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Barattini AE, Gilpin NW, Pahng AR. Chronic inflammatory pain reduces fentanyl intake during early acquisition of fentanyl self-administration, but does not change motivation to take fentanyl in male and female rats. Pharmacol Biochem Behav 2024; 245:173890. [PMID: 39366430 DOI: 10.1016/j.pbb.2024.173890] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/12/2024] [Revised: 09/27/2024] [Accepted: 10/01/2024] [Indexed: 10/06/2024]
Abstract
The co-occurrence of chronic pain and opioid misuse has led to numerous preclinical investigations of pain-opioid interactions to examine how pain manipulations alter the reinforcing properties of opioids. However, preclinical investigations of chronic pain effects on opioid drug self-administration have produced inconsistent results. Our previous work demonstrated that established fentanyl self-administration is resistant to change by induction of chronic inflammatory pain (Complete Freund's Adjuvant; CFA) in male and female rats, while other laboratories have shown that CFA increased fentanyl self-administration in male but not female rats when pain induction precedes self-administration, which may be a critical factor in determining the effects of chronic pain on self-administration. The present study was designed similarly to Higginbotham 2022 to test the effects of CFA on fentanyl self-administration in rats that underwent pain prior to acquisition of fentanyl self-administration. Male and female rats treated with hindpaw CFA or saline were trained to intravenously self-administer (IVSA) fentanyl for 3 weeks under limited access to fentanyl (2 h per day) conditions. After 3 weeks of fentanyl IVSA acquisition, we tested motivation to take fentanyl using progressive ratio testing and dose-response testing. CFA male and female rats self-administered less fentanyl than saline-treated controls during week 1 of acquisition, but not during weeks 2-3 of acquisition. Intra-session analysis of week 1 data demonstrated that chronic inflammatory pain suppressed fentanyl intake towards the end of week 1 and at the end of each operant session. We also report no effects of chronic inflammatory pain on motivation to take fentanyl. We discuss potential methodological explanations for differences between these results and prior reports. Our findings demonstrate that CFA temporarily suppresses fentanyl IVSA in animals without changing motivation to take fentanyl or promoting escalation of opioid use, suggesting that chronic inflammatory pain is unlikely to promote long-term risk of opioid misuse.
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Affiliation(s)
- Angela E Barattini
- Southeast Louisiana Veterans Health Care System, New Orleans, LA, United States; Department of Physiology, LSU Health Sciences Center, New Orleans, LA, United States
| | - Nicholas W Gilpin
- Southeast Louisiana Veterans Health Care System, New Orleans, LA, United States; Department of Physiology, LSU Health Sciences Center, New Orleans, LA, United States; Alcohol & Drug Abuse Center of Excellence, LSU Health Sciences Center, New Orleans, LA, United States; Neuroscience Center of Excellence, LSU Health Sciences Center, New Orleans, LA, United States
| | - Amanda R Pahng
- Southeast Louisiana Veterans Health Care System, New Orleans, LA, United States; Department of Physiology, LSU Health Sciences Center, New Orleans, LA, United States; Alcohol & Drug Abuse Center of Excellence, LSU Health Sciences Center, New Orleans, LA, United States.
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2
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Sharpe AL, Liter LR, Donohue D, Carter KA, Vangeneugden P, Weaver S, Stout MB, Beckstead MJ. Aged mice exhibit faster acquisition of intravenous opioid self-administration with variable effects on intake. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.09.03.611052. [PMID: 39282417 PMCID: PMC11398421 DOI: 10.1101/2024.09.03.611052] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 09/20/2024]
Abstract
Although opioid abuse is more prevalent in young individuals, opioid use, overdose, and use disorders continue to climb at a rapid rate among the elderly. Little is known about abuse potential in a healthy aged population, in part due to technical and logistical difficulties testing intravenous self-administration in aged rodents. The goal of this study was to address the critical gap in the literature regarding age-dependent differences in opioid (remifentanil and fentanyl) self-administration between old and young mice. Male and female mice were grouped into young (mean: 19 weeks) and old (mean: 101 weeks), and were trained to self-administer intravenous fentanyl or remifentanil in daily sessions. In both old and young mice, acquisition, intake, and cue-responding after forced abstinence were measured for both drugs, and a dose-response curve (remifentanil) and dose-escalation (fentanyl) were conducted. Surprisingly, old mice learned to self-administer both remifentanil and fentanyl faster and more accurately than young mice. Baseline intake of remifentanil was also substantially greater in old mice compared to their young counterparts; however, we did not see increased intake of fentanyl with age at either dose tested. Further, compared to young mice, the old mice showed a greater incubation of responding for cues previously associated with remifentanil after a forced abstinence, but again this was not observed with fentanyl. Together these data suggest that an aged population may have an increased drug-abuse vulnerability for opioids compared to young counterparts and underscore the importance of future work on mechanisms responsible for this increased vulnerability.
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Affiliation(s)
- Amanda L Sharpe
- Department of Pharmaceutical Sciences, University of Oklahoma Health Sciences
| | - Laci R Liter
- Aging and Metabolism Research Program, Oklahoma Medical Research Foundation; Graduate Program in Biomedical Sciences, University of Oklahoma Health Sciences
| | - Darius Donohue
- Aging and Metabolism Research Program, Oklahoma Medical Research Foundation
| | - Kelsey A Carter
- Aging and Metabolism Research Program, Oklahoma Medical Research Foundation
| | | | - Sofia Weaver
- Aging and Metabolism Research Program, Oklahoma Medical Research Foundation
| | - Michael B Stout
- Aging and Metabolism Research Program, Oklahoma Medical Research Foundation
| | - Michael J Beckstead
- Aging and Metabolism Research Program, Oklahoma Medical Research Foundation; Oklahoma City Veterans Affairs Medical Center, Oklahoma City, OK, USA
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3
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Sarka BC, Liu S, Banerjee A, Stucky CL, Liu Q, Olsen CM. Neuropathic pain has sex-specific effects on oxycodone-seeking and non-drug-seeking ensemble neurons in the dorsomedial prefrontal cortex of mice. Addict Biol 2024; 29:e13430. [PMID: 39121884 PMCID: PMC11315577 DOI: 10.1111/adb.13430] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2024] [Revised: 07/06/2024] [Accepted: 07/12/2024] [Indexed: 08/12/2024]
Abstract
Approximately 50 million Americans suffer from chronic pain, and nearly a quarter of chronic pain patients have reported misusing opioid prescriptions. Repeated drug seeking is associated with reactivation of an ensemble of neurons sparsely scattered throughout the dorsomedial prefrontal cortex (dmPFC). Prior research has demonstrated that chronic pain increases intrinsic excitability of dmPFC neurons, which may increase the likelihood of reactivation during drug seeking. We tested the hypothesis that chronic pain would increase oxycodone-seeking behaviour and that the pain state would differentially increase intrinsic excitability in dmPFC drug-seeking ensemble neurons. TetTag mice self-administered intravenous oxycodone. After 7 days of forced abstinence, a drug-seeking session was performed, and the ensemble was tagged. Mice received spared nerve injury (SNI) to induce chronic pain during the period between the first and second seeking session. Following the second seeking session, we performed electrophysiology on individual neurons within the dmPFC to assess intrinsic excitability of the drug-seeking ensemble and non-ensemble neurons. SNI had no impact on sucrose seeking or intrinsic excitability of dmPFC neurons from these mice. In females, SNI increased oxycodone seeking and intrinsic excitability of non-ensemble neurons. In males, SNI had no impact on oxycodone seeking or neuron excitability. Data from females are consistent with clinical reports that chronic pain can promote drug craving and relapse and support the hypothesis that chronic pain itself may lead to neuroadaptations which promote opioid seeking.
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Affiliation(s)
- Bailey C. Sarka
- Department of Pharmacology and ToxicologyMedical College of WisconsinMilwaukeeWisconsinUSA
- Neuroscience Research CenterMedical College of WisconsinMilwaukeeWisconsinUSA
| | - Shuai Liu
- Department of Pharmacology and ToxicologyMedical College of WisconsinMilwaukeeWisconsinUSA
- Neuroscience Research CenterMedical College of WisconsinMilwaukeeWisconsinUSA
| | - Anjishnu Banerjee
- Division of BiostatisticsMedical College of WisconsinMilwaukeeWisconsinUSA
| | - Cheryl L. Stucky
- Neuroscience Research CenterMedical College of WisconsinMilwaukeeWisconsinUSA
- Department of Cell Biology, Neurobiology and AnatomyMedical College of WisconsinMilwaukeeWisconsinUSA
| | - Qing‐song Liu
- Department of Pharmacology and ToxicologyMedical College of WisconsinMilwaukeeWisconsinUSA
- Neuroscience Research CenterMedical College of WisconsinMilwaukeeWisconsinUSA
| | - Christopher M. Olsen
- Department of Pharmacology and ToxicologyMedical College of WisconsinMilwaukeeWisconsinUSA
- Neuroscience Research CenterMedical College of WisconsinMilwaukeeWisconsinUSA
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4
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Dagher M, Alayoubi M, Sigal GH, Cahill CM. Unveiling the link between chronic pain and misuse of opioids and cannabis. J Neural Transm (Vienna) 2024; 131:563-580. [PMID: 38570361 DOI: 10.1007/s00702-024-02765-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2023] [Accepted: 03/10/2024] [Indexed: 04/05/2024]
Abstract
Over 50 million Americans endure chronic pain where many do not receive adequate treatment and self-medicate to manage their pain by taking substances like opioids and cannabis. Research has shown high comorbidity between chronic pain and substance use disorders (SUD) and these disorders share many common neurobiological underpinnings, including hypodopaminergic transmission. Drugs commonly used for self-medication such as opioids and cannabis relieve emotional, bothersome components of pain as well as negative emotional affect that perpetuates misuse and increases the risk of progressing towards drug abuse. However, the causal effect between chronic pain and the development of SUDs has not been clearly established. In this review, we discuss evidence that affirms the proposition that chronic pain is a risk factor for the development of opioid and cannabis use disorders by outlining the clinical evidence and detailing neurobiological mechanisms that link pain and drug misuse. Central to the link between chronic pain and opioid and cannabis misuse is hypodopaminergic transmission and the modulation of dopamine signaling in the mesolimbic pathway by opioids and cannabis. Moreover, we discuss the role of kappa opioid receptor activation and neuroinflammation in the context of dopamine transmission, their contribution to opioid and cannabis withdrawal, along with potential new treatments.
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Affiliation(s)
- Merel Dagher
- MacDonald Research Laboratory Building, Department of Psychiatry and Biobehavioral Sciences, Shirley and Stefan Hatos Center for Neuropharmacology, Semel Institute for Neuroscience and Human Behavior, University of California Los Angeles, 675 Charles E Young Drive South, Office 2774, Los Angeles, CA, 90095, USA
| | - Myra Alayoubi
- MacDonald Research Laboratory Building, Department of Psychiatry and Biobehavioral Sciences, Shirley and Stefan Hatos Center for Neuropharmacology, Semel Institute for Neuroscience and Human Behavior, University of California Los Angeles, 675 Charles E Young Drive South, Office 2774, Los Angeles, CA, 90095, USA
- Neuroscience Interdepartmental Program, University of California Los Angeles, Los Angeles, CA, 90095, USA
| | - Gabriella H Sigal
- Department of Integrative Biology and Physiology, University of California Los Angeles, Los Angeles, CA, 90095, USA
| | - Catherine M Cahill
- MacDonald Research Laboratory Building, Department of Psychiatry and Biobehavioral Sciences, Shirley and Stefan Hatos Center for Neuropharmacology, Semel Institute for Neuroscience and Human Behavior, University of California Los Angeles, 675 Charles E Young Drive South, Office 2774, Los Angeles, CA, 90095, USA.
- Neuroscience Interdepartmental Program, University of California Los Angeles, Los Angeles, CA, 90095, USA.
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5
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Lee SM, Jang HB, Fan Y, Lee BH, Kim SC, Bills KB, Steffensen SC, Kim HY. Nociceptive Stimuli Activate the Hypothalamus-Habenula Circuit to Inhibit the Mesolimbic Reward System and Cocaine-Seeking Behaviors. J Neurosci 2022; 42:9180-9192. [PMID: 36280259 PMCID: PMC9761669 DOI: 10.1523/jneurosci.0577-22.2022] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2022] [Revised: 10/06/2022] [Accepted: 10/11/2022] [Indexed: 01/07/2023] Open
Abstract
Nociceptive signals interact with various regions of the brain, including those involved in physical sensation, reward, cognition, and emotion. Emerging evidence points to a role of nociception in the modulation of the mesolimbic reward system. The mechanism by which nociception affects dopamine (DA) signaling and reward is unclear. The lateral hypothalamus (LH) and the lateral habenula (LHb) receive somatosensory inputs and are structurally connected with the mesolimbic DA system. Here, we show that the LH-LHb pathway is necessary for nociceptive modulation of this system using male Sprague Dawley rats. Our extracellular single-unit recordings and head-mounted microendoscopic calcium imaging revealed that nociceptive stimulation by tail pinch excited LHb and LH neurons, which was inhibited by chemical lesion of the LH. Tail pinch increased activity of GABA neurons in ventral tegmental area, decreased the extracellular DA level in the nucleus accumbens ventrolateral shell in intact rats, and reduced cocaine-increased DA concentration, which was blocked by disruption of the LH. Furthermore, tail pinch attenuated cocaine-induced locomotor activity, 22 and 50 kHz ultrasonic vocalizations, and reinstatement of cocaine-seeking behavior, which was inhibited by chemogenetic silencing of the LH-LHb pathway. Our findings suggest that nociceptive stimulation recruits the LH-LHb pathway to inhibit mesolimbic DA system and drug reinstatement.SIGNIFICANCE STATEMENT The LHb and the LH have been implicated in processing nociceptive signals and modulating DA release in the mesolimbic DA system. Here, we show that the LH-LHb pathway is critical for nociception-induced modulation of mesolimbic DA release and cocaine reinstatement. Nociceptive stimulation alleviates extracellular DA release in the mesolimbic DA system, cocaine-induced psychomotor activities, and reinstatement of cocaine-seeking behaviors through the LH-LHb pathway. These findings provide novel evidence for sensory modulation of the mesolimbic DA system and drug addiction.
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Affiliation(s)
- Soo Min Lee
- Emotion, Cognition & Behavior Research Group, Korea Brain Research Institute, Daegu 41062, South Korea
- Department of Physiology, College of Korean Medicine, Daegu Haany University, Daegu 42158, South Korea
| | - Han Byeol Jang
- Department of Physiology, College of Korean Medicine, Daegu Haany University, Daegu 42158, South Korea
| | - Yu Fan
- Department of Human Anatomy and Histoembryology, Nanjing University of Chinese Medicine, Nanjing 210023, China
- Department of Physiology, College of Korean Medicine, Daegu Haany University, Daegu 42158, South Korea
| | - Bong Hyo Lee
- Department of Physiology, College of Korean Medicine, Daegu Haany University, Daegu 42158, South Korea
| | - Sang Chan Kim
- Medical Research Center, College of Korean Medicine, Daegu Haany University, Gyeongsan 38610, South Korea
| | - Kyle B Bills
- Department of Biomedical Sciences, Noorda College of Osteopathic Medicine, Provo, Utah 84606
| | - Scott C Steffensen
- Department of Psychology and Neuroscience, Brigham Young University, Provo, Utah 84602
| | - Hee Young Kim
- Department of Physiology, Yonsei University College of Medicine, Seoul 03722, South Korea
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Higginbotham JA, Markovic T, Massaly N, Morón JA. Endogenous opioid systems alterations in pain and opioid use disorder. Front Syst Neurosci 2022; 16:1014768. [PMID: 36341476 PMCID: PMC9628214 DOI: 10.3389/fnsys.2022.1014768] [Citation(s) in RCA: 22] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2022] [Accepted: 09/26/2022] [Indexed: 11/25/2022] Open
Abstract
Decades of research advances have established a central role for endogenous opioid systems in regulating reward processing, mood, motivation, learning and memory, gastrointestinal function, and pain relief. Endogenous opioid systems are present ubiquitously throughout the central and peripheral nervous system. They are composed of four families, namely the μ (MOPR), κ (KOPR), δ (DOPR), and nociceptin/orphanin FQ (NOPR) opioid receptors systems. These receptors signal through the action of their endogenous opioid peptides β-endorphins, dynorphins, enkephalins, and nociceptins, respectfully, to maintain homeostasis under normal physiological states. Due to their prominent role in pain regulation, exogenous opioids-primarily targeting the MOPR, have been historically used in medicine as analgesics, but their ability to produce euphoric effects also present high risks for abuse. The ability of pain and opioid use to perturb endogenous opioid system function, particularly within the central nervous system, may increase the likelihood of developing opioid use disorder (OUD). Today, the opioid crisis represents a major social, economic, and public health concern. In this review, we summarize the current state of the literature on the function, expression, pharmacology, and regulation of endogenous opioid systems in pain. Additionally, we discuss the adaptations in the endogenous opioid systems upon use of exogenous opioids which contribute to the development of OUD. Finally, we describe the intricate relationship between pain, endogenous opioid systems, and the proclivity for opioid misuse, as well as potential advances in generating safer and more efficient pain therapies.
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Affiliation(s)
- Jessica A. Higginbotham
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, MO, United States
- Pain Center, Washington University in St. Louis, St. Louis, MO, United States
- School of Medicine, Washington University in St. Louis, St. Louis, MO, United States
| | - Tamara Markovic
- Nash Family Department of Neuroscience and Friedman Brain Institute, Icahn School of Medicine at Mount Sinai, New York, NY, United States
| | - Nicolas Massaly
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, MO, United States
- Pain Center, Washington University in St. Louis, St. Louis, MO, United States
- School of Medicine, Washington University in St. Louis, St. Louis, MO, United States
| | - Jose A. Morón
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, MO, United States
- Pain Center, Washington University in St. Louis, St. Louis, MO, United States
- School of Medicine, Washington University in St. Louis, St. Louis, MO, United States
- Department of Neuroscience, Washington University in St. Louis, St. Louis, MO, United States
- Department of Psychiatry, Washington University in St. Louis, St. Louis, MO, United States
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7
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Targeting G protein coupled receptors for alleviating neuropathic pain. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2022; 193:99-117. [PMID: 36357081 DOI: 10.1016/bs.pmbts.2022.06.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Pain sensation is a normal physiological response to alert and prevent further tissue damage. It involves the perception of external stimuli by somatosensory neurons, then transmission of the message to various other types of neurons present in the spinal cord and brain to generate an appropriate response. Currently available analgesics exhibit very modest efficacy, and that too in only a subset of patients with chronic pain conditions, particularly neuropathic pain. The G protein-coupled receptors (GPCRs) are expressed on presynaptic, postsynaptic terminals, and soma of somatosensory neurons, which binds to various types of ligands to modulate neuronal activity and thus pain sensation in both directions. Fundamentally, neuropathic pain arises due to aberrant neuronal plasticity, which includes the sensitization of peripheral primary afferents (dorsal root ganglia and trigeminal ganglia) and the sensitization of central nociceptive neurons in the spinal cord or trigeminal nucleus or brain stem and cortex. Owing to the expression profiles of GPCRs in somatosensory neurons and other neuroanatomical regions involved in pain processing and transmission, this article shall focus only on four families of GPCRs: 1- Opioid receptors, 2-Cannabinoid receptors, 3-Adenosine receptors, and 4-Chemokine receptors.
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8
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Alipio JB, Riggs LM, Plank M, Keller A. Environmental Enrichment Mitigates the Long-Lasting Sequelae of Perinatal Fentanyl Exposure in Mice. J Neurosci 2022; 42:3557-3569. [PMID: 35332082 PMCID: PMC9053848 DOI: 10.1523/jneurosci.2083-21.2022] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2021] [Revised: 03/04/2022] [Accepted: 03/09/2022] [Indexed: 11/21/2022] Open
Abstract
The opioid epidemic is a rapidly evolving societal issue driven, in part, by a surge in synthetic opioid use. A rise in fentanyl use among pregnant women has led to a 40-fold increase in the number of perinatally-exposed infants in the past decade. These children are more likely to develop mood-related and somatosensory-related conditions later in life, suggesting that fentanyl may permanently alter neural development. Here, we examined the behavioral and synaptic consequences of perinatal fentanyl exposure in adolescent male and female C57BL/6J mice and assessed the therapeutic potential of environmental enrichment to mitigate these effects. Dams were given ad libitum access to fentanyl (10 µg/ml, per os) across pregnancy and until weaning [postnatal day (PD)21]. Perinatally-exposed adolescent mice displayed hyperactivity (PD45), enhanced sensitivity to anxiogenic environments (PD46), and sensory maladaptation (PD47), sustained behavioral effects that were completely normalized by environmental enrichment (PD21-PD45). Additionally, environmental enrichment normalized the fentanyl-induced changes in the frequency of miniature EPSCs (mEPSCs) of layer 2/3 neurons in the primary somatosensory cortex (S1). We also demonstrate that fentanyl impairs short-term potentiation (STP) and long-term potentiation (LTP) in S1 layer 2/3 neurons, which, instead, exhibit a sustained depression of synaptic transmission that is restored by environmental enrichment. On its own, environmental enrichment suppressed long-term depression (LTD) of control S1 neurons from vehicle-treated mice subjected to standard housing conditions. These results demonstrate that the lasting effects of fentanyl can be ameliorated with a noninvasive intervention introduced during early development.SIGNIFICANCE STATEMENT Illicit use of fentanyl accounts for a large proportion of opioid-related overdose deaths. Children exposed to opioids during development have a higher risk of developing neuropsychiatric disorders later in life. Here, we employ a preclinical model of perinatal fentanyl exposure that recapitulates these long-term impairments and show, for the first time, that environmental enrichment can reverse deficits in somatosensory circuit function and behavior. These findings have the potential to directly inform and guide ongoing efforts to mitigate the consequences of perinatal opioid exposure.
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Affiliation(s)
- Jason Bondoc Alipio
- Department of Anatomy and Neurobiology, Program in Neuroscience, University of Maryland School of Medicine, Baltimore, MD 21201
| | - Lace Marie Riggs
- Department of Psychiatry, Division of Translational and Basic Science, Program in Neuroscience and Training Program in Integrative Membrane Biology, University of Maryland School of Medicine, Baltimore, MD 21201
| | - Madeline Plank
- Department of Anatomy and Neurobiology, Program in Neuroscience, University of Maryland School of Medicine, Baltimore, MD 21201
| | - Asaf Keller
- Department of Anatomy and Neurobiology, Program in Neuroscience, University of Maryland School of Medicine, Baltimore, MD 21201
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9
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Massaly N, Markovic T, Creed M, Al-Hasani R, Cahill CM, Moron JA. Pain, negative affective states and opioid-based analgesics: Safer pain therapies to dampen addiction. INTERNATIONAL REVIEW OF NEUROBIOLOGY 2022; 157:31-68. [PMID: 33648672 DOI: 10.1016/bs.irn.2020.09.002] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Across centuries and civilizations opioids have been used to relieve pain. In our modern societies, opioid-based analgesics remain one of the most efficient treatments for acute pain. However, the long-term use of opioids can lead to the development of analgesic tolerance, opioid-induced hyperalgesia, opioid use disorders, and overdose, which can ultimately produce respiratory depressant effects with fatal consequences. In addition to the nociceptive sensory component of pain, negative affective states arising from persistent pain represent a risk factor for developing an opioid use disorder. Several studies have indicated that the increase in prescribed opioid analgesics since the 1990s represents the root of our current opioid epidemic. In this review, we will present our current knowledge on the endogenous opioid system within the pain neuroaxis and the plastic changes occurring in this system that may underlie the occurrence of pain-induced negative affect leading to misuse and abuse of opioid medications. Dissecting the allostatic neuronal changes occurring during pain is the most promising avenue to uncover novel targets for the development of safer pain medications. We will discuss this along with current and potential approaches to treat pain-induced negative affective states that lead to drug misuse. Moreover, this chapter will provide a discussion on potential avenues to reduce the abuse potential of new analgesic drugs and highlight a basis for future research and drug development based on recent advances in this field.
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Affiliation(s)
- Nicolas Massaly
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, MO, United States; Washington University in St Louis, Pain Center, St. Louis, MO, United States; Washington University in St Louis, School of Medicine, St. Louis, MO, United States.
| | - Tamara Markovic
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, MO, United States; Washington University in St Louis, Pain Center, St. Louis, MO, United States; Washington University in St Louis, School of Medicine, St. Louis, MO, United States
| | - Meaghan Creed
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, MO, United States; Washington University in St Louis, Pain Center, St. Louis, MO, United States; Washington University in St Louis, School of Medicine, St. Louis, MO, United States; Department of Neuroscience, Washington University in St. Louis, St. Louis, MO, United States; Department of Psychiatry, Washington University in St. Louis, St. Louis, MO, United States; Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO, United States
| | - Ream Al-Hasani
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, MO, United States; Washington University in St Louis, Pain Center, St. Louis, MO, United States; Washington University in St Louis, School of Medicine, St. Louis, MO, United States; Department of Pharmaceutical and Administrative Sciences, St. Louis College of Pharmacy, St. Louis, MO, United States; Center for Clinical Pharmacology, St. Louis College of Pharmacy and Washington University in St. Louis School of Medicine, St. Louis, MO, United States
| | - Catherine M Cahill
- Department of Psychiatry and Biobehavioural Sciences, University of California, Los Angeles, CA, United States; Shirley and Stefan Hatos Center for Neuropharmacology, University of California Los Angeles, Los Angeles, CA, United States; Jane & Terry Semel Institute for Neuroscience and Human Behavior, University of California Los Angeles, Los Angeles, CA, United States
| | - Jose A Moron
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, MO, United States; Washington University in St Louis, Pain Center, St. Louis, MO, United States; Washington University in St Louis, School of Medicine, St. Louis, MO, United States; Department of Neuroscience, Washington University in St. Louis, St. Louis, MO, United States; Department of Psychiatry, Washington University in St. Louis, St. Louis, MO, United States
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10
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Lack of effect of different pain-related manipulations on opioid self-administration, reinstatement of opioid seeking, and opioid choice in rats. Psychopharmacology (Berl) 2021; 238:1885-1897. [PMID: 33765177 PMCID: PMC10041878 DOI: 10.1007/s00213-021-05816-9] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/12/2021] [Accepted: 03/01/2021] [Indexed: 01/26/2023]
Abstract
RATIONALE AND OBJECTIVE Pain-related factors increase the risk for opioid addiction, and pain may function as a negative reinforcer to increase opioid taking and seeking. However, experimental pain-related manipulations generally do not increase opioid self-administration in rodents. This discrepancy may reflect insufficient learning of pain-relief contingencies or confounding effects of pain-related behavioral impairments. Here, we determined if pairing noxious stimuli with opioid self-administration would promote pain-related reinstatement of opioid seeking or increase opioid choice over food. METHODS In Experiment 1, rats self-administered fentanyl in the presence or absence of repeated intraplantar capsaicin injections in distinct contexts to model context-specific exposure to cutaneous nociception. After capsaicin-free extinction in both contexts, we tested if capsaicin would reinstate fentanyl seeking. In Experiment 2, rats self-administered heroin after intraperitoneal (i.p.) lactic acid injections to model acute visceral inflammatory pain. After lactic acid-free extinction, we tested if lactic acid would reinstate heroin seeking. In Experiment 3, we tested if repeated i.p. lactic acid or intraplantar Complete Freund's Adjuvant (CFA; to model sustained inflammatory pain) would increase fentanyl choice over food. RESULTS In Experiments 1-2, neither capsaicin nor lactic acid reinstated opioid seeking after extinction, and lactic acid did not increase heroin-induced reinstatement. In Experiment 3, lactic acid and CFA decreased reinforcement rate without affecting fentanyl choice. CONCLUSIONS Results extend the range of conditions across which pain-related manipulations fail to increase opioid seeking in rats and suggest that enhanced opioid-addiction risk in humans with chronic pain involves factors other than enhanced opioid reinforcement and relapse.
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11
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Alipio JB, Brockett AT, Fox ME, Tennyson SS, deBettencourt CA, El-Metwally D, Francis NA, Kanold PO, Lobo MK, Roesch MR, Keller A. Enduring consequences of perinatal fentanyl exposure in mice. Addict Biol 2021; 26:e12895. [PMID: 32187805 PMCID: PMC7897444 DOI: 10.1111/adb.12895] [Citation(s) in RCA: 28] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2019] [Revised: 02/28/2020] [Accepted: 02/29/2020] [Indexed: 12/14/2022]
Abstract
Opioid use by pregnant women is an understudied consequence associated with the opioid epidemic, resulting in a rise in the incidence of neonatal opioid withdrawal syndrome (NOWS) and lifelong neurobehavioral deficits that result from perinatal opioid exposure. There are few preclinical models that accurately recapitulate human perinatal drug exposure and few focus on fentanyl, a potent synthetic opioid that is a leading driver of the opioid epidemic. To investigate the consequences of perinatal opioid exposure, we administered fentanyl to mouse dams in their drinking water throughout gestation and until litters were weaned at postnatal day (PD) 21. Fentanyl-exposed dams delivered smaller litters and had higher litter mortality rates compared with controls. Metrics of maternal care behavior were not affected by the treatment, nor were there differences in dams' weight or liquid consumption throughout gestation and 21 days postpartum. Twenty-four hours after weaning and drug cessation, perinatal fentanyl-exposed mice exhibited signs of spontaneous somatic withdrawal behavior and sex-specific weight fluctuations that normalized in adulthood. At adolescence (PD 35), they displayed elevated anxiety-like behaviors and decreased grooming, assayed in the elevated plus maze and sucrose splash tests. Finally, by adulthood (PD 55), they displayed impaired performance in a two-tone auditory discrimination task. Collectively, our findings suggest that perinatal fentanyl-exposed mice exhibit somatic withdrawal behavior and change into early adulthood reminiscent of humans born with NOWS.
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Affiliation(s)
- Jason B. Alipio
- Department of Anatomy & Neurobiology, Program in Neuroscience, University of Maryland School of Medicine, Baltimore, MD, USA
| | - Adam T. Brockett
- Department of Psychology, University of Maryland, College Park, MD, USA
- Program in Neuroscience and Cognitive Science, University of Maryland, College Park, MD, USA
| | - Megan E. Fox
- Department of Anatomy & Neurobiology, Program in Neuroscience, University of Maryland School of Medicine, Baltimore, MD, USA
| | - Stephen S. Tennyson
- Department of Psychology, University of Maryland, College Park, MD, USA
- Program in Neuroscience and Cognitive Science, University of Maryland, College Park, MD, USA
| | | | - Dina El-Metwally
- Department of Pediatrics, University of Maryland School of Medicine, Baltimore, MD, USA
| | - Nikolas A. Francis
- Department of Biology, University of Maryland, College Park, MD, USA
- Institute for Systems Research, A. James Clark School of Engineering, University of Maryland, College Park, MD, USA
| | - Patrick O. Kanold
- Department of Biology, University of Maryland, College Park, MD, USA
- Institute for Systems Research, A. James Clark School of Engineering, University of Maryland, College Park, MD, USA
| | - Mary Kay Lobo
- Department of Anatomy & Neurobiology, Program in Neuroscience, University of Maryland School of Medicine, Baltimore, MD, USA
| | - Matthew R. Roesch
- Department of Psychology, University of Maryland, College Park, MD, USA
- Program in Neuroscience and Cognitive Science, University of Maryland, College Park, MD, USA
| | - Asaf Keller
- Department of Anatomy & Neurobiology, Program in Neuroscience, University of Maryland School of Medicine, Baltimore, MD, USA
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12
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Speltz R, Lunzer MM, Shueb SS, Akgün E, Reed R, Kalyuzhny A, Portoghese PS, Simone DA. The bivalent ligand, MMG22, reduces neuropathic pain after nerve injury without the side effects of traditional opioids. Pain 2020; 161:2041-2057. [PMID: 32345918 PMCID: PMC7606301 DOI: 10.1097/j.pain.0000000000001902] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2019] [Accepted: 04/21/2020] [Indexed: 11/26/2022]
Abstract
ABSTRACT Functional interactions between the mu opioid receptor (MOR) and the metabotropic glutamate receptor 5 (mGluR5) in pain and analgesia have been well established. MMG22 is a bivalent ligand containing MOR agonist (oxymorphamine) and mGluR5 antagonist (MPEP) pharmacophores tethered by a 22-atom linker. MMG22 has been shown to produce potent analgesia in several models of chronic inflammatory and neuropathic pain (NP). This study assessed the efficacy of systemic administration of MMG22 at reducing pain behavior in the spared nerve injury (SNI) model of NP in mice, as well as its side-effect profile and abuse potential. MMG22 reduced mechanical hyperalgesia and spontaneous ongoing pain after SNI, with greater potency early (10 days) as compared to late (30 days) after injury. Systemic administration of MMG22 did not induce place preference in naive animals, suggesting absence of abuse liability when compared to traditional opioids. MMG22 also lacked the central locomotor, respiratory, and anxiolytic side effects of its monomeric pharmacophores. Evaluation of mRNA expression showed the transcripts for both receptors were colocalized in cells in the dorsal horn of the lumbar spinal cord and dorsal root ganglia. Thus, MMG22 reduces hyperalgesia after injury in the SNI model of NP without the typical centrally mediated side effects associated with traditional opioids.
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Affiliation(s)
- Rebecca Speltz
- Department of Diagnostic and Biological Sciences, School of Dentistry, University of Minnesota, Minneapolis, MN, United States
- Department of Neuroscience, School of Medicine, University of Minnesota, Minneapolis, MN, United States
| | - Mary M Lunzer
- Department of Medicinal Chemistry, College of Pharmacy, University of Minnesota, Minneapolis, MN, United States
| | - Sarah S Shueb
- Department of Diagnostic and Biological Sciences, School of Dentistry, University of Minnesota, Minneapolis, MN, United States
| | - Eyup Akgün
- Department of Medicinal Chemistry, College of Pharmacy, University of Minnesota, Minneapolis, MN, United States
| | | | - Alex Kalyuzhny
- Department of Diagnostic and Biological Sciences, School of Dentistry, University of Minnesota, Minneapolis, MN, United States
- Bio-Techne, Minneapolis, MN, United States
| | - Philip S Portoghese
- Department of Medicinal Chemistry, College of Pharmacy, University of Minnesota, Minneapolis, MN, United States
| | - Donald A Simone
- Department of Diagnostic and Biological Sciences, School of Dentistry, University of Minnesota, Minneapolis, MN, United States
- Department of Neuroscience, School of Medicine, University of Minnesota, Minneapolis, MN, United States
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13
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Punishment and reinforcement by opioid receptor agonists in a choice procedure in rats. Behav Pharmacol 2020; 30:335-342. [PMID: 30320606 DOI: 10.1097/fbp.0000000000000436] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Intravenous (i.v.) drug self-administration remains the 'gold standard' for assessing abuse potential of drugs. Failure of a drug to maintain self-administration might indicate merely the absence of positive-reinforcing effects but might also indicate presence of aversive effects. Sensitivity to aversive effects is thought to affect the initiation and maintenance of drug use as well as relapse. Choice procedures are used to study positive-reinforcing effects of drugs and to a much lesser extent to study punishing effects of drugs. Experiment 1 compared the μ-opioid receptor agonist remifentanil (0.001-0.01 mg/kg/infusion), the κ-opioid receptor agonist spiradoline (0.0056-0.056 mg/kg/infusion), and histamine (1.0 mg/kg/infusion) in rats choosing between a food pellet only and an i.v. infusion+a food pellet. To test whether a history with one punishing drug affects the punishing effects of a second drug, experiment 2 compared sensitivity with spiradoline in rats with and without a history of histamine punishment. All rats predominantly chose a pellet alone when histamine+a pellet was the alternative, and they predominantly chose remifentanil+a pellet over a pellet alone. In experiment 2, spiradoline was punishing in rats with a history of histamine punishment but not drug-naive rats. This food choice procedure is sensitive to reinforcing and punishing effects of different drugs in the same subjects, suggesting that the procedure is well-suited for studying drug mixtures (e.g. μ and κ agonists) and the impact of different physiological conditions (e.g. pain) on reinforcement and punishment.
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14
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Thompson JB, Conrad SE, Torres C, Papini MR. Inescapable exposure to the Barnes maze increases preference for alcohol over water in rats: Implications for depression and anxiety. LEARNING AND MOTIVATION 2020. [DOI: 10.1016/j.lmot.2019.101602] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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15
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Hou YY, Cai YQ, Pan ZZ. GluA1 in Central Amygdala Promotes Opioid Use and Reverses Inhibitory Effect of Pain. Neuroscience 2019; 426:141-153. [PMID: 31863796 DOI: 10.1016/j.neuroscience.2019.11.032] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2019] [Revised: 11/20/2019] [Accepted: 11/21/2019] [Indexed: 01/22/2023]
Abstract
Increasing evidence suggests that long-term opioids and pain induce similar adaptive changes in the brain's reward circuits, however, how pain alters the addictive properties of opioids remains poorly understood. In this study using a rat model of morphine self-administration (MSA), we found that short-term pain, induced by an intraplantar injection of complete Freund's adjuvant (CFA), acutely decreased voluntary morphine intake, but not food intake, only at a morphine dose that did not affect pain itself. Pre-treatment with indomethacin, a non-opioid inhibitor of pain, before the pain induction blocked the decrease in morphine intake. In rats with steady MSA, the protein level of GluA1 subunits of glutamate AMPA receptors (AMPARs) was significantly increased, but that of GluA2 was decreased, resulting in an increased GluA1/GluA2 ratio in central nucleus of the amygdala (CeA). In contrast, pain decreased the GluA1/GluA2 ratio in the CeA of rats with MSA. Microinjection of NASPM, a selective inhibitor of homomeric GluA1-AMPARs, into CeA inhibited morphine intake. Furthermore, viral overexpression of GluA1 protein in CeA maintained morphine intake at a higher level than controls and reversed the pain-induced reduction in morphine intake. These findings suggest that CeA GluA1 promotes opioid use and its upregulation is sufficient to increase opioid consumption, which counteracts the acute inhibitory effect of pain on opioid intake. These results demonstrate that the CeA GluA1 is a shared target of opioid and pain in regulation of opioid use, which may aid in future development of therapeutic applications in opioid abuse.
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Affiliation(s)
- Yuan-Yuan Hou
- Department of Anesthesiology and Pain Medicine, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030, USA
| | - You-Qing Cai
- Department of Anesthesiology and Pain Medicine, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030, USA
| | - Zhizhong Z Pan
- Department of Anesthesiology and Pain Medicine, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030, USA.
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16
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Bechara A, Berridge KC, Bickel WK, Morón JA, Williams SB, Stein JS. A Neurobehavioral Approach to Addiction: Implications for the Opioid Epidemic and the Psychology of Addiction. Psychol Sci Public Interest 2019; 20:96-127. [PMID: 31591935 PMCID: PMC7001788 DOI: 10.1177/1529100619860513] [Citation(s) in RCA: 44] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Two major questions about addictive behaviors need to be explained by any worthwhile neurobiological theory. First, why do people seek drugs in the first place? Second, why do some people who use drugs seem to eventually become unable to resist drug temptation and so become "addicted"? We will review the theories of addiction that address negative-reinforcement views of drug use (i.e., taking opioids to alleviate distress or withdrawal), positive-reinforcement views (i.e., taking drugs for euphoria), habit views (i.e., growth of automatic drug-use routines), incentive-sensitization views (i.e., growth of excessive "wanting" to take drugs as a result of dopamine-related sensitization), and cognitive-dysfunction views (i.e., impaired prefrontal top-down control), including those involving competing neurobehavioral decision systems (CNDS), and the role of the insula in modulating addictive drug craving. In the special case of opioids, particular attention is paid to whether their analgesic effects overlap with their reinforcing effects and whether the perceived low risk of taking legal medicinal opioids, which are often prescribed by a health professional, could play a role in the decision to use. Specifically, we will address the issue of predisposition or vulnerability to becoming addicted to drugs (i.e., the question of why some people who experiment with drugs develop an addiction, while others do not). Finally, we review attempts to develop novel therapeutic strategies and policy ideas that could help prevent opioid and other substance abuse.
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Affiliation(s)
- Antoine Bechara
- Department of Psychology, University of Southern California
- Brain and Creativity Institute, University of Southern California
| | | | - Warren K. Bickel
- Addiction Recovery Research Center & Center for Transformational Research on Health Behaviors, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, Virginia
| | - Jose A. Morón
- Department of Anesthesiology, Washington University School of Medicine
- Washington University Pain Center, Washington University School of Medicine
| | - Sidney B. Williams
- Department of Anesthesiology, Washington University School of Medicine
- Washington University Pain Center, Washington University School of Medicine
| | - Jeffrey S. Stein
- Addiction Recovery Research Center & Center for Transformational Research on Health Behaviors, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, Virginia
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17
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Abstract
Pain has a useful protective role; through avoidance learning, it helps to decrease the probability of engaging in tissue-damaging, or otherwise dangerous experiences. In our modern society, the experience of acute post-surgical pain and the development of chronic pain states represent an unnecessary negative outcome. This has become an important health issue as more than 30% of the US population reports experiencing "unnecessary" pain at any given time. Opioid therapies are often efficacious treatments for severe and acute pain; however, in addition to their powerful analgesic properties, opioids produce potent reinforcing properties and their inappropriate use has led to the current opioid overdose epidemic in North America. Dissecting the allostatic changes occurring in nociceptors and neuronal pathways in response to pain are the first and most important steps in understanding the physiologic changes underlying the opioid epidemic. Full characterization of these adaptations will provide novel targets for the development of safer pharmacotherapies. In this review, we highlight the current efforts toward safer opioid treatments and describe our current knowledge of the interaction between pain and opioid systems.
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Affiliation(s)
- Nicolas Massaly
- Department of Anesthesiology; Washington University in St. Louis; St. Louis, MO, 63110 ; USA
- Washington University Pain Center; St. Louis, MO, 63110 ; USA
- Washington University in St Louis; School of Medicine; St. Louis, MO, 63110 ; USA
| | - Jose A Morón
- Department of Anesthesiology; Washington University in St. Louis; St. Louis, MO, 63110 ; USA
- Washington University Pain Center; St. Louis, MO, 63110 ; USA
- Washington University in St Louis; School of Medicine; St. Louis, MO, 63110 ; USA
- Department of Neuroscience; Washington University in St. Louis; St. Louis, MO, 63110 ; USA
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18
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Taylor AM. Corticolimbic circuitry in the modulation of chronic pain and substance abuse. Prog Neuropsychopharmacol Biol Psychiatry 2018; 87:263-268. [PMID: 28501595 PMCID: PMC5681440 DOI: 10.1016/j.pnpbp.2017.05.009] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/16/2017] [Revised: 04/14/2017] [Accepted: 05/10/2017] [Indexed: 12/13/2022]
Abstract
The transition from acute to chronic pain is accompanied by increased engagement of emotional and motivational circuits. Adaptations within this corticolimbic circuitry contribute to the cellular and behavioral maladaptations associated with chronic pain. Central regions within the corticolimbic brain include the mesolimbic dopamine system, the amygdala, and the medial prefrontal cortex. The evidence reviewed herein supports the notion that chronic pain induces significant changes within these corticolimbic regions that contribute to the chronicity and intractability of pain. In addition, pain-induced changes in corticolimbic circuitry are poised to impact motivated behavior and reward responsiveness to environmental stimuli, and may modulate the addiction liability of drugs of abuse, such as opioids.
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Affiliation(s)
- Anna M.W. Taylor
- Department of Psychiatry and the Semel Institute for Neuroscience and Human Behavior, University of California, Los Angeles
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19
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Comer SD, Cahill CM. Fentanyl: Receptor pharmacology, abuse potential, and implications for treatment. Neurosci Biobehav Rev 2018; 106:49-57. [PMID: 30528374 DOI: 10.1016/j.neubiorev.2018.12.005] [Citation(s) in RCA: 126] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2018] [Revised: 11/30/2018] [Accepted: 12/04/2018] [Indexed: 12/16/2022]
Abstract
Opioid overdoses, many of which are attributed to use of illicit fentanyl, are currently one of the leading causes of death in the U.S. Although fentanyl has been used safely for decades in clinical settings, the widespread use of illicit fentanyl is a recent phenomenon. Starting in 2013, illicitly manufactured fentanyl and its analogs began to appear on the streets. These substances were added to or sold as heroin, often unbeknownst to the user. Because fentanyl is so potent, only small amounts are needed to produce pharmacological effects, but the margin between safe and toxic doses is narrow. Surprisingly little is known about the exact signaling mechanisms underlying fentanyl-related respiratory depression or the effectiveness of naloxone in reversing this effect. Similarly, little is known about the ability of treatment medications such as buprenorphine, methadone, or naltrexone to reduce illicit fentanyl use. The present article reviews the receptor, preclinical and clinical pharmacology of fentanyl, and how its pharmacology may predict the effectiveness of currently approved medications for treating illicit fentanyl use.
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Affiliation(s)
- Sandra D Comer
- New York State Psychiatric Institute and Columbia University, New York, NY, 10027, United States.
| | - Catherine M Cahill
- Semel Institute for Neuroscience and Human Behavior, University of California Los Angeles, Los Angeles, California, 90095, United States
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20
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Grim TW, Jinhong Park S, Schmid CL, Laprairie RB, Cameron M, Bohn LM. The effect of quinine in two bottle choice procedures in C57BL6 mice: Opioid preference, somatic withdrawal, and pharmacokinetic outcomes. Drug Alcohol Depend 2018; 191:195-202. [PMID: 30138791 PMCID: PMC6317844 DOI: 10.1016/j.drugalcdep.2018.05.034] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/01/2018] [Revised: 05/01/2018] [Accepted: 05/09/2018] [Indexed: 10/28/2022]
Abstract
Previous reports assessing morphine effects in two bottle choice (TBC) paradigms often use taste adulterants such as sweeteners (e.g., saccharin) and/or bitterants (e.g., quinine) to demonstrate morphine preference with C57BL6 mice. The effect of these additional components on the morphine preference of C57BL6 remains poorly understood. Thus, we sought to elucidate the interrelationship of morphine and quinine in the TBC paradigm. As expected, when morphine was included in the opposite bottle from quinine, a preference for the morphine solution was observed. Conversely, when quinine was included in each bottle, or when fentanyl without quinine was used, no preference was observed. All opioid-drinking mice displayed withdrawal signs, and morphine was detectable in plasma and brain. When these results were compared to previous results via conversion to quinine preference scores, quinine was revealed to determine largely the measured morphine preference. Thus, quinine is effective to drive morphine consumption and engender dependence but may confound the ability to measure oral abuse liability of morphine. Together, these results suggest future TBC procedures should consider the effect of quinine upon measured preference for compounds in the opposite bottle, and that excessively high quinine concentrations appear to influence preference more so than the opposite solute when using C57BL6 mice. Alternative conditions to assess oral abuse liability may be necessary to complement and confirm results from TBC experiments utilizing morphine or other opioids.
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Affiliation(s)
- Travis W Grim
- The Scripps Research Institute, 110 Scripps Way, Jupiter, FL, 33458, USA.
| | | | - Cullen L. Schmid
- The Scripps Research Institute, 110 Scripps Way, Jupiter, FL 33458 USA
| | | | - Michael Cameron
- The Scripps Research Institute, 110 Scripps Way, Jupiter, FL, 33458, USA.
| | - Laura M. Bohn
- The Scripps Research Institute, 110 Scripps Way, Jupiter, FL 33458 USA
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21
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Severino AL, Shadfar A, Hakimian JK, Crane O, Singh G, Heinzerling K, Walwyn WM. Pain Therapy Guided by Purpose and Perspective in Light of the Opioid Epidemic. Front Psychiatry 2018; 9:119. [PMID: 29740351 PMCID: PMC5925443 DOI: 10.3389/fpsyt.2018.00119] [Citation(s) in RCA: 60] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/06/2017] [Accepted: 03/21/2018] [Indexed: 12/12/2022] Open
Abstract
Prescription opioid misuse is an ongoing and escalating epidemic. Although these pharmacological agents are highly effective analgesics prescribed for different types of pain, opioids also induce euphoria, leading to increasing diversion and misuse. Opioid use and related mortalities have developed in spite of initial claims that OxyContin, one of the first opioids prescribed in the USA, was not addictive in the presence of pain. These claims allayed the fears of clinicians and contributed to an increase in the number of prescriptions, quantity of drugs manufactured, and the unforeseen diversion of these drugs for non-medical uses. Understanding the history of opioid drug development, the widespread marketing campaign for opioids, the immense financial incentive behind the treatment of pain, and vulnerable socioeconomic and physical demographics for opioid misuse give perspective on the current epidemic as an American-born problem that has expanded to global significance. In light of the current worldwide opioid epidemic, it is imperative that novel opioids are developed to treat pain without inducing the euphoria that fosters physical dependence and addiction. We describe insights from preclinical findings on the properties of opioid drugs that offer insights into improving abuse-deterrent formulations. One finding is that the ability of some agonists to activate one pathway over another, or agonist bias, can predict whether several novel opioid compounds bear promise in treating pain without causing reward among other off-target effects. In addition, we outline how the pharmacokinetic profile of each opioid contributes to their potential for misuse and discuss the emergence of mixed agonists as a promising pipeline of opioid-based analgesics. These insights from preclinical findings can be used to more effectively identify opioids that treat pain without causing physical dependence and subsequent opioid abuse.
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Affiliation(s)
- Amie L. Severino
- Department of Psychiatry and Biobehavioral Sciences, David Geffen School of Medicine at the University of California Los Angeles, Los Angeles, CA, United States
- Vatche and Tamar Manoukian Division of Digestive Diseases, Department of Medicine, David Geffen School of Medicine at the University of California Los Angeles, Los Angeles, CA, United States
- Veteran Affairs Greater Los Angeles Healthcare System, Los Angeles, CA, United States
- UCLA Brain Research Institute, Los Angeles, Los Angeles, CA, United States
| | - Arash Shadfar
- Department of Psychiatry, Western University of Health Sciences, Pomona, CA, United States
| | - Joshua K. Hakimian
- Department of Psychiatry and Biobehavioral Sciences, David Geffen School of Medicine at the University of California Los Angeles, Los Angeles, CA, United States
- UCLA Brain Research Institute, Los Angeles, Los Angeles, CA, United States
| | - Oliver Crane
- Department of Psychiatry and Biobehavioral Sciences, David Geffen School of Medicine at the University of California Los Angeles, Los Angeles, CA, United States
- UCLA Brain Research Institute, Los Angeles, Los Angeles, CA, United States
| | - Ganeev Singh
- Department of Psychiatry and Biobehavioral Sciences, David Geffen School of Medicine at the University of California Los Angeles, Los Angeles, CA, United States
- UCLA Brain Research Institute, Los Angeles, Los Angeles, CA, United States
| | - Keith Heinzerling
- Department of Family Medicine, David Geffen School of Medicine at the University of California, Los Angeles, CA, United States
| | - Wendy M. Walwyn
- Department of Psychiatry and Biobehavioral Sciences, David Geffen School of Medicine at the University of California Los Angeles, Los Angeles, CA, United States
- UCLA Brain Research Institute, Los Angeles, Los Angeles, CA, United States
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22
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Fujita M, Ide S, Ikeda K. Opioid and nondopamine reward circuitry and state-dependent mechanisms. Ann N Y Acad Sci 2018. [PMID: 29512887 DOI: 10.1111/nyas.13605] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
A common notion is that essentially all addictive drugs, including opioids, activate dopaminergic pathways in the brain reward system, and the inappropriate use of such drugs induces drug dependence. However, an opioid reward response is reportedly still observed in several models of dopamine depletion, including in animals that are treated with dopamine blockers, animals that are subjected to dopaminergic neuron lesions, and dopamine-deficient mice. The intracranial self-stimulation response is enhanced by stimulants but reduced by morphine. These findings suggest that dopaminergic neurotransmission may not always be required for opioid reward responses. Previous findings also indicate the possibility that dopamine-independent opioid reward may be observed in opioid-naive states but not in opioid-dependent states. Therefore, a history of opioid use should be considered when evaluating the dopamine dependency of opioid reward.
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Affiliation(s)
- Masayo Fujita
- Addictive Substance Project, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan
| | - Soichiro Ide
- Addictive Substance Project, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan
| | - Kazutaka Ikeda
- Addictive Substance Project, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan
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23
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Mesolimbic dopamine signaling in acute and chronic pain: implications for motivation, analgesia, and addiction. Pain 2017; 157:1194-1198. [PMID: 26797678 PMCID: PMC4866581 DOI: 10.1097/j.pain.0000000000000494] [Citation(s) in RCA: 153] [Impact Index Per Article: 21.9] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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Neelakantan H, Ward SJ, Walker EA. Effects of paclitaxel on mechanical sensitivity and morphine reward in male and female C57Bl6 mice. Exp Clin Psychopharmacol 2016; 24:485-495. [PMID: 27929349 PMCID: PMC5157702 DOI: 10.1037/pha0000097] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
This study evaluated the hypothesis that a paclitaxel treatment regimen sufficient to produce mechanical allodynia would alter sensitivities of male and female mice to the conditioned rewarding and reinforcing effects of morphine. Saline or paclitaxel were administered on Days 1, 3, 5, and 7 in male and female C57Bl/6 mice to induce morphine-reversible mechanical allodynia as measured by the Von Frey filament test. Paclitaxel treatment did not change sensitivity to morphine conditioned place preference (CPP) relative to saline treatment in either male or female mice. Morphine produced peak self-administration under a fixed ratio-1 (FR1) schedule of reinforcement for 0.03 mg/kg morphine per infusion in female mice and 0.1 mg/kg morphine per infusion in male mice. During the progressive ratio experiments, saline treatment in male mice decreased the number of morphine infusions for 12 days whereas the paclitaxel-treated male mice maintained responding for morphine similar to baseline levels during the same time period. However, paclitaxel did not have an overall effect on the reinforcing efficacy of morphine assessed over a limited dose range during the course of the repeated self-administration. These results suggest that the reward-related behavioral effects of morphine are overall not robustly altered by the presence of paclitaxel treatment under the current dosing regimen, with the exception of maintaining a small yet significant higher baseline than saline treatment during the development of allodynia in male mice. (PsycINFO Database Record
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Affiliation(s)
| | | | - Ellen Ann Walker
- Department of Pharmaceutical Sciences & Center for Substance Abuse Research, Temple University
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25
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Massaly N, Morón JA, Al-Hasani R. A Trigger for Opioid Misuse: Chronic Pain and Stress Dysregulate the Mesolimbic Pathway and Kappa Opioid System. Front Neurosci 2016; 10:480. [PMID: 27872581 PMCID: PMC5097922 DOI: 10.3389/fnins.2016.00480] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2016] [Accepted: 10/06/2016] [Indexed: 12/17/2022] Open
Abstract
Pain and stress are protective mechanisms essential in avoiding harmful or threatening stimuli and ensuring survival. Despite these beneficial roles, chronic exposure to either pain or stress can lead to maladaptive hormonal and neuronal modulations that can result in chronic pain and a wide spectrum of stress-related disorders including anxiety and depression. By inducing allostatic changes in the mesolimbic dopaminergic pathway, both chronic pain and stress disorders affect the rewarding values of both natural reinforcers, such as food or social interaction, and drugs of abuse. Despite opioids representing the best therapeutic strategy in pain conditions, they are often misused as a result of these allostatic changes induced by chronic pain and stress. The kappa opioid receptor (KOR) system is critically involved in these neuronal adaptations in part through its control of dopamine release in the nucleus accumbens. Therefore, it is likely that changes in the kappa opioid system following chronic exposure to pain and stress play a key role in increasing the misuse liability observed in pain patients treated with opioids. In this review, we will discuss how chronic pain and stress-induced pathologies can affect mesolimbic dopaminergic transmission, leading to increased abuse liability. We will also assess how the kappa opioid system may underlie these pathological changes.
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Affiliation(s)
- Nicolas Massaly
- Basic Research Division, Department of Anesthesiology, Washington University School of MedicineSt. Louis, MO, USA; Washington University Pain Center, Department of Anesthesiology, Washington University School of MedicineSt. Louis, MO, USA
| | - Jose A Morón
- Basic Research Division, Department of Anesthesiology, Washington University School of MedicineSt. Louis, MO, USA; Washington University Pain Center, Department of Anesthesiology, Washington University School of MedicineSt. Louis, MO, USA
| | - Ream Al-Hasani
- Basic Research Division, Department of Anesthesiology, Washington University School of Medicine St. Louis, MO, USA
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Barrett JE, Haas DA. Perspectives and Trends in Pharmacological Approaches to the Modulation of Pain. ADVANCES IN PHARMACOLOGY (SAN DIEGO, CALIF.) 2016; 75:1-33. [PMID: 26920007 DOI: 10.1016/bs.apha.2015.12.004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Pharmacological approaches to our understanding and treatment of pain have had a long history and have traditionally relied on very few drugs that either have significant side effects and abuse liability, such as the nonsteroidal anti-inflammatory drugs or the opioids, respectively, or those that have been developed for other conditions such as the tricyclic antidepressants. The pathophysiology of pain is undoubtedly complex, complicated in part by the fact that it is not a singular condition, and has a variety of etiologies and a number of associated comorbidities that make treatment interventions challenging. Moreover, there are changes in the central nervous system during the course of the development of chronic pain that, in a manner parallel to neurodegenerative disorders, likely require different pharmacological approaches in the early stages of acute pain compared to those that would be effective when pain has become chronic. This chapter reviews the current status of the field of pain research focusing on some relatively underdeveloped areas, such as pain and its associated comorbidities, and the use of transgenic animals and drug self-administration procedures in the context of analgesic assessment. This chapter also incorporates more recent developments and emerging trends in the area of epigenetics, biomarkers, and the use of induced pluripotent stem cells for pharmacological evaluation, target identification, and validation. Recent progress in the study of "organs-on-a-chip" will also be included in this overview, setting expectations for future progress that integrates these advances for deeper insights into mechanisms, novel treatments, and facilitated efforts in drug discovery.
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Affiliation(s)
- James E Barrett
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania, USA.
| | - Derick A Haas
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania, USA
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Akgün E, Javed MI, Lunzer MM, Powers MD, Sham YY, Watanabe Y, Portoghese PS. Inhibition of Inflammatory and Neuropathic Pain by Targeting a Mu Opioid Receptor/Chemokine Receptor5 Heteromer (MOR-CCR5). J Med Chem 2015; 58:8647-57. [PMID: 26451468 DOI: 10.1021/acs.jmedchem.5b01245] [Citation(s) in RCA: 49] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Chemokine release promotes cross-talk between opioid and chemokine receptors that in part leads to reduced efficacy of morphine in the treatment of chronic pain. On the basis of the possibility that a MOR-CCR5 heteromer is involved in such cross-talk, we have synthesized bivalent ligands (MCC series) that contain mu opioid agonist and CCR5 antagonist pharmacophores linked through homologous spacers (14-24 atoms). When tested on lipopolysaccharide-inflamed mice, a member of the series (MCC22; 3e) with a 22-atom spacer exhibited profound antinociception (i.t. ED50 = 0.0146 pmol/mouse) that was 2000× greater than morphine. Moreover, MCC22 was ~3500× more potent than a mixture of mu agonist and CCR5 antagonist monovalent ligands. These data strongly suggest that MCC22 acts by bridging the protomers of a MOR-CCR5 heteromer having a TM5,6 interface. Molecular simulation studies are consistent with such bridging. This study supports the MOR-CCR5 heteromer as a novel target for the treatment of chronic pain.
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Affiliation(s)
- Eyup Akgün
- Department of Medicinal Chemistry, and ‡Center for Drug Design, University of Minnesota , Minneapolis, Minnesota 55455, United States
| | - Muhammad I Javed
- Department of Medicinal Chemistry, and ‡Center for Drug Design, University of Minnesota , Minneapolis, Minnesota 55455, United States
| | - Mary M Lunzer
- Department of Medicinal Chemistry, and ‡Center for Drug Design, University of Minnesota , Minneapolis, Minnesota 55455, United States
| | - Michael D Powers
- Department of Medicinal Chemistry, and ‡Center for Drug Design, University of Minnesota , Minneapolis, Minnesota 55455, United States
| | - Yuk Y Sham
- Department of Medicinal Chemistry, and ‡Center for Drug Design, University of Minnesota , Minneapolis, Minnesota 55455, United States
| | - Yoshikazu Watanabe
- Department of Medicinal Chemistry, and ‡Center for Drug Design, University of Minnesota , Minneapolis, Minnesota 55455, United States
| | - Philip S Portoghese
- Department of Medicinal Chemistry, and ‡Center for Drug Design, University of Minnesota , Minneapolis, Minnesota 55455, United States
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Fairbanks CA, Goracke-Postle CJ. Neurobiological studies of chronic pain and analgesia: Rationale and refinements. Eur J Pharmacol 2015; 759:169-81. [PMID: 25818751 DOI: 10.1016/j.ejphar.2015.03.049] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2015] [Revised: 03/05/2015] [Accepted: 03/12/2015] [Indexed: 12/27/2022]
Abstract
Chronic pain is a complex condition for which the need for specialized research and therapies has been recognized internationally. This review summarizes the context for the international call for expansion of pain research to improve our understanding of the mechanisms underlying pain in order to achieve improvements in pain management. The methods for conducting sensory assessment in animal models are discussed and the development of animal models of chronic pain is specifically reviewed, with an emphasis on ongoing refinements to more closely mimic a variety of human pain conditions. Pharmacological correspondences between pre-clinical pain models and the human clinical experience are noted. A discussion of the 3Rs Framework (Replacement, Reduction, Refinement) and how each may be considered in pain research is featured. Finally, suggestions are provided for engaging principal investigators, IACUC reviewers, and institutions in the development of strong partnerships to simultaneously expand our knowledge of the mechanisms underlying pain and analgesia while ensuring the humane use of animals in research.
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Affiliation(s)
- Carolyn A Fairbanks
- University of Minnesota, Department of Pharmaceutics, Minneapolis, MN, USA; University of Minnesota, Department of Pharmacology, Minneapolis, MN, USA; University of Minnesota, Department of Neuroscience, Minneapolis, MN, USA.
| | - Cory J Goracke-Postle
- University of Minnesota, Office of the Vice President for Research, Minneapolis, MN, USA
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Elvemo NA, Landrø NI, Borchgrevink PC, Håberg AK. Reward responsiveness in patients with chronic pain. Eur J Pain 2015; 19:1537-43. [PMID: 25766961 PMCID: PMC6680139 DOI: 10.1002/ejp.687] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/19/2015] [Indexed: 12/16/2022]
Abstract
BACKGROUND It is proposed that changes in reward processing in the brain are involved in the pathophysiology of pain based on experimental studies. The first aim of the present study was to investigate if reward drive and/or reward responsiveness was altered in patients with chronic pain (PCP) compared to controls matched for education, age and sex. The second aim was to investigate the relationship between reward processing and nucleus accumbens volume in PCP and controls. Nucleus accumbens is central in reward processing and its structure has been shown to be affected by chronic pain conditions in previous studies. METHODS Reward drive and responsiveness were assessed with the Behavioral Inhibition Scale/Behavioral Activation Scale, and nucleus accumbens volumes obtained from T1-weighted brain MRIs obtained at 3T in 19 PCP of heterogeneous aetiologies and 20 age-, sex- and education-matched healthy controls. Anhedonia was assessed with Beck's Depression Inventory II. RESULTS The PCP group had significantly reduced scores on the reward responsiveness, but not reward drive. There was a trend towards smaller nucleus accumbens volume in the PCP compared to control group. There was a significant positive partial correlation between reward responsiveness and nucleus accumbens volume in the PCP group adjusted for anhedonia, which was significantly different from the same relationship in the control group. CONCLUSIONS Reward responsiveness is reduced in chronic pain patients of heterogeneous aetiology, and this reduction was associated with nucleus accumbens volume. Reduced reward responsiveness could be a marker of chronic pain vulnerability, and may indicate reduced opioid function.
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Affiliation(s)
- N A Elvemo
- Department of Neuroscience, Norwegian University of Science and Technology (NTNU), Trondheim, Norway
| | - N I Landrø
- Clinical Neuroscience Research Group, Department of Psychology, University of Oslo, Norway.,Department of Circulation and Medical Imaging, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.,National Competence Centre for Complex Symptom Disorders, St. Olav's University Hospital, Trondheim, Norway
| | - P C Borchgrevink
- Department of Circulation and Medical Imaging, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.,National Competence Centre for Complex Symptom Disorders, St. Olav's University Hospital, Trondheim, Norway
| | - A K Håberg
- Department of Neuroscience, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.,Department of Medical Imaging, St. Olav's University Hospital, Trondheim, Norway
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Wade CL, Fairbanks CA. The Self-administration of Analgesic Drugs in Experimentally Induced Chronic Pain. Curr Top Behav Neurosci 2014; 20:217-232. [PMID: 25205326 DOI: 10.1007/7854_2014_344] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Systemically and centrally delivered opioids have been comprehensively studied for their effects both in analgesic and addiction models for many decades, primarily in subjects with presumptive normal sensory thresholds. The introduction of disease-based models of persistent hypersensitivity enabled chronic evaluation of opioid analgesic pharmacology under the specific state of chronic pain. These studies have largely (but not uniformly) reported reduced opioid analgesic potency and efficacy under conditions of chronic pain. A comparatively limited set of studies has evaluated the impact of experimentally induced chronic pain on self-administration patterns of opioid and non-opioid analgesics. Similarly, these studies have primarily (but not exclusively) found that responding for opioids is reduced under conditions of chronic pain. Additionally, such experiments have also demonstrated that the condition of chronic pain evokes self-administration or conditioned place preference for non-opioid analgesics. The consensus is that the chronic pain alters responding for opioid and non-opioid analgesics in a manner seemingly related to their respective antiallodynic/antihyperalgesic properties under the specific state of chronic pain.
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Affiliation(s)
- Carrie L Wade
- Committee on the Neurobiology of Addictive Disorders, The Scripps Research Institute, La Jolla, CA, 92037, USA
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