple levels to preserve neuronal survival, including the stabilization of homeostasis and increased pro-survival signaling (e.g., PKC-ERK-Bcl 2) and anti-oxidative capacity. In the heart, PKC and KATP channels are involved in the opioid receptor-mediated cardioprotection. The DOR-mediated neuroprotection and cardioprotection have the potential to significantly alter the clinical pharmacology in terms of prevention and treatment of life-threatening conditions like stroke and myocardial infarction. The main purpose of this article

  20. Mu opioid receptor modulation in the nucleus accumbens lowers voluntary wheel running in rats bred for high running motivation.

    PubMed

    Ruegsegger, Gregory N; Toedebusch, Ryan G; Will, Matthew J; Booth, Frank W

    2015-10-01

    The exact role of opioid receptor signaling in mediating voluntary wheel running is unclear. To provide additional understanding, female rats selectively bred for motivation of low (LVR) versus high voluntary running (HVR) behaviors were used. Aims of this study were 1) to identify intrinsic differences in nucleus accumbens (NAc) mRNA expression of opioid-related transcripts and 2) to determine if nightly wheel running is differently influenced by bilateral NAc injections of either the mu-opioid receptor agonist D-Ala2, NMe-Phe4, Glyo5-enkephalin (DAMGO) (0.25, 2.5 μg/side), or its antagonist, naltrexone (5, 10, 20 μg/side). In Experiment 1, intrinsic expression of Oprm1 and Pdyn mRNAs were higher in HVR compared to LVR. Thus, the data imply that line differences in opioidergic mRNA in the NAc could partially contribute to differences in wheel running behavior. In Experiment 2, a significant decrease in running distance was present in HVR rats treated with 2.5 μg DAMGO, or with 10 μg and 20 μg naltrexone between hours 0-1 of the dark cycle. Neither DAMGO nor naltrexone had a significant effect on running distance in LVR rats. Taken together, the data suggest that the high nightly voluntary running distance expressed by HVR rats is mediated by increased endogenous mu-opioid receptor signaling in the NAc, that is disturbed by either agonism or antagonism. In summary, our findings on NAc opioidergic mRNA expression and mu-opioid receptor modulations suggest HVR rats, compared to LVR rats, express higher running levels mediated by an increase in motivation driven, in part, by elevated NAc opioidergic signaling.

  1. Influence of intramuscular heat stimulation on modulation of nociception: complex role of central opioid receptors in descending facilitation and inhibition.

    PubMed

    You, Hao-Jun; Lei, Jing; Ye, Gang; Fan, Xiao-Li; Li, Qiang

    2014-10-01

    It has been reported that the threshold to activate 'silent' or inactive descending facilitation of nociception is lower than that of descending inhibition. Thus, the development of pain therapy to effectively drive descending inhibition alone, without the confounding influences of facilitation is a challenge. To address this issue we investigated the effects of intramuscular stimulation with a heating-needle on spinal nociception, assessed by measuring nociceptive paw withdrawal reflex in rats. Additionally, involvement of the thalamic 'nociceptive discriminators' (thalamic mediodorsal (MD) and ventromedial (VM) nuclei), and opioid-mediated mechanisms were further explored. Descending facilitation and inhibition were elicited by 46°C noxious heating-needle stimulation, and were regulated by thalamic MD and VM nuclei, respectively. In contrast, innocuous heating-needle stimulation at a temperature of 43°C elicited descending inhibition modulated by the thalamic VM nucleus alone. Microinjection of μ/δ/κ-opioid receptor antagonists β-funaltrexamine hydrochloride/naltrindole/nor-binaltorphimine, into the VM nucleus attenuated the 46°C intramuscular heating-needle stimulation-evoked descending inhibition, whereas treatment of the MD nucleus with β-funaltrexamine hydrochloride significantly decreased the descending facilitation. By contrast, descending inhibition evoked by 43°C heating-needle stimulation was only depressed by naltrindole, as opposed to μ- and κ-opioid receptor antagonists, which failed to influence descending inhibition. The present study reveals distinct roles of μ-opioid receptors in the function of thalamic MD and VM nuclei,which exert facilitatory and inhibitory actions on nociception. Furthermore, innocuous, but not noxious, intramuscular heating-needle stimulation targeting δ-opioid receptors is suggested to be a promising avenue for the effective inhibition of pain.

  2. Enkephalins modulate inhibitory neuromuscular transmission in circular muscle of human colon via delta-opioid receptors.

    PubMed Central

    Hoyle, C H; Kamm, M A; Burnstock, G; Lennard-Jones, J E

    1990-01-01

    1. A sucrose-gap technique was used to investigate the neuromodulatory actions of enkephalins on non-adrenergic, non-cholinergic inhibitory junction potentials (IJPs) in the circular muscle of the human large intestine. 2. The native enkephalins, [Leu5]enkephalin (LENK) and [Met5]enkephalin (MENK) caused a concentration-dependent reduction in amplitude of IJPs without a significant effect on the smooth muscle membrane. 3. The actions of LENK and MENK were mimicked by the delta-selective opioid receptor agonists [D-Pen2, D-Pen5]enkephalin (DPDPE) and [D-Ala2, D-Leu5]enkephalin (DADLE). 4. The actions of LENK, MENK and DPDPE were antagonized to similar extents by the delta-selective opioid receptor antagonist ICI 174,864. 5. The mu-selective opioid receptor agonist [D-Ala2, Me Phe, Gly-ol5]enkephalin was approximately 100-fold less potent than any of the native or synthetic enkephalins at reducing the amplitude of the IJP. Dynorphin A and beta-endorphin both had very weak activity. 6. Responses to all of the agonists were inhibited by naloxone. The degree of antagonism of DPDPE or DADLE by naloxone (1 microM) was the same as that of LENK or MENK. 7. Neither MENK nor LENK affected hyperpolarization of the smooth muscle membrane induced by ATP or 5-hydroxytryptamine. Vasoactive intestinal polypeptide (1 pM-1 microM) did not produce any observable responses and this lack of reactivity was not affected by the enkephalins. 8. It is concluded that in the circular muscle of the human colon, LENK and MENK can act on prejunctional delta-opioid receptors to produce inhibition of non-adrenergic, non-cholinergic inhibitory neuromuscular transmission. Possible physiological significance of this prejunctional receptor is discussed. PMID:1966052

  3. Locus coeruleus kappa-opioid receptors modulate reinstatement of cocaine place preference through a noradrenergic mechanism.

    PubMed

    Al-Hasani, Ream; McCall, Jordan G; Foshage, Audra M; Bruchas, Michael R

    2013-11-01

    Activation of kappa-opioid receptors (KORs) in monoamine circuits results in dysphoria-like behaviors and stress-induced reinstatement of drug seeking in both conditioned place preference (CPP) and self-administration models. Noradrenergic (NA) receptor systems have also been implicated in similar behaviors. Dynorphinergic projections terminate within the locus coeruleus (LC), a primary source of norepinephrine in the forebrain, suggesting a possible link between the NA and dynorphin/kappa opioid systems, yet the implications of these putative interactions have not been investigated. We isolated the necessity of KORs in the LC in kappa opioid agonist (U50,488)-induced reinstatement of cocaine CPP by blocking KORs in the LC with NorBNI (KOR antagonist). KOR-induced reinstatement was significantly attenuated in mice injected with NorBNI in the LC. To determine the sufficiency of KORs in the LC on U50,488-induced reinstatement of cocaine CPP, we virally re-expressed KORs in the LC of KOR knockout mice. We found that KORs expression in the LC alone was sufficient to partially rescue KOR-induced reinstatement. Next we assessed the role of NA signaling in KOR-induced reinstatement of cocaine CPP in the presence and absence of a α2-agonist (clonidine), β-adrenergic receptor antagonist (propranolol), and β(1)- and β(2)-antagonist (betaxolol and ICI-118,551 HCl). Both the blockade of postsynaptic β(1)-adrenergic receptors and the activation of presynaptic inhibitory adrenergic autoreceptors selectively potentiated the magnitude of KOR-induced reinstatement of cocaine CPP but not cocaine-primed CPP reinstatement. Finally, viral restoration of KORs in the LC together with β-adrenergic receptor blockade did not potentiate KOR-induced reinstatement to cocaine CPP, suggesting that adrenergic receptor interactions occur at KOR-expressing regions external to the LC. These results identify a previously unknown interaction between KORs and NA systems and suggest a NA

  4. Pharmacological characterization of an opioid receptor in the ciliate Tetrahymena.

    PubMed

    Chiesa, R; Silva, W I; Renaud, F L

    1993-01-01

    A pharmacological characterization has been performed of the opioid receptor involved in modulation of phagocytosis in the protozoan ciliate Tetrahymena. Studies on inhibition of phagocytosis by mammalian prototypic opioid agonists revealed that morphine and beta-endorphin have the highest intrinsic activity, whereas all the other opioids tested can only be considered partial agonists. However, morphine (a mu-receptor agonist) is twice as potent as beta-endorphin (a delta-receptor agonist). Furthermore, the sensitivity for the opioid antagonist naloxone, determined in the presence of morphine and beta-endorphin, is very similar to the sensitivity exhibited by mammalian tissues rich in mu-opioid receptors. We suggest that the opioid receptor coupled to phagocytosis in Tetrahymena is mu-like in some of its pharmacological characteristics and may serve as a model system for studies on opioid receptor function and evolution.

  5. Role of the thalamic submedius nucleus histamine H1 and H 2 and opioid receptors in modulation of formalin-induced orofacial pain in rats.

    PubMed

    Erfanparast, Amir; Tamaddonfard, Esmaeal; Taati, Mina; Dabaghi, Milad

    2015-10-01

    Histamine and opioid systems are involved in supraspinal modulation of pain. In this study, we investigated the effects of separate and combined microinjections of agonists and antagonists of histamine H1 and H2 and opioid receptors into the thalamic submedius (Sm) nucleus on the formalin-induced orofacial pain. Two guide cannulas were implanted into the right and left sides of the Sm in ketamine- and xylazine-anesthetized rats. Orofacial formalin pain was induced by subcutaneous injection of a diluted formalin solution (50 μl, 1.5%) into the vibrissa pad. Face rubbing durations were recorded at 3-min blocks for 45 min. Formalin produced a biphasic pain response (first phase: 0-3 min and second phase: 15-33 min). Separate and combined microinjections of histamine H1 and H2 receptor agonists, 2-pyridylethylamine (2-PEA) and dimaprit, respectively, and opioid receptor agonist, morphine, attenuated the second phase of pain. The analgesic effects induced by 2-PEA, dimaprit, and morphine were blocked by prior microinjections of fexofenadine (a histamine H1 receptor antagonist), famotidine (a histamine H2 receptor antagonist), and naloxone (an opioid receptor antagonist), respectively. Naloxone also prevented 2-PEA- and dimaprit-induced antinociception, and the analgesic effect induced by morphine was inhibited by fexofenadine and famotidine. These results showed the involvement of histamine H1 and H2 and opioid receptors in the Sm modulation of orofacial pain. Opioid receptor might be involved in analgesia induced by activation of histamine H1 and H2 receptors and vice versa.

  6. Immunomodulatory effects of endogenous and synthetic peptides activating opioid receptors.

    PubMed

    Pomorska, Dorota K; Gach, Katarzyna; Janecka, Anna

    2014-01-01

    The main role of endogenous opioid peptides is the modulation of pain. Opioid peptides exert their analgesic activity by binding to the opioid receptors distributed widely in the central nervous system (CNS). However, opioid receptors are also found on tissues and organs outside the CNS, including the cells of the immune system, indicating that opioids are capable of exerting additional effects in periphery. Morphine, which is a gold standard in the treatment of chronic pain, is well-known for its immunosuppressive effects. Much less is known about the immunomodulatory effects exerted by endogenous (enkephalins, endorphins, dynorphins and endomorphins) and synthetic peptides activating opioid receptors. In this review we tried to summarize opioid peptide-mediated modulation of immune cell functions which can be stimulatory as well as inhibitory.

  7. Opioid System Modulates the Immune Function: A Review

    PubMed Central

    Liang, Xuan; Liu, Renyu; Chen, Chunhua; Ji, Fang; Li, Tianzuo

    2016-01-01

    Opioid receptors and their ligands produce powerful analgesia that is effective in perioperative period and chronic pain managements accompanied with various side effects including respiratory depression, constipation and addiction etc. Opioids can also interfere with the immune system, not only participating in the function of the immune cells, but also modulating innate and acquired immune responses. The traditional notion of opioids is immunosuppressive. Recent studies indicate that the role of opioid receptors on immune function is complicated, working through various different mechanisms. Different opioids or opioids administrations show various effects on the immune system: immunosuppressive, immunostimulatory, or dual effect. It is important to elucidate the relationship between opioids and immune function, since immune system plays critical role in various physiological and pathophysiological processes, including the inflammation, tumor growth and metastasis, drug abuse, and so on. This review article tends to have an overview of the recent work and perspectives on opioids and the immune function. PMID:26985446

  8. Opioid System Modulates the Immune Function: A Review.

    PubMed

    Liang, Xuan; Liu, Renyu; Chen, Chunhua; Ji, Fang; Li, Tianzuo

    Opioid receptors and their ligands produce powerful analgesia that is effective in perioperative period and chronic pain managements accompanied with various side effects including respiratory depression, constipation and addiction etc. Opioids can also interfere with the immune system, not only participating in the function of the immune cells, but also modulating innate and acquired immune responses. The traditional notion of opioids is immunosuppressive. Recent studies indicate that the role of opioid receptors on immune function is complicated, working through various different mechanisms. Different opioids or opioids administrations show various effects on the immune system: immunosuppressive, immunostimulatory, or dual effect. It is important to elucidate the relationship between opioids and immune function, since immune system plays critical role in various physiological and pathophysiological processes, including the inflammation, tumor growth and metastasis, drug abuse, and so on. This review article tends to have an overview of the recent work and perspectives on opioids and the immune function.

  9. Effects of μ-opioid receptor modulation on the hippocampal network activity of sharp wave and ripples

    PubMed Central

    Giannopoulos, Panagiotis; Papatheodoropoulos, Costas

    2013-01-01

    Background and Purpose Hippocampus-dependent memory involves the activity of sharp wave ripples (SWRs), which are thought to participate in the process of memory consolidation. The hippocampus contains high levels of endogenous opioids and of μ-opioid receptors (MORs). Here, we have assessed the role of MOR agonists in the modulation of SWRs. Experimental Approach Using recordings of extracellular potentials from the CA1 field of rat hippocampal slices, we examined the pharmacological actions of morphine, DAMGO and fentanyl on SWRs and on network excitability and paired-pulse inhibition. Key Results All three MOR agonists (1 nM–10 μM) significantly increased the amplitude of sharp waves and the occurrence of SWR sequences, but reduced the initiation of episodes of SWRs. Fentanyl was most potent in producing these effects and morphine the least. Interestingly, although SWRs were reduced by relatively high concentrations (≥100 nM) of all agonists, they were significantly enhanced by very low concentrations of morphine (5–10 nM). Morphine and DAMGO at moderate-to-high concentrations increased network excitability and reduced inhibition. Furthermore, DAMGO suppressed inhibition more readily than it increased excitation, whereas morphine suppressed inhibition only at high concentrations. These drug effects were reversed by the MOR antagonists naloxone and CTOP. Conclusions and Implications We found that the SWRs were significantly modulated by three MOR agonists and that the SWRs were very sensitive to subtle changes in the excitation/inhibition balance induced by MOR agonists. Such modulation might underlie the effects of these agonists on hippocampus-dependent memory. PMID:23043226

  10. Immunocytochemical characterization of Delta-opioid and Mu-opioid receptor protein in the bovine pineal gland.

    PubMed

    Phansuwan-Pujito, Pansiri; Ebadi, Manuchair; Govitrapong, Piyarat

    2006-01-01

    Opioidergic innervation has been identified in the mammalian pineal gland. Recently, opioid receptors in bovine pineal glands have been characterized; the activation of these receptors leads to the stimulation of melatonin synthesis. In this study, the precise localization of opioid receptors in bovine pineal glands was determined by an immunohistochemical technique using antibodies raised against delta-opioid and mu-opioid receptors. Immunoreactivity of these two receptors was present at a moderate level in pinealocytes. A double-labeling study has shown that delta-opioid receptors are localized predominantly with mu-opioid receptors in the same pinealocytes. These immunopositive pinealocytes are often located in a group; however, some of them are dispersed individually. In addition, both types of receptors were found in glial cells and processes. A small number of delta-receptor-immunoreactive nerve fibers were observed in the perivascular space and intraparenchyma of the pineal gland. Mu-opioid receptor immunoreactivity was found in a number of nerve fibers throughout the gland, and in terminal-like dots on pinealocytes. There was immunocolocalization between delta-opioid receptors or mu-opioid receptors and leu-enkephalin in some nerve fibers. The results of this study indicate that the modulatory effect of the opioid system on melatonin secretion in pineal glands might act via opioid receptors on pinealocytes, whereas receptors located on nerve fibers might modulate the release of opioid peptides.

  11. Molecular characterization of opioid receptors

    SciTech Connect

    Howard, A.D.

    1986-01-01

    The aim of this research was to purify and characterize active opioid receptors and elucidate molecular aspects of opioid receptor heterogeneity. Purification to apparent homogeneity of an opioid binding protein from bovine caudate was achieved by solubilization in the non-ionic detergent, digitonin, followed by sequential chromatography on the opiate affinity matrix, ..beta..-naltrexylethylenediamine-CH-Sepharose 4B, and on the lectine affinity matrix, wheat germ agglutinin-agarose. Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS-PAGE) followed by autoradiography revealed that radioiodinated purified receptor gave a single band. Purified receptor preparations showed a specific activity of 12,000-15,000 fmol of opiate bound per mg of protein. Radioiodinated human beta-endorphin (/sup 125/I-beta-end/sub H/) was used as a probe to investigate the ligand binding subunits of mu and delta opioid receptors. /sup 125/I-beta-end/sub H/ was shown to bind to a variety of opioid receptor-containing tissues with high affinity and specificity with preference for mu and delta sites, and with little, if any, binding to kappa sites. Affinity crosslinking techniques were employed to covalently link /sup 125/I-beta-end/sub H/ to opioid receptors, utilizing derivatives of bis-succinimidyl esters that are bifunctional crosslinkers with specificities for amino and sulfhydryl groups. This, and competition experiments with high type-selective ligands, permitted the assignment of two labeled peptides to their receptor types, namely a peptide of M/sub r/ = 65,000 for mu receptors and one of M/sub r/ = 53,000 for delta receptors.

  12. Investigation of the role of βarrestin2 in kappa opioid receptor modulation in a mouse model of pruritus.

    PubMed

    Morgenweck, Jenny; Frankowski, Kevin J; Prisinzano, Thomas E; Aubé, Jeffrey; Bohn, Laura M

    2015-12-01

    The kappa opioid receptor (KOR) is involved in mediating pruritus; agonists targeting this receptor have been used to treat chronic intractable itch. Conversely, antagonists induce an itch response at the site of injection. As a G protein-coupled receptor (GPCR), the KOR has potential for signaling via G proteins and βarrestins, however, it is not clear which of these pathways are involved in the KOR modulation of itch. In this study asked whether the actions of KOR in pruritus involve βarrestins by using βarrestin2 knockout (βarr2-KO) mice as well as a recently described biased KOR agonist that biases receptor signaling toward G protein pathways over βarrestin2 recruitment. We find that the KOR antagonists nor-binaltorphimine (NorBNI) and 5'-guanidinonaltrindole (5'GNTI) induce acute pruritus in C57BL/6J mice, with reduced effects in KOR-KO mice. βArr2-KO mice display less of a response to KOR antagonist-induced itch compared to wild types, however no genotype differences are observed from chloroquine phosphate (CP)-induced itch, suggesting that the antagonists may utilize a KOR-βarrestin2 dependent mechanism. The KOR agonist U50,488H was equally effective in both WT and βarr2-KO mice in suppressing CP-induced itch. Furthermore, the G protein biased agonist, Isoquinolinone 2.1 was as effective as U50,488H in suppressing the itch response induced by KOR antagonist NorBNI or CP in C57BL/6J mice. Together these data suggest that the antipruritic effects of KOR agonists may not require βarrestins.

  13. Investigation of the role of βarrestin2 in kappa opioid receptor modulation in a mouse model of pruritus

    PubMed Central

    Morgenweck, Jenny; Frankowski, Kevin J.; Prisinzano, Thomas E.; Aubé, Jeffrey; Bohn, Laura M.

    2015-01-01

    The kappa opioid receptor (KOR) is involved in mediating pruritus; agonists targeting this receptor have been used to treat chronic intractable itch. Conversely, antagonists induce an inch response at the site of injection. As a G protein-coupled receptor (GPCR), the KOR has potential for signaling via G proteins and βarrestins, however, it is not clear which of these pathways are involved in the KOR modulation of itch. In this study asked whether the actions of KOR in pruritus involve βarrestins by using βarrestin2 knockout (βarr2-KO) mice as well as a recently described biased KOR agonist that biases receptor signaling toward G protein pathways over βarrestin2 recruitment. We find that the KOR antagonists nor-binaltorphimine (NorBNI) and 5′-guanidinonaltrindole (5′GNTI) induce acute pruritus in C57BL/6J mice, with reduced effects in KOR-KO mice. βarr2-KO mice display less of a response to KOR antagonist-induced itch compared to wild types, however no genotype differences are observed from chloroquine phosphate (CP)-induced itch, suggesting that the antagonists may utilize a KOR-βarrestin2 dependent mechanism. The KOR agonist U50,488H was equally effective in both WT and βarr2-KO mice in suppressing CP-induced itch. Furthermore, the G protein biased agonist, Isoquinolinone 2.1 was as effective as U50,488H in suppressing the itch response induced by KOR antagonist NorBNI or CP in C57BL/6J mice. Together these data suggest that the antipruritic effects of KOR agonists may not require βarrestins. PMID:26318102

  14. Sodium modulates opioid receptors through a membrane component different from G-proteins. Demonstration by target size analysis

    SciTech Connect

    Ott, S.; Costa, T.; Herz, A.

    1988-07-25

    The target size for opioid receptor binding was studied after manipulations known to affect the interactions between receptor and GTP-binding regulatory proteins (G-proteins). Addition of GTP or its analogs to the binding reaction, exposure of intact cells to pertussis toxin prior to irradiation, or treatment of irradiated membranes with N-ethylmaleimide did not change the target size (approximately equal to 100 kDa) for opioid receptors in NG 108-15 cells and rat brain. These data suggest that the 100-kDa species does not include an active subunit of a G-protein or alternatively that GTP does not promote the dissociation of the receptor-G-protein complex. The presence of Na+ (100 mM) in the radioligand binding assay induced a biphasic decay curve for agonist binding and a flattening of the monoexponential decay curve for a partial agonist. In both cases the effect was explained by an irradiation-induced loss of the low affinity state of the opioid receptor produced by the addition of Na+. This suggests that an allosteric inhibitor that mediates the effect of sodium on the receptor is destroyed at low doses of irradiation, leaving receptors which are no longer regulated by sodium. The effect of Na+ on target size was slightly increased by the simultaneous addition of GTP but was not altered by pertussis toxin treatment. Thus, the sodium unit is distinct from G-proteins and may represent a new component of the opioid receptor complex. Assuming a simple bimolecular model of one Na+ unit/receptor, the size of this inhibitor can be measured as 168 kDa.

  15. Chemical neuroanatomical and psychopharmacological evidence that κ receptor-mediated endogenous opioid peptide neurotransmission in the dorsal and ventral mesencephalon modulates panic-like behaviour.

    PubMed

    da Silva, Juliana Almeida; de Freitas, Renato Leonardo; Eichenberger, Gustavo Cavalcanti Dutra; Padovan, Cláudia Maria; Coimbra, Norberto Cysne

    2013-01-05

    The chemical neuroanatomy and the effects of central administration of opioid antagonists on the innate fear-induced responses elicited by electrical (at escape behaviour threshold) stimulation of the midbrain tectum were determined. The aim of the present work was to investigate the interaction between the tecto-nigral endogenous opioid peptide-mediated disinhibitory pathways and nigro-tectal inhibitory links in the control of panic-like behaviour and their organisation in the continuum comprised by the deep layers of the superior colliculus (dlSC) and the dorsolateral columns of the periaqueductal grey matter (dlPAG). Beta-endorphin-labelled neurons and fibres were found in the dorsal midbrain and also in the substantia nigra. Opioid varicose fibres and terminal buttons were widely distributed in PAG columns and in all substantia nigra subdivisions. Microinjections of naltrexone (a non-selective opioid receptor antagonist; 5.0 μg/0.2 μl) or nor-binaltorphimine (a selective κ-opioid receptor antagonist; 5.0 μg/0.2 μl) in the dlSC/dlPAG continuum, in independent groups of animals, induced significant increases in the escape thresholds for midbrain tectum electrical stimulation. The microinjection of naltrexone or nor-binaltorphimine into the SNpr also increased the escape behaviour threshold for electrical stimulation of dlSC/dlPAG. These morphological and neuropharmacological findings support previous evidence from our team for the role played by the interaction between opioidergic and GABAergic mechanisms in the modulation of innate fear-induced responses. The present data offer a neuroanatomical basis for both intratectal axo-axonic/pre-synaptic and tecto-nigral axo-somatic opioid inhibition of GABAergic nigro-tectal neurons that modulate the dorsal midbrain neurons related to the organisation of fear-related emotional responses.

  16. The evolution of vertebrate opioid receptors

    PubMed Central

    Stevens, Craig W.

    2011-01-01

    The proteins that mediate the analgesic and other effects of opioid drugs and endogenous opioid peptides are known as opioid receptors. Opioid receptors consist of a family of four closely-related proteins belonging to the large superfamily of G-protein coupled receptors. The three types of opioid receptors shown unequivocally to mediate analgesia in animal models are the mu (MOR), delta (DOR), and kappa (KOR) opioid receptor proteins. The role of the fourth member of the opioid receptor family, the nociceptin or orphanin FQ receptor (ORL), is not as clear as hyperalgesia, analgesia, and no effect was reported after administration of ORL agonists. There are now cDNA sequences for all four types of opioid receptors that are expressed in the brain of six species from three different classes of vertebrates. This review presents a comparative analysis of vertebrate opioid receptors using bioinformatics and data from recent human genome studies. Results indicate that opioid receptors arose by gene duplication, that there is a vector of opioid receptor divergence, and that MOR shows evidence of rapid evolution. PMID:19273128

  17. Using opioid receptors to expand the chemogenetic and optogenetic toolbox.

    PubMed

    Damez-Werno, Diane M; Kenny, Paul J

    2015-05-20

    In this issue of Neuron, innovative new modifications to opioid receptors are used to expand the tools available to modulate neuronal activity. Vardy et al. (2015) describe a new "DREADD" chemogenetic tool based on the inhibitory κ opioid receptor (KORD) that can be used in conjunction with already-available DREADDs. Siuda et al. (2015) report the development of "opto-MOR," a light-activatable μ opioid receptor (MOR) chimera that can be used to better understand the complexities of MOR signaling.

  18. Development of Kappa Opioid Receptor Antagonists

    PubMed Central

    Carroll, F. Ivy; Carlezon, William A.

    2013-01-01

    Kappa opioid receptors (KORs) belong to the G-protein coupled class of receptors (GPCRs). They are activated by the endogenous opioid peptide dynorphin (DYN) and expressed at particularly high levels within brain areas implicated in modulation of motivation, emotion, and cognitive function. Chronic activation of KORs in animal models has maladaptive effects including increases in behaviors that reflect depression, the propensity to engage in drug-seeking behavior, and drug craving. The fact that KOR activation has such a profound influence on behaviors often triggered by stress has led to interest in selective KOR antagonists as potential therapeutic agents. This perspective provides a description of preclinical research conducted in the development of several different classes of selective KOR antagonists, a summary of the clinical studies conducted thus far, and recommendations for the type of work needed in the future to determine if these agents would be useful as pharmacotherapies for neuropsychiatric illness. PMID:23360448

  19. Endothelin-converting enzyme 2 differentially regulates opioid receptor activity

    PubMed Central

    Gupta, A; Fujita, W; Gomes, I; Bobeck, E; Devi, L A

    2015-01-01

    BACKGROUND AND PURPOSE Opioid receptor function is modulated by post-activation events such as receptor endocytosis, recycling and/or degradation. While it is generally understood that the peptide ligand gets co-endocytosed with the receptor, relatively few studies have investigated the role of the endocytosed peptide and peptide processing enzymes in regulating receptor function. In this study, we focused on endothelin-converting enzyme 2 (ECE2), a member of the neprilysin family of metallopeptidases that exhibits an acidic pH optimum, localizes to an intracellular compartment and selectively processes neuropeptides including opioid peptides in vitro, and examined its role in modulating μ receptor recycling and resensitization. EXPERIMENTAL APPROACH The effect of ECE2 inhibition on hydrolysis of the endocytosed peptide was examined using thin-layer chromatography and on μ opioid receptor trafficking using either elisa or microscopy. The effect of ECE2 inhibition on receptor signalling was measured using a cAMP assay and, in vivo, on antinociception induced by intrathecally administered opioids by the tail-flick assay. KEY RESULTS The highly selective ECE2 inhibitor, S136492, significantly impaired μ receptor recycling and signalling by only those ligands that are ECE2 substrates and this was seen both in heterologous cells and in cells endogenously co-expressing μ receptors with ECE2. We also found that ECE2 inhibition attenuated antinociception mediated only by opioid peptides that are ECE2 substrates. CONCLUSIONS AND IMPLICATIONS These results suggest that ECE2, by selectively processing endogenous opioid peptides in the endocytic compartment, plays a role in modulating opioid receptor activity. LINKED ARTICLES This article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-2 PMID:24990314

  20. New technologies for elucidating opioid receptor function

    PubMed Central

    Bruchas, Michael R.; Roth, Bryan L.

    2016-01-01

    Recent advances in technology, including high resolution crystal structures of opioid receptors, novel chemical tools, and new genetic approaches have provided an unparalleled pallette of tools for deconstructing opioid receptor actions in vitro and in vivo. Here we provide a brief description of our understanding of opioid receptor function from both molecular and atomic perspectives, as well as their role in neural circuits in vivo. We then show how insights into the molecular details of opioid actions can facilitate the creation of functionally-selective (biased) and photoswitchable opioid ligands. Finally, we describe how newly engineered opioid receptor-based chemo- and optogenetic tools, and new mouse lines are expanding and transforming our understanding of opioid function and, perhaps, paving the way for new therapeutics. PMID:26833118

  1. Opioid receptors in the gastrointestinal tract

    PubMed Central

    Holzer, Peter

    2011-01-01

    Opium is arguably one of the oldest herbal medicines, being used as analgesic, sedative and antidiarrheal drug for thousands of years. These effects mirror the actions of the endogenous opioid system and are mediated by the principal μ-, κ- and δ-opioid receptors. In the gut, met-enkephalin, leu-enkephalin, β-endorphin and dynorphin occur in both neurons and endocrine cells. When released, opioid peptides activate opioid receptors on the enteric circuitry controlling motility and secretion. As a result, inhibition of gastric emptying, increase in sphincter tone, induction of stationary motor patterns and blockade of peristalsis ensue. Together with inhibition of ion and fluid secretion, these effects cause constipation, one of the most frequent and troublesome adverse reactions of opioid analgesic therapy. Although laxatives are most frequently used to ameliorate opioid-induced bowel dysfunction, their efficacy is unsatisfactory. Specific antagonism of peripheral opioid receptors is a more rational approach. This goal is addressed by the use of opioid receptor antagonists with limited absorption such as oral prolonged-release naloxone and opioid receptor antagonists that do not penetrate the blood-brain barrier such as methylnaltrexone and alvimopan. Preliminary evidence indicates that peripherally restricted opioid receptor antagonists may act as prokinetic drugs in their own right. PMID:19345246

  2. Opioid receptor trafficking and interaction in nociceptors

    PubMed Central

    Zhang, X; Bao, L; Li, S

    2015-01-01

    Opiate analgesics such as morphine are often used for pain therapy. However, antinociceptive tolerance and dependence may develop with long-term use of these drugs. It was found that μ-opioid receptors can interact with δ-opioid receptors, and morphine antinociceptive tolerance can be reduced by blocking δ-opioid receptors. Recent studies have shown that μ- and δ-opioid receptors are co-expressed in a considerable number of small neurons in the dorsal root ganglion. The interaction of μ-opioid receptors with δ-opioid receptors in the nociceptive afferents is facilitated by the stimulus-induced cell-surface expression of δ-opioid receptors, and contributes to morphine tolerance. Further analysis of the molecular, cellular and neural circuit mechanisms that regulate the trafficking and interaction of opioid receptors and related signalling molecules in the pain pathway would help to elucidate the mechanism of opiate analgesia and improve pain therapy. LINKED ARTICLES This article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-2 PMID:24611685

  3. Identification of selective agonists and positive allosteric modulators for µ- and δ-opioid receptors from a single high-throughput screen.

    PubMed

    Burford, Neil T; Wehrman, Tom; Bassoni, Daniel; O'Connell, Jonathan; Banks, Martyn; Zhang, Litao; Alt, Andrew

    2014-10-01

    Hetero-oligomeric complexes of G protein-coupled receptors (GPCRs) may represent novel therapeutic targets exhibiting different pharmacology and tissue- or cell-specific site of action compared with receptor monomers or homo-oligomers. An ideal tool for validating this concept pharmacologically would be a hetero-oligomer selective ligand. We set out to develop and execute a 1536-well high-throughput screen of over 1 million compounds to detect potential hetero-oligomer selective ligands using a β-arrestin recruitment assay in U2OS cells coexpressing recombinant µ- and δ-opioid receptors. Hetero-oligomer selective ligands may bind to orthosteric or allosteric sites, and we might anticipate that the formation of hetero-oligomers may provide novel allosteric binding pockets for ligand binding. Therefore, our goal was to execute the screen in such a way as to identify positive allosteric modulators (PAMs) as well as agonists for µ, δ, and hetero-oligomeric receptors. While no hetero-oligomer selective ligands were identified (based on our selection criteria), this single screen did identify numerous µ- and δ-selective agonists and PAMs as well as nonselective agonists and PAMs. To our knowledge, these are the first µ- and δ-opioid receptor PAMs described in the literature.

  4. Differential opioid agonist regulation of the mouse mu opioid receptor.

    PubMed

    Blake, A D; Bot, G; Freeman, J C; Reisine, T

    1997-01-10

    Mu opioid receptors mediate the analgesia induced by morphine. Prolonged use of morphine causes tolerance development and dependence. To investigate the molecular basis of tolerance and dependence, the cloned mouse mu opioid receptor with an amino-terminal epitope tag was stably expressed in human embryonic kidney (HEK) 293 cells, and the effects of prolonged opioid agonist treatment on receptor regulation were examined. In HEK 293 cells the expressed mu receptor showed high affinity, specific, saturable binding of radioligands and a pertussis toxin-sensitive inhibition of adenylyl cyclase. Pretreatment (1 h, 3 h, or overnight) of cells with 1 microM morphine or [D-Ala2MePhe4,Gly(ol)5]enkephalin (DAMGO) resulted in no apparent receptor desensitization, as assessed by opioid inhibition of forskolin-stimulated cAMP levels. In contrast, the morphine and DAMGO pretreatments (3 h) resulted in a 3-4-fold compensatory increase in forskolin-stimulated cAMP accumulation. The opioid agonists methadone and buprenorphine are used in the treatment of addiction because of a markedly lower abuse potential. Pretreatment of mu receptor-expressing HEK 293 cells with methadone or buprenorphine abolished the ability of opioids to inhibit adenylyl cyclase. No compensatory increase in forskolin-stimulated cAMP accumulation was found with methadone or buprenorphine; these opioids blocked the compensatory effects observed with morphine and DAMGO. Taken together, these results indicate that methadone and buprenorphine interact differently with the mouse mu receptor than either morphine or DAMGO. The ability of methadone and buprenorphine to desensitize the mu receptor and block the compensatory rise in forskolin-stimulated cAMP accumulation may be an underlying mechanism by which these agents are effective in the treatment of morphine addiction.

  5. Opioid receptor modulation of hedonic taste preference and food intake: a single-dose safety, pharmacokinetic, and pharmacodynamic investigation with GSK1521498, a novel μ-opioid receptor inverse agonist.

    PubMed

    Nathan, Pradeep J; O'Neill, Barry V; Bush, Mark A; Koch, Annelize; Tao, Wenli X; Maltby, Kay; Napolitano, Antonella; Brooke, Allison C; Skeggs, Andrew L; Herman, Craig S; Larkin, Andrew L; Ignar, Diane M; Richards, Duncan B; Williams, Pauline M; Bullmore, Edward T

    2012-04-01

    Endogenous opioids and µ-opioid receptors have been linked to hedonic and rewarding aspects of palatable food intake. The authors examined the safety, pharmacokinetic, and pharmacodynamic profile of GSK1521498, a µ-opioid receptor inverse agonist that is being investigated primarily for the treatment of overeating behavior in obesity. In healthy participants, GSK1521498 oral solution and capsule formulations were well tolerated up to a dose of 100 mg. After single doses (10-150 mg), the maximum concentration (C(max)) and area under the curve (AUC) in plasma increased in a dose-proportional manner. GSK1521498 selectively reduced sensory hedonic ratings of high-sugar and high-fat dairy products and caloric intake of high-fat/high-sucrose snack foods. These findings provide encouraging data in support of the development of GSK1521498 for the treatment of disorders of maladaptive ingestive behavior or compulsive consumption.

  6. The delta opioid receptor tool box.

    PubMed

    Vicente-Sanchez, Ana; Segura, Laura; Pradhan, Amynah A

    2016-12-03

    In recent years, the delta opioid receptor has attracted increasing interest as a target for the treatment of chronic pain and emotional disorders. Due to their therapeutic potential, numerous tools have been developed to study the delta opioid receptor from both a molecular and a functional perspective. This review summarizes the most commonly available tools, with an emphasis on their use and limitations. Here, we describe (1) the cell-based assays used to study the delta opioid receptor. (2) The features of several delta opioid receptor ligands, including peptide and non-peptide drugs. (3) The existing approaches to detect delta opioid receptors in fixed tissue, and debates that surround these techniques. (4) Behavioral assays used to study the in vivo effects of delta opioid receptor agonists; including locomotor stimulation and convulsions that are induced by some ligands, but not others. (5) The characterization of genetically modified mice used specifically to study the delta opioid receptor. Overall, this review aims to provide a guideline for the use of these tools with the final goal of increasing our understanding of delta opioid receptor physiology.

  7. Melanocortin and Opioid Peptide Interactions in the Modulation of Binge Alcohol Drinking

    DTIC Science & Technology

    2013-04-01

    0293 TITLE: Melanocortin and Opioid Peptide Interactions in the Modulation of Binge Alcohol Drinking PRINCIPAL INVESTIGATOR: Todd E. Thiele...NUMBER Melanocortin and Opioid Peptide Interactions in the Modulation of Binge 5b. GRANT NUMBER W81XWH-09-1-0293 Alcohol Drinking 5c. PROGRAM...determine if MC receptor (MCR) agonists and opioid receptor antagonists interact to protect against binge-like alcohol drinking in a synergistic manner

  8. Ligand- and cell-dependent determinants of internalization and cAMP modulation by delta opioid receptor (DOR) agonists.

    PubMed

    Charfi, Iness; Nagi, Karim; Mnie-Filali, Ouissame; Thibault, Dominic; Balboni, Gianfranco; Schiller, Peter W; Trudeau, Louis-Eric; Pineyro, Graciela

    2014-04-01

    Signaling bias refers to G protein-coupled receptor ligand ability to preferentially activate one type of signal over another. Bias to evoke signaling as opposed to sequestration has been proposed as a predictor of opioid ligand potential for generating tolerance. Here we measured whether delta opioid receptor agonists preferentially inhibited cyclase activity over internalization in HEK cells. Efficacy (τ) and affinity (KA) values were estimated from functional data and bias was calculated from efficiency coefficients (log τ/KA). This approach better represented the data as compared to alternative methods that estimate bias exclusively from τ values. Log (τ/KA) coefficients indicated that SNC-80 and UFP-512 promoted cyclase inhibition more efficiently than DOR internalization as compared to DPDPE (bias factor for SNC-80: 50 and for UFP-512: 132). Molecular determinants of internalization were different in HEK293 cells and neurons with βarrs contributing to internalization in both cell types, while PKC and GRK2 activities were only involved in neurons. Rank orders of ligand ability to engage different internalization mechanisms in neurons were compared to rank order of E max values for cyclase assays in HEK cells. Comparison revealed a significant reversal in rank order for cyclase E max values and βarr-dependent internalization in neurons, indicating that these responses were ligand-specific. Despite this evidence, and because kinases involved in internalization were not the same across cellular backgrounds, it is not possible to assert if the magnitude and nature of bias revealed by rank orders of maximal responses is the same as the one measured in HEK cells.

  9. Sex differences in opioid analgesia and addiction: interactions among opioid receptors and estrogen receptors

    PubMed Central

    2013-01-01

    Opioids are widely used as the pain reliever and also notorious for being addictive drugs. Sex differences in the opioid analgesia and addiction have been reported and investigated in human subjects and animal models. Yet, the molecular mechanism underlying the differences between males and females is still unclear. Here, we reviewed the literature describing the sex differences in analgesic responses and addiction liabilities to clinically relevant opioids. The reported interactions among opioids, estrogens, opioid receptors, and estrogen receptors are also evaluated. We postulate that the sex differences partly originated from the crosstalk among the estrogen and opioid receptors when stimulated by the exogenous opioids, possibly through common secondary messengers and the downstream gene transcriptional regulators. PMID:24010861

  10. Sex differences in opioid analgesia and addiction: interactions among opioid receptors and estrogen receptors.

    PubMed

    Lee, Cynthia Wei-Sheng; Ho, Ing-Kang

    2013-09-08

    Opioids are widely used as the pain reliever and also notorious for being addictive drugs. Sex differences in the opioid analgesia and addiction have been reported and investigated in human subjects and animal models. Yet, the molecular mechanism underlying the differences between males and females is still unclear. Here, we reviewed the literature describing the sex differences in analgesic responses and addiction liabilities to clinically relevant opioids. The reported interactions among opioids, estrogens, opioid receptors, and estrogen receptors are also evaluated. We postulate that the sex differences partly originated from the crosstalk among the estrogen and opioid receptors when stimulated by the exogenous opioids, possibly through common secondary messengers and the downstream gene transcriptional regulators.

  11. Opioid modulation of taste hedonics within the ventral striatum.

    PubMed

    Kelley, A E; Bakshi, V P; Haber, S N; Steininger, T L; Will, M J; Zhang, M

    2002-07-01

    There is a long-standing interest in the role of endogenous opioid peptides in feeding behavior and, in particular, in the modulation of food reward and palatability. Since drugs such as heroin, morphine, alcohol, and cannabinoids, interact with this system, there may be important common neural substrates between food and drug reward with regard to the brain's opioid systems. In this paper, we review the proposed functional role of opioid neurotransmission and mu opiate receptors within the nucleus accumbens and surrounding ventral striatum. Opioid compounds, particularly those selective for the mu receptor, induce a potent increase in food intake, sucrose, salt, saccharin, and ethanol intake. We have explored this phenomenon with regard to macronutrient selection, regional specificity, role of output structures, Fos mapping, analysis of motivational state, and enkephalin gene expression. We hypothesize that opioid-mediated mechanisms within ventral striatal medium spiny neurons mediate the affective or hedonic response to food ('liking' or food 'pleasure'). A further refinement of this hypothesis is that activation of ventral striatal opioids specifically encodes positive affect induced by tasty and/or calorically dense foods (such as sugar and fat), and promotes behaviors associated with this enhanced palatability. It is proposed that this brain mechanism was beneficial in evolutionary development for ensuring the consumption of relatively scarce, high-energy food sources. However, in modern times, with unlimited supplies of high-calorie food, it has contributed to the present epidemic of obesity.

  12. The automated radiosynthesis and purification of the opioid receptor antagonist, [6-O-methyl-11C]diprenorphine on the GE TRACERlab FXFE radiochemistry module.

    PubMed

    Fairclough, Michael; Prenant, Christian; Brown, Gavin; McMahon, Adam; Lowe, Jonathan; Jones, Anthony

    2014-05-15

    [6-O-Methyl-(11)C]diprenorphine ([(11)C]diprenorphine) is a positron emission tomography ligand used to probe the endogenous opioid system in vivo. Diprenorphine acts as an antagonist at all of the opioid receptor subtypes, that is, μ (mu), κ (kappa) and δ (delta). The radiosynthesis of [(11)C]diprenorphine using [(11)C]methyl iodide produced via the 'wet' method on a home-built automated radiosynthesis set-up has been described previously. Here, we describe a modified synthetic method to [(11)C]diprenorphine performed using [(11)C]methyl iodide produced via the gas phase method on a GE TRACERlab FXFE radiochemistry module. Also described is the use of [(11)C]methyl triflate as the carbon-11 methylating agent for the [(11)C]diprenorphine syntheses. [(11)C]Diprenorphine was produced to good manufacturing practice standards for use in a clinical setting. In comparison to previously reported [(11)C]diprenorphine radiosyntheisis, the method described herein gives a higher specific activity product which is advantageous for receptor occupancy studies. The radiochemical purity of [(11)C]diprenorphine is similar to what has been reported previously, although the radiochemical yield produced in the method described herein is reduced, an issue that is inherent in the gas phase radiosynthesis of [(11)C]methyl iodide. The yields of [(11)C]diprenorphine are nonetheless sufficient for clinical research applications. Other advantages of the method described herein are an improvement to both reproducibility and reliability of the production as well as simplification of the purification and formulation steps. We suggest that our automated radiochemistry route to [(11)C]diprenorphine should be the method of choice for routine [(11)C]diprenorphine productions for positron emission tomography studies, and the production process could easily be transferred to other radiochemistry modules such as the TRACERlab FX C pro.

  13. State-dependent μ-opioid modulation of social motivation

    PubMed Central

    Loseth, Guro E.; Ellingsen, Dan-Mikael; Leknes, Siri

    2014-01-01

    Social mammals engage in affiliative interactions both when seeking relief from negative affect and when searching for pleasure and joy. These two motivational states are both modulated by μ-opioid transmission. The μ-opioid receptor (MOR) system in the brain mediates pain relief and reward behaviors, and is implicated in social reward processing and affiliative bonding across mammalian species. However, pharmacological manipulation of the μ-opioid system has yielded opposite effects on rodents and primates: in rodents, social motivation is generally increased by MOR agonists and reduced by antagonists, whereas the opposite pattern has been shown in primates. Here, we address this paradox by taking into account differences in motivational state. We first review evidence for μ-opioid mediation of reward processing, emotion regulation, and affiliation in humans, non-human primates, rodents and other species. Based on the consistent cross-species similarities in opioid functioning, we propose a unified, state-dependent model for μ-opioid modulation of affiliation across the mammalian species. Finally, we show that this state-dependent model is supported by evidence from both rodent and primate studies, when species and age differences in social separation response are taken into account. PMID:25565999

  14. State-dependent μ-opioid modulation of social motivation.

    PubMed

    Loseth, Guro E; Ellingsen, Dan-Mikael; Leknes, Siri

    2014-01-01

    Social mammals engage in affiliative interactions both when seeking relief from negative affect and when searching for pleasure and joy. These two motivational states are both modulated by μ-opioid transmission. The μ-opioid receptor (MOR) system in the brain mediates pain relief and reward behaviors, and is implicated in social reward processing and affiliative bonding across mammalian species. However, pharmacological manipulation of the μ-opioid system has yielded opposite effects on rodents and primates: in rodents, social motivation is generally increased by MOR agonists and reduced by antagonists, whereas the opposite pattern has been shown in primates. Here, we address this paradox by taking into account differences in motivational state. We first review evidence for μ-opioid mediation of reward processing, emotion regulation, and affiliation in humans, non-human primates, rodents and other species. Based on the consistent cross-species similarities in opioid functioning, we propose a unified, state-dependent model for μ-opioid modulation of affiliation across the mammalian species. Finally, we show that this state-dependent model is supported by evidence from both rodent and primate studies, when species and age differences in social separation response are taken into account.

  15. Effects of defeat stress on behavioral flexibility in males and females: modulation by the mu-opioid receptor.

    PubMed

    Laredo, Sarah A; Steinman, Michael Q; Robles, Cindee F; Ferrer, Emilio; Ragen, Benjamin J; Trainor, Brian C

    2015-02-01

    Behavioral flexibility is a component of executive functioning that allows individuals to adapt to changing environmental conditions. Independent lines of research indicate that the mu opioid receptor (MOR) is an important mediator of behavioral flexibility and responses to psychosocial stress. The current study bridges these two lines of research and tests the extent to which social defeat and MOR affect behavioral flexibility and whether sex moderates these effects in California mice (Peromyscus californicus). Males and females assigned to social defeat or control conditions were tested in a Barnes maze. In males, defeat impaired behavioral flexibility but not acquisition. Female performance was unaffected by defeat. MOR binding in defeated and control mice in the orbitofrontal cortex (OFC), striatum and hippocampus was examined via autoradiography. Stressed males had reduced MOR binding in the OFC whereas females were unaffected. The MOR antagonist beta-funaltrexamine (1 mg/kg) impaired performance in males naïve to defeat during the reversal phase but had no effect on females. Finally, we examined the effects of the MOR agonist morphine (2.5 and 5 mg/kg) on stressed mice. As expected, morphine improved behavioral flexibility in stressed males. The stress-induced deficits in behavioral flexibility in males are consistent with a proactive coping strategy, including previous observations that stressed male California mice exhibit strong social approach and aggression. Our pharmacological data suggest that a down-regulation of MOR signaling in males may contribute to sex differences in behavioral flexibility following stress. This is discussed in the framework of coping strategies for individuals with mood disorders.

  16. Nitric oxide and histone deacetylases modulate cocaine-induced mu-opioid receptor levels in PC12 cells

    PubMed Central

    2012-01-01

    Background Cocaine exposure has been reported to alter central μ-opioid receptor (MOR) expression in vivo. The present study employed an in vitro cellular model to explore possible mechanisms that may be involved in this action of cocaine. Methods To assess the effects of cocaine on MOR levels, two treatment regimens were tested in PC12 cells: single continuous or multiple intermittent. MOR protein levels were assessed by western blot analysis and quantitative PCR was used to determine relative MOR mRNA expression levels. To evaluate the role of nitric oxide (NO) and histone acetylation in cocaine-induced MOR expression, cells were pre-treated with the NO synthase inhibitor Nω-nitro-L-arginine methylester (L-NAME) or the non-selective histone acetyltransferase inhibitor curcumin. Results Both cocaine treatment regimens significantly increased MOR protein levels and protein stability, but only multiple intermittent treatments increased MOR mRNA levels as well as c-fos mRNA levels and activator protein 1 binding activity. Both regimens increased NO production, and pre-treatment with L-NAME prevented cocaine-induced increases in MOR protein and mRNA levels. Single and multiple cocaine treatment regimens inhibited histone deacetylase activity, and pre-treatment with curcumin prevented cocaine-induced up-regulation of MOR protein expression. Conclusions In the PC12 cell model, both NO and histone deacetylase activity regulate cocaine-induced MOR expression at both the transcriptional and post-transcriptional levels. Based on these novel findings, it is hypothesized that epigenetic mechanisms are implicated in cocaine’s action on MOR expression in neurons. PMID:23079001

  17. Opioid research in amphibians: an alternative pain model yielding insights on the evolution of opioid receptors.

    PubMed

    Stevens, Craig W

    2004-10-01

    This review summarizes the work from our laboratory investigating mechanisms of opioid analgesia using the Northern grass frog, Rana pipiens. Over the last dozen years, we have accumulated data on the characterization of behavioral effects after opioid administration on radioligand binding by using opioid agonist and antagonist ligands in amphibian brain and spinal cord homogenates, and by cloning and sequencing opioid-like receptor cDNA from amphibian central nervous system (CNS) tissues. The relative analgesic potency of mu, delta, and kappa opioids is highly correlated between frogs and other mammals, including humans. Radioligand binding studies using selective opioid agonists show a similar selectivity profile in amphibians and mammals. In contrast, opioid antagonists that are highly selective for mammalian mu, delta, and kappa opioid receptors were not selective in behavioral and binding studies in amphibians. Three opioid-like receptor cDNAs were cloned and sequenced from amphibian brain tissues and are orthologs to mammalian mu, delta, and kappa opioid receptors. Bioinformatics analysis of the three types of opioid receptor cDNAs from all vertebrate species with full datasets gave a pattern of the molecular evolution of opioid receptors marked by the divergence of mu, delta, and kappa opioid receptor sequences during vertebrate evolution. This divergence in receptor amino acid sequence in later-evolved vertebrates underlies the hypothesis that opioid receptors are more type-selective in mammals than in nonmammalian vertebrates. The apparent order of receptor type evolution is kappa, then delta, and, most recently, the mu opioid receptor. Finally, novel bioinformatics analyses suggest that conserved extracellular receptor domains determine the type selectivity of vertebrate opioid receptors.

  18. Opioid receptors: Structural and mechanistic insights into pharmacology and signaling

    PubMed Central

    Shang, Yi; Filizola, Marta

    2015-01-01

    Opioid receptors are important drug targets for pain management, addiction, and mood disorders. Although substantial research on these important subtypes of G protein-coupled receptors has been conducted over the past two decades to discover ligands with higher specificity and diminished side effects, currently used opioid therapeutics remain suboptimal. Luckily, recent advances in structural biology of opioid receptors provide unprecedented insights into opioid receptor pharmacology and signaling. We review here a few recent studies that have used the crystal structures of opioid receptors as a basis for revealing mechanistic details of signal transduction mediated by these receptors, and for the purpose of drug discovery. PMID:25981301

  19. Opioid receptors: Structural and mechanistic insights into pharmacology and signaling.

    PubMed

    Shang, Yi; Filizola, Marta

    2015-09-15

    Opioid receptors are important drug targets for pain management, addiction, and mood disorders. Although substantial research on these important subtypes of G protein-coupled receptors has been conducted over the past two decades to discover ligands with higher specificity and diminished side effects, currently used opioid therapeutics remain suboptimal. Luckily, recent advances in structural biology of opioid receptors provide unprecedented insights into opioid receptor pharmacology and signaling. We review here a few recent studies that have used the crystal structures of opioid receptors as a basis for revealing mechanistic details of signal transduction mediated by these receptors, and for the purpose of drug discovery.

  20. Cortisol Stress Response in Men and Women Modulated Differentially by the Mu-Opioid Receptor Gene Polymorphism OPRM1 A118G.

    PubMed

    Lovallo, William R; Enoch, Mary-Anne; Acheson, Ashley; Cohoon, Andrew J; Sorocco, Kristen H; Hodgkinson, Colin A; Vincent, Andrea S; Glahn, David C; Goldman, David

    2015-10-01

    Differences in stress reactivity may affect long-term health outcomes, but there is little information on how these differences arise. The stress axis is regulated by, in part, the endogenous opioid, beta-endorphin, acting on mu-opioid receptors. Persons carrying one or two copies of the G allele of the mu-opioid receptor gene (OPRM1 A118G) may have higher receptor binding for beta-endorphin compared with AA homozygotes that may contribute to individual differences in cortisol reactivity to stress, leading to a relative blunting of cortisol stress reactivity in G allele genotypes. We measured cortisol in 251 young adults (69 GA/GG vs 182 AA genotypes) exposed to mental arithmetic plus public speaking stress relative to a resting control day. Women had smaller cortisol responses than men (F=10.2, p=0.002), and women with GA or GG genotypes (N=39) had an absence of cortisol response relative to AA carriers (N=110) (F=18.4, p<0.0001). Male genotypes had no such difference in response (F=0.29). Cortisol response following mu-opioid receptor blockade using naltrexone in 119 of these subjects unmasked a greater tonic opioid inhibition of cortisol secretion in women (N=64), consistent with their blunted stress reactivity. Compared with men, women may have cortisol stress responses that are more heavily regulated by endogenous opioid mechanisms, and the OPRM1 GA/GG genotypes may affect females differentially relative to males. Diminished cortisol responses to stress may have consequences for health behaviors in women with GA/GG genotypes.

  1. Splice variation of the mu-opioid receptor and its effect on the action of opioids.

    PubMed

    Gretton, Sophy K; Droney, Joanne

    2014-11-01

    An individual's response to opioids is influenced by a complex combination of genetic, molecular and phenotypic factors.Intra- and inter-individual variations in response to mu opioids have led to the suggestion that mu-opioid receptor subtypes exist.Scientists have now proven that mu-opioid receptor subtypes exist and that they occur through a mechanism promoting protein diversity, called alternative splicing.The ability of mu opioids to differentially activate splice variants may explain some of the clinical differences observed between mu opioids.This article examines how differential activation of splice variants by mu opioids occurs through alternative mu-opioid receptor binding, through differential receptor activation, and as a result of the distinct distribution of variants located regionally and at the cellular level.

  2. Kappa Opioid Receptor Agonist and Brain Ischemia

    PubMed Central

    Chunhua, Chen; Chunhua, Xi; Megumi, Sugita; Renyu, Liu

    2014-01-01

    Opioid receptors, especially Kappa opioid receptor (KOR) play an important role in the pathophysiological process of cerebral ischemia reperfusion injury. Previously accepted KOR agonists activity has included anti-nociception, cardiovascular, anti-pruritic, diuretic, and antitussive effects, while compelling evidence from various ischemic animal models indicate that KOR agonist have neuroprotective effects through various mechanisms. In this review, we aimed to demonstrate the property of KOR agonist and its role in global and focal cerebral ischemia. Based on current preclinical research, the KOR agonists may be useful as a neuroprotective agent. The recent discovery of salvinorin A, highly selective non-opioid KOR agonist, offers a new tool to study the role of KOR in brain HI injury and the protective effects of KOR agonist. The unique pharmacological profile of salvinorin A along with the long history of human usage provides its high candidacy as a potential alternative medication for brain HI injury. PMID:25574482

  3. Opioid receptors: toward separation of analgesic from undesirable effects.

    PubMed

    Law, Ping-Yee; Reggio, Patricia H; Loh, Horace H

    2013-06-01

    The use of opioid analgesics for pain has always been hampered by their many side effects; in particular, the addictive liability associated with chronic use. Recently, attempts to develop analgesic agents with reduced side effects have targeted either the putative opioid receptor splice variants or the receptor hetero-oligomers. This review discusses the potential for receptor splice variant- and the hetero-oligomer-based discovery of new opioid analgesics. We also examine an alternative approach of using receptor mutants for pain management. Finally, we discuss the role of the biased agonism observed and the recently reported opioid receptor crystal structures in guiding the future development of opioid analgesics.

  4. Exposure to the Selective κ-Opioid Receptor Agonist Salvinorin A Modulates the Behavioral and Molecular Effects of Cocaine in Rats

    PubMed Central

    Chartoff, Elena H; Potter, David; Damez-Werno, Diane; Cohen, Bruce M; Carlezon, William A

    2008-01-01

    Stress and chronic exposure to drugs of abuse can trigger addictive and depressive disorders. Both stimuli increase activity of dynorphin, a neuropeptide that acts at κ-opioid receptors (KORs). In humans, KOR agonists cause dysphoria, raising the possibility that dynorphin modulates the depressive-like effects of stress and chronic drug use. We examined if KOR activation alters sensitivity to stimulant drugs by assessing the effects of the selective KOR agonist, salvinorin A (SalvA), on cocaine-induced locomotor activity and c-Fos expression. Acute administration of SalvA blocked the locomotor-stimulant effects of cocaine, whereas repeated SalvA together with concomitant exposure to activity testing chambers potentiated the locomotor response to a cocaine challenge. In contrast, repeated SalvA administered in home cages rather than the activity chambers failed to potentiate the locomotor response to a cocaine challenge. One potential explanation for these findings is that activation of KORs disrupts context conditioning: acute locomotor responses to SalvA alone did not fully habituate with repeated testing in the activity chambers. The effects of SalvA on locomotor activity paralleled its effects on cocaine-induced c-Fos expression in the dorsal striatum: acute SalvA attenuated cocaine-induced c-Fos, whereas repeated SalvA potentiated it when administered in the activity chambers but not the home cage. Acute SalvA also blocked the locomotor stimulant effects of the DI receptor agonist SKF 82958, whereas repeated SalvA potentiated these effects when administered in the activity chambers. These findings suggest that SalvA regulates the stimulant effects of cocaine through interactions with DI receptor-mediated signaling in the dorsal striatum. PMID:18185499

  5. Polymorphism in the µ-opioid receptor gene (OPRM1) modulates neural processing of physical pain, social rejection and error processing.

    PubMed

    Bonenberger, M; Plener, P L; Groschwitz, R C; Grön, G; Abler, B

    2015-09-01

    Variations of the µ-opioid receptor gene OPRM1 have been shown to modulate pain perception with some evidence pointing towards a modulation of not only physical but also "psychological pain". In line with suggestions of a common neural network involved in the processing of physical pain and negative and distressing stimuli, like social rejection as a psychologically harmful event, we examined the influence of the A118G polymorphism on the neural processing of physical and non-physical pain. Using fMRI, we investigated a sample of 23 females with the more frequent AA genotype, and eight females with the relatively rare but more pain-sensitive AG genotype during electrical stimulation to the dorsum of the non-dominant hand. Non-physical pain was investigated using Cyberball, a virtual ball-tossing game, to induce experiences of non-self-dependent social rejection. A Go/NoGo task with an increased risk of self-dependent erroneous performance was used as a control task to investigate the effects of negative feedback as a more cognitive form of distress. Relative to A118G homozygous A-allele carriers, G-allele carriers showed significantly increased activation of the supplementary motor area/superior frontal gyrus and the precentral gyrus during electrical stimulation. Increased activation of the secondary sensorimotor cortex (SII) was found during social exclusion and during negative feedback. We demonstrate that brain regions particularly related to the somatosensory component of pain processing are modulated by variations in OPRM1. Influences were evident for both physical and psychological pain processing supporting the assumption of shared neural pathways.

  6. Opioid receptors: distinct roles in mood disorders

    PubMed Central

    Lutz, Pierre-Eric; Kieffer, Brigitte L.

    2012-01-01

    The roles of opioid receptors in pain and addiction have been extensively studied, but their function in mood disorders has received less attention. Accumulating evidence from animal research reveal that mu, delta and kappa opioid receptors (MORs, DORs and KORs, respectively) exert highly distinct controls over mood-related processes. DOR agonists and KOR antagonists have promising antidepressant potential, whereas the risk-benefit ratio of currently available MOR agonists as antidepressants remain difficult to evaluate, in addition to their inherent abuse liability. At present, both human and animal studies have mainly examined MORs in the etiology of depressive disorders, and future studies will address delta and kappa receptor function in established and emerging neurobiological aspects of depression, including neurogenesis, neurodevelopment and social behaviors. PMID:23219016

  7. The role of the dynorphin/κ opioid receptor system in anxiety.

    PubMed

    Hang, Ai; Wang, Yu-jun; He, Ling; Liu, Jing-gen

    2015-07-01

    Anxiety disorders are the most common and prevalent forms of psychiatric disease, although the biological basis of anxiety is not well understood. The dynorphin/κ opioid receptor system is widely distributed in the central nervous system and has been shown to play a critical role in modulating mood and emotional behaviors. In the present review, we summarize current literature relating to the role played by the dynorphin/κ opioid receptor system in anxiety and κ opioid receptor antagonists as potential therapeutic agents for the treatment of anxiety disorders.

  8. The role of the dynorphin/κ opioid receptor system in anxiety

    PubMed Central

    Hang, Ai; Wang, Yu-jun; He, Ling; Liu, Jing-gen

    2015-01-01

    Anxiety disorders are the most common and prevalent forms of psychiatric disease, although the biological basis of anxiety is not well understood. The dynorphin/κ opioid receptor system is widely distributed in the central nervous system and has been shown to play a critical role in modulating mood and emotional behaviors. In the present review, we summarize current literature relating to the role played by the dynorphin/κ opioid receptor system in anxiety and κ opioid receptor antagonists as potential therapeutic agents for the treatment of anxiety disorders. PMID:25982631

  9. A novel opioid mechanism seems to modulate phagocytosis in Tetrahymena.

    PubMed

    Renaud, F L; Colon, I; Lebron, J; Ortiz, N; Rodriguez, F; Cadilla, C

    1995-01-01

    We have previously reported that a beta-endorphin-like substance inhibits phagocytosis in Tetrahymena perhaps by a mu-like opioid receptor. We now report a further characterization of the elements involved in the signal transduction mechanism of this opioid. Affinity chromatography followed by immunoblots of both intracellular extracts and extracellular medium reveal the presence of two main proteins of 64 and 75 kDa. These molecular weights are much higher than that of any known opioid peptide or precursor protein and suggest that we may be dealing with either a novel opioid or with proteins that by chance cross-react with anti-beta-endorphin antibody. Nevertheless, when the biological activity of these proteins was tested it was found that they had an effect similar to that of mammalian beta-endorphin, namely inhibition of phagocytosis by a naloxone-reversible mechanism. We have probed a size-selected Tetrahymena library with a pro-opiomelanocortin probe and have obtained several positive clones; the sequencing of their inserts should establish whether we are dealing with a bona fide member of the opioid family. Another aspect we have been studying is the G-proteins which appear to be involved in the modulation of phagocytosis. We have found, by means of Western blotting (using an antibody against the conserved GTP-binding region of the alpha-subunit), two bands of 51 and 59 kDa; no alpha-subunit of 59 kDa had been reported previously and may represent a novel G-protein. In spite of these differences, the opioid signal transduction mechanism appears to remarkably resemble that present in more complex organisms.

  10. T394A Mutation at the μ Opioid Receptor Blocks Opioid Tolerance and Increases Vulnerability to Heroin Self-Administration in Mice.

    PubMed

    Wang, Xiao-Fei; Barbier, Elisabeth; Chiu, Yi-Ting; He, Yi; Zhan, Jia; Bi, Guo-Hua; Zhang, Hai-Ying; Feng, Bo; Liu-Chen, Lee-Yuan; Wang, Jia Bei; Xi, Zheng-Xiong

    2016-10-05

    The etiology and pathophysiology underlying opioid tolerance and dependence are still unknown. Because mu opioid receptor (MOR) plays an essential role in opioid action, many vulnerability-related studies have focused on single nucleotide polymorphisms of MOR, particularly on A118G. In this study, we found that a single-point mutation at the MOR T394 phosphorylation site could be another important susceptive factor in the development of opioid tolerance and dependence in mice. T394A mutation, in which a threonine at 394 was replaced by an alanine, did not alter agonist binding to MOR and opioid analgesia, but resulted in loss of etorphine-induced MOR internalization in spinal dorsal horn neurons and opioid analgesic tolerance induced by either morphine or etorphine. In addition, this mutation also caused an increase in intravenous heroin self-administration and in nucleus accumbens dopamine response to heroin. These findings suggest that T394 phosphorylation following MOR activation causes MOR internalization and desensitization, which subsequently contributes to the development of tolerance in both opioid analgesia and opioid reward. Accordingly, T394A mutation blocks opioid tolerance and leads to an increase in brain dopamine response to opioids and in opioid-taking behavior. Thus, the T394 may serve as a new drug target for modulating opioid tolerance and the development of opioid abuse and addiction.

  11. Inhibition of opioid release in the rat spinal cord by α2C adrenergic receptors

    PubMed Central

    Chen, Wenling; Song, Bingbing; Marvizón, Juan Carlos G.

    2008-01-01

    Neurotransmitter receptors that control the release of opioid peptides in the spinal cord may play an important role in pain modulation. Norepinephrine, released by a descending pathway originating in the brainstem, is a powerful inducer of analgesia in the spinal cord. Adrenergic α2C receptors are present in opioid-containing terminals in the dorsal horn, where they could modulate opioid release. The goal of this study was to investigate this possibility. Opioid release was evoked from rat spinal cord slices by incubating them with the sodium channel opener veratridine in the presence of peptidase inhibitors (actinonin, captopril and thiorphan), and was measured in situ through the internalization of μ-opioid receptors in dorsal horn neurons. Veratridine produced internalization in 70% of these neurons. The α2 receptor agonists clonidine, guanfacine, medetomidine and UK-14304 inhibited the evoked μ-opioid receptor internalization with IC50s of 1.7 μM, 248 nM, 0.3 nM and 22 nM, respectively. However, inhibition by medetomidine was only partial, and inhibition by UK-14304 reversed itself at concentrations higher than 50 nM. None of these agonists inhibited μ-opioid receptor internalization produced by endomorphin-2, showing that they inhibited opioid release and not the internalization itself. The inhibition produced by clonidine, guanfacine or UK-14304 was completely reversed by the selective α2C antagonist JP-1203. In contrast, inhibition by guanfacine was not prevented by the α2A antagonist BRL-44408. These results show that α2C receptors inhibit the release of opioids in the dorsal horn. This action may serve to shut down the opioid system when the adrenergic system is active. PMID:18343461

  12. BU74, a complex oripavine derivative with potent kappa opioid receptor agonism and delayed opioid antagonism.

    PubMed

    Husbands, Stephen M; Neilan, Claire L; Broadbear, Jillian; Grundt, Peter; Breeden, Simon; Aceto, Mario D; Woods, James H; Lewis, John W; Traynor, John R

    2005-02-21

    In the search for opioid agonists with delayed antagonist actions as potential treatments for substance abuse, the bridged morphinan BU74 (17-cyclopropylmethyl-3-hydroxy-[5beta,7beta,3',5']-pyrrolidino-2'[S]-phenyl-7alpha-methyl-6,14-endoetheno morphinan) (3f) was synthesized. In isolated tissue and [35S]GTPgammaS opioid receptor functional assays BU74 was shown to be a potent long-lasting kappa opioid receptor agonist, delta opioid receptor partial agonist and mu opioid receptor antagonist. In antinociceptive tests in the mouse, BU74 showed high efficacy and potent kappa opioid receptor agonism. When its agonist action had waned BU74 became an antagonist of kappa and mu opioid receptor agonists in the tail flick assay and of delta, kappa and mu opioid receptor agonists in the acetic acid writhing assay. The slow onset, long-duration kappa opioid receptor agonist effects of BU74 suggests that it could be a lead compound for the discovery of a treatment for cocaine abuse.

  13. Nicotinic and opioid receptor regulation of striatal dopamine D2-receptor mediated transmission

    PubMed Central

    Mamaligas, Aphroditi A.; Cai, Yuan; Ford, Christopher P.

    2016-01-01

    In addition to dopamine neuron firing, cholinergic interneurons (ChIs) regulate dopamine release in the striatum via presynaptic nicotinic receptors (nAChRs) on dopamine axon terminals. Synchronous activity of ChIs is necessary to evoke dopamine release through this pathway. The frequency-dependence of disynaptic nicotinic modulation has led to the hypothesis that nAChRs act as a high-pass filter in the dopaminergic microcircuit. Here, we used optogenetics to selectively stimulate either ChIs or dopamine terminals directly in the striatum. To measure the functional consequence of dopamine release, D2-receptor synaptic activity was assessed via virally overexpressed potassium channels (GIRK2) in medium spiny neurons (MSNs). We found that nicotinic-mediated dopamine release was blunted at higher frequencies because nAChRs exhibit prolonged desensitization after a single pulse of synchronous ChI activity. However, when dopamine neurons alone were stimulated, nAChRs had no effect at any frequency. We further assessed how opioid receptors modulate these two mechanisms of release. Bath application of the κ opioid receptor agonist U69593 decreased D2-receptor activation through both pathways, whereas the μ opioid receptor agonist DAMGO decreased D2-receptor activity only as a result of cholinergic-mediated dopamine release. Thus the release of dopamine can be independently modulated when driven by either dopamine neurons or cholinergic interneurons. PMID:27886263

  14. Receptome: Interactions between three pain-related receptors or the "Triumvirate" of cannabinoid, opioid and TRPV1 receptors.

    PubMed

    Zádor, Ferenc; Wollemann, Maria

    2015-12-01

    A growing amount of data demonstrates the interactions between cannabinoid, opioid and the transient receptor potential (TRP) vanilloid type 1 (TRPV1) receptors. These interactions can be bidirectional, inhibitory or excitatory, acute or chronic in their nature, and arise both at the molecular level (structurally and functionally) and in physiological processes, such as pain modulation or perception. The interactions of these three pain-related receptors may also reserve important and new therapeutic applications for the treatment of chronic pain or inflammation. In this review, we summarize the main findings on the interactions between the cannabinoid, opioid and the TRPV1 receptor regarding to pain modulation.

  15. Leukocyte opioid receptors mediate analgesia via Ca(2+)-regulated release of opioid peptides.

    PubMed

    Celik, Melih Ö; Labuz, Dominika; Henning, Karen; Busch-Dienstfertig, Melanie; Gaveriaux-Ruff, Claire; Kieffer, Brigitte L; Zimmer, Andreas; Machelska, Halina

    2016-10-01

    Opioids are the most powerful analgesics. As pain is driven by sensory transmission and opioid receptors couple to inhibitory G proteins, according to the classical concept, opioids alleviate pain by activating receptors on neurons and blocking the release of excitatory mediators (e.g., substance P). Here we show that analgesia can be mediated by opioid receptors in immune cells. We propose that activation of leukocyte opioid receptors leads to the secretion of opioid peptides Met-enkephalin, β-endorphin and dynorphin A (1-17), which subsequently act at local neuronal receptors, to relieve pain. In a mouse model of neuropathic pain induced by a chronic constriction injury of the sciatic nerve, exogenous agonists of δ-, μ- and κ-opioid receptors injected at the damaged nerve infiltrated by opioid peptide- and receptor-expressing leukocytes, produced analgesia, as assessed with von Frey filaments. The analgesia was attenuated by pharmacological or genetic inactivation of opioid peptides, and by leukocyte depletion. This decrease in analgesia was restored by the transfer of wild-type, but not opioid receptor-lacking leukocytes. Ex vivo, exogenous opioids triggered secretion of opioid peptides from wild-type immune cells isolated from damaged nerves, which was diminished by blockade of Gαi/o or Gβγ (but not Gαs) proteins, by chelator of intracellular (but not extracellular) Ca(2+), by blockers of phospholipase C (PLC) and inositol 1,4,5-trisphosphate (IP3) receptors, and was partially attenuated by protein kinase C inhibitor. Similarly, the leukocyte depletion-induced decrease in exogenous opioid analgesia was re-established by transfer of immune cells ex vivo pretreated with extracellular Ca(2+) chelator, but was unaltered by leukocytes pretreated with intracellular Ca(2+) chelator or blockers of Gαi/o and Gβγ proteins. Thus, both ex vivo opioid peptide release and in vivo analgesia were mediated by leukocyte opioid receptors coupled to the G

  16. Methylnaltrexone, a novel peripheral opioid receptor antagonist for the treatment of opioid side effects.

    PubMed

    Yuan, Chun-Su; Israel, Robert J

    2006-05-01

    Methylnaltrexone is an investigational peripheral opioid receptor antagonist, a quaternary derivative of naltrexone. Methylnaltrexone has greater polarity and lower lipid solubility, thus it does not cross the blood-brain barrier in humans. Methylnaltrexone offers the therapeutic potential to block or reverse the undesired side effects of opioids that are mediated by receptors located in the periphery (e.g., in the gastrointestinal tract), without affecting analgesia or precipitating the opioid withdrawal symptoms that are predominantly mediated by receptors in the CNS. This article reviews preclinical studies and clinical opioid bowel dysfunction trial data, and briefly discusses other potential roles of this compound in clinical practice.

  17. The mu-opioid receptor gene-dose dependent reductions in G-protein activation in the pons/medulla and antinociception induced by endomorphins in mu-opioid receptor knockout mice.

    PubMed

    Mizoguchi, H; Narita, M; Oji, D E; Suganuma, C; Nagase, H; Sora, I; Uhl, G R; Cheng, E Y; Tseng, L F

    1999-01-01

    There appear to be different relationships between mu-opioid receptor densities and the acute and neuroadaptive mu-opioid agonist-induced responses of the multiple opioid neuronal systems, including important pons/medulla circuits. The recent success in creating mu-opioid receptor knockout mice allows studies of mu-opioid agonist-induced pharmacological and physiological effects in animals that express no, one or two copies of the mu-opioid receptor gene. We now report that the binding of mu-opioid receptor ligand, [3H][D-Ala2,NHPhe4,Gly-ol]enkephalin to membrane preparations of the pons/medulla was reduced by half in heterozygous mu-opioid receptor knockout mice and eliminated in homozygous mu-opioid receptor knockout mice. The endogenous mu-opioid agonist peptides endomorphin-1 and -2 activate G-proteins in the pons/medulla from wild-type mice in a concentration-dependent fashion, as assessed using [35S]guanosine-5'-o-(3-thio)triphosphate binding. This stimulation was reduced to half of the wild-type levels in heterozygous mice and eliminated in homozygous knockout mice. The intracerebroventricular injection of either endomorphin-1 or endomorphin-2 produced marked antinociception in the hot-plate and tail-flick tests in wild-type mice. These antinociceptive actions were significantly reduced in heterozygous mu-opioid receptor knockout mice, and virtually abolished in homozygous knockout mice. The mu-opioid receptors are the principal molecular targets for endomorphin-induced G-protein activation in the pons/medulla and the antinociception caused by the intracerebroventricular administration of mu-opioid agonists. These data support the notion that there are limited physiological mu-opioid receptor reserves for inducing G-protein activation in the pons/medulla and for the nociceptive modulation induced by the central administration of endomorphin-1 and -2.

  18. The mu opioid receptor: A new target for cancer therapy?

    PubMed

    Singleton, Patrick A; Moss, Jonathan; Karp, Daniel D; Atkins, Johnique T; Janku, Filip

    2015-08-15

    Mu opioids are among the most widely used drugs for patients with cancer with both acute and chronic pain as well as in the perioperative period. Several retrospective studies have suggested that opioid use might promote tumor progression and as a result negatively impact survival in patients with advanced cancer; however, in the absence of appropriate prospective validation, any changes in recommendations for opioid use are not warranted. In this review, the authors present preclinical and clinical data that support their hypothesis that the mu opioid receptor is a potential target for cancer therapy because of its plausible role in tumor progression. The authors also propose the hypothesis that peripheral opioid antagonists such as methylnaltrexone, which reverses the peripheral effects of mu opioids but maintains centrally mediated analgesia and is approved by the US Food and Drug Administration for the treatment of opioid-induced constipation, can be used to target the mu opioid receptor.

  19. Discovery of Novel Triazole-Based Opioid Receptor Antagonists

    PubMed Central

    Zhang, Qiang; Keenan, Susan M.; Peng, Youyi; Nair, Anil C.; Yu, Seong Jae; Howells, Richard D.; Welsh, William J.

    2009-01-01

    We report the computer-aided design, chemical synthesis, and biological evaluation of a novel family of δ opioid receptor (DOR) antagonists containing a 1,2,4-triazole core structure that are structurally distinct from other known opioid receptor active ligands. Among those δ antagonists sharing this core structure, 8 exhibited strong binding affinity (Ki = 50 nM) for the DOR and appreciable selectivity for δ over μ and opioid receptors (δ/μ = 80; δ/κ > 200). PMID:16821764

  20. [Opioid receptors of the CNS: function, structure and distribution].

    PubMed

    Slamberová, R

    2004-01-01

    Even though the alkaloids of opium, such as morphine and codeine, were isolated at the beginning of 19th century, the opioid receptors were not determined until 1970's. The discovery of endogenous opioid peptides, such as endorphins, enkephalins and dynorphins, has helped to differentiate between the specific opioid receptor subtypes, mu, delta and kappa, that are used up to now. Opioid receptors are distributed in the central nervous system unevenly. Each receptor subtype has its own specific and nonspecific agonists and antagonists. Opioides, as exogenous opioid receptor agonists, are drugs that are often used in medicine for their analgesic effects, but they are also some of the most heavily abused drugs in the world. Opioides may also induce long-term changes in the numbers and binding activities of opioid receptors. Some of our studies in fact demonstrate that prenatal morphine exposure can alter opioid receptors of adult rats. This may begin to provide insight into the sources of some of the morphological and behavioral changes in the progeny of mothers that received or abused opioides during pregnancy.

  1. Recent developments in the study of opioid receptors.

    PubMed

    Cox, Brian M

    2013-04-01

    It is now about 40 years since Avram Goldstein proposed the use of the stereoselectivity of opioid receptors to identify these receptors in neural membranes. In 2012, the crystal structures of the four members of the opioid receptor family were reported, providing a structural basis for understanding of critical features affecting the actions of opiate drugs. This minireview summarizes these recent developments in our understanding of opiate receptors. Receptor function is also influenced by amino acid substitutions in the protein sequence. Among opioid receptor genes, one polymorphism is much more frequent in human populations than the many others that have been found, but the functional significance of this single nucleotide polymorphism (SNP) has been unclear. Recent studies have shed new light on how this SNP might influence opioid receptor function. In this minireview, the functional significance of the most prevalent genetic polymorphism among the opioid receptor genes is also considered.

  2. Salvinorin A: allosteric interactions at the mu-opioid receptor.

    PubMed

    Rothman, Richard B; Murphy, Daniel L; Xu, Heng; Godin, Jonathan A; Dersch, Christina M; Partilla, John S; Tidgewell, Kevin; Schmidt, Matthew; Prisinzano, Thomas E

    2007-02-01

    Salvinorin A [(2S,4aR,6aR,7R,9S,10aS,10bR)-9-(acetyloxy)-2-(3-furanyl)-dodecahydro-6a,10b-dimethyl-4,10-dioxo-2h-naphtho[2,1-c]pyran-7-carboxylic acid methyl ester] is a hallucinogenic kappa-opioid receptor agonist that lacks the usual basic nitrogen atom present in other known opioid ligands. Our first published studies indicated that Salvinorin A weakly inhibited mu-receptor binding, and subsequent experiments revealed that Salvinorin A partially inhibited mu-receptor binding. Therefore, we hypothesized that Salvinorin A allosterically modulates mu-receptor binding. To test this hypothesis, we used Chinese hamster ovary cells expressing the cloned human opioid receptor. Salvinorin A partially inhibited [(3)H]Tyr-D-Ala-Gly-N-Me-Phe-Gly-ol (DAMGO) (0.5, 2.0, and 8.0 nM) binding with E(MAX) values of 78.6, 72.1, and 45.7%, respectively, and EC(50) values of 955, 1124, and 4527 nM, respectively. Salvinorin A also partially inhibited [(3)H]diprenorphine (0.02, 0.1, and 0.5 nM) binding with E(MAX) values of 86.2, 64, and 33.6%, respectively, and EC(50) values of 1231, 866, and 3078 nM, respectively. Saturation binding studies with [(3)H]DAMGO showed that Salvinorin A (10 and 30 microM) decreased the mu-receptor B(max) and increased the K(d) in a dose-dependent nonlinear manner. Saturation binding studies with [(3)H]diprenorphine showed that Salvinorin A (10 and 40 microM) decreased the mu-receptor B(max) and increased the K(d) in a dose-dependent nonlinear manner. Similar findings were observed in rat brain with [(3)H]DAMGO. Kinetic experiments demonstrated that Salvinorin A altered the dissociation kinetics of both [(3)H]DAMGO and [(3)H]diprenorphine binding to mu receptors. Furthermore, Salvinorin A acted as an uncompetitive inhibitor of DAMGO-stimulated guanosine 5'-O-(3-[(35)S]thio)-triphosphate binding. Viewed collectively, these data support the hypothesis that Salvinorin A allosterically modulates the mu-opioid receptor.

  3. INTERACTION BETWEEN DELTA OPIOID RECEPTORS AND BENZODIAZEPINES IN CO2- INDUCED RESPIRATORY RESPONSES IN MICE

    PubMed Central

    Borkowski, Anne H.; Barnes, Dylan C.; Blanchette, Derek R.; Castellanos, F. Xavier; Klein, Donald F.; Wilson, Donald A.

    2011-01-01

    The false-suffocation hypothesis of panic disorder (Klein, 1993) suggested δ-opioid receptors as a possible source of the respiratory dysfunction manifested in panic attacks occurring in panic disorder (Preter and Klein, 2008). This study sought to determine if a lack of δ-opioid receptors in a mouse model affects respiratory response to elevated CO2, and whether the response is modulated by benzodiazepines, which are widely used to treat panic disorder. In a whole-body plethysmograph, respiratory responses to 5% CO2 were compared between δ-opioid receptor knockout mice and wild-type mice after saline, diazepam (1 mg/kg), and alprazolam (0.3 mg/kg) injection. The results show that lack of δ-opioid receptors does not affect normal response to elevated CO2, but does prevent benzodiazepines from modulating that response. Thus, in the presence of benzodiazepine agonists, respiratory responses to elevated CO2 were enhanced in δ-opioid receptor knockout mice compared to wild-type mice. This suggests an interplay between benzodiazepine receptors and δ-opioid receptors in regulating the respiratory effects of elevated CO2, which might be related to CO2 induced panic. PMID:21561601

  4. Neurokinin 1 and opioid receptors: relationships and interactions in nervous system

    PubMed Central

    Xiao, Jie; Zeng, Si; Wang, Xiangrui; Babazada, Hasan; Li, Zhanchun; Liu, Renyu; Yu, Weifeng

    2017-01-01

    Opioid receptors and neurokinin 1 receptor (NK1R) are found highly expressed in the central nervous system. The co-localization of these two kinds of receptors suggests that they might interact with each other in both the transmission and modulation of the pain signal. In this review, we explore the relationships between opioid receptors and NK1R. Substance P (SP) plays a modulatory role in the pain transmission by activating the NK1R. Opioid receptor activation can inhibit SP release. NK1R is found participating in the mechanisms of the side effects of the opioids, including opioid analgesic tolerance, hyperalgesia, anxiety behaviors of morphine reward and opioids related respiratory depression. A series of compounds such as NK1R antagonists and ligands works on both mu/delta opioid receptor (MOR/DOR) and NK1R were synthesized as novel analgesics that enhance the clinical pain management efficacy and reduce the dosage and side effects. The current status of these novel ligands and the limitations are discussed in this review. Although the working mechanisms of these ligands remained unclear, they could be used as research tool for developing novel analgesic drugs in the future.

  5. Activation of Mas oncogene-related gene (Mrg) C receptors enhances morphine-induced analgesia through modulation of coupling of μ-opioid receptor to Gi-protein in rat spinal dorsal horn.

    PubMed

    Wang, D; Chen, T; Zhou, X; Couture, R; Hong, Y

    2013-12-03

    Mas oncogene-related gene (Mrg) G protein-coupled receptors are exclusively expressed in small-sized neurons in trigeminal and dorsal root ganglia (DRG) in mammals. The present study investigated the effect of MrgC receptor activation on morphine analgesic potency and addressed its possible mechanisms. Intrathecal (i.t.) administration of the specific MrgC receptor agonist bovine adrenal medulla 8-22 (BAM8-22, 3 nmol) increased morphine-induced analgesia and shifted the morphine dose-response curve to the left in rats. Acute morphine (5 μg) reduced the coupling of μ-opioid receptors (MORs) to Gi-, but not Gs-, protein in the spinal dorsal horn. The i.t. BAM8-22 (3 nmol) prevented this change of G-protein repertoire while the inactive MrgC receptor agonist BAM8-18 (3 nmol, i.t.) failed to do so. A double labeling study showed the co-localization of MrgC and MORs in DRG neurons. The i.t. BAM8-22 also increased the coupling of MORs to Gi-protein and recruited Gi-protein from cytoplasm to the cell membrane in the spinal dorsal horn. Application of BAM8-22 (10nM) in the cultured ganglion explants for 30 min increased Gi-protein mRNA, but not Gs-protein mRNA. The present study demonstrated that acute administration of morphine inhibited the repertoire of MOR/Gi-protein coupling in the spinal dorsal horn in vivo. The findings highlight a novel mechanism by which the activation of MrgC receptors can modulate the coupling of MORs with Gi-protein to enhance morphine-induced analgesia. Hence, adjunct treatment of MrgC agonist BAM8-22 may be of therapeutic value to relieve pain.

  6. Nucleus accumbens dopamine and mu-opioid receptors modulate the reinstatement of food-seeking behavior by food-associated cues.

    PubMed

    Guy, Elizabeth G; Choi, Eugene; Pratt, Wayne E

    2011-06-01

    The high attrition rates for dietary interventions aimed at promoting a healthier body mass may be caused, at least in part, by constant exposure to environmental stimuli that are associated with palatable foods. In both humans and animals, conditioned stimuli (CSs) that signal reward availability reliably reinstate food- and drug-seeking behaviors. The nucleus accumbens (NAcc) is critically involved in the cue-evoked reinstatement of food-seeking, but the role of individual neurotransmitter systems within the NAcc remains to be determined. These experiments tested the effects of intra-accumbal pharmacological manipulations of dopamine (DA) D(1) and D(2) receptors, mu-opioid receptors, or serotonin (5-HT) receptors on cue-evoked relapse to food-seeking. Rats were trained to lever press for sucrose pellets and the concurrent presentation of a light-tone CS. Once training was complete, lever-pressing was extinguished in the absence of either sucrose or CS presentation. Once each rat had reached extinction criterion, they received two reinstatement sessions in which lever pressing was renewed by response-contingent presentation of the CS. Prior to each reinstatement test, rats received NAcc microinfusions of saline or the selective D(1) receptor antagonist SCH 23390, the D(2) receptor antagonist raclopride, the mu-opioid receptor agonist [D-Ala2, N-MePhe4, Gly-ol]-enkephalin (DAMGO), or 5-HT hydrogen maleate. Compared to saline test days, intra-accumbens infusions of SCH 23390 (1 μg/0.5 μL), raclopride (1 μg/0.5 μL), or DAMGO (0.25 μg/0.5 μL) effectively blocked the cue-evoked reinstatement of food-seeking. In contrast, stimulation of serotonin (5-HT) receptors by 5-HT hydrogen maleate (5 μg/0.5 μL) had no effect on cue-induced reinstatement. These novel data support roles for NAcc DA D(1), D(2), and mu-opioid receptors in the cue-evoked reinstatement of food seeking.

  7. Delta opioid receptors presynaptically regulate cutaneous mechanosensory neuron input to the spinal cord dorsal horn.

    PubMed

    Bardoni, Rita; Tawfik, Vivianne L; Wang, Dong; François, Amaury; Solorzano, Carlos; Shuster, Scott A; Choudhury, Papiya; Betelli, Chiara; Cassidy, Colleen; Smith, Kristen; de Nooij, Joriene C; Mennicken, Françoise; O'Donnell, Dajan; Kieffer, Brigitte L; Woodbury, C Jeffrey; Basbaum, Allan I; MacDermott, Amy B; Scherrer, Grégory

    2014-03-19

    Cutaneous mechanosensory neurons detect mechanical stimuli that generate touch and pain sensation. Although opioids are generally associated only with the control of pain, here we report that the opioid system in fact broadly regulates cutaneous mechanosensation, including touch. This function is predominantly subserved by the delta opioid receptor (DOR), which is expressed by myelinated mechanoreceptors that form Meissner corpuscles, Merkel cell-neurite complexes, and circumferential hair follicle endings. These afferents also include a small population of CGRP-expressing myelinated nociceptors that we now identify as the somatosensory neurons that coexpress mu and delta opioid receptors. We further demonstrate that DOR activation at the central terminals of myelinated mechanoreceptors depresses synaptic input to the spinal dorsal horn, via the inhibition of voltage-gated calcium channels. Collectively our results uncover a molecular mechanism by which opioids modulate cutaneous mechanosensation and provide a rationale for targeting DOR to alleviate injury-induced mechanical hypersensitivity.

  8. Agonist Binding and Desensitization of the μ-Opioid Receptor Is Modulated by Phosphorylation of the C-Terminal Tail Domain

    PubMed Central

    Arttamangkul, Seksiri; Bunzow, James R.; Williams, John T.

    2015-01-01

    Sustained activation of G protein–coupled receptors can lead to a rapid decline in signaling through acute receptor desensitization. In the case of the μ-opioid receptor (MOPr), this desensitization may play a role in the development of analgesic tolerance. It is understood that phosphorylation of MOPr promotes association with β-arrestin proteins, which then facilitates desensitization and receptor internalization. Agonists that induce acute desensitization have been shown to induce a noncanonical high-affinity agonist binding state in MOPr, conferring a persistent memory of prior receptor activation. In the current study, live-cell confocal imaging was used to investigate the role of receptor phosphorylation in agonist binding to MOPr. A phosphorylation cluster in the C-terminal tail of MOPr was identified as a mediator of agonist-induced affinity changes in MOPr. This site is unique from the primary phosphorylation cluster responsible for β-arrestin binding and internalization. Electrophysiologic measurements of receptor function suggest that both phosphorylation clusters may play a parallel role during acute receptor desensitization. Desensitization was unaffected by alanine mutation of either phosphorylation cluster, but was largely eliminated when both clusters were mutated. Overall, this work suggests that there are multiple effects of MOPr phosphorylation that appear to regulate MOPr function: one affecting β-arrestin binding and a second affecting agonist binding. PMID:25934731

  9. Revolution in GPCR signalling: opioid receptor heteromers as novel therapeutic targets: IUPHAR review 10.

    PubMed

    Fujita, Wakako; Gomes, Ivone; Devi, Lakshmi A

    2014-09-01

    GPCRs can interact with each other to form homomers or heteromers. Homomers involve interactions with the same receptor type while heteromers involve interactions between two different GPCRs. These receptor-receptor interactions modulate not only the binding but also the signalling and trafficking properties of individual receptors. Opioid receptor heteromerization has been extensively investigated with the objective of identifying novel therapeutic targets that are as potent as morphine but without the side effects associated with chronic morphine use. In this context, studies have described heteromerization between the different types of opioid receptors and between opioid receptors and a wide range of GPCRs including adrenoceptors, cannabinoid, 5-HT, metabotropic glutamate and sensory neuron-specific receptors. Recent advances in the field involving the generation of heteromer-specific reagents (antibodies or ligands) or of membrane-permeable peptides that disrupt the heteromer interaction are helping to elucidate the physiological role of opioid receptor heteromers and the contribution of the partner receptor to the side effects associated with opioid use. For example, studies using membrane-permeable peptides targeting the heteromer interface have implicated μ and δ receptor heteromers in the development of tolerance to morphine, and heteromers of μ and gastrin-releasing peptide receptors in morphine-induced itch. In addition, a number of ligands that selectively target opioid receptor heteromers exhibit potent antinociception with a decrease in the side effects commonly associated with morphine use. In this review, we summarize the latest findings regarding the biological and functional characteristics of opioid receptor heteromers both in vitro and in vivo.

  10. Constitutive opioid receptor activation: a prerequisite mechanism involved in acute opioid withdrawal.

    PubMed

    Freye, E; Levy, Jv

    2005-06-01

    The opioid receptor antagonist naltrexone, which is used in detoxification and rehabilitation programmes in opioid addicts, can precipitate opioid withdrawal symptoms even in patients who have no opioid present. We tested the hypothesis that in order to precipitate withdrawal, opioids need to convert the inactive opioid receptor site via protein kinase C into a constitutively active form on which the antagonist precipitates withdrawal. Acute microg/kg), given for 6 days, which was followed by the antagonist naltrexone (20 microg/kg i.v.) in the awake trained canine (n = 10). Abrupt displacement of opioid binding resulted in acute withdrawal symptoms: increase in blood pressure, heart rate, increase in amplitude height of somatosensory evoked potential, reduced tolerance to colon distention and a significant increase in grading of vegetative variables (restlessness, panting, thrashing of the head, whining, yawning, gnawing, salivation and/or rhinorrhoea, mydriasis, stepping of extremities and vomiting). Following a washout period of 14 days, the same animals were given the highly specific protein kinase C inhibitor H7 (250 microg/kg) prior to the same dosages of sufentanil and naltrexone. Such pretreatment was able to either attenuate or completely abolish the acute withdrawal symptoms. The data suggest that for precipitation of withdrawal, intracellular phosphorylation is a prerequisite in order to activate the opioid mu-receptor. In such a setting, naltrexone acts like an 'inverse agonist' relative to the action of the antagonist on a non-preoccupied receptor site not being exposed previously to a potent opioid agonist.

  11. The opioid receptors as targets for drug abuse medication.

    PubMed

    Noble, Florence; Lenoir, Magalie; Marie, Nicolas

    2015-08-01

    The endogenous opioid system is largely expressed in the brain, and both endogenous opioid peptides and receptors are present in areas associated with reward and motivation. It is well known that this endogenous system plays a key role in many aspects of addictive behaviours. The present review summarizes the modifications of the opioid system induced by chronic treatment with drugs of abuse reported in preclinical and clinical studies, as well as the action of opioid antagonists and agonists on the reinforcing effects of drugs of abuse, with therapeutic perspectives. We have focused on the effects of chronic psychostimulants, alcohol and nicotine exposure. Taken together, the changes in both opioid peptides and opioid receptors in different brain structures following acute or chronic exposure to these drugs of abuse clearly identify the opioid system as a potential target for the development of effective pharmacotherapy for the treatment of addiction and the prevention of relapse.

  12. The opioid receptors as targets for drug abuse medication

    PubMed Central

    Noble, Florence; Lenoir, Magalie; Marie, Nicolas

    2015-01-01

    The endogenous opioid system is largely expressed in the brain, and both endogenous opioid peptides and receptors are present in areas associated with reward and motivation. It is well known that this endogenous system plays a key role in many aspects of addictive behaviours. The present review summarizes the modifications of the opioid system induced by chronic treatment with drugs of abuse reported in preclinical and clinical studies, as well as the action of opioid antagonists and agonists on the reinforcing effects of drugs of abuse, with therapeutic perspectives. We have focused on the effects of chronic psychostimulants, alcohol and nicotine exposure. Taken together, the changes in both opioid peptides and opioid receptors in different brain structures following acute or chronic exposure to these drugs of abuse clearly identify the opioid system as a potential target for the development of effective pharmacotherapy for the treatment of addiction and the prevention of relapse. PMID:25988826

  13. Pharmacological traits of delta opioid receptors: pitfalls or opportunities?

    PubMed Central

    van Rijn, Richard M.; DeFriel, Julia N.; Whistler, Jennifer L.

    2013-01-01

    Delta opioid receptors (DORs) have been considered as a potential target to relieve pain as well as treat depression and anxiety disorders, and are known to modulate other physiological responses, including ethanol and food consumption. A small number of DOR selective drugs are in clinical trials, but no DOR selective drugs have been approved by the Federal Drug Administration and some candidates have failed in phase II clinical trials, highlighting current difficulties producing effective delta opioid based therapies. Recent studies have provided new insights into the pharmacology of the DOR, which is often complex and at times paradoxical. This review will discuss the existing literature focusing on four aspects: 1) Two DOR subtypes have been postulated based on differences in pharmacological effects of existing DOR-selective ligands 2) DORs are expressed ubiquitously throughout the body and central nervous system and are, thus, positioned to play a role in a multitude of diseases. 3) DOR expression is often dynamic, with many reports of increased expression during exposure to chronic stimuli, such as stress, inflammation, neuropathy, morphine, or changes in endogenous opioid tone. 4) A large structural variety in DOR ligands implies potential different mechanisms of activating the receptor. These combined features of DOR pharmacology illustrate the potential benefit of designing tailored or biased DOR ligands. PMID:23649885

  14. Structure of the [delta]-opioid receptor bound to naltrindole

    SciTech Connect

    Granier, Sébastien; Manglik, Aashish; Kruse, Andrew C.; Kobilka, Tong Sun; Thian, Foon Sun; Weis, William I.; Kobilka, Brian K.

    2012-07-11

    The opioid receptor family comprises three members, the {mu}-, {delta}- and {kappa}-opioid receptors, which respond to classical opioid alkaloids such as morphine and heroin as well as to endogenous peptide ligands like endorphins. They belong to the G-protein-coupled receptor (GPCR) superfamily, and are excellent therapeutic targets for pain control. The {delta}-opioid receptor ({delta}-OR) has a role in analgesia, as well as in other neurological functions that remain poorly understood. The structures of the {mu}-OR and {kappa}-OR have recently been solved. Here we report the crystal structure of the mouse {delta}-OR, bound to the subtype-selective antagonist naltrindole. Together with the structures of the {mu}-OR and {kappa}-OR, the {delta}-OR structure provides insights into conserved elements of opioid ligand recognition while also revealing structural features associated with ligand-subtype selectivity. The binding pocket of opioid receptors can be divided into two distinct regions. Whereas the lower part of this pocket is highly conserved among opioid receptors, the upper part contains divergent residues that confer subtype selectivity. This provides a structural explanation and validation for the 'message-address' model of opioid receptor pharmacology, in which distinct 'message' (efficacy) and 'address' (selectivity) determinants are contained within a single ligand. Comparison of the address region of the {delta}-OR with other GPCRs reveals that this structural organization may be a more general phenomenon, extending to other GPCR families as well.

  15. Influence of candidate polymorphisms on the dipeptidyl peptidase IV and μ-opioid receptor genes expression in aspect of the β-casomorphin-7 modulation functions in autism.

    PubMed

    Cieślińska, Anna; Sienkiewicz-Szłapka, Edyta; Wasilewska, Jolanta; Fiedorowicz, Ewa; Chwała, Barbara; Moszyńska-Dumara, Małgorzata; Cieśliński, Tomasz; Bukało, Marta; Kostyra, Elżbieta

    2015-03-01

    Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder with population prevalence of approximately 60-70 per 10,000. Data shows that both opioid system function enhancement and opiate administration can result in autistic-like symptoms. Cow milk opioid peptides, including β-casomorphin-7 (BCM7, Tyr-Pro-Phe-Pro-Gly-Pro-Ile), affect the μ-opioid receptor (MOR) and are subjected to degradation resulting from the proline dipeptidyl peptidase IV (DPPIV, EC 3.4.14.5) enzyme activity. The presence of MOR and DPPIV activity are crucial factors determining biological activity of BCM7 in the human body. Our study examined the effect of β-casomorphin-7 on the MOR and DPPIV genes expression according to specific point mutations in these genes. In addition, we investigated frequency of A118G SNP in the MOR gene and rs7608798 of the DPPIV (A/G) gene in healthy and autistic children. Our research indicated correlation in DPPIV gene expression under the influence of BCM7 and hydrolyzed milk between healthy and ASD-affected children with genotype GG (P<0.0001). We also observed increased MOR gene expression in healthy children with genotype AG at polymorphic site A118G under influence of BCM7 and hydrolyzed milk. The G allele frequency was 0.09 in MOR gene and 0.68 in the DPPIV gene. But our results suggest no association between presence of the alleles G and A at position rs7608798 in DPPIV gene nor alleles A and G at position A118G of the MOR and increased incidence of ASD. Our studies emphasize the compulsion for genetic analysis in correlation with genetic factors affecting development and enhancement of autism symptoms.

  16. Overview of genetic analysis of human opioid receptors.

    PubMed

    Spampinato, Santi M

    2015-01-01

    The human μ-opioid receptor gene (OPRM1), due to its genetic and structural variation, has been a target of interest in several pharmacogenetic studies. The μ-opioid receptor (MOR), encoded by OPRM1, contributes to regulate the analgesic response to pain and also controls the rewarding effects of many drugs of abuse, including opioids, nicotine, and alcohol. Genetic polymorphisms of opioid receptors are candidates for the variability of clinical opioid effects. The non-synonymous polymorphism A118G of the OPRM1 has been repeatedly associated with the efficacy of opioid treatments for pain and various types of dependence. Genetic analysis of human opioid receptors has evidenced the presence of numerous polymorphisms either in exonic or in intronic sequences as well as the presence of synonymous coding variants that may have important effects on transcription, mRNA stability, and splicing, thus affecting gene function despite not directly disrupting any specific residue. Genotyping of opioid receptors is still in its infancy and a relevant progress in this field can be achieved by using advanced gene sequencing techniques described in this review that allow the researchers to obtain vast quantities of data on human genomes and transcriptomes in a brief period of time and with affordable costs.

  17. Opioid receptor desensitization: mechanisms and its link to tolerance

    PubMed Central

    Allouche, Stéphane; Noble, Florence; Marie, Nicolas

    2014-01-01

    Opioid receptors (OR) are part of the class A of G-protein coupled receptors and the target of the opiates, the most powerful analgesic molecules used in clinic. During a protracted use, a tolerance to analgesic effect develops resulting in a reduction of the effectiveness. So understanding mechanisms of tolerance is a great challenge and may help to find new strategies to tackle this side effect. This review will summarize receptor-related mechanisms that could underlie tolerance especially receptor desensitization. We will focus on the latest data obtained on molecular mechanisms involved in opioid receptor desensitization: phosphorylation, receptor uncoupling, internalization, and post-endocytic fate of the receptor. PMID:25566076

  18. Dual allosteric modulation of opioid antinociceptive potency by α2A-adrenoceptors.

    PubMed

    Chabot-Doré, Anne-Julie; Millecamps, Magali; Naso, Lina; Devost, Dominic; Trieu, Phan; Piltonen, Marjo; Diatchenko, Luda; Fairbanks, Carolyn A; Wilcox, George L; Hébert, Terence E; Stone, Laura S

    2015-12-01

    Opioid and α2-adrenoceptor (AR) agonists are analgesic when administered in the spinal cord and show a clinically beneficial synergistic interaction when co-administered. However, α2-AR antagonists can also inhibit opioid antinociception, suggesting a complex interaction between the two systems. The α2A-AR subtype is necessary for spinal adrenergic analgesia and synergy with opioids for most agonist combinations. Therefore, we investigated whether spinal opioid antinociception and opioid-adrenergic synergy were under allosteric control of the α2A-AR. Drugs were administered intrathecally in wild type (WT) and α2A-knock-out (KO) mice and antinociception was measured using the hot water tail immersion or substance P behavioral assays. The α2A-AR agonist clonidine was less effective in α2A-KO mice in both assays. The absence of the α2A-AR resulted in 10-70-fold increases in the antinociceptive potency of the opioid agonists morphine and DeltII. In contrast, neither morphine nor DeltII synergized with clonidine in α2A-KO mice, indicating that the α2AAR has both positive and negative modulatory effects on opioid antinociception. Depletion of descending adrenergic terminals with 6-OHDA resulted in a significant decrease in morphine efficacy in WT but not in α2A-KO mice, suggesting that endogenous norepinephrine acts through the α2A-AR to facilitate morphine antinociception. Based on these findings, we propose a model whereby ligand-occupied versus ligand-free α2A-AR produce distinct patterns of modulation of opioid receptor activation. In this model, agonist-occupied α2A-ARs potentiate opioid analgesia, while non-occupied α2A-ARs inhibit opioid analgesia. Exploiting such interactions between the two receptors could lead to the development of better pharmacological treatments for pain management.

  19. Dual allosteric modulation of opioid antinociceptive potency by a2A-adrenoceptors

    PubMed Central

    Chabot-Doré, Anne-Julie; Millecamps, Magali; Naso, Lina; Devost, Dominic; Trieu, Phan; Piltonen, Marjo; Diatchenko, Luda; Fairbanks, Carolyn A.; Wilcox, George L.; Hébert, Terence E.; Stone, Laura S.

    2015-01-01

    Opioid and α2-adrenoceptor (AR) agonists are analgesic when administered in the spinal cord and show a clinically beneficial synergistic interaction when co-administered. However, α2-AR antagonists can also inhibit opioid antinociception, suggesting a complex interaction between the two systems. The α2A-AR subtype is necessary for spinal adrenergic analgesia and synergy with opioids for most agonist combinations. Therefore, we investigated whether spinal opioid antinociception and opioid-adrenergic synergy were under allosteric control of the α2A-AR. Drugs were administered intrathecally in wild type (WT) and α2A-knock-out (KO) mice and antinociception was measured using hot water tail immersion or substance P behavioral assays. The α2A-AR agonist clonidine was less effective in α2A-KO mice in both assays. The absence of the α2A-AR resulted in 10–70-fold increases in the antinociceptive potency of the opioid agonists morphine and DeltII. In contrast, neither morphine nor DeltII synergized with clonidine in α2AKO mice, indicating that the α2AAR has both positive and negative modulatory effects on opioid antinociception. Depletion of descending adrenergic terminals with 6-OHDA resulted in a significant decrease in morphine efficacy in WT but not in α2A-KO mice, suggesting that endogenous norepinephrine acts through the α2A-AR to facilitate morphine antinociception. Based on these findings, we propose a model whereby ligand-occupied versus ligand-free α2A-AR produce distinct patterns of modulation of opioid receptor activation. In this model, agonist-occupied α2A-ARs potentiate opioid analgesia, while non-occupied α2A-ARs inhibit opioid analgesia. Exploiting such interactions between the two receptors could lead to the development of better pharmacological treatments for pain management. PMID:26254859

  20. [Functional selectivity of opioid receptors ligands].

    PubMed

    Audet, Nicolas; Archer-Lahlou, Elodie; Richard-Lalonde, Mélissa; Piñeyro-Filpo, Graciela

    2010-01-01

    Opiates are the most effective analgesics available for the treatment of severe pain. However, their clinical use is restricted by unwanted side effects such as tolerance, physical dependence and respiratory depression. The strategy to develop new opiates with reduced side effects has mainly focused on the study and production of ligands that specifically bind to different opiate receptors subtypes. However, this strategy has not allowed the production of novel therapeutic ligands with a better side effects profile. Thus, other research strategies need to be explored. One which is receiving increasing attention is the possibility of exploiting ligand ability to stabilize different receptor conformations with distinct signalling profiles. This newly described property, termed functional selectivity, provides a potential means of directing the stimulus generated by an activated receptor towards a specific cellular response. Here we summarize evidence supporting the existence of ligand-specific active conformations for two opioid receptors subtypes (delta and mu), and analyze how functional selectivity may contribute in the production of longer lasting, better tolerated opiate analgesics. double dagger.

  1. Opioid receptors and legal highs: Salvia divinorum and Kratom.

    PubMed

    Babu, Kavita M; McCurdy, Christopher R; Boyer, Edward W

    2008-02-01

    Salvia divinorum and Mitragyna speciosa ("Kratom"), two unscheduled dietary supplements whose active agents are opioid receptor agonists, have discrete psychoactive effects that have contributed to their increasing popularity. Salvia divinorum contains the highly selective kappa- opioid receptor agonist salvinorin A; this compound produces visual hallucinations and synesthesia. Mitragynine, the major alkaloid identified from Kratom, has been reported as a partial opioid agonist producing similar effects to morphine. An interesting minor alkaloid of Kratom, 7-hydroxymitragynine, has been reported to be more potent than morphine. Both Kratom alkaloids are reported to activate supraspinal mu- and delta- opioid receptors, explaining their use by chronic narcotics users to ameliorate opioid withdrawal symptoms. Despite their widespread Internet availability, use of Salvia divinorum and Kratom represents an emerging trend that escapes traditional methods of toxicologic monitoring. The purpose of this article is to familiarize toxicologists and poison control specialists with these emerging psychoactive dietary supplements.

  2. Analysis of potassium and calcium imaging to assay the function of opioid receptors.

    PubMed

    Spahn, Viola; Nockemann, Dinah; Machelska, Halina

    2015-01-01

    As the activation of opioid receptors leads to the modulation of potassium and calcium channels, the ion imaging represents an attractive method to analyze the function of the receptors. Here, we describe the imaging of potassium using the FluxOR™ potassium ion channel assay, and of calcium using Fura-2 acetoxymethyl ester. Specifically, we (1) characterize the activation of the G-protein-coupled inwardly rectifying potassium 2 channel by agonists of μ- and δ-opioid receptors with the aid of the FluxOR™ assay in cultured mouse dorsal root ganglion neurons, and (2) describe calcium imaging protocols to measure capsaicin-induced transient receptor potential vanilloid 1 channel activity during opioid withdrawal in transfected human embryonic kidney 293 cells.

  3. Animal models of motivation for drinking in rodents with a focus on opioid receptor neuropharmacology.

    PubMed

    Koob, George F; Roberts, Amanda J; Kieffer, Brigitte L; Heyser, Charles J; Katner, Simon N; Ciccocioppo, Roberto; Weiss, Friedbert

    2003-01-01

    Ethanol, like other drugs of abuse, has motivating properties that can be developed as animal models of self-administration. A major strength of the operant approach where an animal must work to obtain ethanol is that it reduces confounds due to palatability and controls for nonspecific malaise-inducing effects. In the domain of opioid peptide systems, limited access paradigms have good predictive validity. In addition, animal models of excessive drinking-either environmentally or genetically induced-also appear sensitive to blockade or inactivation of opioid peptide receptors. Ethanol availability can be predicted by cues associated with positive reinforcement, and these models are sensitive to the administration of opioid antagonists. Perhaps most exciting are the recent results suggesting that the key element in opioid peptide systems that is important for the positive reinforcing effects of ethanol is the mu-opioid receptor. How exactly ethanol modulates mu-receptor function will be a major challenge of future research. Nevertheless, the apparently critical role of the mu receptor in ethanol reinforcement refocuses the neuropharmacology of ethanol reinforcement in the opioid peptide domain and opens a novel avenue for exploring medications for treating alcoholism.

  4. Imaging of opioid receptors in the central nervous system

    PubMed Central

    Henriksen, Gjermund

    2008-01-01

    In vivo functional imaging by means of positron emission tomography (PET) is the sole method for providing a quantitative measurement of μ-, κ and δ-opioid receptor-mediated signalling in the central nervous system. During the last two decades, measurements of changes to the regional brain opioidergic neuronal activation—mediated by endogenously produced opioid peptides, or exogenously administered opioid drugs—have been conducted in numerous chronic pain conditions, in epilepsy, as well as by stimulant- and opioidergic drugs. Although several PET-tracers have been used clinically for depiction and quantification of the opioid receptors changes, the underlying mechanisms for regulation of changes to the availability of opioid receptors are still unclear. After a presentation of the general signalling mechanisms of the opioid receptor system relevant for PET, a critical survey of the pharmacological properties of some currently available PET-tracers is presented. Clinical studies performed with different PET ligands are also reviewed and the compound-dependent findings are summarized. An outlook is given concluding with the tailoring of tracer properties, in order to facilitate for a selective addressment of dynamic changes to the availability of a single subclass, in combination with an optimization of the quantification framework are essentials for further progress in the field of in vivo opioid receptor imaging. PMID:18048446

  5. Endomorphins fully activate a cloned human mu opioid receptor.

    PubMed

    Gong, J; Strong, J A; Zhang, S; Yue, X; DeHaven, R N; Daubert, J D; Cassel, J A; Yu, G; Mansson, E; Yu, L

    1998-11-13

    Endomorphins were recently identified as endogenous ligands with high selectivity for mu opioid receptors. We have characterized the ability of endomorphins to bind to and functionally activate the cloned human mu opioid receptor. Both endomorphin-1 and endomorphin-2 exhibited binding selectivity for the mu opioid receptor over the delta and kappa opioid receptors. Both agonists inhibited forskolin-stimulated increase of cAMP in a dose-dependent fashion. When the mu opioid receptor was coexpressed in Xenopus oocytes with G protein-activated K+ channels, application of either endomorphin activated an inward K+ current. This activation was dose-dependent and blocked by naloxone. Both endomorphins acted as full agonists with efficacy similar to that of [D-Ala2,N-Me-Phe4,Gly-ol5]enkephalin (DAMGO). These data indicate that endomorphins act as full agonists at the human mu opioid receptor, capable of stimulating the receptor to inhibit the cAMP/adenylyl cyclase pathway and activate G-protein-activated inwardly rectifying potassium (GIRK) channels.

  6. Opioid receptors on guinea-pig intestinal crypt epithelial cells.

    PubMed Central

    Lang, M E; Davison, J S; Bates, S L; Meddings, J B

    1996-01-01

    1. Opioid peptides promote net intestinal absorption via two mechanisms: stimulation of Na+ and Cl- absorption and inhibition of Cl- secretion. Although these transport changes are predominantly mediated by submucosal neurones, it is currently unclear whether opioid peptides can regulate enterocyte function directly. We therefore tested the hypothesis that enterocytes have specific opioid receptors. 2. Villus and crypt jejunal epithelial cells were isolated by the distended sac method from anaesthetized guinea-pigs. Flow cytometry was used to resolve enterocytes from other cell types and to determine whether binding of a fluorescently labelled opioid antagonist, naltrexone-FITC, could be prevented by unlabelled mu- and delta-opioid receptor agonists. A population of crypt enterocytes (approximately 21%) exhibited high-affinity naltrexone-FITC binding to both mu- and delta-type binding sites that was stereoselective and sodium dependent. Villus enterocytes did not exhibit any of these characteristics. 3. Basal cAMP production was elevated in both villus and crypt cells treated with IBMX (3-isobutyl-1-methylxanthine). Villus cells did not respond to 100 nM vasoactive intestinal peptide (VIP), nor were they affected by opioid peptides. In contrast, 100 nM VIP significantly increased cAMP production in crypt epithelial cells, which was significantly reduced by both morphiceptin and D-Ser2-Leu-Enk-Thr. This opioid-mediated effect was stereoselective and blocked by the opioid receptor antagonist naltrexone. 4. These experiments suggest that enterocytes isolated from the crypt epithelium of guineapigs have both mu- and delta-types of opioid receptors. It is possible that these cells participate in opioid-mediated regulation of intestinal secretion. Images Figure 12 PMID:8951719

  7. Naloxegol: First oral peripherally acting mu opioid receptor antagonists for opioid-induced constipation

    PubMed Central

    Anantharamu, Tejus; Sharma, Sushil; Gupta, Ajay Kumar; Dahiya, Navdeep; Singh Brashier, Dick B.; Sharma, Ashok Kumar

    2015-01-01

    Opioid-induced constipation (OIC) is one of the most troublesome and the most common effects of opioid use leading to deterioration in quality of life of the patients and also has potentially deleterious repercussions on adherence and compliance to opioid therapy. With the current guidelines advocating liberal use of opioids by physicians even for non-cancer chronic pain, the situation is further complicated as these individuals are not undergoing palliative care and hence there cannot be any justification to subject these patients to the severe constipation brought on by opioid therapy which is no less debilitating than the chronic pain. The aim in these patients is to prevent the opioid-induced constipation but at the same time allow the analgesic activity of opioids. Many drugs have been used with limited success but the most specific among them were the peripherally acting mu opioid receptor antagonists (PAMORA). Methylnaltrexone and alvimopan were the early drugs in this group but were not approved for oral use in OIC. However naloxegol, the latest PAMORA has been very recently approved as the first oral drug for OIC. This article gives an overview of OIC, its current management and more specifically the development and approval of naloxegol, including pharmacokinetics, details of various clinical trials, adverse effects and its current status for the management of OIC. PMID:26312011

  8. Clinically employed opioid analgesics produce antinociception via μ-δ opioid receptor heteromers in Rhesus monkeys.

    PubMed

    Yekkirala, Ajay S; Banks, Matthew L; Lunzer, Mary M; Negus, Stevens S; Rice, Kenner C; Portoghese, Philip S

    2012-09-19

    Morphine and related drugs are widely employed as analgesics despite the side effects associated with their use. Although morphine is thought to mediate analgesia through mu opioid receptors, delta opioid receptors have been implicated in mediating some side effects such as tolerance and dependence. Here we present evidence in rhesus monkeys that morphine, fentanyl, and possibly methadone selectively activate mu-delta heteromers to produce antinociception that is potently antagonized by the delta opioid receptor antagonist, naltrindole (NTI). Studies with HEK293 cells expressing mu-delta heteromeric opioid receptors exhibit a similar antagonism profile of receptor activation in the presence of NTI. In mice, morphine was potently inhibited by naltrindole when administered intrathecally, but not intracerebroventricularly, suggesting the possible involvement of mu-delta heteromers in the spinal cord of rodents. Taken together, these results strongly suggest that, in primates, mu-delta heteromers are allosterically coupled and mediate the antinociceptive effects of three clinically employed opioid analgesics that have been traditionally viewed as mu-selective. Given the known involvement of delta receptors in morphine tolerance and dependence, our results implicate mu-delta heteromers in mediating both antinociception and these side effects in primates. These results open the door for further investigation in humans.

  9. Opioid receptors and cardioprotection - 'opioidergic conditioning' of the heart.

    PubMed

    Headrick, John P; See Hoe, Louise E; Du Toit, Eugene F; Peart, Jason N

    2015-04-01

    Ischaemic heart disease (IHD) remains a major cause of morbidity/mortality globally, firmly established in Westernized or 'developed' countries and rising in prevalence in developing nations. Thus, cardioprotective therapies to limit myocardial damage with associated ischaemia-reperfusion (I-R), during infarction or surgical ischaemia, is a very important, although still elusive, clinical goal. The opioid receptor system, encompassing the δ (vas deferens), κ (ketocyclazocine) and μ (morphine) opioid receptors and their endogenous opioid ligands (endorphins, dynorphins, enkephalins), appears as a logical candidate for such exploitation. This regulatory system may orchestrate organism and organ responses to stress, induces mammalian hibernation and associated metabolic protection, triggers powerful adaptive stress resistance in response to ischaemia/hypoxia (preconditioning), and mediates cardiac benefit stemming from physical activity. In addition to direct myocardial actions, central opioid receptor signalling may also enhance the ability of the heart to withstand I-R injury. The δ- and κ-opioid receptors are strongly implicated in cardioprotection across models and species (including anti-infarct and anti-arrhythmic actions), with mixed evidence for μ opioid receptor-dependent protection in animal and human tissues. A small number of clinical trials have provided evidence of cardiac benefit from morphine or remifentanil in cardiopulmonary bypass or coronary angioplasty patients, although further trials of subtype-specific opioid receptor agonists are needed. The precise roles and utility of this GPCR family in healthy and diseased human myocardium, and in mediating central and peripheral survival responses, warrant further investigation, as do the putative negative influences of ageing, IHD co-morbidities, and relevant drugs on opioid receptor signalling and protective responses.

  10. Interactions between opioid-peptides-containing pathways and GABA(A)-receptors-mediated systems modulate panic-like-induced behaviors elicited by electric and chemical stimulation of the inferior colliculus.

    PubMed

    Calvo, Fabrício; Coimbra, Norberto Cysne

    2006-08-09

    Aiming to clarify the effect of interactive interconnections between the endogenous opioid peptides-neural links and GABAergic pathways on panic-like responses, in the present work, the effect of the peripheral and central administration of morphine or the non-specific opioid receptors antagonist naloxone was evaluated on the fear-induced responses (defensive attention, defensive immobility and escape behavior) elicited by electric and chemical stimulation of the inferior colliculus. Central microinjections of opioid drugs in the inferior colliculus were also performed followed by local administration of the GABA(A)-receptor antagonist bicuculline. The defensive behavior elicited by the blockade of GABAergic receptors in the inferior colliculus had been quantitatively analyzed, recording the number of crossing, jump, rotation and rearing, in each minute, during 30 min, in the open-field test. The opioid receptors stimulation with morphine decreased the defensive attention, the defensive immobility and escape behavior thresholds, and the non-specific opioid receptors blockade caused opposite effects, enhancing the defensive behavior thresholds. These effects were corroborated by either the stimulation or the inhibition of opioid receptors followed by the GABA(A) receptor blockade with bicuculline, microinjected into the inferior colliculus. There was a significant increase in the diverse fear-induced responses caused by bicuculline with the pretreatment of the inferior colliculus with morphine, and the opposite effect was recorded after the pretreatment of the inferior colliculus nuclei with naloxone followed by bicuculline local administration. These findings suggest an interaction between endogenous opioid-peptides-containing connections and GABA(A)-receptor-mediated system with direct influence on the organization of the panic-like or fear-induced responses elaborated in the inferior colliculus during critical emotional states.

  11. Anti-nociception mediated by a κ opioid receptor agonist is blocked by a δ receptor agonist

    PubMed Central

    Taylor, A M W; Roberts, K W; Pradhan, A A; Akbari, H A; Walwyn, W; Lutfy, K; Carroll, F I; Cahill, C M; Evans, C J

    2015-01-01

    BACKGROUND AND PURPOSE The opioid receptor family comprises four structurally homologous but functionally distinct sub-groups, the μ (MOP), δ (DOP), κ (KOP) and nociceptin (NOP) receptors. As most opioid agonists are selective but not specific, a broad spectrum of behaviours due to activation of different opioid receptors is expected. In this study, we examine whether other opioid receptor systems influenced KOP-mediated antinociception. EXPERIMENTAL APPROACH We used a tail withdrawal assay in C57Bl/6 mice to assay the antinociceptive effect of systemically administered opioid agonists with varying selectivity at KOP receptors. Pharmacological and genetic approaches were used to analyse the interactions of the other opioid receptors in modulating KOP-mediated antinociception. KEY RESULTS Etorphine, a potent agonist at all four opioid receptors, was not anti-nociceptive in MOP knockout (KO) mice, although etorphine is an efficacious KOP receptor agonist and specific KOP receptor agonists remain analgesic in MOP KO mice. As KOP receptor agonists are aversive, we considered KOP-mediated antinociception might be a form of stress-induced analgesia that is blocked by the anxiolytic effects of DOP receptor agonists. In support of this hypothesis, pretreatment with the DOP antagonist, naltrindole (10 mg·kg−1), unmasked etorphine (3 mg·kg−1) antinociception in MOP KO mice. Further, in wild-type mice, KOP-mediated antinociception by systemic U50,488H (10 mg·kg−1) was blocked by pretreatment with the DOP agonist SNC80 (5 mg·kg−1) and diazepam (1 mg·kg−1). CONCLUSIONS AND IMPLICATIONS Systemic DOP receptor agonists blocked systemic KOP antinociception, and these results identify DOP receptor agonists as potential agents for reversing stress-driven addictive and depressive behaviours mediated through KOP receptor activation. LINKED ARTICLES This article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles

  12. Wheat peptides reduce oxidative stress and inhibit NO production through modulating μ-opioid receptor in a rat NSAID-induced stomach damage model.

    PubMed

    Yin, Hong; Cai, Hui-Zhen; Wang, Shao-Kang; Yang, Li-Gang; Sun, Gui-Ju

    2015-01-01

    Non-steroidal anti-inflammatory drugs (NSAIDs) induce tissue damage and oxidative stress in animal models of stomach damage. In the present study, the protective effects of wheat peptides were evaluated in a NSAID-induced stomach damage model in rats. Different doses of wheat peptides or distilled water were administered daily by gavage for 30 days before the rat stomach damage model was established by administration of NSAIDs (aspirin and indomethacin) into the digestive tract twice. The treatment of wheat peptides decreased the NSAID-induced gastric epithelial cell degeneration and oxidative stress and NO levels in the rats. Wheat peptides significantly increased the superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities and decreased iNOS activity in stomach. The mRNA expression level of μ-opioid receptor was significantly decreased in wheat peptides-treated rats than that in in the control rats. The results suggest that NSAID drugs induced stomach damage in rats, wchih can be prevented by wheat peptides. The mechanisms for the protective effects were most likely through reducing NSAID-induced oxidative stress.

  13. TGF-β and opioid receptor signaling crosstalk results in improvement of endogenous and exogenous opioid analgesia under pathological pain conditions.

    PubMed

    Lantero, Aquilino; Tramullas, Mónica; Pílar-Cuellar, Fuencisla; Valdizán, Elsa; Santillán, Rosa; Roques, Bernard P; Hurlé, María A

    2014-04-09

    Transforming growth factor-β1 (TGF-β1) protects against neuroinflammatory events underlying neuropathic pain. TGF-β signaling enhancement is a phenotypic characteristic of mice lacking the TGF-β pseudoreceptor BAMBI (BMP and activin membrane-bound inhibitor), which leads to an increased synaptic release of opioid peptides and to a naloxone-reversible hypoalgesic/antiallodynic phenotype. Herein, we investigated the following: (1) the effects of BAMBI deficiency on opioid receptor expression, functional efficacy, and analgesic responses to endogenous and exogenous opioids; and (2) the involvement of the opioid system in the antiallodynic effect of TGF-β1. BAMBI-KO mice were subjected to neuropathic pain by sciatic nerve crash injury (SNI). Gene (PCR) and protein (Western blot) expressions of μ- and δ-opioid receptors were determined in the spinal cord. The inhibitory effects of agonists on the adenylyl cyclase pathway were investigated. Two weeks after SNI, wild-type mice developed mechanical allodynia and the functionality of μ-opioid receptors was reduced. By this time, BAMBI-KO mice were protected against allodynia and exhibited increased expression and function of opioid receptors. Four weeks after SNI, when mice of both genotypes had developed neuropathic pain, the analgesic responses induced by morphine and RB101 (an inhibitor of enkephalin-degrading enzymes, which increases the synaptic levels of enkephalins) were enhanced in BAMBI-KO mice. Similar results were obtained in the formalin-induced chemical-inflammatory pain model. Subcutaneous TGF-β1 infusion prevented pain development after SNI. The antiallodynic effect of TGF-β1 was naloxone-sensitive. In conclusion, modulation of the endogenous opioid system by TGF-β signaling improves the analgesic effectiveness of exogenous and endogenous opioids under pathological pain conditions.

  14. Delta Opioid Receptor and Its Peptide: A Receptor-Ligand Neuroprotection

    PubMed Central

    Staples, Meaghan; Acosta, Sandra; Tajiri, Naoki; Pabon, Mibel; Kaneko, Yuji; Borlongan, Cesar V.

    2013-01-01

    In pursuit of neurological therapies, the opioid system, specifically delta opioid receptors and delta opioid peptides, demonstrates promising therapeutic potential for stroke, Parkinson’s disease, and other degenerative neurological conditions. Recent studies offer strong evidence in support of the therapeutic use of delta opioid receptors, and provide insights into the underlying mechanisms of action. Delta opioid receptors have been shown to confer protective effects by mediating ionic homeostasis and activating endogenous neuroprotective pathways. Additionally, delta opioid agonists such as (D-Ala 2, D-Leu 5) enkephalin (DADLE) have been shown to decrease apoptosis and promote neuronal survival. In its entirety, the delta opioid system represents a promising target for neural therapies. PMID:23979422

  15. Biased Agonism of Endogenous Opioid Peptides at the μ-Opioid Receptor.

    PubMed

    Thompson, Georgina L; Lane, J Robert; Coudrat, Thomas; Sexton, Patrick M; Christopoulos, Arthur; Canals, Meritxell

    2015-08-01

    Biased agonism is having a major impact on modern drug discovery, and describes the ability of distinct G protein-coupled receptor (GPCR) ligands to activate different cell signaling pathways, and to result in different physiologic outcomes. To date, most studies of biased agonism have focused on synthetic molecules targeting various GPCRs; however, many of these receptors have multiple endogenous ligands, suggesting that "natural" bias may be an unappreciated feature of these GPCRs. The μ-opioid receptor (MOP) is activated by numerous endogenous opioid peptides, remains an attractive therapeutic target for the treatment of pain, and exhibits biased agonism in response to synthetic opiates. The aim of this study was to rigorously assess the potential for biased agonism in the actions of endogenous opioids at the MOP in a common cellular background, and compare these to the effects of the agonist d-Ala2-N-MePhe4-Gly-ol enkephalin (DAMGO). We investigated activation of G proteins, inhibition of cAMP production, extracellular signal-regulated kinase 1 and 2 phosphorylation, β-arrestin 1/2 recruitment, and MOP trafficking, and applied a novel analytical method to quantify biased agonism. Although many endogenous opioids displayed signaling profiles similar to that of DAMGO, α-neoendorphin, Met-enkephalin-Arg-Phe, and the putatively endogenous peptide endomorphin-1 displayed particularly distinct bias profiles. These may represent examples of natural bias if it can be shown that they have different signaling properties and physiologic effects in vivo compared with other endogenous opioids. Understanding how endogenous opioids control physiologic processes through biased agonism can reveal vital information required to enable the design of biased opioids with improved pharmacological profiles and treat diseases involving dysfunction of the endogenous opioid system.

  16. β-arrestins: regulatory role and therapeutic potential in opioid and cannabinoid receptor-mediated analgesia.

    PubMed

    Raehal, Kirsten M; Bohn, Laura M

    2014-01-01

    Pain is a complex disorder with neurochemical and psychological components contributing to the severity, the persistence, and the difficulty in adequately treating the condition. Opioid and cannabinoids are two classes of analgesics that have been used to treat pain for centuries and are arguably the oldest of "pharmacological" interventions used by man. Unfortunately, they also produce several adverse side effects that can complicate pain management. Opioids and cannabinoids act at G protein-coupled receptors (GPCRs), and much of their effects are mediated by the mu-opioid receptor (MOR) and cannabinoid CB1 receptor (CB1R), respectively. These receptors couple to intracellular second messengers and regulatory proteins to impart their biological effects. In this chapter, we review the role of the intracellular regulatory proteins, β-arrestins, in modulating MOR and CB1R and how they influence the analgesic and side-effect profiles of opioid and cannabinoid drugs in vivo. This review of the literature suggests that the development of opioid and cannabinoid agonists that bias MOR and CB1R toward G protein signaling cascades and away from β-arrestin interactions may provide a novel mechanism by which to produce analgesia with less severe adverse effects.

  17. β-Arrestins: Regulatory Role and Therapeutic Potential in Opioid and Cannabinoid Receptor-Mediated Analgesia

    PubMed Central

    Bohn, Laura M.

    2016-01-01

    Pain is a complex disorder with neurochemical and psychological components contributing to the severity, the persistence, and the difficulty in adequately treating the condition. Opioid and cannabinoids are two classes of analgesics that have been used to treat pain for centuries and are arguably the oldest of “pharmacological” interventions used by man. Unfortunately, they also produce several adverse side effects that can complicate pain management. Opioids and cannabinoids act at G protein-coupled receptors (GPCRs), and much of their effects are mediated by the mu-opioid receptor (MOR) and cannabinoid CB1 receptor (CB1R), respectively. These receptors couple to intracellular second messengers and regulatory proteins to impart their biological effects. In this chapter, we review the role of the intracellular regulatory proteins, β-arrestins, in modulating MOR and CB1R and how they influence the analgesic and side-effect profiles of opioid and cannabinoid drugs in vivo. This review of the literature suggests that the development of opioid and cannabinoid agonists that bias MOR and CB1R toward G protein signaling cascades and away from β-arrestin interactions may provide a novel mechanism by which to produce analgesia with less severe adverse effects. PMID:24292843

  18. Combined autoradiographic-immunocytochemical analysis of opioid receptors and opioid peptide neuronal systems in brain

    SciTech Connect

    Lewis, M.E.; Khachaturian, H.; Watson, S.J.

    1985-01-01

    Using adjacent section autoradiography-immunocytochemistry, the distribution of (TH)naloxone binding sites was studied in relation to neuronal systems containing (Leu)enkephalin, dynorphin A, or beta-endorphin immunoreactivity in rat brain. Brain sections from formaldehyde-perfused rats show robust specific binding of (TH)naloxone, the pharmacological (mu-like) properties of which appear unaltered. In contrast, specific binding of the delta ligand (TH)D-Ala2,D-Leu5-enkephalin was virtually totally eliminated as a result of formaldehyde perfusion. Using adjacent section analysis, the authors have noted associations between (TH)naloxone binding sites and one, two, or all three opioid systems in different brain regions; however, in some areas, no apparent relationship could be observed. Within regions, the relationship was complex. The complexity of the association between (TH)naloxone binding sites and the multiple opioid systems, and previous reports of co-localization of mu and kappa receptors in rat brain, are inconsistent with a simple-one-to-one relationship between a given opioid precursor and opioid receptor subtype. Instead, since differential processing of the three precursors gives rise to peptides of varying receptor subtype potencies and selectivities, the multiple peptide-receptor relationships may point to a key role of post-translational processing in determining the physiological consequences of opioid neurotransmission.

  19. [Endomorphins--endogenous ligands of the mu-opioid receptor].

    PubMed

    Perlikowska, Renata; Fichna, Jakub; Janecka, Anna

    2009-01-01

    Two endogenous opioid peptides with extremely high mu-opioid receptor affinity and selectivity, endomorphin-1 and endomorphin-2, were: discovered and isolated from the mammalian brain in 1997. Endomorphins are amidated tetrapeptides, structurally different from so called typical opioids: enkephalins, dynorphins and endorphins. A protein precursor of endomorphins and a gene encoding their sequence remain unknown. Endomorphins are unable to cross the blood-brain barrier because of their low hydrophobicity. In animal models, these peptides turned out to be very potent in relieving neuropathic and inflammatory pain. In comparison with morphine, a prototype opioid receptor ligand, endomorphins produces less undesired side effects. In this article we describe the discovery of endomorphins, their cellular localization and functions in the organism, as well as their structure-activity relationships and biodegradation pathways.

  20. Periaqueductal gray μ and κ opioid receptors determine behavioral selection from maternal to predatory behavior in lactating rats.

    PubMed

    Klein, Marianne Orlandini; Cruz, Aline de Mello; Machado, Franciele Corrêa; Picolo, Gisele; Canteras, Newton Sabino; Felicio, Luciano Freitas

    2014-11-01

    Every mother must optimize her time between caring for her young and her subsistence. The rostro lateral portion of the periaqueductal grey (rlPAG) is a critical site that modulates the switch between maternal and predatory behavior. Opioids play multiple roles in both maternal behavior and this switching process. The present study used a pharmacological approach to evaluate the functional role of rlPAG μ and κ opioid receptors in behavioral selection. Rat dams were implanted with a guide cannula in the rlPAG and divided into three experiments in which we tested the role of opioid agonists (Experiment 1), the influence of μ and κ opioid receptor blockade in the presence of morphine (Experiment 2), and the influence of μ and κ opioid receptor blockade (Experiment 3). After behavioral test, in Experiment 4, we evaluated rlPAG μ and κ receptor activation in all Experiments 1-3. The results showed that massive opioidergic activation induced by morphine in the rlPAG inhibited maternal behavior without interfering with predatory hunting. No behavioral changes and no receptor activation were promoted by the specific agonist alone. However, κ receptor blockade increased hunting behavior and increased the level of μ receptor activation in the rlPAG. Thus, endogenous opioidergic tone might be modulated by a functional interaction between opioid receptor subtypes. Such a compensatory receptor interaction appears to be relevant for behavioral selection among motivated behaviors. These findings indicate a role for multiple opioid receptor interactions in the modulation of behavioral selection between maternal and predatory behaviors in the PAG.

  1. Dysregulation of kappa-opioid receptor systems by chronic nicotine modulate the nicotine withdrawal syndrome in an age-dependent manner

    PubMed Central

    Tejeda, Hugo A.; Natividad, Luis A.; Orfila, James E.; Torres, Oscar V.; O’Dell, Laura E.

    2012-01-01

    Rationale The mechanisms that mediate age differences during nicotine withdrawal are unclear. Objective This study compared kappa opioid receptor (KOR) activation in naïve and nicotine-treated adolescent and adult rats using behavioral and neurochemical approaches to study withdrawal. Methods The behavioral models used to assess withdrawal included conditioned place and elevated plus maze procedures. Deficits in dopamine transmission in the nucleus accumbens (NAcc) were examined using microdialysis procedures. Lastly, the effects of KOR stimulation and blockade on physical signs produced upon removal of nicotine were examined in adults. Results Nicotine-treated adults displayed a robust aversion to an environment paired with a KOR agonist versus naïve adults. Neither of the adolescent groups displayed a place aversion. KOR activation produced an increase in anxiety-like behavior that was highest in nicotine-treated adults versus all other groups. KOR activation produced a decrease in NAcc dopamine that was largest in nicotine-treated adults versus all other groups. Lastly, KOR activation facilitated physical signs of upon removal of nicotine and KOR blockade reduced this effect. Conclusion Chronic nicotine enhanced the affective, anxiogenic, and neurochemical effects produced by KOR activation in adult rats. Our data suggest that chronic nicotine elicits an increase in KOR function, and this may contribute to nicotine withdrawal since KOR activation facilitated and KOR blockade prevented withdrawal signs upon removal of nicotine. Given that chronic nicotine facilitated the neurochemical effects of KOR agonists in adults but not adolescents, it is suggested that KOR regulation of mesolimbic dopamine may contribute to age differences in nicotine withdrawal. PMID:22659976

  2. Biased mu-opioid receptor ligands: a promising new generation of pain therapeutics.

    PubMed

    Siuda, Edward R; Carr, Richard; Rominger, David H; Violin, Jonathan D

    2016-12-06

    Opioid chemistry and biology occupy a pivotal place in the history of pharmacology and medicine. Morphine offers unmatched efficacy in alleviating acute pain, but is also associated with a host of adverse side effects. The advent of biased agonism at G protein-coupled receptors has expanded our understanding of intracellular signaling and highlighted the concept that certain ligands are able to differentially modulate downstream pathways. The ability to target one pathway over another has allowed for the development of biased ligands with robust clinical efficacy and fewer adverse events. In this review we summarize these concepts with an emphasis on biased mu opioid receptor pharmacology and highlight how far opioid pharmacology has evolved.

  3. Endogenous μ-opioid peptides modulate immune response towards malignant melanoma.

    PubMed

    Boehncke, Sandra; Hardt, Katja; Schadendorf, Dirk; Henschler, Reinhard; Boehncke, Wolf-Henning; Duthey, Beatrice

    2011-01-01

    Opioids exert major effects not only in the central nervous system but also in immune responses. We investigated the effects of μ-opioid peptides, secreted by tumor cells, on anti-tumor immune responses. For this purpose, tumor growth was studied in wild-type and μ-opioid receptor-deficient (MOR-/-) mice injected with B16 melanoma cells. The ability of these cells to produce opioids was studied by Western blots in vitro. Finally, biopsy material from human melanomas was investigated by immunohistochemistry for ß endorphin expression. Injection of B16 melanoma cells, producing endogenous ß endorphin, in the flank of MOR-/- mice revealed a profound reduction in tumor growth, paralleled by a significantly higher infiltration of immune cells into the tumors, when compared to tumor growth after injection of B16 melanoma cells into wild-type mice. Opioids present in B16 cell supernatant significantly reduced the proliferation of normal but not MOR-/- leucocytes. Immunohistochemical analyses of biopsies from human melanoma tissues showed a positive correlation between expression of ß endorphin and tumor progression. Our data provide evidence that μ-opioid peptides may play a major role in cancer progression by modulating immune response. This finding may have implications for the future optimization of immunointerventions for cancer.

  4. Nucleus accumbens μ-opioid receptors mediate social reward.

    PubMed

    Trezza, Viviana; Damsteegt, Ruth; Achterberg, E J Marijke; Vanderschuren, Louk J M J

    2011-04-27

    Positive social interactions are essential for emotional well-being and proper behavioral development of young individuals. Here, we studied the neural underpinnings of social reward by investigating the involvement of opioid neurotransmission in the nucleus accumbens (NAc) in social play behavior, a highly rewarding social interaction in adolescent rats. Intra-NAc infusion of morphine (0.05-0.1 μg) increased pinning and pouncing, characteristic elements of social play behavior in rats, and blockade of NAc opioid receptors with naloxone (0.5 μg) prevented the play-enhancing effects of systemic morphine (1 mg/kg, s.c.) administration. Thus, stimulation of opioid receptors in the NAc was necessary and sufficient for morphine to increase social play. Intra-NAc treatment with the selective μ-opioid receptor agonist [D-Ala(2),N-MePhe(4),Gly(5)-ol]enkephalin (DAMGO) (0.1-10 ng) and the μ-opioid receptor antagonist Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH(2) (CTAP) (0.3-3 μg) increased and decreased social play, respectively. The δ-opioid receptor agonist DPDPE ([D-Pen(2),D-Pen(5)]-enkephalin) (0.3-3 μg) had no effects, whereas the κ-opioid receptor agonist U69593 (N-methyl-2-phenyl-N-[(5R,7S,8S)-7-(pyrrolidin-1-yl)-1-oxaspiro[4.5]dec-8-yl]acetamide) (0.01-1 μg) decreased social play. Intra-NAc treatment with β-endorphin (0.01-1 μg) increased social play, but met-enkephalin (0.1-5 μg) and the enkephalinase inhibitor thiorphan (0.1-1 μg) were ineffective. DAMGO (0.1-10 ng) increased social play after infusion into both the shell and core subregions of the NAc. Last, intra-NAc infusion of CTAP (3 μg) prevented the development of social play-induced conditioned place preference. These findings identify NAc μ-opioid receptor stimulation as an important neural mechanism for the attribution of positive value to social interactions in adolescent rats. Altered NAc μ-opioid receptor function may underlie social impairments in psychiatric disorders such as autism

  5. Non-analgesic effects of opioids: management of opioid-induced constipation by peripheral opioid receptor antagonists: prevention or withdrawal?

    PubMed

    Holzer, Peter

    2012-01-01

    The therapeutic action of opioid analgesics is compromised by peripheral adverse effects among which opioid-induced constipation (OIC) is the most disabling, with a prevalence reported to vary between 15 and 90 %. Although OIC is usually treated with laxatives, there is insufficient clinical evidence that laxatives are efficacious in this indication. In contrast, there is ample evidence from double- blind, randomized and placebo-controlled trials that peripheral opioid receptor antagonists (PORAs) counteract OIC. This specific treatment modality is currently based on subcutaneous methylnaltrexone for the interruption of OIC in patients with advanced illness, and a fixed combination of oral prolonged-release naloxone with prolonged-release oxycodone for the prevention of OIC in the treatment of non-cancer and cancer pain. Both drugs counteract OIC while the analgesic effect of opioids remains unabated. The clinical studies show that more than 50 % of the patients with constipation under opioid therapy may benefit from the use of PORAs, while PORA-resistant patients are likely to suffer from non-opioid-induced constipation, the prevalence of which increases with age. While the addition of naloxone to oxycodone seems to act by preventing OIC, the intermittent dosing of methylnaltrexone every other day seems to stimulate defaecation by provoking an intestinal withdrawal response. The availability of PORAs provides a novel opportunity to specifically control OIC and other peripheral adverse effects of opioid analgesics (e.g., urinary retention and pruritus). The continuous dosing of a PORA has the advantage of few adverse effects, while intermittent dosing of a PORA can be associated with abdominal cramp-like pain.

  6. Opioid receptor agonists reduce brain edema in stroke.

    PubMed

    Yang, Li; Wang, Hezhen; Shah, Kaushik; Karamyan, Vardan T; Abbruscato, Thomas J

    2011-04-06

    Cerebral edema is a leading cause of mortality in stroke patients. The purpose of this study was to assess a non-selective opioid receptor agonist, biphalin, in decreasing reducing brain edema formation using both in vitro and in vivo models of stroke. For the in situ model of ischemia, hippocampal slices were exposed to oxygen glucose deprivation (OGD) conditions and we observed that hippocampal water content was increased, compared to normoxia. Treatment with the mu agonist, Tyr-D-Ala', N-CH, -Phe4, Glyol-Enkephalin (DAMGO), delta opioid agonists, D-pen(2), D-phe(5) enkephalin (DPDPE), and kappa agonist, U50 488, all significantly decreased brain slice water gain. Interestingly, the non-selective agonist, biphalin, exhibited a statistically significant (P<0.01) greater effect in decreasing water content in OGD-exposed hippocampal slices, compared with mu, delta, and kappa selective opioid agonists. Moreover, biphalin exhibited anti-edematous effects in a dose responsive manner. The non-selective opioid antagonist, naloxone, returned the water content nearly back to original OGD values for all opioid agonist treatments, supporting that these effects were mediated by an opioid receptor pathway. Furthermore, biphalin significantly decreased edema (53%) and infarct (48%) ratios, and neuronal recovery from stroke, compared with the vehicle-treated groups in a 12h permanent middle cerebral artery occlusion (MCAO) model of focal ischemia. Biphalin also significantly decreased the cell volume increase in primary neuronal cells exposed to OGD condition. These data suggest that opioid receptor activation may provide neuroprotection during stroke and further investigations are needed in the development of novel opioid agonist as efficacious treatments for brain ischemia.

  7. Actions of tilidine and nortilidine on cloned opioid receptors.

    PubMed

    Thierry, Christophe; Boeynaems, Jean-Marie; Paolo, Meoni

    2005-01-04

    Tilidine, alone or combined with naloxone to prevent drug abuse, is used as an oral opioid analgesic. Although the analgesic action of tilidine and its active metabolite nortilidine is reversed by naloxone and therefore believed to involve the activation of the Mu opioid (MOP, OP3, mu) receptor, this has never been studied in recombinant systems. We have measured the selectivity of tilidine and nortilidine for human opioid and opioid-like receptors stably expressed in CHO-K1 cells, using the inhibition of the forskolin (FK)-induced accumulation of cAMP as endpoint. In cells expressing the MOP receptor, tilidine and nortilidine inhibited cAMP accumulation with IC50 of 11 microM and 110 nM, respectively. The agonist effects of nortilidine and [D-Ala2-MePhe4-Gly5-ol]enkephalin (DAMGO) on the MOP receptor were reversed by naloxone with very similar IC50 (1.2 versus 1.8 nM). At concentrations up to 100 microM, tilidine and nortilidine had no agonist effect on the DOP, KOP and NOP receptors. In conclusion, this study on cloned human receptors demonstrates that nortilidine is a selective agonist of the MOP receptor.

  8. Opioid receptors regulate the extinction of Pavlovian fear conditioning.

    PubMed

    McNally, Gavan P; Westbrook, R Frederick

    2003-12-01

    Rats received a single pairing of an auditory conditioned stimulus (CS) with a footshock unconditioned stimulus (US). The fear (freezing) that had accrued to the CS was then extinguished. Injection of naloxone prior to this extinction significantly impaired the development of extinction. This impairment was mediated by opioid receptors in the brain and was not observed when naloxone was injected after extinction training. Finally, an injection of naloxone on test failed to reinstate extinguished responding that had already accrued to the CS. These experiments show that opioid receptors regulate the development, but not the expression, of fear extinction and are discussed with reference to the roles of opioid receptors in US processing, memory, and appetitive motivation.

  9. Role of opioid receptors in the reinstatement of opioid-seeking behavior: an overview.

    PubMed

    Fattore, Liana; Fadda, Paola; Antinori, Silvia; Fratta, Walter

    2015-01-01

    Opioid abuse in humans is characterized by discontinuous periods of drug use and abstinence. With time, the probability of falling into renewed drug consumption becomes particularly high and constitutes a considerable problem in the management of heroin addicts. The major problem in the treatment of opioid dependence still remains the occurrence of relapse, to which stressful life events, renewed use of heroin, and exposure to drug-associated environmental cues are all positively correlated. To study the neurobiology of relapse, many research groups currently use the reinstatement animal model, which greatly contributed to disentangle the mechanisms underlying relapse to drug-seeking in laboratory animals. The use of this model is becoming increasingly popular worldwide, and new versions have been recently developed to better appreciate the differential contribution of each opioid receptor subtype to the relapse phenomenon. In this chapter we review the state of the art of our knowledge on the specific role of the opioid receptors as unrevealed by the reinstatement animal model of opioid-seeking behavior.

  10. Supraspinal peroxynitrite modulates pain signaling by suppressing the endogenous opioid pathway

    PubMed Central

    Little, Joshua W.; Chen, Zhoumou; Doyle, Tim; Porreca, Frank; Ghaffari, Mahsa; Neumann, William L.; Salvemini, Daniela

    2012-01-01

    Peroxynitrite (PN, ONOO−) is a potent oxidant and nitrating agent that contributes to pain through peripheral and spinal mechanisms, but its supraspinal role is unknown. We present evidence here that PN in the rostral ventromedial medulla (RVM) is essential for descending nociceptive modulation in rats during inflammatory and neuropathic pain through PN-mediated suppression of opioid signaling. Carrageenan-induced thermal hyperalgesia was associated with increased 3-nitrotyrosine (NT), a PN biomarker, in the RVM. Furthermore, intra-RVM microinjections of the PN decomposition catalyst (PNDC), Fe(III)-5,10,15,20-tetrakis(N-methyl-pyridinium-4-yl)porphyrin (FeTMPyP5+) dose-dependently reversed this thermal hyperalgesia. These effects of FeTMPyP5+ were abrogated by intra-RVM naloxone, implicating potential interplay between PN and opioids. In support, we identified NT co-localization with the endogenous opioid, enkephalin (ENK), in the RVM during thermal hyperalgesia, suggesting potential in situ interactions. To address the functional significance of such interactions, we exposed methionine-enkephalin (MENK) to PN and identified the major metabolite, 3-nitrotyrosine-methionine-sulfoxide (NSO-MENK), using liquid chromatography-mass spectrometry (LCMS). Next, we isolated, purified, and tested NSO-MENK for opioid receptor binding affinity and analgesic effects. Compared to MENK, this NSO-MENK metabolite lacked appreciable binding affinity for δ, µ, and κ opioid receptors. Intrathecal injection of NSO-MENK in rats did not evoke antinociception suggesting that PN-mediated chemical modifications of ENK suppress opioid signaling. When extended to chronic pain, intra-RVM FeTMPyP5+ produced naloxone-sensitive reversal of mechanical allodynia in rats following chronic constriction injury (CCI) of the sciatic nerve. Collectively, our data reveal the central role of PN in RVM descending facilitation during inflammatory and neuropathic pain potentially through anti-opioid

  11. Peripheral δ-opioid receptors attenuate the exercise pressor reflex.

    PubMed

    Leal, Anna K; Yamauchi, Katsuya; Kim, Joyce; Ruiz-Velasco, Victor; Kaufman, Marc P

    2013-10-15

    In rats with ligated femoral arteries, the exercise pressor reflex is exaggerated, an effect that is attenuated by stimulation of peripheral μ-opioid receptors on group IV metabosensitive afferents. In contrast, δ-opioid receptors are expressed mostly on group III mechanosensitive afferents, a finding that prompted us to determine whether stimulation of these opioid receptors could also attenuate the exaggerated exercise pressor reflex in "ligated" rats. We found femoral arterial injection of [D-Pen2,D-Pen5]enkephalin (DPDPE; 1.0 μg), a δ-opioid agonist, significantly attenuated the pressor and cardioaccelerator components of the exercise pressor reflex evoked by hindlimb muscle contraction in both rats with ligated and patent femoral arteries. DPDPE significantly decreased the pressor responses to muscle mechanoreflex activation, evoked by tendon stretch, in ligated rats only. DPDPE (1.0 μg) had no effect in either group on the pressor and cardioaccelerator responses to capsaicin (0.2 μg), which primarily stimulates group IV afferents. DPDPE (1.0 μg) had no effect on the pressor and cardioaccelerator responses to lactic acid (24 mM), which stimulates group III and IV afferents, in rats with patent femoral arteries but significantly decreased the pressor response in ligated rats. Western blots revealed the amount of protein comprising the δ-opioid receptor was greater in dorsal root ganglia innervating hindlimbs with ligated femoral arteries than in dorsal root ganglia innervating hindlimbs with patent femoral arteries. Our findings support the hypothesis that stimulation of δ-opioid receptors on group III afferents attenuated the exercise pressor reflex.

  12. Peripheral δ-opioid receptors attenuate the exercise pressor reflex

    PubMed Central

    Yamauchi, Katsuya; Kim, Joyce; Ruiz-Velasco, Victor; Kaufman, Marc P.

    2013-01-01

    In rats with ligated femoral arteries, the exercise pressor reflex is exaggerated, an effect that is attenuated by stimulation of peripheral μ-opioid receptors on group IV metabosensitive afferents. In contrast, δ-opioid receptors are expressed mostly on group III mechanosensitive afferents, a finding that prompted us to determine whether stimulation of these opioid receptors could also attenuate the exaggerated exercise pressor reflex in “ligated” rats. We found femoral arterial injection of [D-Pen2,D-Pen5]enkephalin (DPDPE; 1.0 μg), a δ-opioid agonist, significantly attenuated the pressor and cardioaccelerator components of the exercise pressor reflex evoked by hindlimb muscle contraction in both rats with ligated and patent femoral arteries. DPDPE significantly decreased the pressor responses to muscle mechanoreflex activation, evoked by tendon stretch, in ligated rats only. DPDPE (1.0 μg) had no effect in either group on the pressor and cardioaccelerator responses to capsaicin (0.2 μg), which primarily stimulates group IV afferents. DPDPE (1.0 μg) had no effect on the pressor and cardioaccelerator responses to lactic acid (24 mM), which stimulates group III and IV afferents, in rats with patent femoral arteries but significantly decreased the pressor response in ligated rats. Western blots revealed the amount of protein comprising the δ-opioid receptor was greater in dorsal root ganglia innervating hindlimbs with ligated femoral arteries than in dorsal root ganglia innervating hindlimbs with patent femoral arteries. Our findings support the hypothesis that stimulation of δ-opioid receptors on group III afferents attenuated the exercise pressor reflex. PMID:23934854

  13. Opioid receptor internalization contributes to dermorphin-mediated antinociception

    PubMed Central

    Macey, Tara A.; Ingram, Susan L.; Bobeck, Erin N.; Hegarty, Deborah M.; Aicher, Sue A.; Arttamangkul, Seksiri; Morgan, Michael M.

    2010-01-01

    Microinjection of opioids into the ventrolateral periaqueductal gray (vlPAG) produces antinociception in part by binding to mu-opioid receptors (MOPrs). Although both high and low efficacy agonists produce antinociception, low efficacy agonists such as morphine produce limited MOPr internalization suggesting that MOPr internalization and signaling leading to antinociception are independent. This hypothesis was tested in awake, behaving rats using DERM-A594, a fluorescently labeled dermorphin analog, and internalization blockers. Microinjection of DERM-A594 into the vlPAG produced both antinociception and internalization of DERM-A594. Administration of the irreversible opioid receptor antagonist beta-CNA prior to DERM-A594 microinjection reduced both the antinociceptive effect and the number of DERM-A594 labeled cells demonstrating that both effects are opioid receptor-mediated. Pretreatment with the internalization blockers dynamin dominant-negative inhibitory peptide (dynamin-DN) and concanavalinA (ConA) attenuated both DERM-A594 internalization and antinociception. Microinjection of dynamin-DN and ConA also decreased the antinociceptive potency of the unlabeled opioid agonist dermorphin when microinjected into the vlPAG as demonstrated by rightward shifts in the dose-response curves. In contrast, administration of dynamin-DN had no effect on the antinociceptive effect of microinjecting the GABAA antagonist bicuculline into the vlPAG. The finding that dermorphin-induced antinociception is attenuated by blocking receptor internalization indicates that key parts of opioid receptor-mediated signaling depend on internalization. PMID:20394808

  14. Morphine Protects against Methylmercury Intoxication: A Role for Opioid Receptors in Oxidative Stress?

    PubMed Central

    Costa-Malaquias, Allan; Almeida, Mauro B.; Souza Monteiro, José R.; Macchi, Barbarella de Matos; do Nascimento, José Luiz M.; Crespo-Lopez, María Elena

    2014-01-01

    Mercury is an extremely dangerous environmental contaminant responsible for episodes of human intoxication throughout the world. Methylmercury, the most toxic compound of this metal, mainly targets the central nervous system, accumulating preferentially in cells of glial origin and causing oxidative stress. Despite studies demonstrating the current exposure of human populations, the consequences of mercury intoxication and concomitant use of drugs targeting the central nervous system (especially drugs used in long-term treatments, such as analgesics) are completely unknown. Morphine is a major option for pain management; its global consumption more than quadrupled in the last decade. Controversially, morphine has been proposed to function in oxidative stress independent of the activation of the opioid receptors. In this work, a therapeutic concentration of morphine partially protected the cellular viability of cells from a C6 glioma cell line exposed to methylmercury. Morphine treatment also reduced lipid peroxidation and totally prevented increases in nitrite levels in those cells. A mechanistic study revealed no alteration in sulfhydryl groups or direct scavenging at this opioid concentration. Interestingly, the opioid antagonist naloxone completely eliminated the protective effect of morphine against methylmercury intoxication, pointing to opioid receptors as the major contributor to this action. Taken together, the experiments in the current study provide the first demonstration that a therapeutic concentration of morphine is able to reduce methylmercury-induced oxidative damage and cell death by activating the opioid receptors. Thus, these receptors may be a promising pharmacological target for modulating the deleterious effects of mercury intoxication. Although additional studies are necessary, our results support the clinical safety of using this opioid in methylmercury-intoxicated patients, suggesting that normal analgesic doses could confer an additional

  15. The critical role of spinal 5-HT7 receptors in opioid and non-opioid type stress-induced analgesia.

    PubMed

    Yesilyurt, Ozgur; Seyrek, Melik; Tasdemir, Serdar; Kahraman, Serdar; Deveci, Mehmet Salih; Karakus, Emre; Halici, Zekai; Dogrul, Ahmet

    2015-09-05

    The opioid and non-opioid types of stress-induced analgesia have been well defined. One of the non-opioid type involve the endocannabinoid system. We previously reported that the spinal serotonin 7 receptor (5-HT7) blockers inhibit both morphine and cannabinoid-induced analgesia, thus we hypothesized that descending serotonergic pathways-spinal 5-HT7 receptor loop might contribute to stress-induced analgesia. Stress-induced analgesia was induced with warm (32°C) or cold (20°C) water swim stress in male Balb-C mice. The effects of intrathecal injection of a selective 5-HT7 receptor antagonist, SB 269970, of the denervation of serotonergic neurons by intrathecal administration of 5,7-dihydroxytryptamine (5,7-DHT) and of lesions of the dorsolateral funiculus on opioid and non-opioid type stress-induced analgesia were evaluated with the tail-flick and hot plate tests. The expression of 5-HT7 receptors mRNA in the dorsal lumbar region of spinal cord were analyzed by RT-PCR following spinal serotonin depletion or dorsolateral funiculus lesion. The effects of the selective 5-HT7 receptor agonists LP 44 and AS 19 were tested on nociception. Intrathecal SB 269970 blocked both opioid and non-opioid type stress-induced analgesia. Dorsolateral funiculus lesion or denervation of the spinal serotonergic neurons resulted in a marked decrease in 5-HT7 receptor expression in the dorsal lumbar spinal cord, accompanied by inhibition of opioid and non-opioid type stress-induced analgesia. However, the systemic or intrathecal LP 44 and AS 19 alone did not produce analgesia in unstressed mice. These results indicate that descending serotonergic pathways and the spinal 5-HT7 receptor loop play a crucial role in mediating both opioid and non-opioid type stress-induced analgesia.

  16. Antitussive activity of Withania somnifera and opioid receptors.

    PubMed

    Nosálová, Gabriela; Sivová, Veronika; Ray, Bimalendu; Fraňová, Soňa; Ondrejka, Igor; Flešková, Dana

    2015-01-01

    Arabinogalactan is a polysaccharide isolated from the roots of the medicinal plant Withania somnifera L. It contains 65% arabinose and 18% galactose. The aim of the present study was to evaluate the antitussive activity of arabinogalactan in conscious, healthy adult guinea pigs and the role of the opioid pathway in the antitussive action. A polysaccharide extract was given orally in a dose of 50 mg/kg. Cough was induced by an aerosol of citric acid in a concentration 0.3 mol/L, generated by a jet nebulizer into a plethysmographic chamber. The intensity of cough response was defined as the number of cough efforts counted during a 3-min exposure to the aerosol. The major finding was that arabinogalactan clearly suppressed the cough reflex; the suppression was comparable with that of codeine that was taken as a reference drug. The involvement of the opioid system was tested with the use of a blood-brain barrier penetrable, naloxone hydrochloride, and non-penetrable, naloxone methiodide, to distinguish between the central and peripheral mu-opioid receptor pathways. Both opioid antagonists acted to reverse the arabinogalactan-induced cough suppression; the reversion was total over time with the latter antagonist. We failed to confirm the presence of a bronchodilating effect of the polysaccharide, which could be involved in its antitussive action. We conclude that the polysaccharide arabinogalactan from Withania somnifera has a distinct antitussive activity consisting of cough suppression and that this action involves the mu-opioid receptor pathways.

  17. It's MORe exciting than mu: crosstalk between mu opioid receptors and glutamatergic transmission in the mesolimbic dopamine system.

    PubMed

    Chartoff, Elena H; Connery, Hilary S

    2014-01-01

    Opioids selective for the G protein-coupled mu opioid receptor (MOR) produce potent analgesia and euphoria. Heroin, a synthetic opioid, is considered one of the most addictive substances, and the recent exponential rise in opioid addiction and overdose deaths has made treatment development a national public health priority. Existing medications (methadone, buprenorphine, and naltrexone), when combined with psychosocial therapies, have proven efficacy in reducing aspects of opioid addiction. Unfortunately, these medications have critical limitations including those associated with opioid agonist therapies (e.g., sustained physiological dependence and opioid withdrawal leading to high relapse rates upon discontinuation), non-adherence to daily dosing, and non-renewal of monthly injection with extended-release naltrexone. Furthermore, current medications fail to ameliorate key aspects of addiction such as powerful conditioned associations that trigger relapse (e.g., cues, stress, the drug itself). Thus, there is a need for developing novel treatments that target neural processes corrupted with chronic opioid use. This requires a basic understanding of molecular and cellular mechanisms underlying effects of opioids on synaptic transmission and plasticity within reward-related neural circuits. The focus of this review is to discuss how crosstalk between MOR-associated G protein signaling and glutamatergic neurotransmission leads to immediate and long-term effects on emotional states (e.g., euphoria, depression) and motivated behavior (e.g., drug-seeking, relapse). Our goal is to integrate findings on how opioids modulate synaptic release of glutamate and postsynaptic transmission via α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid and N-methyl-D-aspartate receptors in the nucleus accumbens and ventral tegmental area with the clinical (neurobehavioral) progression of opioid dependence, as well as to identify gaps in knowledge that can be addressed in future studies.

  18. A mu-delta opioid receptor brain atlas reveals neuronal co-occurrence in subcortical networks.

    PubMed

    Erbs, Eric; Faget, Lauren; Scherrer, Gregory; Matifas, Audrey; Filliol, Dominique; Vonesch, Jean-Luc; Koch, Marc; Kessler, Pascal; Hentsch, Didier; Birling, Marie-Christine; Koutsourakis, Manoussos; Vasseur, Laurent; Veinante, Pierre; Kieffer, Brigitte L; Massotte, Dominique

    2015-03-01

    Opioid receptors are G protein-coupled receptors (GPCRs) that modulate brain function at all levels of neural integration, including autonomic, sensory, emotional and cognitive processing. Mu (MOR) and delta (DOR) opioid receptors functionally interact in vivo, but whether interactions occur at circuitry, cellular or molecular levels remains unsolved. To challenge the hypothesis of MOR/DOR heteromerization in the brain, we generated redMOR/greenDOR double knock-in mice and report dual receptor mapping throughout the nervous system. Data are organized as an interactive database offering an opioid receptor atlas with concomitant MOR/DOR visualization at subcellular resolution, accessible online. We also provide co-immunoprecipitation-based evidence for receptor heteromerization in these mice. In the forebrain, MOR and DOR are mainly detected in separate neurons, suggesting system-level interactions in high-order processing. In contrast, neuronal co-localization is detected in subcortical networks essential for survival involved in eating and sexual behaviors or perception and response to aversive stimuli. In addition, potential MOR/DOR intracellular interactions within the nociceptive pathway offer novel therapeutic perspectives.

  19. Heteromers of μ-δ opioid receptors: new pharmacology and novel therapeutic possibilities

    PubMed Central

    Fujita, Wakako; Gomes, Ivone; Devi, Lakshmi A

    2015-01-01

    Several studies suggest that heteromerization between μ (MOP) and δ (DOP) opioid receptors modulates the signalling properties of the individual receptors. For example, whereas activation of MOP receptors by an agonist induces G protein-mediated signalling, the same agonist induces β-arrestin-mediated signalling in the context of the MOP-DOP receptor heteromer. Moreover, heteromer-mediated signalling is allosterically modulated by a combination of MOP and DOP receptor ligands. This has implications in analgesia given that morphine-induced antinociception can be potentiated by DOP receptor ligands. Recently reagents selectively targeting the MOP-DOP receptor heteromer such as bivalent ligands, antibodies or membrane permeable peptides have been generated; these reagents are enabling studies to elucidate the contribution of endogenously expressed heteromers to analgesia as well as to the development of side-effects associated with chronic opioid use. Recent advances in drug screening technology have led to the identification of a MOP-DOP receptor heteromer-biased agonist that activates both G protein-mediated and β-arrestin-mediated signalling. Moreover, this heteromer-biased agonist exhibits potent antinociceptive activity but with reduced side-effects, suggesting that ligands targeting the MOP-DOP receptor heteromer form a basis for the development of novel therapeutics for the treatment of pain. In this review, we summarize findings regarding the biological and functional characteristics of the MOP-DOP receptor heteromer and the in vitro and in vivo properties of heteromer-selective ligands. LINKED ARTICLES This article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-2 PMID:24571499

  20. Targeting peripheral opioid receptors to promote analgesic and anti-inflammatory actions

    PubMed Central

    Iwaszkiewicz, Katerina S.; Schneider, Jennifer J.; Hua, Susan

    2013-01-01

    Mechanisms of endogenous pain control are significant. Increasing studies have clearly produced evidence for the clinical usefulness of opioids in peripheral analgesia. The immune system uses mechanisms of cell migration not only to fight pathogens but also to control pain and inflammation within injured tissue. It has been demonstrated that peripheral inflammatory pain can be effectively controlled by an interaction of immune cell-derived opioid peptides with opioid receptors on peripheral sensory nerve terminals. Experimental and clinical studies have clearly shown that activation of peripheral opioid receptors with exogenous opioid agonists and endogenous opioid peptides are able to produce significant analgesic and anti-inflammatory effects, without central opioid mediated side effects (e.g., respiratory depression, sedation, tolerance, dependence). This article will focus on the role of opioids in peripheral inflammatory conditions and the clinical implications of targeting peripheral opioid receptors. PMID:24167491

  1. µ-opioid Receptor Availability in the Amygdala is Associated with Smoking for Negative Affect Relief

    PubMed Central

    Falcone, Mary; Gold, Allison B.; Wileyto, E. Paul; Ray, Riju; Ruparel, Kosha; Newberg, Andrew; Dubroff, Jacob; Logan, Jean; Zubieta, Jon-Kar; Blendy, Julie A.; Lerman, Caryn

    2013-01-01

    Rationale The perception that smoking relieves negative affect contributes to smoking persistence. Endogenous opioid neurotransmission, and the µ-opioid receptor (MOR) in particular, plays a role in affective regulation and is modulated by nicotine. Objectives We examined the relationship of µ-opioid receptor binding availability in the amygdala to the motivation to smoke for negative affect relief and to the acute effects of smoking on affective responses. Methods Twenty-two smokers were scanned on two separate occasions after overnight abstinence using [11C]carfentanil positron emission tomography imaging: after smoking a nicotine-containing cigarette and after smoking a denicotinized cigarette. Self-reports of smoking motives were collected at baseline, and measures of positive and negative affect were collected pre- and post- cigarette smoking. Results Higher MOR availability in the amygdala was associated with motivation to smoke to relieve negative affect. However, MOR availability was unrelated to changes in affect after smoking either cigarette. Conclusions Increased MOR availability in amygdala may underlie the motivation to smoke for negative affective relief. These results are consistent with previous data highlighting the role of µ-opioid receptor neurotransmission in smoking behavior. PMID:22389047

  2. Lobeline, a potential pharmacotherapy for drug addiction, binds to mu opioid receptors and diminishes the effects of opioid receptor agonists.

    PubMed

    Miller, Dennis K; Lever, John R; Rodvelt, Kelli R; Baskett, James A; Will, Matthew J; Kracke, George R

    2007-07-10

    Lobeline diminishes the behavioral and neurochemical effects of nicotine and amphetamines, and is considered a potential pharmacotherapy for drug abuse and addiction. Lobeline has high affinity for nicotinic acetylcholine receptors and inhibits the function of vesicular monoamine and dopamine transporters. The present study investigated the less-explored interaction of lobeline and the endogenous opioid system. In guinea pig brain homogenates, lobeline displaced (K(i)=0.74 microM) the binding of [(3)H]DAMGO [(D-Ala(2), N-ME-Phe(4), Gly(5)-ol)-enkephalin]. In a functional assay system comprised of MOR-1 mu opioid receptors and GIRK2 potassium channels expressed in Xenopus oocytes, lobeline had no effect on the resting current, but maximally inhibited (IC(50)=1.1 microM) morphine- and DAMGO-activated potassium current in a concentration-dependent manner. In a second functional assay, lobeline-evoked [(3)H]overflow from rat striatal slices preloaded with [(3)H]dopamine was not blocked by naltrexone. Importantly, concentrations of lobeline (0.1-0.3 microM) that did not have intrinsic activity attenuated ( approximately 50%) morphine-evoked [(3)H]overflow. Overall, the results suggest that lobeline functions as a mu opioid receptor antagonist. The ability of lobeline to block psychostimulant effects may be mediated by opioid receptor antagonism, and lobeline could be investigated as a treatment for opiate addiction.

  3. Interacting Cannabinoid and Opioid Receptors in the Nucleus Accumbens Core Control Adolescent Social Play

    PubMed Central

    Manduca, Antonia; Lassalle, Olivier; Sepers, Marja; Campolongo, Patrizia; Cuomo, Vincenzo; Marsicano, Giovanni; Kieffer, Brigitte; Vanderschuren, Louk J. M. J; Trezza, Viviana; Manzoni, Olivier J. J.

    2016-01-01

    Social play behavior is a highly rewarding, developmentally important form of social interaction in young mammals. However, its neurobiological underpinnings remain incompletely understood. Previous work has suggested that opioid and endocannabinoid neurotransmission interact in the modulation of social play. Therefore, we combined behavioral, pharmacological, electrophysiological, and genetic approaches to elucidate the role of the endocannabinoid 2-arachidonoylglycerol (2-AG) in social play, and how cannabinoid and opioid neurotransmission interact to control social behavior in adolescent rodents. Systemic administration of the 2-AG hydrolysis inhibitor JZL184 or the opioid receptor agonist morphine increased social play behavior in adolescent rats. These effects were blocked by systemic pretreatment with either CB1 cannabinoid receptor (CB1R) or mu-opioid receptor (MOR) antagonists. The social play-enhancing effects of systemic morphine or JZL184 treatment were also prevented by direct infusion of the CB1R antagonist SR141716 and the MOR antagonist naloxone into the nucleus accumbens core (NAcC). Searching for synaptic correlates of these effects in adolescent NAcC excitatory synapses, we observed that CB1R antagonism blocked the effect of the MOR agonist DAMGO and, conversely, that naloxone reduced the effect of a cannabinoid agonist. These results were recapitulated in mice, and completely abolished in CB1R and MOR knockout mice, suggesting that the functional interaction between CB1R and MOR in the NAcC in the modulation of social behavior is widespread in rodents. The data shed new light on the mechanism by which endocannabinoid lipids and opioid peptides interact to orchestrate rodent socioemotional behaviors. PMID:27899885

  4. Interacting Cannabinoid and Opioid Receptors in the Nucleus Accumbens Core Control Adolescent Social Play.

    PubMed

    Manduca, Antonia; Lassalle, Olivier; Sepers, Marja; Campolongo, Patrizia; Cuomo, Vincenzo; Marsicano, Giovanni; Kieffer, Brigitte; Vanderschuren, Louk J M J; Trezza, Viviana; Manzoni, Olivier J J

    2016-01-01

    Social play behavior is a highly rewarding, developmentally important form of social interaction in young mammals. However, its neurobiological underpinnings remain incompletely understood. Previous work has suggested that opioid and endocannabinoid neurotransmission interact in the modulation of social play. Therefore, we combined behavioral, pharmacological, electrophysiological, and genetic approaches to elucidate the role of the endocannabinoid 2-arachidonoylglycerol (2-AG) in social play, and how cannabinoid and opioid neurotransmission interact to control social behavior in adolescent rodents. Systemic administration of the 2-AG hydrolysis inhibitor JZL184 or the opioid receptor agonist morphine increased social play behavior in adolescent rats. These effects were blocked by systemic pretreatment with either CB1 cannabinoid receptor (CB1R) or mu-opioid receptor (MOR) antagonists. The social play-enhancing effects of systemic morphine or JZL184 treatment were also prevented by direct infusion of the CB1R antagonist SR141716 and the MOR antagonist naloxone into the nucleus accumbens core (NAcC). Searching for synaptic correlates of these effects in adolescent NAcC excitatory synapses, we observed that CB1R antagonism blocked the effect of the MOR agonist DAMGO and, conversely, that naloxone reduced the effect of a cannabinoid agonist. These results were recapitulated in mice, and completely abolished in CB1R and MOR knockout mice, suggesting that the functional interaction between CB1R and MOR in the NAcC in the modulation of social behavior is widespread in rodents. The data shed new light on the mechanism by which endocannabinoid lipids and opioid peptides interact to orchestrate rodent socioemotional behaviors.

  5. Antinociceptive role of oxytocin in the nucleus raphe magnus of rats, an involvement of mu-opioid receptor.

    PubMed

    Wang, Jing-Wen; Lundeberg, Thomas; Yu, Long-Chuan

    2003-10-15

    Recent studies showed that oxytocin plays an important role in nociceptive modulation in the central nervous system. The present study was undertaken to investigate the role of oxytocin in antinociception in the nucleus raphe magnus (NRM) of rats and the possible interaction between oxytocin and the opioid systems. Intra-NRM injection of oxytocin induced dose-dependent increases in hindpaw withdrawal latencies (HWLs) to noxious thermal and mechanical stimulation in rats. The antinociceptive effect of oxytocin was significantly attenuated by subsequent intra-NRM injection of the oxytocin antagonist 1-deamino-2-D-Tyr-(Oet)-4-Thr-8-Orn-oxytocin. Intra-NRM injection of naloxone dose-dependently antagonized the increased HWLs induced by preceding intra-NRM injection of oxytocin, indicating an involvement of opioid receptors in oxytocin-induced antinociception in the NRM of rats. Furthermore, the antinociceptive effect of oxytocin was dose-dependently attenuated by subsequent intra-NRM injection of the mu-opioid antagonist beta-funaltrexamine (beta-FNA), but not by the kappa-opioid antagonist nor-binaltorphimine (nor-BNI) or the delta-opioid antagonist naltrindole. The results demonstrated that oxytocin plays an antinociceptive role in the NRM of rats through activating the oxytocin receptor. Moreover, mu-opioid receptors, not kappa and delta receptors, are involved in the oxytocin-induced antinociception in the NRM of rats.

  6. Delta opioid receptors in brain function and diseases

    PubMed Central

    Chung, Paul Chu Sin; Kieffer, Brigitte L.

    2013-01-01

    Evidence that the delta opioid receptor (DOR) is an attractive target for the treatment of brain disorders has strengthened in recent years. This receptor is broadly expressed in the brain, binds endogenous opioid peptides, and shows as functional profile highly distinct from those of mu and kappa opioid receptors. Our knowledge of DOR function has enormously progressed from in vivo studies using pharmacological tools and genetic approaches. The important role of this receptor in reducing chronic pain has been extensively overviewed; therefore this review focuses on facets of delta receptor activity relevant to psychiatric and other neurological disorders. Beneficial effects of DOR agonists are now well established in the context of emotional responses and mood disorders. DOR activation also regulates drug reward, inhibitory controls and learning processes, but whether delta compounds may represent useful drugs in the treatment of drug abuse remains open. Epileptogenic and locomotor-stimulating effects of delta agonists appear drug-dependent, and the possibility of biased agonism at DOR for these effects is worthwhile further investigations to increase benefit/risk ratio of delta therapies. Neuroprotective effects of DOR activity represent a forthcoming research area. Future developments in DOR research will benefit from in-depth investigations of DOR function at cellular and circuit levels. PMID:23764370

  7. Mu Opioids and Their Receptors: Evolution of a Concept

    PubMed Central

    Pan, Ying-Xian

    2013-01-01

    Opiates are among the oldest medications available to manage a number of medical problems. Although pain is the current focus, early use initially focused upon the treatment of dysentery. Opium contains high concentrations of both morphine and codeine, along with thebaine, which is used in the synthesis of a number of semisynthetic opioid analgesics. Thus, it is not surprising that new agents were initially based upon the morphine scaffold. The concept of multiple opioid receptors was first suggested almost 50 years ago (Martin, 1967), opening the possibility of new classes of drugs, but the morphine-like agents have remained the mainstay in the medical management of pain. Termed mu, our understanding of these morphine-like agents and their receptors has undergone an evolution in thinking over the past 35 years. Early pharmacological studies identified three major classes of receptors, helped by the discovery of endogenous opioid peptides and receptor subtypes—primarily through the synthesis of novel agents. These chemical biologic approaches were then eclipsed by the molecular biology revolution, which now reveals a complexity of the morphine-like agents and their receptors that had not been previously appreciated. PMID:24076545

  8. In vivo neuronal co-expression of mu and delta opioid receptors uncovers new therapeutic perspectives

    PubMed Central

    Erbs, Eric; Faget, Lauren; Veinante, Pierre; Kieffer, Brigitte L; Massotte, Dominique

    2015-01-01

    Opioid receptors belong to the G protein coupled receptor family. They modulate brain function at all levels of neural integration and therefore impact on autonomous, sensory, emotional and cognitive processing. In vivo functional interaction between mu and delta opioid receptors are known to take place though it is still debated whether interactions occur at circuitry, cellular or molecular level. Also, the notion of receptor crosstalk via mu-delta heteromers is well documented in vitro but in vivo evidence remains scarce. To identify neurons in which receptor interactions could take place, we designed a unique double mutant knock-in mouse line that expresses functional red-fluorescent mu receptors and green-fluorescent delta receptors. We mapped mu and delta receptor distribution and co-localization throughout the nervous system and created the first interactive brain atlas with concomitant mu-delta visualization at subcellular resolution (http://mordor.ics-mci.fr/). Mu and delta receptors co-localize in neurons from subcortical networks but are mainly detected in separate neurons in the forebrain. Also, co-immunoprecipitation experiments indicated physical proximity in the hippocampus, a prerequisite to mu-delta heteromerization. Altogether, data suggest that mu-delta functional interactions take place at systems level for high-order emotional and cognitive processing whereas mu-delta may interact at cellular level in brain networks essential for survival, which has potential implications for innovative drug design in pain control, drug addiction and eating disorders. PMID:25938125

  9. In vivo neuronal co-expression of mu and delta opioid receptors uncovers new therapeutic perspectives.

    PubMed

    Erbs, Eric; Faget, Lauren; Veinante, Pierre; Kieffer, Brigitte L; Massotte, Dominique

    2014-09-01

    Opioid receptors belong to the G protein coupled receptor family. They modulate brain function at all levels of neural integration and therefore impact on autonomous, sensory, emotional and cognitive processing. In vivo functional interaction between mu and delta opioid receptors are known to take place though it is still debated whether interactions occur at circuitry, cellular or molecular level. Also, the notion of receptor crosstalk via mu-delta heteromers is well documented in vitro but in vivo evidence remains scarce. To identify neurons in which receptor interactions could take place, we designed a unique double mutant knock-in mouse line that expresses functional red-fluorescent mu receptors and green-fluorescent delta receptors. We mapped mu and delta receptor distribution and co-localization throughout the nervous system and created the first interactive brain atlas with concomitant mu-delta visualization at subcellular resolution (http://mordor.ics-mci.fr/). Mu and delta receptors co-localize in neurons from subcortical networks but are mainly detected in separate neurons in the forebrain. Also, co-immunoprecipitation experiments indicated physical proximity in the hippocampus, a prerequisite to mu-delta heteromerization. Altogether, data suggest that mu-delta functional interactions take place at systems level for high-order emotional and cognitive processing whereas mu-delta may interact at cellular level in brain networks essential for survival, which has potential implications for innovative drug design in pain control, drug addiction and eating disorders.

  10. Non-opioid actions of opioid peptides.

    PubMed

    Wollemann, Mária; Benyhe, Sándor

    2004-06-04

    Beside the well known actions of opioid peptides on mu-, delta- and kappa-opioid receptors, increasing amount of pharmacological and biochemical evidence has recently been published about non-opioid actions of various opioid peptides. These effects are not abolished by naloxone treatments. Such non-opioid effects are observed both in nervous tissues and in the cellular elements of the immune system. Peptides exhibiting non-opioid effects include beta-endorphin, dynorphin A, nociceptin/OFQ, endomorphins, hemorphins and a number of Proenkephalin A derived peptides, such as Met-enkephalin, Met-enkephalin-Arg-Phe (MERF) and bovine adrenal medullary peptide (BAM22). Non-opioid actions are exerted through different neuronal receptors, e.g., dynorphin hyperalgesia through NMDA receptor, Met-enkephalin induced regulation of cell growth through zeta receptors, pain modulation by nociceptin through ORL-1 or NOP receptors, while BAM22 acts through sensory neuron specific G protein-coupled receptors (SNSR). We have investigated Met-enkephalin-Arg-Phe (MERF) and its analogues by the means of direct and indirect radioligand binding assays. It has been found that in addition to kappa(2) and delta-opioid receptors, MERF can act also through sigma(2)- or probably via FMRF-NH(2) receptors in rat cerebellum. A role of functionally assembling heterodimer receptors in mediating the non-conventional actions of these peptide ligands can not be excluded as well.

  11. Dark chocolate receptors: epicatechin-induced cardiac protection is dependent on δ-opioid receptor stimulation

    PubMed Central

    Panneerselvam, Mathivadhani; Tsutsumi, Yasuo M.; Bonds, Jacqueline A.; Horikawa, Yousuke T.; Saldana, Michelle; Dalton, Nancy D.; Head, Brian P.; Patel, Piyush M.; Roth, David M.

    2010-01-01

    Epicatechin, a flavonoid, is a well-known antioxidant linked to a variety of protective effects in both humans and animals. In particular, its role in protection against cardiovascular disease has been demonstrated by epidemiologic studies. Low-dose epicatechin, which does not have significant antioxidant activity, is also protective; however, the mechanism by which low-dose epicatechin induces this effect is unknown. Our laboratory tested the hypothesis that low-dose epicatechin mediates cardiac protection via opioid receptor activation. C57BL/6 mice were randomly assigned to 1 of 10 groups: control, epicatechin, naloxone (nonselective opioid receptor antagonist), epicatechin + naloxone, naltrindole (δ-specific opioid receptor antagonist), epicatechin + naltrindole, norbinaltorphimine (nor-BNI, κ-specific opioid receptor antagonist), epicatechin + nor-BNI, 5-hydroxydecanoic acid [5-HD, ATP-sensitive potassium channel antagonist], and epicatechin + 5-HD. Epicatechin (1 mg/kg) or other inhibitors (5 mg/kg) were administered by oral gavage or intraperitoneal injection, respectively, daily for 10 days. Mice were subjected to 30 min coronary artery occlusion followed by 2 h of reperfusion, and infarct size was determined via planimetry. Whole heart homogenates were assayed for downstream opioid receptor signaling targets. Infarct size was significantly reduced in epicatechin- and epicatechin + nor-BNI-treated mice compared with control mice. This protection was blocked by naloxone, naltrindole, and 5-HD. Epicatechin and epicatechin + nor-BNI increased the phosphorylation of Src, Akt, and IκBα, while simultaneously decreasing the expression of c-Jun NH2-terminal kinase and caspase-activated DNase. All signaling effects are consistent with opioid receptor stimulation and subsequent cardiac protection. Naloxone, naltrindole, and 5-HD attenuated these effects. In conclusion, epicatechin acts via opioid receptors and more specifically through the δ-opioid receptor to

  12. Differential effects of exercise on brain opioid receptor binding and activation in rats.

    PubMed

    Arida, Ricardo Mario; Gomes da Silva, Sérgio; de Almeida, Alexandre Aparecido; Cavalheiro, Esper Abrão; Zavala-Tecuapetla, Cecilia; Brand, Serge; Rocha, Luisa

    2015-01-01

    Physical exercise stimulates the release of endogenous opioid peptides supposed to be responsible for changes in mood, anxiety, and performance. Exercise alters sensitivity to these effects that modify the efficacy at the opioid receptor. Although there is evidence that relates exercise to neuropeptide expression in the brain, the effects of exercise on opioid receptor binding and signal transduction mechanisms downstream of these receptors have not been explored. Here, we characterized the binding and G protein activation of mu opioid receptor, kappa opioid receptor or delta opioid receptor in several brain regions following acute (7 days) and chronic (30 days) exercise. As regards short- (acute) or long-term effects (chronic) of exercise, overall, higher opioid receptor binding was observed in acute-exercise animals and the opposite was found in the chronic-exercise animals. The binding of [(35) S]GTPγS under basal conditions (absence of agonists) was elevated in sensorimotor cortex and hippocampus, an effect more evident after chronic exercise. Divergence of findings was observed for mu opioid receptor, kappa opioid receptor, and delta opioid receptor receptor activation in our study. Our results support existing evidence of opioid receptor binding and G protein activation occurring differentially in brain regions in response to diverse exercise stimuli. We characterized the binding and G protein activation of mu, kappa, and delta opioid receptors in several brain regions following acute (7 days) and chronic (30 days) exercise. Higher opioid receptor binding was observed in the acute exercise animal group and opposite findings in the chronic exercise group. Higher G protein activation under basal conditions was noted in rats submitted to chronic exercise, as visible in the depicted pseudo-color autoradiograms.

  13. Irradiation exposure modulates central opioid functions

    SciTech Connect

    Dougherty, P.M.; Dafny, N.

    1987-11-01

    Exposure to low doses of gamma irradiation results in the modification of both the antinociceptive properties of morphine and the severity of naloxone-precipitated withdrawal in morphine-dependent rats. To better define the interactions between gamma irradiation and these opiate-mediated phenomena, dose-response studies were undertaken of the effect of irradiation on morphine-induced antinociception, and on the naloxone-precipitated withdrawal syndrome of morphine-dependent rats. In addition, electrophysiologic studies were conducted in rats after irradiation exposure and morphine treatment correlating with the behavioral studies. The observations obtained demonstrated that the antinociceptive effects of morphine as well as naloxone-precipitated withdrawal were modified in a dose-dependent manner by irradiation exposure. In addition, irradiation-induced changes in the evoked responses obtained from four different brain regions demonstrated transient alterations in both baseline and morphine-treated responses that may reflect the alterations observed in the behavioral paradigms. These results suggest that the effects of irradiation on opiate activities resulted from physiologic alterations of central endogenous opioid systems due to alterations manifested within peripheral targets.

  14. Involvement of peripheral mu opioid receptors in scratching behavior in mice.

    PubMed

    Yamamoto, Atsuki; Sugimoto, Yukio

    2010-12-15

    Pruritus is a common adverse effect of opioid treatment. However, the mechanism by which pruritus is induced by opioid administration is unclear. In this study, we examined the effects of the intradermal injection of loperamide, a peripherally restricted opioid receptor agonist, on the itch sensation. When injected intradermally into the rostral part of the back in mice, loperamide elicited scratching behavior. We also examined the effects of the selective mu opioid receptor agonist [d-Ala², N-Me-Phe⁴, Gly⁵-ol]-enkephalin acetate (DAMGO), the selective delta opioid receptor agonist [d-Pen(2,5)]-enkephalin (DPDPE), and the selective kappa opioid receptor agonist U-50488H on scratching behavior in mice in order to determine which subtype is involved in opioid-induced pruritus. Following intradermal injection into the rostral part of the back in mice, DAMGO elicited scratching behavior, while DPDPE and U-50488H did not. This suggests that peripheral mu opioid activation elicits the itch sensation. Next, we focused on the treatment of opioid-induced itch sensation without central adverse effects. Naloxone methiodide is a peripherally restricted opioid receptor antagonist. In the present study, naloxone methiodide significantly suppressed scratching behavior induced by loperamide and DAMGO. These findings suggest that mu opioid receptors play a primary role in peripheral pruritus and that naloxone methiodide may represent a possible remedy for opioid-induced itching.

  15. Selective Glucocorticoid Receptor modulators.

    PubMed

    De Bosscher, Karolien

    2010-05-31

    The ancient two-faced Roman god Janus is often used as a metaphor to describe the characteristics of the Glucocorticoid Receptor (NR3C1), which exhibits both a beneficial side, that serves to halt inflammation, and a detrimental side responsible for undesirable effects. However, recent developments suggest that the Glucocorticoid Receptor has many more faces with the potential to express a range of different functionalities, depending on factors that include the tissue type, ligand type, receptor variants, cofactor surroundings and target gene promoters. This behavior of the receptor has made the development of safer ligands, that trigger the expression program of only a desirable subset of genes, a real challenge. Thus more knowledge-based fundamental research is needed to ensure the design and development of selective Glucocorticoid Receptor modulators capable of reaching the clinic. Recent advances in the characterization of novel selective Glucocorticoid Receptor modulators, specifically in the context of anti-inflammatory strategies, will be described in this review.

  16. The Effect of Opioid Receptor Blockade on the Neural Processing of Thermal Stimuli

    PubMed Central

    Schoell, Eszter D.; Bingel, Ulrike; Eippert, Falk; Yacubian, Juliana; Christiansen, Kerrin; Andresen, Hilke; May, Arne; Buechel, Christian

    2010-01-01

    The endogenous opioid system represents one of the principal systems in the modulation of pain. This has been demonstrated in studies of placebo analgesia and stress-induced analgesia, where anti-nociceptive activity triggered by pain itself or by cognitive states is blocked by opioid antagonists. The aim of this study was to characterize the effect of opioid receptor blockade on the physiological processing of painful thermal stimulation in the absence of cognitive manipulation. We therefore measured BOLD (blood oxygen level dependent) signal responses and intensity ratings to non-painful and painful thermal stimuli in a double-blind, cross-over design using the opioid receptor antagonist naloxone. On the behavioral level, we observed an increase in intensity ratings under naloxone due mainly to a difference in the non-painful stimuli. On the neural level, painful thermal stimulation was associated with a negative BOLD signal within the pregenual anterior cingulate cortex, and this deactivation was abolished by naloxone. PMID:20811582

  17. Peripherally acting μ-opioid receptor antagonists as treatment options for constipation in noncancer pain patients on chronic opioid therapy

    PubMed Central

    Pergolizzi, Joseph V; Raffa, Robert B; Pappagallo, Marco; Fleischer, Charles; Pergolizzi, Joseph; Zampogna, Gianpietro; Duval, Elizabeth; Hishmeh, Janan; LeQuang, Jo Ann; Taylor, Robert

    2017-01-01

    Opioid-induced constipation (OIC), a prevalent and distressing side effect of opioid therapy, does not reliably respond to treatment with conventional laxatives. OIC can be a treatment-limiting adverse event. Recent advances in medications with peripherally acting μ-opioid receptor antagonists, such as methylnaltrexone, naloxegol, and alvimopan, hold promise for treating OIC and thus extending the benefits of opioid analgesia to more chronic pain patients. Peripherally acting μ-opioid receptor antagonists have been clinically tested to improve bowel symptoms without compromise to pain relief, although there are associated side effects, including abdominal pain. Other treatment options include fixed-dose combination products of oxycodone analgesic together with naloxone. PMID:28176913

  18. Ligand/kappa-Opioid Receptor Interactions: Insights from the X-Ray Crystal Structure

    PubMed Central

    Martinez-Mayorga, Karina; Byler, Kendall G.; Yongye, Austin B.; Giulianotti, Marc A.; Dooley, Colette T.; Houghten, Richard A.

    2013-01-01

    During the past five years, the three-dimensional structures of 14 different G-protein coupled receptors (GPCRs) have been resolved by X-ray crystallography. The most recently published structures, those of the opioid receptors (ORs), are remarkably important in pain modulation, drug addiction, and mood disorders. These structures, confirmed previously proposed key interactions conferring potency and antagonistic properties, including the well-known interaction with Asp138, conserved in all aminergic GPCRs. In addition, crystallization of the opioid receptors highlighted the potential function of the ECL2 and ICL2 loops. We have previously reported a set of potent and selective kappa opioid receptor peptide agonists, of which ff(D-nle)r-NH2 is among the most potent and selective ones. These peptides were identified from the deconvolution of a 6,250,000 tetrapeptide combinatorial library. A derivative of this set is currently the subject of a phase 2 clinical trial in the United States. In this work, we describe comparative molecular modeling studies of kappa-OR peptide agonists with the co-crystallized antagonist, JDTic, and also report structure-activity relationships of 23 tetrapeptides. The overall binding and contact interactions are sound and interactions known to favor selectivity and potency were observed. Additional modeling studies will reveal conformational changes that the kappa-OR undergoes upon binding to these peptide agonists. PMID:23792349

  19. Identification of rat brain opioid (enkephalin) receptor by photoaffinity labeling

    SciTech Connect

    Yeung, C.W.

    1986-01-01

    A photoreactive, radioactive enkephalin derivative was prepared and purified by high performance liquid chromatography. Rat brain and spinal cord plasma membranes were incubated with this radioiodinated photoprobe and were subsequently photolysed. Autoradiography of the sodium dodecyl sulfate gel electrophoresis of the solubilized and reduced membranes showed that a protein having an apparent molecular weight of 46,000 daltons was specifically labeled, suggesting that this protein may be the opioid (enkephalin) receptor.

  20. Kappa-opioid receptor signaling and brain reward function

    PubMed Central

    Bruijnzeel, Adrie W.

    2009-01-01

    The dynorphin-like peptides have profound effects on the state of the brain reward system and human and animal behavior. The dynorphin-like peptides affect locomotor activity, food intake, sexual behavior, anxiety-like behavior, and drug intake. Stimulation of kappa-opioid receptors, the endogenous receptor for the dynorphin-like peptides, inhibits dopamine release in the striatum (nucleus accumbens and caudate putamen) and induces a negative mood state in humans and animals. The administration of drugs of abuse increases the release of dopamine in the striatum and mediates the concomitant release of dynorphin-like peptides in this brain region. The reviewed studies suggest that chronic drug intake leads to an upregulation of the brain dynorphin system in the striatum and in particular in the dorsal part of the striatum/caudate putamen. This might inhibit drug-induced dopamine release and provide protection against the neurotoxic effects of high dopamine levels. After the discontinuation of chronic drug intake these neuroadaptations remain unopposed which has been suggested to contribute to the negative emotional state associated with drug withdrawal and increased drug intake. Kappa-opioid receptor agonists have also been shown to inhibit calcium channels. Calcium channel inhibitors have antidepressant-like effects and inhibit the release of norepinephrine. This might explain that in some studies kappa-opioid receptor agonists attenuate nicotine and opioid withdrawal symptomatology. A better understanding of the role of dynorphins in the regulation of brain reward function might contribute to the development of novel treatments for mood disorders and other disorders that stem from a dysregulation of the brain reward system. PMID:19804796

  1. The Effect of CRH, Dexamethasone and Naltrexone on the Mu, Delta and Kappa Opioid Receptor Agonist Binding in Lamb Hypothalamic-Pituitary-Adrenal Axis.

    PubMed

    Pierzchała-Koziec, Krystyna; Dziedzicka-Wasylewska, Marta; Oeltgen, Peter; Zubel-Łojek, Joanna; Latacz, Anna; Ocłon, Ewa

    2015-01-01

    The aim of the study was to evaluate changes in the opioid receptor binding (mu, delta and kappa) in the hypothalamus, anterior pituitary and adrenal cortex (HPA) of lambs treated in vivo with corticotrophin releasing hormone (CRH), naltrexone, an opioid receptor antagonist (NAL), and dexamethasone, a potent cortisol analog (DEX). Experiment was carried out on 3 months old female lambs of polish mountain strain. Lambs received a single i.v. injection of NaCl (control), CRH (alone or in combination with naltrexone), naltrexone or dexamethasone. One hour later animals were decapitated under anaesthesia, tissues were dissected out and receptor binding assays were performed with radioligands for each type of opioid receptors--3H-DAGO, 3H-DPDPE and 3H-EKC for mu, delta and kappa receptor, respectively. Coexistence of specific binding sites for each type of opioid receptor was demonstrated in all levels of HPA axis of control lambs, however their distribution was uneven. Acute treatment with CRH, DEX and NAL caused downregulation or upregulation of mu, delta, kappa receptor binding in each level of HPA axis. CRH effects on mu, delta and kappa opioid receptor binding varied within the HPA axis and were modulated by naltrexone. Treatment with naltrexone increased in vitro mu, delta and kappa receptor binding in most tested structures except delta receptor binding in adrenal (decrease by 52%) and kappa receptor binding in pituitary (decrease by 41%). Dexamethasone significantly decreased the mu, delta and kappa opioid receptor binding in adrenal cortex but differentially affected opioid receptor binding in hypothalamus and pituitary. It seems probable that endogenous opioid peptides acting through mu, delta and kappa receptors interact with the hormones released from the hypothalamic-pituitary-adrenal axis in physiological and pathophysiological situations.

  2. Sigma and opioid receptors in human brain tumors

    SciTech Connect

    Thomas, G.E.; Szuecs, M.; Mamone, J.Y.; Bem, W.T.; Rush, M.D.; Johnson, F.E.; Coscia, C.J. )

    1990-01-01

    Human brain tumors and nude mouse-borne human neuroblastomas and gliomas were analyzed for sigma and opioid receptor content. Sigma binding was assessed using ({sup 3}H) 1, 3-di-o-tolylguanidine (DTG), whereas opioid receptor subtypes were measured with tritiated forms of the following: {mu}, (D-ala{sup 2}, mePhe{sup 4}, gly-ol{sup 5}) enkephalin (DAMGE); {kappa}, ethylketocyclazocine (EKC) or U69,593; {delta}, (D-pen{sup 2}, D-pen{sup 5}) enkephalin (DPDPE) or (D-ala{sup 2}, D-leu{sup 5}) enkephalin (DADLE) with {mu} suppressor present. Binding parameters were estimated by homologous displacement assays followed by analysis using the LIGAND program. Sigma binding was detected in 15 of 16 tumors examined with very high levels found in a brain metastasis from an adenocarcinoma of lung and a human neuroblastoma (SK-N-MC) passaged in nude mice. {kappa} opioid receptor binding was detected in 4 of 4 glioblastoma multiforme specimens and 2 of 2 human astrocytoma cell lines tested but not in the other brain tumors analyzed.

  3. Does the kappa opioid receptor system contribute to pain aversion?

    PubMed

    Cahill, Catherine M; Taylor, Anna M W; Cook, Christopher; Ong, Edmund; Morón, Jose A; Evans, Christopher J

    2014-01-01

    The kappa opioid receptor (KOR) and the endogenous peptide-ligand dynorphin have received significant attention due the involvement in mediating a variety of behavioral and neurophysiological responses, including opposing the rewarding properties of drugs of abuse including opioids. Accumulating evidence indicates this system is involved in regulating states of motivation and emotion. Acute activation of the KOR produces an increase in motivational behavior to escape a threat, however, KOR activation associated with chronic stress leads to the expression of symptoms indicative of mood disorders. It is well accepted that KOR can produce analgesia and is engaged in chronic pain states including neuropathic pain. Spinal studies have revealed KOR-induced analgesia in reversing pain hypersensitivities associated with peripheral nerve injury. While systemic administration of KOR agonists attenuates nociceptive sensory transmission, this effect appears to be a stress-induced effect as anxiolytic agents, including delta opioid receptor agonists, mitigate KOR agonist-induced analgesia. Additionally, while the role of KOR and dynorphin in driving the dysphoric and aversive components of stress and drug withdrawal has been well characterized, how this system mediates the negative emotional states associated with chronic pain is relatively unexplored. This review provides evidence that dynorphin and the KOR system contribute to the negative affective component of pain and that this receptor system likely contributes to the high comorbidity of mood disorders associated with chronic neuropathic pain.

  4. Does the kappa opioid receptor system contribute to pain aversion?

    PubMed Central

    Cahill, Catherine M.; Taylor, Anna M. W.; Cook, Christopher; Ong, Edmund; Morón, Jose A.; Evans, Christopher J.

    2014-01-01

    The kappa opioid receptor (KOR) and the endogenous peptide-ligand dynorphin have received significant attention due the involvement in mediating a variety of behavioral and neurophysiological responses, including opposing the rewarding properties of drugs of abuse including opioids. Accumulating evidence indicates this system is involved in regulating states of motivation and emotion. Acute activation of the KOR produces an increase in motivational behavior to escape a threat, however, KOR activation associated with chronic stress leads to the expression of symptoms indicative of mood disorders. It is well accepted that KOR can produce analgesia and is engaged in chronic pain states including neuropathic pain. Spinal studies have revealed KOR-induced analgesia in reversing pain hypersensitivities associated with peripheral nerve injury. While systemic administration of KOR agonists attenuates nociceptive sensory transmission, this effect appears to be a stress-induced effect as anxiolytic agents, including delta opioid receptor agonists, mitigate KOR agonist-induced analgesia. Additionally, while the role of KOR and dynorphin in driving the dysphoric and aversive components of stress and drug withdrawal has been well characterized, how this system mediates the negative emotional states associated with chronic pain is relatively unexplored. This review provides evidence that dynorphin and the KOR system contribute to the negative affective component of pain and that this receptor system likely contributes to the high comorbidity of mood disorders associated with chronic neuropathic pain. PMID:25452729

  5. Antidepressant-like Effects of δ Opioid Receptor Agonists in Animal Models

    PubMed Central

    Saitoh, Akiyoshi; Yamada, Mitsuhiko

    2012-01-01

    Recently, δ opioid receptor agonists have been proposed to be attractive targets for the development of novel antidepressants. Several studies revealed that single treatment of δ opioid receptor agonists produce antidepressant-like effects in the forced swimming test, which is one of the most popular animal models for screening antidepressants. In addition, subchronic treatment with δ opioid receptor agonists has been shown to completely attenuate the hyperemotional responses found in olfactory bulbectomized rats. This animal model exhibits hyperemotional behavior that may mimic the anxiety, aggression, and irritability found in depressed patients, suggesting that δ opioid receptor agonists could be effective in the treatment of these symptoms in depression. On the other hand, prototype δ opioid receptor agonists produce convulsive effects, which limit their therapeutic potential and clinical development. In this review, we presented the current knowledge regarding the antidepressant-like effects of δ opioid receptor agonists, which include some recently developed drugs lacking convulsive effects. PMID:23449756

  6. Effect of sodium ion on the affinity of naloxone for the kappa opioid receptor

    SciTech Connect

    Cheney, B.V.; Lahti, R.A.

    1987-03-16

    Several investigators have observed that sodium ion enhances the binding of naloxone to opioid receptors. This effect has generally been attributed to allosteric modulation of the state of the mu receptor. However, a recent claim has been made that the enhancement does not involve a change in the mu receptor, but instead occurs because naloxone becomes a more kappa-specific drug when sodium ion is present in high concentration. Since the claim was not based on experimental evidence from binding studies involving known high-affinity kappa ligands, the authors have investigated the competition of naloxone for the kappa site using (/sup 3/H)U-69593 as the marker for receptor binding. Assays were carried out in the presence and absence of 100 mM NaCl. The results of the study indicate that sodium ion does not increase the affinity of naloxone or U-69593 for the kappa receptor. 9 references, 1 figure.

  7. Nociceptin/Orphanin FQ Receptor Structure, Signaling, Ligands, Functions, and Interactions with Opioid Systems

    PubMed Central

    Bruchas, Michael R.; Calo', Girolamo; Cox, Brian M.; Zaveri, Nurulain T.

    2016-01-01

    The NOP receptor (nociceptin/orphanin FQ opioid peptide receptor) is the most recently discovered member of the opioid receptor family and, together with its endogenous ligand, N/OFQ, make up the fourth members of the opioid receptor and opioid peptide family. Because of its more recent discovery, an understanding of the cellular and behavioral actions induced by NOP receptor activation are less well developed than for the other members of the opioid receptor family. All of these factors are important because NOP receptor activation has a clear modulatory role on mu opioid receptor-mediated actions and thereby affects opioid analgesia, tolerance development, and reward. In addition to opioid modulatory actions, NOP receptor activation has important effects on motor function and other physiologic processes. This review discusses how NOP pharmacology intersects, contrasts, and interacts with the mu opioid receptor in terms of tertiary structure and mechanism of receptor activation; location of receptors in the central nervous system; mechanisms of desensitization and downregulation; cellular actions; intracellular signal transduction pathways; and behavioral actions with respect to analgesia, tolerance, dependence, and reward. This is followed by a discussion of the agonists and antagonists that have most contributed to our current knowledge. Because NOP receptors are highly expressed in brain and spinal cord and NOP receptor activation sometimes synergizes with mu receptor-mediated actions and sometimes opposes them, an understanding of NOP receptor pharmacology in the context of these interactions with the opioid receptors will be crucial to the development of novel therapeutics that engage the NOP receptor. PMID:26956246

  8. Studies Toward the Pharmacophore of Salvinorin A, a Potent Kappa Opioid Receptor Agonist

    PubMed Central

    Munro, Thomas A.; Rizzacasa, Mark A.; Roth, Bryan L.; Toth, Beth A.; Yan, Feng

    2009-01-01

    Salvinorin A (1), from the sage Salvia divinorum, is a potent and selective kappa opioid receptor (KOR) agonist. We screened other salvinorins and derivatives for binding affinity and functional activity at opioid receptors. Our results suggest that the methyl ester and furan ring are required for activity, but that the lactone and ketone functionalities are not. Other salvinorins showed negligible binding affinity at the KOR. None of the compounds bound to mu or delta opioid receptors. PMID:15658846

  9. Studies toward the pharmacophore of salvinorin A, a potent kappa opioid receptor agonist.

    PubMed

    Munro, Thomas A; Rizzacasa, Mark A; Roth, Bryan L; Toth, Beth A; Yan, Feng

    2005-01-27

    Salvinorin A (1), from the sage Salvia divinorum, is a potent and selective kappa opioid receptor (KOR) agonist. We screened other salvinorins and derivatives for binding affinity and functional activity at opioid receptors. Our results suggest that the methyl ester and furan ring are required for activity but that the lactone and ketone functionalities are not. Other salvinorins showed negligible binding affinity at the KOR. None of the compounds bound to mu or delta opioid receptors.

  10. Opioid mediated activity and expression of mu and delta opioid receptors in isolated human term non-labouring myometrium.

    PubMed

    Fanning, Rebecca A; McMorrow, Jason P; Campion, Deirdre P; Carey, Michael F; O'Connor, John J

    2013-01-05

    The existence of opioid receptors in mammalian myometrial tissue is now widely accepted. Previously enkephalin degrading enzymes have been shown to be elevated in pregnant rat uterus and a met-enkephalin analogue has been shown to alter spontaneous contractility of rat myometrium. Here we have undertaken studies to determine the effects of met-enkephalin on in vitro human myometrial contractility and investigate the expression of opioid receptors in pregnant myometrium. Myometrial biopsies were taken from women undergoing elective caesarean delivery at term. Organ bath experiments were used to investigate the effect of the met-enkephalin analogue [d-Ala 2, d-met 5] enkephalin (DAMEA) on spontaneous contractility. A confocal immunofluorescent technique and real time PCR were used to determine the expression of protein and mRNA, respectively for two opioid receptor subtypes, mu and delta. DAMEA had a concentration dependent inhibitory effect on contractile activity (1 × 10(-7)M-1 × 10(-4)M; 54% reduction in contractile activity, P<0.001 at 1 × 10(-4)M concentration). Mu and delta opioid receptor protein sub-types and their respective mRNA were identified in all tissues sampled. This is the first report of opioid receptor expression and of an opioid mediated uterorelaxant action in term human non-labouring myometrium in vitro.

  11. The imidazoline receptors and ligands in pain modulation

    PubMed Central

    Bektas, Nurcan; Nemutlu, Dilara; Arslan, Rana

    2015-01-01

    Pain is an unpleasant experience and effects daily routine negatively. Although there are various drugs, many of them are not entirely successful in relieving pain, since pain modulation is a complex process involving numerous mediators and receptors. Therefore, it is a rational approach to identify the factors involved in the complex process and develop new agents that act on these pain producing mechanisms. In this respect, the involvement of the imidazoline receptors in pain modulation has drawn attention in recent years. In this review, it is aimed to focus on the imidazoline receptors and their ligands which contribute to the pain modulation. It is demonstrated that imidazoline-2 (I2) receptors are steady new drug targets for analgesics. Even if the mechanism of I2 receptor is not well known in the modulation of pain, it is known that it plays a role in tonic and chronic pain but not in acute phasic pain. Moreover, the I2 receptor ligands increase the analgesic effects of opioids in both acute and chronic pain and prevent the development of opioid tolerance. So, they are valuable for the chronic pain treatment and also therapeutic coadjuvants in the management of chronic pain with opiate drugs due to the attenuation of opioid tolerance and addiction. Thus, the use of the ligands which bind to the imidazoline receptors is an effective strategy for relieving pain. This educational forum exhibits the role of imidazoline receptors and ligands in pain process by utilizing experimental studies. PMID:26600633

  12. Opioid neurotransmission in the post-ictal analgesia: involvement of mu(1)-opioid receptor.

    PubMed

    Coimbra, N C; Freitas, R L; Savoldi, M; Castro-Souza, C; Segato, E N; Kishi, R; Weltson, A; Resende, G C

    2001-06-08

    Pentylenetetrazol (PTZ), a non-competitive antagonist that blocks GABA-mediated Cl(-) flux, was used in the present work to induce seizures in animals. The aim of this work is to study the neurochemical basis of the antinociception induced by convulsions elicited by peripheral administration of PTZ (64 mg/kg). The analgesia was measured by the tail-flick test, in eight rats per group. Convulsions were followed by significative increase in the tail-flick latencies (TFL), for at least 120 min of the post-ictal period. Peripheral administration of naltrexone (5 mg/kg, 10 mg/kg and 20 mg/kg) caused a significant decrease in the TFL in seizing animals, as compared to controls. These data were corroborated with peripheral administration of naloxonazine (10 mg/kg and 20 mg/kg), a mu(1)-opioid blocker, in the same doses used for non-specific antagonist. These results indicate that endogenous opioids may be involved in the post-ictal analgesia. The involvement of mu(1)-opioid receptor was also considered.

  13. Kinetic study of N-type calcium current modulation by delta-opioid receptor activation in the mammalian cell line NG108-15.

    PubMed Central

    Toselli, M; Tosetti, P; Taglietti, V

    1999-01-01

    The voltage-dependent inhibition of N-type Ca2+ channel current by the delta-opioid agonist [D-pen2, D-pen5]-enkephalin (DPDPE) was investigated in the mammalian cell line NG108-15 with 10 microM nifedipine to block L-type channels, with whole-cell voltage clamp methods. In in vitro differentiated NG108-15 cells DPDPE reversibly decreased omega-conotoxin GVIA-sensitive Ba2+ currents in a concentration-dependent way. Inhibition was maximal with 1 microM DPDPE (66% at 0 mV) and was characterized by a slowing of Ba2+ current activation at low test potentials. Both inhibition and kinetic slowing were attenuated at more positive potentials and could be relieved up to 90% by strong conditioning depolarizations. The kinetics of removal of inhibition (de-inhibition) and of its retrieval (re-inhibition) were also voltage dependent. Both de-inhibition and re-inhibition were single exponentials and, in the voltage range from -20 to +10 mV, had significantly different time constants at a given membrane potential, the time course of re-inhibition being faster than that of de-inhibition. The kinetics of de-inhibition at -20 mV and of reinhibition at -40 mV were also concentration dependent, both processes becoming slower at lower agonist concentrations. The rate of de-inhibition at +80/+120 mV was similar to that of Ca2+ channel activation at the same potentials measured during application of DPDPE (approximately 7 ms), both processes being much slower than channel activation in controls (<1 ms). Moreover, the amplitude but not the time course of tail currents changed as the depolarization to +80/+120 mV was made longer. The state-dependent properties of DPDPE Ca2+ channel inhibition could be simulated by a model that assumes that inhibition by DPDPE results from voltage- and concentration-dependent binding of an inhibitory molecule to the N-type channel. PMID:10233071

  14. Impact of efficacy at the μ-opioid receptor on antinociceptive effects of combinations of μ-opioid receptor agonists and cannabinoid receptor agonists.

    PubMed

    Maguire, David R; France, Charles P

    2014-11-01

    Cannabinoid receptor agonists, such as Δ(9)-tetrahydrocannabinol (Δ(9)-THC), enhance the antinociceptive effects of μ-opioid receptor agonists, which suggests that combining cannabinoids with opioids would improve pain treatment. Combinations with lower efficacy agonists might be preferred and could avoid adverse effects associated with large doses; however, it is unclear whether interactions between opioids and cannabinoids vary across drugs with different efficacy. The antinociceptive effects of μ-opioid receptor agonists alone and in combination with cannabinoid receptor agonists were studied in rhesus monkeys (n = 4) using a warm water tail withdrawal procedure. Etorphine, fentanyl, morphine, buprenorphine, nalbuphine, Δ(9)-THC, and CP 55,940 (2-[(1R,2R,5R)-5-hydroxy-2-(3-hydroxypropyl) cyclohexyl]-5-(2-methyloctan-2-yl)phenol) each increased tail withdrawal latency. Pretreatment with doses of Δ(9)-THC (1.0 mg/kg) or CP 55,940 (0.032 mg/kg) that were ineffective alone shifted the fentanyl dose-effect curve leftward 20.6- and 52.9-fold, respectively, and the etorphine dose-effect curve leftward 12.4- and 19.6-fold, respectively. Δ(9)-THC and CP 55,940 shifted the morphine dose-effect curve leftward only 3.4- and 7.9-fold, respectively, and the buprenorphine curve only 5.4- and 4.1-fold, respectively. Neither Δ(9)-THC nor CP 55,940 significantly altered the effects of nalbuphine. Cannabinoid receptor agonists increase the antinociceptive potency of higher efficacy opioid receptor agonists more than lower efficacy agonists; however, because much smaller doses of each drug can be administered in combinations while achieving adequate pain relief and that other (e.g., abuse-related) effects of opioids do not appear to be enhanced by cannabinoids, these results provide additional support for combining opioids with cannabinoids to treat pain.

  15. Fluoxetine alters mu opioid receptor expression in obese Zucker rat extrahypothalamic regions.

    PubMed

    Churruca, Itziar; Portillo, María P; Zumalabe, José María; Macarulla, María T; Sáenz Del Burgo, Laura; Zarate, Jon; Echevarría, Enrique

    2006-03-01

    The aim of this article was to describe the effects of chronic fluoxetine on mu opioid receptor expression in obese Zucker rat extrahypothalamic regions. Male obese Zucker (fa/fa) rats were administered with fluoxetine (10 mg/kg; i.p.) daily for two weeks. Brain regional immunostaining for mu opioid receptor was carried out. An increase in the numbers of neural cells immunostained for mu opioid receptor in caudatus-putamen, dentate gyrus, lateral septum, amygdala, and frontal, parietal, and piriform cortices was observed. Increased mu opioid receptor expression in the central amygdaloid nuclei suggests a decreased opioidergic tone at this level that could be involved in fluoxetine anorectic action.

  16. Development of concepts on the interaction of drugs with opioid receptors

    NASA Astrophysics Data System (ADS)

    Kuzmina, N. E.; Kuzmin, V. S.

    2011-02-01

    The development of concepts on the molecular mechanisms of the action of medicinal drugs on the opioid receptors is briefly surveyed. The modern point of view on the mechanism of activation of opioid receptors is given based on the data from chimeric and site-directed mutagenesis of the cloned opioid receptors and the computer-aided simulations of the reception zone and ligand-receptor complexes. Three-dimensional models of the opioid pharmacophore derived by both conventional methods and a comparative analysis of molecular fields are described in detail.

  17. Analysis of central opioid receptor subtype antagonism of hypotonic and hypertonic saline intake in water-deprived rats.

    PubMed

    Bodnar, R J; Glass, M J; Koch, J E

    1995-01-01

    Intake of either hypotonic or hypertonic saline solutions is modulated in part by the endogenous opioid system. Morphine and selective mu and delta opioid agonists increase saline intake, while general opioid antagonists reduce saline intake in rats. The present study evaluated whether intracerebroventricular administration of general (naltrexone) and selective mu (beta-funaltrexamine, 5-20 micrograms), mu, (naloxonazine, 50 micrograms), kappa (nor-binaltorphamine, 5-20 micrograms), delta (naltrindole, 20 micrograms), or delta 1 (DALCE, 40 micrograms) opioid receptor subtype antagonists altered water intake and either hypotonic (0.6%) or hypertonic (1.7%) saline intake in water-deprived (24 h) rats over a 3-h time course in a two-bottle choice test. Whereas peripheral naltrexone (0.5-2.5 mg/kg) significantly reduced water intake and hypertonic saline intake, central naltrexone (1-50 micrograms) significantly reduced water intake and hypotonic saline intake. Water intake was significantly reduced following mu and kappa receptor antagonism, but not following mu 1, delta, or delta 1 receptor antagonism. In contrast, neither hypotonic nor hypertonic saline intake was significantly altered by any selective antagonist. These data are discussed in terms of opioid receptor subtype control over saline intake relative to the animal's hydrational state and the roles of palatability and/or salt appetite.

  18. Molecular mechanism for opioid dichotomy: bidirectional effect of μ-opioid receptors on P2X₃ receptor currents in rat sensory neurones.

    PubMed

    Chizhmakov, Igor; Kulyk, Vyacheslav; Khasabova, Iryna; Khasabov, Sergey; Simone, Donald; Bakalkin, Georgy; Gordienko, Dmitri; Verkhratsky, Alexei; Krishtal, Oleg

    2015-06-01

    Here, we describe a molecular switch associated with opioid receptors-linked signalling cascades that provides a dual opioid control over P2X3 purinoceptor in sensory neurones. Leu-enkephalin inhibited P2X3-mediated currents with IC50 ~10 nM in ~25% of small nociceptive rat dorsal root ganglion (DRG) neurones. In contrast, in neurones pretreated with pertussis toxin leu-enkephalin produced stable and significant increase of P2X3 currents. All effects of opioid were abolished by selective μ-opioid receptor antagonist D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2 (CTOP), nonselective inhibitor naloxone, and by PLC inhibitor U73122. Thus, we discovered a dual link between purinoceptors and μ-opioid receptors: the latter exert both inhibitory (pertussis toxin-sensitive) and stimulatory (pertussis toxin-insensitive) actions on P2X3 receptors through phospholipase C (PLC)-dependent pathways. This dual opioid control of P2X3 receptors may provide a molecular explanation for dichotomy of opioid therapy. Pharmacological control of this newly identified facilitation/inhibition switch may open new perspectives for the adequate medical use of opioids, the most powerful pain-killing agents known today.

  19. High-affinity carbamate analogues of morphinan at opioid receptors.

    PubMed

    Peng, Xuemei; Knapp, Brian I; Bidlack, Jean M; Neumeyer, John L

    2007-03-15

    A series of carbamate analogues were synthesized from levorphanol (1a), cyclorphan (2a) or butorphan (3a) and evaluated in vitro for their binding affinity at mu, delta, and kappa opioid receptors. Functional activities of these compounds were measured in the [(35)S]GTPgammaS binding assay. Phenyl carbamate derivatives 2d and 3d showed the highest binding affinity for kappa receptor (K(i)=0.046 and 0.051 nM) and for mu receptor (K(i)=0.11 and 0.12 nM). Compound 1c showed the highest mu selectivity. The preliminary assay for agonist and antagonist properties of these ligands in stimulating [(35)S]GTPgammaS binding mediated by the kappa opioid receptor illustrated that all of these ligands were kappa agonists. At the mu receptor, compounds 1b, 1c, 2b, and 3b were agonists, while compounds 2c-e and 3c-e were mu agonists/antagonists.

  20. Early role of the κ opioid receptor in ethanol-induced reinforcement.

    PubMed

    Pautassi, Ricardo Marcos; Nizhnikov, Michael E; Acevedo, Ma Belén; Spear, Norman E

    2012-03-20

    Effects of early ethanol exposure on later ethanol intake emphasize the importance of understanding the neurobiology of ethanol-induced reinforcement early in life. Infant rats exhibit ethanol-induced appetitive conditioning and ethanol-induced locomotor activation, which have been linked in theory and may have mechanisms in common. The appetitive effects of ethanol are significantly modulated by μ and δ opioid receptors, whereas μ but not δ receptors are involved in the motor stimulant effects of ethanol during early development. The involvement of the κ opioid receptor (KOR) system in the motivational effects of ethanol has been much less explored. The present study assessed, in preweanling (infant) rats, the modulatory role of the KOR system in several paradigms sensitive to ethanol-induced reinforcement. Kappa opioid activation and blockade were examined in second-order conditioned place preference with varied timing before conditioning and with varied ethanol doses. The role of KOR on ethanol-induced locomotion and ethanol-induced taste conditioning was also explored. The experiments were based on the assumption that ethanol concurrently induces appetitive and aversive effects and that the latter may be mediated by activation of kappa receptors. The main result was that blockade of kappa function facilitated the expression of appetitive ethanol reinforcement in terms of tactile and taste conditioning. The effects of kappa activation on ethanol conditioning seemed to be independent from ethanol's stimulant effects. Kappa opioid activation potentiated the motor depressing effects of ethanol but enhanced motor activity in control subjects. Overall, the results support the hypothesis that a reduced function of the KOR system in nondependent subjects should attenuate the aversive consequences of ethanol.

  1. Early role of the κ opioid receptor in ethanol-induced reinforcement

    PubMed Central

    Pautassi, Ricardo Marcos; Nizhnikov, Michael E.; Acevedo, Ma. Belén; Spear, Norman E.

    2012-01-01

    Effects of early ethanol exposure on later ethanol intake emphasize the importance of understanding the neurobiology of ethanol-induced reinforcement early in life. Infant rats exhibit ethanol-induced appetitive conditioning and ethanol-induced locomotor activation, which have been linked in theory and may have mechanisms in common. The appetitive effects of ethanol are significantly modulated by μ and δ opioid receptors, whereas μ but not δ receptors are involved in the motor stimulant effects of ethanol during early development. The involvement of the κ opioid receptor (KOR) system in the motivational effects of ethanol has been much less explored. The present study assessed, in preweanling (infant) rats, the modulatory role of the KOR system in several paradigms sensitive to ethanol-induced reinforcement. Kappa opioid activation and blockade was examined in second-order conditioned place preference with varied timing before conditioning and with varied ethanol doses. The role of KOR on ethanol-induced locomotion and ethanol-induced taste conditioning was also explored. The experiments were based on the assumption that ethanol concurrently induces appetitive and aversive effects and that the latter may be mediated by activation of kappa receptors. The main result was that blockade of kappa function facilitated the expression of appetitive ethanol reinforcement in terms of tactile and taste conditioning. The effects of kappa activation on ethanol conditioning seemed to be independent from ethanol's stimulant effects. Kappa opioid activation potentiated the motor depressing effects of ethanol but enhanced motor activity in control subjects. Overall, the results support the hypothesis that a reduced function of the KOR system in nondependent subjects should attenuate the aversive consequences of ethanol. PMID:22261437

  2. Synaptic localization of. kappa. opioid receptors in guinea pig neostriatum

    SciTech Connect

    Jomary, C.; Beaudet, A. ); Gairin, J.E. )

    1992-01-15

    Distribution of {kappa} opioid receptors was examined by EM radioautography in sections of guinea pig neostriatum with the selective {sup 125}I-labeled dynorphin analog (D-Pro{sup 10})dynorphin-(1-11). Most specifically labeled binding sites were found by probability circle analysis to be associated with neuronal membrane appositions. Because of limitations in resolution of the method, the radioactive sources could not be ascribed directly to either one of the apposed plasma membranes. Nevertheless, three lines of evidence favored a predominant association of ligand with dendrites of intrinsic striatal neurons: (1) the high frequency with which labeled interfaces implicated a dendrite, (2) the enrichment of dendrodendritic interfaces, and (3) the occurrence of dendritic profiles labeled at several contact points along their plasma membranes. A small proportion of labeled sites was associated with axo-axonic interfaces, which may subserve the {kappa} opioid-induced regulation of presynaptic dopamine and acetylcholine release documented in guinea pig neostriatum. These results support the hypothesis that in mammalian brain {kappa} opioid receptors are conformationally and functionally distinct from {mu} and {delta} types.

  3. Synaptic localization of kappa opioid receptors in guinea pig neostriatum.

    PubMed Central

    Jomary, C; Gairin, J E; Beaudet, A

    1992-01-01

    Distribution of kappa opioid receptors was examined by EM radioautography in sections of guinea pig neostriatum with the selective 125I-labeled dynorphin analog [D-Pro10]dynorphin-(1-11). Most specifically labeled binding sites were found by probability circle analysis to be associated with neuronal membrane appositions. Because of limitations in resolution of the method, the radioactive sources could not be ascribed directly to either one of the apposed plasma membranes. Nevertheless, three lines of evidence favored a predominant association of ligand with dendrites of intrinsic striatal neurons: (i) the high frequency with which labeled interfaces implicated a dendrite, (ii) the enrichment of dendro-dendritic interfaces, and (iii) the occurrence of dendritic profiles labeled at several contact points along their plasma membranes. A small proportion of labeled sites was associated with axo-axonic interfaces, which may subserve the kappa opioid-induced regulation of presynaptic dopamine and acetylcholine release documented in guinea pig neostriatum. Although most membrane-associated kappa sites were found at extrasynaptic locations, approximately 23% were associated with synaptic specializations. This proportion is markedly higher than that previously reported for either mu or delta sites in rat neostriatum. Whether labeled synapses represent preferential sites of action for kappa ligands remains to be established. In any event, these results support the hypothesis that in mammalian brain kappa opioid receptors are conformationally and functionally distinct from mu and delta types. Images PMID:1346233

  4. Functional interaction between alpha2-adrenoceptors, mu- and kappa-opioid receptors in the guinea pig myenteric plexus: effect of chronic desipramine treatment.

    PubMed

    Canciani, Luca; Giaroni, Cristina; Zanetti, Elena; Giuliani, Daniela; Pisani, Rossana; Moro, Elisabetta; Trinchera, Marco; Crema, Francesca; Lecchini, Sergio; Frigo, Gianmario

    2006-12-28

    The existence of a functional interplay between alpha(2)-adrenoceptor and opioid receptor inhibitory pathways modulating neurotransmitter release has been demonstrated in the enteric nervous system by development of sensitivity changes to alpha(2)-adrenoceptor, mu- and kappa-opioid receptor agents on enteric cholinergic neurons after chronic sympathetic denervation. In the present study, to further examine this hypothesis we evaluated whether manipulation of alpha(2)-adrenoceptor pathways by chronic treatment with the antidepressant drug, desipramine (10 mg/kg i.p. daily, for 21 days), could entail changes in enteric mu- and kappa-opioid receptor pathways in the myenteric plexus of the guinea pig distal colon. In this region, subsensitivity to the inhibitory effect of both UK14,304 and U69,593, respectively alpha(2A)-adrenoceptor and kappa-opioid receptor agonist, on the peristaltic reflex developed after chronic desipramine treatment. On opposite, in these experimental conditions, supersensitivity developed to the inhibitory effect of [D-Ala, N-Me-Phe4-Gly-ol5]-enkephalin (DAMGO), mu-opioid receptor agonist, on propulsion velocity. Immunoreactive expression levels of alpha(2A)-adrenoceptors, mu- and kappa-opioid receptors significantly decreased in the myenteric plexus of the guinea pig colon after chronic desipramine treatment. In these experimental conditions, mRNA levels of alpha(2A)-adrenoceptors, mu- and kappa-opioid receptors significantly increased, excluding a direct involvement of transcription mechanisms in the regulation of receptor expression. Levels of G protein-coupled receptor kinase 2/3 and of inhibitory G(i/o) proteins were significantly reduced in the myenteric plexus after chronic treatment with desipramine. Such changes might represent possible molecular mechanisms involved in the development of subsensitivity to UK14,304 and U69,593 on the efficiency of peristalsis. Alternative molecular mechanisms, including a higher efficiency in the

  5. Mu Opioid Receptor Actions in the Lateral Habenula

    PubMed Central

    Margolis, Elyssa B.; Fields, Howard L.

    2016-01-01

    Increased activity of lateral habenula (LHb) neurons is correlated with aversive states including pain, opioid abstinence, rodent models of depression, and failure to receive a predicted reward. Agonists at the mu opioid receptor (MOR) are among the most powerful rewarding and pain relieving drugs. Injection of the MOR agonist morphine directly into the habenula produces analgesia, raising the possibility that MOR acts locally within the LHb. Consequently, we examined the synaptic actions of MOR agonists in the LHb using whole cell patch clamp recording. We found that the MOR selective agonist DAMGO inhibits a subset of LHb neurons both directly and by inhibiting glutamate release onto these cells. Paradoxically, DAMGO also presynaptically inhibited GABA release onto most LHb neurons. The behavioral effect of MOR activation will thus depend upon both the level of intrinsic neuronal activity in the LHb and the balance of activity in glutamate and GABA inputs to different LHb neuronal populations. PMID:27427945

  6. Modulation by peripheral opioids of basal and distension-stimulated gastric acid secretion in the rat.

    PubMed Central

    Esplugues, J. V.; Barrachina, M. D.; Esplugues, J.

    1992-01-01

    1. The influence of opioids in modulating gastric acid secretory responses has been investigated in the continuously perfused stomach of the anaesthetized rat. 2. Intravenous administration of morphine (0.75-3 mg kg-1) or the peripherally acting enkephalin analogue, BW443C (0.75-3 mg kg-1), substantially augmented acid secretion in basal conditions. These effects were significantly inhibited by the opioid antagonists naloxone (1 mg kg-1) and the peripherally acting N-methylnalorphine (2 mg kg-1). When administered alone, neither opioid antagonist influenced basal acid output. 3. Acid secretory responses to different levels of gastric distension (5-20 cmH2O) were significantly and dose-dependently reduced in rats pretreated with morphine (3 mg kg-1) or BW443C (1.5 mg kg-1). Previous administration of either naloxone or N-methyl nalorphine reversed the inhibitory effects of opioids on gastric acid secretion stimulated by distension. Likewise, blockade of opioid receptors with naloxone or N-methylnalorphine significantly increased acid output induced by distension. 4. Levels of serum gastrin in control animals were not increased after intragastric distension (20 cmH2O). Pretreatment with BW443C (1.5 mg kg-1) did not modify the levels of gastrin present during basal or distension stimulated conditions. 5. Pretreatment with morphine or BW443C did not influence the acid responses to i.v. injection of pentagastrin (100 micrograms kg-1), histamine (5 mg kg-1) or carbachol (4 micrograms kg-1). Acid secretion induced by i.v. administration of 2-deoxy-D-glucose (150 mg kg-1) was reduced in rats pretreated with morphine but not with BW443C. Gastric secretory responses to insulin (0.3 i.u. kg-1) were not modified by i.v. morphine.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:1504729

  7. μ Opioid receptor: novel antagonists and structural modeling

    PubMed Central

    Kaserer, Teresa; Lantero, Aquilino; Schmidhammer, Helmut; Spetea, Mariana; Schuster, Daniela

    2016-01-01

    The μ opioid receptor (MOR) is a prominent member of the G protein-coupled receptor family and the molecular target of morphine and other opioid drugs. Despite the long tradition of MOR-targeting drugs, still little is known about the ligand-receptor interactions and structure-function relationships underlying the distinct biological effects upon receptor activation or inhibition. With the resolved crystal structure of the β-funaltrexamine-MOR complex, we aimed at the discovery of novel agonists and antagonists using virtual screening tools, i.e. docking, pharmacophore- and shape-based modeling. We suggest important molecular interactions, which active molecules share and distinguish agonists and antagonists. These results allowed for the generation of theoretically validated in silico workflows that were employed for prospective virtual screening. Out of 18 virtual hits evaluated in in vitro pharmacological assays, three displayed antagonist activity and the most active compound significantly inhibited morphine-induced antinociception. The new identified chemotypes hold promise for further development into neurochemical tools for studying the MOR or as potential therapeutic lead candidates. PMID:26888328

  8. μ Opioid receptor: novel antagonists and structural modeling

    NASA Astrophysics Data System (ADS)

    Kaserer, Teresa; Lantero, Aquilino; Schmidhammer, Helmut; Spetea, Mariana; Schuster, Daniela

    2016-02-01

    The μ opioid receptor (MOR) is a prominent member of the G protein-coupled receptor family and the molecular target of morphine and other opioid drugs. Despite the long tradition of MOR-targeting drugs, still little is known about the ligand-receptor interactions and structure-function relationships underlying the distinct biological effects upon receptor activation or inhibition. With the resolved crystal structure of the β-funaltrexamine-MOR complex, we aimed at the discovery of novel agonists and antagonists using virtual screening tools, i.e. docking, pharmacophore- and shape-based modeling. We suggest important molecular interactions, which active molecules share and distinguish agonists and antagonists. These results allowed for the generation of theoretically validated in silico workflows that were employed for prospective virtual screening. Out of 18 virtual hits evaluated in in vitro pharmacological assays, three displayed antagonist activity and the most active compound significantly inhibited morphine-induced antinociception. The new identified chemotypes hold promise for further development into neurochemical tools for studying the MOR or as potential therapeutic lead candidates.

  9. Muscarinic and opioid receptor modulation of release of (Met/sup 5/-enkephalin immunoreactive material and catecholamines from the bovine adrenal gland

    SciTech Connect

    Barron, B.A.

    1985-01-01

    Retrogradely perfused bovine adrenal glands were stimulated by acetylcholine (ACh) and 1,1-dimethyl-4-phenyl-piperazinium (DMPP), with or without: hexamethonium (C-6), atropine, imipramine, methacholine, pilocarpine, etorphine, or diprenorphine. Stimulation by either ACh DMPP resulted in an increased release of both (Met/sup 5/)-enkephalin immunoreactive material (ME-IRM) and catecholamines as measured by radioimmunoassay and high performance liquid chromatography with electrochemical detection, respectively. ACh (5 x 10/sup -5/ M) and DMPP (5 x 10/sup -5/ M) stimulated the release of norepinephrine greater than the release of epinephrine. The action of these agents was antagonized by C-6(5 x 10/sup -4/ M). Atropine (5 x 10/sup -7/ M) antagonized the action of ACh to stimulate norepinephrine and MI-IRM release while having no effect on DMPP-stimulated release. Imipramine (5 x 10/sup -6/ M) had no effect on either ACh or DMPP-stimulated release. Methacholine (4 x 10/sup -5/ M) potentiated the DMPP (1 x 10/sup -5/ M) stimulation of ME-IRM and catecholamine release; pilocarpine (4 x 10/sup -5/ M) significantly potentiated only the DMPP-stimulated release of norepinephrine. Pilocarpine (5 x 10/sup -5/ M) and muscarine (5 x 10/sup -5/ M) had no effect on the secretion of MI-IRM and catecholamines from the bovine adrenal gland. Etorphine (5 x 10/sup -7/ M) significantly decreased the ACh and DMPP stimulation ME-IRM and catecholamine release. The activity of a muscarinic cholinergic receptor in the bovine adrenal medulla in stimulus-secretion coupling has been controversial. The binding of /sup 3/H-quinuclidinyl benzilate to chromaffin granule membranes was investigated to further characterize muscarinic receptors in the bovine adrenal gland.

  10. δ-Opioid receptor agonists inhibit migraine-related hyperalgesia, aversive state and cortical spreading depression in mice

    PubMed Central

    Pradhan, Amynah A; Smith, Monique L; Zyuzin, Jekaterina; Charles, Andrew

    2014-01-01

    Background and Purpose Migraine is an extraordinarily common brain disorder for which treatment options continue to be limited. Agonists that activate the δ-opioid receptor may be promising for the treatment of migraine as they are highly effective for the treatment of chronic rather than acute pain, do not induce hyperalgesia, have low abuse potential and have anxiolytic and antidepressant properties. The aim of this study was to investigate the therapeutic potential of δ-opioid receptor agonists for migraine by characterizing their effects in mouse migraine models. Experimental Approach Mechanical hypersensitivity was assessed in mice treated with acute and chronic doses of nitroglycerin (NTG), a known human migraine trigger. Conditioned place aversion to NTG was also measured as a model of migraine-associated negative affect. In addition, we assessed evoked cortical spreading depression (CSD), an established model of migraine aura, in a thinned skull preparation. Key Results NTG evoked acute and chronic mechanical and thermal hyperalgesia in mice, as well as conditioned place aversion. Three different δ-opioid receptor agonists, SNC80, ARM390 and JNJ20788560, significantly reduced NTG-evoked hyperalgesia. SNC80 also abolished NTG-induced conditioned place aversion, suggesting that δ-opioid receptor activation may also alleviate the negative emotional state associated with migraine. We also found that SNC80 significantly attenuated CSD, a model that is considered predictive of migraine preventive therapies. Conclusions and Implications These data show that δ-opioid receptor agonists modulate multiple basic mechanisms associated with migraine, indicating that δ-opioid receptors are a promising therapeutic target for this disorder. PMID:24467301

  11. Induced association of mu opioid (MOP) and type 2 cholecystokinin (CCK2) receptors by novel bivalent ligands

    PubMed Central

    Zheng, Yaguo; Akgün, Eyup; Harikumar, Kaleeckal G.; Hopson, Jessika; Powers, Michael D.; Lunzer, Mary M.; Miller, Laurence J.; Portoghese, Philip S.

    2009-01-01

    Both mu opioid (MOP)† and type 2 cholecystokinin (CCK2) receptors are present in areas of the central nervous system that are involved in modulation of pain processing. We conducted bioluminescence resonance energy transfer (BRET) studies on COS cells coexpressing MOP and CCK2 receptors to determine whether receptor heterodimerization is involved in such modulation. These studies revealed the absence of constitutive or monovalent ligand-induced heterodimerization. Heterodimerization of MOP and CCK2 receptors therefore is unlikely to be responsible for the opposing effects between morphine and CCK in the CNS. However, association was induced, as indicated by a positive BRET signal, on exposure of the cells to bivalent ligands containing mu-opioid agonist and CCK2 receptor antagonist pharmacophores linked through spacers containing 16 to 22 atoms, but not with a shorter (9-atom) spacer. These studies demonstrate for the first time that an appropriately designed bivalent ligand is capable of inducing association of G protein-coupled receptors. The finding that opioid tolerance studies with these ligands in mice showed no correlation with the BRET data is consistent with the absence of association of MOP and CCK2 receptors in vivo. PMID:19113864

  12. A role for the mu opioid receptor in the antidepressant effects of buprenorphine.

    PubMed

    Robinson, Shivon A; Erickson, Rebecca L; Browne, Caroline A; Lucki, Irwin

    2017-02-15

    Buprenorphine (BPN), a mixed opioid drug with high affinity for mu (MOR) and kappa (KOR) opioid receptors, has been shown to produce behavioral responses in rodents that are similar to those of antidepressant and anxiolytic drugs. Although recent studies have identified KORs as a primary mediator of BPN's effects in rodent models of depressive-like behavior, the role of MORs in BPN's behavioral effects has not been as well explored. The current studies investigated the role of MORs in mediating conditioned approach behavior in the novelty-induced hypophagia (NIH) test, a behavioral measure previously shown to be sensitive to chronic treatment with antidepressant drugs. The effects of BPN were evaluated in the NIH test 24h post-administration in mice with genetic deletion of the MOR (Oprm1(-/-)) or KOR (Oprk1(-/-)), or after pharmacological blockade with the non-selective opioid receptor antagonist naltrexone and selective MOR antagonist cyprodime. We found that behavioral responses to BPN in the NIH test were blocked in Oprm1(-/-) mice, but not in Oprk1(-/-) mice. Both cyprodime and naltrexone significantly reduced approach latency at doses experimentally proven to antagonize the MOR. In contrast the selective MOR agonist morphine and the selective KOR antagonist nor-BNI were both ineffective. Moreover, antinociceptive studies revealed persistence of the MOR antagonist properties of BPN at 24h post-administration, the period of behavioral reactivity. These data support modulation of MOR activity as a key component of BPN's antidepressant-like effects in the NIH paradigm.

  13. Alvimopan: a peripherally acting mu-opioid receptor antagonist.

    PubMed

    Leslie, John B

    2007-09-01

    Postoperative ileus (POI), a transient cessation of coordinated bowel motility after surgery, is an important factor in extending the length of hospital stay. The etiology of POI is multifactorial, and related to both the surgical and anesthetic pathways chosen. Additionally, opioids used to manage non-cancer-related and cancer-related chronic pain may also decrease gastrointestinal (GI) motility resulting in opioid-induced bowel dysfunction (OBD). Postoperative ileus has been associated with prolonged hospital stay and readmission, and thus may increase the overall hospital costs per patient with POI. Alvimopan, a peripherally acting mu-opioid receptor antagonist, accelerated time to GI recovery and reduced postoperative hospital length of stay in phase III POI clinical trials and improved symptoms of OBD compared with placebo in phase II/III clinical trials. The U.S. Food and Drug Administration is currently evaluating alvimopan for the management of POI after bowel resection. Alvimopan may provide clinically meaningful benefits to patients and may lower the economic burden of POI to the healthcare system.

  14. Opioid Receptors Mediate Direct Predictive Fear Learning: Evidence from One-Trial Blocking

    ERIC Educational Resources Information Center

    Cole, Sindy; McNally, Gavan P.

    2007-01-01

    Pavlovian fear learning depends on predictive error, so that fear learning occurs when the actual outcome of a conditioning trial exceeds the expected outcome. Previous research has shown that opioid receptors, including [mu]-opioid receptors in the ventrolateral quadrant of the midbrain periaqueductal gray (vlPAG), mediate such predictive fear…

  15. Binding-site analysis of opioid receptors using monoclonal anti-idiotypic antibodies

    SciTech Connect

    Conroy, W.G.

    1988-01-01

    Structural relatedness between the variable region of anti-ligand antibodies and opioid binding sites allowed the generation of anti-idiotypic antibodies which recognized opioid receptors. The IgG{sub 3}k antibodies which bound to opioid receptors were obtained when an anti-morphine antiserum was the idiotype. Both antibodies bound to opioid receptors, but only one of these blocked the binding of ({sup 3}H)naloxone. The antibody which did not inhibit the binding of ({sup 3}H)naloxone was itself displaced from the receptor by opioid ligands. The unique binding properties displayed by this antibody indicated that anti-idiotypic antibodies are not always a perfect image of the original ligand, and therefore may be more useful than typical ligands as probes for the receptor. An auto-anti-idiotypic technique was successfully used to obtain anti-opioid receptor antibodies. Another IgG{sub 3}k antibody that blocked the binding of ({sup 3}H)naloxone to rat brain opioid receptors was obtained when a mouse was immunized with naloxone conjugated to bovine serum albumin. These data confirmed that an idiotype-anti-idiotype network which can generate an anti-receptor antibody normally functions when an opioid ligand is introduced into an animal in an immunogenic form.

  16. In silico design of novel probes for the atypical opioid receptor MRGPRX2.

    PubMed

    Lansu, Katherine; Karpiak, Joel; Liu, Jing; Huang, Xi-Ping; McCorvy, John D; Kroeze, Wesley K; Che, Tao; Nagase, Hiroshi; Carroll, Frank I; Jin, Jian; Shoichet, Brian K; Roth, Bryan L

    2017-03-13

    The primate-exclusive MRGPRX2 G protein-coupled receptor (GPCR) has been suggested to modulate pain and itch. Despite putative peptide and small-molecule MRGPRX2 agonists, selective nanomolar-potency probes have not yet been reported. To identify a MRGPRX2 probe, we first screened 5,695 small molecules and found that many opioid compounds activated MRGPRX2, including (-)- and (+)-morphine, hydrocodone, sinomenine, dextromethorphan, and the prodynorphin-derived peptides dynorphin A, dynorphin B, and α- and β-neoendorphin. We used these to select for mutagenesis-validated homology models and docked almost 4 million small molecules. From this docking, we predicted ZINC-3573-a potent MRGPRX2-selective agonist, showing little activity against 315 other GPCRs and 97 representative kinases-along with an essentially inactive enantiomer. ZINC-3573 activates endogenous MRGPRX2 in a human mast cell line, inducing degranulation and calcium release. MRGPRX2 is a unique atypical opioid-like receptor important for modulating mast cell degranulation, which can now be specifically modulated with ZINC-3573.

  17. Kappa-opioid receptor-selective dicarboxylic ester-derived salvinorin A ligands.

    PubMed

    Polepally, Prabhakar R; White, Kate; Vardy, Eyal; Roth, Bryan L; Ferreira, Daneel; Zjawiony, Jordan K

    2013-05-15

    Salvinorin A, the active ingredient of the hallucinogenic plant Salvia divinorum is the most potent known naturally occurring hallucinogen and is a selective κ-opioid receptor agonist. To better understand the ligand-receptor interactions, a series of dicarboxylic ester-type of salvinorin A derivatives were synthesized and evaluated for their binding affinity at κ-, δ- and μ-opioid receptors. Most of the analogues show high affinity to the κ-opioid receptor. Methyl malonyl derivative 4 shows the highest binding affinity (Ki=2nM), analogues 5, 7, and 14 exhibit significant affinity for the κ-receptor (Ki=21, 36 and 39nM).

  18. Kappa-Opioid Receptor-Selective Dicarboxylic Ester-Derived Salvinorin A Ligands

    PubMed Central

    Polepally, Prabhakar R.; White, Kate; Vardy, Eyal; Roth, Bryan L.; Ferreira, Daneel; Zjawiony, Jordan K.

    2013-01-01

    Salvinorin A, the active ingredient of the hallucinogenic plant Salvia divinorum is the most potent known naturally occurring hallucinogen and is a selective κ-opioid receptor agonist. To better understand the ligand-receptor interactions, a series of dicarboxylic ester-type of salvinorin A derivatives were synthesized and evaluated for their binding affinity at κ, δ, and μ-opioid receptors. Most of the analogues show high affinity to the κ-opioid receptor. Methyl malonyl derivative 4 shows the highest binding affinity (Ki = 2 nM), analogues 5, 7, and 14 exhibit significant affinity for the κ-receptor (Ki = 21, 36 and 39 nM). PMID:23587424

  19. 17-Cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6β-(4'-pyridylcarboxamido)morphinan (NAP) Modulating the Mu Opioid Receptor in a Biased Fashion.

    PubMed

    Zhang, Yan; Williams, Dwight A; Zaidi, Saheem A; Yuan, Yunyun; Braithwaite, Amanda; Bilsky, Edward J; Dewey, William L; Akbarali, Hamid I; Streicher, John M; Selley, Dana E

    2016-03-16

    Mounting evidence has suggested that G protein-coupled receptors can be stabilized in multiple conformations in response to distinct ligands, which exert discrete functions through selective activation of various downstream signaling events. In accordance with this concept, we report biased signaling of one C6-heterocyclic substituted naltrexamine derivative, namely, 17-cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6β-(4'-pyridylcarboxamido)morphinan (NAP) at the mu opioid receptor (MOR). NAP acted as a low efficacy MOR partial agonist in the G protein-mediated [(35)S]GTPγS binding assay, whereas it did not significantly induce calcium flux or β-arrestin2 recruitment. In contrast, it potently blocked MOR full agonist-induced β-arrestin2 recruitment and translocation. Additionally, NAP dose-dependently antagonized MOR full agonist-induced intracellular calcium flux and β-arrestin2 recruitment. Further results in an isolated organ bath preparation confirmed that NAP reversed the morphine-induced reduction in colon motility. Ligand docking and dynamics simulation studies of NAP at the MOR provided more supporting evidence for biased signaling of NAP at an atomic level. Due to the fact that NAP is MOR selective and preferentially distributed peripherally upon systemic administration while β-arrestin2 is reportedly required for impairment of intestinal motility by morphine, biased antagonism of β-arrestin2 recruitment by NAP further supports its utility as a treatment for opioid-induced constipation.

  20. The delta-opioid receptor is sufficient, but not necessary, for spinal opioid-adrenergic analgesic synergy.

    PubMed

    Chabot-Doré, Anne-Julie; Millecamps, Magali; Stone, Laura S

    2013-12-01

    Spinal administration of opioid and α2-adrenergic receptor (α2AR) agonists produces analgesia, and agonists interact synergistically when coadministered. The molecular mechanism underlying this synergy is largely unknown. Pharmacological studies have identified both the delta and the mu-opioid receptors (DOR and MOR) as candidate receptors capable of interacting synergistically with α2AR agonists. However, recent studies attribute the antinociceptive effect of DOR agonists to actions at the MOR, calling the role of DOR in opioid-adrenergic synergy into question. Other studies suggesting that DOR is implicated in morphine antinociception raise the possibility that DOR is nonetheless required for morphine synergy with α2AR agonists. This study aimed to determine whether DOR activation is sufficient and necessary to mediate opioid-adrenergic synergistic interactions in the spinal cord. The antinociceptive effects of clonidine, [D-Ala(2)]-deltorphin II (DeltII), morphine, and [D-Ala(2), N-Me-Phe(4), Gly-ol(5)]-enkephalin (DAMGO) were evaluated using the substance P (SP) behavioral assay in wild type (WT) and DOR-knockout (KO) mice. Opioid-adrenergic drug interactions were evaluated after spinal coadministration of clonidine with DeltII, morphine, or DAMGO. Isobolographic analyses of dose-response curves determined whether interactions were synergistic or additive. The absence of DeltII antinociceptive efficacy in DOR-KO confirmed its selectivity in the SP assay. Although DeltII+clonidine interacted synergistically in WT mice, no interaction with clonidine was observed in DOR-KO mice. Clonidine was synergistic with morphine in both mouse strains. DAMGO did not synergize with clonidine in either strain. These findings confirm that although other opioid receptors can interact synergistically with α2AR agonists, DOR is sufficient for spinal opioid-adrenergic interactions.

  1. AM-251 and rimonabant act as direct antagonists at mu-opioid receptors: implications for opioid/cannabinoid interaction studies.

    PubMed

    Seely, Kathryn A; Brents, Lisa K; Franks, Lirit N; Rajasekaran, Maheswari; Zimmerman, Sarah M; Fantegrossi, William E; Prather, Paul L

    2012-10-01

    Mu-opioid and CB1-cannabinoid agonists produce analgesia; however, adverse effects limit use of drugs in both classes. Additive or synergistic effects resulting from concurrent administration of low doses of mu- and CB1-agonists may produce analgesia with fewer side effects. Synergism potentially results from interaction between mu-opioid receptors (MORs) and CB1 receptors (CB1Rs). AM-251 and rimonabant are CB1R antagonist/inverse agonists employed to validate opioid-cannabinoid interactions, presumed to act selectively at CB1Rs. Therefore, the potential for direct action of these antagonists at MORs is rarely considered. This study determined if AM-251 and/or rimonabant directly bind and modulate the function of MORs. Surprisingly, AM-251 and rimonabant, but not a third CB1R inverse agonist AM-281, bind with mid-nanomolar affinity to human MORs with a rank order of affinity (K(i)) of AM-251 (251 nM) > rimonabant (652 nM) > AM281 (2135 nM). AM-251 and rimonabant, but not AM-281, also competitively antagonize morphine induced G-protein activation in CHO-hMOR cell homogenates (K(b) = 719 or 1310 nM, respectively). AM-251 and rimonabant block morphine inhibition of cAMP production, while only AM-251 elicits cAMP rebound in CHO-hMOR cells chronically exposed to morphine. AM-251 and rimonabant (10 mg/kg) attenuate morphine analgesia, whereas the same dose of AM-281 produces little effect. Therefore, in addition to high CB1R affinity, AM-251 and rimonabant bind to MORs with mid-nanomolar affinity and at higher doses may affect morphine analgesia via direct antagonism at MORs. Such CB1-independent of these antagonists effects may contribute to reported inconsistencies when CB1/MOR interactions are examined via pharmacological methods in CB1-knockout versus wild-type mice.

  2. A Novel Approach for Effectively Treating SCI Pain, Improving Opioid Efficacy, and Preventing Opioid-Induced Constipation: Key Role of Toll-Like Receptor 4 (TLR4)

    DTIC Science & Technology

    2015-10-01

    pain ; however, morphine for 7 d post-SCI has little effect on chronic thermal nociceptive thresholds in this model. Establishing effects of post-SCI...AWARD NUMBER: W81XWH-13-1-0277 TITLE: A Novel Approach for Effectively Treating SCI Pain , Improving Opioid Efficacy, and Preventing Opioid...SCI Pain , Improving Opioid Efficacy, and Preventing Opioid-Induced Constipation: Key Role of Toll-Like Receptor 4 (TLR4) 5a. CONTRACT NUMBER 5b

  3. Peripheral Sensitization Increases Opioid Receptor Expression and Activation by Crotalphine in Rats

    PubMed Central

    Zambelli, Vanessa Olzon; Fernandes, Ana Carolina de Oliveira; Gutierrez, Vanessa Pacciari; Ferreira, Julio Cesar Batista; Parada, Carlos Amilcar; Mochly-Rosen, Daria; Cury, Yara

    2014-01-01

    Inflammation enhances the peripheral analgesic efficacy of opioid drugs, but the mechanisms involved in this phenomenon have not been fully elucidated. Crotalphine (CRP), a peptide that was first isolated from South American rattlesnake C.d. terrificus venom, induces a potent and long-lasting anti-nociceptive effect that is mediated by the activation of peripheral opioid receptors. Because the high efficacy of CRP is only observed in the presence of inflammation, we aimed to elucidate the mechanisms involved in the CRP anti-nociceptive effect induced by inflammation. Using real-time RT-PCR, western blot analysis and ELISA assays, we demonstrate that the intraplantar injection of prostaglandin E2 (PGE2) increases the mRNA and protein levels of the µ- and κ-opioid receptors in the dorsal root ganglia (DRG) and paw tissue of rats within 3 h of the injection. Using conformation state-sensitive antibodies that recognize activated opioid receptors, we show that PGE2, alone does not increase the activation of these opioid receptors but that in the presence of PGE2, the activation of specific opioid receptors by CRP and selective µ- and κ-opioid receptor agonists (positive controls) increases. Furthermore, PGE2 down-regulated the expression and activation of the δ-opioid receptor. CRP increased the level of activated mitogen-activated protein kinases in cultured DRG neurons, and this increase was dependent on the activation of protein kinase Cζ. This CRP effect was much more prominent when the cells were pretreated with PGE2. These results indicate that the expression and activation of peripheral opioid receptors by opioid-like drugs can be up- or down-regulated in the presence of an acute injury and that acute tissue injury enhances the efficacy of peripheral opioids. PMID:24594607

  4. Kappa opioid receptor signaling protects cartilage tissue against posttraumatic degeneration

    PubMed Central

    Zhang, Shu; Shkhyan, Ruzanna; Lee, Siyoung; Gullo, Francesca; Petrigliano, Frank A.; Ba, Kai; Wang, Jing

    2017-01-01

    Osteoarthritis is the most common form of arthritis, and pain relief with opioid-like drugs is a commonly used therapeutic for osteoarthritic patients. Recent studies published by our group showed that the kappa opioid receptor (KOR) is highly expressed during human development in joint-forming cells. However, the precise role of this receptor in the skeletal system remains elusive. The main aim of the current study was to investigate the role of KOR signaling in synovial and cartilaginous tissues in pathological conditions. Our data demonstrate that KOR null mice exhibit accelerated cartilage degeneration after injury when compared with WT mice. Activation of KOR signaling increased the expression of anabolic enzymes and inhibited cartilage catabolism and degeneration in response to proinflammatory cytokines such as TNF-α. In addition, selective KOR agonists increased joint lubrication via the activation of cAMP/CREB signaling in chondrocytes and synovial cells. Taken together, these results demonstrate direct effects of KOR agonists on cartilage and synovial cells and reveals a protective effect of KOR signaling against cartilage degeneration after injury. In addition to pain control, local administration of dynorphin or other KOR agonist represents an attractive therapeutic approach in patients with early stages of osteoarthritis. PMID:28097228

  5. delta- and mu-opioid receptor mobilization of intracellular calcium in SH-SY5Y human neuroblastoma cells.

    PubMed Central

    Connor, M.; Henderson, G.

    1996-01-01

    ). This treatment did not significantly affect the response of the cells to carbachol. 8. The opioids appeared to elevate [Ca2+]i by mobilizing Ca2+ from intracellular stores. Both DPDPE and DAMGO continued to elevate [Ca2+]i when applied in nominally Ca(2+)-free external buffer or when applied in a buffer containing a cocktail of Ca2+ entry inhibitors. Thapsigargin (100 nM), an agent which discharges intracellular Ca2+ stores, also blocked the opioid elevations of [Ca2+]i. 9. delta and mu Opioids did not appear to mobilize intracellular Ca2+ by modulating the activity of protein kinases. The application of H-89 (10 microM), an inhibitor of protein kinase A, H-7 (100 microM), an inhibitor of protein kinase C, protein kinase A and cyclic GMP-dependent protein kinase, or Bis I, an inhibitor of protein kinase C, did not alter the opioid mobilization of [Ca2+]i. 10. Thus, in SH-SY5Y cells, opioids can mobilize Ca2+ from intracellular stores but they require ongoing muscarinic receptor activation. Opioids do not elevate [Ca2+]i when applied alone. PMID:8789387

  6. Unexpected Opioid Activity Profiles of Analogs of the Novel Peptide Kappa Opioid Receptor Ligand CJ-15,208

    PubMed Central

    Aldrich, Jane V.; Kulkarni, Santosh S.; Senadheera, Sanjeewa N.; Ross, Nicolette C.; Reilley, Kate J.; Eans, Shainnel O.; Ganno, Michelle L.; Murray, Thomas F.; McLaughlin, Jay P.

    2013-01-01

    An alanine scan was performed on the novel kappa opioid receptor (KOR) peptide ligand CJ-15,208 to determine which residues contribute to the potent in vivo agonist activity observed for the parent peptide. These cyclic tetrapeptides were synthesized by a combination of solid phase peptide synthesis of the linear precursors, followed by cyclization in solution. Like the parent peptide, each of the analogs exhibited agonist activity and KOR antagonist activity in an antinociceptive assay in vivo. Unlike the parent peptide, the agonist activity of the potent analogs was mediated predominantly if not exclusively by mu opioid receptors (MOR). Thus analogs 2 and 4, in which one of the phenylalanine residues was replaced by alanine, exhibited both potent MOR agonist activity and KOR antagonist activity in vivo. These peptides represent novel lead compounds for the development of peptide-based opioid analgesics. PMID:21761566

  7. Life-Threatening Opioid Toxicity

    DTIC Science & Technology

    1987-01-01

    receptor is currently the object of much it- "ention. This receptor is postulated to me- diate hallucinations, delusions, and dys- occurring peptides ...teraction with endogenous opioid receptors, peptides have also been shown to function opiate drugs are classified as agonists as neurotransmitters...activity of others; Table 1). function.Ŗ’ 3 Delta sleep-inducing peptide Modulation of opioid receptor activity oc- (DSIP) has also been implicated

  8. MicroRNA 339 down-regulates μ-opioid receptor at the post-transcriptional level in response to opioid treatment

    PubMed Central

    Wu, Qifang; Hwang, Cheol Kyu; Zheng, Hui; Wagley, Yadav; Lin, Hong-Yiou; Kim, Do Kyung; Law, Ping-Yee; Loh, Horace H.; Wei, Li-Na

    2013-01-01

    μ-Opioid receptor (MOR) level is directly related to the function of opioid drugs, such as morphine and fentanyl. Although agonist treatment generally does not affect transcription of mor, previous studies suggest that morphine can affect the translation efficiency of MOR transcript via microRNAs (miRNAs). On the basis of miRNA microarray analyses of the hippocampal total RNA isolated from mice chronically treated with μ-opioid agonists, we found a miRNA (miR-339-3p) that was consistently and specifically increased by morphine (2-fold) and by fentanyl (3.8-fold). miR-339-3p bound to the MOR 3′-UTR and specifically suppressed reporter activity. Suppression was blunted by adding miR-339-3p inhibitor or mutating the miR-339-3p target site. In cells endogenously expressing MOR, miR-339-3p inhibited the production of MOR protein by destabilizing MOR mRNA. Up-regulation of miR-339-3p by fentanyl (EC50=0.75 nM) resulted from an increase in primary miRNA transcript. Mapping of the miR-339-3p primary RNA and its promoter revealed that the primary miR-339-3p was embedded in a noncoding 3′-UTR region of an unknown host gene and was coregulated by the host promoter. The identified promoter was activated by opioid agonist treatment (10 nM fentanyl or 10 μM morphine), a specific effect blocked by the opioid antagonist naloxone (10 μM). Taken together, these results suggest that miR-339-3p may serve as a negative feedback modulator of MOR signals by regulating intracellular MOR biosynthesis.—Wu, Q., Hwang, C. K., Zheng, H., Wagley, Y., Lin, H.-Y., Kim, D. K., Law, P.-Y., Loh, H. H., Wei, L.-N. MicroRNA 339 downregulates mu opioid receptor at the post-transcriptional level in response to opioid treatment. PMID:23085997

  9. Differential Effect of Membrane Cholesterol Removal on μ- and δ-Opioid Receptors

    PubMed Central

    Levitt, Erica S.; Clark, Mary J.; Jenkins, Paul M.; Martens, Jeffrey R.; Traynor, John R.

    2009-01-01

    According to the lipid raft theory, the plasma membrane contains small domains enriched in cholesterol and sphingolipid, which may serve as platforms to organize membrane proteins. Using methyl-β-cyclodextrin (MβCD) to deplete membrane cholesterol, many G protein-coupled receptors have been shown to depend on putative lipid rafts for proper signaling. Here we examine the hypothesis that treatment of HEK293 cells stably expressing FLAG-tagged μ-opioid receptors (HEK FLAG-μ) or δ-opioid receptors (HEK FLAG-δ) with MβCD will reduce opioid receptor signaling to adenylyl cyclase. The ability of the μ-opioid agonist [d-Ala2,N-Me-Phe4,Gly5-ol]enkephalin to acutely inhibit adenylyl cyclase or to cause sensitization of adenylyl cyclase following chronic treatment was attenuated with MβCD. These effects were due to removal of cholesterol, because replenishment of cholesterol restored [d-Ala2,N-Me-Phe4,Gly5-ol]enkephalin responses back to control values, and were confirmed in SH-SY5Y cells endogenously expressing μ-opioid receptors. The effects of MβCD may be due to uncoupling of the μ receptor from G proteins but were not because of decreases in receptor number and were not mimicked by cytoskeleton disruption. In contrast to the results in HEK FLAG-μ cells, MβCD treatment of HEK FLAG-δ cells had no effect on acute inhibition or sensitization of adenylyl cyclase by δ-opioid agonists. The differential responses of μ- and δ-opioid agonists to cholesterol depletion suggest that μ-opioid receptors are more dependent on cholesterol for efficient signaling than δ receptors and can be partly explained by localization of μ- but not δ-opioid receptors in cholesterol- and caveolin-enriched membrane domains. PMID:19520863

  10. Nicotine enhancement and reinforcer devaluation: Interaction with opioid receptors.

    PubMed

    Kirshenbaum, Ari P; Suhaka, Jesse A; Phillips, Jessie L; Voltolini de Souza Pinto, Maiary

    In rats, nicotine enhances responding maintained by non-pharmacological reinforcers, and discontinuation of nicotine devalues those same reinforcers. The goal of this study was to assess the interaction of nicotine and opioid receptors and to evaluate the degree to which nicotine enhancement and nicotine-induced devaluation are related to opioid activation. Nicotine (0.4mg/kg), or nicotine plus naloxone (0.3 or 3.0mg/kg), was delivered to rats prior to progressive ratio (PR) schedule sessions in which sucrose was used as a reinforcer. PR-schedule responding was assessed during ten daily sessions of drug delivery, and for three post-dosing days/sessions. Control groups for this investigation included a saline-only condition, and naloxone-only (0.3 or 3.0mg/kg) conditions. When administered in conjunction with nicotine, both naloxone doses attenuated nicotine enhancement of the sucrose reinforcer, and the combination of the larger dose of naloxone (3.0mg/kg) with nicotine produced significant impairments in sucrose reinforced responding. When administered alone, neither dose of naloxone (0.3 & 3.0mg/kg) significantly altered responding in comparison to saline. Furthermore, when dosing was discontinued after ten once-daily doses, all nicotine groups (nicotine-only and nicotine+naloxone combination) demonstrated significant decreases in sucrose reinforcement compared to the saline group. Although opioid antagonism attenuated reinforcement enhancement by nicotine, it did not prevent reinforcer devaluation upon discontinuation of nicotine dosing, and the higher dose of naloxone (3.0mg/kg) produced decrements upon discontinuation on its own in the absence of nicotine.

  11. A6V polymorphism of the human μ-opioid receptor decreases signalling of morphine and endogenous opioids in vitro

    PubMed Central

    Knapman, Alisa; Santiago, Marina; Connor, Mark

    2015-01-01

    Background and Purpose Polymorphisms of the μ opioid receptor (MOPr) may contribute to the variation in responses to opioid drugs in clinical and unregulated situations. The A6V variant of MOPr (MOPr-A6V) is present in up to 20% of individuals in some populations, and may be associated with heightened susceptibility to drug abuse. There are no functional studies examining the acute signalling of MOPr-A6V in vitro, so we investigated potential functional differences between MOPr and MOPr-A6V at several signalling pathways using structurally distinct opioid ligands. Experimental Approach CHO and AtT-20 cells stably expressing MOPr and MOPr-A6V were used. AC inhibition and ERK1/2 phosphorylation were assayed in CHO cells; K channel activation was assayed in AtT-20 cells. Key Results Buprenorphine did not inhibit AC or stimulate ERK1/2 phosphorylation in CHO cells expressing MOPr-A6V, but buprenorphine activation of K channels in AtT-20 cells was preserved. [D-Ala2, N-MePhe4, Gly-ol]-enkephalin, morphine and β-endorphin inhibition of AC was significantly reduced via MOPr-A6V, as was signalling of all opioids to ERK1/2. However, there was little effect of the A6V variant on K channel activation. Conclusions and Implications Signalling to AC and ERK via the mutant MOPr-A6V was decreased for many opioids, including the clinically significant drugs morphine, buprenorphine and fentanyl, as well endogenous opioids. The MOPr-A6V variant is common and this compromised signalling may affect individual responses to opioid therapy, while the possible disruption of the endogenous opioid system may contribute to susceptibility to substance abuse. PMID:25521224

  12. Opioid Receptor Antagonists in the Treatment of Alcoholism.

    PubMed

    Serecigni, Josep Guardia

    2015-09-29

    Objetivos: A partir de los recientes progresos en la farmacoterapia del alcoholismo, hemos efectuado una revisión sobre los fármacos antagonistas de los receptores opioides, que tienen aprobada la indicación para el tratamiento del alcoholismo, como son naltrexona y nalmefeno. Metodología: Hemos revisado más de 100 publicaciones sobre péptidos y receptores opioides, el efecto de los fármacos antagonistas de los receptores opioides sobre el consumo de alcohol, tanto en animales como en humanos, tanto en el laboratorio como para el tratamiento del alcoholismo. También se describen las características farmacológicas de naltrexona y de nalmefeno y su utilidad en la práctica clínica. Resultados: Múltiples evidencias han demostrado la eficacia de naltrexona y nalmefeno para reducir el consumo de alcohol, tanto en animales de laboratorio como también en personas estudiadas en situación de bar experimental, aunque debido al diferente perfil receptorial, nalmefeno ha sido relacionado con una mayor eficacia para la reducción del consumo de alcohol, en ratas que presentan dependencia del alcohol. Además, un gran número de ensayos clínicos controlados han demostrado la eficacia de naltrexona para la prevención de recaídas, en personas que presentan un trastorno por dependencia del alcohol. Ensayos clínicos controlados recientes han demostrado la eficacia de nalmefeno “a demanda” para reducir el consumo de alcohol, en personas que presentan un trastorno por dependencia del alcohol de baja gravedad. Conclusiones: Tanto naltrexona como nalmefeno han demostrado ser fármacos seguros, bien tolerados, de manejo sencillo, y eficaces para el tratamiento del trastorno por dependencia del alcohol, (actualmente llamado trastorno por consumo de alcohol). A partir de recientes ensayos clínicos controlados se ha comprobado que nalmefeno produce una reducción significativa del consumo de alcohol, lo cual supone un nuevo objetivo que amplía las posibilidades de

  13. Mu opioid receptors are in discrete hippocampal interneuron subpopulations.

    PubMed

    Drake, Carrie T; Milner, Teresa A

    2002-01-01

    In the rat hippocampal formation, application of mu opioid receptor (MOR) agonists disinhibits principal cells, promoting excitation-dependent processes such as epileptogenesis and long-term potentiation. However, the precise location of MORs in particular inhibitory circuits, has not been determined, and the roles of MORs in endogenous functioning are unclear. To address these issues, the distribution of MOR-like immunoreactivity (-li) was examined in several populations of inhibitory hippocampal neurons in the CA1 region using light and electron microscopy. We found that MOR-li was present in many parvalbumin-containing basket cells, but absent from cholecystokinin-labeled basket cells. MOR-li was also commonly in interneurons containing somatostatin-li or neuropeptide Y-li that resembled the "oriens-lacunosum-moleculare" (O-LM) interneurons innervating pyramidal cell distal dendrites. Finally, MOR-li was in some vasoactive intestinal peptide- or calretinin-containing profiles resembling interneurons that primarily innervate other interneurons. These findings indicate that MOR-containing neurons form a neurochemically and functionally heterogeneous subset of hippocampal GABAergic neurons. MORs are most frequently on interneurons that are specialized to inhibit pyramidal cells, and are on a limited number of interneurons that target other interneurons. Moreover, the distribution of MORs to different neuronal types in several laminae, some relatively far from endogenous opioids, suggests normal functional roles that are different from the actions seen with exogenous agonists such as morphine.

  14. Hormonal responses to opioid receptor blockade: during rest and exercise in cold and hot environments.

    PubMed

    Armstrong, David W; Hatfield, Bradley D

    2006-05-01

    Opioid receptors appear to modulate a variety of physiological and metabolic homeostatic responses to stressors such as exercise and thermally extreme environments. To more accurately determine the role of the naloxone (NAL) sensitive opioid receptor system during rest and exercise, subjects were subjected to concomitant environmental thermal stress. Fifteen untrained men rested or performed low intensity (60% VO2peak) or high intensity (80% VO2peak) exercise on a cycle ergometer for 60 min in an environmental chamber during cold (0 degrees C) hot (35 degrees C) air exposure while receiving an infusion of normal saline (SAL) or NAL (0.1 mg kg(-1)). Plasma adrenocorticotropin hormone (ACTH), immunoreactive beta-endorphin (IBE), cortisol and growth hormone were measured at baseline and every 15 min while in the chamber. Time to exhaustion was significantly reduced during high intensity exercise in the heat (P<0.0001). NAL significantly (P=0.0004) reduced the time to exhaustion (38.3+/-2.1 min) during high intensity exercise in the heat compared to SAL (49.4+/-2.1 min). ACTH and IBE increased during hot conditions and cold attenuated this response. Plasma concentrations of IBE, ACTH, and growth hormone increased significantly with NAL during high intensity exercise in the heat compared to SAL. Cold attenuated the response of ACTH, IBE and cortisol to NAL. NAL administration exaggerates plasma hormone concentration during high intensity exercise in the heat, but not cold. These results support a regulatory effect of the opioid receptor system on physiological responses during exercise in thermally stressful environments. Future research should be directed to more clearly defining the effect of environmental temperature on the mechanism of hypothalamic-pituitary-adrenal hormonal release during exercise and hot environmental temperatures.

  15. Mu and kappa opioid receptors of the periaqueductal gray stimulate and inhibit thermogenesis, respectively, during psychological stress in rats.

    PubMed

    Cristina-Silva, Caroline; Martins, Victor; Gargaglioni, Luciane H; Bícego, Kênia C

    2017-04-04

    The periaqueductal gray matter (PAG) is rich in mu and kappa opioid receptors, and this system is involved in thermoregulation, analgesia, and defensive behaviors. No study approached the involvement of the PAG opioids in body temperature (Tb) regulation during psychological stress such as restraint. Because activation of mu and kappa receptors increases and reduces Tb, respectively, we tested the hypothesis that they exert excitatory and inhibitory modulation, respectively, of the restraint-induced fever in rats. To this end, Tb, heat loss index (HLI, inference for peripheral vasoconstriction/vasodilation), and oxygen consumption (inference for thermogenesis) were monitored in unanesthetized rats, restrained or unrestrained, before and after intra-PAG microinjection of the selective mu opioid receptor antagonist (D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH2 cyclic, CTAP; 1 and 10 μg/100 nL) or the selective kappa opioid receptor antagonist (nor-binaltorphimine dihydrochloride, nor-BNI; 1 and 4 μg/100 nL) or saline (100 nL). CTAP and nor-BNI did not change the Tb or HLI of euthermic animals. During restraint, Tb increased (1.0 ± 0.1 °C) in all groups; however, this effect was lower in those animals treated with CTAP and higher in animals treated with nor-BNI. The HLI decreased during restraint and increased after animals were released, but this response was not affected by any treatment. Restraint stress increased oxygen consumption (35.9 ± 3.9% elevation), but this response was diminished by CTAP and overstimulated by nor-BNI. Confirming our hypothesis, the results indicate that the mu and kappa opioid receptors in the PAG of rats play a pyrogenic and antipyretic role, respectively, during fever induced by restraint by affecting the thermogenic but not the heat conservation effector.

  16. Ghrelin receptor agonist, GHRP-2, produces antinociceptive effects at the supraspinal level via the opioid receptor in mice.

    PubMed

    Zeng, Ping; Li, Shu; Zheng, Yue-hui; Liu, Fu-Yan; Wang, Jing-lei; Zhang, Da-lei; Wei, Jie

    2014-05-01

    GHRP-2 is a synthetic agonist of ghrelin receptor. GHRP-2 has similar physiological functions with ghrelin. In our previous study, ghrelin (i.c.v.) could induce analgesic effect through an interaction with GHS-R1α and with the central opioid system in the acute pain in mice. To date, the function of GHRP-2 in pain processing was not understood. Therefore the aim of this study was to investigate the effects of GHRP-2 on pain modulation at supraspinal level in mice using the tail immersion test. Intracerebroventricular (i.c.v.) administration of GHRP-2 (0.1, 0.3, 1, 3 and 10 nmol/L) produced a concentration- and time-related antinociceptive effect. This effect could be fully antagonized by GHS-R1α antagonist [d-Lys(3)]-GHRP-6, indicating that the analgesic effect induced by GHRP-2 is mediated through the activation of GHS-R1α. Interestingly, naloxone, naltrindole and nor-binaltorphimine, but not β-funaltrexamine, could also block the analgesic effect markedly, suggesting that δ- and κ-opioid receptor is involved in the analgesic response evoked by GHRP-2. Moreover, i.c.v. administration of GHRP-2 potentiated the analgesic effect induced by morphine (i.c.v., 1 nmol/L) and this potentiated effect could not be reversed by [d-Lys(3)]-GHRP-6. Thus these findings may be a new strategy on investigating the interaction between ghrelin system and opioids on pain modulation. Furthermore, GHRP-2 may be a promising peptide for developing new analgesic drugs.

  17. Structural insights into µ-opioid receptor activation.

    PubMed

    Huang, Weijiao; Manglik, Aashish; Venkatakrishnan, A J; Laeremans, Toon; Feinberg, Evan N; Sanborn, Adrian L; Kato, Hideaki E; Livingston, Kathryn E; Thorsen, Thor S; Kling, Ralf C; Granier, Sébastien; Gmeiner, Peter; Husbands, Stephen M; Traynor, John R; Weis, William I; Steyaert, Jan; Dror, Ron O; Kobilka, Brian K

    2015-08-20

    Activation of the μ-opioid receptor (μOR) is responsible for the efficacy of the most effective analgesics. To shed light on the structural basis for μOR activation, here we report a 2.1 Å X-ray crystal structure of the murine μOR bound to the morphinan agonist BU72 and a G protein mimetic camelid antibody fragment. The BU72-stabilized changes in the μOR binding pocket are subtle and differ from those observed for agonist-bound structures of the β2-adrenergic receptor (β2AR) and the M2 muscarinic receptor. Comparison with active β2AR reveals a common rearrangement in the packing of three conserved amino acids in the core of the μOR, and molecular dynamics simulations illustrate how the ligand-binding pocket is conformationally linked to this conserved triad. Additionally, an extensive polar network between the ligand-binding pocket and the cytoplasmic domains appears to play a similar role in signal propagation for all three G-protein-coupled receptors.

  18. Direct association of Mu-opioid and NMDA glutamate receptors supports their cross-regulation: molecular implications for opioid tolerance.

    PubMed

    Garzón, Javier; Rodríguez-Muñoz, María; Sánchez-Blázquez, Pilar

    2012-09-01

    In the nervous system, the interaction of opioids like morphine and its derivatives, with the G protein-coupled Mu-opioid receptor (MOR) provokes the development of analgesic tolerance, as well as physical dependence. Tolerance implies that increasing doses of the drug are required to achieve the same effect, a phenomenon that contributes significantly to the social problems surrounding recreational opioid abuse. In recent years, our understanding of the mechanisms that control MOR function in the nervous system, and that eventually produce opioid tolerance, has increased greatly. Pharmacological studies have identified a number of signaling proteins involved in morphine-induced tolerance, including the N-methyl-D-aspartate acid glutamate receptor (NMDAR), nitric oxide synthase (NOS), protein kinase C (PKC), protein kinase A (PKA), calcium (Ca²⁺)/calmodulin (CaM)-dependent kinase II (CaMKII), delta-opioid receptor (DOR) and the regulators of G-protein signaling (RGS) proteins. There is general agreement on the critical role of the NMDAR/nNOS/CaMKII pathway in this process, which is supported by the recent demonstration of a physical association between MORs and NMDARs in post-synaptic structures. Indeed, it is feasible that treatments that diminish morphine tolerance may target distinct elements within the same regulatory MOR-NMDAR pathway. Accordingly, we propose a model that incorporates the most relevant signaling components implicated in opioid tolerance in which, certain signals originating from the activated MOR are perceived by the associated NMDAR, which in turn exerts a negative feedback effect on MOR signaling. MOR- and NMDAR-mediated signals work together in a sequential and interconnected manner to ultimately induce MOR desensitization. Future studies of these phenomena should focus on adding further components to this signaling pathway in order to better define the mechanism underlying MOR desensitization in neural cells.

  19. Neuropathic Pain Activates the Endogenous κ Opioid System in Mouse Spinal Cord and Induces Opioid Receptor Tolerance

    PubMed Central

    Xu, Mei; Petraschka, Michael; McLaughlin, Jay P.; Westenbroek, Ruth E.; Caron, Marc G.; Lefkowitz, Robert J.; Czyzyk, Traci A.; Pintar, John E.; Terman, Gregory W.; Chavkin, Charles

    2008-01-01

    Release of endogenous dynorphin opioids within the spinal cord after partial sciatic nerve ligation (pSNL) is known to contribute to the neuropathic pain processes. Using a phosphoselective antibody [κ opioid receptor (KOR-P)] able to detect the serine 369 phosphorylated form of the KOR, we determined possible sites of dynorphin action within the spinal cord after pSNL. KOR-P immunoreactivity (IR) was markedly increased in the L4 –L5 spinal dorsal horn of wild-type C57BL/6 mice (7–21 d) after lesion, but not in mice pretreated with the KOR antagonist nor-binaltorphimine (norBNI). In addition, knock-out mice lacking prodynorphin, KOR, or G-protein receptor kinase 3 (GRK3) did not show significant increases in KOR-P IR after pSNL. KOR-P IR was colocalized in both GABAergic neurons and GFAP-positive astrocytes in both ipsilateral and contralateral spinal dorsal horn. Consistent with sustained opioid release, KOR knock-out mice developed significantly increased tactile allodynia and thermal hyperalgesia in both the early (first week) and late (third week) interval after lesion. Similarly, mice pretreated with norBNI showed enhanced hyperalgesia and allodynia during the 3 weeks after pSNL. Because sustained activation of opioid receptors might induce tolerance, we measured the antinociceptive effect of the κ agonist U50,488 using radiant heat applied to the ipsilateral hindpaw, and we found that agonist potency was significantly decreased 7 d after pSNL. In contrast, neither prodynorphin nor GRK3 knock-out mice showed U50,488 tolerance after pSNL. These findings suggest that pSNL induced a sustained release of endogenous prodynorphin-derived opioid peptides that activated an anti-nociceptive KOR system in mouse spinal cord. Thus, endogenous dynorphin had both pronociceptive and antinociceptive actions after nerve injury and induced GRK3-mediated opioid tolerance. PMID:15140929

  20. Synthetic studies of neoclerodane diterpenoids from Salvia splendens and evaluation of Opioid Receptor affinity.

    PubMed

    Fontana, Gianfranco; Savona, Giuseppe; Rodríguez, Benjamín; Dersch, Christina M; Rothman, Richard B; Prisinzano, Thomas E

    2008-12-20

    Salvinorin A (1), a neoclerodane diterpene from the hallucinogenic mint Salvia divinorum, is the only known non-nitrogenous and specific kappa-opioid agonist. Several structural congeners of 1 isolated from Salvia splendens (2 - 8) together with a series of semisynthetic derivatives (9 - 24), some of which possess a pyrazoline structural moiety (9, 19 - 22), have been tested for affinity at human mu, delta, and kappa opioid receptors. None of these compounds showed high affinity binding to these receptors. However, 10 showed modest affinity for kappa receptors suggesting other naturally neoclerodanes from different Salvia species may possess opioid affinity.

  1. Basal μ-opioid receptor availability in the amygdala predicts the inhibition of pain-related brain activity during heterotopic noxious counter-stimulation.

    PubMed

    Piché, Mathieu; Watanabe, Nobuhiro; Sakata, Muneyuki; Oda, Keiichi; Toyohara, Jun; Ishii, Kenji; Ishiwata, Kiichi; Hotta, Harumi

    2014-01-01

    The aim of this study was to investigate the association between the magnitude of anti-nociceptive effects induced by heterotopic noxious counter-stimulation (HNCS) and the basal μ-opioid receptor availability in the amygdala. In 8 healthy volunteers (4 females and 4 males), transcutaneous electrical stimulation was applied to the right sural nerve to produce the nociceptive flexion reflex (RIII-reflex), moderate pain, and scalp somatosensory evoked potentials (SEPs). Immersion of the left hand in cold water for 20min was used as HNCS. In a separate session, basal μ-opioid receptor availability was measured using positron emission tomography with the radiotracer [(11)C]carfentanil. HNCS produced a reduction of the P260 amplitude (p<0.05), a late component of SEP that reflects activity in the anterior cingulate cortex. This reduction was associated with higher basal μ-opioid receptor availability in the amygdala on the right (R(2)=0.55, p=0.03) with a similar trend on the left (R(2)=0.24, p=0.22). Besides, HNCS did not induce significant changes in pain and RIII-reflex amplitude (p>0.05). These results suggest that activation of μ-opioid receptors in the amygdala may contribute to the anti-nociceptive effects of HNCS. The lack of RIII-reflex modulation further suggests that μ-opioid receptor activation in the amygdala contributes to decrease pain-related brain activity through a cerebral mechanism independent of descending modulation.

  2. 15 years of genetic approaches in vivo for addiction research: Opioid receptor and peptide gene knockout in mouse models of drug abuse.

    PubMed

    Charbogne, Pauline; Kieffer, Brigitte L; Befort, Katia

    2014-01-01

    The endogenous opioid system is expressed throughout the brain reinforcement circuitry, and plays a major role in reward processing, mood control and the development of addiction. This neuromodulator system is composed of three receptors, mu, delta and kappa, interacting with a family of opioid peptides derived from POMC (β-endorphin), preproenkephalin (pEnk) and preprodynorphin (pDyn) precursors. Knockout mice targeting each gene of the opioid system have been created almost two decades ago. Extending classical pharmacology, these mutant mice represent unique tools to tease apart the specific role of each opioid receptor and peptide in vivo, and a powerful approach to understand how the opioid system modulates behavioral effects of drugs of abuse. The present review summarizes these studies, with a focus on major drugs of abuse including morphine/heroin, cannabinoids, psychostimulants, nicotine or alcohol. Genetic data, altogether, set the mu receptor as the primary target for morphine and heroin. In addition, this receptor is essential to mediate rewarding properties of non-opioid drugs of abuse, with a demonstrated implication of β-endorphin for cocaine and nicotine. Delta receptor activity reduces levels of anxiety and depressive-like behaviors, and facilitates morphine-context association. pEnk is involved in these processes and delta/pEnk signaling likely regulates alcohol intake. The kappa receptor mainly interacts with pDyn peptides to limit drug reward, and mediate dysphoric effects of cannabinoids and nicotine. Kappa/dynorphin activity also increases sensitivity to cocaine reward under stressful conditions. The opioid system remains a prime candidate to develop successful therapies in addicted individuals, and understanding opioid-mediated processes at systems level, through emerging genetic and imaging technologies, represents the next challenging goal and a promising avenue in addiction research. This article is part of a Special Issue entitled 'NIDA

  3. μ-Opioid receptors in the stimulation of mesolimbic dopamine activity by ethanol and morphine in Long-Evans rats: a delayed effect of ethanol

    PubMed Central

    Valenta, John P.; Job, Martin O.; Mangieri, Regina A.; Schier, Christina J.; Howard, Elaina C.; Gonzales, Rueben A.

    2013-01-01

    Rationale Naltrexone, a non-selective opioid antagonist, decreases the euphoria and positive subjective responses to alcohol in heavy drinkers. It has been proposed that the μ-opioid receptor plays a role in ethanol reinforcement through modulation of ethanol-stimulated mesolimbic dopamine release. Objective To investigate the ability of naltrexone and β-funaltrexamine, an irreversible μ-opioid specific antagonist, to inhibit ethanol-stimulated and morphine-stimulated mesolimbic dopamine release and to determine whether opioid receptors on mesolimbic neurons contribute to these mechanisms. Methods Ethanol-naïve male Long Evans rats were given opioid receptor antagonists either intravenously, subcutaneously, or intracranially into the ventral tegmental area (VTA), followed by intravenous administration of ethanol or morphine. We measured extracellular dopamine in vivo using microdialysis probes inserted into the nucleus accumbens shell (n=114). Results Administration of naltrexone (intravenously) and β-funaltrexamine (subcutaneously), as well as intracranial injection of naltrexone into the VTA did not prevent the initiation of dopamine release by intravenous ethanol administration, but prevented it from being as prolonged. In contrast, morphine-stimulated mesolimbic dopamine release was effectively suppressed. Conclusions Our results provide novel evidence that there are two distinct mechanisms that mediate ethanol-stimulated mesolimbic dopamine release (an initial phase and a delayed phase), and that opioid receptor activation is required to maintain the delayed-phase dopamine release. Moreover, μ-opioid receptors account for this delayed-phase dopamine response, and the VTA is potentially the site of action of this mechanism. We conclude that μ-opioid receptors play different roles in the mechanisms of stimulation of mesolimbic dopamine activity by ethanol and morphine. PMID:23503684

  4. A new splice of life for the μ-opioid receptor.

    PubMed

    Iadarola, Michael J; Sapio, Matthew R; Mannes, Andrew J

    2015-07-01

    μ-Opioid agonists mediate their analgesic effect through GPCRs that are generated via alternate splicing of the Oprm1 transcript. While the majority of μ-opioids interact with receptors comprising the canonical 7 transmembrane (7TM) domain, a recently identified class of μ-opioids appears to require a 6TM domain variant. In this issue of the JCI, Lu and colleagues provide an in vivo proof-of-concept demonstration that a 6TM isoform of the μ-opioid receptor can support functional analgesia in Oprm1-deficent animals. The 6TM isoform was pharmacologically distinct from the canonical 7TM μ-opioid receptor, and 6TM agonists had a reduced side effect profile, which confers a strong therapeutic advantage over standard opioid analgesics. The observations of Lu et al. extend the reach of opioid-receptor neurobiology and pharmacology into a new era of analgesic discovery. This advance emerges from a series of fundamental research analyses in which elements of the endogenous opioid system were frequently in the vanguard.

  5. Contributions of peripheral and central opioid receptors to antinociception in rat muscle pain models.

    PubMed

    Sánchez, Eva Ma; Bagües, Ana; Martín, Ma Isabel

    2010-10-01

    Administration of hypertonic saline (HS) is an accepted model to study muscular pain. HS-induced nociceptive responses were tested in masseter, already described, and in two new pain models of spinally innervated muscles (gastrocnemius and triceps) developed in rats at our laboratory. HS administration in the masseter induced vigorous hindpaw shaking and in the gastrocnemius or triceps, paw withdrawal or flexing. Participation of the central and peripheral opioid receptors in HS-induced pain is compared in these muscles: masseter, innervated by trigeminal nerve, and gastrocnemius and triceps by spinal nerves. Morphine and loperamide were used to reveal peripheral and central components of opioid analgesia. Both agonists reduced HS-induced nociceptive behaviours in the masseter and were antagonised by the opioid antagonist naloxone and by naloxone methiodide, an opioid receptor antagonist that poorly penetrates the blood-brain barrier. Unexpectedly, in the gastrocnemius and triceps, morphine, but not loperamide, decreased the nociceptive behaviour and this effect was only reversed by naloxone. So, peripheral opioid receptors seem to participate in HS-induced masseter pain, whereas only central opioid receptors reduced the nociception in gastrocnemius and triceps. Our results suggest that the use of peripheral opioids can be more advantageous than central opioids for treatment of orofacial muscular pain.

  6. Central N/OFQ-NOP Receptor System in Pain Modulation

    PubMed Central

    Kiguchi, Norikazu; Ding, Huiping; Ko, Mei-Chuan

    2016-01-01

    It has been two decades since the peptide, nociceptin/orphanin FQ (N/OFQ), and its cognate (NOP) receptor were discovered. Although NOP receptor activation causes a similar pattern of intracellular actions as mu opioid (MOP) receptors, NOP receptor-mediated pain modulation in rodents are more complicated than MOP receptor activation. In this review, we highlight the functional evidence of spinal, supraspinal, and systemic actions of NOP receptor agonists for regulating pain. In rodents, effects of the N/OFQ-NOP receptor system in spinal and supraspinal sites for modulating pain are bidirectional depending on the doses, assays, and pain modalities. The net effect of systemically administered NOP receptor agonists may depend on relative contribution of spinal and supraspinal actions of the N/OFQ-NOP receptor signaling in rodents under different pain states. In stark contrast, NOP receptor agonists produce only antinociception and antihypersensitivity in spinal and supraspinal regions of nonhuman primates regardless of doses and assays. More importantly, NOP receptor agonists and a few bifunctional NOP/MOP receptor agonists do not exhibit reinforcing effects (abuse liability), respiratory depression, itch pruritus, nor do they delay the gastrointestinal transit function (constipation) in nonhuman primates. Depending upon their intrinsic efficacies for activating NOP and MOP receptors, bifunctional NOP/MOP receptor agonists warrant additional investigation in primates regarding their side effect profiles. Nevertheless, NOP receptor-related agonists display a much wider therapeutic window as compared to that of MOP receptor agonists in primates. Both selective NOP receptor agonists and bifunctional NOP/MOP receptor agonists hold a great potential as effective and safe analgesics without typical opioid-associated side effects in humans. PMID:26920014

  7. Central N/OFQ-NOP Receptor System in Pain Modulation.

    PubMed

    Kiguchi, Norikazu; Ding, Huiping; Ko, Mei-Chuan

    2016-01-01

    Two decades have passed since the peptide, nociceptin/orphanin FQ (N/OFQ), and its cognate (NOP) receptor were discovered. Although NOP receptor activation causes a similar pattern of intracellular actions as mu-opioid (MOP) receptors, NOP receptor-mediated pain modulation in rodents are more complicated than MOP receptor activation. This review highlights the functional evidence of spinal, supraspinal, and systemic actions of NOP receptor agonists for regulating pain. In rodents, effects of the N/OFQ-NOP receptor system in spinal and supraspinal sites for modulating pain are bidirectional depending on the doses, assays, and pain modalities. The net effect of systemically administered NOP receptor agonists may depend on relative contribution of spinal and supraspinal actions of the N/OFQ-NOP receptor signaling in rodents under different pain states. In stark contrast, NOP receptor agonists produce only antinociception and antihypersensitivity in spinal and supraspinal regions of nonhuman primates regardless of doses and assays. More importantly, NOP receptor agonists and a few bifunctional NOP/MOP receptor agonists do not exhibit reinforcing effects (abuse liability), respiratory depression, itch pruritus, nor do they delay the gastrointestinal transit function (constipation) in nonhuman primates. Depending upon their intrinsic efficacies for activating NOP and MOP receptors, bifunctional NOP/MOP receptor agonists warrant additional investigation in primates regarding their side effect profiles. Nevertheless, NOP receptor-related agonists display a much wider therapeutic window as compared to that of MOP receptor agonists in primates. Both selective NOP receptor agonists and bifunctional NOP/MOP receptor agonists hold great potential as effective and safe analgesics without typical opioid-associated side effects in humans.

  8. Morphine mediates a proinflammatory phenotype via μ-opioid receptor-PKCɛ-Akt-ERK1/2 signaling pathway in activated microglial cells.

    PubMed

    Merighi, Stefania; Gessi, Stefania; Varani, Katia; Fazzi, Debora; Stefanelli, Angela; Borea, Pier Andrea

    2013-08-15

    Anti-nociceptive tolerance to opioids severely limits their clinical efficacy for the treatment of chronic pain syndromes. Glia has a central role in the development of morphine tolerance. Here, we characterized the receptor-proximal signaling events that link μ-opioid receptors to activation of Akt and ERKs in lipopolysaccharide (LPS)-stimulated murine microglial cells with the aim to define the molecular mechanism contributing to the ability of morphine to increase inflammatory mediators such as nitric oxide (NO), tumor necrosis factor (TNF)-α, interleukin (IL)-1β and IL-6 in activated microglial cells. In particular, the role of PKCɛ isoform in μ-opioid-induced inflammatory response in microglia was investigated. The results indicate that morphine increases the LPS-induced expression and activation of PKCɛ and stimulates Akt pathway upstream of ERK1/2 and iNOS. Furthermore, we found that morphine enhanced the release of IL-1β, TNF-α, IL-6, and of NO via μ-opioid receptor-PKCɛ signaling pathway in activated microglial cells, mediating a proinflammatory phenotype in mouse microglial cells. Together, these data suggest that the modulation of μ-opioid receptor signaling on microglia through PKCɛ selective inhibition may provide a means to attenuate glial activation and, as a consequence, to treat opioid development of tolerance and dependence.

  9. An Opioid Agonist that Does Not Induce μ-Opioid Receptor—Arrestin Interactions or Receptor Internalization

    PubMed Central

    Groer, C. E.; Tidgewell, K.; Moyer, R. A.; Harding, W. W.; Rothman, R. B.; Prisinzano, T. E.; Bohn, L. M.

    2013-01-01

    G protein-coupled receptor desensitization and trafficking are important regulators of opioid receptor signaling that can dictate overall drug responsiveness in vivo. Furthermore, different μ-opioid receptor (μOR) ligands can lead to varying degrees of receptor regulation, presumably because of distinct structural conformations conferred by agonist binding. For example, morphine binding produces a μOR with low affinity for β-arrestin proteins and limited receptor internalization, whereas enkephalin analogs promote robust trafficking of both β-arrestins and the receptors. Here, we evaluate μOR trafficking in response to activation by a novel μ-selective agonist derived from the naturally occurring plant product, salvinorin A. It is interesting that this compound, termed herkinorin, does not promote the recruitment of β-arrestin-2 to the μOR and does not lead to receptor internalization. Moreover, whereas G protein-coupled receptor kinase overexpression can promote morphine-induced β-arrestin interactions and μOR internalization, such manipulations do not promote herkinorin-induced trafficking. Studies in mice have shown that β-arrestin-2 plays an important role in the development of morphine-induced tolerance, constipation, and respiratory depression. Therefore, drugs that can activate the receptor without recruiting the arrestins may be a promising step in the development of opiate analgesics that distinguish between agonist activity and receptor regulation and may ultimately lead to therapeutics designed to provide pain relief without the adverse side effects normally associated with the opiate narcotics. PMID:17090705

  10. Regulation of ingestive behaviors in the rat by GSK1521498, a novel micro-opioid receptor-selective inverse agonist.

    PubMed

    Ignar, Diane M; Goetz, Aaron S; Noble, Kimberly Nichols; Carballo, Luz Helena; Stroup, Andrea E; Fisher, Julie C; Boucheron, Joyce A; Brainard, Tracy A; Larkin, Andrew L; Epperly, Andrea H; Shearer, Todd W; Sorensen, Scott D; Speake, Jason D; Hommel, Jonathan D

    2011-10-01

    μ-Opioid receptor (MOR) agonism induces palatable food consumption principally through modulation of the rewarding properties of food. N-{[3,5-difluoro-3'-(1H-1,2,4-triazol-3-yl)-4-biphenylyl]methyl}-2,3-dihydro-1H-inden-2-amine (GSK1521498) is a novel opioid receptor inverse agonist that, on the basis of in vitro affinity assays, is greater than 10- or 50-fold selective for human or rat MOR, respectively, compared with κ-opioid receptors (KOR) and δ-opioid receptors (DOR). Likewise, preferential MOR occupancy versus KOR and DOR was observed by autoradiography in brain slices from Long Evans rats dosed orally with the drug. GSK1521498 suppressed nocturnal food consumption of standard or palatable chow in lean and diet-induced obese (DIO) Long Evans rats. Both the dose-response relationship and time course of efficacy in lean rats fed palatable chow correlated with μ receptor occupancy and the plasma concentration profile of the drug. Chronic oral administration of GSK1521498 induced body weight loss in DIO rats, which comprised fat mass reduction. The reduction in body weight was equivalent to the cumulative reduction in food consumption; thus, the effect of GSK1521498 on body weight is related to inhibition of food consumption. GSK1521498 suppressed the preference for sucrose-containing solutions in lean rats. In operant response models also using lean rats, GSK1521498 reduced the reinforcement efficacy of palatable food reward and enhanced satiety. In conclusion, GSK1521498 is a potent, MOR-selective inverse agonist that modulates the hedonic aspects of ingestion and, therefore, could represent a pharmacological treatment for obesity and binge-eating disorders.

  11. The endogenous opioid system in cocaine addiction: what lessons have opioid peptide and receptor knockout mice taught us?

    PubMed Central

    Yoo, Ji Hoon; Kitchen, Ian; Bailey, Alexis

    2012-01-01

    Cocaine addiction has become a major concern in the UK as Britain tops the European ‘league table’ for cocaine abuse. Despite its devastating health and socio-economic consequences, no effective pharmacotherapy for treating cocaine addiction is available. Identifying neurochemical changes induced by repeated drug exposure is critical not only for understanding the transition from recreational drug use towards compulsive drug abuse but also for the development of novel targets for the treatment of the disease and especially for relapse prevention. This article focuses on the effects of chronic cocaine exposure and withdrawal on each of the endogenous opioid peptides and receptors in rodent models. In addition, we review the studies that utilized opioid peptide or receptor knockout mice in order to identify and/or clarify the role of different components of the opioid system in cocaine-addictive behaviours and in cocaine-induced alterations of brain neurochemistry. The review of these studies indicates a region-specific activation of the µ-opioid receptor system following chronic cocaine exposure, which may contribute towards the rewarding effect of the drug and possibly towards cocaine craving during withdrawal followed by relapse. Cocaine also causes a region-specific activation of the κ-opioid receptor/dynorphin system, which may antagonize the rewarding effect of the drug, and at the same time, contribute to the stress-inducing properties of the drug and the triggering of relapse. These conclusions have important implications for the development of effective pharmacotherapy for the treatment of cocaine addiction and the prevention of relapse. PMID:22428846

  12. β‐Arrestin 2 dependence of δ opioid receptor agonists is correlated with alcohol intake

    PubMed Central

    Chiang, T; Sansuk, K

    2016-01-01

    Background and Purpose δ Opioid receptor agonists are being developed as potential treatments for depression and alcohol use disorders. This is particularly interesting as depression is frequently co‐morbid with alcohol use disorders. Yet we have previously shown that δ receptor agonists range widely in their ability to modulate alcohol intake; certain δ receptor agonists actually increase alcohol consumption in mice. We propose that variations in β‐arrestin 2 recruitment contribute to the differential behavioural profile of δ receptor agonists. Experimental Approach We used three diarylmethylpiperazine‐based non‐peptidic δ receptor selective agonists (SNC80, SNC162 and ARM390) and three structurally diverse δ receptor agonists (TAN‐67, KNT127 and NIH11082). We tested these agonists in cAMP and β‐arrestin 2 recruitment assays and a behavioural assay of alcohol intake in male C57BL/6 mice. We used β‐arrestin 2 knockout mice and a model of depression‐like behaviour to further study the role of β‐arrestin 2 in δ receptor pharmacology. Key Results All six tested δ receptor agonists were full agonists in the cAMP assay but displayed distinct β‐arrestin 2 recruitment efficacy. The efficacy of δ receptor agonists to recruit β‐arrestin 2 positively correlated with their ability to increase alcohol intake (P < 0.01). The effects of the very efficacious recruiter SNC80 on alcohol intake, alcohol place preference and depression‐like behaviour were β‐arrestin 2‐dependent. Conclusions and Implications Our finding that δ receptor agonists that strongly recruit β‐arrestin 2 can increase alcohol intake carries important ramifications for drug development of δ receptor agonists for treatment of alcohol use disorders and depressive disorders. © 2015 The British Pharmacological Society PMID:26507558

  13. Mu-opioid receptor (MOR) expression in the human spiral ganglia

    PubMed Central

    Nguyen, Kimanh D.; Mowlds, Donald; Lopez, Ivan A.; Hosokawa, Seiji; Ishiyama, Akira; Ishiyama, Gail

    2015-01-01

    Opioid peptides and their receptors have been localized to the inner ear of the rat and guinea pig mammalian models. The expression of mu opioid receptor (MOR) in the human and mouse cochlea is not yet known. We present MOR protein localization by immunohistochemistry and mRNA expression by in situ hybridization in the human and mouse spiral ganglia (SG) and organ of Corti. In the human most of the (SG) neurons were immunoreactive; a subset was non-immunoreactive. In situ hybridization revealed a similar labeling pattern across the neurons of the SG. A similar distribution MOR pattern was demonstrated in the mouse SG. In the mouse organ of Corti MOR was expressed in inner and outer hair cells. Fibers underneath the inner hair cells were also MOR immunoreactive. These results are consistent with a role of MOR in neuro-modulation of the auditory periphery. The present results show that the expression of MORs is well-conserved across multiple mammalian species, indicative of an important role in auditory processing. PMID:25278190

  14. Characterization of methadone as a β-arrestin-biased μ-opioid receptor agonist

    PubMed Central

    Doi, Seira; Mori, Tomohisa; Uzawa, Naoki; Arima, Takamichi; Takahashi, Tomoyuki; Uchida, Masashi; Yawata, Ayaka; Narita, Michiko; Uezono, Yasuhito; Suzuki, Tsutomu

    2016-01-01

    Background Methadone is a unique µ-opioid receptor agonist. Although several researchers have insisted that the pharmacological effects of methadone are mediated through the blockade of NMDA receptor, the underlying mechanism by which methadone exerts its distinct pharmacological effects compared to those of other µ-opioid receptor agonists is still controversial. In the present study, we further investigated the pharmacological profile of methadone compared to those of fentanyl and morphine as measured mainly by the discriminative stimulus effect and in vitro assays for NMDA receptor binding, µ-opioid receptor-internalization, and µ-opioid receptor-mediated β-arrestin recruitment. Results We found that fentanyl substituted for the discriminative stimulus effects of methadone, whereas a relatively high dose of morphine was required to substitute for the discriminative stimulus effects of methadone in rats. Under these conditions, the non-competitive NMDA receptor antagonist MK-801 did not substitute for the discriminative stimulus effects of methadone. In association with its discriminative stimulus effect, methadone failed to displace the receptor binding of MK801 using mouse brain membrane. Methadone and fentanyl, but not morphine, induced potent µ-opioid receptor internalization accompanied by the strong recruitment of β-arrestin-2 in µ-opioid receptor-overexpressing cells. Conclusions These results suggest that methadone may, at least partly, produce its pharmacological effect as a β-arrestin-biased µ-opioid receptor agonist, similar to fentanyl, and NMDA receptor blockade is not the main contributor to the pharmacological profile of methadone. PMID:27317580

  15. Mu opioid receptor antagonism in the nucleus accumbens shell blocks consumption of a preferred sucrose solution in an anticipatory contrast paradigm.

    PubMed

    Katsuura, Y; Taha, S A

    2014-03-07

    Binge eating, a central feature of multiple eating disorders, is characterized by excessive consumption occurring during discrete, often brief, intervals. Highly palatable foods play an important role in these binge episodes - foods chosen during bingeing are typically higher in fat or sugar than those normally consumed. Multiple lines of evidence suggest a central role for signaling by endogenous opioids in promoting palatability-driven eating. This role extends to binge-like feeding studied in animal models, which is reduced by administration of opioid antagonists. However, the neural circuits and specific opioid receptors mediating these effects are not fully understood. In the present experiments, we tested the hypothesis that endogenous opioid signaling in the nucleus accumbens promotes consumption in a model of binge eating. We used an anticipatory contrast paradigm in which separate groups of rats were presented sequentially with 4% sucrose and then either 20% or 0% sucrose solutions. In rats presented with 4% and then 20% sucrose, daily training in this paradigm produced robust intake of 20% sucrose, preceded by learned hypophagia during access to 4% sucrose. We tested the effects of site-specific infusions of naltrexone (a nonspecific opioid receptor antagonist: 0, 1, 10, and 50μg/side in the nucleus accumbens core and shell), naltrindole (a delta opioid receptor antagonist: 0, 0.5, 5, and 10μg/side in the nucleus accumbens shell) and beta-funaltrexamine (a mu opioid receptor antagonist: 0 and 2.5μg/side in the nucleus accumbens shell) on consumption in this contrast paradigm. Our results show that signaling through the mu opioid receptor in the nucleus accumbens shell is dynamically modulated during formation of learned food preferences, and promotes binge-like consumption of palatable foods based on these learned preferences.

  16. Involvement of mu opioid receptors of periaqueductal gary (PAG) in acupuncture inhibition of noxious blood pressure response in rabbits.

    PubMed

    Gao, M; Xu, W; Chen, W; He, L

    1994-01-01

    Strong electric shock stimulation of the rabbit front paw elicited a pressor blood pressure response regarded as noxious response. Ligands of mu opioid receptors were microinjected into the PAG to observe their effects on acupunture inhibition of the pressor response. (1) Ohmefentanyl (OMF), a mu agonist, significantly attenuated the pressor response. Mu antagonist TCTAP greatly enhanced the pressor response. (2) Electroacupuncture (EA) significantly inhibited the pressor response, the inhibition being readily reversed by TCTAP. The response after TCTAP was significantly greater than that of the control before EA. The results suggest that noxious stimulation is able to activate the mu opioid receptor of the PAG to modulate the noxious response and EA is able to enhance the activation.

  17. Hormonal regulation of delta opioid receptor immunoreactivity in interneurons and pyramidal cells in the rat hippocampus.

    PubMed

    Williams, Tanya J; Torres-Reveron, Annelyn; Chapleau, Jeanette D; Milner, Teresa A

    2011-02-01

    Clinical and preclinical studies indicate that women and men differ in relapse vulnerability to drug-seeking behavior during abstinence periods. As relapse is frequently triggered by exposure of the recovered addict to objects previously associated with drug use and the formation of these associations requires memory systems engaged by the hippocampal formation (HF), studies exploring ovarian hormone modulation of hippocampal function are warranted. Previous studies revealed that ovarian steroids alter endogenous opioid peptide levels and trafficking of mu opioid receptors in the HF, suggesting cooperative interaction between opioids and estrogens in modulating hippocampal excitability. However, whether ovarian steroids affect the levels or trafficking of delta opioid receptors (DORs) in the HF is unknown. Here, hippocampal sections of adult male and normal cycling female Sprague-Dawley rats were processed for quantitative immunoperoxidase light microscopy and dual label fluorescence or immunoelectron microscopy using antisera directed against the DOR and neuropeptide Y (NPY). Consistent with previous studies in males, DOR-immunoreactivity (-ir) localized to select interneurons and principal cells in the female HF. In comparison to males, females, regardless of estrous cycle phase, show reduced DOR-ir in the granule cell layer of the dentate gyrus and proestrus (high estrogen) females, in particular, display reduced DOR-ir in the CA1 pyramidal cell layer. Ultrastructural analysis of DOR-labeled profiles in CA1 revealed that while females generally show fewer DORs in the distal apical dendrites of pyramidal cells, proestrus females, in particular, exhibit DOR internalization and trafficking towards the soma. Dual label studies revealed that DORs are found in NPY-labeled interneurons in the hilus, CA3, and CA1. While DOR colocalization frequency in NPY-labeled neuron somata was similar between animals in the hilus, proestrus females had fewer NPY-labeled neurons that

  18. In-vitro investigation of oxazol and urea analogues of morphinan at opioid receptors.

    PubMed

    Peng, Xuemei; Knapp, Brian I; Bidlack, Jean M; Neumeyer, John L

    2007-06-15

    A series of 2-amino-oxazole (7 and 8) analogs and 2-one-oxazole analogs (9 and 10) were synthesized from cyclorphan (1) or butorphan (2) and evaluated in-vitro by their binding affinity at mu, delta, and kappa opioid receptors and compared with their 2-aminothiozole analogs 5 and 6. Ligands 7-10 showed decreased affinities at kappa and mu receptors. Urea analogs (11-14) were also prepared from 2-aminocyclorphan (3) or 2-aminobutorphan (4) and evaluated in-vitro by their binding affinity at mu, delta, and kappa opioid receptors. The urea derived opioids retained their affinities at mu receptors while showing increased affinities at delta receptors and decreased affinities at kappa receptors. Functional activities of these compounds were measured in the [35S]GTPgammaS binding assay, illustrating that all of these ligands were kappa agonists. At the mu receptor, compounds 11 and 12 were mu agonist/antagonists.

  19. Differential Regulation of 6- and 7-Transmembrane Helix Variants of μ-Opioid Receptor in Response to Morphine Stimulation

    PubMed Central

    Convertino, Marino; Samoshkin, Alexander; Viet, Chi T.; Gauthier, Josee; Li Fraine, Steven P.; Sharif-Naeini, Reza; Schmidt, Brian L.; Maixner, William; Diatchenko, Luda; Dokholyan, Nikolay V.

    2015-01-01

    The pharmacological effect of opioids originates, at the cellular level, by their interaction with the μ-opioid receptor (mOR) resulting in the regulation of voltage-gated Ca2+ channels and inwardly rectifying K+ channels that ultimately modulate the synaptic transmission. Recently, an alternative six trans-membrane helix isoform of mOR, (6TM-mOR) has been identified, but its function and signaling are still largely unknown. Here, we present the structural and functional mechanisms of 6TM-mOR signaling activity upon binding to morphine. Our data suggest that despite the similarity of binding modes of the alternative 6TM-mOR and the dominant seven trans-membrane helix variant (7TM-mOR), the interaction with morphine generates different dynamic responses in the two receptors, thus, promoting the activation of different mOR-specific signaling pathways. We characterize a series of 6TM-mOR-specific cellular responses, and observed that they are significantly different from those for 7TM-mOR. Morphine stimulation of 6TM-mOR does not promote a cellular cAMP response, while it increases the intracellular Ca2+ concentration and reduces the cellular K+ conductance. Our findings indicate that 6TM-mOR has a unique contribution to the cellular opioid responses. Therefore, it should be considered as a relevant target for the development of novel pharmacological tools and medical protocols involving the use of opioids. PMID:26554831

  20. Activation of μ opioid receptors in the LPBN facilitates sodium intake in rats.

    PubMed

    Pavan, Carolina G; Roncari, Camila F; Barbosa, Silas P; De Paula, Patrícia M; Colombari, Débora S A; De Luca, Laurival A; Colombari, Eduardo; Menani, José V

    2015-07-15

    Important inhibitory mechanisms for the control of water and sodium intake are present in the lateral parabrachial nucleus (LPBN). Opioid receptors are expressed by LPBN neurons and injections of β-endorphin (nonspecific opioid receptor agonist) in this area induce 0.3M NaCl and water intake in satiated rats. In the present study, we investigated the effects of the injections of endomorphin-1 (μ opioid receptor agonist) alone or combined with the blockade of μ, κ or δ opioid receptors into the LPBN on 0.3M NaCl and water intake induced by subcutaneous injections of the diuretic furosemide (FURO) combined with low dose of the angiotensin converting enzyme inhibitor captopril (CAP). Male Holtzman rats with stainless steel cannulas implanted bilaterally in the LPBN were used. Bilateral injections of endomorphin-1 (0.1, 0.25, 0.5, 1.0, 2.0 and 4.0nmol/0.2μl) into the LPBN increased 0.3M NaCl and water intake induced by FURO+CAP. The previous blockade of μ opioid receptor with CTAP (1.0nmol/0.2μl) into the LPBN reduced the effect of endomorphin-1 on FURO+CAP-induced 0.3M NaCl. GNTI (κ opioid receptor antagonist; 2.0nmol/0.2μl) and naltrindole (δ opioid receptor antagonist; 2.0nmol/0.2μl) injected into the LPBN did not change the effects of endomorphin-1 on FURO+CAP-induced 0.3M NaCl. The results suggest that μ opioid receptors in the LPBN are involved in the control of sodium intake.

  1. Novel approaches for the treatment of psychostimulant and opioid abuse – focus on opioid receptor-based therapies

    PubMed Central

    Bailey, Chris P.; Husbands, Steve M.

    2015-01-01

    Introduction Psychostimulant and opioid addiction are poorly treated. The majority of abstinent users relapse back to drug-taking within a year of abstinence, making ‘anti-relapse’ therapies the focus of much current research. There are two fundamental challenges to developing novel treatments for drug addiction. Firstly, there are 3 key stimuli that precipitate relapse back to drug-taking: stress, presentation of drug-conditioned cue, taking a small dose of drug. The most successful novel treatment would be effective against all 3 stimuli. Secondly, a large number of drug users are poly-drug users: taking more than one drug of abuse at a time. The ideal anti-addiction treatment would therefore be effective against all classes of drugs of abuse. Areas Covered In this review, the authors discuss the clinical need and animal models used to uncover potential novel treatments. There is a very broad range of potential treatment approaches and targets currently being examined as potential anti-relapse therapies. These broadly fit into 2 categories: ‘memory-based’ and ‘receptor-based’ and the authors discuss the key targets here within. Expert opinion Opioid receptors and ligands have been widely studied, and research into how different opioid subtypes affect behaviours related to addiction (reward, dysphoria, motivation) suggests that they are tractable targets as anti-relapse treatments. Regarding opioid ligands as novel ‘anti-relapse’ medications targets - research suggests that a ‘non-selective’ approach to targeting opioid receptors will be the most effective. PMID:25253272

  2. Cyclic endomorphin analogs in targeting opioid receptors to achieve pain relief.

    PubMed

    Janecka, Anna; Gentilucci, Luca

    2014-01-01

    Endomorphins, the endogenous ligands of the µ-opioid receptor, are attractive candidates for opioid-based pain-relieving agents. These tetrapeptides, with their remarkable affinity for the µ-opioid receptor, display favorable antinociceptive activity when injected directly into the brain of experimental animals. However, the application of endomorphins as clinical analgesics has been impeded by their instability in body fluids and inability to reach the brain after systemic administration. Among numerous modifications of the endomorphin structure aimed at improving their pharmacological properties, cyclization can be viewed as an interesting option. Here, we have summarized recent advances in obtaining endomorphin-based cyclic peptide analogs.

  3. Human native kappa opioid receptor functions not predicted by recombinant receptors: Implications for drug design

    PubMed Central

    Broad, John; Maurel, Damien; Kung, Victor W. S.; Hicks, Gareth A.; Schemann, Michael; Barnes, Michael R.; Kenakin, Terrence P.; Granier, Sébastien; Sanger, Gareth J.

    2016-01-01

    If activation of recombinant G protein-coupled receptors in host cells (by drugs or other ligands) has predictive value, similar data must be obtained with native receptors naturally expressed in tissues. Using mouse and human recombinant κ opioid receptors transfected into a host cell, two selectively-acting compounds (ICI204448, asimadoline) equi-effectively activated both receptors, assessed by measuring two different cell signalling pathways which were equally affected without evidence of bias. In mouse intestine, naturally expressing κ receptors within its nervous system, both compounds also equi-effectively activated the receptor, inhibiting nerve-mediated muscle contraction. However, whereas ICI204448 acted similarly in human intestine, where κ receptors are again expressed within its nervous system, asimadoline was inhibitory only at very high concentrations; instead, low concentrations of asimadoline reduced the activity of ICI204448. This demonstration of species-dependence in activation of native, not recombinant κ receptors may be explained by different mouse/human receptor structures affecting receptor expression and/or interactions with intracellular signalling pathways in native environments, to reveal differences in intrinsic efficacy between receptor agonists. These results have profound implications in drug design for κ and perhaps other receptors, in terms of recombinant-to-native receptor translation, species-dependency and possibly, a need to use human, therapeutically-relevant, not surrogate tissues. PMID:27492592

  4. Human Opiorphin, a natural antinociceptive modulator of opioid-dependent pathways

    PubMed Central

    Wisner, Anne; Dufour, Evelyne; Messaoudi, Michaël; Nejdi, Amine; Marcel, Audrey; Ungeheuer, Marie-Noelle; Rougeot, Catherine

    2006-01-01

    Mammalian zinc ectopeptidases play important roles in turning off neural and hormonal peptide signals at the cell surface, notably those processing sensory information. We report here the discovery of a previously uncharacterized physiological inhibitor of enkephalin-inactivating zinc ectopeptidases in humans, which we have named Opiorphin. It is a QRFSR peptide that inhibits two enkephalin-catabolizing ectoenzymes, human neutral ecto-endopeptidase, hNEP (EC 3.4.24.11), and human ecto-aminopeptidase, hAP-N (EC 3.4.11.2). Opiorphin displays potent analgesic activity in chemical and mechanical pain models by activating endogenous opioid-dependent transmission. Its function is closely related to the rat sialorphin peptide, which is an inhibitor of pain perception and acts by potentiating endogenous μ- and δ-opioid receptor-dependent enkephalinergic pathways. Here we demonstrate the functional specificity in vivo of human Opiorphin. The pain-suppressive potency of Opiorphin is as effective as morphine in the behavioral rat model of acute mechanical pain, the pin-pain test. Thus, our discovery of Opiorphin is extremely exciting from a physiological point of view in the context of endogenous opioidergic pathways, notably in modulating mood-related states and pain sensation. Furthermore, because of its in vivo properties, Opiorphin may have therapeutic implications. PMID:17101991

  5. Human Opiorphin, a natural antinociceptive modulator of opioid-dependent pathways.

    PubMed

    Wisner, Anne; Dufour, Evelyne; Messaoudi, Michaël; Nejdi, Amine; Marcel, Audrey; Ungeheuer, Marie-Noelle; Rougeot, Catherine

    2006-11-21

    Mammalian zinc ectopeptidases play important roles in turning off neural and hormonal peptide signals at the cell surface, notably those processing sensory information. We report here the discovery of a previously uncharacterized physiological inhibitor of enkephalin-inactivating zinc ectopeptidases in humans, which we have named Opiorphin. It is a QRFSR peptide that inhibits two enkephalin-catabolizing ectoenzymes, human neutral ecto-endopeptidase, hNEP (EC 3.4.24.11), and human ecto-aminopeptidase, hAP-N (EC 3.4.11.2). Opiorphin displays potent analgesic activity in chemical and mechanical pain models by activating endogenous opioid-dependent transmission. Its function is closely related to the rat sialorphin peptide, which is an inhibitor of pain perception and acts by potentiating endogenous mu- and delta-opioid receptor-dependent enkephalinergic pathways. Here we demonstrate the functional specificity in vivo of human Opiorphin. The pain-suppressive potency of Opiorphin is as effective as morphine in the behavioral rat model of acute mechanical pain, the pin-pain test. Thus, our discovery of Opiorphin is extremely exciting from a physiological point of view in the context of endogenous opioidergic pathways, notably in modulating mood-related states and pain sensation. Furthermore, because of its in vivo properties, Opiorphin may have therapeutic implications.

  6. Effects of morphine on pentobarbital-induced responses in mu-opioid receptor knockout mice.

    PubMed

    Park, Y; Ho, I K; Jang, C G; Tanaka, S; Ma, T; Loh, H H; Ko, K H

    2001-03-15

    Effects of morphine on the potentiation of pentobarbital-induced responses were investigated using mu-opioid receptor knockout mice. The duration of loss of righting reflex, hypothermia, and loss of motor coordination induced by pentobarbital were measured after pretreatment with either morphine or saline. Morphine pretreatment failed to show potentiation of both pentobarbital-induced loss of righting reflex and hypothermia in mu-opioid receptor knockout mice, while it significantly potentiated these responses in the wild-type controls. For motor incoordination test, morphine potentiated pentobarbital-induced motor incoordination in the wild-type mice. However, morphine may have opposite effects in the mu-opioid receptor knockout mice. These results demonstrate that synergism between morphine and pentobarbital is not detected in mu-opioid receptor knockout mice and that potentiation of pentobarbital-induced loss of righting reflex and hypothermia by morphine is mediated through mu-opioid receptor. It was interesting to note that pentobarbital-induced decrease in body temperature was less severe in mu-opioid receptor knockout mice than in wild-type mice.

  7. Opioid receptors and cardioprotection – ‘opioidergic conditioning’ of the heart

    PubMed Central

    Headrick, John P; See Hoe, Louise E; Du Toit, Eugene F; Peart, Jason N

    2015-01-01

    Ischaemic heart disease (IHD) remains a major cause of morbidity/mortality globally, firmly established in Westernized or ‘developed’ countries and rising in prevalence in developing nations. Thus, cardioprotective therapies to limit myocardial damage with associated ischaemia–reperfusion (I–R), during infarction or surgical ischaemia, is a very important, although still elusive, clinical goal. The opioid receptor system, encompassing the δ (vas deferens), κ (ketocyclazocine) and μ (morphine) opioid receptors and their endogenous opioid ligands (endorphins, dynorphins, enkephalins), appears as a logical candidate for such exploitation. This regulatory system may orchestrate organism and organ responses to stress, induces mammalian hibernation and associated metabolic protection, triggers powerful adaptive stress resistance in response to ischaemia/hypoxia (preconditioning), and mediates cardiac benefit stemming from physical activity. In addition to direct myocardial actions, central opioid receptor signalling may also enhance the ability of the heart to withstand I–R injury. The δ- and κ-opioid receptors are strongly implicated in cardioprotection across models and species (including anti-infarct and anti-arrhythmic actions), with mixed evidence for μ opioid receptor-dependent protection in animal and human tissues. A small number of clinical trials have provided evidence of cardiac benefit from morphine or remifentanil in cardiopulmonary bypass or coronary angioplasty patients, although further trials of subtype-specific opioid receptor agonists are needed. The precise roles and utility of this GPCR family in healthy and diseased human myocardium, and in mediating central and peripheral survival responses, warrant further investigation, as do the putative negative influences of ageing, IHD co-morbidities, and relevant drugs on opioid receptor signalling and protective responses. PMID:25521834

  8. Opioid and nicotine receptors affect growth regulation of human lung cancer cell lines

    SciTech Connect

    Maneckjee, R.; Minna, J.D. Uniformed Services Univ. of the Health Sciences, Bethesda, MD )

    1990-05-01

    Using specific radioactively-labeled ligands, the authors find that lung cancer cell lines of diverse histologic types express multiple, high-affinity membrane receptors for {mu}, {delta}, and {kappa} opioid agonists and for nicotine and {alpha}-bungarotoxin. These receptors are biologically active because cAMP levels decreased in lung cancer cells after opioid and nicotine application. Nicotine at concentrations found in the blood of smokers had no effect on in vitro lung cancer cell growth, whereas {mu}, {delta}, and {kappa} opioid agonists at low concentrations inhibited lung cancer growth in vitro. They also found that lung cancer cells expressed various combinations of immunoreactive opioid peptides ({beta}-endorphin, enkephalin, or dynorphin), suggesting the participation of opioids in a negative autocrine loop or tumor-suppressing system. Due to the almost universal exposure of patients with lung cancer to nicotine, they tested whether nicotine affected the response of lung cancer cell growth to opioids and found that nicotine at concentrations of 100-200 nM partially or totally reversed opioid-induced growth inhibition in 9/14 lung cancer cell lines. These in vitro results for lung cancer cells suggest that opioids could function as part of a tumor suppressor system and that nicotine can function to circumvent this system in the pathogenesis of lung cancer.

  9. Heterologous desensitization of opioid receptors by chemokines inhibits chemotaxis and enhances the perception of pain.

    PubMed

    Szabo, Imre; Chen, Xiao-Hong; Xin, Li; Adler, Martin W; Howard, O M Z; Oppenheim, Joost J; Rogers, Thomas J

    2002-08-06

    The chemokines use G protein-coupled receptors to regulate the migratory and proadhesive responses of leukocytes. Based on observations that G protein-coupled receptors undergo heterologous desensitization, we have examined the ability of chemokines to also influence the perception of pain by cross-desensitizing opioid G protein-coupled receptors function in vitro and in vivo. We find that the chemotactic activities of both mu- and delta-opioid receptors are desensitized following activation of the chemokine receptors CCR5, CCR2, CCR7, and CXCR4 but not of the CXCR1 or CXCR2 receptors. Furthermore, we also find that pretreatment with RANTES/CCL5, the ligand for CCR1, and CCR5 or SDF-1alpha/CXCL12, the ligand for CXCR4, followed by opioid administration into the periaqueductal gray matter of the brain results in an increased rat tail flick response to a painful stimulus. Because chemokine administration into the periaqueductal gray matter inhibits opioid-induced analgesia, we propose that the activation of proinflammatory chemokine receptors down-regulates the analgesic functions of opioid receptors, and this enhances the perception of pain at inflammatory sites.

  10. Striatal opioid receptor availability is related to acute and chronic pain perception in arthritis: does opioid adaptation increase resilience to chronic pain?

    PubMed

    Brown, Christopher A; Matthews, Julian; Fairclough, Michael; McMahon, Adam; Barnett, Elizabeth; Al-Kaysi, Ali; El-Deredy, Wael; Jones, Anthony K P

    2015-11-01

    The experience of pain in humans is modulated by endogenous opioids, but it is largely unknown how the opioid system adapts to chronic pain states. Animal models of chronic pain point to upregulation of opioid receptors (OpR) in the brain, with unknown functional significance. We sought evidence for a similar relationship between chronic pain and OpR availability in humans. Using positron emission tomography and the radiotracer (11)C-diprenorphine, patients with arthritis pain (n = 17) and healthy controls (n = 9) underwent whole-brain positron emission tomography scanning to calculate parametric maps of OpR availability. Consistent with the upregulation hypothesis, within the arthritis group, greater OpR availability was found in the striatum (including the caudate) of patients reporting higher levels of recent chronic pain, as well as regions of interest in the descending opioidergic pathway including the anterior cingulate cortex, thalamus, and periaqueductal gray. The functional significance of striatal changes were clarified with respect to acute pain thresholds: data across patients and controls revealed that striatal OpR availability was related to reduced pain perception. These findings are consistent with the view that chronic pain may upregulate OpR availability to dampen pain. Finally, patients with arthritis pain, compared with healthy controls, had overall less OpR availability within the striatum specifically, consistent with the greater endogenous opioid binding that would be expected in chronic pain states. Our observational evidence points to the need for further studies to establish the causal relationship between chronic pain states and OpR adaptation.

  11. Delta- and kappa-opioid receptors in the caudal midline medulla mediate haemorrhage-evoked hypotension.

    PubMed

    Henderson, Luke A; Keay, Kevin A; Bandler, Richard

    2002-04-16

    In mammals blood loss can trigger, shock, an abrupt, life-threatening hypotension and bradycardia. In the halothane-anaesthetised rat this response is blocked by inactivation of a discrete, vasodepressor area in the caudal midline medulla (CMM). Haemorrhagic shock is blocked also by systemic or ventricular injections of the opioid antagonist, naloxone. This study investigated, in the halothane anaesthetised rat, the contribution of delta-, kappa- and mu-opioid receptors in the CMM vasodepressor region to haemorrhage-evoked shock (i.e. hypotension and bradycardia) and its recovery. It was found that microinjections into the CMM of the delta-opioid receptor antagonist, naltrindole delayed and attenuated the hypotension and bradycardia evoked by haemorrhage, but did not promote recompensation. In contrast, CMM microinjections of the kappa-opioid receptor antagonist, nor-binaltorphamine, although it did not alter haemorrhage-evoked hypotension and bradycardia, did lead to a rapid restoration of AP, but not HR. CMM microinjections of the mu-opioid receptor antagonist, CTAP had no effect on haemorrhage-evoked shock or recompensation. These data indicate that delta- and kappa- (but not mu-) opioid receptor-mediated events within the CMM contribute to the hypotension and bradycardia evoked by haemorrhage and the effectiveness of naloxone in reversing shock.

  12. Inhibition of GABAergic Neurotransmission by HIV-1 Tat and Opioid Treatment in the Striatum Involves μ-Opioid Receptors

    PubMed Central

    Xu, Changqing; Fitting, Sylvia

    2016-01-01

    Due to combined antiretroviral therapy (cART), human immunodeficiency virus type 1 (HIV-1) is considered a chronic disease with high prevalence of mild forms of neurocognitive impairments, also referred to as HIV-associated neurocognitive disorders (HAND). Although opiate drug use can exacerbate HIV-1 Tat-induced neuronal damage, it remains unknown how and to what extent opioids interact with Tat on the GABAergic system. We conducted whole-cell recordings in mouse striatal slices and examined the effects of HIV-1 Tat in the presence and absence of morphine (1 μM) and damgo (1 μM) on GABAergic neurotransmission. Results indicated a decrease in the frequency and amplitude of spontaneous inhibitory postsynaptic currents (sIPSCs) and miniature IPSCs (mIPSCs) by Tat (5–50 nM) in a concentration-dependent manner. The significant Tat-induced decrease in IPSCs was abolished when removing extracellular and/or intracellular calcium. Treatment with morphine or damgo alone significantly decreased the frequency, but not amplitude of IPSCs. Interestingly, morphine but not damgo indicated an additional downregulation of the mean frequency of mIPSCs in combination with Tat. Pretreatment with naloxone (1 μM) and CTAP (1 μM) prevented the Tat-induced decrease in sIPSCs frequency but only naloxone prevented the combined Tat and morphine effect on mIPSCs frequency. Results indicate a Tat- or opioid-induced decrease in GABAergic neurotransmission via μ-opioid receptors with combined Tat and morphine effects involving additional opioid receptor-related mechanisms. Exploring the interactions between Tat and opioids on the GABAergic system may help to guide future research on HAND in the context of opiate drug use. PMID:27877102

  13. Synthesis and opioid receptor binding affinities of 2-substituted and 3-aminomorphinans: ligands for mu, kappa, and delta opioid receptors.

    PubMed

    Decker, Michael; Si, Yu-Gui; Knapp, Brian I; Bidlack, Jean M; Neumeyer, John L

    2010-01-14

    The phenolic group of the potent mu and kappa opioid morphinan agonist/antagonists cyclorphan and butorphan was replaced by phenylamino and benzylamino groups including compounds with para-substituents in the benzene ring. These compounds are highly potent mu and kappa ligands, e.g., p-methoxyphenylaminocyclorphan showing a K(i) of 0.026 nM at the mu receptor and a K(i) of 0.03 nM at the kappa receptor. Phenyl carbamates and phenylureas were synthesized and investigated. Selective o-formylation of butorphan and levorphanol was achieved. This reaction opened the way to a large set of 2-substituted 3-hydroxymorphinans, including 2-hydroxymethyl-, 2-aminomethyl-, and N-substituted 2-aminomethyl-3-hydroxymorphinans. Bivalent ligands bridged in the 2-position were also synthesized and connected with secondary and tertiary aminomethyl groups, amide bonds, and hydroxymethylene groups, respectively. Although most of the 2-substituted morphinans showed considerably lower affinities compared to their parent compounds, the bivalent ligand approach led to significantly higher affinities compared to the univalent 2-substituted morphinans.

  14. Selective Estrogen Receptor Modulators

    PubMed Central

    2016-01-01

    Selective estrogen receptor modulators (SERMs) are now being used as a treatment for breast cancer, osteoporosis and postmenopausal symptoms, as these drugs have features that can act as an estrogen agonist and an antagonist, depending on the target tissue. After tamoxifen, raloxifene, lasofoxifene and bazedoxifene SERMs have been developed and used for treatment. The clinically decisive difference among these drugs (i.e., the key difference) is their endometrial safety. Compared to bisphosphonate drug formulations for osteoporosis, SERMs are to be used primarily in postmenopausal women of younger age and are particularly recommended if there is a family history of invasive breast cancer, as their use greatly reduces the incidence of this type of cancer in women. Among the above mentioned SERMs, raloxifene has been widely used in prevention and treatment of postmenopausal osteoporosis and vertebral compression fractures, and clinical studies are now underway to test the comparative advantages of raloxifene with those of bazedoxifene, a more recently developed SERM. Research on a number of adverse side effects of SERM agents is being performed to determine the long-term safety of this class of compouds for treatment of osteoporosis. PMID:27559463

  15. Ca2+ channel inhibition by endomorphins via the cloned mu-opioid receptor expressed in NG108-15 cells.

    PubMed

    Mima, H; Morikawa, H; Fukuda, K; Kato, S; Shoda, T; Mori, K

    1997-12-11

    Endomorphin-1 and -2, recently isolated endogenous peptides specific for the mu-opioid receptor, inhibited Ca2+ channel currents with EC50 of 6 and 9 nM, respectively, in NG108-15 cells transformed to express the cloned rat mu-opioid receptor. On the other hand, they elicited no response in nontransfected NG108-15 cells. It is concluded that endomorphin-1 and -2 induce Ca2+ channel inhibition by selectively activating the mu-opioid receptor.

  16. Synergy between mu opioid ligands: evidence for functional interactions among mu opioid receptor subtypes.

    PubMed

    Bolan, Elizabeth A; Tallarida, Ronald J; Pasternak, Gavril W

    2002-11-01

    Pharmacological differences among mu opioid drugs have been observed in in vitro and in vivo preclinical models, as well as clinically, implying that all mu opioids may not be working through the same mechanism of action. Here we demonstrate analgesic synergy between L-methadone and several mu opioid ligands. Of the compounds examined, L-methadone selectively synergizes with morphine, morphine-6beta-glucuronide, codeine, and the active metabolite of heroin, 6-acetylmorphine. Morphine synergizes only with L-methadone. In analgesic assays, D-methadone was inactive alone and did not enhance morphine analgesia when the two were given together, confirming that L-methadone was not acting through N-methyl-D-aspartate mechanisms. Both L-methadone and morphine displayed only additive effects when paired with oxymorphone, oxycodone, fentanyl, alfentanyl, or meperidine. Although it displays synergy in analgesic assays, the L-methadone/morphine combination does not exhibit synergy in the gastrointestinal transit assay. This analgesic synergy of L-methadone with selective mu opioid drugs and the differences in opioid-mediated actions suggest that these drugs may be acting via different mechanisms. These findings provide further evidence for the complexity of the pharmacology of mu opioids.

  17. mu-Opioid receptor knockout mice are insensitive to methamphetamine-induced behavioral sensitization.

    PubMed

    Shen, Xine; Purser, Chris; Tien, Lu-Tai; Chiu, Chi-Tso; Paul, Ian A; Baker, Rodney; Loh, Horace H; Ho, Ing K; Ma, Tangeng

    2010-08-01

    Repeated administration of psychostimulants to rodents can lead to behavioral sensitization. Previous studies, using nonspecific opioid receptor (OR) antagonists, revealed that ORs were involved in modulation of behavioral sensitization to methamphetamine (METH). However, the contribution of OR subtypes remains unclear. In the present study, using mu-OR knockout mice, we examined the role of mu-OR in the development of METH sensitization. Mice received daily intraperitoneal injection of drug or saline for 7 consecutive days to initiate sensitization. To express sensitization, animals received one injection of drug (the same as for initiation) or saline on day 11. Animal locomotor activity and stereotypy were monitored during the periods of initiation and expression of sensitization. Also, the concentrations of METH and its active metabolite amphetamine in the blood were measured after single and repeated administrations of METH. METH promoted significant locomotor hyperactivity at low doses and stereotyped behaviors at relative high doses (2.5 mg/kg and above). Repeated administration of METH led to the initiation and expression of behavioral sensitization in wild-type mice. METH-induced behavioral responses were attenuated in the mu-OR knockout mice. Haloperidol (a dopamine receptor antagonist) showed a more potent effect in counteracting METH-induced stereotypy in the mu-OR knockout mice. Saline did not induce behavioral sensitization in either genotype. No significant difference was observed in disposition of METH and amphetamine between the two genotypes. Our study indicated that the mu-opioid system is involved in modulating the development of behavioral sensitization to METH. (c) 2010 Wiley-Liss, Inc.

  18. Prospects for Creation of Cardioprotective and Antiarrhythmic Drugs Based on Opioid Receptor Agonists

    PubMed Central

    Maslov, Leonid N; Oeltgen, Peter R.; Naryzhnaya, Natalia V.; Pei, Jian‐Ming; Brown, Stephen A.; Lishmanov, Yury B.; Downey, James M.

    2016-01-01

    Abstract It has now been demonstrated that the μ, δ1, δ2, and κ1 opioid receptor (OR) agonists represent the most promising group of opioids for the creation of drugs enhancing cardiac tolerance to the detrimental effects of ischemia/reperfusion (I/R). Opioids are able to prevent necrosis and apoptosis of cardiomyocytes during I/R and improve cardiac contractility in the reperfusion period. The OR agonists exert an infarct‐reducing effect with prophylactic administration and prevent reperfusion‐induced cardiomyocyte death when ischemic injury of heart has already occurred; that is, opioids can mimic preconditioning and postconditioning phenomena. Furthermore, opioids are also effective in preventing ischemia‐induced arrhythmias. PMID:27197922

  19. Ovarian steroids alter mu opioid receptor trafficking in hippocampal parvalbumin GABAergic interneurons.

    PubMed

    Torres-Reveron, Annelyn; Williams, Tanya J; Chapleau, Jeanette D; Waters, Elizabeth M; McEwen, Bruce S; Drake, Carrie T; Milner, Teresa A

    2009-09-01

    The endogenous hippocampal opioid systems are implicated in learning associated with drug use. Recently, we showed that ovarian hormones regulate enkephalin levels in the mossy fiber pathway. This pathway overlaps with parvalbumin (PARV)-basket interneurons that contain the enkephalin-activated mu opioid receptors (MORs) and are important for controlling the "temporal timing" of granule cells. Here, we evaluated the influence of ovarian steroids on the trafficking of MORs in PARV interneurons. Two groups of female rats were analyzed: cycling rats in proestrus (relatively high estrogens) or diestrus; and ovariectomized rats euthanized 6, 24 or 72 h after estradiol benzoate (10 microg, s.c.) administration. Dorsal hippocampal sections were dually immunolabeled for MOR and PARV and examined by light and electron microscopy. As in males, in females MOR-immunoreactivity (-ir) was in numerous PARV-labeled perikarya, dendrites and terminals in the dentate hilar region. Variation in ovarian steroid levels altered the subcellular distribution of MORs in PARV-labeled dendrites but not terminals. In normal cycling rats, MOR-gold particles on the plasma membrane of small PARV-labeled dendrites (area <1 microm2) had higher density in proestrus rats than in diestrus rats. Likewise, in ovariectomized rats MORs showed higher density on the plasma membrane of small PARV-labeled dendrites 72 h after estradiol exposure. The number of PARV-labeled cells was not affected by estrous cycle phase or estrogen levels. These results demonstrate that estrogen levels positively regulate the availability of MORs on GABAergic interneurons in the dentate gyrus, suggesting cooperative interaction between opioids and estrogens in modulating principal cell excitability.

  20. Sex and estrogen receptor expression influence opioid peptide levels in the mouse hippocampal mossy fiber pathway.

    PubMed

    Van Kempen, Tracey A; Kahlid, Sana; Gonzalez, Andreina D; Spencer-Segal, Joanna L; Tsuda, Mumeko C; Ogawa, Sonoko; McEwen, Bruce S; Waters, Elizabeth M; Milner, Teresa A

    2013-09-27

    The opioid peptides, dynorphin (DYN) and enkephalin (L-ENK) are contained in the hippocampal mossy fiber pathway where they modulate synaptic plasticity. In rats, the levels of DYN and L-ENK immunoreactivity (-ir) are increased when estrogen levels are elevated (Torres-Reveron et al., 2008, 2009). Here, we used quantitative immunocytochemistry to examine whether opioid levels are similarly regulated in wildtype (WT) mice over the estrous cycle, and how these compared to males. Moreover, using estrogen receptor (ER) alpha and beta knock-out mice (AERKO and BERKO, respectively), the present study examined the role of ERs in rapid, membrane-initiated (6 h), or slower, nucleus-initiated (48 h) estradiol effects on mossy fiber opioid levels. Unlike rats, the levels of DYN and L-ENK-ir did not change over the estrous cycle. However, compared to males, females had higher levels of DYN-ir in CA3a and L-ENK-ir in CA3b. In WT and BERKO ovariectomized (OVX) mice, neither DYN- nor L-ENK-ir changed following 6 or 48 h estradiol benzoate (EB) administration. However, DYN-ir significantly increased 48 h after EB in the dentate gyrus (DG) and CA3b of AERKO mice only. These findings suggest that cyclic hormone levels regulate neither DYN nor L-ENK levels in the mouse mossy fiber pathway as they do in the rat. This may be due to species-specific differences in the mossy fiber pathway. However, in the mouse, DYN levels are regulated by exogenous EB in the absence of ERα possibly via an ERβ-mediated pathway requiring new gene transcription.

  1. Naloxegol: the first orally administered, peripherally acting, mu opioid receptor antagonist, approved for the treatment of opioid-induced constipation.

    PubMed

    Corsetti, M; Tack, J

    2015-08-01

    Treatment of opioid-induced constipation (OIC) is becoming a relevant clinical challenge as most of the treatments demonstrated to be more effective than placebo in treating OIC have safety issues limiting a broad clinical application. Naloxegol is the first orally administered, peripherally acting, µ opioid receptor antagonist approved by the FDA and EMA specifically for the treatment of noncancer patients with OIC. This review summarizes the results of the studies regarding the effects of naloxegol in OIC. Pharmacodynamic studies have demonstrated that naloxegol was able to inhibit gastrointestinal opioid effects while preserving central analgesic actions. Phase II and phase III studies in patients with noncancer OIC have confirmed the efficacy of naloxegol to inhibit OIC, and the most consistent efficacy was seen with the 25-mg dose once daily. Side effects were mainly gastrointestinal in origin (and usually transient and mild) and there were no signs of opioid withdrawal in the studies. Safety and tolerability were shown in a long-term safety study. Considering its efficacy, safety, route of administration and the limitations of most of the other available treatments, naloxegol has the potential to become the first-line treatment for noncancer patients with OIC.

  2. The presence of mu-, delta-, and kappa-opioid receptors in human heart tissue.

    PubMed

    Sobanski, Piotr; Krajnik, Malgorzata; Shaqura, Mohammed; Bloch-Boguslawska, Elzbieta; Schäfer, Michael; Mousa, Shaaban A

    2014-11-01

    Functional evidence suggests that the stimulation of peripheral and central opioid receptors (ORs) is able to modulate heart function. Moreover, selective stimulation of either cardiac or central ORs evokes preconditioning and, therefore, protects the heart against ischemic injury. However, anatomic evidence for OR subtypes in the human heart is scarce. Human heart tissue obtained during autopsy after sudden death was examined immunohistochemically for mu- (MOR), kappa- (KOR), and delta- (DOR) OR subtypes. MOR and DOR immunoreactivity was found mainly in myocardial cells, as well as on sparse individual nerve fibers. KOR immunoreactivity was identified predominantly in myocardial cells and on intrinsic cardiac adrenergic (ICA) cell-like structures. Double immunofluorescence confocal microscopy revealed that DOR colocalized with the neuronal marker PGP9.5, as well as with the sensory neuron marker calcitonin gene-related peptide (CGRP). CGRP-immunoreactive (IR) fibers were detected either in nerve bundles or as sparse individual fibers containing varicose-like structures. Our findings offer the first hint of an anatomic basis for the existence of OR subtypes in the human heart by demonstrating their presence in CGRP-IR sensory nerve fibers, small cells with an eccentric nucleus resembling ICA cells, and myocardial cells. Taken together, this suggests the role of opioids in both the neural transmission and regulation of myocardial cell function.

  3. Opioid peptides in peripheral pain control.

    PubMed

    Lesniak, Anna; Lipkowski, Andrzej W

    2011-01-01

    Opioids have a long history of therapeutic use as a remedy for various pain states ranging from mild acute nociceptive pain to unbearable chronic advanced or end-stage disease pain. Analgesia produced by classical opioids is mediated extensively by binding to opioid receptors located in the brain or the spinal cord. Nevertheless, opioid receptors are also expressed outside the CNS in the periphery and may become valuable assets in eliciting analgesia devoid of shortcomings typical for the activation of their central counterparts. The discovery of endogenous opioid peptides that participate in the formation, transmission, modulation and perception of pain signals offers numerous opportunities for the development of new analgesics. Novel peptidic opioid receptor analogs, which show limited access through the blood brain barrier may support pain therapy requiring prolonged use of opioid drugs.

  4. Cellular signalling of non-synonymous single-nucleotide polymorphisms of the human μ-opioid receptor (OPRM1)

    PubMed Central

    Knapman, Alisa; Connor, Mark

    2015-01-01

    There is significant variability in individual responses to opioid drugs, which is likely to have a significant genetic component. A number of non-synonymous single-nucleotide polymorphisms (SNPs) in the coding regions of the μ-opioid receptor gene (OPRM1) have been postulated to contribute to this variability. Although many studies have investigated the clinical influences of these μ-opioid receptor variants, the outcomes are reported in the context of thousands of other genes and environmental factors, and we are no closer to being able to predict individual response to opioids based on genotype. Investigation of how μ-opioid receptor SNPs affect their expression, coupling to second messengers, desensitization and regulation is necessary to understand how subtle changes in receptor structure can impact individual responses to opioids. To date, the few functional studies that have investigated the consequences of SNPs on the signalling profile of the μ-opioid receptor in vitro have shown that the common N40D variant has altered functional responses to some opioids, while other, rarer, variants display altered signalling or agonist-dependent regulation. Here, we review the data available on the effects of μ-opioid receptor polymorphisms on receptor function, expression and regulation in vitro, and discuss the limitations of the studies to date. Whether or not μ-opioid receptor SNPs contribute to individual variability in opioid responses remains an open question, in large part because we have relatively little good data about how the amino acid changes affect μ-opioid receptor function. LINKED ARTICLES This article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-2 PMID:24527749

  5. The interaction between histamine H1 receptor and μ- opioid receptor in scratching behavior in ICR mice.

    PubMed

    Nakasone, Tasuku; Sugimoto, Yumi; Kamei, Chiaki

    2016-04-15

    In this study, we examined the interaction between histamine H1 receptor and μ-opioid receptor in scratching behavior in ICR mice. Both histamine and morphine caused scratching and simultaneous injection of histamine and morphine had an additive effect. Chlorpheniramine and naloxone inhibited histamine-induced scratching behavior. These two drugs also inhibited morphine-induced scratching behavior. Simultaneous injection of chlorpheniramine and naloxone caused a significant inhibition of histamine-induced scratching compared with separate injections. The same findings were also noted for morphine-induced scratching. These results strongly indicate a close relationship between histamine H1 receptor and μ-opioid receptor in scratching behavior in ICR mice.

  6. N-methyl-D-aspartate receptors and large conductance calcium-sensitive potassium channels inhibit the release of opioid peptides that induce mu-opioid receptor internalization in the rat spinal cord.

    PubMed

    Song, B; Marvizón, J C G

    2005-01-01

    Endogenous opioids in the spinal cord play an important role in nociception, but the mechanisms that control their release are poorly understood. To simultaneously detect all opioids able to activate the mu-opioid receptor, we measured mu-opioid receptor internalization in rat spinal cord slices stimulated electrically or chemically to evoke opioid release. Electrical stimulation of the dorsal horn in the presence of peptidase inhibitors produced mu-opioid receptor internalization in half of the mu-opioid receptor neurons. This internalization was rapidly abolished by N-methyl-D-aspartate (IC50=2 microM), and N-methyl-D-aspartate antagonists prevented this effect. mu-Opioid receptor internalization evoked by high K+ or veratridine was also inhibited by N-methyl-D-aspartate receptor activation. N-methyl-D-aspartate did not affect mu-opioid receptor internalization induced by exogenous endomorphins, confirming that the effect of N-methyl-D-aspartate was on opioid release. We hypothesized that this inhibition was mediated by large conductance Ca2+-sensitive K+ channels BK(Ca2+). Indeed, inhibition by N-methyl-D-aspartate was prevented by tetraethylammonium and by the selective BK(Ca2+) blockers paxilline, penitrem A and verruculogen. Paxilline did not increase mu-opioid receptor internalization in the absence of N-methyl-D-aspartate, indicating that it does not produce an increase in opioid release unrelated to the inhibition by N-methyl-d-aspartate. The BK(Ca2+) involved appears to be a subtype with slow association kinetics for iberiotoxin, which was effective only with long incubations. The BK(Ca2+) opener NS-1619 also inhibited the evoked mu-opioid receptor internalization, and iberiotoxin prevented this effect. We concluded that Ca2+ influx through N-methyl-D-aspartate receptors causes the opening of BK(Ca2+) and hyperpolarization in opioid-containing dorsal horn neurons, resulting in the inhibition of opioid release. Since mu-opioid receptors in the dorsal horn

  7. N-METHYL-d-ASPARTATE RECEPTORS AND LARGE CONDUCTANCE CALCIUM-SENSITIVE POTASSIUM CHANNELS INHIBIT THE RELEASE OF OPIOID PEPTIDES THAT INDUCE μ-OPIOID RECEPTOR INTERNALIZATION IN THE RAT SPINAL CORD

    PubMed Central

    SONG, B.; MARVIZÓN, J. C. G.

    2006-01-01

    Endogenous opioids in the spinal cord play an important role in nociception, but the mechanisms that control their release are poorly understood. To simultaneously detect all opioids able to activate the μ-opioid receptor, we measured μ-opioid receptor internalization in rat spinal cord slices stimulated electrically or chemically to evoke opioid release. Electrical stimulation of the dorsal horn in the presence of peptidase inhibitors produced μ-opioid receptor internalization in half of the μ-opioid receptor neurons. This internalization was rapidly abolished by N-methyl-d-aspartate (IC50=2 μM), and N-methyl-d-aspartate antagonists prevented this effect. μ-Opioid receptor internalization evoked by high K+ or veratridine was also inhibited by N-methyl-d-aspartate receptor activation. N-methyl-d-aspartate did not affect μ-opioid receptor internalization induced by exogenous endomorphins, confirming that the effect of N-methyl-d-aspartate was on opioid release. We hypothesized that this inhibition was mediated by large conductance Ca2+-sensitive K+ channels BK(Ca2+). Indeed, inhibition by N-methyl-d-aspartate was prevented by tetraethylammonium and by the selective BK(Ca2+) blockers paxilline, penitrem A and verruculogen. Paxilline did not increase μ-opioid receptor internalization in the absence of N-methyl-d-aspartate, indicating that it does not produce an increase in opioid release unrelated to the inhibition by N-methyl-d-aspartate. The BK(Ca2+) involved appears to be a subtype with slow association kinetics for iberiotoxin, which was effective only with long incubations. The BK(Ca2+) opener NS-1619 also inhibited the evoked μ-opioid receptor internalization, and iberiotoxin prevented this effect. We concluded that Ca2+ influx through N-methyl-d-aspartate receptors causes the opening of BK(Ca2+) and hyperpolarization in opioid-containing dorsal horn neurons, resulting in the inhibition of opioid release. Since μ-opioid receptors in the dorsal horn

  8. Prefrontal Cortical Kappa Opioid Receptors Attenuate Responses to Amygdala Inputs.

    PubMed

    Tejeda, Hugo A; Hanks, Ashley N; Scott, Liam; Mejias-Aponte, Carlos; Hughes, Zoë A; O'Donnell, Patricio

    2015-12-01

    Kappa opioid receptors (KORs) have been implicated in anxiety and stress, conditions that involve activation of projections from the basolateral amygdala (BLA) to the medial prefrontal cortex (mPFC). Although KORs have been studied in several brain regions, their role on mPFC physiology and on BLA projections to the mPFC remains unclear. Here, we explored whether KORs modify synaptic inputs from the BLA to the mPFC using in vivo electrophysiological recordings with electrical and optogenetic stimulation. Systemic administration of the KOR agonist U69,593 inhibited BLA-evoked synaptic responses in the mPFC without altering hippocampus-evoked responses. Intra-mPFC U69,593 inhibited electrical and optogenetic BLA-evoked synaptic responses, an effect blocked by the KOR antagonist nor-BNI. Bilateral intra-mPFC injection of the KOR antagonist nor-BNI increased center time in the open field test, suggesting an anxiolytic effect. The data demonstrate that mPFC KORs negatively regulate glutamatergic synaptic transmission in the BLA-mPFC pathway and anxiety-like behavior. These findings provide a framework whereby KOR signaling during stress and anxiety can regulate the flow of emotional state information from the BLA to the mPFC.

  9. Kappa opioid receptors stimulate phosphoinositide turnover in rat brain

    SciTech Connect

    Periyasamy, S.; Hoss, W. )

    1990-01-01

    The effects of various subtype-selective opioid agonists and antagonists on the phosphoinositide (PI) turnover response were investigated in the rat brain. The {kappa}-agonists U-50,488H and ketocyclazocine produced a concentration-dependent increase in the accumulation of IP's in hippocampal slices. The other {kappa}-agonists Dynorphin-A (1-13) amide, and its protected analog D(Ala){sup 2}-dynorphin-A (1-13) amide also produced a significant increase in the formation of ({sup 3}H)-IP's, whereas the {mu}-selective agonists (D-Ala{sup 2}-N-Me-Phe{sup 4}-Gly{sup 5}-ol)-enkephalin and morphine and the {delta}-selective agonist (D-Pen{sup 2,5})-enkephalin were ineffective. The increase in IP's formation elicited by U-50,488H was partially antagonized by naloxone and more completely antagonized by the {kappa}-selective antagonists nor-binaltorphimine and MR 2266. The formation of IP's induced by U-50,488H varies with the regions of the brain used, being highest in hippocampus and amygdala, and lowest in striatum and pons-medullar. The results indicate that brain {kappa}- but neither {mu}- nor {delta}- receptors are coupled to the PI turnover response.

  10. The role of δ-opioid receptors in learning and memory underlying the development of addiction

    PubMed Central

    Klenowski, Paul; Morgan, Michael; Bartlett, Selena E

    2015-01-01

    Opioids are important endogenous ligands that exist in both invertebrates and vertebrates and signal by activation of opioid receptors to produce analgesia and reward or pleasure. The μ-opioid receptor is the best known of the opioid receptors and mediates the acute analgesic effects of opiates, while the δ-opioid receptor (DOR) has been less well studied and has been linked to effects that follow from chronic use of opiates such as stress, inflammation and anxiety. Recently, DORs have been shown to play an essential role in emotions and increasing evidence points to a role in learning actions and outcomes. The process of learning and memory in addiction has been proposed to involve strengthening of specific brain circuits when a drug is paired with a context or environment. The DOR is highly expressed in the hippocampus, amygdala, striatum and other basal ganglia structures known to participate in learning and memory. In this review, we will focus on the role of the DOR and its potential role in learning and memory underlying the development of addiction. LINKED ARTICLES This article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-2 PMID:24641428

  11. Salvinorin A analogs and other κ-opioid receptor compounds as treatments for cocaine abuse.

    PubMed

    Kivell, Bronwyn M; Ewald, Amy W M; Prisinzano, Thomas E

    2014-01-01

    Acute activation of kappa-opioid receptors produces anti-addictive effects by regulating dopamine levels in the brain. Unfortunately, classic kappa-opioid agonists have undesired side effects such as sedation, aversion, and depression, which restrict their clinical use. Salvinorin A (Sal A), a novel kappa-opioid receptor agonist extracted from the plant Salvia divinorum, has been identified as a potential therapy for drug abuse and addiction. Here, we review the preclinical effects of Sal A in comparison with traditional kappa-opioid agonists and several new analogs. Sal A retains the anti-addictive properties of traditional kappa-opioid receptor agonists with several improvements including reduced side effects. However, the rapid metabolism of Sal A makes it undesirable for clinical development. In an effort to improve the pharmacokinetics and tolerability of this compound, kappa-opioid receptor agonists based on the structure of Sal A have been synthesized. While work in this field is still in progress, several analogs with improved pharmacokinetic profiles have been shown to have anti-addictive effects. While in its infancy, it is clear that these compounds hold promise for the future development of anti-addictive therapeutics.

  12. Salvinorin A analogs and other kappa opioid receptor compounds as treatments for cocaine abuse

    PubMed Central

    Kivell, Bronwyn M; Ewald, Amy WM; Prisinzano, Thomas E

    2014-01-01

    Acute activation of κ opioid receptors produces anti-addictive effects by regulating dopamine levels in the brain. Unfortunately, classic κ opioid agonists have undesired side effects such as sedation, aversion and depression which restrict their clinical use. Salvinorin A (Sal A), a novel κ opioid receptor agonist extracted from the plant Salvia divinorum, has been identified as a potential therapy for drug abuse and addiction. Here, we review the preclinical effects of Sal A in comparison with traditional κ opioid agonists and several new analogues. Sal A retains the anti-addictive properties of traditional κ opioid receptors agonists with several improvements including reduced side effects. However, the rapid metabolism of Sal A makes it undesirable for clinical development. In an effort to improve the pharmacokinetics and tolerability of this compound, κ opioid receptor agonists based on the structure of Sal A have been synthesized. While work in this field is still in progress, several analogues with improved pharmacokinetic profiles have been shown to have anti-addiction effects. While in its infancy, it is clear that these compounds hold promise for the future development of anti-addiction therapeutics. PMID:24484985

  13. The role of mu and kappa opioid receptors within the periaqueductal gray in the expression of conditional hypoalgesia.

    PubMed

    Bellgowan, P S; Helmstetter, F J

    1998-04-27

    The periaqueductal gray (PAG) is a midbrain structure involved in the modulation of pain and expression of classically conditioned fear responses. Non-selective opioid antagonists applied to the PAG block the expression of hypoalgesia in rats exposed to a Pavlovian signal for shock. This study was conducted to determine the anatomical and pharmacological specificity of the PAG's role in conditional hypoalgesia. Rat subjects received injections of either the mu opioid antagonist CTAP (6.6 nMol), the kappa opioid antagonist Nor-binaltorphimine (Nor-BNI, 6.6 nMol) or saline. Injections were made into either the dorsolateral (dlPAG) or ventrolateral (vlPAG) PAG prior to the presentation of an auditory stimulus that had previously been paired with foot shock while measuring nociception with the radiant heat tail flick (TF) test. Elevation in TF latency in response to the auditory stimulus was blocked only by administration of CTAP into the vlPAG. These results suggest that conditional hypoalgesia (CHA) is subserved by mu but not kappa opioid receptors located in the vlPAG but not the dlPAG.

  14. Allosteric Modulation of Chemoattractant Receptors

    PubMed Central

    Allegretti, Marcello; Cesta, Maria Candida; Locati, Massimo

    2016-01-01

    Chemoattractants control selective leukocyte homing via interactions with a dedicated family of related G protein-coupled receptor (GPCR). Emerging evidence indicates that the signaling activity of these receptors, as for other GPCR, is influenced by allosteric modulators, which interact with the receptor in a binding site distinct from the binding site of the agonist and modulate the receptor signaling activity in response to the orthosteric ligand. Allosteric modulators have a number of potential advantages over orthosteric agonists/antagonists as therapeutic agents and offer unprecedented opportunities to identify extremely selective drug leads. Here, we resume evidence of allosterism in the context of chemoattractant receptors, discussing in particular its functional impact on functional selectivity and probe/concentration dependence of orthosteric ligands activities. PMID:27199992

  15. Potent Dmt-Tic pharmacophoric delta- and mu-opioid receptor antagonists.

    PubMed

    Li, Tingyou; Fujita, Yoshio; Shiotani, Kimitaka; Miyazaki, Anna; Tsuda, Yuko; Ambo, Akihiro; Sasaki, Yusuke; Jinsmaa, Yunden; Marczak, Ewa; Bryant, Sharon D; Salvadori, Severo; Lazarus, Lawrence H; Okada, Yoshio

    2005-12-15

    A series of dimeric Dmt-Tic (2',6'-dimethyl-L-tyrosyl-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid) analogues (8-14, 18-22) were covalently linked through diaminoalkane and symmetric or asymmetric 3,6-diaminoalkyl-2(1H)-pyrazinone moieties. All the compounds exhibited high affinity for both delta-opioid receptors [Ki(delta) = 0.06-1.53 nM] and mu-opioid receptors [Ki(mu) = 1.37-5.72 nM], resulting in moderate delta-receptor selectivity [Ki(mu)/Ki(delta) = 3-46]. Regardless of the type of linker between the Dmt-Tic pharmacophores, delta-opioid-mediated antagonism was extraordinarily high in all analogues (pA2 = 10.42-11.28), while in vitro agonism (MVD and GPI bioassays) was essentially absent (ca. 3 to >10 microM). While an unmodified N-terminus (9, 13, 18) revealed weak mu-opioid antagonism (pA2 = 6.78-6.99), N,N'-dimethylation (21, 22), which negatively impacts on mu-opioid-associated agonism (Balboni et al., Bioorg. Med. Chem. 2003, 11, 5435-5441), markedly enhanced mu-opioid antagonism (pA2 = 8.34 and 7.71 for 21 and 22, respectively) without affecting delta-opioid activity. These data are the first evidence that a single dimeric opioid ligand containing the Dmt-Tic pharmacophore exhibits highly potent delta- and mu-opioid antagonist activities.

  16. Opiates modulate thermosensation by internalizing cold receptor TRPM8.

    PubMed

    Shapovalov, George; Gkika, Dimitra; Devilliers, Maily; Kondratskyi, Artem; Gordienko, Dmitri; Busserolles, Jerome; Bokhobza, Alexandre; Eschalier, Alain; Skryma, Roman; Prevarskaya, Natalia

    2013-08-15

    Stimulation of μ-opioid receptors (OPRMs) brings powerful pain relief, but it also leads to the development of tolerance and addiction. Ensuing withdrawal in abstinent patients manifests itself with severe symptoms, including cold hyperalgesia, often preventing addicted patients from successfully completing the rehabilitation. Unsurprisingly, OPRMs have been a central point of many studies. Nonetheless, a satisfactory understanding of the pathways leading to distorted sensory responses during opiate administration and abstinence is far from complete. Here, we present a mechanism that leads to modulation by OPRMs of one of the sensory responses, thermosensation. Activation of OPRM1 leads to internalization of a cold-sensor TRPM8, which can be reversed by a follow-up treatment with the inverse OPRM agonist naloxone. Knockout of TRPM8 protein leads to a decrease in morphine-induced cold analgesia. The proposed pathway represents a universal mechanism that is probably shared by regulatory pathways modulating general pain sensation in response to opioid treatment.

  17. Differentiation of δ, μ, and κ opioid receptor agonists based on pharmacophore development and computed physicochemical properties

    NASA Astrophysics Data System (ADS)

    Filizola, Marta; Villar, Hugo O.; Loew, Gilda H.

    2001-04-01

    Compounds that bind with significant affinity to the opioid receptor types, δ, μ, and κ, with different combinations of activation and inhibition at these three receptors could be promising behaviorally selective agents. Working on this hypothesis, the chemical moieties common to three different sets of opioid receptor agonists with significant affinity for each of the three receptor types δ, μ, or κ were identified. Using a distance analysis approach, common geometric arrangements of these chemical moieties were found for selected δ, μ, or κ opioid agonists. The chemical and geometric commonalities among agonists at each opioid receptor type were then compared with a non-specific opioid recognition pharmacophore recently developed. The comparison provided identification of the additional requirements for activation of δ, μ, and κ opioid receptors. The distance analysis approach was able to clearly discriminate κ-agonists, while global molecular properties for all compounds were calculated to identify additional requirements for activation of δ and μ receptors. Comparisons of the combined geometric and physicochemical properties calculated for each of the three sets of agonists allowed the determination of unique requirements for activation of each of the three opioid receptors. These results can be used to improve the activation selectivity of known opioid agonists and as a guide for the identification of novel selective opioid ligands with potential therapeutic usefulness.

  18. Discovery of the first small-molecule opioid pan antagonist with nanomolar affinity at mu, delta, kappa, and nociceptin opioid receptors.

    PubMed

    Zaveri, Nurulain T; Journigan, V Blair; Polgar, Willma E

    2015-04-15

    The trans-(3R,4R)-dimethyl-4-(3-hydroxyphenyl)piperidine scaffold is a known pharmacophore for mu opioid (MOP), kappa opioid (KOP), and delta opioid (DOP) receptor antagonists; however, it has not been explored in nociceptin opioid (NOP/ORL-1) receptor ligands. We recently found that the selective KOP antagonist JDTic, (3R)-7-hydroxy-N-((1S)-1-{[(3R,4R)-4-(3-hydroxyphenyl)-3,4-dimethyl-1-piperidinyl]methyl}-2-methylpropyl)-1,2,3,4-tetrahydro-3-isoquinolinecarboxamide, containing this opioid antagonist pharmacophore, has significant binding affinity at the NOP receptor (Ki 16.67 ± 0.76 nM), with no intrinsic activity in the [(35)S]GTPγS functional assay. Since this is the first ligand containing the trans-(3R,4R)-dimethyl-4-(3-hydroxyphenyl)piperidine opioid antagonist pharmacophore to have affinity for the NOP receptor, we explored the structural determinants of its NOP binding affinity. When rational chemical modifications of JDTic were carried out, based on our previously established NOP pharmacophoric structure-activity relationship (SAR) model, most modifications led to a significant decrease in NOP and opioid binding affinity compared to JDTic. Interestingly, however, removal of the 3,4-dimethyl groups of the trans-(3R,4R)-dimethyl-4-(3-hydroxyphenyl)piperidine antagonist scaffold of JDTic increased the binding affinity at NOP by 10-fold (Ki 1.75 ± 0.74 nM) while maintaining comparable affinity for KOP, MOP, and DOP receptors (Ki 1.14 ± 0.63, 1.67 ± 0.6, and 19.6 ± 1.3 nM, respectively). In vitro functional efficacy studies using the [(35)S]GTPγS assay showed that this compound AT-076 functions as an antagonist at all four opioid receptors. Detailed characterization of the antagonist activity of AT-076 shows that it has a noncompetitive antagonist profile at the NOP and KOP receptors (insurmountable antagonism), but is a potent competitive antagonist at the MOP and DOP receptors, with Ke values 3-6-fold more potent than those of JDTic. AT-076 is the

  19. Opioid microinjection into raphe magnus modulates cardiorespiratory function in mice and rats.

    PubMed

    Hellman, Kevin M; Mendelson, Scott J; Mendez-Duarte, Marco A; Russell, James L; Mason, Peggy

    2009-11-01

    The raphe magnus (RM) participates in opioid analgesia and contains pain-modulatory neurons with respiration-related discharge. Here, we asked whether RM contributes to respiratory depression, the most prevalent lethal effect of opioids. To investigate whether opioidergic transmission in RM produces respiratory depression, we microinjected a mu-opioid receptor agonist, DAMGO, or morphine into the RM of awake rodents. In mice, opioid microinjection produced sustained decreases in respiratory rate (170 to 120 breaths/min), as well as heart rate (520 to 400 beats/min). Respiratory sinus arrhythmia, indicative of enhanced parasympathetic activity, was prevalent in mice receiving DAMGO microinjection. We performed similar experiments in rats but observed no changes in breathing rate or heart rate. Both rats and mice experienced significantly more episodes of bradypnea, indicative of impaired respiratory drive, after opioid microinjection. During spontaneous arousals, rats showed less tachycardia after opioid microinjection than before microinjection, suggestive of an attenuated sympathetic tone. Thus, activation of opioidergic signaling within RM produces effects beyond analgesia, including the unwanted destabilization of cardiorespiratory function. These adverse effects on homeostasis consequent to opioid microinjection imply a role for RM in regulating the balance of sympathetic and parasympathetic tone.

  20. Reproductive aging in Japanese quail, Coturnix japonica is associated with changes in central opioid receptors.

    PubMed

    Ottinger, M A; Corbitt, C; Hoffman, R; Thompson, N; Russek-Cohen, E; Deviche, P

    2006-12-18

    Quantitative in vitro autoradiography was used to measure specific mu and delta opioid receptor densities in regions of the Japanese quail, Coturnix japonica, brain that regulates reproductive endocrine and behavioral responses to determine the possible involvement of the opioid system in reproductive decline seen during aging. Densities were measured in selected brain regions of young sexually active (YAM), young photoregressed (YPM), old reproductively senescent (OIM) male, young active (YF), and old senescent female (OF) Japanese quail. Medial and lateral septum (SM, SL), medial preoptic area (POM), and n. intercollicularis (ICo) were of particular interest for reproductive responses. Similar to previous observations, mu and delta opioid receptors showed differential distributions in the areas measured. Some age-related changes were observed, with lower SM mu receptor densities in aged males (OIM) than females or young males (YAM). Densities of mu receptors in the POM and in other areas examined did not vary with sex or age. Similarly, OIM males had lower densities of delta receptors in the SM than young males (YAM and YPM); POM delta receptor densities were also low in OIM males compared to the YPM males, and YAM males were intermediate. Interestingly, photoregressed males (YPM) had higher SL delta receptor densities than any other group. Thus there were age-related differences detected in mu receptor densities among groups in the SM of OIM relative to other groups; and the mu and delta receptor densities did not differ in females with brain region. Additionally for delta receptors specifically, YF and OF did not differ from OIM for any brain region and similarly had lower densities of delta receptors compared to YAM males. These data provide support for regional differences in opioid receptor distribution and for age- and sex-related differences in delta opioid receptor densities. The direction of change presents an interesting dichotomy in that, compared to

  1. Delta opioid receptor analgesia: recent contributions from pharmacology and molecular approaches

    PubMed Central

    Gavériaux-Ruff, Claire; Kieffer, Brigitte Lina

    2012-01-01

    Delta opioid receptors represent a promising target for the development of novel analgesics. A number of tools have been developed recently that have significantly improved our knowledge of delta receptor function in pain control. These include several novel delta agonists with potent analgesic properties, as well as genetic mouse models with targeted mutations in the delta opioid receptor gene. Also, recent findings have further documented the regulation of delta receptor function at cellular level, which impacts on the pain-reducing activity of the receptor. These regulatory mechanisms occur at transcriptional and post-translational levels, along agonist-induced receptor activation, signaling and trafficking, or in interaction with other receptors and neuromodulatory systems. All these tools for in vivo research, as well as proposed mechanisms at molecular level, have tremendously increased our understanding of delta receptor physiology, and contribute to designing innovative strategies for the treatment of chronic pain and other diseases such as mood disorders. PMID:21836459

  2. In Vivo Techniques to Investigate the Internalization Profile of Opioid Receptors

    PubMed Central

    Pradhan, Amynah A.; Tawfik, Vivianne L.; Laboy, Alycia F.; Scherrer, Grégory

    2015-01-01

    G-protein-coupled receptors (GPCRs) regulate a remarkable diversity of biological functions, and are thus often targeted for drug therapies. Receptor internalization is commonly observed following agonist binding and activation. Receptor trafficking events have been well characterized in cell systems, but the in vivo significance of GPCR internalization is still poorly understood. To address this issue, we have developed an innovative knock-in mouse model, where an opioid receptor is directly visible in vivo. These knockin mice express functional fluorescent delta opioid receptors (DOR-eGFP) in place of the endogenous receptor, and these receptors are expressed at physiological levels within their native environment. DOR-eGFP mice have proven to be an extraordinary tool in studying receptor neuroanatomy, real-time receptor trafficking in live neurons, and in vivo receptor internalization. We have used this animal model to determine the relationship between receptor trafficking in neurons and receptor function at a behavioral level. Here, we describe in detail the construction and characterization of this knockin mouse. We also outline how to use these mice to examine the behavioral consequences of agonist-specific trafficking at the delta opioid receptor. These techniques are potentially applicable to any GPCR, and highlight the powerful nature of this imaging tool. PMID:25293318

  3. Purification and characterization of mu-specific opioid receptor from rat brain

    SciTech Connect

    Hasegawa, J.; Cho, T.M.; Ge, B.L.; Loh, H.H.

    1986-03-05

    A mu-specific opioid receptor was purified to apparent homogeneity from rat brain membranes by 6-succinylmorphine affinity chromatography, Ultrogel filtration, wheat germ agglutinin affinity chromatography, and isoelectric focusing. The purified receptor had a molecular weight of 58,000 as determined by polyacrylamide gel electrophoresis, and was judged to be homogeneous by the following criteria: (1) a single band on the SDS gel; and (2) a specific opioid binding activity of 17,720 pmole/mg protein, close to the theoretical value. In addition, the 58,000 molecular weight value agrees closely with that determined by covalently labelling purified receptor with bromoacetyl-/sup 3/H-dihydromorphine or with /sup 125/I-beta-endorphin and dimethyl suberimidate. To their knowledge, this is the first complete purification of an opioid receptor that retains its ability to bind opiates.

  4. Calcitonin Receptor-Like Receptor and Receptor Activity Modifying Protein 1 in the rat dorsal horn: localization in glutamatergic presynaptic terminals containing opioids and adrenergic α2C receptors

    PubMed Central

    Marvizón, Juan Carlos G.; Pérez, Orlando A.; Song, Bingbing; Chen, Wenling; Bunnett, Nigel W.; Grady, Eileen F.; Todd, Andrew J.

    2008-01-01

    others CRLR may form other receptors, possibly by dimerizing with RAMP2 or RAMP3. These findings suggest that CGRP or adrenomedullin receptors modulate opioid release in the dorsal horn. PMID:17614212

  5. Evidence of morphine like substance and μ-opioid receptor expression in Toxacara canis (Nematoda: Ascaridae)

    PubMed Central

    Golabi, Mostafa; Naem, Soraya; Imani, Mehdi; Dalirezh, Nowruz

    2016-01-01

    Toxocara canis (Nematoda: Ascaridae) is an intestinal nematode parasite of dogs, which can also cause disease in humans. Transmission to humans usually occurs because of direct contact with T. canis eggs present in soil contaminated with the feces of infected dogs. This nematode has extraordinary abilities to survive for many years in different tissues of vertebrates, and develop to maturity in the intestinal tract of its definitive host. Survival of parasitic nematodes within a host requires immune evasion using complicated pathways. Morphine-like substance, as well as opioids, which are known as down regulating agents, can modulate both innate and acquired immune responses, and let the parasite survives in their hosts. In the present study, we aimed to find evidences of morphine-like substance and µ-opiate receptor expression in T. canis, using high performance liquid chromatography (HPLC) and reverse transcription polymerase chain reaction (RT-PCR). The results indicated that T. canis produced morphine-like substances at the level of 2.31± 0.26 ng g-1 wet weight, and expressed µ-opiate receptor as in expected size of 441 bp. According to our findings, it was concluded that T. canis, benefits using morphine-like substance to modulate host immunity. PMID:28144426

  6. Antinociception induced by acute oral administration of sweet substance in young and adult rodents: the role of endogenous opioid peptides chemical mediators and μ(1)-opioid receptors.

    PubMed

    de Freitas, Renato Leonardo; Kübler, João Marcus Lopes; Elias-Filho, Daoud Hibraim; Coimbra, Norberto Cysne

    2012-04-01

    The present work aimed to investigate the effects of acute sucrose treatment on the perception of painful stimuli. Specifically, we sought to determine the involvement of the endogenous opioid peptide-mediated system as well as the role of the μ(1)-opioid receptor in antinociception organisation induced by acute sucrose intake. Nociception was assessed with the tail-flick test in rats (75, 150 and 250 g) of different ages acutely pre-treated with 500 μL of a sucrose solution (25, 50, 150 and 250 g/L) or tap water. Young and Adult rats (250 g) showed antinociception after treatment with 50 g/L (during 5 min) and 150 g/L and 250 g/L (during 20 min) sucrose solutions. Surprisingly, this antinociception was more consistent in mature adult rodents than in pups. To evaluate the role of opioid systems, mature adult rodents were pre-treated with different doses (0.25, 1 or 4 mg/kg) of the non-selective opioid receptor antagonist naloxone, the selective μ(1)-opioid receptor antagonist naloxonazine or vehicle followed by 250 g/L sucrose solution treatment. Sucrose-induced antinociception was reduced by pre-treatment with both naloxone and naloxonazine. The present findings suggest that sweet substance-induced hypo-analgesia is augmented by increasing sucrose concentrations in young and adult rodents. Acute oral sucrose treatment inhibits pain in laboratory animal by mediating endogenous opioid peptide and μ(1)-opioid receptor actions.

  7. Evaluation of Analgesic Activity of Papaver libanoticum Extract in Mice: Involvement of Opioids Receptors.

    PubMed

    Hijazi, Mohamad Ali; El-Mallah, Ahmed; Aboul-Ela, Maha; Ellakany, Abdalla

    2017-01-01

    Papaver libanoticum is an endemic plant to Lebanese region (family Papaveraceae) that has not been investigated before. The present study aimed to explore the analgesic activity of dried ethanolic extract of Papaver libanoticum (PLE) using tail flick, hot plate, and acetic acid induced writhing models in mice. The involvement of opioid receptors in the analgesic mechanism was investigated using naloxone antagonism. Results demonstrated that PLE exhibited a potent dose dependent analgesic activity in all tested models for analgesia. The analgesic effect involved activation of opioid receptors in the central nervous system, where both spinal and supraspinal components might be involved. The time course for analgesia revealed maximum activity after three hours in both tail flick and hot plate methods, which was prolonged to 24 hours. Metabolites of PLE could be responsible for activation of opioid receptors. The EC50 of PLE was 79 and 50 mg/kg in tail flick and hot plate tests, respectively. The total coverage of analgesia by PLE was double that of morphine in both tests. In conclusion, PLE proved to have opioid agonistic activity with a novel feature of slow and prolonged effect. The present study could add a potential tool in the armaments of opioid drugs as a natural potent analgesic and for treatment of opioid withdrawal syndrome.

  8. Evaluation of Analgesic Activity of Papaver libanoticum Extract in Mice: Involvement of Opioids Receptors

    PubMed Central

    El-Mallah, Ahmed; Aboul-Ela, Maha; Ellakany, Abdalla

    2017-01-01

    Papaver libanoticum is an endemic plant to Lebanese region (family Papaveraceae) that has not been investigated before. The present study aimed to explore the analgesic activity of dried ethanolic extract of Papaver libanoticum (PLE) using tail flick, hot plate, and acetic acid induced writhing models in mice. The involvement of opioid receptors in the analgesic mechanism was investigated using naloxone antagonism. Results demonstrated that PLE exhibited a potent dose dependent analgesic activity in all tested models for analgesia. The analgesic effect involved activation of opioid receptors in the central nervous system, where both spinal and supraspinal components might be involved. The time course for analgesia revealed maximum activity after three hours in both tail flick and hot plate methods, which was prolonged to 24 hours. Metabolites of PLE could be responsible for activation of opioid receptors. The EC50 of PLE was 79 and 50 mg/kg in tail flick and hot plate tests, respectively. The total coverage of analgesia by PLE was double that of morphine in both tests. In conclusion, PLE proved to have opioid agonistic activity with a novel feature of slow and prolonged effect. The present study could add a potential tool in the armaments of opioid drugs as a natural potent analgesic and for treatment of opioid withdrawal syndrome. PMID:28280516

  9. Antidepressant-like Effects of Buprenorphine are Mediated by Kappa Opioid Receptors.

    PubMed

    Falcon, Edgardo; Browne, Caroline A; Leon, Rosa M; Fleites, Vanessa C; Sweeney, Rachel; Kirby, Lynn G; Lucki, Irwin

    2016-08-01

    Previous studies have identified potential antidepressant effects of buprenorphine (BPN), a drug with high affinity for mu opioid receptor (MORs) and kappa opioid receptors (KORs) and some affinity at delta opioid receptor (DOR) and opioid receptor-like 1 (ORL-1) receptors. Therefore, these studies examined which opioid receptors were involved in BPN's effects on animal behavior tests sensitive to antidepressant drugs. The acute effects of BPN were tested in the forced swim test (FST) using mice with genetic deletion of individual opioid receptors or after pharmacological blockade of receptors. For evaluating the effects of BPN on chronic stress, separate groups of mice were exposed to unpredictable chronic mild stress (UCMS) for 3 weeks and treated with BPN for at least 7 days before behavioral assessment and subsequent measurement of Oprk1, Oprm1, and Pdyn mRNA expression in multiple brain regions. BPN did not reduce immobility in mice with KOR deletion or after pretreatment with norbinaltorphimine, even though desipramine remained effective. In contrast, BPN reduced immobility in MOR and DOR knockout mice and in mice pretreated with the ORL-1 antagonist JTC-801. UCMS reduced sucrose preference, decreased time in the light side of the light/dark box, increased immobility in the FST and induced region-specific alterations in Oprk1, Oprm1, and PDYN mRNA expression in the frontal cortex and striatum. All of these changes were normalized following BPN treatment. The KOR was identified as a key player mediating the effects of BPN in tests sensitive to antidepressant drugs in mice. These studies support further development of BPN as a novel antidepressant.

  10. Intrauterine growth restriction modifies the hedonic response to sweet taste in newborn pups - Role of the accumbal μ-opioid receptors.

    PubMed

    Laureano, D P; Dalle Molle, R; Alves, M B; Luft, C; Desai, M; Ross, M G; Silveira, P P

    2016-05-13

    Intrauterine growth restriction (IUGR) is associated with increased preference for palatable foods. The hedonic response to sweet taste, modulated by the nucleus accumbens μ-opioid-receptors, may be involved. We investigated hedonic responses and receptor levels in IUGR and Control animals. From pregnancy day 10, Sprague-Dawley dams received either an ad libitum (Control), or a 50% food restricted (FR) diet. At birth, pups were cross-fostered, and nursed by Adlib fed dams. The hedonic response was evaluated at 1 day after birth and at 90 days of life, by giving sucrose solution or water and analyzing the hedonic facial responses (within 60s). Control pups exposed either to water or sucrose resolved their hedonic responses after 16 and 18s, respectively, while FR hedonic responses to sucrose persisted over 20s. FR pups had deceased phospho-μ-opioid-receptor (p=0.009) and reduced phosphor:total mu opioid receptor ratio compared to controls pups (p=0.003). In adults, there was an interaction between group and solution at the end of the evaluation (p=0.044): Control decreased the response after sucrose solution, FR did not change over time. There were no differences in phosphorylation of μ-opioid-receptor in adults. These results demonstrate IUGR newborn rats exhibit alterations in hedonic response accompanied by a decrease in μ-opioid-receptor phosphorylation, though these alterations do not persist at 3 months of age. Opioid system alterations in early life may contribute to the development of preference for highly palatable foods and contribute to rapid weight gain and obesity in IUGR offspring.

  11. Mouse δ opioid receptors are located on presynaptic afferents to hippocampal pyramidal cells.

    PubMed

    Rezaï, Xavier; Faget, Lauren; Bednarek, Ewa; Schwab, Yannick; Kieffer, Brigitte L; Massotte, Dominique

    2012-05-01

    Delta opioid receptors participate in the control of chronic pain and emotional responses. Recent data have also identified their implication in drug-context associations pointing to a modulatory role on hippocampal activity. We used fluorescent knock-in mice that express a functional delta opioid receptor fused at its carboxy terminus with the green fluorescent protein in place of the native receptor to investigate the receptor neuroanatomical distribution in this structure. Fine mapping of the pyramidal layer was performed in hippocampal acute brain slices and organotypic cultures using fluorescence confocal imaging, co-localization with pre- and postsynaptic markers and correlative light-electron microscopy. The different approaches concurred to identify delta opioid receptors on presynaptic afferents to glutamatergic principal cells. In the latter, only scarce receptors were detected that were confined within the Golgi or vesicular intracellular compartments with no receptor present at the cell surface. In the mouse hippocampus, expression of functional delta opioid receptors is therefore mostly associated with interneurons emphasizing a presynaptic modulatory effect on the pyramidal cell firing rate.

  12. Maturational alterations in constitutive activity of medial prefrontal cortex kappa-opioid receptors in Wistar rats.

    PubMed

    Sirohi, Sunil; Walker, Brendan M

    2015-11-01

    Opioid receptors can display spontaneous agonist-independent G-protein signaling (basal signaling/constitutive activity). While constitutive κ-opioid receptor (KOR) activity has been documented in vitro, it remains unknown if KORs are constitutively active in native systems. Using [(35) S] guanosine 5'-O-[gamma-thio] triphosphate coupling assay that measures receptor functional state, we identified the presence of medial prefrontal cortex KOR constitutive activity in young rats that declined with age. Furthermore, basal signaling showed an age-related decline and was insensitive to neutral opioid antagonist challenge. Collectively, the present data are first to demonstrate age-dependent alterations in the medial prefrontal cortex KOR constitutive activity in rats and changes in the constitutive activity of KORs can differentially impact KOR ligand efficacy. These data provide novel insights into the functional properties of the KOR system and warrant further consideration of KOR constitutive activity in normal and pathophysiological behavior. Opioid receptors exhibit agonist-independent constitutive activity; however, kappa-opioid receptor (KOR) constitutive activity has not been demonstrated in native systems. Our results confirm KOR constitutive activity in the medial prefrontal cortex (mPFC) that declines with age. With the ability to presynaptically inhibit multiple neurotransmitter systems in the mPFC, maturational or patho-logical alterations in constitutive activity could disrupt corticofugal glutamatergic pyramidal projection neurons mediating executive function. Regulation of KOR constitutive activity could serve as a therapeutic target to treat compromised executive function.

  13. Characterization of the complex morphinan derivative BU72 as a high efficacy, long-lasting mu-opioid receptor agonist.

    PubMed

    Neilan, Claire L; Husbands, Stephen M; Breeden, Simon; Ko, M C Holden; Aceto, Mario D; Lewis, John W; Woods, James H; Traynor, John R

    2004-09-19

    The development of buprenorphine as a treatment for opiate abuse and dependence has drawn attention to opioid ligands that have agonist actions followed by long-lasting antagonist actions. In a search for alternatives to buprenorphine, we discovered a bridged pyrrolidinomorphinan (BU72). In vitro, BU72 displayed high affinity and efficacy for mu-opioid receptors, but was also a partial delta-opioid receptor agonist and a full kappa-opioid receptor agonist. BU72 was a highly potent and long-lasting antinociceptive agent against both thermal and chemical nociception in the mouse and against thermal nociception in the monkey. These effects were prevented by mu-, but not kappa- or delta-, opioid receptor antagonists. Once the agonist effects of BU72 had subsided, the compound acted to attenuate the antinociceptive action of morphine. BU72 is too efficacious for human use but manipulation to reduce efficacy could provide a lead to the development of a treatment for opioid dependence.

  14. Comparing analgesia and μ-opioid receptor internalization produced by intrathecal enkephalin

    PubMed Central

    Chen, Wenling; Song, Bingbing; Lao, Lijun; Pérez, Orlando A.; Kim, Woojae; Marvizón, Juan Carlos G.

    2007-01-01

    Summary Opioid receptors in the spinal cord produce strong analgesia, but the mechanisms controlling their activation by endogenous opioids remain unclear. We have previously shown in spinal cord slices that peptidases preclude μ-opioid receptor (MOR) internalization by opioids. Our present goals were to investigate whether enkephalin-induced analgesia is also precluded by peptidases, and whether it is mediated by MORs or δ-opioid receptors (DORs). Tail-flick analgesia and MOR internalization were measured in rats injected intrathecally with Leu-enkephalin and peptidase inhibitors. Without peptidase inhibitors, Leu-enkephalin produced neither analgesia nor MOR internalization at doses up to 100 nmol, whereas with peptidase inhibitors it produced analgesia at 0.3 nmol and MOR internalization at 1 nmol. Leu-enkephalin was ten times more potent to produce analgesia than to produce MOR internalization, suggesting that DORs were involved. Selective MOR or DOR antagonists completely blocked the analgesia elicited by 0.3 nmol Leu-enkephalin (a dose that produced little MOR internalization), indicating that it involved these two receptors, possibly by an additive or synergistic interaction. The selective MOR agonist endomorphin-2 produced analgesia even in the presence of a DOR antagonist, but at doses substantially higher than Leu-enkephalin. Unlike Leu-enkephalin, endomorphin-2 had the same potencies to induce analgesia and MOR internalization. We concluded that low doses of enkephalins produce analgesia by activating both MORs and DORs. Analgesia can also be produced exclusively by MORs at higher agonist doses. Since peptidases prevent the activation of spinal opioid receptors by enkephalins, the coincident release of opioids and endogenous peptidase inhibitors may be required for analgesia. PMID:17845806

  15. Alvimopan: an oral, peripherally acting, mu-opioid receptor antagonist for the treatment of opioid-induced bowel dysfunction--a 21-day treatment-randomized clinical trial.

    PubMed

    Paulson, Daniel M; Kennedy, Daniel T; Donovick, Roger A; Carpenter, Randall L; Cherubini, Maryann; Techner, Lee; Du, Wei; Ma, Yuju; Schmidt, William K; Wallin, Bruce; Jackson, David

    2005-03-01

    Alvimopan has been shown to reverse the inhibitory effect of opioids on gastrointestinal transit without affecting analgesia. We evaluated oral alvimopan, 0.5 or 1 mg, versus placebo, once daily for 21 days, in 168 patients with opioid-induced bowel dysfunction (OBD) who were receiving chronic opioid therapy (minimum, 1 month) for nonmalignant pain (n = 148) or opioid dependence (n = 20). The primary outcome was the proportion of patients having at least one bowel movement (BM) within 8 hours of study drug on each day during the 21-day treatment period. Averaged over the 21-day treatment period, 54%, 43%, and 29% of patients had a BM within 8 hours after alvimopan 1 mg, 0.5 mg, or placebo, respectively (P < .001). Secondary outcomes of median times to first BM were 3, 7, and 21 hours after initial doses of 1 mg, 0.5 mg, and placebo, respectively (P < .001; 1 mg vs placebo). Weekly BMs and overall patient satisfaction were increased after the 1-mg dose (P < .001 at weeks 1 and 2 vs placebo, and P = .046, respectively). Treatment-emergent adverse events were primarily bowel-related, occurred during the first week of treatment, and were of mild to moderate severity. Alvimopan was generally well tolerated and did not antagonize opioid analgesia. Patients treated with chronic opioid therapy often experience opioid-induced bowel dysfunction as a result of undesirable effects on peripheral opioid receptors located in the gastrointestinal tract. Alvimopan, a novel peripheral opioid mu-receptor antagonist, has demonstrated significant efficacy for the management of opioid-induced bowel dysfunction without compromise of centrally mediated opioid-induced analgesia.

  16. Stress-induced activation of the dynorphin/κ-opioid receptor system in the amygdala potentiates nicotine conditioned place preference

    PubMed Central

    Smith, Jeffrey S.; Schindler, Abigail G.; Martinelli, Emma; Gustin, Richard M.; Bruchas, Michael R.; Chavkin, Charles

    2012-01-01

    Many smokers describe the anxiolytic and stress-reducing effects of nicotine, the primary addictive component of tobacco, as a principal motivation for continued drug use. Recent evidence suggests that activation of the stress circuits, including the dynorphin/κ-opioid receptor system, modulates the rewarding effects of addictive drugs. In the present study, we find that nicotine produced dose-dependent conditioned place preference (CPP) in mice. κ-Receptor activation, either by repeated forced swim stress or U50,488 (5 mg/kg or 10 mg/kg, i.p.) administration, significantly potentiated the magnitude of nicotine CPP. The increase in nicotine CPP was blocked by the κ-receptor antagonist norBNI either systemically (10 mg/kg, i.p.) or by local injection in the amygdala (2.5 μg) without affecting nicotine reward in the absence of stress. U50,488 (5 mg/kg, i.p.) produced anxiety-like behaviors in the elevated-plus maze and novel object exploration assays, and the anxiety-like behaviors were attenuated both by systemic nicotine (0.5 mg/kg, s.c.) and local injection of norBNI into the amygdala. Local norBNI injection in the ventral posterior thalamic nucleus (an adjacent brain region) did not block the potentiation of nicotine CPP or the anxiogenic-like effects of κ-receptor activation. These results suggest that the rewarding effects of nicotine may include a reduction in the stress-induced anxiety responses caused by activation of the dynorphin/κ-opioid system. Together, these data implicate the amygdala as a key region modulating the appetitive properties of nicotine, and suggest that κ-opioid antagonists may be useful therapeutic tools to reduce stress-induced nicotine craving. PMID:22279233

  17. Delta Opioid Receptors: The Link between Exercise and Cardioprotection

    PubMed Central

    Borges, Juliana P.; Verdoorn, Karine S.; Daliry, Anissa; Powers, Scott K.; Ortenzi, Victor H.; Fortunato, Rodrigo S.; Tibiriçá, Eduardo; Lessa, Marcos Adriano

    2014-01-01

    This study investigated the role of opioid receptor (OR) subtypes as a mechanism by which endurance exercise promotes cardioprotection against myocardial ischemia-reperfusion (IR) injury. Wistar rats were randomly divided into one of seven experimental groups: 1) control; 2) exercise-trained; 3) exercise-trained plus a non-selective OR antagonist; 4) control sham; 5) exercise-trained plus a kappa OR antagonist; 6) exercise-trained plus a delta OR antagonist; and 7) exercise-trained plus a mu OR antagonist. The exercised animals underwent 4 consecutive days of treadmill training (60 min/day at ∼70% of maximal oxygen consumption). All groups except the sham group were exposed to an in vivo myocardial IR insult, and the myocardial infarct size (IS) was determined histologically. Myocardial capillary density, OR subtype expression, heat shock protein 72 (HSP72) expression, and antioxidant enzyme activity were measured in the hearts of both the exercised and control groups. Exercise training significantly reduced the myocardial IS by approximately 34%. Pharmacological blockade of the kappa or mu OR subtypes did not blunt exercise-induced cardioprotection against IR-mediated infarction, whereas treatment of animals with a non-selective OR antagonist or a delta OR antagonist abolished exercise-induced cardioprotection. Exercise training enhanced the activities of myocardial superoxide dismutase (SOD) and catalase but did not increase the left ventricular capillary density or the mRNA levels of HSP72, SOD, and catalase. In addition, exercise significantly reduced the protein expression of kappa and delta ORs in the heart by 44% and 37%, respectively. Together, these results indicate that ORs contribute to the cardioprotection conferred by endurance exercise, with the delta OR subtype playing a key role in this response. PMID:25415192

  18. In vitro and in vivo efficacy of a potent opioid receptor agonist, biphalin, compared to subtype-selective opioid receptor agonists for stroke treatment.

    PubMed

    Yang, Li; Islam, Mohammad R; Karamyan, Vardan T; Abbruscato, Thomas J

    2015-06-03

    To meet the challenge of identification of new treatments for stroke, this study was designed to evaluate a potent, nonselective opioid receptor (OR) agonist, biphalin, in comparison to subtype selective OR agonists, as a potential neuroprotective drug candidate using in vitro and in vivo models of ischemic stroke. Our in vitro approach included mouse primary neuronal cells that were challenged with glutamate and hypoxic/aglycemic (H/A) conditions. We observed that 10nM biphalin, exerted a statistically significant neuroprotective effect after glutamate challenge, compared to all selective opioid agonists, according to lactate dehydrogenase (LDH) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays. Moreover, 10nM biphalin provided superior neuroprotection after H/A-reoxygenation compared to selective opioid agonists in all cases. Our in vitro investigations were supported by in vivo studies which indicate that the nonselective opioid agonist, biphalin, achieves enhanced neuroprotective potency compared to any of the selective opioid agonists, evidenced by reduced edema and infarct ratios. Reduction of edema and infarction was accompanied by neurological improvement of the animals in two independent behavioral tests. Collectively these data strongly suggest that concurrent agonist stimulation of mu, kappa and delta ORs with biphalin is neuroprotective and superior to neuroprotection by activation of any single OR subtype.

  19. In vitro and in vivo efficacy of a potent opioid receptor agonist, biphalin, compared to subtype-selective opioid receptor agonists for stroke treatment

    PubMed Central

    Yang, Li; Islam, Mohammad R; Karamyan, Vardan T.; Abbruscato, Thomas J.

    2015-01-01

    To meet the challenge of identification of new treatments for stroke, this study was designed to evaluate a potent, nonselective opioid receptor (OR) agonist, biphalin, in comparison to subtype selective OR agonists, as a potential neuroprotective drug candidate using in vitro and in vivo models of ischemic stroke. Our in vitro approach included mouse primary neuronal cells that were challenged with glutamate and hypoxic/aglycemic (H/A) conditions. We observed that 10 nM biphalin, exerted a statistically significant neuroprotective effect after glutamate challenge, compared to all selective opioid agonists, according to lactate dehydrogenase (LDH) and 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assays. Moreover, 10 nM biphalin provided superior neuroprotection after H/A-reoxygenation compared to selective opioid agonists in all cases. Our in vitro investigations were supported by in vivo studies which indicate that the nonselective opioid agonist, biphalin, achieves enhanced neuroprotective potency compared to any of the selective opioid agonists, evidenced by reduced edema and infarct ratios. Reduction of edema and infarction was accompanied by neurological improvement of the animals in two independent behavioral tests. Collectively these data strongly suggest that concurrent agonist stimulation of mu, kappa and delta ORs with biphalin is neuroprotective and superior to neuroprotection by activation of any single OR subtype. PMID:25801116

  20. Distribution of delta opioid receptor expressing neurons in the mouse hippocampus

    PubMed Central

    Eric, ERBS; Lauren, FAGET; Gregory, SCHERRER; Pascal, KESSLER; Didier, HENTSCH; Jean-Luc, VONESCH; Audrey, MATIFAS; Brigitte L., KIEFFER; Dominique, MASSOTTE

    2012-01-01

    Delta opioid receptors participate to the control of chronic pain and emotional responses. Recent data also identified their implication in spatial memory and drug-context associations pointing to a critical role of hippocampal delta receptors. We examined the distribution of delta receptor-expressing cells in the hippocampus using fluorescent knock-in mice that express a functional delta receptor fused at its carboxyterminus with the green fluorescent protein in place of the native receptor. Colocalization with markers for different neuronal populations was performed by immunohistochemical detection. Fine mapping in the dorsal hippocampus confirmed that delta opioid receptors are mainly present in GABAergic neurons. Indeed, they are mostly expressed in parvalbumin-immunopositive neurons both in the Ammon’s horn and dentate gyrus. These receptors, therefore, most likely participate to the dynamic regulation of hippocampal activity. PMID:22750239

  1. Distribution of delta opioid receptor-expressing neurons in the mouse hippocampus.

    PubMed

    Erbs, E; Faget, L; Scherrer, G; Kessler, P; Hentsch, D; Vonesch, J-L; Matifas, A; Kieffer, B L; Massotte, D

    2012-09-27

    Delta opioid receptors participate to the control of chronic pain and emotional responses. Recent data also identified their implication in spatial memory and drug-context associations pointing to a critical role of hippocampal delta receptors. We examined the distribution of delta receptor-expressing cells in the hippocampus using fluorescent knock-in mice that express a functional delta receptor fused at its carboxyterminus with the green fluorescent protein in place of the native receptor. Colocalization with markers for different neuronal populations was performed by immunohistochemical detection. Fine mapping in the dorsal hippocampus confirmed that delta opioid receptors are mainly present in GABAergic neurons. Indeed, they are mostly expressed in parvalbumin-immunopositive neurons both in the Ammon's horn and dentate gyrus. These receptors, therefore, most likely participate in the dynamic regulation of hippocampal activity.

  2. Neuropeptide FF-sensitive confinement of mu opioid receptor does not involve lipid rafts in SH-SY5Y cells

    SciTech Connect

    Mouledous, Lionel

    2008-08-15

    *: Mu opioid (MOP) receptor activation can be functionally modulated by stimulation of Neuropeptide FF 2 (NPFF{sub 2}) G protein-coupled receptors. Fluorescence recovery after photobleaching experiments have shown that activation of the NPFF{sub 2} receptor dramatically reduces the fraction of MOP receptors confined in microdomains of the plasma membrane of SH-SY5Y neuroblastoma cells. The aim of the present work was to assess if the direct observation of receptor compartmentation by fluorescence techniques in living cells could be related to indirect estimation of receptor partitioning in lipid rafts after biochemical fractionation of the cell. Our results show that MOP receptor distribution in lipid rafts is highly dependent upon the method of purification, questioning the interpretation of previous data regarding MOP receptor compartmentation. Moreover, the NPFF analogue 1DMe does not modify the distribution profile of MOP receptors, clearly demonstrating that membrane fractionation data do not correlate with direct measurement of receptor compartmentation in living cells.

  3. [Opioid overdose].

    PubMed

    Reingardiene, Dagmara; Vilcinskaite, Jolita

    2002-01-01

    The dangers of opioid overdose have been recognized for as long as the use of opium itself. When used correctly for medical purposes, opioids are remarkably safe and effective agents. However, excessive dosing, whether with therapeutic, suicidal, or euphoric intent, may results in significant toxicity. In a number of countries the use of heroin and other opioids in nonmedical contexts in associated with on increasing rate of overdose and often of fatal opioid overdose. This review article discusses opioid-receptor pharmacology, which is necessary for understanding of the signs and symptoms of opioid ingestion and management principles, clinical and toxic effects mediated with the opioids, the diagnosis and management guidelines in opioid intoxication, a clinical prediction rule to identify patients who can be safely discharge from hospital, the problems of the significant morbidity and mortality associated with opioid overdose.

  4. Activation of the δ-opioid receptor promotes cutaneous wound healing by affecting keratinocyte intercellular adhesion and migration

    PubMed Central

    Bigliardi, P L; Neumann, C; Teo, Y L; Pant, A; Bigliardi-Qi, M

    2015-01-01

    BACKGROUND AND PURPOSE In addition to its analgesic functions, the peripheral opioid receptor system affects skin homeostasis by influencing cell differentiation, migration and adhesion; also, wound healing is altered in δ-opioid receptor knockout mice (DOPr–/–). Hence, we investigated δ-opioid receptor effects on the expression of several proteins of the desmosomal junction complex and on the migratory behaviour of keratinocytes. EXPERIMENTAL APPROACH Expression levels of desmosomal cadherins in wild-type and DOPr–/– mice, and the morphology of intercellular adhesion in human keratinocytes were analysed by immunofluorescence. To investigate the δ-opioid receptor activation pathway, protein expression was studied using Western blot and its effect on cellular migration determined by in vitro live cell migration recordings from human keratinocytes. KEY RESULTS Expression of the desmosomal cadherins, desmogleins 1 and 4, was up-regulated in skin from DOPr–/– mice, and down-regulated in δ-opioid receptor-overexpressing human keratinocytes. The localization of desmoplakin expression was rearranged from linear arrays emanating from cell borders to puncta in cell periphery, resulting in less stable intercellular adhesion. Migration and wound recovery were enhanced in human keratinocyte monolayers overexpressing δ-opioid receptors in vitro. These δ-opioid receptor effects were antagonized by specific PKCα/β inhibition indicating they were mediated through the PKC signalling pathway. Finally, cells overexpressing δ-opioid receptors developed characteristically long but undirected protrusions containing filamentous actin and δ-opioid receptors, indicating an enhanced migratory phenotype. CONCLUSION AND IMPLICATIONS Opioid receptors affect intercellular adhesion and wound healing mechanisms, underlining the importance of a cutaneous neuroendocrine system in wound healing and skin homeostasis. LINKED ARTICLES This article is part of a themed section on

  5. A structural feature of the non-peptide ligand interactions with mice mu-opioid receptors.

    PubMed

    Noori, Hamid R; Mucksch, Christian; Urbassek, Herbert M

    2014-01-01

    By binding to and activating the G-protein coupled μ-, κ- and δ-opioid receptors in the central nervous system, opiates are known to induce analgesic and sedative effects. In particular, non-peptide opioid ligands are often used in clinical applications to induce these therapeutically beneficial effects, due to their superior pharmacokinetics and bioavailability in comparison to endogenous neuropeptides. However, since opioid alkaloids are highly addictive substances, it is necessary to understand the exact mechanisms of their actions, specifically the ligand-binding properties of the target receptors, in order to safely apply opiates for therapeutic purposes. Using an in silico molecular docking approach (AutoDock Vina) combined with two-step cluster analysis, we have computationally obtained the docking scores and the ligand-binding pockets of twelve representative non-peptide nonendogenous agonists and antagonists at the crystallographically identified μ-opioid receptor. Our study predicts the existence of two main binding sites that are congruently present in all opioid receptor types. Interestingly, in terms of the agonist or antagonist properties of the substances on the receptors, the clustering analysis suggests a relationship with the position of the ligand-binding pockets, particularly its depth within the receptor structure. Furthermore, the binding affinity of the substances is directly correlated to the proximity of the binding pockets to the extracellular space. In conclusion, the results provide further insights into the structural features of the functional pharmacology of opioid receptors, suggesting the importance of the binding position of non-peptide agonists and antagonists- specifically the distance and the level of exposure to the extracellular space- to their dissociation kinetics and subsequent potency.

  6. Pharmacogenomic study of the role of the nociceptin/orphanin FQ receptor and opioid receptors in diabetic hyperalgesia.

    PubMed

    Rutten, Kris; Tzschentke, Thomas M; Koch, Thomas; Schiene, Klaus; Christoph, Thomas

    2014-10-15

    Targeting functionally independent receptors may provide synergistic analgesic effects in neuropathic pain. To examine the interdependency between different opioid receptors (µ-opioid peptide [MOP], δ-opioid peptide [DOP] and κ-opioid peptide [KOP]) and the nociceptin/orphanin FQ peptide (NOP) receptor in streptozotocin (STZ)-induced diabetic polyneuropathy, nocifensive activity was measured using a hot plate test in wild-type and NOP, MOP, DOP and KOP receptor knockout mice in response to the selective receptor agonists Ro65-6570, morphine, SNC-80 and U50488H, or vehicle. Nocifensive activity was similar in non-diabetic wild-type and knockout mice at baseline, before agonist or vehicle administration. STZ-induced diabetes significantly increased heat sensitivity in all mouse strains, but MOP, DOP and KOP receptor knockouts showed a smaller degree of hyperalgesia than wild-type mice and NOP receptor knockouts. For each agonist, a significant antihyperalgesic effect was observed in wild-type diabetic mice (all P<0.05 versus vehicle); the effect was markedly attenuated in diabetic mice lacking the cognate receptor compared with wild-type diabetic mice. Morphine was the only agonist that demonstrated near-full antihyperalgesic efficacy across all non-cognate receptor knockouts. Partial or near-complete reductions in efficacy were observed with Ro65-6570 in DOP and KOP receptor knockouts, with SNC-80 in NOP, MOP and KOP receptor knockouts, and with U50488H in NOP and DOP receptor knockouts. There was no evidence of NOP and MOP receptor interdependency in response to selective agonists for these receptors. These findings suggest that concurrent activation of NOP and MOP receptors, which showed functional independence, may yield an effective and favorable therapeutic analgesic profile.

  7. Molecular modeling study of the differential ligand-receptor interaction at the μ, δ and κ opioid receptors

    NASA Astrophysics Data System (ADS)

    Filizola, Marta; Carteni-Farina, Maria; Perez, Juan J.

    1999-07-01

    3D models of the opioid receptors μ, δ and κ were constructed using BUNDLE, an in-house program to build de novo models of G-protein coupled receptors at the atomic level. Once the three opioid receptors were constructed and before any energy refinement, models were assessed for their compatibility with the results available from point-site mutations carried out on these receptors. In a subsequent step, three selective antagonists to each of three receptors (naltrindole, naltrexone and nor-binaltorphamine) were docked onto each of the three receptors and subsequently energy minimized. The nine resulting complexes were checked for their ability to explain known results of structure-activity studies. Once the models were validated, analysis of the distances between different residues of the receptors and the ligands were computed. This analysis permitted us to identify key residues tentatively involved in direct interaction with the ligand.

  8. Synthesis and pharmacological evaluation of aminothiazolomorphinans at the mu and kappa opioid receptors.

    PubMed

    Provencher, Brian A; Sromek, Anna W; Li, Wei; Russell, Shayla; Chartoff, Elena; Knapp, Brian I; Bidlack, Jean M; Neumeyer, John L

    2013-11-14

    Previous studies with aminothiazolomorphinans suggested that this class of opioid ligands may be useful as a potential pharmacotherapeutic to decrease drug abuse. Novel aminothiazole derivatives of cyclorphan were prepared to evaluate a series of aminothiazolomorphinans with varying pharmacological properties at the κ opioid receptor (KOR) and μ opioid receptor (MOR). This study was focused on exploring the regioisomeric analogs with the aminothiazole on the C-ring of the morphinan skeleton. Receptor binding and [(35)S]GTPγS binding assays were used to characterize the affinity and pharmacological properties of the aminothiazolomorphinans. Intracranial self-stimulation (ICSS) was used to compare the effects of a representative aminothiazolomorphinan with the morphinan mixed-KOR/MOR agonist butorphan (MCL-101) on brain-stimulation reward.

  9. Cannabinoid and heroin activation of mesolimbic dopamine transmission by a common mu1 opioid receptor mechanism.

    PubMed

    Tanda, G; Pontieri, F E; Di Chiara, G

    1997-06-27

    The effects of the active ingredient of Cannabis, Delta9-tetrahydrocannabinol (Delta9-THC), and of the highly addictive drug heroin on in vivo dopamine transmission in the nucleus accumbens were compared in Sprague-Dawley rats by brain microdialysis. Delta9-THC and heroin increased extracellular dopamine concentrations selectively in the shell of the nucleus accumbens; these effects were mimicked by the synthetic cannabinoid agonist WIN55212-2. SR141716A, an antagonist of central cannabinoid receptors, prevented the effects of Delta9-THC but not those of heroin. Naloxone, a generic opioid antagonist, administered systemically, or naloxonazine, an antagonist of micro1 opioid receptors, infused into the ventral tegmentum, prevented the action of cannabinoids and heroin on dopamine transmission. Thus, Delta9-THC and heroin exert similar effects on mesolimbic dopamine transmission through a common mu1 opioid receptor mechanism located in the ventral mesencephalic tegmentum.

  10. Modification of kappa-opioid receptor agonist-induced antinociception by diabetes in the mouse brain and spinal cord.

    PubMed

    Ohsawa, Masahiro; Kamei, Junzo

    2005-05-01

    The supraspinal and spinal antinociceptive effects of several kappa-opioid receptor agonists were examined in diabetic and non-diabetic mice using the tail-flick assay. The antinociception induced by intrathecal (i.t.), but not intracerebroventricular (i.c.v.), CI-977, a highly selective kappa(1)-opioid receptor agonist, in diabetic mice was less than that in non-diabetic mice. The antinociceptive effects of ICI-199,441 and R-84760, high potency kappa(1)-opioid receptor agonists, given i.c.v., but not i.t., were attenuated in diabetic mice compared to those in non-diabetic mice. On the other hand, the antinociceptive effects of the new kappa-opioid receptor agonist TRK-820, which has high affinity for kappa(2)- and/or kappa(3)-opioid receptors, injected both i.c.v. and i.t. in diabetic mice were markedly less than those in non-diabetic mice. These results indicate that the antinociceptive effects of those kappa-opioid receptor agonists in diabetic mice are altered in a region-specific manner in the central nervous system (CNS). The dysfunction of kappa-opioid receptor subtypes in diabetic mice may underlie this CNS region-specific variation in the effects of these kappa-opioid receptor agonists.

  11. Effects of the Mu Opioid Receptor Polymorphism (OPRM1 A118G) on Pain Regulation, Placebo Effects and Associated Personality Trait Measures

    PubMed Central

    Peciña, Marta; Love, Tiffany; Stohler, Christian S; Goldman, David; Zubieta, Jon-Kar

    2015-01-01

    Mu-opioid receptors (MOPRs) are critically involved in the modulation of pain and analgesia, and represent a candidate mechanism for the development of biomarkers of pain conditions and their responses to treatment. To further understand the human implications of genetic variation within the opioid system in pain and opioid-mediated placebo responses, we investigated the association between the functional single-nucleotide polymorphism (SNP) in the μ-opioid receptor gene (OPRM1), A118G, and psychophysical responses, personality traits, and neurotransmitter systems (dopamine (DA), opioid) related to pain and placebo analgesia. OPRM1 G carriers, compared with AA homozygotes, showed an overall reduction of baseline μ-opioid receptor availability in regions implicated in pain and affective regulation. In response to a sustained painful stimulus, we found no effect of A118G on pain-induced endogenous opioid release. Instead, AA homozygotes showed a blunted DA response in the nucleus accumbens (NAc) in response to the pain challenge. After placebo administration, G carriers showed more pronounced mood disturbances and lower placebo-induced μ-opioid system activation in the anterior insula (aINS), the amygdala (AMY), the NAc, the thalamus (THA), and the brainstem, as well as lower levels of DA D2/3 activation in the NAc. At a trait level, G carriers reported higher NEO-Neuroticism scores; a personality trait previously associated with increased pain and lower placebo responses, which were negatively correlated with baseline μ-opioid receptor availability in the aINS and subgenual anterior cingulate cortex (sgACC). Our results demonstrate that the A118G OPRM1 polymorphism contributes to interindividual variations in the function of neurotransmitters responsive to pain (endogenous opioid and dopamine), as well as their regulation through cognitive-emotional influences in the context of therapeutic expectations, the so-called placebo effect. These effects are relevant to

  12. Effects of the Mu opioid receptor polymorphism (OPRM1 A118G) on pain regulation, placebo effects and associated personality trait measures.

    PubMed

    Peciña, Marta; Love, Tiffany; Stohler, Christian S; Goldman, David; Zubieta, Jon-Kar

    2015-03-01

    Mu-opioid receptors (MOPRs) are critically involved in the modulation of pain and analgesia, and represent a candidate mechanism for the development of biomarkers of pain conditions and their responses to treatment. To further understand the human implications of genetic variation within the opioid system in pain and opioid-mediated placebo responses, we investigated the association between the functional single-nucleotide polymorphism (SNP) in the μ-opioid receptor gene (OPRM1), A118G, and psychophysical responses, personality traits, and neurotransmitter systems (dopamine (DA), opioid) related to pain and placebo analgesia. OPRM1 G carriers, compared with AA homozygotes, showed an overall reduction of baseline μ-opioid receptor availability in regions implicated in pain and affective regulation. In response to a sustained painful stimulus, we found no effect of A118G on pain-induced endogenous opioid release. Instead, AA homozygotes showed a blunted DA response in the nucleus accumbens (NAc) in response to the pain challenge. After placebo administration, G carriers showed more pronounced mood disturbances and lower placebo-induced μ-opioid system activation in the anterior insula (aINS), the amygdala (AMY), the NAc, the thalamus (THA), and the brainstem, as well as lower levels of DA D2/3 activation in the NAc. At a trait level, G carriers reported higher NEO-Neuroticism scores; a personality trait previously associated with increased pain and lower placebo responses, which were negatively correlated with baseline μ-opioid receptor availability in the aINS and subgenual anterior cingulate cortex (sgACC). Our results demonstrate that the A118G OPRM1 polymorphism contributes to interindividual variations in the function of neurotransmitters responsive to pain (endogenous opioid and dopamine), as well as their regulation through cognitive-emotional influences in the context of therapeutic expectations, the so-called placebo effect. These effects are relevant to

  13. Distinct roles of exogenous opioid agonists and endogenous opioid peptides in the peripheral control of neuropathy-triggered heat pain

    PubMed Central

    Labuz, Dominika; Celik, Melih Ö.; Zimmer, Andreas; Machelska, Halina

    2016-01-01

    Neuropathic pain often results from peripheral nerve damage, which can involve immune response. Local leukocyte-derived opioid peptides or exogenous opioid agonists inhibit neuropathy-induced mechanical hypersensitivity in animal models. Since neuropathic pain can also be augmented by heat, in this study we investigated the role of opioids in the modulation of neuropathy-evoked heat hypersensitivity. We used a chronic constriction injury of the sciatic nerve in wild-type and opioid peptide-knockout mice, and tested opioid effects in heat and mechanical hypersensitivity using Hargreaves and von Frey tests, respectively. We found that although perineural exogenous opioid agonists, including peptidergic ligands, were effective, the endogenous opioid peptides β-endorphin, Met-enkephalin and dynorphin A did not alleviate heat hypersensitivity. Specifically, corticotropin-releasing factor, an agent triggering opioid peptide secretion from leukocytes, applied perineurally did not attenuate heat hypersensitivity in wild-type mice. Exogenous opioids, also shown to release opioid peptides via activation of leukocyte opioid receptors, were equally analgesic in wild-type and opioid peptide-knockout mice, indicating that endogenous opioids do not contribute to exogenous opioid analgesia in heat hypersensitivity. Furthermore, exogenously applied opioid peptides were ineffective as well. Conversely, opioid peptides relieved mechanical hypersensitivity. Thus, both opioid type and sensory modality may determine the outcome of neuropathic pain treatment. PMID:27605249

  14. Distinct roles of exogenous opioid agonists and endogenous opioid peptides in the peripheral control of neuropathy-triggered heat pain.

    PubMed

    Labuz, Dominika; Celik, Melih Ö; Zimmer, Andreas; Machelska, Halina

    2016-09-08

    Neuropathic pain often results from peripheral nerve damage, which can involve immune response. Local leukocyte-derived opioid peptides or exogenous opioid agonists inhibit neuropathy-induced mechanical hypersensitivity in animal models. Since neuropathic pain can also be augmented by heat, in this study we investigated the role of opioids in the modulation of neuropathy-evoked heat hypersensitivity. We used a chronic constriction injury of the sciatic nerve in wild-type and opioid peptide-knockout mice, and tested opioid effects in heat and mechanical hypersensitivity using Hargreaves and von Frey tests, respectively. We found that although perineural exogenous opioid agonists, including peptidergic ligands, were effective, the endogenous opioid peptides β-endorphin, Met-enkephalin and dynorphin A did not alleviate heat hypersensitivity. Specifically, corticotropin-releasing factor, an agent triggering opioid peptide secretion from leukocytes, applied perineurally did not attenuate heat hypersensitivity in wild-type mice. Exogenous opioids, also shown to release opioid peptides via activation of leukocyte opioid receptors, were equally analgesic in wild-type and opioid peptide-knockout mice, indicating that endogenous opioids do not contribute to exogenous opioid analgesia in heat hypersensitivity. Furthermore, exogenously applied opioid peptides were ineffective as well. Conversely, opioid peptides relieved mechanical hypersensitivity. Thus, both opioid type and sensory modality may determine the outcome of neuropathic pain treatment.

  15. Impact of chronic morphine on delta opioid receptor expressing neurons in the mouse hippocampus

    PubMed Central

    Eric, Erbs; Lauren, Faget; Alice, Ceredig Rhian; Audrey, Matifas; Jean-Luc, Vonesch; L., Kieffer Brigitte; Dominique, Massotte

    2015-01-01

    Delta opioid receptors participate to the control of chronic pain and emotional responses. Recent data also identified their implication in spatial memory and drug-context associations pointing to a critical role of hippocampal delta receptors. To better appreciate the impact of repeated drug exposure on their modulatory activity, we used fluorescent knock-in mice that express a functional delta receptor fused at its carboxy-terminus with the green fluorescent protein in place of the native receptor. We then tested the impact of chronic morphine treatment on the density and distribution of delta receptor-expressing cells in the hippocampus. A decrease in delta receptor positive cell density was observed in the CA1, CA3 and dentate gyrus without alteration of the distribution across the different GABAergic populations that mainly express delta receptors. This effect partly persisted after four weeks of morphine abstinence. In addition, we observed increased delta opioid receptor expression at the cell surface compared to saline treated animals. In the hippocampus, chronic morphine administration thus induces delta opioid receptor cellular redistribution and durably decreases delta receptor-expressing cell density. Such modifications are likely to alter hippocampal physiology, and to contribute to long-term cognitive deficits. PMID:26480813

  16. Structural basis for bifunctional peptide recognition at human δ-opioid receptor

    DOE PAGES

    Fenalti, Gustavo; Zatsepin, Nadia A.; Betti, Cecilia; ...

    2015-02-16

    Bi-functional μ- and δ- opioid receptor (OR) ligands are potential therapeutic alternatives to alkaloid opiate analgesics with diminished side effects. We solved the structure of human δ-OR bound to the bi-functional δ-OR antagonist and μ-OR agonist tetrapeptide H-Dmt-Tic-Phe-Phe-NH2 (DIPP-NH2) by serial femtosecond crystallography, revealing a cis-peptide bond between H-Dmt and Tic. In summary, the observed receptor-peptide interactions are critical to understand the pharmacological profiles of opioid peptides, and to develop improved analgesics.

  17. Structural basis for bifunctional peptide recognition at human δ-opioid receptor

    SciTech Connect

    Fenalti, Gustavo; Zatsepin, Nadia A.; Betti, Cecilia; Giguere, Patrick; Han, Gye Won; Ishchenko, Andrii; Liu, Wei; Guillemyn, Karel; Zhang, Haitao; James, Daniel; Wang, Dingjie; Weierstall, Uwe; Spence, John C. H.; Boutet, Sébastien; Messerschmidt, Marc; Williams, Garth J.; Gati, Cornelius; Yefanov, Oleksandr M.; White, Thomas A.; Oberthuer, Dominik; Metz, Markus; Yoon, Chun Hong; Barty, Anton; Chapman, Henry N.; Basu, Shibom; Coe, Jesse; Conrad, Chelsie E.; Fromme, Raimund; Fromme, Petra; Tourwé, Dirk; Schiller, Peter W.; Roth, Bryan L.; Ballet, Steven; Katritch, Vsevolod; Stevens, Raymond C.; Cherezov, Vadim

    2015-02-16

    Bi-functional μ- and δ- opioid receptor (OR) ligands are potential therapeutic alternatives to alkaloid opiate analgesics with diminished side effects. We solved the structure of human δ-OR bound to the bi-functional δ-OR antagonist and μ-OR agonist tetrapeptide H-Dmt-Tic-Phe-Phe-NH2 (DIPP-NH2) by serial femtosecond crystallography, revealing a cis-peptide bond between H-Dmt and Tic. In summary, the observed receptor-peptide interactions are critical to understand the pharmacological profiles of opioid peptides, and to develop improved analgesics.

  18. Structural basis for bifunctional peptide recognition at human δ-Opioid receptor

    PubMed Central

    Fenalti, Gustavo; Zatsepin, Nadia A.; Betti, Cecilia; Giguere, Patrick; Han, Gye Won; Ishchenko, Andrii; Liu, Wei; Guillemyn, Karel; Zhang, Haitao; James, Daniel; Wang, Dingjie; Weierstall, Uwe; Spence, John C.H.; Boutet, Sébastien; Messerschmidt, Marc; Williams, Garth J.; Gati, Cornelius; Yefanov, Oleksandr M.; White, Thomas A.; Oberthuer, Dominik; Metz, Markus; Yoon, Chun Hong; Barty, Anton; Chapman, Henry N.; Basu, Shibom; Coe, Jesse; Conrad, Chelsie E.; Fromme, Raimund; Fromme, Petra; Tourwé, Dirk; Schiller, Peter W.; Roth, Bryan L.; Ballet, Steven; Katritch, Vsevolod; Stevens, Raymond C.; Cherezov, Vadim

    2015-01-01

    Bi-functional μ- and δ- opioid receptor (OR) ligands are potential therapeutic alternatives to alkaloid opiate analgesics with diminished side effects. We solved the structure of human δ-OR bound to the bi-functional δ-OR antagonist and μ-OR agonist tetrapeptide H-Dmt(1)-Tic(2)-Phe(3)-Phe(4)-NH2 (DIPP-NH2) by serial femtosecond crystallography, revealing a cis-peptide bond between H-Dmt(1) and Tic(2). The observed receptor-peptide interactions are critical to understand the pharmacological profiles of opioid peptides, and to develop improved analgesics. PMID:25686086

  19. Mu receptor binding of some commonly used opioids and their metabolites

    SciTech Connect

    Chen, Zhaorong; Irvine, R.J. ); Somogyi, A.A.; Bochner, F. Royal Adelaide Hospital )

    1991-01-01

    The binding affinity to the {mu} receptor of some opioids chemically related to morphine and some of their metabolites was examined in rat brain homogenates with {sup 3}H-DAMGO. The chemical group at position 6 of the molecule had little effect on binding. Decreasing the length of the alkyl group at position 3 decreased the K{sub i} values (morphine < codeine < ethylmorphine < pholcodine). Analgesics with high clinical potency containing a methoxyl group at position 3 had relatively weak receptor binding, while their O-demethylated metabolites had much stronger binding. Many opioids may exert their pharmacological actions predominantly through metabolites.

  20. Deficit in attachment behavior in mice lacking the mu-opioid receptor gene.

    PubMed

    Moles, Anna; Kieffer, Brigitte L; D'Amato, Francesca R

    2004-06-25

    Endogenous opioid binding to micro receptors is hypothesized to mediate natural rewards and has been proposed to be the basis of infant attachment behavior. Here, we report that micro-opioid receptor knockout mouse pups emit fewer ultrasonic vocalizations when removed from their mothers but not when exposed to cold or male mice odors. Moreover these knockout pups do not show a preference toward their mothers' cues and do not show ultrasonic calls potentiation after brief maternal exposure. Results from this study may indicate a molecular mechanism for diseases characterized by deficits in attachment behavior, such as autism or reactive attachment disorder.

  1. Neuroanatomical and neuropharmacological study of opioid pathways in the mesencephalic tectum: effect of mu(1)- and kappa-opioid receptor blockade on escape behavior induced by electrical stimulation of the inferior colliculus.

    PubMed

    Osaki, M Y; Castellan-Baldan, L; Calvo, F; Carvalho, A D; Felippotti, T T; de Oliveira, R; Ubiali, W A; Paschoalin-Maurin, T; Elias-Filho, D H; Motta, V; da Silva, L A; Coimbra, N C

    2003-12-05

    Deep layers of the superior colliculus (DLSC), the dorsal and ventral periaqueductal gray matter (PAG), and inferior colliculus (IC) are midbrain structures involved in the generation of defensive behavior. beta-Endorphin and Leu-enkephalin are some neurotransmitters that may modulate such behavior in mammals. Light microscopy immunocytochemistry with streptavidin method was used for the localization of the putative cells of defensive behavior with antibodies for endogenous opioids in rat brainstem. Midbrain structures showed positive neurons to beta-endorphin and Leu-enkephalin in similar distributions in the experimental animals, but we also noted the presence of varicose fibers positive to endogenous opioids in the PAG. Neuroanatomical techniques showed varicose fibers from the central nucleus of the inferior colliculus to ventral aspects of the PAG, at more caudal levels. Naloxonazine and nor-binaltorphimine, competitive antagonists that block mu(1)- and kappa-opioid receptors, were then used in the present work to investigate the involvement of opioid peptide neural system in the control of the fear-induced reactions evoked by electrical stimulation of the neural substrates of the inferior colliculus. The fear-like responses were measured by electrical stimulation of the central nucleus of the inferior colliculus, eliciting the escape behavior, which is characterized by vigorous running and jumping. Central administration of opioid antagonists (2.5 microg/0.2 microl and 5.0 microg/0.2 microl) was performed in non-anesthetized animals (Rattus norvegicus), and the behavioral manifestations of fear were registered after 10 min, 2 h, and 24 h of the pretreatment. Naloxonazine caused an increase of the defensive threshold, as compared to control, suggesting an antiaversive effect of the antagonism on mu(1)-opioid receptor. This finding was corroborated with central administration of nor-binaltorphimine, which also induced a decrease of the fear-like responses

  2. Melanocortin and Opioid Peptide Interactions in the Modulation of Binge Alcohol Drinking

    DTIC Science & Technology

    2012-04-01

    receptor ligands on ethanol intake and opioid levels in alcohol-preferring AA rats. Brain Res Bull 59:97– 104. Pritchard LE, Turnbull AV, White A... trouts ol < Tf’gether these data suggest that. in anrmals prone to drinking excess amounts of< ar ticipatory behaviors related to ethanol-seeking

  3. Mu opioid receptor up-regulation and participation in excitability of hippocampal pyramidal cell electrophysiology

    SciTech Connect

    Moudy, A.M.

    1988-01-01

    Chronic administration of opiate antagonists to rats results in up-regulation of their brain opioid receptors. Using subcellular fractionation techniques, brain opioid receptors were resolved into two membrane populations, one associated with synaptic plasma membranes (SPM) and the other enriched in smooth endoplasmic reticulum and Golgi (microsomes). This study addressed in part the question of whether an antagonist induces up-regulation uniformly in these two populations. Rats were administered naltrexone by subcutaneously implanted osmotic minipumps. Forebrain mu receptor levels were determined by homologous displacement of ({sup 3}H)D-ala{sup 2}-mePhe{sup 4}-gly-ol{sup 5}-enkephalin (DAGO) followed by computer estimation of binding parameters. Receptor levels in crude membranes rose 77% after treatment. Microsomes displayed a 92% increase, a two-fold greater change than in SPMs (51%). These results establish that naltrexone induces up-regulation of both membrane populations; and that microsomal and SPM receptors represent discrete populations of intracellular and cell surface sites, respectively. Binding experiments on isolated hippocampi also demonstrated up-regulation (71%) of mu receptors. To demonstrate up-regulation of opioid receptors electrophysiologically, hippocampal slices were prepared from rats which had been chronically treated with naltrexone. After superfusion with DAGO, these slices showed a 42% greater population spike output than controls in response to the same EPSP input. Hippocampi from animals treated for two weeks showed an additional increase in sensitivity. The results support a disinhibitory role for opioids in pyramidal cell hyper-excitability. More importantly, they demonstrate a significant physiological correlate to opioid receptor up-regulation.

  4. Supersensitive Kappa Opioid Receptors Promotes Ethanol Withdrawal-Related Behaviors and Reduce Dopamine Signaling in the Nucleus Accumbens

    PubMed Central

    Rose, Jamie H.; Karkhanis, Anushree N.; Chen, Rong; Gioia, Dominic; Lopez, Marcelo F.; Becker, Howard C.; McCool, Brian A.

    2016-01-01

    Background: Chronic ethanol exposure reduces dopamine transmission in the nucleus accumbens, which may contribute to the negative affective symptoms associated with ethanol withdrawal. Kappa opioid receptors have been implicated in withdrawal-induced excessive drinking and anxiety-like behaviors and are known to inhibit dopamine release in the nucleus accumbens. The effects of chronic ethanol exposure on kappa opioid receptor-mediated changes in dopamine transmission at the level of the dopamine terminal and withdrawal-related behaviors were examined. Methods: Five weeks of chronic intermittent ethanol exposure in male C57BL/6 mice were used to examine the role of kappa opioid receptors in chronic ethanol-induced increases in ethanol intake and marble burying, a measure of anxiety/compulsive-like behavior. Drinking and marble burying were evaluated before and after chronic intermittent ethanol exposure, with and without kappa opioid receptor blockade by nor-binaltorphimine (10mg/kg i.p.). Functional alterations in kappa opioid receptors were assessed using fast scan cyclic voltammetry in brain slices containing the nucleus accumbens. Results: Chronic intermittent ethanol-exposed mice showed increased ethanol drinking and marble burying compared with controls, which was attenuated with kappa opioid receptor blockade. Chronic intermittent ethanol-induced increases in behavior were replicated with kappa opioid receptor activation in naïve mice. Fast scan cyclic voltammetry revealed that chronic intermittent ethanol reduced accumbal dopamine release and increased uptake rates, promoting a hypodopaminergic state of this region. Kappa opioid receptor activation with U50,488H concentration-dependently decreased dopamine release in both groups; however, this effect was greater in chronic intermittent ethanol-treated mice, indicating kappa opioid receptor supersensitivity in this group. Conclusions: These data suggest that the chronic intermittent ethanol-induced increase

  5. Obesity is associated with decreased μ-opioid but unaltered dopamine D2 receptor availability in the brain.

    PubMed

    Karlsson, Henry K; Tuominen, Lauri; Tuulari, Jetro J; Hirvonen, Jussi; Parkkola, Riitta; Helin, Semi; Salminen, Paulina; Nuutila, Pirjo; Nummenmaa, Lauri

    2015-03-04

    Neurochemical pathways involved in pathological overeating and obesity are poorly understood. Although previous studies have shown increased μ-opioid receptor (MOR) and decreased dopamine D2 receptor (D2R) availability in addictive disorders, the role that these systems play in human obesity still remains unclear. We studied 13 morbidly obese women [mean body mass index (BMI), 42 kg/m(2)] and 14 nonobese age-matched women, and measured brain MOR and D2R availability using PET with selective radioligands [(11)C]carfentanil and [(11)C]raclopride, respectively. We also used quantitative meta-analytic techniques to pool previous evidence on the effects of obesity on altered D2R availability. Morbidly obese subjects had significantly lower MOR availability than control subjects in brain regions relevant for reward processing, including ventral striatum, insula, and thalamus. Moreover, in these areas, BMI correlated negatively with MOR availability. Striatal MOR availability was also negatively associated with self-reported food addiction and restrained eating patterns. There were no significant differences in D2R availability between obese and nonobese subjects in any brain region. Meta-analysis confirmed that current evidence for altered D2R availability in obesity is only modest. Obesity appears to have unique neurobiological underpinnings in the reward circuit, whereby it is more similar to opioid addiction than to other addictive disorders. The opioid system modulates motivation and reward processing, and low μ-opioid availability may promote overeating to compensate decreased hedonic responses in this system. Behavioral and pharmacological strategies for recovering opioidergic function might thus be critical to curb the obesity epidemic.

  6. Opioid desensitization: interactions with G-protein-coupled receptors in the locus coeruleus.

    PubMed

    Fiorillo, C D; Williams, J T

    1996-02-15

    In rat locus coeruleus (LC) neurons, alpha 2 adrenoceptors, mu-opioid and somatostatin receptors all activate the same potassium conductance. Chronic treatment with morphine causes a loss of sensitivity that is specific to the mu-opioid response, with no change in the alpha 2 adrenoceptor-mediated response. Acute desensitization induced by opioid, somatostatin, and alpha 2-adrenoceptor agonists was studied in brain slices of rat LC using intracellular recording. A supramaximal concentration of the opioid agonist Met5-enkephalin induced a profound homologous desensitization but little heterologous desensitization to an alpha 2-adrenoceptor agonist (UK 14304) or somatostatin. All desensitized currents showed partial recovery. A supramaximal concentration of UK14304 caused a relatively small amount of desensitization. Although little interaction was observed among inhibitory G-protein-coupled receptors, activation of an excitatory receptor had marked effects on inhibitory responses. Muscarinic agonists, which produce an inward current in LC neurons, reduced the magnitude of agonist-induced outward currents and increased both the rate and amount of opioid desensitization. Muscarinic activation did not alter desensitization of alpha 2-adrenoceptor responses. Acute desensitization shares several characteristics with the tolerance induced by chronic morphine treatment of animals.

  7. Regulation of µ-Opioid Receptors: Desensitization, Phosphorylation, Internalization, and Tolerance

    PubMed Central

    Williams, John T.; Ingram, Susan L.; Henderson, Graeme; Chavkin, Charles; von Zastrow, Mark; Schulz, Stefan; Koch, Thomas; Evans, Christopher J.

    2013-01-01

    Morphine and related µ-opioid receptor (MOR) agonists remain among the most effective drugs known for acute relief of severe pain. A major problem in treating painful conditions is that tolerance limits the long-term utility of opioid agonists. Considerable effort has been expended on developing an understanding of the molecular and cellular processes that underlie acute MOR signaling, short-term receptor regulation, and the progression of events that lead to tolerance for different MOR agonists. Although great progress has been made in the past decade, many points of contention and controversy cloud the realization of this progress. This review attempts to clarify some confusion by clearly defining terms, such as desensitization and tolerance, and addressing optimal pharmacological analyses for discerning relative importance of these cellular mechanisms. Cellular and molecular mechanisms regulating MOR function by phosphorylation relative to receptor desensitization and endocytosis are comprehensively reviewed, with an emphasis on agonist-biased regulation and areas where knowledge is lacking or controversial. The implications of these mechanisms for understanding the substantial contribution of MOR signaling to opioid tolerance are then considered in detail. While some functional MOR regulatory mechanisms contributing to tolerance are clearly understood, there are large gaps in understanding the molecular processes responsible for loss of MOR function after chronic exposure to opioids. Further elucidation of the cellular mechanisms that are regulated by opioids will be necessary for the successful development of MOR-based approaches to new pain therapeutics that limit the development of tolerance. PMID:23321159

  8. Fourteen. beta. -(bromoacetamido)morphine irreversibly labels. mu. opioid receptors in rat brain membranes

    SciTech Connect

    Bidlack, J.M.; Frey, D.K.; Seyed-Mozaffari, A.; Archer, S. )

    1989-05-16

    The binding properties of 14{beta}-(bromoacetamido)morphine (BAM) and the ability of BAM to irreversibly inhibit opioid binding to rat brain membranes were examined to characterize the affinity and selectivity of BAM as an irreversible affinity ligand for opioid receptors. BAM had the same receptor selectivity as morphine, with a 3-5-fold decrease in affinity for the different types of opioid receptors. When brain membranes were incubated with BAM, followed by extensive washing, opioid binding was restored to control levels. However, when membranes were incubated with dithiothreitol (DTT), followed by BAM, and subsequently washed, 90% of the 0.25 nM ({sup 3}H)(D-Ala{sup 2},(Me)Phe{sup 4},Gly(ol){sup 5})enkephalin (DAGO) binding was irreversibly inhibited as a result of the specific alkylation of a sulfhydryl group at the {mu} binding site. This inhibition was dependent on the concentrations of both DTT and BAM. The {mu} receptor specificity of BAM alkylation was demonstrated by the ability of BAM alkylated membranes to still bind the {delta}-selective peptide ({sup 3}H)(D-penicillamine{sup 2},D-penicillamine{sup 5})enkephalin (DPDPE) and (-)-({sup 3}H)bremazocine in the presence of {mu} and {delta} blockers, selective for {kappa} binding sites. Morphine and naloxone partially protected the binding site from alkylation with BAM, while ligands that did not bind to the {mu}s site did not afford protection. These studies have demonstrated that when a disulfide bond at or near {mu} opioid binding sites was reduced, BAM could then alkylate this site, resulting in the specific irreversible labeling of {mu} opioid receptors.

  9. Desensitization of functional µ-opioid receptors increases agonist off-rate.

    PubMed

    Williams, John T

    2014-07-01

    Desensitization of µ-opioid receptors (MORs) develops over 5-15 minutes after the application of some, but not all, opioid agonists and lasts for tens of minutes after agonist removal. The decrease in function is receptor selective (homologous) and could result from 1) a reduction in receptor number or 2) a decrease in receptor coupling. The present investigation used photolysis of two caged opioid ligands to examine the kinetics of MOR-induced potassium conductance before and after MOR desensitization. Photolysis of a caged antagonist, carboxynitroveratryl-naloxone (caged naloxone), blocked the current induced by a series of agonists, and the time constant of decline was significantly decreased after desensitization. The increase in the rate of current decay was not observed after partial blockade of receptors with the irreversible antagonist, β-chlornaltrexamine (β-CNA). The time constant of current decay after desensitization was never more rapid than 1 second, suggesting an increased agonist off-rate rather than an increase in the rate of channel closure downstream of the receptor. The rate of G protein-coupled K(+) channel (GIRK) current activation was examined using photolysis of a caged agonist, carboxynitrobenzyl-tyrosine-[Leu(5)]-enkephalin. After acute desensitization or partial irreversible block of MORs with β-CNA, there was an increase in the time it took to reach a peak current. The decrease in the rate of agonist-induced GIRK conductance was receptor selective and dependent on receptor number. The results indicate that opioid receptor desensitization reduced the number of functional receptor and that the remaining active receptors have a reduced agonist affinity.

  10. Sigma opioid receptor: characterization and co-identity with the phencyclidine receptor

    SciTech Connect

    Mendelsohn, L.G.; Kalra, V.; Johnson, B.G.; Kerchner, G.A.

    1985-06-01

    The properties of the sigma opioid receptor of rat brain cortex have been characterized using the prototypic ligand (+)-(/sup 3/H) SKF 10,047. Binding to this receptor was rapid, and equilibrium was obtained within 30 min at 37 degrees C. Specific binding was linear with protein concentration up to 500 micrograms/2 ml and was dependent upon protein integrity. Denaturation by boiling destroyed over 95% of the specific binding. A high-affinity binding site with a KD of 150 +/- 40 nM and a maximum binding of 2.91 +/- 0.84 pmol/mg of protein was determined from a Scatchard plot of the binding data. The addition of salt, either NaCl or CaCl/sub 2/, to the buffers markedly decreased binding, with CaCl/sub 2/ being more potent than NaCl. A broad pH optimum for specific binding was observed; maximum binding was at pH 9.0. The affinity of a number of ligands for the sigma site and the phencyclidine receptor were compared. The binding (IC50) of 13 ligands to the sigma site showed a correlation of 0.86 (P less than .01) with binding to the phencyclidine site. The data demonstrate that the biochemical properties of the sigma and phencyclidine receptors are similar and support the view that these receptors are one and the same site.

  11. Delta opioid receptors colocalize with corticotropin releasing factor in hippocampal interneurons.

    PubMed

    Williams, T J; Milner, T A

    2011-04-14

    The hippocampal formation (HF) is an important site at which stress circuits and endogenous opioid systems intersect, likely playing a critical role in the interaction between stress and drug addiction. Prior study findings suggest that the stress-related neuropeptide corticotropin releasing factor (CRF) and the delta opioid receptor (DOR) may localize to similar neuronal populations within HF lamina. Here, hippocampal sections of male and cycling female adult Sprague-Dawley rats were processed for immunolabeling using antisera directed against the DOR and CRF peptide, as well as interneuron subtype markers somatostatin or parvalbumin, and analyzed by fluorescence and electron microscopy. Both DOR- and CRF-labeling was observed in interneurons in the CA1, CA3, and dentate hilus. Males and normal cycling females displayed a similar number of CRF immunoreactive neurons co-labeled with DOR and a similar average number of CRF-labeled neurons in the dentate hilus and stratum oriens of CA1 and CA3. In addition, 70% of DOR/CRF dual-labeled neurons in the hilar region co-labeled with somatostatin, suggesting a role for these interneurons in regulating perforant path input to dentate granule cells. Ultrastructural analysis of CRF-labeled axon terminals within the hilar region revealed that proestrus females have a similar number of CRF-labeled axon terminals that contain DORs compared to males but an increased number of CRF-labeled axon terminals without DORs. Taken together, these findings suggest that while DORs are anatomically positioned to modulate CRF immunoreactive interneuron activity and CRF peptide release, their ability to exert such regulatory activity may be compromised in females when estrogen levels are high.

  12. Synthesis and opioid receptor binding of indium (III) and [(111)In]-labeled macrocyclic conjugates of diprenorphine: novel ligands designed for imaging studies of peripheral opioid receptors.

    PubMed

    Srivastava, Shefali; Fergason-Cantrell, Emily A; Nahas, Roger I; Lever, John R

    2016-10-06

    Radiolabeled diprenorphine (DPN) and analogs are widely used ligands for non-invasive brain imaging of opioid receptors. To develop complementary radioligands optimized for studies of the peripheral opioid receptors, we prepared a pair of hydrophilic DPN derivatives, conjugated to the macrocyclic chelator DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid), for complexation with trivalent metals. The non-radioactive indium (III) complexes, tethered to the C6-oxygen position of the DPN scaffold by 6- to 9-atom spacers, displayed high affinities for binding to μ, δ and κ opioid receptors in vitro. Use of the 9-atom linker conferred picomolar affinities equipotent to those of the parent ligand DPN. The [(111)In]-labeled complexes were prepared in good yield (>70%), with high radiochemical purity (~99%) and high specific radioactivity (>4000 mCi/μmol). Their log D7.4 values were -2.21 to -1.66. In comparison, DPN is lipophilic, with a log D7.4 of +2.25. Further study in vivo is warranted to assess the suitability of these [(111)In]-labeled DPN-DOTA conjugates for imaging trials.

  13. Cannabinoid-induced stimulation of motor activity in planaria through an opioid receptor-mediated mechanism.

    PubMed

    Buttarelli, Francesca R; Pontieri, Francesco E; Margotta, Vito; Palladini, Guido

    2002-01-01

    Planaria, the most primitive example of centralization and cephalization of the nervous system along phylogeny, shows specific stereotyped behavioral patterns following exposure to drugs acting on neural transmission. In this study, the authors investigated the effects of exposure to the synthetic cannabinoid receptor agonist WTN55212.2 on motor activity in planaria. WTN55212.2 produced dose-dependent stimulation of motor behavior. High doses of the drug caused stereotyped activities identical to those seen previously with opioid agonists. These effects were antagonized by coexposure to cannabinoid or opioid receptor antagonists. The results indicate that functional interactions between cannabinoid and opioid systems are highly conserved along phylogeny, at least at the behavioral level.

  14. Synthesis and κ-Opioid Receptor Activity of Furan-Substituted Salvinorin A Analogues

    PubMed Central

    2015-01-01

    The neoclerodane diterpene salvinorin A, found in the leaves of Salvia divinorum, is a potent κ-opioid receptor agonist, making it an attractive scaffold for development into a treatment for substance abuse. Although several successful semisynthetic studies have been performed to elucidate structure–activity relationships, the lack of analogues with substitutions to the furan ring of salvinorin A has prevented a thorough understanding of its role in binding to the κ-opioid receptor. Herein we report the synthesis of several salvinorin A derivatives with modified furan rings. Evaluation of these compounds in a functional assay indicated that sterically less demanding substitutions are preferred, suggesting the furan ring is bound in a congested portion of the binding pocket. The most potent of the analogues successfully reduced drug-seeking behavior in an animal model of drug-relapse without producing the sedation observed with other κ-opioid agonists. PMID:25426797

  15. Synthesis and κ-opioid receptor activity of furan-substituted salvinorin A analogues.

    PubMed

    Riley, Andrew P; Groer, Chad E; Young, David; Ewald, Amy W; Kivell, Bronwyn M; Prisinzano, Thomas E

    2014-12-26

    The neoclerodane diterpene salvinorin A, found in the leaves of Salvia divinorum, is a potent κ-opioid receptor agonist, making it an attractive scaffold for development into a treatment for substance abuse. Although several successful semisynthetic studies have been performed to elucidate structure-activity relationships, the lack of analogues with substitutions to the furan ring of salvinorin A has prevented a thorough understanding of its role in binding to the κ-opioid receptor. Herein we report the synthesis of several salvinorin A derivatives with modified furan rings. Evaluation of these compounds in a functional assay indicated that sterically less demanding substitutions are preferred, suggesting the furan ring is bound in a congested portion of the binding pocket. The most potent of the analogues successfully reduced drug-seeking behavior in an animal model of drug-relapse without producing the sedation observed with other κ-opioid agonists.

  16. Effects of continuous opioid receptor blockade on alcohol intake and up-regulation of opioid receptor subtype signalling in a genetic model of high alcohol drinking.

    PubMed

    Hyytiä, P; Ingman, K; Soini, S L; Laitinen, J T; Korpi, E R

    1999-10-01

    Effects of a continuous naloxone infusion via osmotic pumps on alcohol drinking and opioid receptor density and function in the high-drinking AA (Alko, Alcohol) rats were examined. AA rats were trained to drink 10% (v/v) ethanol in a 1-h limited access procedure and implanted with subcutaneous osmotic pumps delivering either saline, a low dose (0.3 mg/kg per hour), or a high dose (3.0 mg/kg per hour) of naloxone for 7 days. The pumps were then removed and alcohol, food and water intakes were measured for another 4 days. Compared with saline, both naloxone doses significantly suppressed 1-h alcohol intake during the 7-day infusion. The suppression was smaller than that by a bolus injection of the same daily dose 15 min before the session, although a complete blockade of morphine-induced antinociception was achieved even with the smaller naloxone infusion. Significant decreases were also seen in daily food and water intake during the first days, but they quickly returned to their previous baselines. After pump removal, rats of both naloxone-treated groups rapidly increased their alcohol drinking and reached the pretreatment baseline, while their food and water intakes significantly surpassed their baselines. Naloxone infusion at 3.0 mg/kg per hour for 7 days significantly decreased 24-h alcohol drinking without affecting alcohol preference. Twenty-four hours after pump removal, autoradiography with [3H]DAMGO, [3H]DPDPE and [3H]U-69,543 revealed an up-regulation of mu-, delta- and kappa-opioid receptor binding sites in many brain areas of these animals. This receptor up-regulation was functional, because receptor coupling to G-protein activation was enhanced by agonist ligands, as revealed by [35S]GTPgammaS autoradiography. A good correlation existed between ligand binding densities and G-protein activation for mu- and kappa-receptors in control and naloxone-treated brain sections. Furthermore, morphine-induced analgesia in a hot-plate test showed a leftward shift in

  17. Preferred Supramolecular Organization and Dimer Interfaces of Opioid Receptors from Simulated Self-Association

    PubMed Central

    Provasi, Davide; Boz, Mustafa Burak; Johnston, Jennifer M.; Filizola, Marta

    2015-01-01

    Substantial evidence in support of the formation of opioid receptor (OR) di-/oligomers suggests previously unknown mechanisms used by these proteins to exert their biological functions. In an attempt to guide experimental assessment of the identity of the minimal signaling unit for ORs, we conducted extensive coarse-grained (CG) molecular dynamics (MD) simulations of different combinations of the three major OR subtypes, i.e., μ-OR, δ-OR, and κ-OR, in an explicit lipid bilayer. Specifically, we ran multiple, independent MD simulations of each homomeric μ-OR/μ-OR, δ-OR/δ-OR, and κ-OR/κ-OR complex, as well as two of the most studied heteromeric complexes, i.e., δ-OR/μ-OR and δ-OR/κ-OR, to derive the preferred supramolecular organization and dimer interfaces of ORs in a cell membrane model. These simulations yielded over 250 microseconds of accumulated data, which correspond to approximately 1 millisecond of effective simulated dynamics according to established scaling factors of the CG model we employed. Analysis of these data indicates similar preferred supramolecular organization and dimer interfaces of ORs across the different receptor subtypes, but also important differences in the kinetics of receptor association at specific dimer interfaces. We also investigated the kinetic properties of interfacial lipids, and explored their possible role in modulating the rate of receptor association and in promoting the formation of filiform aggregates, thus supporting a distinctive role of the membrane in OR oligomerization and, possibly, signaling. PMID:25822938

  18. NOP Receptor Mediates Anti-analgesia Induced by Agonist-Antagonist Opioids

    PubMed Central

    Gear, Robert W.; Bogen, Oliver; Ferrari, Luiz F.; Green, Paul G.; Levine, Jon D.

    2014-01-01

    Clinical studies have shown that agonist-antagonist opioid analgesics that produce their analgesic effect via action on the kappa-opioid receptor, produce a delayed-onset anti-analgesia in men but not women, an effect blocked by co-administration of a low dose of naloxone. We now report the same time-dependent anti-analgesia and its underlying mechanism in an animal model. Using the Randall-Selitto paw-withdrawal assay in male rats, we found that nalbuphine, pentazocine, and butorphanol each produced analgesia during the first hour followed by anti-analgesia starting at ~90 minutes after administration in males but not females, closely mimicking its clinical effects. As observed in humans, co-administration of nalbuphine with naloxone in a dose ratio of 12.5:1 blocked anti-analgesia but not analgesia. Administration of the highly selective kappa-opioid receptor agonist U69,593 produced analgesia without subsequent anti-analgesia, and confirmed by the failure of the selective kappa antagonist nor-binaltorphimine to block nalbuphine-induced anti-analgesia, indicating that anti-analgesia is not mediated by kappa-opioid receptors. We therefore tested the role of other receptors in nalbuphine anti-analgesia. Nociceptin/orphanin FQ (NOP) and sigma-1 and sigma-2 receptors were chosen on the basis of their known anti-analgesic effects and receptor binding studies. The selective NOP receptor antagonists, JTC801, and J113397, but not the sigma receptor antagonist, BD 1047, antagonized nalbuphine anti-analgesia. Furthermore, the NOP receptor agonist NNC 63-0532 produced anti-analgesia with the same delay in onset observed with the three agonist-antagonists, but without producing preceding analgesia and this anti-analgesia was also blocked by naloxone. These results strongly support the suggestion that clinically used agonist-antagonists act at the NOP receptor to produce anti-analgesia. PMID:24188792

  19. The role of the Asn40Asp polymorphism of the mu opioid receptor gene (OPRM1) on alcoholism etiology and treatment: a critical review.

    PubMed

    Ray, Lara A; Barr, Christina S; Blendy, Julie A; Oslin, David; Goldman, David; Anton, Raymond F

    2012-03-01

    The endogenous opioid system has been implicated in the pathophysiology of alcoholism as it modulates the neurobehavioral effects of alcohol. A variant in the mu opioid receptor gene (OPRM1), the Asn40Asp polymorphism, has received attention as a functional variant that may influence a host of behavioral phenotypes for alcoholism as well as clinical response to opioid antagonists. This paper will review converging lines of evidence on the effect of the Asn40Asp SNP on alcoholism phenotypes, including: (i) genetic association studies; (ii) behavioral studies of alcoholism; (iii) neuroimaging studies; (iv) pharmacogenetic studies and clinical trials; and (v) preclinical animal studies. Together, these lines of research seek to elucidate the effects of this functional polymorphism on alcoholism etiology and treatment response.

  20. Herkinorin dilates cerebral vessels via kappa opioid receptor and cyclic adenosine monophosphate (cAMP) in a piglet model.

    PubMed

    Ji, Fang; Wang, Zhenhong; Ma, Nan; Riley, John; Armstead, William M; Liu, Renyu

    2013-01-15

    Since herkinorin is the first non-opioid mu agonist derived from salvinorin A that has the ability to induce cerebral vascular dilatation, we hypothesized that herkinorin could have similar vascular dilatation effect via the mu and kappa opioid receptors and the cAMP pathway. The binding affinities of herkinorin to kappa and mu opioid receptors were determined by in-vitro competition binding assays. The cerebral arteries were monitored in piglets equipped with a closed cranial window and the artery responses were recorded before and every 30s after injection of artificial cerebrospinal fluid (CSF) in the presence or absence of the investigated drugs: herkinorion, norbinaltorphimine (NTP), a kappa opioid receptor antagonist, β-funaltrexamine (β-FNA), a mu opioid receptor antagonist, or Rp-8-Br-cAMPS (Rp-cAMPS), an inhibitor of protein kinase A (PKA). CSF samples were collected before and 10 min after herkinorin and NTP administration for the measurement of cAMP levels. Data were analyzed by repeated-measures analysis of variance. Our results show that herkinorin binds to both kappa and mu opioid receptors. Its vasodilation effect is totally abolished by NTP, but is not affected by β-FNA. The levels of cAMP in the CSF elevate after herkinorin administration, but are abolished with NTP administration. The cerebral vasodilative effect of herkinorin is also blunted by Rp-cAMPS. In conclusion, as a non-opioid kappa and mu opioid receptor agonist, herkinorin exhibits cerebral vascular dilatation effect. The dilatation is mediated though the kappa opioid receptor rather than the mu opioid receptor. cAMP signaling also plays an important role in this process.

  1. δ-Opioid and Dopaminergic Processes in Accumbens Shell Modulate the Cholinergic Control of Predictive Learning and Choice

    PubMed Central

    Laurent, Vincent; Bertran-Gonzalez, Jesus; Chieng, Billy C.

    2014-01-01

    Decision-making depends on the ability to extract predictive information from the environment to guide future actions. Outcome-specific Pavlovian-instrumental transfer (PIT) provides an animal model of this process in which a stimulus predicting a particular outcome biases choice toward actions earning that outcome. Recent evidence suggests that cellular adaptations of δ-opioid receptors (DORs) on cholinergic interneurons (CINs) in the nucleus accumbens shell (NAc-S) are necessary for PIT. Here we found that modulation of DORs in CINs critically influences D1-receptor (D1R)-expressing projection neurons in the NAc-S to promote PIT. First, we assessed PIT-induced changes in signaling processes in dopamine D1- and D2-receptor-expressing neurons using drd2-eGFP mice, and found that PIT-related signaling was restricted to non-D2R-eGFP-expressing neurons, suggesting major involvement of D1R-neurons. Next we confirmed the role of D1Rs pharmacologically: the D1R antagonist SCH-23390, but not the D2R antagonist raclopride, infused into the NAc-S abolished PIT in rats, an effect that depended on DOR activity. Moreover, asymmetrical infusion of SCH-23390 and the DOR antagonist naltrindole into the NAc-S also abolished PIT. DOR agonists were found to sensitize the firing responses of CINs in brain slices prepared immediately after the PIT test. We confirmed the opioid-acetylcholinergic influence over D1R-neurons by selectively blocking muscarinic M4 receptors in the NAc-S, which tightly regulate the activity of D1Rs, a treatment that rescued the deficit in PIT induced by naltrindole. We describe a model of NAc-S function in which DORs modulate CINs to influence both D1R-neurons and stimulus-guided choice between goal-directed actions. PMID:24453326

  2. δ-opioid and dopaminergic processes in accumbens shell modulate the cholinergic control of predictive learning and choice.

    PubMed

    Laurent, Vincent; Bertran-Gonzalez, Jesus; Chieng, Billy C; Balleine, Bernard W

    2014-01-22

    Decision-making depends on the ability to extract predictive information from the environment to guide future actions. Outcome-specific Pavlovian-instrumental transfer (PIT) provides an animal model of this process in which a stimulus predicting a particular outcome biases choice toward actions earning that outcome. Recent evidence suggests that cellular adaptations of δ-opioid receptors (DORs) on cholinergic interneurons (CINs) in the nucleus accumbens shell (NAc-S) are necessary for PIT. Here we found that modulation of DORs in CINs critically influences D1-receptor (D1R)-expressing projection neurons in the NAc-S to promote PIT. First, we assessed PIT-induced changes in signaling processes in dopamine D1- and D2-receptor-expressing neurons using drd2-eGFP mice, and found that PIT-related signaling was restricted to non-D2R-eGFP-expressing neurons, suggesting major involvement of D1R-neurons. Next we confirmed the role of D1Rs pharmacologically: the D1R antagonist SCH-23390, but not the D2R antagonist raclopride, infused into the NAc-S abolished PIT in rats, an effect that depended on DOR activity. Moreover, asymmetrical infusion of SCH-23390 and the DOR antagonist naltrindole into the NAc-S also abolished PIT. DOR agonists were found to sensitize the firing responses of CINs in brain slices prepared immediately after the PIT test. We confirmed the opioid-acetylcholinergic influence over D1R-neurons by selectively blocking muscarinic M4 receptors in the NAc-S, which tightly regulate the activity of D1Rs, a treatment that rescued the deficit in PIT induced by naltrindole. We describe a model of NAc-S function in which DORs modulate CINs to influence both D1R-neurons and stimulus-guided choice between goal-directed actions.

  3. Kappa Opioid Receptors Mediate where Fear Is Expressed Following Extinction Training

    ERIC Educational Resources Information Center

    Cole, Sindy; Richardson, Rick; McNally, Gavan P.

    2011-01-01

    Six experiments used a within-subjects renewal design to examine the involvement of kappa opioid receptors (KORs) in regulating the expression and recovery of extinguished fear. Rats were trained to fear a tone conditioned stimulus (CS) via pairings with foot shock in a distinctive context (A). This was followed by extinction training of the CS in…

  4. Recent advances on the δ opioid receptor: from trafficking to function

    PubMed Central

    Gendron, Louis; Mittal, Nitish; Beaudry, Hélène; Walwyn, Wendy

    2015-01-01

    Within the opioid family of receptors, δ (DOPrs) and μ opioid receptors (MOPrs) are typical GPCRs that activate canonical second-messenger signalling cascades to influence diverse cellular functions in neuronal and non-neuronal cell types. These receptors activate well-known pathways to influence ion channel function and pathways such as the map kinase cascade, AC and PI3K. In addition new information regarding opioid receptor-interacting proteins, downstream signalling pathways and resultant functional effects has recently come to light. In this review, we will examine these novel findings focusing on the DOPr and, in doing so, will contrast and compare DOPrs with MOPrs in terms of differences and similarities in function, signalling pathways, distribution and interactions. We will also discuss and clarify issues that have recently surfaced regarding the expression and function of DOPrs in different cell types and analgesia. LINKED ARTICLES This article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-2 PMID:24665909

  5. A unique binding epitope for salvinorin A, a non-nitrogenous kappa opioid receptor agonist.

    PubMed

    Kane, Brian E; Nieto, Marcelo J; McCurdy, Christopher R; Ferguson, David M

    2006-05-01

    Salvinorin A is a potent kappa opioid receptor (KOP) agonist with unique structural and pharmacological properties. This non-nitrogenous ligand lacks nearly all the structural features commonly associated with opioid ligand binding and selectivity. This study explores the structural basis to salvinorin A binding and selectivity using a combination of chimeric and single-point mutant opioid receptors. The experiments were designed based on previous models of salvinorin A that locate the ligand within a pocket formed by transmembrane (TM) II, VI, and VII. More traditional sites of opioid recognition were also explored, including the highly conserved aspartate in TM III (D138) and the KOP selectivity site E297, to determine the role, if any, that these residues play in binding and selectivity. The results indicate that salvinorin A recognizes a cluster of residues in TM II and VII, including Q115, Y119, Y312, Y313, and Y320. Based on the position of these residues within the receptor, and prior study on salvinorin A, a model is proposed that aligns the ligand vertically, between TM II and VII. In this orientation, the ligand spans residues that are spaced one to two turns down the face of the helices within the receptor cavity. The ligand is also in close proximity to EL-2 which, based on chimeric data, is proposed to play an indirect role in salvinorin A binding and selectivity.

  6. Chronic exposure to morphine decreases the expression of EAAT3 via opioid receptors in hippocampal neurons.

    PubMed

    Guo, Mingyan; Cao, Dexiong; Zhu, Siyu; Fu, Ganglan; Wu, Qiang; Liang, Jianjun; Cao, Minghui

    2015-12-02

    Alterations in glutamate transporter expression are closely related to opiate addition behavior, but the role of opioid receptors is unclear. In this study, we used primary cultures of hippocampal neurons from neonatal rats to study the effects of chronic exposure to morphine on excitatory amino acid transporter 3 (EAAT3) expression and the roles of µ opioid receptor (MOR), δ opioid receptor (DOR), and κ opioid receptor (KOR) in the morphine-dependent alterations in EAAT3 expression. The results showed that the EAAT3 protein and mRNA expression levels decreased significantly after chronic exposure to morphine (10μmol/L) for 48h, whereas the concentration of extracellular glutamate increased. In addition, we found that both the MOR inhibitor CTOP and the DOR inhibitor naltrindole could reverse the decreased expression of EAAT3 after exposure to morphine, whereas the MOR activator DAMGO and the DOR activator DPDPE significantly decreased EAAT3 expression. The KOR inhibitor had no effect on the expression of EAAT3, whereas its activator increased EAAT3 expression. These results suggest that the down-regulation of morphine-dependent EAAT3 expression in primary rat hippocampal cultures may be mediated by MOR and DOR and that KOR may not contribute significantly to this effect.

  7. Opioid receptor selectivity profile change via isosterism for 14-O-substitued naltrexone derivatives

    PubMed Central

    Zhang, Yan; Elbegdorj, Orgil; Yuan, Yunyun; Beletskaya, Irina O.; Selley, Dana E.

    2013-01-01

    Isosterism is commonly used in drug discovery and development to address stability, selectivity, toxicity, pharmacokinetics, and efficacy issues. A series of 14-O-substituted naltrexone derivatives were identified as potent mu opioid receptor (MOR) antagonists with improved selectivity over the kappa opioid receptor (KOR) and the delta opioid receptor (DOR), compared to naltrexone. Since esters are not metabolically very stable under typical physiological conditions, their corresponding amide analogs were thus synthesized and biologically evaluated. Unlike their isosteres, most of these novel ligands seem to be dually selective for the MOR and the KOR over the DOR. The restricted flexibility of the amide bond linkage might be responsible for their altered selectivity profile. However, the majority of the 14-N-substituted naltrexone derivatives produced marginal or no MOR stimulation in the 35S-GTP[γS] assay, which resembled their ester analogs. The current study thus indicated that the 14-substituted naltrexone isosteres are not bioisosteres since they have distinctive pharmacological profile with the regard to their opioid receptor binding affinity and selectivity. PMID:23721804

  8. Opioid receptor selectivity profile change via isosterism for 14-O-substituted naltrexone derivatives.

    PubMed

    Zhang, Yan; Elbegdorj, Orgil; Yuan, Yunyun; Beletskaya, Irina O; Selley, Dana E

    2013-07-01

    Isosterism is commonly used in drug discovery and development to address stability, selectivity, toxicity, pharmacokinetics, and efficacy issues. A series of 14-O-substituted naltrexone derivatives were identified as potent mu opioid receptor (MOR) antagonists with improved selectivity over the kappa opioid receptor (KOR) and the delta opioid receptor (DOR), compared to naltrexone. Since esters are not metabolically very stable under typical physiological conditions, their corresponding amide analogs were thus synthesized and biologically evaluated. Unlike their isosteres, most of these novel ligands seem to be dually selective for the MOR and the KOR over the DOR. The restricted flexibility of the amide bond linkage might be responsible for their altered selectivity profile. However, the majority of the 14-N-substituted naltrexone derivatives produced marginal or no MOR stimulation in the (35)S-GTP[γS] assay, which resembled their ester analogs. The current study thus indicated that the 14-substituted naltrexone isosteres are not bioisosteres since they have distinctive pharmacological profile with the regard to their opioid receptor binding affinity and selectivity.

  9. Sex Differences in Kappa Opioid Receptor Function and Their Potential Impact on Addiction

    PubMed Central

    Chartoff, Elena H.; Mavrikaki, Maria

    2015-01-01

    Behavioral, biological, and social sequelae that lead to drug addiction differ between men and women. Our efforts to understand addiction on a mechanistic level must include studies in both males and females. Stress, anxiety, and depression are tightly linked to addiction, and whether they precede or result from compulsive drug use depends on many factors, including biological sex. The neuropeptide dynorphin (DYN), an endogenous ligand at kappa opioid receptors (KORs), is necessary for stress-induced aversive states and is upregulated in the brain after chronic exposure to drugs of abuse. KOR agonists produce signs of anxiety, fear, and depression in laboratory animals and humans, findings that have led to the hypothesis that drug withdrawal-induced DYN release is instrumental in negative reinforcement processes that drive addiction. However, these studies were almost exclusively conducted in males. Only recently is evidence available that there are sex differences in the effects of KOR activation on affective state. This review focuses on sex differences in DYN and KOR systems and how these might contribute to sex differences in addictive behavior. Much of what is known about how biological sex influences KOR systems is from research on pain systems. The basic molecular and genetic mechanisms that have been discovered to underlie sex differences in KOR function in pain systems may apply to sex differences in KOR function in reward systems. Our goals are to discuss the current state of knowledge on how biological sex contributes to KOR function in the context of pain, mood, and addiction and to explore potential mechanisms for sex differences in KOR function. We will highlight evidence that the function of DYN-KOR systems is influenced in a sex-dependent manner by: polymorphisms in the prodynorphin (pDYN) gene, genetic linkage with the melanocortin-1 receptor (MC1R), heterodimerization of KORs and mu opioid receptors (MORs), and gonadal hormones. Finally, we

  10. Synthesis and SAR study of opioid receptor ligands: mono- and bis-indolomorphinans.

    PubMed

    Li, Fuying; Yin, Chenlei; Chen, Jie; Liu, Jinggen; Xie, Xin; Zhang, Ao

    2009-10-01

    Mono- and bis-indolomorphinans were synthesized through a multi-step synthetic approach from the alkaloid, thebaine, to further explore the C-ring SAR (structure-activity relationship) of morphinan scaffold. Both mono-indoles displayed good binding affinity and selectivity for the delta receptor, with compound 6b possessed the highest K(i) value of 1.45 nm at this receptor. Bisindolomorphinans 7a,b did not have appreciable affinity for both delta and kappa receptors, but moderate binding at the mu receptor was observed. Functional assays indicated that the newly synthesized mono-indole 6b was delta-agonist, opposite to the delta-antagonist profile of naltrindole. Bisindoles 7a,b were mu-agonists. This work further confirms that the phenol component in opioids is essential for higher binding to the opioid receptors. The different binding ability, receptor selectivity, and the functional activity profiles of naltrindole 2, monoindole 6b, and bisindole 7b clearly indicated that they interact with the opioid receptors in different modes.

  11. Ligand-Specific Regulation of the Endogenous Mu-Opioid Receptor by Chronic Treatment with Mu-Opioid Peptide Agonists

    PubMed Central

    Murányi, Marianna; Cinar, Resat; Kékesi, Orsolya; Birkás, Erika; Fábián, Gabriella; Bozó, Beáta; Zentai, András; Tóth, Géza; Kicsi, Emese Gabriella; Mácsai, Mónika; Szabó, Gyula; Szücs, Mária

    2013-01-01

    Since the discovery of the endomorphins (EM), the postulated endogenous peptide agonists of the mu-opioid receptors, several analogues have been synthesized to improve their binding and pharmacological profiles. We have shown previously that a new analogue, cis-1S,2R-aminocyclohexanecarboxylic acid2-endomorphin-2 (ACHC-EM2), had elevated mu-receptor affinity, selectivity, and proteolytic stability over the parent compound. In the present work, we have studied its antinociceptive effects and receptor regulatory processes. ACHC-EM2 displayed a somewhat higher (60%) acute antinociceptive response than the parent peptide, EM2 (45%), which peaked at 10 min after intracerebroventricular (icv) administration in the rat tail-flick test. Analgesic tolerance developed to the antinociceptive effect of ACHC-EM2 upon its repeated icv injection that was complete by a 10-day treatment. This was accompanied by attenuated coupling of mu-sites to G-proteins in subcellular fractions of rat brain. Also, the density of mu-receptors was upregulated by about 40% in the light membrane fraction, with no detectable changes in surface binding. Distinct receptor regulatory processes were noted in subcellular fractions of rat brains made tolerant by the prototypic full mu-agonist peptide, DAMGO, and its chloromethyl ketone derivative, DAMCK. These results are discussed in light of the recently discovered phenomenon, that is, the “so-called biased agonism” or “functional selectivity”. PMID:24350273

  12. Ligand-specific regulation of the endogenous mu-opioid receptor by chronic treatment with mu-opioid peptide agonists.

    PubMed

    Murányi, Marianna; Cinar, Resat; Kékesi, Orsolya; Birkás, Erika; Fábián, Gabriella; Bozó, Beáta; Zentai, András; Tóth, Géza; Kicsi, Emese Gabriella; Mácsai, Mónika; Dochnal, Roberta; Szabó, Gyula; Szücs, Mária

    2013-01-01

    Since the discovery of the endomorphins (EM), the postulated endogenous peptide agonists of the mu-opioid receptors, several analogues have been synthesized to improve their binding and pharmacological profiles. We have shown previously that a new analogue, cis-1S,2R-aminocyclohexanecarboxylic acid(2)-endomorphin-2 (ACHC-EM2), had elevated mu-receptor affinity, selectivity, and proteolytic stability over the parent compound. In the present work, we have studied its antinociceptive effects and receptor regulatory processes. ACHC-EM2 displayed a somewhat higher (60%) acute antinociceptive response than the parent peptide, EM2 (45%), which peaked at 10 min after intracerebroventricular (icv) administration in the rat tail-flick test. Analgesic tolerance developed to the antinociceptive effect of ACHC-EM2 upon its repeated icv injection that was complete by a 10-day treatment. This was accompanied by attenuated coupling of mu-sites to G-proteins in subcellular fractions of rat brain. Also, the density of mu-receptors was upregulated by about 40% in the light membrane fraction, with no detectable changes in surface binding. Distinct receptor regulatory processes were noted in subcellular fractions of rat brains made tolerant by the prototypic full mu-agonist peptide, DAMGO, and its chloromethyl ketone derivative, DAMCK. These results are discussed in light of the recently discovered phenomenon, that is, the "so-called biased agonism" or "functional selectivity".

  13. Activation of mu-opioid receptors in the ventrolateral orbital cortex inhibits the GABAergic miniature inhibitory postsynaptic currents in rats.

    PubMed

    Qu, Chao-Ling; Huo, Fu-Quan; Huang, Fen-Sheng; Tang, Jing-Shi

    2015-04-10

    Previous studies have indicated that mu-opioid receptors in the ventrolateral orbital cortex (VLO) are involved in antinociception in tail flick tests and GABAergic neurons or terminals express mu-opioid receptors in the VLO. The current study examined the effect of selective mu-opioid receptor agonist DAMGO on the GABAergic miniature inhibitory postsynaptic currents (mIPSCs) in the VLO in rats using the whole-cell patch clamp. The results demonstrated that 5 μM DAMGO application into the rat VLO slices significantly reduced the GABAergic mIPSCs frequency, without any effect on its amplitude, and this effect of DAMGO was reversed by pretreatment with selective mu-opioid receptor antagonist 1 μM CTOP. Importantly, application of CTOP alone into the VLO slices did not produce any effect on the frequency and amplitude of GABAergic mIPSCs. These results indicate a presynaptic effect of mu-opioid receptor activation on the GABAergic neurons in the VLO. The current data suggests that a presynaptic inhibition of the GABA release may contribute to the mu-opioid receptor mediated effects in the VLO and provides novel electrophysiological evidence for the underlying mechanisms of mu-opioid receptors in the VLO.

  14. Micro opioid receptor A118G polymorphism and post-operative pain: opioids' effects on heterozygous patients.

    PubMed

    De Capraris, A; Cinnella, G; Marolla, A; Salatto, P; Da Lima, S; Vetuschi, P; Consoletti, L; Gesualdo, L; Dambrosio, M

    2011-01-01

    The single-nucleotide-polymorphism (SNP) 118A>G in the micro-1 opioid receptor gene (OPRM1) is associated with a decrease in the analgesic effects of opioids. The aim of this study is to assess whether 118A >G polymorphism could influence the analgesic response to opioid-based postoperative pain (POP) therapy. The study consisted of two parts: section alpha, observational, included 199 subjects undergoing scheduled surgical procedures with pain management standardized on surgery invasiveness and on expected level of postoperative pain; section beta, randomized, included 41 women undergoing scheduled caesarean delivery with continuous intra-operative epidural anesthesia and post-operative analgesia (CEA). In both sections, POP was measured over 48 h (T6h-T24h-T48h) by the visual analogue scale (VAS). In section beta we also tested the responsiveness of hypothalamic-pituitary-adrenal axis (HPA) expressed by cortisol levels. In section alpha, with cluster analysis, subjects were analyzed according to their genotype: a group (no. 1) of 34 patients reporting VAS score >3 at every time lapse was identified and included only A118G carriers, while wild-type (A118A - absence of 118A>G polymorphism) patients were unevenly distributed between those with cluster no. 2 (VAS score <3 at every study steps) and those with cluster no. 3 (VAS score progressively reducing from T6h). In section beta, A118G carriers receiving epidural sufentanil had the lowest VAS scores at T24h; also in these patients, cortisol levels remained more stable, with a mild decrease at T6h. This study shows that the OPRM1 118A>G polymorphism affects postoperative pain response in heterozygous patients: they have a different postoperative pain response than patients with wild-type genes, which may affect the efficacy of the analgesic therapy.

  15. Oxycodone with an opioid receptor antagonist: A review.

    PubMed

    Davis, Mellar P; Goforth, Harold W

    2016-01-01

    The rationale for putting opioid antagonists with an agonist is to improve pain control, to reduce side effects, and/or to reduce abuse. The combination of prolonged release (PR) oxycodone and naloxone reduces constipation as demonstrated in multiple studies and has been designated a tamper-resistant opioid by the Food and Drug Administration. Bioequivalence of the combination product compared with PR oxycodone has not been established. Several of the pivotal studies provided suboptimal laxative support in the control arm of the randomized trials. Two noninferiority trials have demonstrated equivalent analgesia between PR oxycodone and the combination product at doses of less than 120 mg of oxycodone per day. There appears to be an analgesic ceiling above 80-120 mg of oxycodone per day. Safety monitoring during randomized trials was not been well described in published manuscripts. Benefits appear to be better for those with chronic noncancer pain compared with individuals with cancer when constipation was the primary outcome.

  16. The in vitro pharmacology of the peripherally restricted opioid receptor antagonists, alvimopan, ADL 08-0011 and methylnaltrexone.

    PubMed

    Beattie, D T; Cheruvu, M; Mai, N; O'Keefe, M; Johnson-Rabidoux, S; Peterson, C; Kaufman, E; Vickery, R

    2007-05-01

    This study characterized the pharmacology of the peripherally restricted opioid receptor antagonists, alvimopan, its metabolite, ADL 08-0011, and methylnaltrexone. The activities of the compounds were investigated with respect to human or guinea pig opioid receptor binding and function in recombinant cell lines and mechanical responsiveness of the guinea pig ileum. Alvimopan and ADL 08-0011 had higher binding affinity than methylnaltrexone at human mu opioid receptors (pK (i) values of 9.6, 9.6, and 8.0, respectively). The compounds had different selectivities for the mu receptor over human delta and guinea pig kappa opioid receptors. ADL 08-0011 had the highest mu receptor selectivity. With respect to their mu opioid receptor functional activity ([(35)S]GTPgammaS incorporation), methylnaltrexone had a positive intrinsic activity, consistent with partial agonism, unlike alvimopan and ADL 08-0011, which had negative intrinsic activities. Alvimopan, ADL 08-0011, and methylnaltrexone antagonized inhibitory responses mediated by the mu opioid agonist, endomorphin-1 (pA (2) values of 9.6, 9.4, and 7.6, respectively) and by U69593, a kappa opioid agonist (pA (2) values of 8.4, 7.2, and 6.7, respectively). In morphine-naive guinea pig ileum, methylnaltrexone reduced, while alvimopan and ADL 08-0011 increased, the amplitude of electrically evoked contractions and spontaneous mechanical activity. In tissue from morphine-dependent animals, alvimopan and ADL 08-0011 increased spontaneous activity to a greater degree than methylnaltrexone. The data suggested that alvimopan-induced contractions resulted predominantly from an interaction with kappa opioid receptors. It is concluded that alvimopan, ADL 08-0011, and methylnaltrexone differ in their in vitro pharmacological properties, particularly with respect to opioid receptor subtype selectivity and intrinsic activity. The clinical significance of the data from this study remains to be determined.

  17. Remifentanil produces cross-desensitization and tolerance with morphine on the mu-opioid receptor.

    PubMed

    Nowoczyn, M; Marie, N; Coulbault, L; Hervault, M; Davis, A; Hanouz, J L; Allouche, S

    2013-10-01

    Remifentanil is a powerful mu-opioid (MOP) receptor agonist used in anaesthesia with a very short half-life. However, per-operative perfusion of remifentanil was shown to increase morphine consumption during post-operative period to relieve pain. In the present study, we aimed to describe the cellular mechanisms responsible for this apparent reduction of morphine efficacy. For this purpose, we first examined the pharmacological properties of both remifentanil and morphine at the MOP receptor, endogenously expressed in the human neuroblastoma SH-SY5Y cell line, to regulate adenylyl cyclase and the MAP kinase ERK1/2 pathway, their potency to promote MOP receptor phosphorylation, arrestin 3-CFP (cyan fluorescent protein) recruitment and receptor trafficking during acute and sustained exposure. In the second part of this work, we studied the effects of a prior exposure of remifentanil on morphine-induced inhibition of cAMP accumulation, activation of ERK1/2 and analgesia. We showed that sustained exposure to remifentanil promoted a rapid desensitization of opioid receptors on both signalling pathways and a pretreatment with this agonist reduced signal transduction produced by a second challenge with morphine. While both opioid agonists promoted Ser(375) phosphorylation on MOP receptor, remifentanil induced a rapid internalization of opioid receptors compared to morphine but without detectable arrestin 3-CFP translocation to the plasma membrane in our experimental conditions. Lastly, a cross-tolerance between remifentanil and morphine was observed in mice using the hot plate test. Our in vitro and in vivo data thus demonstrated that remifentanil produced a rapid desensitization and internalization of the MOP receptor that would reduce the anti-nociceptive effects of morphine.

  18. Agonist-Specific Recruitment of Arrestin Isoforms Differentially Modify Delta Opioid Receptor Function

    PubMed Central

    Perroy, Julie; Walwyn, Wendy M.; Smith, Monique L.; Vicente-Sanchez, Ana; Segura, Laura; Bana, Alia; Kieffer, Brigitte L.; Evans, Christopher J.

    2016-01-01

    Ligand-specific recruitment of arrestins facilitates functional selectivity of G-protein-coupled receptor signaling. Here, we describe agonist-selective recruitment of different arrestin isoforms to the delta opioid receptor in mice. A high-internalizing delta opioid receptor agonist (SNC80) preferentially recruited arrestin 2 and, in arrestin 2 knock-outs (KOs), we observed a significant increase in the potency of SNC80 to inhibit mechanical hyperalgesia and decreased acute tolerance. In contrast, the low-internalizing delta agonists (ARM390, JNJ20788560) preferentially recruited arrestin 3 with unaltered behavioral effects in arrestin 2 KOs. Surprisingly, arrestin 3 KO revealed an acute tolerance to these low-internalizing agonists, an effect never observed in wild-type animals. Furthermore, we examined delta opioid receptor–Ca2+ channel coupling in dorsal root ganglia desensitized by ARM390 and the rate of resensitization was correspondingly decreased in arrestin 3 KOs. Live-cell imaging in HEK293 cells revealed that delta opioid receptors are in pre-engaged complexes with arrestin 3 at the cell membrane and that ARM390 strengthens this membrane interaction. The disruption of these complexes in arrestin 3 KOs likely accounts for the altered responses to low-internalizing agonists. Together, our results show agonist-selective recruitment of arrestin isoforms and reveal a novel endogenous role of arrestin 3 as a facilitator of resensitization and an inhibitor of tolerance mechanisms. SIGNIFICANCE STATEMENT Agonists that bind to the same receptor can produce highly distinct signaling events and arrestins are a major mediator of this ligand bias. Here, we demonstrate that delta opioid receptor agonists differentially recruit arrestin isoforms. We found that the high-internalizing agonist SNC80 preferentially recruits arrestin 2 and knock-out (KO) of this protein results in increased efficacy of SNC80. In contrast, low-internalizing agonists (ARM390 and JNJ20788560

  19. Bioorthogonal click chemistry to assay mu-opioid receptor palmitoylation using 15-hexadecynoic acid and immunoprecipitation

    PubMed Central

    Ebersole, Brittany; Petko, Jessica; Levenson, Robert

    2014-01-01

    We have developed a modification of bioorthogonal click chemistry to assay the palmitoylation of cellular proteins. This assay utilizes 15-hexadecynoic acid (15-HDYA) as a chemical probe in combination with protein immunoprecipitation using magnetic beads in order to detect S-palmitoylation of proteins of interest. Here we demonstrate the utility of this approach for the mu-opioid receptor (MOR), a GPCR responsible for mediating the analgesic and addictive properties of most clinically relevant opioid agonist drugs. This technique provides a rapid, non-isotopic, and efficient method to assay the palmitoylation status of a variety of cellular proteins including most GPCRs. PMID:24463015

  20. Kinase Cascades and Ligand-Directed Signaling at the Kappa Opioid Receptor

    PubMed Central

    Bruchas, Michael R.; Chavkin, Charles

    2013-01-01

    Background and Rationale The dynorphin / kappa-opioid receptor (KOR) system has been implicated as a critical component of the stress response. Stress-induced activation of dynorphin-KOR is well-known to produce analgesia, and more recently it has been implicated as a mediator of stress-induced responses including anxiety, depression, and reinstatement of drug seeking. Objective Drugs selectively targeting specific KOR signaling pathways may prove potentially useful as therapeutic treatments for mood and addiction disorders. Results KOR is a member of the seven transmembrane spanning (7TM) G-protein coupled receptor (GPCR) superfamily. KOR activation of pertussis toxin-sensitive G proteins leads to Gαi/o inhibition of adenylyl cyclase production of cAMP and releases Gβγ, which modulates the conductances of Ca+2 and K+ channels. In addition, KOR agonists activate kinase cascades including G-protein coupled Receptor Kinases (GRK) and members of the mitogen-activated protein kinase (MAPK) family: ERK1/2, p38 and JNK. Recent pharmacological data suggests that GPCRs exist as dynamic, multi-conformational protein complexes that can be directed by specific ligands towards distinct signaling pathways. Ligand-induced conformations of KOR that evoke β–arrestin-dependent p38 MAPK activation result in aversion; whereas ligand-induced conformations that activate JNK without activating arrestin produce long-lasting inactivation of KOR signaling. Conclusions In this review, we discuss the current status of KOR signal transduction research and the data that support two novel hypotheses: 1) KOR selective partial agonists that do not efficiently activate p38 MAPK may be useful analgesics without producing the dysphoric or hallucinogenic effects of selective, highly efficacious KOR agonists and 2) KOR antagonists that do not activate JNK may be effective short-acting drugs that may promote stress-resilience. PMID:20401607

  1. Involvement of Mu Opioid Receptor Signaling in the Protective Effect of Opioid against 6-Hydroxydopamine-Induced SH-SY5Y Human Neuroblastoma Cells Apoptosis

    PubMed Central

    Eftekhar-Vaghefi, Shahrzad; Esmaeili-Mahani, Saeed; Elyasi, Leila; Abbasnejad, Mehdi

    2015-01-01

    Introduction: The neuroprotective role of opioid morphine against 6-hydroxydopamine-induced cell death has been demonstrated. However, the exact mechanism(s) underlying such neuroprotection, especially the role of subtype receptors, has not yet been fully clarified. Methods: Here, we investigated the effects of different opioid agonists on 6-OHDA-induced neurotoxicity in human neuroblastoma SH-SY5Y cell line as an in vitro model of Parkinson’s disease. Cell damage was induced by 150 μM 6-OHDA and the cells viability was examined by MTT assay. Intracellular calcium, reactive oxygen species and mitochondrial membrane potential were assessed by fluorescence spectrophotometry method. Immunoblot technique was used to evaluate cytochrome-c and activated caspase-3 as biochemical markers of apoptosis induction. Results: The data showed that 6-OHDA caused significant cell damage, loss of mitochondrial membrane potential and increase in intracellular reactive oxygen species and calcium levels as well as activated caspase-3 and cytochrome-c release. Incubation of SH-SY5Y cells with μ-opioid agonists, morphine and DAMGO, but not with δ-opioid agonist, DADLE, elicited protective effect and reduced biochemical markers of cell damage and death. Discussion: The results suggest that μ-opioid receptors signaling participate in the opioid neuroprotective effects against 6-OHDA-induced neurotoxicity. PMID:26904174

  2. Synthetic studies of neoclerodane diterpenes from Salvia divinorum: role of the furan in affinity for opioid receptors.

    PubMed

    Simpson, Denise S; Lovell, Kimberly M; Lozama, Anthony; Han, Nina; Day, Victor W; Dersch, Christina M; Rothman, Richard B; Prisinzano, Thomas E

    2009-09-21

    Further synthetic modification of the furan ring of salvinorin A (1), the major active component of Salvia divinorum, has resulted in novel neoclerodane diterpenes with opioid receptor affinity and activity. A computational study has predicted 1 to be a reproductive toxicant in mammals and is suggestive that use of 1 may be associated with adverse effects. We report in this study that piperidine 21 and thiomorpholine 23 have been identified as selective partial agonists at kappa opioid receptors. This indicates that additional structural modifications of 1 may provide ligands with good selectivity for opioid receptors but with reduced potential for toxicity.

  3. Exploration of Bivalent Ligands Targeting Putative Mu Opioid Receptor and Chemokine Receptor CCR5 Dimerization

    PubMed Central

    Arnatt, Christopher K.; Falls, Bethany A.; Yuan, Yunyun; Raborg, Thomas J.; Masvekar, Ruturaj R.; El-Hage, Nazira; Selley, Dana E.; Nicola, Anthony V.; Knapp, Pamela E.; Hauser, Kurt F.; Zhang, Yan

    2016-01-01

    Modern antiretroviral therapies have provided HIV-1 infected patients longer lifespans and better quality of life. However, several neurological complications are now being seen in these patients due to HIV-1 associated injury of neurons by infected microglia and astrocytes. In addition, these effects can be further exacerbated with opiate use and abuse. One possible mechanism for such potentiation effects of opiates is the interaction of the mu opioid receptor (MOR) with the chemokine receptor CCR5 (CCR5), a known HIV-1 co-receptor, to form MOR-CCR5 heterodimer. In an attempt to understand this putative interaction and its relevance to neuroAIDS, we designed and synthesized a series of bivalent ligands targeting the putative CCR5-MOR heterodimer. To understand how these bivalent ligands may interact with the heterodimer, biological studies including calcium mobilization inhibition, binding affinity, HIV-1 invasion, and cell fusion assays were applied. In particular, HIV-1 infection assays using human peripheral blood mononuclear cells, macrophages, and astrocytes revealed a notable synergy in activity for one particular bivalent ligand. Further, a molecular model of the putative CCR5-MOR heterodimer was constructed, docked with the bivalent ligand, and molecular dynamics simulations of the complex was performed in a membrane-water system to help understand the biological observation. PMID:27720326

  4. Molecular signatures of mu opioid receptor and somatostatin receptor 2 in pancreatic cancer

    PubMed Central

    Jorand, Raphael; Biswas, Sunetra; Wakefield, Devin L.; Tobin, Steven J.; Golfetto, Ottavia; Hilton, Kelsey; Ko, Michelle; Ramos, Joe W.; Small, Alexander R.; Chu, Peiguo; Singh, Gagandeep; Jovanovic-Talisman, Tijana

    2016-01-01

    Pancreatic ductal adenocarcinoma (PDAC), a particularly aggressive malignancy, has been linked to atypical levels, certain mutations, and aberrant signaling of G-protein–coupled receptors (GPCRs). GPCRs have been challenging to target in cancer because they organize into complex networks in tumor cells. To dissect such networks with nanometer-scale precision, here we combine traditional biochemical approaches with superresolution microscopy methods. A novel interaction specific to PDAC is identified between mu opioid receptor (MOR) and somatostatin receptor 2 (SSTR2). Although MOR and SSTR2 did not colocalize in healthy pancreatic cells or matching healthy patient tissues, the pair did significantly colocalize in pancreatic cancer cells, multicellular tumor spheroids, and cancerous patient tissues. Moreover, this association in pancreatic cancer cells correlated with functional cross-talk and increased metastatic potential of cells. Coactivation of MOR and SSTR2 in PDAC cells led to increased expression of mesenchymal markers and decreased expression of an epithelial marker. Together these results suggest that the MOR-SSTR2 heteromer may constitute a novel therapeutic target for PDAC. PMID:27682590

  5. Molecular signatures of mu opioid receptor and somatostatin receptor 2 in pancreatic cancer.

    PubMed

    Jorand, Raphael; Biswas, Sunetra; Wakefield, Devin L; Tobin, Steven J; Golfetto, Ottavia; Hilton, Kelsey; Ko, Michelle; Ramos, Joe W; Small, Alexander R; Chu, Peiguo; Singh, Gagandeep; Jovanovic-Talisman, Tijana

    2016-11-07

    Pancreatic ductal adenocarcinoma (PDAC), a particularly aggressive malignancy, has been linked to atypical levels, certain mutations, and aberrant signaling of G-protein-coupled receptors (GPCRs). GPCRs have been challenging to target in cancer because they organize into complex networks in tumor cells. To dissect such networks with nanometer-scale precision, here we combine traditional biochemical approaches with superresolution microscopy methods. A novel interaction specific to PDAC is identified between mu opioid receptor (MOR) and somatostatin receptor 2 (SSTR2). Although MOR and SSTR2 did not colocalize in healthy pancreatic cells or matching healthy patient tissues, the pair did significantly colocalize in pancreatic cancer cells, multicellular tumor spheroids, and cancerous patient tissues. Moreover, this association in pancreatic cancer cells correlated with functional cross-talk and increased metastatic potential of cells. Coactivation of MOR and SSTR2 in PDAC cells led to increased expression of mesenchymal markers and decreased expression of an epithelial marker. Together these results suggest that the MOR-SSTR2 heteromer may constitute a novel therapeutic target for PDAC.

  6. Synthesis of iboga-like isoquinuclidines: Dual opioid receptors agonists having antinociceptive properties.

    PubMed

    Banerjee, Tuhin Suvro; Paul, Sibasish; Sinha, Surajit; Das, Sumantra

    2014-11-01

    Some novel iboga-analogues consisting of benzofuran moiety and dehydroisoquinuclidine ring connected by -CH2-, (CH2)2 and (CH2)3 linkers have been synthesized with the view to develop potential antinociceptive drugs. The compounds 14 and 21 showed binding at the μ-opioid receptor (MOR), while the compound 11a exhibited dual affinities at both MOR and κ-opioid receptor (KOR). MAP kinase activation indicated all three compounds have opioid agonistic properties. The presence of a double bond and endo-methylcarboxylate group in the dehydroisoquinuclidine ring and the benzofuran and methylene spacer appeared to be essential for opioid receptor binding. Further studies demonstrated 11a caused significant antinociception in mice in the hot-plate test which was comparable to that produced by morphine. The compound 11a was also found to be nontremorigenic unlike various iboga congeners. This study identifies a new pharmacophore which may lead to the development of suitable substitute of morphine in the treatment of pain.

  7. PET imaging reveals sex differences in kappa opioid receptor availability in humans, in vivo.

    PubMed

    Vijay, Aishwarya; Wang, Shuo; Worhunsky, Patrick; Zheng, Ming-Qiang; Nabulsi, Nabeel; Ropchan, Jim; Krishnan-Sarin, Suchitra; Huang, Yiyun; Morris, Evan D

    2016-01-01

    Opioid receptors may play critical roles in alcoholism and other addictions, addiction withdrawal, and depression and are considered pharmacological targets for treatment of these conditions. Sex differences have been demonstrated in mu (MOR) and delta (DOR) opioid receptors in humans, in vivo. In addition, sex differences have been observed in efficacy of treatment targeting kappa opioid receptors (KOR). Our goal in the present study was to compare the availability of KOR (1) between healthy control (HC) men and women. Twenty-seven subjects-18 males (M) and 9 females (F)-underwent PET scans with [(11)C] LY2795050, a selective kappa antagonist tracer. Partial volume correction was applied to all PET data. Volume of distribution (V T) of the tracer was estimated regionally as well as at the voxel level. V T values of males versus females were compared for 19 defined ROIs. Results at the regional and voxel levels were consistent. Males had significantly higher V T and thus a higher KOR availability than women in multiple brain regions. To our knowledge, this is the first report of sex differences in the KOR system in humans, in vivo. These findings could have implications for the treatment of pain with kappa opioid analgesics. The results may also have an impact on the diagnosis and treatment of addictive and other disorders.

  8. PET imaging reveals sex differences in kappa opioid receptor availability in humans, in vivo

    PubMed Central

    Vijay, Aishwarya; Wang, Shuo; Worhunsky, Patrick; Zheng, Ming-Qiang; Nabulsi, Nabeel; Ropchan, Jim; Krishnan-Sarin, Suchitra; Huang, Yiyun; Morris, Evan D

    2016-01-01

    Opioid receptors may play critical roles in alcoholism and other addictions, addiction withdrawal, and depression and are considered pharmacological targets for treatment of these conditions. Sex differences have been demonstrated in mu (MOR) and delta (DOR) opioid receptors in humans, in vivo. In addition, sex differences have been observed in efficacy of treatment targeting kappa opioid receptors (KOR). Our goal in the present study was to compare the availability of KOR (1) between healthy control (HC) men and women. Twenty-seven subjects-18 males (M) and 9 females (F)-underwent PET scans with [11C] LY2795050, a selective kappa antagonist tracer. Partial volume correction was applied to all PET data. Volume of distribution (V T) of the tracer was estimated regionally as well as at the voxel level. V T values of males versus females were compared for 19 defined ROIs. Results at the regional and voxel levels were consistent. Males had significantly higher V T and thus a higher KOR availability than women in multiple brain regions. To our knowledge, this is the first report of sex differences in the KOR system in humans, in vivo. These findings could have implications for the treatment of pain with kappa opioid analgesics. The results may also have an impact on the diagnosis and treatment of addictive and other disorders. PMID:27648372

  9. Differential migratory properties of mouse, fish, and frog leukocytes treated with agonists of opioid receptors.

    PubMed

    Chadzinska, Magdalena; Plytycz, Barbara

    2004-07-01

    Zymosan-induced peritoneal inflammation was inhibited by morphine co-injection in mice and fish but not in anuran amphibians. In present experiments, an in vitro migration of mouse, goldfish, and frog leukocytes to L15 medium, control serum (S) or zymosan-activated serum (ZAS) was recorded following cell preincubation with L15 or with agonists of mu, delta, or kappa opioid receptors (morphine, deltorphine, or U-50,488H, respectively). In all species, migration of control leukocytes was in the order ZAS > S > L15. Pretreatment with morphine or deltorphine (but not with U-50,488H) enhanced leukocyte migration to L15 and S in each species, while it inhibited migration of mouse and fish (but not frog) leukocytes to ZAS, phenomena reversed by specific antagonists of mu and delta opioid receptors (CTOP or naltrindole, respectively). It seems that final effects of opioids on cell migration are dependent on a species-specific balance between up- and down-regulation of leukocyte migration resulted from interplay between receptors for opioids and chemotactic factors.

  10. Anatomical and functional correlation of the endomorphins with mu opioid receptor splice variants.

    PubMed

    Abbadie, C; Rossi, G C; Orciuolo, A; Zadina, J E; Pasternak, G W

    2002-09-01

    The present study characterizes the relationship between the endogenous mu opioid peptides endomorphin-1 (EM-1) and endomorphin-2 (EM-2) and several splice variants of the cloned mu opioid receptor (MOR-1) encoded by the mu opioid receptor gene (Oprm). Confocal laser microscopy revealed that fibers containing EM-2-like immunoreactivity (-LI) were distributed in close apposition to fibers showing MOR-1-LI (exon 4-LI) and to MOR-1C-LI (exons 7/8/9-LI) in the superficial laminae of the lumbar spinal cord. We also observed colocalization of EM-2-LI and MOR-1-LI in a few fibers of lamina II, and colocalization of EM-2-LI and MOR-1C-LI in laminae I-II, and V-VI. To assess the functional relevance of the MOR-1 variants in endomorphin analgesia, we examined the effects of antisense treatments that targeted individual exons within the Oprm1 gene on EM-1 and EM-2 analgesia in the tail flick test. This antisense mapping study implied mu opioid receptor mechanisms for the endomorphins are distinct from those of morphine or morphine-6beta-glucuronide (M6G).

  11. Antinociceptive effects of the 6-O-sulfate ester of morphine in normal and diabetic rats: Comparative role of mu- and delta-opioid receptors.

    PubMed

    Yadlapalli, Jai Shankar K; Ford, Benjamin M; Ketkar, Amit; Wan, Anqi; Penthala, Narasimha R; Eoff, Robert L; Prather, Paul L; Dobretsov, Maxim; Crooks, Peter A

    2016-11-01

    This study determined the antinociceptive effects of morphine and morphine-6-O-sulfate (M6S) in both normal and diabetic rats, and evaluated the comparative role of mu-opioid receptors (mu-ORs) and delta-opioid receptors (delta-ORs) in the antinociceptive action of these opioids. In vitro characterization of mu-OR and delta-OR-mediated signaling by M6S and morphine in stably transfected Chinese hamster ovary (CHO-K1) cells showed that M6S exhibited a 6-fold higher affinity for delta-ORs and modulated G-protein and adenylyl cyclase activity via delta-ORs more potently than morphine. Interestingly, while morphine acted as a full agonist at delta-ORs in both functional assays examined, M6S exhibited either partial or full agonist activity for modulation of G-protein or adenylyl cyclase activity, respectively. Molecular docking studies indicated that M6S but not morphine binds equally well at the ligand binding site of both mu- and delta-ORs. In vivo analgesic effects of M6S and morphine in both normal and streptozotocin-induced diabetic Sprague-Dawley rats utilizing the hot water tail flick latency test showed that M6S produced more potent antinociception than morphine in both normal rats and diabetic rats. This difference in potency was abrogated following antagonism of delta- but not mu- or kappa (kappa-ORs) opioid receptors. During 9days of chronic treatment, tolerance developed to morphine-treated but not to M6S-treated rats. Rats that developed tolerance to morphine still remained responsive to M6S. Collectively, this study demonstrates that M6S is a potent and efficacious mu/delta opioid analgesic with a delayed tolerance profile when compared to morphine in both normal and diabetic rats.

  12. Activation of kappa opioid receptors in the rostral ventromedial medulla blocks stress-induced antinociception.

    PubMed

    Foo, H; Helmstetter, F J

    2000-10-20

    Prior work has shown that kappa opioids may attenuate the effects of analgesic mu receptor agonists in some neural circuits related to pain modulation. This study examined whether hypoalgesia following exposure to a signal for shock is attenuated by infusions of the kappa agonist U69593 into the rostral ventromedial medulla (RVM). Rats were trained with paired or unpaired presentations of white noise and foot shock. On test days, tail flick latencies were measured before, during, and after exposure to the auditory conditioned stimulus (CS). One of three doses of U69593 (0.0445, 0.178 and 1.00 microg) or an equivalent volume of saline was injected into the RVM. Rats that had received noise-shock pairings displayed conditional hypoalgesia (CHA) compared to those given unpaired presentations. Expression of CHA was completely blocked by the highest dose of U69593 (1.00 microg) injected 20 min before testing, indicating an antagonistic effect of U69593 on expression of CHA. These findings are discussed in terms of the evidence for antagonism of morphine- and DAMGO-induced hypoalgesia by kappa agonists.

  13. Endogenous opioids regulate moment-to-moment neuronal communication and excitability

    PubMed Central

    Winters, Bryony L.; Gregoriou, Gabrielle C.; Kissiwaa, Sarah A.; Wells, Oliver A.; Medagoda, Danashi I.; Hermes, Sam M.; Burford, Neil T.; Alt, Andrew; Aicher, Sue A.; Bagley, Elena E.

    2017-01-01

    Fear and emotional learning are modulated by endogenous opioids but the cellular basis for this is unknown. The intercalated cells (ITCs) gate amygdala output and thus regulate the fear response. Here we find endogenous opioids are released by synaptic stimulation to act via two distinct mechanisms within the main ITC cluster. Endogenously released opioids inhibit glutamate release through the δ-opioid receptor (DOR), an effect potentiated by a DOR-positive allosteric modulator. Postsynaptically, the opioids activate a potassium conductance through the μ-opioid receptor (MOR), suggesting for the first time that endogenously released opioids directly regulate neuronal excitability. Ultrastructural localization of endogenous ligands support these functional findings. This study demonstrates a new role for endogenously released opioids as neuromodulators engaged by synaptic activity to regulate moment-to-moment neuronal communication and excitability. These distinct actions through MOR and DOR may underlie the opposing effect of these receptor systems on anxiety and fear. PMID:28327612

  14. Sex-specificity and estrogen-dependence of kappa opioid receptor-mediated antinociception and antihyperalgesia

    PubMed Central

    Lawson, Kera P.; Nag, Subodh; Thompson, Analisa D.; Mokha, Sukhbir S.

    2010-01-01

    This investigation determined whether activation of the kappa opioid receptor (KOR) in the spinal cord produces estrogen-dependent, sex-specific modulation of acute and inflammation-induced persistent nociception. We demonstrate for the first time that KOR antinociception and gene expression are enhanced by exogenous or endogenous estrogen in the female. The lack of KOR antinociception and KOR gene expression are not altered by hormonal status (testosterone or estrogen) in males. Cannulae were implanted intrathecally in male, gonadectomized male (GDX), intact and ovariectomized female (OVX) Sprague-Dawley rats. Estradiol was injected subcutaneously, 48 h before testing (GDX+E and OVX+E). Intrathecal injection of U50, 488H, a selective KOR agonist, dose dependently increased heat-evoked tail flick latencies (TFLs) in proestrous and OVX+E groups, but not in male, GDX, GDX+E, OVX, and diestrous groups. Further, estrogen dose-dependently enhanced the effect of U50,488H in OVX rats. KOR selective antagonist, nor-binaltorphimine (Nor-BNI), blocked the antinociceptive effect of U50,488H. U50,488H reversed the carrageenan-induced thermal hyperalgesia in OVX+E rats, but not in male or OVX rats. However, U50,488H treatment did not alter mechanical thresholds in any group, with or without inflammation. KOR gene expression was enhanced in proestrous and OVX+E groups as compared to any other group. We conclude that selective activation of KOR in the spinal cord produces sex-specific, stimulus- and estrogen-dependent attenuation of acute and inflammatory pain in the rat via estrogen-induced upregulation of the KOR gene expression in the spinal cord. These findings may further implicate estrogen dependence of KOR effects in learning, epilepsy, stress response, addiction etc. Selective activation of the kappa opioid receptor by intrathecal U50,488H produces antinociception and antihyperalgesia which are sex-specific, stimulus dependent and require the presence of estrogen. PMID

  15. Optimisation of in silico derived 2-aminobenzimidazole hits as unprecedented selective kappa opioid receptor agonists.

    PubMed

    Sasmal, Pradip K; Krishna, C Vamsee; Adabala, S Sudheerkumar; Roshaiah, M; Rawoof, Khaji Abdul; Thadi, Emima; Sukumar, K Pavan; Cheera, Srisailam; Abbineni, Chandrasekhar; Rao, K V L Narasimha; Prasanthi, A; Nijhawan, Kamal; Jaleel, Mahaboobi; Iyer, Lakshmi Ramachandran; Chaitanya, T Krishna; Tiwari, Nirbhay Kumar; Krishna, N Lavanya; Potluri, Vijay; Khanna, Ish; Frimurer, Thomas M; Lückmann, Michael; Rist, Øystein; Elster, Lisbeth; Högberg, Thomas

    2015-02-15

    Kappa opioid receptor (KOR) is an important mediator of pain signaling and it is targeted for the treatment of various pains. Pharmacophore based mining of databases led to the identification of 2-aminobenzimidazole derivative as KOR agonists with selectivity over the other opioid receptors DOR and MOR. A short SAR exploration with the objective of identifying more polar and hence less brain penetrant agonists is described herewith. Modeling studies of the recently published structures of KOR, DOR and MOR are used to explain the receptor selectivity. The synthesis, biological evaluation and SAR of novel benzimidazole derivatives as KOR agonists are described. The in vivo proof of principle for anti-nociceptive effect with a lead compound from this series is exemplified.

  16. The opioid peptide dynorphin directly blocks NMDA receptor channels in the rat.

    PubMed Central

    Chen, L; Gu, Y; Huang, L Y

    1995-01-01

    1. The actions of dynorphin on N-methyl-D-aspartate (NMDA) responses were examined in acutely dissociated trigeminal neurons in rat. Whole-cell and single-channel currents were recorded using the patch clamp technique. 2. Dynorphins reduced NMDA-activated currents (INMDA). The IC50 was 0.25 microM for dynorphin (1-32), 1.65 microM for dynorphin (1-17) and 1.8 microM for dynorphin (1-13). 3. The blocking action of dynorphin is voltage independent. 4. The inhibitory action of dynorphin cannot be blocked by high concentration of the non-selective opioid receptor antagonist naloxone, nor by the specific kappa-opioid receptor antagonist nor-Binaltorphimine (nor-BNI). 5. Single-channel analyses indicate that dynorphin reduces the fraction of time the channel is open without altering the channel conductance. 6. We propose that dynorphin acts directly on NMDA receptors. PMID:7537820

  17. Tuned-Affinity Bivalent Ligands for the Characterization of Opioid Receptor Heteromers

    PubMed Central

    2012-01-01

    Opioid receptors, including the μ- and δ-opioid receptors (MOR and DOR), are important targets for the treatment of pain. Although there is mounting evidence that these receptors form heteromers, the functional role of the MOR/DOR heteromer remains unresolved. We have designed and synthesized bivalent ligands as tools to elucidate the functional role of the MOR/DOR heteromer. Our ligands (L2 and L4) are comprised of a compound with low affinity at the DOR tethered to a compound with high affinity at the MOR, with the goal of producing ligands with “tuned affinity” at MOR/DOR heteromers as compared to DOR homomers. Here, we show that both L2 and L4 demonstrate enhanced affinity at MOR/DOR heteromers as compared to DOR homomers, thereby providing unique pharmacological tools to dissect the role of the MOR/DOR heteromer in pain. PMID:23585918

  18. Low-dose naltrexone targets the opioid growth factor-opioid growth factor receptor pathway to inhibit cell proliferation: mechanistic evidence from a tissue culture model.

    PubMed

    Donahue, Renee N; McLaughlin, Patricia J; Zagon, Ian S

    2011-09-01

    Naltrexone (NTX) is an opioid antagonist that inhibits or accelerates cell proliferation in vivo when utilized in a low (LDN) or high (HDN) dose, respectively. The mechanism of opioid antagonist action on growth is not well understood. We established a tissue culture model of LDN and HDN using short-term and continuous opioid receptor blockade, respectively, in human ovarian cancer cells, and found that the duration of opioid receptor blockade determines cell proliferative response. The alteration of growth by NTX also was detected in cells representative of pancreatic, colorectal and squamous cell carcinomas. The opioid growth factor (OGF; [Met(5)]-enkephalin) and its receptor (OGFr) were responsible for mediating the action of NTX on cell proliferation. NTX upregulated OGF and OGFr at the translational but not at the transcriptional level. The mechanism of inhibition by short-term NTX required p16 and/or p21 cyclin-dependent inhibitory kinases, but was not dependent on cell survival (necrosis, apoptosis). Sequential administration of short-term NTX and OGF had a greater inhibitory effect on cell proliferation than either agent alone. Given the parallels between short-term NTX in vitro and LDN in vivo, we now demonstrate at the molecular level that the OGF-OGFr axis is a common pathway that is essential for the regulation of cell proliferation by NTX.

  19. Dietary peptides induce satiety via cholecystokinin-A and peripheral opioid receptors in rats.

    PubMed

    Pupovac, Jelena; Anderson, G Harvey

    2002-09-01

    We hypothesized that the digestion of proteins gives rise to peptides that initiate several satiety signals from the gut, and that the signals arising will be dependent on the protein source. The role of peripheral opioid and cholecystokinin (CCK)-A receptors was investigated. Casein, soy protein, and casein and soy hydrolysates were administered to rats by gavage (0.5 g protein/4 mL water). Food intake was measured over 2 h. The opioid receptor antagonist, naloxone methiodide (1.0 mg/kg) given intraperitoneally (i.p.), increased food intake when given at the same time as the hydrolysate preloads, 25 min after the casein preloads and 55 min after the soy protein preloads. The CCK-A receptor antagonist, devazepide (which reverses protein-induced food intake suppression), when given at 0.25 mg/kg, i.p., 60 min before preloads of each of three soy hydrolysates, also blocked suppression of food intake, but the strength and duration of the interaction depended on the preparation. When the two receptor antagonists were both administered with soy or casein preloads, their effects were additive. We conclude that peptides arising from digestion contribute to satiety by independent activation of both opioid and CCK-A receptors.

  20. Buprenorphine is a weak partial agonist that inhibits opioid receptor desensitization

    PubMed Central

    Virk, Michael S.; Arttamangkul, Seksiri; Birdsong, William T.; Williams, John T.

    2009-01-01

    Buprenorphine is a weak partial agonist at mu-opioid receptors that is used for treatment of pain and addiction. Intracellular and whole cell recordings were made from locus coeruleus (LC) neurons in rat brain slices to characterize the actions of buprenorphine. Acute application of buprenorphine caused a hyperpolarization that was prevented by previous treatment of slices with the irreversible opioid antagonist, β-chlornaltrexamine (β-CNA), but was not reversed by a saturating concentration of naloxone. As expected for a partial agonist, sub-saturating concentrations of buprenorphine decreased the [Met]5 enkephalin (ME) induced hyperpolarization or outward current. When the ME induced current was decreased below a critical value, desensitization and internalization of μ-opioid receptors (MOR) was eliminated. The inhibition of desensitization by buprenorphine was not the result of prior desensitization, slow dissociation from the receptor, or elimination of receptor reserve. Treatment of slices with sub-saturating concentrations of etorphine, methadone, oxymorphone or β-CNA also reduced the current induced by ME but did not block ME-induced desensitization. Treatment of animals with buprenorphine for a week resulted in the inhibition of the current induced by ME and a block of desensitization that was not different from the acute application of buprenorphine to brain slices. These observations show the unique characteristics of buprenorphine and further demonstrate the range of agonist selective actions that are possible through G-protein coupled receptors. PMID:19494155

  1. Opioid receptor agonists may favorably affect bone mechanical properties in rats with estrogen deficiency-induced osteoporosis.

    PubMed

    Janas, Aleksandra; Folwarczna, Joanna

    2017-02-01

    The results of epidemiological, clinical, and in vivo and in vitro experimental studies on the effect of opioid analgesics on bone are inconsistent. The aim of the present study was to investigate the effect of morphine (an agonist of opioid receptors), buprenorphine (a partial μ opioid receptor agonist and κ opioid receptor antagonist), and naloxone (an antagonist of opioid receptors) on the skeletal system of female rats in vivo. The experiments were carried out on 3-month-old Wistar rats, divided into two groups: nonovariectomized (intact; NOVX) rats and ovariectomized (OVX) rats. The bilateral ovariectomy was performed 7 days before the start of drug administration. Morphine hydrochloride (20 mg/kg/day s.c.), buprenorphine (0.05 mg/kg/day s.c.), or naloxone hydrochloride dihydrate (2 mg/kg/day s.c.) were administered for 4 weeks to NOVX and OVX rats. In OVX rats, the use of morphine and buprenorphine counteracted the development of osteoporotic changes in the skeletal system induced by estrogen deficiency. Morphine and buprenorphine beneficially affected also the skeletal system of NOVX rats, but the effects were much weaker than those in OVX rats. Naloxone generally did not affect the rat skeletal system. The results confirmed the role of opioid receptors in the regulation of bone remodeling processes and demonstrated, in experimental conditions, that the use of opioid analgesics at moderate doses may exert beneficial effects on the skeletal system, especially in estrogen deficiency.

  2. Recovery from Mu-opioid Receptor Desensitization following Chronic Treatment with Morphine and Methadone

    PubMed Central

    Quillinan, Nidia; Lau, Elaine; Virk, Michael; von Zastrow, Mark; Williams, John T

    2011-01-01

    Chronic treatment with morphine results in a decrease in mu-opioid receptor sensitivity, an increase in acute desensitization and a reduction in the recovery from acute desensitization in locus coeruleus neurons. With acute administration, morphine is unlike many other opioid agonists in that it does not mediate robust acute desensitization or induce receptor trafficking. This study compares mu-opioid receptor desensitization and trafficking in brain slices taken from rats treated for 6–7 days with a range of doses of morphine (60, 30, 15 mg/kg/day) and methadone (60, 30, 5 mg/kg/day) applied by subcutaneous implantation of osmotic mini pumps. Mice were treated with 45 mg/kg/day. In morphine treated animals, recovery from acute [Met]5enkephalin-induced desensitization and receptor recycling was diminished. In contrast, recovery and recycling were unchanged in slices from methadone treated animals. Remarkably the reduced recovery from desensitization and receptor recycling found in slices from morphine treated animals were not observed in animals lacking β-arrestin2. Further, pharmacological inhibition of GRK2, while not affecting the ability of [Met]5enkephalin to induce desensitization, acutely reversed the delay in recovery from desensitization produced by chronic morphine treatment. These results characterize a previously unidentified function of the GRK/arrestin system in mediating opioid regulation in response to chronic morphine administration. They also suggest that the GRK/arrestin system, rather then serving as a primary mediator of acute desensitization, controls recovery from desensitization by regulating receptor reinsertion to the plasma membrane after chronic treatment with morphine. The sustained GRK/arrestin dependent desensitization is another way in which morphine and methadone are distinguished. PMID:21430144

  3. Analgesia produced by exposure to 2450-MHz radiofrequency radiation (RFR) is mediated by brain mu- and kappa-opioid receptors

    SciTech Connect

    Salomon, G.; Park, E.J.; Quock, R.M. )

    1992-02-26

    This study was conducted to identify the opioid receptor subtype(s) responsible for RFR-induced analgesia. Male Swiss Webster mice, 20-25 g, were exposed to 20 mW/cm{sup 2} RFR in a 2,450-MHz waveguide system for 10 min, then tested 15 min later in the abdominal constriction paradigm which detects {mu}- and {kappa}-opioid activity. Immediately following RFR exposure, different groups of mice were pretreated intracerebroventricularly with different opioid receptor blockers with selectivity for {mu}- or {kappa}-opioid receptors. Results show that RFR-induced analgesia was attenuated by higher but not lower doses of the non-selective antagonist naloxone, but the selective {mu}-opioid antagonist {beta}-funaltrexamine and by the selective {kappa}-opioid antagonist norbinaltorphimine. RFR-induced analgesia was also reduced by subcutaneous pretreatment with 5.0 mg/kg of the {mu}-/{kappa}-opioid antagonist({minus})-5,9-diethyl-{alpha}-5,9-dialkyl-2{prime}-hydroxy-6,7-benzomorphan(MR-2266). These findings suggest that RFR-induced analgesia may be mediated by both {mu}- and {kappa}-opioid mechanisms.

  4. Abuse Potential and Pharmacodynamic Characteristics of Oral and Intranasal Eluxadoline, a Mixed μ- and κ-Opioid Receptor Agonist and δ-Opioid Receptor Antagonist

    PubMed Central

    McIntyre, G.; Bonifacio, L.; McDonnell, M.; Davenport, J. M.; Covington, P. S.; Dove, L. S.; Sellers, E. M.

    2016-01-01

    Drugs with μ-opioid receptor (OR) activity can be associated with abuse and misuse. The peripherally acting mixed μ-OR and κ-OR agonist and δ-OR antagonist eluxadoline is approved in the United States for the treatment of irritable bowel syndrome with diarrhea. In two separate crossover studies, we evaluated the oral and intranasal abuse potential of eluxadoline versus placebo and the active control oxycodone. Healthy recreational opioid users received eluxadoline 100, 300, and 1000 mg, oxycodone 30 and 60 mg, and placebo (oral study), or eluxadoline 100 and 200 mg, oxycodone 15 and 30 mg, and placebos matched to eluxadoline and oxycodone (intranasal study). In the oral study, Drug Liking Visual Analog Scale (VAS) peak (maximum) effect (Emax) score (primary endpoint) was significantly greater with eluxadoline 300 and 1000 mg versus placebo, but scores were significantly lower versus oxycodone. Following intranasal insufflation of eluxadoline, Drug Liking VAS Emax scores were not statistically different versus placebo, and were significantly lower versus oxycodone. Across other subjective measures, eluxadoline was generally similar to or disliked versus placebo. Pupillometry indicated no or minimal central effects with oral and intranasal eluxadoline, respectively. Adverse events of euphoric mood were reported with oral and intranasal eluxadoline but at a far lower frequency versus oxycodone. These data demonstrate that eluxadoline has less abuse potential than oxycodone in recreational opioid users. PMID:27647873

  5. Major Depressive Disorder and Kappa Opioid Receptor Antagonists

    PubMed Central

    Li, Wei; Sun, Huijiao; Chen, Hao; Yang, Xicheng; Xiao, Li; Liu, Renyu; Shao, Liming; Qiu, Zhuibai

    2016-01-01

    Major depressive disorder (MDD) is a common psychiatric disease worldwide. The clinical use of tricyclic antidepressants (TCAs), monoamine oxidase inhibitors (MAOIs) and selective serotonin reuptake inhibitors (SSRIs)/serotonin–norepinephrine reuptake inhibitor (SNRIs) for this condition have been widely accepted, but they were challenged by unacceptable side-effects, potential drug-drug interactions (DDIs) or slow onset/lack of efficacy. The endogenous opioid system is involved in stress and emotion regulatory processes and its role in MDD has been implicated. Although several KOR antagonists including JDTic and PF-04455242 were discontinued in early clinical trials, ALKS 5461 and CERC-501(LY-2456302) survived and entered into Phase-III and Phase-II trials, respectively. Considering the efficacy and safety of early off-label use of buprenorphine in the management of the treatment-resistant depression (TRD), it will be not surprising to predict the potential success of ALKS 5461 (a combination of buprenorphine and ALKS-33) in the near future. Moreover, CERC-501 will be expected to be available as monotherapy or adjuvant therapy with other first-line antidepressants in the treatment of TRD, if ongoing clinical trials continue to provide positive benefit-risk profiles. Emerging new researches might bring more drug candidates targeting the endogenous opioid system to clinical trials to address current challenges in MDD treatment in clinical practice. PMID:27213169

  6. New 2',6'-dimethyl-L-tyrosine (Dmt) opioid peptidomimetics based on the Aba-Gly scaffold. Development of unique mu-opioid receptor ligands.

    PubMed

    Ballet, Steven; Salvadori, Severo; Trapella, Claudio; Bryant, Sharon D; Jinsmaa, Yunden; Lazarus, Lawrence H; Negri, Lucia; Giannini, Elisa; Lattanzi, Roberta; Tourwé, Dirk; Balboni, Gianfranco

    2006-06-29

    The Aba-Gly scaffold, incorporated into Dmt-Tic ligands (H-Dmt-Tic-Gly-NH-CH2-Ph, H-Dmt-Tic-Gly-NH-Ph, H-Dmt-Tic-NH-CH2-Bid), exhibited mixed micro/delta or delta opioid receptor activities with micro agonism. Substitution of Tic by Aba-Gly coupled to -NH-CH2-Ph (1), -NH-Ph (2), or -Bid (Bid=1H-benzimidazole-2-yl) (3) shifted affinity (Ki(micro)=0.46, 1.48, and 19.9 nM, respectively), selectivity, and bioactivity to micro-opioid receptors. These compounds represent templates for a new class of lead opioid agonists that are easily synthesized and suitable for therapeutic pain relief.

  7. Antagonism of κ opioid receptor in the nucleus accumbens prevents the depressive-like behaviors following prolonged morphine abstinence.

    PubMed

    Zan, Gui-Ying; Wang, Qian; Wang, Yu-Jun; Liu, Yao; Hang, Ai; Shu, Xiao-Hong; Liu, Jing-Gen

    2015-09-15

    The association between morphine withdrawal and depressive-like symptoms is well documented, however, the role of dynorphin/κ opioid receptor system and the underlying neural substrates have not been fully understood. In the present study, we found that four weeks morphine abstinence after a chronic escalating morphine regimen significantly induced depressive-like behaviors in mice. Prodynorphin mRNA and protein levels were increased in the nucleus accumbens (NAc) after four weeks of morphine withdrawal. Local injection of κ opioid receptor antagonist nor-Binaltorphimine (norBNI) in the NAc significantly blocked the expression of depressive-like behaviors without influencing general locomotor activity. Thus, the present study extends previous findings by showing that prolonged morphine withdrawal-induced depressive-like behaviors are regulated by dynorphin/κ opioid receptor system, and shed light on the κ opioid receptor antagonists as potential therapeutic agents for the treatment of depressive-like behaviors induced by opiate withdrawal.

  8. Human Mu Opioid Receptor (OPRM1 A118G) polymorphism is associated with brain mu-opioid receptor binding potential in smokers

    PubMed Central

    Ray, Riju; Ruparel, Kosha; Newberg, Andrew; Wileyto, E. Paul; Loughead, James W.; Divgi, Chaitanya; Blendy, Julie A.; Logan, Jean; Zubieta, Jon-Kar; Lerman, Caryn

    2011-01-01

    Evidence points to the endogenous opioid system, and the mu-opioid receptor (MOR) in particular, in mediating the rewarding effects of drugs of abuse, including nicotine. A single nucleotide polymorphism (SNP) in the human MOR gene (OPRM1 A118G) has been shown to alter receptor protein level in preclinical models and smoking behavior in humans. To clarify the underlying mechanisms for these associations, we conducted an in vivo investigation of the effects of OPRM1 A118G genotype on MOR binding potential (BPND or receptor availability). Twenty-two smokers prescreened for genotype (12 A/A, 10 */G) completed two [11C]carfentanil positron emission tomography (PET) imaging sessions following overnight abstinence and exposure to a nicotine-containing cigarette and a denicotinized cigarette. Independent of session, smokers homozygous for the wild-type OPRM1 A allele exhibited significantly higher levels of MOR BPND than smokers carrying the G allele in bilateral amygdala, left thalamus, and left anterior cingulate cortex. Among G allele carriers, the extent of subjective reward difference (denicotinized versus nicotine cigarette) was associated significantly with MOR BPND difference in right amygdala, caudate, anterior cingulate cortex, and thalamus. Future translational investigations can elucidate the role of MORs in nicotine addiction, which may lead to development of novel therapeutics. PMID:21576462

  9. Human Mu Opioid Receptor (OPRM1A118G) polymorphism is associated with brain mu- opioid receptor binding potential in smokers

    SciTech Connect

    Ray, R.; Logan, J.; Ray, R.; Ruparel, K.; Newberg, A.; Wileyto, E.P.; Loughead, J.W.; Divgi, C.; Blendy, J.A.; Logan, J.; Zubieta, J.-K.; Lerman, C.

    2011-04-15

    Evidence points to the endogenous opioid system, and the mu-opioid receptor (MOR) in particular, in mediating the rewarding effects of drugs of abuse, including nicotine. A single nucleotide polymorphism (SNP) in the human MOR gene (OPRM1 A118G) has been shown to alter receptor protein level in preclinical models and smoking behavior in humans. To clarify the underlying mechanisms for these associations, we conducted an in vivo investigation of the effects of OPRM1 A118G genotype on MOR binding potential (BP{sub ND} or receptor availability). Twenty-two smokers prescreened for genotype (12 A/A, 10 */G) completed two [{sup 11}C] carfentanil positron emission tomography (PET) imaging sessions following overnight abstinence and exposure to a nicotine-containing cigarette and a denicotinized cigarette. Independent of session, smokers homozygous for the wild-type OPRM1 A allele exhibited significantly higher levels of MOR BP{sub ND} than smokers carrying the G allele in bilateral amygdala, left thalamus, and left anterior cingulate cortex. Among G allele carriers, the extent of subjective reward difference (denicotinized versus nicotine cigarette) was associated significantly with MOR BP{sub ND} difference in right amygdala, caudate, anterior cingulate cortex, and thalamus. Future translational investigations can elucidate the role of MORs in nicotine addiction, which may lead to development of novel therapeutics.

  10. Galpha-subunits differentially alter the conformation and agonist affinity of kappa-opioid receptors.

    PubMed

    Yan, Feng; Mosier, Philip D; Westkaemper, Richard B; Roth, Bryan L

    2008-02-12

    Although ligand-induced conformational changes in G protein-coupled receptors (GPCRs) are well-documented, there is little direct evidence for G protein-induced changes in GPCR conformation. To investigate this possibility, the effects of overexpressing Galpha-subunits (Galpha16 or Galphai2) with the kappa-opioid receptor (KOR) were examined. The changes in KOR conformation were subequently examined via the substituted cysteine accessibility method (SCAM) in transmembrane domains 6 (TM6) and 7 (TM7) and extracellular loop 2 (EL2). Significant conformational changes were observed on TM7, the extracellular portion of TM6, and EL2. Seven SCAM-sensitive residues (S3107.33, F3147.37, and I3167.39 to Y3207.43) on TM7 presented a cluster pattern when the KOR was exposed to baseline amounts of G protein, and additional residues became sensitive upon overexpression of various G proteins. In TM7, S3117.34 and N3267.49 were found to be sensitive in Galpha16-overexpressed cells and Y3137.36, N3227.45, S3237.46, and L3297.52 in Galphai2-overexpressed cells. In addition, the degree of sensitivity for various TM7 residues was augmented, especially in Galphai2-overexpressed cells. A similar phenomenon was also observed for residues in TM6 and EL2. In addition to an enhanced sensitivity of certain residues, our findings also indicated that a slight rotation was predicted to occur in the upper part of TM7 upon G protein overexpression. These relatively modest conformational changes engendered by G protein overexpression had both profound and differential effects on the abilities of agonists to bind to KOR. These data are significant because they demonstrate that Galpha-subunits differentially modulate the conformation and agonist affinity of a prototypical GPCR.

  11. mu-Opioid receptor-independent fashion of the suppression of sodium currents by mu-opioid analgesics in thalamic neurons.

    PubMed

    Hashimoto, Keisuke; Amano, Taku; Kasakura, Akiko; Uhl, George R; Sora, Ichiro; Sakai, Norio; Kuzumaki, Naoko; Suzuki, Tsutomu; Narita, Minoru

    2009-03-27

    Most reports in the literature have shown that the effects of opioid analgesics are primarily mediated by mu-opioid receptor (MOR), whereas other potential targets of opioid analgesics have not been thoroughly characterized. In this study, we found that extracellular application of morphine, fentanyl or oxycodone, which are all considered to be MOR agonists, at relatively high concentrations, but not endogenous mu-opioid peptides, produced a concentration-dependent suppression of sodium currents in cultured thalamic neurons. These effects of opioids were not affected by either a MOR antagonist naloxone or a deletion of MOR gene. Among these opioids, fentanyl strongly suppressed sodium currents to the same degree as lidocaine, and both morphine and oxycodone slightly but significantly reduced sodium currents when they were present extracellularly. In contrast, the intracellular application of morphine, but not oxycodone, fentanyl or lidocaine, reduced sodium currents. These results suggest that morphine, fentanyl and oxycodone each produce the MOR-independent suppression of sodium currents by distinct mechanisms in thalamic neurons.

  12. Ligands Raise the Constraint That Limits Constitutive Activation in G Protein-coupled Opioid Receptors*

    PubMed Central

    Vezzi, Vanessa; Onaran, H. Ongun; Molinari, Paola; Guerrini, Remo; Balboni, Gianfranco; Calò, Girolamo; Costa, Tommaso

    2013-01-01

    Using a cell-free bioluminescence resonance energy transfer strategy we compared the levels of spontaneous and ligand-induced receptor-G protein coupling in δ (DOP) and μ (MOP) opioid receptors. In this assay GDP can suppress spontaneous coupling, thus allowing its quantification. The level of constitutive activity was 4–5 times greater at the DOP than at the MOP receptor. A series of opioid analogues with a common peptidomimetic scaffold displayed remarkable inversions of efficacy in the two receptors. Agonists that enhanced coupling above the low intrinsic level of the MOP receptor were inverse agonists in reducing the greater level of constitutive coupling of the DOP receptor. Yet the intrinsic activities of such ligands are identical when scaled over the GDP base line of both receptors. This pattern is in conflict with the predictions of the ternary complex model and the “two state” extensions. According to this theory, the order of spontaneous and ligand-induced coupling cannot be reversed if a shift of the equilibrium between active and inactive forms raises constitutive activation in one receptor type. We propose that constitutive activation results from a lessened intrinsic barrier that restrains spontaneous coupling. Any ligand, regardless of its efficacy, must enhance this constraint to stabilize the ligand-bound complexed form. PMID:23836900

  13. Ligands raise the constraint that limits constitutive activation in G protein-coupled opioid receptors.

    PubMed

    Vezzi, Vanessa; Onaran, H Ongun; Molinari, Paola; Guerrini, Remo; Balboni, Gianfranco; Calò, Girolamo; Costa, Tommaso

    2013-08-16

    Using a cell-free bioluminescence resonance energy transfer strategy we compared the levels of spontaneous and ligand-induced receptor-G protein coupling in δ (DOP) and μ (MOP) opioid receptors. In this assay GDP can suppress spontaneous coupling, thus allowing its quantification. The level of constitutive activity was 4-5 times greater at the DOP than at the MOP receptor. A series of opioid analogues with a common peptidomimetic scaffold displayed remarkable inversions of efficacy in the two receptors. Agonists that enhanced coupling above the low intrinsic level of the MOP receptor were inverse agonists in reducing the greater level of constitutive coupling of the DOP receptor. Yet the intrinsic activities of such ligands are identical when scaled over the GDP base line of both receptors. This pattern is in conflict with the predictions of the ternary complex model and the "two state" extensions. According to this theory, the order of spontaneous and ligand-induced coupling cannot be reversed if a shift of the equilibrium between active and inactive forms raises constitutive activation in one receptor type. We propose that constitutive activation results from a lessened intrinsic barrier that restrains spontaneous coupling. Any ligand, regardless of its efficacy, must enhance this constraint to stabilize the ligand-bound complexed form.

  14. Epigenetic Activation of μ-Opioid Receptor Gene via Increased Expression and Function of Mitogen- and Stress-Activated Protein Kinase 1.

    PubMed

    Wagley, Yadav; Law, Ping-Yee; Wei, Li-Na; Loh, Horace H

    2017-04-01

    Since the discovery of μ-opioid receptor (MOR) gene two decades ago, various regulatory factors have been shown to interact with the MOR promoter and modulate transcript levels. However, the majority of early transcriptional studies on MOR gene have not addressed how intracellular signaling pathways mediate extracellular modulators. In this study, we demonstrate that MOR epigenetic regulation requires multiple coordinated signals converging at the MOR promoter, involving mitogen-activated protein kinase (MAPK) activation and mitogen- and stress-activated protein kinase 1 (MSK1)-ranges of intracellular signaling pathways similar to those activated by opioid agonists. Inhibiting p38 MAPK or extracellular signal-regulated kinase (ERK) 1/2 MAPK (upstream activators of MSK1) reduced MOR expression levels; accordingly, the functional role of MSK1, but not MSK2, was demonstrated using genetic approaches. However, for maximal MSK1 effect, an open chromatin configuration was required, because in vitro CpG methylation of the MOR promoter abolished MSK1 activity. Finally, endogenous MSK1 levels concomitantly increased to regulate MOR gene expression during neuronal differentiation of P19 cells, suggesting a conserved role of this kinase in the epigenic activation of MOR in neurons. Taken together, our findings indicate that the expression of MOR gene requires the activity of intracellular signaling pathways that have been implicated in the behavioral outcomes of opioid drugs, which suggests that an autoregulatory mechanism may function in opioid systems.

  15. δ-Opioid receptors in the accumbens shell mediate the influence of both excitatory and inhibitory predictions on choice

    PubMed Central

    Laurent, Vincent; Wong, Felix L; Balleine, Bernard W

    2015-01-01

    BACKGROUND AND PURPOSE Stimuli that predict rewarding events can control choice between future actions, and this control could be mediated by δ-opioid receptors in the nucleus accumbens shell (NAc-S). Stimuli predicting the absence of important events can also guide choice, although it remains unknown whether they do so via changes in an accumbal δ-opioid receptor-related process. EXPERIMENTAL APPROACH δ-opioid receptor-eGFP mice were trained to perform two instrumental actions that delivered different food outcomes. Choice between the two actions was then tested in the presence of stimuli paired with either the delivery or the non-delivery of each of the two outcomes. Bilateral infusions of the δ-opioid receptor antagonist naltrindole into the NAc-S were used to determine the role of these receptors at the time of choice and δ-opioid receptor expression in the NAc-S used to assess functional activity. KEY RESULTS A stimulus predicting a specific outcome biased choice performance towards the action previously earning that same outcome. In contrast, a stimulus signalling the absence of that outcome biased performance away from the action that delivered that outcome towards actions associated with the absence of that outcome. Both effects were associated with increased δ-opioid receptor expression on the membrane of cholinergic interneurons within the NAc-S. Furthermore, both effects were blocked by naltrindole infused into the NAc-S. CONCLUSIONS AND IMPLICATIONS These findings suggest that δ-opioid receptors in the NAc-S were involved in the effects of predictive learning on choice between actions, whether those predictions involve the presence or absence of specific rewarding events. LINKED ARTICLES This article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-2 PMID:24758591

  16. Effect of prenatal methadone and ethanol on opioid receptor development in rats

    SciTech Connect

    Peters, M.A.; Braun, R.L. )

    1991-03-11

    The current literature shows that the offspring of female rats exposed to methadone or ethanol display similar neurochemical and neurobehavioral alterations, and suggests that these drugs may be operating through a common mechanism. If this hypothesis is true, their effect on the endogenous opioid systems should be qualitatively similar. In this study virgin females were treated with methadone or 10% ethanol oral solution starting prior to conception and continued throughout gestation. When the offspring had reached 15 or 30 days of age they were sacrificed, the brain was removed and prepared for opioid receptor binding studies. ({sup 3}H)DAGO and ({sup 3}H)DADLE were used as ligands for the mu and delta receptors, respectively. These studies show significant treatment-related differences in both the number of mu and delta binding sites as well as in apparent receptor affinity. Significant sex- and age-related differences between treatments were also observed. These data show that methadone and ethanol, while manifesting some similar neurochemical and behavioral effects, have unique effects on opioid receptor binding, suggesting that they may be acting by different mechanisms.

  17. Coupling of human delta-opioid receptor to retinal rod transducin in Chinese hamster ovary cells.

    PubMed

    Varga, E V; Stropova, D; Kim, T; Wang, M; Roeske, W R; Yamamura, H I

    2000-01-01

    Reverse transcription-polymerase chain reaction was used to identify the pertussis toxin (Ptx)-sensitive G protein alpha-subunit pool in Chinese hamster ovary (CHO) and mouse fibroblast (B82) cells. We detected the presence of mRNA for G(ialpha2), G(ialpha3), and G(oalpha) in both cell lines. G(ialpha1) and G(alphaz) mRNAs were not detected. We also found a homolog of the retinal rod transducin (G(talpha1)) in CHO, and the mouse cone transducin (G(talpha2)) in B82 cells. The presence of the transducin alpha-subunit proteins in CHO and B82 cells was confirmed by immunoprecipitation with specific antibodies. To test the interaction of heterologously expressed receptors with transducin in CHO cells, a Ptx-insensitive (C347S) rod transducin mutant was transfected into a CHO cell line stably expressing the human delta-opioid receptor (hDOR/CHO). (+)-4-[(alphaR)-alpha-((2S,2R)-4-allyl-2, 5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide, a selective delta-opioid receptor agonist, stimulated guanosine-5'-O-(3-[(35)S]thio)triphosphate binding by 293 +/- 36% after Ptx pretreatment in the mutant cell line with an EC(50) value of 54 +/- 32 nM, showing that transducin can functionally couple to the human delta-opioid receptors in these cells.

  18. In vivo receptor binding of opioid drugs at the mu site

    SciTech Connect

    Rosenbaum, J.S.; Holford, N.H.; Sadee, W.

    1985-06-01

    The in vivo receptor binding of a series of opioid drugs was investigated in intact rats after s.c. administration of (/sup 3/H)etorphine tracer, which selectively binds to mu sites in vivo. Receptor binding was determined by a membrane filtration assay immediately after sacrifice of the animals and brain homogenization. Coadministration of unlabeled opioid drugs together with tracer led to a dose-dependent decrease of in vivo tracer binding. Estimates of the doses required to occupy 50% of the mu sites in vivo established the following potency rank order: diprenorphine, naloxone, buprenorphine, etorphine, levallorphan, cyclazocine, sufentanil, nalorphine, ethylketocyclazocine, ketocyclazocine, pentazocine, morphine. In vivo-in vitro differences among the relative receptor binding potencies were only partially accounted for by differences in their access to the brain and the regulatory effects of Na+ and GTP, which are expected to reduce agonist affinities in vivo. The relationship among mu receptor occupancy in vivo and pharmacological effects of the opioid drugs is described.

  19. Specific binding of a ligand of sigma-opioid receptors - N-allylnormetazocine (SKF 10047) - with liver membranes

    SciTech Connect

    Samovilova, N.N.; Yarygin, K.N.; Vinogradov, V.A.

    1986-08-01

    A ligand of the sigma-opioid receptors - N-allylnormetazocine (SKF 10047) -binds specifically and reversible with rat liver membranes. In relation to a number of properties, the sites binding SKF 10047 in the liver are similar to the sigma-opioid receptors of the central nervous system. They do not interact with classical opiates (morphine, naloxone) and with opioid peptides, but bind well benzomorphans (bremazocine, SKF 10047) and a number of compounds of different chemical structures with a pronounced psychtropic action (haloperidol, imipramine, phencyclidine, etc.).

  20. Targeting Itch with Ligands Selective for κ Opioid Receptors.

    PubMed

    Cowan, Alan; Kehner, George B; Inan, Saadet

    2015-01-01

    Several chemically diverse pruritogens, including bombesin, compound 48/80, norbinaltorphimine, and 5'-GNTI, cause rodents to scratch excessively in a stable, uniform manner and consequently provide convenient animal models of itch against which potential antipruritics may be evaluated, structure-activity relationships established, and the nature of spontaneous, repetitive behavior itself analyzed. Decreasing the number of scratching bouts in these apparently simple models has been the requisite first step in the progress of kappa opioid agonists such as nalbuphine, asimadoline, and CR845 toward clinical testing as antipruritics. Nalfurafine is the prime example of a kappa agonist spanning the developmental divide between scratching mice models and commercialization within 10 years. Patients undergoing hemodialysis and suffering from the itching associated with uremic pruritus, and potentially those inflicted with atopic dermatitis, are the beneficiaries.

  1. The Dynorphin-Kappa Opioid System as a Modulator of Stress-induced and Pro-addictive Behaviors

    PubMed Central

    Bruchas, M.R.; Land, B.B.; Chavkin, C.

    2009-01-01

    Stress is a complex experience that carries both aversive and motivating properties. Chronic stress causes an increase in the risk of depression, is well known to increase relapse of drug seeking behavior, and can adversely impact health. Several brain systems have been demonstrated to be critical in mediating the negative affect associated with stress, and recent evidence directly links the actions of the endogenous opioid neuropeptide dynorphin in modulating mood and increasing the rewarding effects of abused drugs. These results suggest that activation of the dynorphin/kappa opioid receptor (KOR) system is likely to play a major role in the pro-addictive effects of stress. This review explores the relationship between dynorphin and corticotropin releasing factor (CRF) in the induction of dysphoria, the potentiation of drug seeking, and stress-induced reinstatement. We also provide an overview of the signal transduction events responsible for CRF and dynorphin/KOR-dependent behaviors. Understanding the recent work linking activation of CRF and dynorphin/KOR systems and their specific roles in brain stress systems and behavioral models of addiction provides novel insight to neuropeptide systems that regulate affective state. PMID:19716811

  2. 2012 David W. Robertson Award for Excellence in Medicinal Chemistry: Neoclerodanes as Atypical Opioid Receptor Ligands⊥

    PubMed Central

    Prisinzano, Thomas E.

    2013-01-01

    The neoclerodane diterpene salvinorin A is the major active component of the hallucinogenic mint plant Salvia divinorum Epling & Játiva (Lamiaceae). Since the finding that salvinorin A exerts its potent psychotropic actions through the activation of opioid receptors, the site of action of morphine and related analogues, there has been much interest in elucidating the underlying mechanisms behind its effects. These effects are particularly remarkable, because (1) salvinorin A is the first reported non-nitrogenous opioid receptor agonist, and (2) its effects are not mediated through the previously investigated targets of psychotomimetics. This perspective outlines our research program, illustrating a new direction to the development of tools to further elucidate the biological mechanisms of drug tolerance and dependence. The information gained from these efforts is expected to facilitate the design of novel agents to treat pain, drug abuse, and other CNS disorders. PMID:23548164

  3. Endomorphins 1 and 2, endogenous mu-opioid receptor agonists, impair passive avoidance learning in mice.

    PubMed

    Ukai, M; Watanabe, Y; Kameyama, T

    2001-06-08

    The effects of intracerebroventricular administration of endomorphin-1 and endomorphin-2, endogenous mu-opioid receptor agonists, on passive avoidance learning associated with long-term memory were investigated in mice. Endomorphin-1 (10 and 17.5 microg) and endomorphin-2 (17.5 microg) produced a significant decrease in step-down latency in a passive avoidance learning task. beta-Funaltrexamine (5 microg) almost completely reversed the endomorphin-1 (17.5 microg)- and endomorphin-2 (17.5 microg)-induced shortening of step-down latency, although neither naltrindole (4 ng) nor nor-binaltorphimine (4 microg) produced any significant effects on the effects of endomorphins 1 and 2. These results suggest that endomorphins 1 and 2 impair long-term memory through the mediation of mu-opioid receptors in the brain.

  4. Synthesis of quinolinomorphinan-4-ol derivatives as δ opioid receptor agonists.

    PubMed

    Ida, Yoshihiro; Nemoto, Toru; Hirayama, Shigeto; Fujii, Hideaki; Osa, Yumiko; Imai, Masayuki; Nakamura, Takashi; Kanemasa, Toshiyuki; Kato, Akira; Nagase, Hiroshi

    2012-01-15

    The previously reported morphinan derivative SN-28 showed high selectivity and agonist activity for the δ opioid receptor. In the course of examining the structure-activity relationship of SN-28 derivatives, the derivatives with the 4-hydroxy group (SN-24, 26, 27) showed higher selectivities for the δ receptor over the μ receptor than the corresponding SN-28 derivatives with the 3-hydroxy group (SN-11, 23, 28). Derivatives with the 4-hydroxy group showed potent agonist activities for the δ receptor in the [(35)S]GTPγS binding assay. Although the 17-cyclopropylmethyl derivative (SN-11) with a 3-hydroxy group showed the lowest selectivity for the δ receptor among the morphinan derivatives, the agonist activity toward the δ receptor was the most potent for candidates with the 3-hydroxy group.

  5. Photoaffinity labeling of opioid receptor with morphine-7,8-oxide (morphine epoxide)

    SciTech Connect

    Takayanagi, I.; Shibata, R.; Miyata, N.; Hirobe, M.

    1982-05-01

    The opioid receptor mediating inhibitory action of morphine in the electrically stimulated guinea pig ileum was irreversibly photoinactivated by morphine epoxide (3 X 10(-6) M). Morphine epoxide (up to 3 X 10(-5) M) did not influence the responses of rat vas deferens (epsilon-receptor) or rabbit vas deferens (kappa-receptor) to electrical stimulation. Effective concentrations of morphine epoxide were much lower in the guinea pig ileum (mu-receptor) than in the mouse vas deference (delta-receptor). The inhibitory action of (Met)-enkephalin on the twitch responses of the rat vas deferens and mouse vas deferens to electrical stimulation were not influenced after irradiation in the presence of morphine epoxide (3 X 10(-6) M). Therefore, morphine epoxide is probably a useful probe for photoaffinity labeling of the mu-receptor in vitro.

  6. In vivo visualization of delta opioid receptors upon physiological activation uncovers a distinct internalization profile

    PubMed Central

    FAGET, Lauren; ERBS, Eric; LE MERRER, Julie; SCHERRER, Gregory; MATIFAS, Audrey; BENTURQUIA, Nadia; NOBLE, Florence; DECOSSAS, Marion; KOCH, Marc; KESSLER, Pascal; VONESCH, Jean-Luc; SCHWAB, Yannick; KIEFFER, Brigitte L.; MASSOTTE, Dominique

    2012-01-01

    G protein-coupled receptors (GPCRs) mediate numerous physiological functions and represent prime therapeutic targets. Receptor trafficking upon agonist stimulation is critical for GPCR function, but examining this process in vivo remains a true challenge. Using knock-in mice expressing functional fluorescent delta opioid receptors under the control of the endogenous promoter, we visualized in vivo internalization of this native GPCR upon physiological stimulation. We developed a paradigm in which animals were made dependent to morphine in a drug-paired context. When re-exposed to this context in a drug-free state, mice showed context-dependent withdrawal signs and activation of the hippocampus. Receptor internalization was transiently detected in a subset of CA1 neurons, uncovering regionally restricted opioid peptide release. Importantly, a pool of surface receptors always remained, which contrasts with the in vivo profile previously established for exogenous drug-induced internalization. Therefore, a distinct response is observed at the receptor level upon a physiological or pharmacological stimulation. Altogether, direct in vivo GPCR visualization enables mapping receptor stimulation promoted by a behavioral challenge, and represents a powerful approach to study endogenous GPCR physiology. PMID:22623675

  7. In vivo visualization of delta opioid receptors upon physiological activation uncovers a distinct internalization profile.

    PubMed

    Faget, Lauren; Erbs, Eric; Le Merrer, Julie; Scherrer, Gregory; Matifas, Audrey; Benturquia, Nadia; Noble, Florence; Decossas, Marion; Koch, Marc; Kessler, Pascal; Vonesch, Jean-Luc; Schwab, Yannick; Kieffer, Brigitte L; Massotte, Dominique

    2012-05-23

    G-protein-coupled receptors (GPCRs) mediate numerous physiological functions and represent prime therapeutic targets. Receptor trafficking upon agonist stimulation is critical for GPCR function, but examining this process in vivo remains a true challenge. Using knock-in mice expressing functional fluorescent delta opioid receptors under the control of the endogenous promoter, we visualized in vivo internalization of this native GPCR upon physiological stimulation. We developed a paradigm in which animals were made dependent on morphine in a drug-paired context. When re-exposed to this context in a drug-free state, mice showed context-dependent withdrawal signs and activation of the hippocampus. Receptor internalization was transiently detected in a subset of CA1 neurons, uncovering regionally restricted opioid peptide release. Importantly, a pool of surface receptors always remained, which contrasts with the in vivo profile previously established for exogenous drug-induced internalization. Therefore, a distinct response is observed at the receptor level upon a physiological or pharmacological stimulation. Altogether, direct in vivo GPCR visualization enables mapping receptor stimulation promoted by a behavioral challenge and represents a powerful approach to study endogenous GPCR physiology.

  8. μ-Opioid Receptor Gene A118G Polymorphism Predicts Survival in Patients with Breast Cancer

    PubMed Central

    Bortsov, Andrey V.; Millikan, Robert C.; Belfer, Inna; Boortz-Marx, Richard L.; Arora, Harendra; McLean, Samuel A.

    2012-01-01

    Background Preclinical studies suggest that opioids may promote tumor growth. Genetic polymorphisms have been shown to affect opioid receptor function and to modify the clinical effects of morphine. In this study we assessed the association between six common polymorphisms in the μ-opioid receptor gene, including the well known A118G polymorphism, and breast cancer survival. Methods A total of 2,039 women ages 23–74 yr (38% African American, 62% European American, 55% postmenopausal) diagnosed with breast cancer between 1993 – 2001 were followed through 2006. Genotyping was performed using the TaqMan platform (Applied Biosystems Inc., Foster City, CA). Kaplan-Meyer curves, log-rank tests, and Cox proportional hazard models were used to examine the association between each genotype and survival. Results After Bonferroni adjustment for multiple testing, patient genotype at A118G was associated with breast cancer-specific mortality at 10 yr. Women with one or more copies of the G allele had decreased breast cancer-specific mortality (p < .001). This association was limited to invasive cases only; effect size appeared to increase with clinical stage. Cox regression model adjusted for age and ethnicity also showed decreased mortality in A/G and G/G genotypes compared to A/A genotype (hazard ratio = 0.57 [0.38, 0.85] and 0.32 [0.22, 0.49], respectively; p = .006). Conclusions These results suggest that opioid pathways may be involved in tumor growth. Further studies examining the association between genetic variants influencing opioid system function and cancer survival are warranted. PMID:22433205

  9. Synthetic studies of neoclerodane diterpenes from Salvia divinorum: preparation and opioid receptor activity of salvinicin analogues.

    PubMed

    Simpson, Denise S; Katavic, Peter L; Lozama, Anthony; Harding, Wayne W; Parrish, Damon; Deschamps, Jeffrey R; Dersch, Christina M; Partilla, John S; Rothman, Richard B; Navarro, Hernan; Prisinzano, Thomas E

    2007-07-26

    Further modification of salvinorin A (1a), the major active component of Salvia divinorum, has resulted in the synthesis of novel neoclerodane diterpenes with opioid receptor affinity and activity. We report in this study that oxadiazole 11a and salvidivin A (12a), a photooxygenation product of 1a, have been identified as the first neoclerodane diterpenes with kappa antagonist activity. This indicates that additional structural modifications of 1a may lead to analogues with higher potency and utility as drug abuse medications.

  10. Intact brain cells: a novel model system for studying opioid receptor binding

    SciTech Connect

    Rogers, N.F.; El-Fakahany, E.E.

    1985-07-29

    The use of a novel tissue preparation to study opioid receptor binding in viable, intact cells derived from whole brains of adult rats is presented. Mechanically dissociated and sieved cells, which were not homogenized at any stage of the experimental protocol, and iso-osmotic physiological buffer were used in these experiments. This system was adapted in order to avoid mechanical and chemical disruption of cell membranes, cytoskeletal ultrastructure or receptor topography by homogenization or by the use of nonphysiological buffers, and to mimic in vivo binding conditions as much as possible. Using (/sup 3/H)naloxone as the radioligand, the studies showed saturable and stereospecific high-affinity binding of this opioid antagonist in intact cells, which in turn showed consistently high viability. (/sup 3/H)Naloxone binding was also linear over a wide range of tissue concentrations. This technique provides a very promising model for future studies of the binding of opioids and of many other classes of drugs to brain tissue receptors in a more physiologically relevant system than those commonly used to date.

  11. Crystal structure of the µ-opioid receptor bound to a morphinan antagonist.

    PubMed

    Manglik, Aashish; Kruse, Andrew C; Kobilka, Tong Sun; Thian, Foon Sun; Mathiesen, Jesper M; Sunahara, Roger K; Pardo, Leonardo; Weis, William I; Kobilka, Brian K; Granier, Sébastien

    2012-03-21

    Opium is one of the world's oldest drugs, and its derivatives morphine and codeine are among the most used clinical drugs to relieve severe pain. These prototypical opioids produce analgesia as well as many undesirable side effects (sedation, apnoea and dependence) by binding to and activating the G-protein-coupled µ-opioid receptor (µ-OR) in the central nervous system. Here we describe the 2.8 Å crystal structure of the mouse µ-OR in complex with an irreversible morphinan antagonist. Compared to the buried binding pocket observed in most G-protein-coupled receptors published so far, the morphinan ligand binds deeply within a large solvent-exposed pocket. Of particular interest, the µ-OR crystallizes as a two-fold symmetrical dimer through a four-helix bundle motif formed by transmembrane segments 5 and 6. These high-resolution insights into opioid receptor structure will enable the application of structure-based approaches to develop better drugs for the management of pain and addiction.

  12. Crystal structure of the[mu]-opioid receptor bound to a morphinan antagonist

    SciTech Connect

    Manglik, Aashish; Kruse, Andrew C.; Kobilka, Tong Sun; Thian, Foon Sun; Mathiesen, Jesper M.; Sunahara, Roger K.; Pardo, Leonardo; Weis, William I.; Kobilka, Brian K.; Granier, Sébastien

    2012-06-27

    Opium is one of the world's oldest drugs, and its derivatives morphine and codeine are among the most used clinical drugs to relieve severe pain. These prototypical opioids produce analgesia as well as many undesirable side effects (sedation, apnoea and dependence) by binding to and activating the G-protein-coupled {mu}-opioid receptor ({mu}-OR) in the central nervous system. Here we describe the 2.8 {angstrom} crystal structure of the mouse {mu}-OR in complex with an irreversible morphinan antagonist. Compared to the buried binding pocket observed in most G-protein-coupled receptors published so far, the morphinan ligand binds deeply within a large solvent-exposed pocket. Of particular interest, the {mu}-OR crystallizes as a two-fold symmetrical dimer through a four-helix bundle motif formed by transmembrane segments 5 and 6. These high-resolution insights into opioid receptor structure will enable the application of structure-based approaches to develop better drugs for the management of pain and addiction.

  13. Intracerebroventricular administration of morphine confers remote cardioprotection--role of opioid receptors and calmodulin.

    PubMed

    Zhang, Ye; Irwin, Michael G; Lu, Yao; Mei, Bin; Zuo, You-Mei; Chen, Zhi-Wu; Wong, Tak-Ming

    2011-04-10

    The current study aimed to delineate the mechanism of remote preconditioning by intracerebroventricular morphine (RMPC) against myocardial ischemia-reperfusion injury. Male Sprague-Dawley rats were given an intracerebroventricular morphine injection before myocardial ischemia and reperfusion injury. Ischemia-reperfusion injury was achieved by 30min of left coronary artery occlusion followed by 120min of reperfusion. The effects of remote preconditioning by intracerebroventricular morphine preconditioning were also determined upon selective blockade of the δ, κ or μ-opioid receptors, or calmodulin (CaM). The infarct size, as a percentage of the area at risk, was determined by 2,3,5-triphenyltetrazolium staining. Remote preconditioning by intracerebroventricular morphine reduced infarct size in the ischemic/reperfused myocardium, and the effect was abolished by the selective blockade of any one of the three δ, κ and μ opioid receptors or CaM. Furthermore, remote preconditioning by intracerebroventricular morphine increased the expression of CaM in the hippocampus and the plasma level of calcitonin gene-related peptide (CGRP). The results of the present study provide evidence that the cardioprotection of remote preconditioning by intracerebroventricular morphine involves not only all three types of opioid receptors in the central nervous system, but also CaM, which releases CGRP, one of the mediators of remote preconditioning.

  14. The neural mobilization technique modulates the expression of endogenous opioids in the periaqueductal gray and improves muscle strength and mobility in rats with neuropathic pain

    PubMed Central

    2014-01-01

    Background The neural mobilization (NM) technique is a noninvasive method that has been proven to be clinically effective in reducing pain; however, the molecular mechanisms involved remain poorly understood. The aim of this study was to analyze whether NM alters the expression of the mu-opioid receptor (MOR), the delta-opioid receptor (DOR) and the Kappa-opioid receptor (KOR) in the periaqueductal gray (PAG) and improves locomotion and muscle force after chronic constriction injury (CCI) in rats. Methods The CCI was imposed on adult male rats followed by 10 sessions of NM every other day, starting 14 days after the CCI injury. At the end of the sessions, the PAG was analyzed using Western blot assays for opioid receptors. Locomotion was analyzed by the Sciatic functional index (SFI), and muscle force was analyzed by the BIOPAC system. Results An improvement in locomotion was observed in animals treated with NM compared with injured animals. Animals treated with NM showed an increase in maximal tetanic force of the tibialis anterior muscle of 172% (p < 0.001) compared with the CCI group. We also observed a decrease of 53% (p < 0.001) and 23% (p < 0.05) in DOR and KOR levels, respectively, after CCI injury compared to those from naive animals and an increase of 17% (p < 0.05) in KOR expression only after NM treatment compared to naive animals. There were no significant changes in MOR expression in the PAG. Conclusion These data provide evidence that a non-pharmacological NM technique facilitates pain relief by endogenous analgesic modulation. PMID:24884961

  15. Chronic Morphine Reduces Surface Expression of δ-Opioid Receptors in Subregions of Rostral Striatum.

    PubMed

    Leah, Paul M; Heath, Emily M L; Balleine, Bernard W; Christie, Macdonald J

    2016-03-01

    The delta opioid receptor (DOPr), whilst not the primary target of clinically used opioids, is involved in development of opioid tolerance and addiction. There is growing evidence that DOPr trafficking is involved in drug addiction, e.g., a range of studies have shown increased plasma membrane DOPr insertion during chronic treatment with opioids. The present study used a transgenic mouse model in which the C-terminal of the DOPr is tagged with enhanced-green fluorescence protein to examine the effects of chronic morphine treatment on surface membrane expression in striatal cholinergic interneurons that are implicated in motivated learning following both chronic morphine and morphine sensitization treatment schedules in male mice. A sex difference was noted throughout the anterior striatum, which was most prominent in the nucleus accumbens core region. Incontrast with previous studies in other neurons, chronic exposure to a high dose of morphine for 6 days had no effect, or slightly decreased (anterior dorsolateral striatum) surface DOPr expression. A morphine sensitization schedule produced similar results with a significant decrease in surface DOPr expression in nucleus accumbens shell. These results suggest that chronic morphine and morphine sensitisation treatment may have effects on instrumental reward-seeking behaviours and learning processes related to drug addiction, via effects on striatal DOPr function.

  16. Novel endomorphin analogues with antagonist activity at the mu-opioid receptor in the gastrointestinal tract.

    PubMed

    Fichna, Jakub; Gach, Katarzyna; Perlikowska, Renata; Cravezic, Aurore; Bonnet, Jean Jacques; do-Rego, Jean-Claude; Janecka, Anna; Storr, Martin A

    2010-06-08

    Opioid bowel dysfunction (OBD) summarizes common adverse side effects of opiate-based management of pain. A promising therapeutic approach to prevent OBD and other opioid-related disorders of the gastrointestinal (GI) tract is the co-administration of opiates with peripherally-restricted mu-opioid receptor (MOR)-selective antagonists. The aim of this study was to investigate the selectivity and efficacy of three novel peptide antagonists: antanal-1, antanal-2, and antanal-2A at MOR in the GI tract in vitro and in vivo. The effects of the antanals on GI motility were studied in vitro, using isolated preparations of mouse ileum and colon and in vivo, by measuring colonic propulsion in mice. Additionally, in vitro stability against enzymatic degradation and blood-brain barrier (BBB) permeability using the hot plate test in mice were examined. The antanals significantly reduced the inhibitory effect of the MOR agonists endomorphin-2, morphine, and loperamide on mouse ileum and colon contractions in vitro and blocked morphine-induced decrease of colonic bead expulsion in vivo. The hot plate test in mice showed that the antagonist activity of all antanals was restricted to the periphery. Antanal-1, antanal-2, and antanal-2A are promising MOR antagonists with limited BBB permeability, which may be developed into future therapeutics of opioid-related GI dysfunction.

  17. Stimulation of μ-opioid receptors dilates retinal arterioles by neuronal nitric oxide synthase-derived nitric oxide in rats.

    PubMed

    Someya, Eriko; Mori, Asami; Sakamoto, Kenji; Ishii, Kunio; Nakahara, Tsutomu

    2017-03-21

    Opioids contribute to the regulation of cerebral vascular tone. The purpose of this study was to examine the effects of herkinorin, a non-opioid μ-opioid receptor agonist derived from salvinorin A, on blood vessels in the rat retina and to investigate the mechanism underlying the herkinorin-induced retinal vasodilatory response. Ocular fundus images were captured using an original high-resolution digital fundus camera in vivo. The retinal vascular responses were evaluated by measuring the diameter of retinal arterioles in the fundus images. Both systemic blood pressure and heart rate were continuously recorded. Herkinorin increased the retinal arteriolar diameter without significantly changing mean blood pressure and heart rate. The retinal vasodilator response to herkinorin was almost completely prevented following treatment with naloxone, a nonselective opioid receptor antagonist and H-D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2 (CTOP), a selective μ-opioid receptor antagonist. N(ω)-nitro-L-arginine methyl ester, a nonselective nitric oxide (NO) synthase inhibitor, or indomethacin, a cyclooxygenase inhibitor, significantly attenuated the herkinorin-induced retinal vasodilator responses. In addition, N(ω)-propyl-L-arginine, an inhibitor of neuronal NO synthase, diminished the herkinorin-induced retinal vasodilator responses. Seven days after an intravitreal injection of N-methyl-d-aspartic acid, loss of inner retinal neurons and abolishment of the retinal vasodilator response to herkinorin were observed. These results suggest that herkinorin dilates rat retinal arterioles through stimulation of retinal μ-opioid receptors. The μ-opioid receptor-mediated retinal vasodilator response is likely mediated by NO generated by neuronal NO synthase. Retinal neurons play an important role in the retinal vasodilator mechanism involving μ-opioid receptors in rats.

  18. EVALUATION OF THE EFFECTS OF SPECIFIC OPIOID RECEPTOR AGONISTS IN A RODENT MODEL OF SPINAL CORD INJURY

    PubMed Central

    Aceves, Miriam; Mathai, Babetta B.; Hook, Michelle A.

    2016-01-01

    Objective The current study aimed to evaluate the contribution(s) of specific opioid receptor systems to the analgesic and detrimental effects of morphine, observed after spinal cord injury in prior studies. Study Design We used specific opioid receptor agonists to assess the effects of µ- (DAMGO), δ- (DPDPE), and κ- (GR89696) opioid receptor activation on locomotor (BBB, tapered beam, ladder tests) and sensory (girdle, tactile, and tail-flick tests) recovery in a rodent contusion model (T12). We also tested the contribution of non-classic opioid binding using [+]- morphine. Methods First, a dose-response curve for analgesic efficacy was generated for each opioid agonist. Baseline locomotor and sensory reactivity was assessed 24 h after injury. Subjects were then treated with an intrathecal dose of a specific agonist and re-tested after 30 min. To evaluate effects on recovery, subjects were treated with a single dose of an agonist and both locomotor and sensory function were monitored for 21 d. Results All agonists for the classic opioid receptors, but not the [+]- morphine enantiomer, produced antinociception at a concentration equivalent to a dose of morphine previously shown to produce strong analgesic effects (0.32 μmol). DAMGO and [+]- morphine did not affect long-term recovery. GR89696, however, significantly undermined recovery of locomotor function at all doses tested. Conclusions Based on these data, we hypothesize that the analgesic efficacy of morphine is primarily mediated by binding to the classic μ-opioid receptor. Conversely, the adverse effects of morphine may be linked to activation of the κ-opioid receptor. Ultimately, elucidating the molecular mechanisms underlying the effects of morphine is imperative in order to develop safe and effective pharmacological interventions in a clinical setting. Setting USA PMID:26927293

  19. A heroin addiction severity-associated intronic single nucleotide polymorphism modulates alternative pre-mRNA splicing of the μ opioid receptor gene OPRM1 via hnRNPH interactions.

    PubMed

    Xu, Jin; Lu, Zhigang; Xu, Mingming; Pan, Ling; Deng, Yi; Xie, Xiaohu; Liu, Huifen; Ding, Shixiong; Hurd, Yasmin L; Pasternak, Gavril W; Klein, Robert J; Cartegni, Luca; Zhou, Wenhua; Pan, Ying-Xian

    2014-08-13

    Single nucleotide polymorphisms (SNPs) in the OPRM1 gene have been associated with vulnerability to opioid dependence. The current study identifies an association of an intronic SNP (rs9479757) with the severity of heroin addiction among Han-Chinese male heroin addicts. Individual SNP analysis and haplotype-based analysis with additional SNPs in the OPRM1 locus showed that mild heroin addiction was associated with the AG genotype, whereas severe heroin addiction was associated with the GG genotype. In vitro studies such as electrophoretic mobility shift assay, minigene, siRNA, and antisense morpholino oligonucleotide studies have identified heterogeneous nuclear ribonucleoprotein H (hnRNPH) as the major binding partner for the G-containing SNP site. The G-to-A transition weakens hnRNPH binding and facilitates exon 2 skipping, leading to altered expressions of OPRM1 splice-variant mRNAs and hMOR-1 proteins. Similar changes in splicing and hMOR-1 proteins were observed in human postmortem prefrontal cortex with the AG genotype of this SNP when compared with the GG genotype. Interestingly, the altered splicing led to an increase in hMOR-1 protein levels despite decreased hMOR-1 mRNA levels, which is likely contributed by a concurrent increase in single transmembrane domain variants that have a chaperone-like function on MOR-1 protein stability. Our studies delineate the role of this SNP as a modifier of OPRM1 alternative splicing via hnRNPH interactions, and suggest a functional link between an SNP-containing splicing modifier and the severity of heroin addiction.

  20. Hypothalamic kappa opioid receptor mediates both diet‐induced and melanin concentrating hormone–induced liver damage through inflammation and endoplasmic reticulum stress

    PubMed Central

    Imbernon, Monica; Sanchez‐Rebordelo, Estrella; Romero‐Picó, Amparo; Kalló, Imre; Chee, Melissa J.; Porteiro, Begoña; Al‐Massadi, Omar; Contreras, Cristina; Fernø, Johan; Senra, Ana; Gallego, Rosalia; Folgueira, Cintia; Seoane, Luisa M.; van Gestel, Margriet; Adan, Roger A.; Liposits, Zsolt; Dieguez, Carlos; López, Miguel

    2016-01-01

    The opioid system is widely known to modulate the brain reward system and thus affect the behavior of humans and other animals, including feeding. We hypothesized that the hypothalamic opioid system might also control energy metabolism in peripheral tissues. Mice lacking the kappa opioid receptor (κOR) and adenoviral vectors overexpressing or silencing κOR were stereotaxically delivered in the lateral hypothalamic area (LHA) of rats. Vagal denervation was performed to assess its effect on liver metabolism. Endoplasmic reticulum (ER) stress was inhibited by pharmacological (tauroursodeoxycholic acid) and genetic (overexpression of the chaperone glucose‐regulated protein 78 kDa) approaches. The peripheral effects on lipid metabolism were assessed by histological techniques and western blot. We show that in the LHA κOR directly controls hepatic lipid metabolism through the parasympathetic nervous system, independent of changes in food intake and body weight. κOR colocalizes with melanin concentrating hormone receptor 1 (MCH‐R1) in the LHA, and genetic disruption of κOR reduced melanin concentrating hormone–induced liver steatosis. The functional relevance of these findings was given by the fact that silencing of κOR in the LHA attenuated both methionine choline–deficient, diet‐induced and choline‐deficient, high‐fat diet–induced ER stress, inflammation, steatohepatitis, and fibrosis, whereas overexpression of κOR in this area promoted liver steatosis. Overexpression of glucose‐regulated protein 78 kDa in the liver abolished hypothalamic κOR‐induced steatosis by reducing hepatic ER stress. Conclusions: This study reveals a novel hypothalamic–parasympathetic circuit modulating hepatic function through inflammation and ER stress independent of changes in food intake or body weight; these findings might have implications for the clinical use of opioid receptor antagonists. (Hepatology 2016;64:1086‐1104) PMID:27387967

  1. Blocking opioid receptors alters short-term feed intake and oro-sensorial preferences in weaned calves.

    PubMed

    Montoro, C; Ipharraguerre, I R; Bach, A

    2012-05-01

    during the first 4 h after feeding and tended to prefer SF only after 6 h from feeding. Plasma glucose, insulin, and cholecystokinin concentrations were greater in FED than in FAS calves. Injection of naloxone decreased plasma glucagon-like peptide-1 (GLP-1) in NAL calves. Blocking opioid receptors reduced intake the first 2 h after naloxone injection in FED calves, altered oro-sensorial preferences, and reduced plasma GLP-1 concentration. In conclusion, the opioid peptide system may control short-term feed intake by modulating the oro-sensorial response triggered by feed consumption, especially when calves are fed ad libitum.

  2. Altered gene expression and functional activity of opioid receptors in the cerebellum of CB1 cannabinoid receptor knockout mice after acute treatments with cannabinoids.

    PubMed

    Páldyová, Estera; Bereczki, E; Sántha, M; Wenger, T; Borsodi, Anna; Benyhe, S

    2007-01-01

    Numerous studies have shown functional links between the cannabinoid and opioid systems. The goal of this study was to evaluate whether acute treatments by endogenous cannabinoid agonist, selective CB1 or CB2 receptor antagonists modulate the expression of mu- (MOR) and delta- (DOR) opioid receptor mRNA levels and functional activity in the cerebellum of transgenic mice deficient in the CB1 type of cannabis receptors. We examined the effect of noladin ether (endogenous cannabinoid agonist) pretreatment on MOR and DOR mRNA expression by using reverse transcription and real-time polimerase chain reaction (PCR) and the ability of subsequent application of the opioid agonists to activate G-proteins, as measured by [35S]GTPgammaS binding, in wild-type (CB1+/+) and CB1 cannabinoid receptor deficient (CB1-/-, 'knockout', K.O.) mice. The acute administration of noladin ether markedly reduced MOR-mediated G-protein activation and caused a significant increase in the level of MOR mRNAs in the cerebella of wildtype, but not in the CB1-/- mice. No significant differences were observed in DOR functional activity and mRNA expression in wild-type animals. In CB1-/- mice the expression of DOR mRNA increased after noladin ether treatment, but no changes were found in DOR functional activity. In addition, Rimonabant (selective central cannabinoid CB1 receptor antagonist) and SR144528 (selective peripheral cannabinoid CB2 receptor antagonist) caused significant potentiation in MOR functional activity in the wild-type animals, whereas DOR mediated G-protein activation was increased in the CB1-/- mice. In contrast, Rimonabant and SR144528 decreased the MOR and DOR mRNA expressions in both CB1+/+ and CB1-/- mice. Taken together, these results indicate that acute treatment with cannabinoids causes alterations in MOR and DOR mRNA expression and functional activity in the cerebella of wild-type and CB1 knockout mice indicating indirect interactions between these two signaling systems.

  3. The influences of reproductive status and acute stress on the levels of phosphorylated mu opioid receptor immunoreactivity in rat hippocampus.

    PubMed

    Gonzales, Keith L; Chapleau, Jeanette D; Pierce, Joseph P; Kelter, David T; Williams, Tanya J; Torres-Reveron, Annelyn; McEwen, Bruce S; Waters, Elizabeth M; Milner, Teresa A

    2011-08-19

    Opioids play a critical role in hippocampally dependent behavior and plasticity. In the hippocampal formation, mu opioid receptors (MOR) are prominent in parvalbumin (PARV) containing interneurons. Previously we found that gonadal hormones modulate the trafficking of MORs in PARV interneurons. Although sex differences in response to stress are well documented, the point at which opioids, sex and stress interact to influence hippocampal function remains elusive. Thus, we used quantitative immunocytochemistry in combination with light and electron microscopy for the phosphorylated MOR at the SER375 carboxy-terminal residue (pMOR) in male and female rats to assess these interactions. In both sexes, pMOR-immunoreactivity (ir) was prominent in axons and terminals and in a few neuronal somata and dendrites, some of which contained PARV in the mossy fiber pathway region of the dentate gyrus (DG) hilus and CA3 stratum lucidum. In unstressed rats, the levels of pMOR-ir in the DG or CA3 were not affected by sex or estrous cycle stage. However, immediately following 30 minutes of acute immobilization stress (AIS), males had higher levels of pMOR-ir whereas females at proestrus and estrus (high estrogen stages) had lower levels of pMOR-ir within the DG. In contrast, the number and types of neuronal profiles with pMOR-ir were not altered by AIS in either males or proestrus females. These data demonstrate that although gonadal steroids do not affect pMOR levels at resting conditions, they are differentially activated both pre- and post-synaptic MORs following stress. These interactions may contribute to the reported sex differences in hippocampally dependent behaviors in stressed animals.

  4. Kappa Opioid Receptor-Induced Aversion Requires p38 MAPK Activation in VTA Dopamine Neurons

    PubMed Central

    Ehrich, Jonathan M.; Messinger, Daniel I.; Knakal, Cerise R.; Kuhar, Jamie R.; Schattauer, Selena S.; Bruchas, Michael R.; Zweifel, Larry S.; Kieffer, Brigitte L.; Phillips, Paul E.M.

    2015-01-01

    The endogenous dynorphin-κ opioid