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Withey SL, Deshpande HU, Cao L, Bergman J, Kohut SJ. Effects of chronic naltrexone treatment on relapse-related behavior and neural responses to fentanyl in awake nonhuman primates. Psychopharmacology (Berl) 2024:10.1007/s00213-024-06633-6. [PMID: 39122918 DOI: 10.1007/s00213-024-06633-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/31/2023] [Accepted: 06/03/2024] [Indexed: 08/12/2024]
Abstract
Naltrexone, an opioid antagonist that blocks the reinforcing properties of opioid agonists, is often prescribed to preclude relapse to opioid use disorder (OUD) following detoxification. However, few laboratory studies have directly investigated the ability of naltrexone to alter relapse-inducing effects of opioid agonists, including their priming strength in reinstatement studies and their impact in brain regions known to be involved in drug-induced reinforcement in MRI studies. Here we directly address this issue by investigating the effects of continuous exposure to naltrexone on 1) fentanyl-induced reinstatement of drug-seeking behavior, 2) fentanyl-induced patterns of blood oxygenation level dependent (BOLD) activation in the nucleus accumbens (NAcc), and 3) fentanyl-induced changes in NAcc functional connectivity (FC) in awake non-human primates that are engaged in ongoing opioid self-administration studies. We found that naltrexone antagonizes the priming strength of fentanyl as shown by a rightward shift in its reinstatement dose-effect curve and that naltrexone surmountably antagonizes the BOLD response induced by fentanyl. However, while naltrexone also countered fentanyl's effects on NAcc FC, the effects were not surmounted by a higher dose of fentanyl. Together, these data suggest that, in contrast to naltrexone's modulation of fentanyl's effects on behavior and BOLD responses, their interactive effects on FC between multiple brain regions do not reflect their receptor-mediated activity. Additionally, we demonstrated opposing effects in the absence and presence of naltrexone on NAcc FC at baseline (i.e., in the absence of any fentanyl prime) suggesting that naltrexone alters FC at baseline, even though naltrexone appears behaviorally silent in the absence of an agonist prime. Together these data provide additional insight into ways in which naltrexone interacts with opioid agonists, both behaviorally and in the brain. Further understanding the effects of opioid agonists on patterns of FC could help elucidate our understanding of the neural processes that contribute to the initiation of and relapse to opioid-seeking behavior in OUD.
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Affiliation(s)
- Sarah L Withey
- Behavioral Biology Program, McLean Hospital/Harvard Medical School, 115 Mill St., Belmont, MA, 02478, USA
- Department of Psychiatry, Harvard Medical School, Boston, MA, USA
| | - Harshawardhan U Deshpande
- Behavioral Biology Program, McLean Hospital/Harvard Medical School, 115 Mill St., Belmont, MA, 02478, USA
- Department of Psychiatry, Harvard Medical School, Boston, MA, USA
- Behavioral Neuroimaging Laboratory, McLean Hospital, Belmont, MA, USA
| | - Lei Cao
- Behavioral Biology Program, McLean Hospital/Harvard Medical School, 115 Mill St., Belmont, MA, 02478, USA
- Behavioral Neuroimaging Laboratory, McLean Hospital, Belmont, MA, USA
| | - Jack Bergman
- Behavioral Biology Program, McLean Hospital/Harvard Medical School, 115 Mill St., Belmont, MA, 02478, USA
- Department of Psychiatry, Harvard Medical School, Boston, MA, USA
| | - Stephen J Kohut
- Behavioral Biology Program, McLean Hospital/Harvard Medical School, 115 Mill St., Belmont, MA, 02478, USA.
- Department of Psychiatry, Harvard Medical School, Boston, MA, USA.
- Behavioral Neuroimaging Laboratory, McLean Hospital, Belmont, MA, USA.
- McLean Imaging Center, McLean Hospital, Belmont, MA, USA.
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Maguire DR, Gerak LR, Woods JH, Husbands SM, Disney A, France CP. Long-Lasting Effects of Methocinnamox on Opioid Self-Administration in Rhesus Monkeys. J Pharmacol Exp Ther 2019; 368:88-99. [PMID: 30401680 PMCID: PMC11046729 DOI: 10.1124/jpet.118.252353] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2018] [Accepted: 11/05/2018] [Indexed: 01/05/2023] Open
Abstract
Opioid abuse remains a serious public health challenge, despite the availability of medications that are effective in some patients (naltrexone, buprenorphine, and methadone). This study explored the potential of a pseudoirreversible mu-opioid receptor antagonist [methocinnamox (MCAM)] as a treatment for opioid abuse by examining its capacity to attenuate the reinforcing effects of mu-opioid receptor agonists in rhesus monkeys. In one experiment, monkeys responded for heroin (n = 5) or cocaine (n = 4) under a fixed-ratio schedule. Another group (n = 3) worked under a choice procedure with one alternative delivering food and the other alternative delivering the mu-opioid receptor agonist remifentanil. A third group (n = 4) responded for food and physiologic parameters were measured via telemetry. The effects of MCAM were determined in all experiments and, in some cases, were compared with those of naltrexone. When given immediately before sessions, naltrexone dose-dependently decreased responding for heroin and decreased choice of remifentanil while increasing choice of food, with responding returning to baseline levels 1 day after naltrexone injection. MCAM also decreased responding for heroin and decreased choice of remifentanil while increasing choice of food; however, opioid-maintained responding remained decreased for several days after treatment. Doses of MCAM that significantly decreased opioid-maintained responding did not decrease responding for cocaine or food. MCAM did not impact heart rate, blood pressure, body temperature, or activity at doses that decreased opioid self-administration. Because MCAM selectively attenuates opioid self-administration for prolonged periods, this novel drug could be a safe and effective alternative to currently available treatments for opioid abuse.
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Affiliation(s)
- David R Maguire
- Department of Pharmacology (D.R.M., L.R.G., J.H.W., C.P.F.), Department of Psychiatry (C.P.F.), and Addiction Research, Treatment & Training Center of Excellence (D.R.M., L.R.G., J.H.W., C.P.F.), University of Texas Health Science Center at San Antonio, San Antonio, Texas; and Department of Pharmacy and Pharmacology, University of Bath, Bath, United Kingdom (S.M.H., A.D.)
| | - Lisa R Gerak
- Department of Pharmacology (D.R.M., L.R.G., J.H.W., C.P.F.), Department of Psychiatry (C.P.F.), and Addiction Research, Treatment & Training Center of Excellence (D.R.M., L.R.G., J.H.W., C.P.F.), University of Texas Health Science Center at San Antonio, San Antonio, Texas; and Department of Pharmacy and Pharmacology, University of Bath, Bath, United Kingdom (S.M.H., A.D.)
| | - James H Woods
- Department of Pharmacology (D.R.M., L.R.G., J.H.W., C.P.F.), Department of Psychiatry (C.P.F.), and Addiction Research, Treatment & Training Center of Excellence (D.R.M., L.R.G., J.H.W., C.P.F.), University of Texas Health Science Center at San Antonio, San Antonio, Texas; and Department of Pharmacy and Pharmacology, University of Bath, Bath, United Kingdom (S.M.H., A.D.)
| | - Stephen M Husbands
- Department of Pharmacology (D.R.M., L.R.G., J.H.W., C.P.F.), Department of Psychiatry (C.P.F.), and Addiction Research, Treatment & Training Center of Excellence (D.R.M., L.R.G., J.H.W., C.P.F.), University of Texas Health Science Center at San Antonio, San Antonio, Texas; and Department of Pharmacy and Pharmacology, University of Bath, Bath, United Kingdom (S.M.H., A.D.)
| | - Alex Disney
- Department of Pharmacology (D.R.M., L.R.G., J.H.W., C.P.F.), Department of Psychiatry (C.P.F.), and Addiction Research, Treatment & Training Center of Excellence (D.R.M., L.R.G., J.H.W., C.P.F.), University of Texas Health Science Center at San Antonio, San Antonio, Texas; and Department of Pharmacy and Pharmacology, University of Bath, Bath, United Kingdom (S.M.H., A.D.)
| | - Charles P France
- Department of Pharmacology (D.R.M., L.R.G., J.H.W., C.P.F.), Department of Psychiatry (C.P.F.), and Addiction Research, Treatment & Training Center of Excellence (D.R.M., L.R.G., J.H.W., C.P.F.), University of Texas Health Science Center at San Antonio, San Antonio, Texas; and Department of Pharmacy and Pharmacology, University of Bath, Bath, United Kingdom (S.M.H., A.D.)
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3
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Gerak LR, Maguire DR, Woods JH, Husbands SM, Disney A, France CP. Reversal and Prevention of the Respiratory-Depressant Effects of Heroin by the Novel μ-Opioid Receptor Antagonist Methocinnamox in Rhesus Monkeys. J Pharmacol Exp Ther 2018; 368:229-236. [PMID: 30463875 DOI: 10.1124/jpet.118.253286] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2018] [Accepted: 11/19/2018] [Indexed: 12/25/2022] Open
Abstract
One consequence of the ongoing opioid epidemic is a large number of overdose deaths. Naloxone reverses opioid-induced respiratory depression; however, its short duration of action limits the protection it can provide. Methocinnamox (MCAM) is a novel opioid receptor antagonist with a long duration of action. This study examined the ability of MCAM to prevent and reverse the respiratory-depressant effects (minute volume [VE]) of heroin in five monkeys. MCAM (0.32 mg/kg) was given before heroin to determine whether it prevents respiratory depression; heroin dose-effect curves were generated 1, 2, 4, and 8 days later, and these effects were compared with those of naltrexone (0.032 mg/kg). Heroin dose dependently decreased VE MCAM and naltrexone prevented respiratory depression, shifting the heroin dose-effect curve rightward at least 10-fold. MCAM, but not naltrexone, attenuated these effects of heroin for 4 days. MCAM (0.1-0.32 mg/kg) was given 30 minutes after heroin to determine whether it reverses respiratory depression; heroin dose-effect curves were generated 1, 2, 4, 8, and 16 days later, and these effects were compared with those of naloxone (0.0032-0.1 mg/kg). MCAM and naloxone reversed respiratory depression within 30 minutes, although only MCAM antagonized heroin on subsequent days. Thus, MCAM prevents and reverses respiratory depression, the potentially lethal effect of heroin, longer than opioid receptor antagonists currently in use. Because of its sustained effects, MCAM might provide more effective rescue from and protection against the fatal respiratory-depressant effects of opioids, thereby improving treatment of opioid overdose.
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Affiliation(s)
- Lisa R Gerak
- Departments of Pharmacology (L.R.G., D.R.M., J.H.W., C.P.F.) and Psychiatry (C.P.F.) and Addiction Research, Treatment & Training Center of Excellence (L.R.G., D.R.M., J.H.W., C.P.F.), University of Texas Health Science Center at San Antonio, San Antonio, Texas; and Department of Pharmacy and Pharmacology, University of Bath, Bath, United Kingdom (S.M.H., A.D.)
| | - David R Maguire
- Departments of Pharmacology (L.R.G., D.R.M., J.H.W., C.P.F.) and Psychiatry (C.P.F.) and Addiction Research, Treatment & Training Center of Excellence (L.R.G., D.R.M., J.H.W., C.P.F.), University of Texas Health Science Center at San Antonio, San Antonio, Texas; and Department of Pharmacy and Pharmacology, University of Bath, Bath, United Kingdom (S.M.H., A.D.)
| | - James H Woods
- Departments of Pharmacology (L.R.G., D.R.M., J.H.W., C.P.F.) and Psychiatry (C.P.F.) and Addiction Research, Treatment & Training Center of Excellence (L.R.G., D.R.M., J.H.W., C.P.F.), University of Texas Health Science Center at San Antonio, San Antonio, Texas; and Department of Pharmacy and Pharmacology, University of Bath, Bath, United Kingdom (S.M.H., A.D.)
| | - Stephen M Husbands
- Departments of Pharmacology (L.R.G., D.R.M., J.H.W., C.P.F.) and Psychiatry (C.P.F.) and Addiction Research, Treatment & Training Center of Excellence (L.R.G., D.R.M., J.H.W., C.P.F.), University of Texas Health Science Center at San Antonio, San Antonio, Texas; and Department of Pharmacy and Pharmacology, University of Bath, Bath, United Kingdom (S.M.H., A.D.)
| | - Alex Disney
- Departments of Pharmacology (L.R.G., D.R.M., J.H.W., C.P.F.) and Psychiatry (C.P.F.) and Addiction Research, Treatment & Training Center of Excellence (L.R.G., D.R.M., J.H.W., C.P.F.), University of Texas Health Science Center at San Antonio, San Antonio, Texas; and Department of Pharmacy and Pharmacology, University of Bath, Bath, United Kingdom (S.M.H., A.D.)
| | - Charles P France
- Departments of Pharmacology (L.R.G., D.R.M., J.H.W., C.P.F.) and Psychiatry (C.P.F.) and Addiction Research, Treatment & Training Center of Excellence (L.R.G., D.R.M., J.H.W., C.P.F.), University of Texas Health Science Center at San Antonio, San Antonio, Texas; and Department of Pharmacy and Pharmacology, University of Bath, Bath, United Kingdom (S.M.H., A.D.)
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Cornelissen JC, Obeng S, Rice KC, Zhang Y, Negus SS, Banks ML. Application of Receptor Theory to the Design and Use of Fixed-Proportion Mu-Opioid Agonist and Antagonist Mixtures in Rhesus Monkeys. J Pharmacol Exp Ther 2018; 365:37-47. [PMID: 29330156 PMCID: PMC5830633 DOI: 10.1124/jpet.117.246439] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2017] [Accepted: 01/09/2018] [Indexed: 01/17/2023] Open
Abstract
Receptor theory predicts that fixed-proportion mixtures of a competitive, reversible agonist (e.g., fentanyl) and antagonist (e.g., naltrexone) at a common receptor [e.g., mu-opioid receptors (MORs)] will result in antagonist proportion-dependent decreases in apparent efficacy of the agonist/antagonist mixtures and downward shifts in mixture dose-effect functions. The present study tested this hypothesis by evaluating behavioral effects of fixed-proportion fentanyl/naltrexone mixtures in a warm-water tail-withdrawal procedure in rhesus monkeys (n = 4). Fentanyl (0.001-0.056 mg/kg) alone, naltrexone (0.032-1.0 mg/kg, i.m.) alone, and fixed-proportion mixtures of fentanyl/naltrexone (1:0.025, 1:0.074, and 1:0.22) were administered in a cumulative-dosing procedure, and the proportions were based on published fentanyl and naltrexone Kd values at MOR in monkey brain. Fentanyl alone produced dose-dependent antinociception at both 50 and 54°C thermal intensities. Up to the largest dose tested, naltrexone alone did not alter nociception. Consistent with receptor theory predictions, naltrexone produced a proportion-dependent decrease in the effectiveness of fentanyl/naltrexone mixtures to produce antinociception. The maximum effects of fentanyl, naltrexone, and each mixture were also used to generate an efficacy-effect scale for antinociception at each temperature, and this scale was evaluated for its utility in quantifying 1) efficacy requirements for antinociception at 50 and 54°C and 2) relative efficacy of six MOR agonists that vary in their efficacies to produce agonist-stimuated GTPγS binding in vitro (from lowest to highest efficacy: 17-cyclopropylmethyl-3,14β-dihyroxy-4,5α-epoxy-6α-[(3'-isoquinolyl)acetamindo]morphine, nalbuphine, buprenorphine, oxycodone, morphine, and methadone). These results suggest that fixed-proportion agonist/antagonist mixtures may offer a useful strategy to manipulate apparent drug efficacy for basic research or therapeutic purposes.
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Affiliation(s)
- Jeremy C Cornelissen
- Department of Pharmacology and Toxicology, School of Medicine (J.C.C., S.S.N., M.L.B.), and Department of Medicinal Chemistry, School of Pharmacy (S.O., Y.Z.), Virginia Commonwealth University, Richmond, Virginia; and Drug Design and Synthesis Section, Molecular Targets and Medications Discovery Branch, National Institute on Drug Abuse and National Institute on Alcohol Abuse and Alcoholism, Bethesda, Maryland (K.C.R.)
| | - Samuel Obeng
- Department of Pharmacology and Toxicology, School of Medicine (J.C.C., S.S.N., M.L.B.), and Department of Medicinal Chemistry, School of Pharmacy (S.O., Y.Z.), Virginia Commonwealth University, Richmond, Virginia; and Drug Design and Synthesis Section, Molecular Targets and Medications Discovery Branch, National Institute on Drug Abuse and National Institute on Alcohol Abuse and Alcoholism, Bethesda, Maryland (K.C.R.)
| | - Kenner C Rice
- Department of Pharmacology and Toxicology, School of Medicine (J.C.C., S.S.N., M.L.B.), and Department of Medicinal Chemistry, School of Pharmacy (S.O., Y.Z.), Virginia Commonwealth University, Richmond, Virginia; and Drug Design and Synthesis Section, Molecular Targets and Medications Discovery Branch, National Institute on Drug Abuse and National Institute on Alcohol Abuse and Alcoholism, Bethesda, Maryland (K.C.R.)
| | - Yan Zhang
- Department of Pharmacology and Toxicology, School of Medicine (J.C.C., S.S.N., M.L.B.), and Department of Medicinal Chemistry, School of Pharmacy (S.O., Y.Z.), Virginia Commonwealth University, Richmond, Virginia; and Drug Design and Synthesis Section, Molecular Targets and Medications Discovery Branch, National Institute on Drug Abuse and National Institute on Alcohol Abuse and Alcoholism, Bethesda, Maryland (K.C.R.)
| | - S Stevens Negus
- Department of Pharmacology and Toxicology, School of Medicine (J.C.C., S.S.N., M.L.B.), and Department of Medicinal Chemistry, School of Pharmacy (S.O., Y.Z.), Virginia Commonwealth University, Richmond, Virginia; and Drug Design and Synthesis Section, Molecular Targets and Medications Discovery Branch, National Institute on Drug Abuse and National Institute on Alcohol Abuse and Alcoholism, Bethesda, Maryland (K.C.R.)
| | - Matthew L Banks
- Department of Pharmacology and Toxicology, School of Medicine (J.C.C., S.S.N., M.L.B.), and Department of Medicinal Chemistry, School of Pharmacy (S.O., Y.Z.), Virginia Commonwealth University, Richmond, Virginia; and Drug Design and Synthesis Section, Molecular Targets and Medications Discovery Branch, National Institute on Drug Abuse and National Institute on Alcohol Abuse and Alcoholism, Bethesda, Maryland (K.C.R.)
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Kangas BD, Bergman J. Operant nociception in nonhuman primates. Pain 2014; 155:1821-1828. [PMID: 24968803 PMCID: PMC4157960 DOI: 10.1016/j.pain.2014.06.010] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2014] [Revised: 06/10/2014] [Accepted: 06/16/2014] [Indexed: 01/05/2023]
Abstract
The effective management of pain is a longstanding public health concern. Morphine-like opioids have long been front-line analgesics, but produce undesirable side effects that can limit their application. Slow progress in the introduction of novel improved medications for pain management over the last 5 decades has prompted a call for innovative translational research, including new preclinical assays. Most current in vivo procedures (eg, tail flick, hot plate, warm water tail withdrawal) assay the effects of nociceptive stimuli on simple spinal reflexes or unconditioned behavioral reactions. However, clinical treatment goals may include the restoration of previous behavioral activities, which can be limited by medication-related side effects that are not measured in such procedures. The present studies describe an apparatus and procedure to study the disruptive effects of nociceptive stimuli on voluntary behavior in nonhuman primates, and the ability of drugs to restore such behavior through their analgesic actions. Squirrel monkeys were trained to pull a cylindrical thermode for access to a highly palatable food. Next, sessions were conducted in which the temperature of the thermode was increased stepwise until responding stopped, permitting the determination of stable nociceptive thresholds. Tests revealed that several opioid analgesics, but not d-amphetamine or Δ(9)-THC, produced dose-related increases in threshold that were antagonist sensitive and efficacy dependent, consistent with their effects using traditional measures of antinociception. Unlike traditional reflex-based measures, however, the results also permitted the concurrent evaluation of response disruption, providing an index with which to characterize the behavioral selectivity of antinociceptive drugs.
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Affiliation(s)
- Brian D Kangas
- Harvard Medical School, McLean Hospital, Belmont, MA, USA
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Quantitative pharmacological analyses of the interaction between flumazenil and midazolam in monkeys discriminating midazolam: Determination of the functional half life of flumazenil. Eur J Pharmacol 2014; 723:405-9. [PMID: 24216249 DOI: 10.1016/j.ejphar.2013.10.065] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2013] [Revised: 09/25/2013] [Accepted: 10/25/2013] [Indexed: 11/21/2022]
Abstract
The duration of action of a drug is commonly estimated using plasma concentration, which is not always practical to obtain or an accurate estimate of functional half life. For example, flumazenil is used clinically to reverse the effects of benzodiazepines like midazolam; however, its elimination can be altered by other drugs, including some benzodiazepines, thereby altering its half life. This study used Schild analyses to characterize antagonism of midazolam by flumazenil and determine the functional half life of flumazenil. Four monkeys discriminated 0.178mg/kg midazolam while responding under a fixed-ratio 10 schedule of stimulus-shock termination; flumazenil was given at various times before determination of a midazolam dose-effect curve. There was a time-related decrease in the magnitude of shift of the midazolam dose-effect curve as the interval between flumazenil and midazolam increased. The potency of flumazenil, estimated by apparent pA2 values (95% CI), was 7.30 (7.12, 7.49), 7.17 (7.03, 7.31), 6.91 (6.72, 7.10) and 6.80 (6.67, 6.92) at 15, 30, 60 and 120min after flumazenil administration, respectively. The functional half life of flumazenil, derived from potency estimates, was 57±13min. Thus, increasing the interval between flumazenil and midazolam causes orderly decreases in flumazenil potency; however, across a broad range of conditions, the qualitative nature of the interaction does not change, as indicated by slopes of Schild plots at all time points that are not different from unity. Differences in potency of flumazenil are therefore due to elimination of flumazenil and not due to pharmacodynamic changes over time.
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Helms CM, Rogers LSM, Grant KA. Antagonism of the ethanol-like discriminative stimulus effects of ethanol, pentobarbital, and midazolam in cynomolgus monkeys reveals involvement of specific GABA(A) receptor subtypes. J Pharmacol Exp Ther 2009; 331:142-52. [PMID: 19641166 DOI: 10.1124/jpet.109.156810] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The gamma-aminobutyric acid (GABA)(A) receptors mediating the discriminative stimulus effects of ethanol were studied by comparing the potency of ethyl-8-azido-5,6-dihydro-5-methyl-6-oxo-4H-imidazol(1,5-a)benzodiazepine-3-carboxylate (Ro15-4513) and ethyl 8-fluoro-5,6-dihydro-5-methyl-6-oxo-4H-imidazol(1,5-a)-benzodiazepine-3-carboxylate (flumazenil, Ro15-1788) to antagonize ethanol, pentobarbital (PB), and midazolam substitution for ethanol. Ro15-4513 has high affinity for receptors containing alpha(4/6) and alpha(5) subunits and lower affinity for alpha(1), alpha(2), and alpha(3) subunits. Flumazenil is nonselective for GABA(A) receptors containing alpha(1), alpha(2), alpha(3), and alpha(5) subunits and has low affinity for alpha(4/6)-containing receptors. Male (n = 9) and female (n = 8) cynomolgus monkeys (Macaca fascicularis) were trained to discriminate ethanol (1.0 or 2.0 g/kg i.g., 30-min pretreatment) from water. Ethanol, PB, and midazolam dose-dependently substituted for ethanol (80% ethanol-appropriate responding). Ro15-4513 (0.003-0.56 mg/kg i.m., 5-min pretreatment) shifted the ethanol, PB, and midazolam dose-response functions rightward in a vast majority of monkeys tested (15/15, 16/17, and 11/12, respectively). In contrast, flumazenil (0.30-10.0 mg/kg i.m., 5-min pretreatment) shifted the ethanol, PB, and midazolam dose-response functions rightward in 9 of 16, 12 of 16, and 7 of 9 monkeys tested, respectively. In the monkeys showing antagonism with both Ro15-4513 and flumazenil, ethanol and PB substitution were antagonized more potently by Ro15-4513 than by flumazenil, whereas midazolam substitution was antagonized with similar potency. There were no sex or training dose differences, with the exception that flumazenil failed to antagonize ethanol substitution in males trained to discriminate 2.0 g/kg ethanol. GABA(A) receptors with high affinity for Ro15-4513 (i.e., containing alpha(4/6) and alpha(5) subunits) may be particularly important mediators of the multiple discriminative stimulus effects of ethanol through GABA(A) receptor systems.
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Affiliation(s)
- Christa M Helms
- Oregon National Primate Research Center, Oregon Health and Science University, Beaverton, 97006-6448, USA.
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8
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Koek W, Mercer SL, Coop A, France CP. Behavioral effects of gamma-hydroxybutyrate, its precursor gamma-butyrolactone, and GABA(B) receptor agonists: time course and differential antagonism by the GABA(B) receptor antagonist 3-aminopropyl(diethoxymethyl)phosphinic acid (CGP35348). J Pharmacol Exp Ther 2009; 330:876-83. [PMID: 19564487 DOI: 10.1124/jpet.109.151845] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Gamma-hydroxybutyrate (GHB) is used therapeutically and recreationally. The mechanism by which GHB produces its therapeutic and recreational effects is not entirely clear, although GABA(B) receptors seem to play an important role. This role could be complex, because there are indications that different GABA(B) receptor mechanisms mediate the effects of GHB and the prototypical GABA(B) receptor agonist baclofen. To further explore possible differences in underlying GABA(B) receptor mechanisms, the present study examined the effects of GHB and baclofen on operant responding and their antagonism by the GABA(B) receptor antagonist 3-aminopropyl(diethoxymethyl)phosphinic acid (CGP35348). Pigeons were trained to peck a key for access to food during response periods that started at different times after the beginning of the session. In these pigeons, GHB, its precursor gamma-butyrolactone (GBL), and the GABA(B) receptor agonists baclofen and 3-aminopropyl(methyl)phosphinic acid hydrochloride (SKF97541) decreased the rate of responding in a dose- and time-dependent manner. CGP35348 shifted the dose-response curve of each agonist to the right, but the magnitude of the shift differed among the agonists. Schild analysis yielded a pA(2) value of CGP35348 to antagonize GHB and GBL [i.e., 3.9 (3.7-4.2)] that was different (P = 0.0011) from the pA(2) value to antagonize baclofen and SKF97541 [i.e., 4.5 (4.4-4.7)]. This finding is further evidence that the GABA(B) receptor mechanisms mediating the effects of GHB and prototypical GABA(B) receptor agonists are not identical. A better understanding of the similarities and differences between these mechanisms, and their involvement in the therapeutic effects of GHB and baclofen, could lead to more effective medications with fewer adverse effects.
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Affiliation(s)
- Wouter Koek
- Department of Psychiatry, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, Mail Code 7792, San Antonio, TX 78229-3900, USA.
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Apparent affinity estimates of rimonabant in combination with anandamide and chemical analogs of anandamide in rhesus monkeys discriminating Delta9-tetrahydrocannabinol. Psychopharmacology (Berl) 2009; 203:219-28. [PMID: 18592221 PMCID: PMC4879883 DOI: 10.1007/s00213-008-1230-8] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/30/2007] [Accepted: 06/04/2008] [Indexed: 10/21/2022]
Abstract
RATIONALE Anandamide and Delta(9)-tetrahydrocannabinol (Delta(9)-THC) sometimes produce different discriminative stimulus effects and, therefore, appear to differ in their mechanism of action. In order to understand the widespread use of cannabis and the therapeutic potential of cannabinoids, mechanisms responsible for behavioral effects need to be identified. OBJECTIVE Drug discrimination was used to compare the mechanism of action of Delta(9)-THC, anandamide, and two structural analogs of anandamide in rhesus monkeys. MATERIALS AND METHODS Monkeys discriminated Delta(9)-THC (0.1 mg/kg i.v.) from vehicle. Delta(9)-THC, anandamide, methanandamide, and arachidonylcyclopropylamide (ACPA) were administered i.v. alone and in combination with at least one dose of rimonabant. Schild analysis and single-dose apparent affinity estimates were used to estimate the potency of rimonabant as an antagonist of each cannabinoid; these values were compared to examine whether the same receptors mediated discriminative stimulus effects. RESULTS Delta(9)-THC, ACPA, methanandamide, and anandamide produced greater than 96% of responses on the Delta(9)-THC lever. The ED(50) values were 0.024 mg/kg for Delta(9)-THC, 0.14 mg/kg for ACPA, 0.28 mg/kg for methanandamide, and 1.7 mg/kg for anandamide. The duration of action of Delta(9)-THC was 4-6 h and longer than the duration of action ACPA, methanandamide, and anandamide (i.e., each less than 50 min). Rimonabant surmountably antagonized the discriminative stimulus effects of each agonist, and the apparent affinity estimates (pA (2) and pK (B) values) were 6.24-6.83. CONCLUSIONS Rimonabant can produce surmountable antagonism of the behavioral effects of not only Delta(9)-THC but also anandamide, methanandamide, and ACPA, and the interactions appear simple, competitive, and reversible. These cannabinoid agonists act at the same receptors to produce discriminative stimulus effects.
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Li JX, Rice KC, France CP. Discriminative stimulus effects of 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane in rhesus monkeys: antagonism and apparent pA2 analyses. J Pharmacol Exp Ther 2009; 328:976-81. [PMID: 19098164 PMCID: PMC2682264 DOI: 10.1124/jpet.108.145458] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2008] [Accepted: 12/15/2008] [Indexed: 11/22/2022] Open
Abstract
Discriminative stimulus effects of the serotonin (5-HT) receptor agonist 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM) have been studied in rats and, more recently, in rhesus monkeys. This study examined DOM, 2,5-dimethoxy-4-(n)-propylthiophenethylamine (2C-T-7), and dipropyltryptamine hydrochloride (DPT) alone and in combination with three antagonists, MDL100907 [(+/-)2,3-dimethoxyphenyl-1-[2-(4-piperidine)-methanol]], ketanserin [3-[2-[4-(4-fluorobenzoyl)piperidin-1-yl]ethyl]-1H-quinazoline-2,4-dione], and ritanserin [6-[2-[4-[bis(4-fluorophenyl)methylidene]piperidin-1-yl]ethyl]-7-methyl-[1,3]thiazolo[2,3-b]pyrimidin-5-one], to identify the 5-HT receptor subtype(s) that mediates the discriminative stimulus effects of these 5-HT receptor agonists. Four adult rhesus monkeys discriminated between 0.32 mg/kg s.c. DOM and vehicle while responding under a fixed ratio 5 schedule of stimulus shock termination. DOM, 2C-T-7, and DPT dose-dependently increased responding on the DOM-associated lever. MDL100907 (0.001-0.01 mg/kg), ketanserin (0.01-0.1 mg/kg), and ritanserin (0.01-0.1 mg/kg) each shifted the dose-response curves of DOM, 2C-T-7, and DPT rightward in a parallel manner. Schild analysis of each drug combination was consistent with a simple, competitive, and reversible interaction. Similar apparent affinity (pA(2)) values were obtained for MDL100907 in combination with DOM (8.61), 2C-T-7 (8.58), or DPT (8.50), for ketanserin with DOM (7.67), 2C-T-7 (7.75), or DPT (7.71), and for ritanserin with DOM (7.65), 2C-T-7 (7.75), or DPT (7.65). Potency of antagonists in this study was correlated with binding affinity at 5-HT(2A) receptors and not at 5-HT(2C) or alpha(1) adrenergic receptors. This study used Schild analysis to examine receptor mechanisms mediating the discriminative stimulus effects of hallucinogenic drugs acting at 5-HT receptors; results provide quantitative evidence for the predominant, if not exclusive, role of 5-HT(2A) receptors in the discriminative stimulus effects of DOM, 2C-T-7, and DPT in rhesus monkeys.
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Affiliation(s)
- Jun-Xu Li
- Department of Pharmacology, The University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900, USA
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Abstract
This paper is the thirtieth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2007 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.
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Affiliation(s)
- Richard J Bodnar
- Department of Psychology and Neuropsychology Doctoral Sub-Program, Queens College, City University of New York, 65-30 Kissena Blvd.,Flushing, NY 11367, United States.
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Li JX, McMahon LR, France CP. Comparison of naltrexone, 6alpha-naltrexol, and 6beta-naltrexol in morphine-dependent and in nondependent rhesus monkeys. Psychopharmacology (Berl) 2008; 195:479-86. [PMID: 17874317 DOI: 10.1007/s00213-007-0914-9] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/30/2007] [Accepted: 08/04/2007] [Indexed: 11/25/2022]
Abstract
RATIONALE Some opioid receptor ligands that appear to be neutral antagonists can have inverse agonist activity under conditions of increased constitutive activity (e.g., agonist treatment). OBJECTIVES This study compared the opioid receptor antagonist naltrexone and its metabolites 6alpha-naltrexol and 6beta-naltrexol in nondependent and morphine-dependent monkeys to see whether their potencies varied according to drug treatment and, presumably, to differences in constitutive activity of mu opioid receptors. RESULTS In monkeys (n = 4) receiving 3.2 mg/kg per day of morphine and discriminating 0.0178 mg/kg naltrexone, naltrexone and each metabolite increased responding on the naltrexone lever in a dose-related manner with naltrexone being 8- and 71-fold more potent than 6alpha- and 6beta-naltrexol, respectively. After 27 h of no-morphine treatment, monkeys responded on the naltrexone lever, and this effect was reversed by morphine. Naltrexone and each metabolite prevented morphine reversal of naltrexone-lever responding, and their rank order potency was the same as their substitution for naltrexone; however, the potency between naltrexone and each metabolite was slightly greater in morphine-dependent as compared to morphine-deprived monkeys. In a separate group (n = 3) of nondependent monkeys discriminating 1.78 mg/kg of morphine, all three compounds antagonized morphine with the same potency as in the reversal study (morphine-dependent monkeys), with Schild analyses showing no difference in apparent affinities (pA (2)) between nondependent and morphine-dependent monkeys. CONCLUSION Naltrexone and 6alpha- and 6beta-naltrexol have qualitatively similar effects, and their potencies do not vary markedly with opioid treatment, suggesting that under these conditions, they do not vary with regard to inverse agonism.
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Affiliation(s)
- Jun-Xu Li
- Department of Pharmacology, The University of Texas Health Science Center, San Antonio, TX 78229-3900, USA
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