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De Almeida SS, Drinkuth CR, Sartor GC. Comparing withdrawal- and anxiety-like behaviors following oral and subcutaneous oxycodone administration in C57BL/6 mice. Behav Pharmacol 2024; 35:269-279. [PMID: 38847447 PMCID: PMC11226370 DOI: 10.1097/fbp.0000000000000780] [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] [Indexed: 07/06/2024]
Abstract
Excessive prescribing and misuse of prescription opioids, such as oxycodone, significantly contributed to the current opioid crisis. Although oxycodone is typically consumed orally by humans, parenteral routes of administration have primarily been used in preclinical models of oxycodone dependence. To address this issue, more recent studies have used oral self-administration procedures to study oxycodone seeking and withdrawal in rodents. Behavioral differences, however, following oral oxycodone intake versus parenteral oxycodone administration remain unclear. Thus, the goal of the current studies was to compare anxiety- and withdrawal-like behaviors using established opioid dependence models of either home cage oral intake of oxycodone (0.5 mg/ml) or repeated subcutaneous (s.c.) injections of oxycodone (10 mg/kg) in male and female mice. Here, mice received 10 days of oral or s.c. oxycodone administration, and following 72 h of forced abstinence, anxiety- and withdrawal-like behaviors were measured using elevated zero maze, open field, and naloxone-induced precipitated withdrawal procedures. Global withdrawal scores were increased to a similar degree following oral and s.c. oxycodone use, while both routes of oxycodone administration had minimal effects on anxiety-like behaviors. When examining individual withdrawal-like behaviors, mice receiving s.c. oxycodone exhibited more paw tremors and jumps during naloxone-induced precipitated withdrawal compared with oral oxycodone mice. These results indicate that both models of oxycodone administration are sufficient to elevate global withdrawal scores, but, when compared with oral consumption, s.c. oxycodone injections yielded more pronounced effects on some withdrawal-like behaviors.
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Affiliation(s)
| | | | - Gregory C. Sartor
- Department of Pharmaceutical Sciences, Institute for the Brain and Cognitive Sciences (IBACS), University of Connecticut, Storrs, CT 06269
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2
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Downs AM, Kmiec G, McElligott ZA. Oral Fentanyl Consumption and Withdrawal Impairs Fear Extinction Learning and Enhances Basolateral Amygdala Principal Neuron Excitatory-Inhibitory Balance in Male and Female Mice. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2023.11.28.569085. [PMID: 38076868 PMCID: PMC10705490 DOI: 10.1101/2023.11.28.569085] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2024]
Abstract
The number of opioid overdose deaths has increased over the past several years, mainly driven by an increase in the availability of highly potent synthetic opioids, like fentanyl, in the un-regulated drug supply. Over the last few years, changes in the drug supply, and in particular the availability of counterfeit pills containing fentanyl, have made oral use of opioids a more common route of administration. Here, we used a drinking in the dark (DiD) paradigm to model oral fentanyl self-administration using increasing fentanyl concentrations in male and female mice over 5 weeks. Fentanyl consumption peaked in both female and male mice at the 30 µg/mL dose, with female mice consuming significantly more fentanyl than male mice. Mice consumed sufficient fentanyl such that withdrawal was precipitated with naloxone, with males having more withdrawal symptoms, despite lower pharmacological exposure. We also performed behavioral assays to measure avoidance behavior and reward-seeking during fentanyl abstinence. Female mice displayed reduced avoidance behaviors in the open field assay, whereas male mice showed increased avoidance in the light/dark box assay. Female mice also exhibited increased reward-seeking in the sucrose preference test. Fentanyl-consuming mice of both sexes showed impaired cued fear extinction learning following fear conditioning and increased excitatory synaptic drive and increased excitability of BLA principal neurons. Our experiments demonstrate that long-term oral fentanyl consumption results in wide-ranging physiological and behavioral disruptions. This model could be useful to further study fentanyl withdrawal syndrome and behaviors and neuroplasticity associated with protracted fentanyl withdrawal.
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Peart DR, Nolan CJ, Stone AP, Williams MA, Karlovcec JM, Murray JE. Disruption of positive- and negative-feature morphine interoceptive occasion setters by dopamine receptor agonism and antagonism in male and female rats. Psychopharmacology (Berl) 2024:10.1007/s00213-024-06584-y. [PMID: 38580732 DOI: 10.1007/s00213-024-06584-y] [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: 07/16/2023] [Accepted: 03/29/2024] [Indexed: 04/07/2024]
Abstract
RATIONALE Internally perceived stimuli evoked by morphine administration can form Pavlovian associations such that they can function as occasion setters (OSs) for externally perceived reward cues in rats, coming to modulate reward-seeking behaviour. Though much research has investigated mechanisms underlying opioid-related reinforcement and analgesia, neurotransmitter systems involved in the functioning of opioids as Pavlovian interoceptive discriminative stimuli remain to be disentangled despite documented differences in the development of tolerance to analgesic versus discriminative stimulus effects. OBJECTIVES Dopamine has been implicated in many opioid-related behaviours, so we aimed to investigate the role of this neurotransmitter in expression of morphine occasion setting. METHODS Male and female rats were assigned to positive- (FP) or negative-feature (FN) groups and received an injection of morphine or saline before each training session. A 15-s white noise conditioned stimulus (CS) was presented 8 times during every training session; offset of this stimulus was followed by 4-s access to liquid sucrose on morphine, but not saline, sessions for FP rats. FN rats learned the reverse contingency. Following stable discrimination, rats began generalization testing for expression of morphine-guided sucrose seeking after systemic pretreatment with different doses of the non-selective dopamine receptor antagonist, flupenthixol, and the non-selective dopamine receptor agonist, apomorphine, combined with training doses of morphine or saline in a Latin-square design. RESULTS The morphine discrimination was acquired under both FP and FN contingencies by males and females. Neither flupenthixol nor apomorphine at any dose substituted for morphine, but both apomorphine and flupenthixol disrupted expression of the morphine OS. This inhibition was specific to sucrose seeking during CS presentations rather than during the period before CS onset and, in the case of apomorphine more so than flupenthixol, to trials on which access to sucrose was anticipated. CONCLUSIONS Our findings lend support to a mechanism of occasion setting involving gating of CS-induced dopamine release rather than by direct dopaminergic modulation by the morphine stimulus.
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Affiliation(s)
- Davin R Peart
- Department of Psychology, University of Guelph, 50 Stone Road East, Guelph, ON, N1G 2W1, Canada
- Collaborative Neurosciences Graduate Program, University of Guelph, 50 Stone Road East, Guelph, ON, N1G 2W1, Canada
| | - Caitlin J Nolan
- Collaborative Neurosciences Graduate Program, University of Guelph, 50 Stone Road East, Guelph, ON, N1G 2W1, Canada
- Department of Biomedical Sciences, University of Guelph, Guelph, ON, Canada
| | - Adiia P Stone
- Department of Psychology, University of Guelph, 50 Stone Road East, Guelph, ON, N1G 2W1, Canada
- Collaborative Neurosciences Graduate Program, University of Guelph, 50 Stone Road East, Guelph, ON, N1G 2W1, Canada
| | - Mckenna A Williams
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada
| | - Jessica M Karlovcec
- Department of Psychology, University of Guelph, 50 Stone Road East, Guelph, ON, N1G 2W1, Canada
- Collaborative Neurosciences Graduate Program, University of Guelph, 50 Stone Road East, Guelph, ON, N1G 2W1, Canada
| | - Jennifer E Murray
- Department of Psychology, University of Guelph, 50 Stone Road East, Guelph, ON, N1G 2W1, Canada.
- Collaborative Neurosciences Graduate Program, University of Guelph, 50 Stone Road East, Guelph, ON, N1G 2W1, Canada.
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McGovern DJ, Polter AM, Prévost ED, Ly A, McNulty CJ, Rubinstein B, Root DH. Ventral tegmental area glutamate neurons establish a mu-opioid receptor gated circuit to mesolimbic dopamine neurons and regulate opioid-seeking behavior. Neuropsychopharmacology 2023; 48:1889-1900. [PMID: 37407648 PMCID: PMC10584944 DOI: 10.1038/s41386-023-01637-w] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/02/2022] [Revised: 06/14/2023] [Accepted: 06/16/2023] [Indexed: 07/07/2023]
Abstract
A two-neuron model of ventral tegmental area (VTA) opioid function classically involves VTA GABA neuron regulation of VTA dopamine neurons via a mu-opioid receptor dependent inhibitory circuit. However, this model predates the discovery of a third major type of neuron in the VTA: glutamatergic neurons. We found that about one-quarter of VTA neurons expressing the mu-opioid receptor are glutamate neurons without molecular markers of GABA co-release. Glutamate-Mu opioid receptor neurons are largely distributed in the anterior VTA. The majority of remaining VTA mu-opioid receptor neurons are GABAergic neurons that are mostly within the posterior VTA and do not express molecular markers of glutamate co-release. Optogenetic stimulation of VTA glutamate neurons resulted in excitatory currents recorded from VTA dopamine neurons that were reduced by presynaptic activation of the mu-opioid receptor ex vivo, establishing a local mu-opioid receptor dependent excitatory circuit from VTA glutamate neurons to VTA dopamine neurons. This VTA glutamate to VTA dopamine pathway regulated dopamine release to the nucleus accumbens through mu-opioid receptor activity in vivo. Behaviorally, VTA glutamate calcium-related neuronal activity increased following oral oxycodone consumption during self-administration and response-contingent oxycodone-associated cues during abstinent reinstatement of drug-seeking behavior. Further, chemogenetic inhibition of VTA glutamate neurons reduced abstinent oral oxycodone-seeking behavior in male but not female mice. These results establish 1) a three-neuron model of VTA opioid function involving a mu-opioid receptor gated VTA glutamate neuron pathway to VTA dopamine neurons that controls dopamine release within the nucleus accumbens, and 2) that VTA glutamate neurons participate in opioid-seeking behavior.
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Affiliation(s)
- Dillon J McGovern
- Department of Psychology and Neuroscience, University of Colorado Boulder, 2860 Wilderness Pl, Boulder, CO, 80301, USA
| | - Abigail M Polter
- Department of Pharmacology and Physiology, George Washington University, Washington, DC, 20052, USA
| | - Emily D Prévost
- Department of Psychology and Neuroscience, University of Colorado Boulder, 2860 Wilderness Pl, Boulder, CO, 80301, USA
| | - Annie Ly
- Department of Psychology and Neuroscience, University of Colorado Boulder, 2860 Wilderness Pl, Boulder, CO, 80301, USA
| | - Connor J McNulty
- Department of Psychology and Neuroscience, University of Colorado Boulder, 2860 Wilderness Pl, Boulder, CO, 80301, USA
| | - Bodhi Rubinstein
- Department of Psychology and Neuroscience, University of Colorado Boulder, 2860 Wilderness Pl, Boulder, CO, 80301, USA
| | - David H Root
- Department of Psychology and Neuroscience, University of Colorado Boulder, 2860 Wilderness Pl, Boulder, CO, 80301, USA.
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Coffey KR, Nickelson WB, Dawkins AJ, Neumaier JF. Rapid appearance of negative emotion during oral fentanyl self-administration in male and female rats. Addict Biol 2023; 28:e13344. [PMID: 38017643 PMCID: PMC10745948 DOI: 10.1111/adb.13344] [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: 06/20/2023] [Revised: 09/14/2023] [Accepted: 09/21/2023] [Indexed: 11/30/2023]
Abstract
Opioid use disorder has become an epidemic in the United States, fuelled by the widespread availability of fentanyl, which produces rapid and intense euphoria followed by severe withdrawal and emotional distress. We developed a new preclinical model of fentanyl seeking in outbred male and female rats using volitional oral self-administration (SA) that can be readily applied in labs without intravascular access. Using a traditional two-lever operant procedure, rats learned to take oral fentanyl vigorously, escalated intake across sessions, and readily reinstated responding to conditioned cues after extinction. Oral SA also revealed individual and sex differences that are essential to studying substance use risk propensity. During a behavioural economics task, rats displayed inelastic demand curves and maintained stable intake across a wide range of fentanyl concentrations. Oral SA was also neatly patterned, with distinct 'loading' and 'maintenance' phases of responding within each session. Using our software DeepSqueak, we analysed ultrasonic vocalizations (USVs), which are innate expressions of current emotional state in rats. Rats produced 50 kHz USVs during loading then shifted quickly to 22 kHz calls despite ongoing maintenance of oral fentanyl taking, reflecting a transition to negative reinforcement. Using fibre photometry, we found that the lateral habenula differentially processed drug cues and drug consumption depending on affective state, with potentiated modulation by drug cues and consumption during the negative affective maintenance phase. Together, these results indicate a rapid progression from positive to negative reinforcement occurs even within an active drug taking session, revealing a within-session opponent process.
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Affiliation(s)
- Kevin R. Coffey
- Department of Psychiatry & Behavioral Sciences, University of Washington School of Medicine, Seattle, WA, 98105, USA
| | - William B. Nickelson
- Mental Illness Research, Education and Clinical Center, Puget Sound VA Health Care System, 1660 S Columbian Way, Seattle, WA 98108
| | - Aliyah J. Dawkins
- Mental Illness Research, Education and Clinical Center, Puget Sound VA Health Care System, 1660 S Columbian Way, Seattle, WA 98108
| | - John F. Neumaier
- Mental Illness Research, Education and Clinical Center, Puget Sound VA Health Care System, 1660 S Columbian Way, Seattle, WA 98108
- Department of Psychiatry & Behavioral Sciences, University of Washington School of Medicine, Seattle, WA, 98105, USA
- Department of Pharmacology, University of Washington School of Medicine, Seattle, WA, 98105, USA
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Falconnier C, Caparros-Roissard A, Decraene C, Lutz PE. Functional genomic mechanisms of opioid action and opioid use disorder: a systematic review of animal models and human studies. Mol Psychiatry 2023; 28:4568-4584. [PMID: 37723284 PMCID: PMC10914629 DOI: 10.1038/s41380-023-02238-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/20/2022] [Revised: 08/17/2023] [Accepted: 08/24/2023] [Indexed: 09/20/2023]
Abstract
In the past two decades, over-prescription of opioids for pain management has driven a steep increase in opioid use disorder (OUD) and death by overdose, exerting a dramatic toll on western countries. OUD is a chronic relapsing disease associated with a lifetime struggle to control drug consumption, suggesting that opioids trigger long-lasting brain adaptations, notably through functional genomic and epigenomic mechanisms. Current understanding of these processes, however, remain scarce, and have not been previously reviewed systematically. To do so, the goal of the present work was to synthesize current knowledge on genome-wide transcriptomic and epigenetic mechanisms of opioid action, in primate and rodent species. Using a prospectively registered methodology, comprehensive literature searches were completed in PubMed, Embase, and Web of Science. Of the 2709 articles identified, 73 met our inclusion criteria and were considered for qualitative analysis. Focusing on the 5 most studied nervous system structures (nucleus accumbens, frontal cortex, whole striatum, dorsal striatum, spinal cord; 44 articles), we also conducted a quantitative analysis of differentially expressed genes, in an effort to identify a putative core transcriptional signature of opioids. Only one gene, Cdkn1a, was consistently identified in eleven studies, and globally, our results unveil surprisingly low consistency across published work, even when considering most recent single-cell approaches. Analysis of sources of variability detected significant contributions from species, brain structure, duration of opioid exposure, strain, time-point of analysis, and batch effects, but not type of opioid. To go beyond those limitations, we leveraged threshold-free methods to illustrate how genome-wide comparisons may generate new findings and hypotheses. Finally, we discuss current methodological development in the field, and their implication for future research and, ultimately, better care.
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Affiliation(s)
- Camille Falconnier
- Centre National de la Recherche Scientifique, Université de Strasbourg, Institut des Neurosciences Cellulaires et Intégratives UPR 3212, 67000, Strasbourg, France
| | - Alba Caparros-Roissard
- Centre National de la Recherche Scientifique, Université de Strasbourg, Institut des Neurosciences Cellulaires et Intégratives UPR 3212, 67000, Strasbourg, France
| | - Charles Decraene
- Centre National de la Recherche Scientifique, Université de Strasbourg, Institut des Neurosciences Cellulaires et Intégratives UPR 3212, 67000, Strasbourg, France
- Centre National de la Recherche Scientifique, Université de Strasbourg, Laboratoire de Neurosciences Cognitives et Adaptatives UMR 7364, 67000, Strasbourg, France
| | - Pierre-Eric Lutz
- Centre National de la Recherche Scientifique, Université de Strasbourg, Institut des Neurosciences Cellulaires et Intégratives UPR 3212, 67000, Strasbourg, France.
- Douglas Mental Health University Institute, Montreal, QC, Canada.
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7
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Barrett JE, Shekarabi A, Inan S. Oxycodone: A Current Perspective on Its Pharmacology, Abuse, and Pharmacotherapeutic Developments. Pharmacol Rev 2023; 75:1062-1118. [PMID: 37321860 PMCID: PMC10595024 DOI: 10.1124/pharmrev.121.000506] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2021] [Revised: 04/30/2023] [Accepted: 06/05/2023] [Indexed: 06/17/2023] Open
Abstract
Oxycodone, a semisynthetic derivative of naturally occurring thebaine, an opioid alkaloid, has been available for more than 100 years. Although thebaine cannot be used therapeutically due to the occurrence of convulsions at higher doses, it has been converted to a number of other widely used compounds that include naloxone, naltrexone, buprenorphine, and oxycodone. Despite the early identification of oxycodone, it was not until the 1990s that clinical studies began to explore its analgesic efficacy. These studies were followed by the pursuit of several preclinical studies to examine the analgesic effects and abuse liability of oxycodone in laboratory animals and the subjective effects in human volunteers. For a number of years oxycodone was at the forefront of the opioid crisis, playing a significant role in contributing to opioid misuse and abuse, with suggestions that it led to transitioning to other opioids. Several concerns were expressed as early as the 1940s that oxycodone had significant abuse potential similar to heroin and morphine. Both animal and human abuse liability studies have confirmed, and in some cases amplified, these early warnings. Despite sharing a similar structure with morphine and pharmacological actions also mediated by the μ-opioid receptor, there are several differences in the pharmacology and neurobiology of oxycodone. The data that have emerged from the many efforts to analyze the pharmacological and molecular mechanism of oxycodone have generated considerable insight into its many actions, reviewed here, which, in turn, have provided new information on opioid receptor pharmacology. SIGNIFICANCE STATEMENT: Oxycodone, a μ-opioid receptor agonist, was synthesized in 1916 and introduced into clinical use in Germany in 1917. It has been studied extensively as a therapeutic analgesic for acute and chronic neuropathic pain as an alternative to morphine. Oxycodone emerged as a drug with widespread abuse. This article brings together an integrated, detailed review of the pharmacology of oxycodone, preclinical and clinical studies of pain and abuse, and recent advances to identify potential opioid analgesics without abuse liability.
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Affiliation(s)
- James E Barrett
- Center for Substance Abuse Research, Lewis Katz School of Medicine, Temple University. Philadelphia, Pennsylvania
| | - Aryan Shekarabi
- Center for Substance Abuse Research, Lewis Katz School of Medicine, Temple University. Philadelphia, Pennsylvania
| | - Saadet Inan
- Center for Substance Abuse Research, Lewis Katz School of Medicine, Temple University. Philadelphia, Pennsylvania
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8
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Hinds NM, Wojtas ID, Gallagher CA, Corbett CM, Manvich DF. Effects of sex and estrous cycle on intravenous oxycodone self-administration and the reinstatement of oxycodone-seeking behavior in rats. Front Behav Neurosci 2023; 17:1143373. [PMID: 37465001 PMCID: PMC10350507 DOI: 10.3389/fnbeh.2023.1143373] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2023] [Accepted: 06/09/2023] [Indexed: 07/20/2023] Open
Abstract
Introduction The increasing misuse of both prescription and illicit opioids has culminated in a national healthcare crisis in the United States. Oxycodone is among the most widely prescribed and misused opioid pain relievers and has been associated with a high risk for transition to compulsive opioid use. Here, we sought to examine potential sex differences and estrous cycle-dependent effects on the reinforcing efficacy of oxycodone, as well as on stress-induced or cue-induced oxycodone-seeking behavior, using intravenous (IV) oxycodone self-administration and reinstatement procedures. Methods In experiment 1, adult male and female Long-Evans rats were trained to self-administer 0.03 mg/kg/inf oxycodone according to a fixed-ratio 1 schedule of reinforcement in daily 2-h sessions, and a dose-response function was subsequently determined (0.003-0.03 mg/kg/inf). In experiment 2, a separate group of adult male and female Long-Evans rats were trained to self-administer 0.03 mg/kg/inf oxycodone for 8 sessions, followed by 0.01 mg/kg/inf oxycodone for 10 sessions. Responding was then extinguished, followed by sequential footshock-induced and cue-induced reinstatement tests. Results In the dose-response experiment, oxycodone produced a typical inverted U-shape function with 0.01 mg/kg/inf representing the maximally effective dose in both sexes. No sex differences were detected in the reinforcing efficacy of oxycodone. In the second experiment, the reinforcing effects of 0.01-0.03 mg//kg/inf oxycodone were significantly attenuated in females during proestrus/estrus as compared to metestrus/diestrus phases of the estrous cycle. Neither males nor females displayed significant footshock-induced reinstatement of oxycodone seeking, but both sexes exhibited significant cue-induced reinstatement of oxycodone seeking at magnitudes that did not differ either by sex or by estrous cycle phase. Discussion These results confirm and extend previous work suggesting that sex does not robustly influence the primary reinforcing effects of oxycodone nor the reinstatement of oxycodone-seeking behavior. However, our findings reveal for the first time that the reinforcing efficacy of IV oxycodone varies across the estrous cycle in female rats.
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Affiliation(s)
- Nicole M. Hinds
- Graduate School of Biomedical Sciences, Rowan University School of Osteopathic Medicine, Stratford, NJ, United States
- Department of Cell Biology and Neuroscience, Rowan University School of Osteopathic Medicine, Stratford, NJ, United States
| | - Ireneusz D. Wojtas
- Department of Cell Biology and Neuroscience, Rowan University School of Osteopathic Medicine, Stratford, NJ, United States
| | - Corinne A. Gallagher
- Graduate School of Biomedical Sciences, Rowan University School of Osteopathic Medicine, Stratford, NJ, United States
- Department of Cell Biology and Neuroscience, Rowan University School of Osteopathic Medicine, Stratford, NJ, United States
| | - Claire M. Corbett
- Department of Cell Biology and Neuroscience, Rowan University School of Osteopathic Medicine, Stratford, NJ, United States
| | - Daniel F. Manvich
- Graduate School of Biomedical Sciences, Rowan University School of Osteopathic Medicine, Stratford, NJ, United States
- Department of Cell Biology and Neuroscience, Rowan University School of Osteopathic Medicine, Stratford, NJ, United States
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9
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Hinds NM, Wojtas ID, Gallagher CA, Corbett CM, Manvich DF. Effects of sex and estrous cycle on intravenous oxycodone self-administration and the reinstatement of oxycodone-seeking behavior in rats. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.06.02.543393. [PMID: 37333293 PMCID: PMC10274722 DOI: 10.1101/2023.06.02.543393] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/20/2023]
Abstract
The increasing misuse of both prescription and illicit opioids has culminated in a national healthcare crisis in the United States. Oxycodone is among the most widely prescribed and misused opioid pain relievers and has been associated with a high risk for transition to compulsive opioid use. Here, we sought to examine potential sex differences and estrous cycle-dependent effects on the reinforcing efficacy of oxycodone, as well as on stress-induced or cue-induced oxycodone-seeking behavior, using intravenous (IV) oxycodone self-administration and reinstatement procedures. In experiment 1, adult male and female Long-Evans rats were trained to self-administer 0.03 mg/kg/inf oxycodone according to a fixed-ratio 1 schedule of reinforcement in daily 2-hr sessions, and a dose-response function was subsequently determined (0.003-0.03 mg/kg/inf). In experiment 2, a separate group of adult male and female Long-Evans rats were trained to self-administer 0.03 mg/kg/inf oxycodone for 8 sessions, followed by 0.01 mg/kg/inf oxycodone for 10 sessions. Responding was then extinguished, followed by sequential footshock-induced and cue-induced reinstatement tests. In the dose-response experiment, oxycodone produced a typical inverted U-shape function with 0.01 mg/kg/inf representing the maximally effective dose in both sexes. No sex differences were detected in the reinforcing efficacy of oxycodone. In the second experiment, the reinforcing effects of 0.01-0.03 mg//kg/inf oxycodone were significantly attenuated in females during proestrus/estrus as compared to metestrus/diestrus phases of the estrous cycle. Neither males nor females displayed significant footshock-induced reinstatement of oxycodone seeking, but both sexes exhibited significant cue-induced reinstatement of oxycodone seeking at magnitudes that did not differ either by sex or by estrous cycle phase. These results confirm and extend previous work suggesting that sex does not robustly influence the primary reinforcing effects of oxycodone nor the reinstatement of oxycodone-seeking behavior. However, our findings reveal for the first time that the reinforcing efficacy of IV oxycodone varies across the estrous cycle in female rats.
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10
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Extended access to fentanyl vapor self-administration leads to addiction-like behaviors in mice: Blood chemokine/cytokine levels as potential biomarkers. ADDICTION NEUROSCIENCE 2023; 5:100057. [PMID: 36683829 PMCID: PMC9851134 DOI: 10.1016/j.addicn.2022.100057] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Rodent models are useful for understanding the mechanisms that underlie opioid addiction, but most preclinical studies have focused on rewarding and consummatory aspects of opioids without components of dependence-induced escalation of drug taking or seeking. We characterized several opioid-related behaviors in mice using a model of vaporized fentanyl self-administration. Male and female C57BL/6J mice were assigned to short-access (ShA; 1 h, nondependent) or long-access (LgA; 6 h, dependent) fentanyl vapor self-administration and subsequently tested in a battery of behavioral tests, followed by blood collection during withdrawal. Compared with mice in the ShA group, mice in the LgA group escalated their fentanyl intake, were more motivated to work to obtain the drug, exhibited greater hyperalgesia, and exhibited greater signs of naloxone-precipitated withdrawal. Principal component analysis indicated the emergence of two independent behavioral constructs: "intake/motivation" and "hyperalgesia/punished seeking." In mice in the LgA condition only, "hyperalgesia/punished seeking" was associated with plasma levels of proinflammatory interleukin-17 (IL-17), chemokine (C-C motif) ligand 4 (CCL-4), and tumor necrosis factor α (TNF-α). Overall, the results suggest that extended access to opioids leads to addiction-like behavior, and some constructs that are associated with addiction-like behavior may be associated with levels of the proinflammatory cytokines/chemokines IL-17, TNF-α, and CCL-4 in blood.
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Slivicki RA, Earnest T, Chang YH, Pareta R, Casey E, Li JN, Tooley J, Abiraman K, Vachez YM, Wolf DK, Sackey JT, Kumar Pitchai D, Moore T, Gereau RW, Copits BA, Kravitz AV, Creed MC. Oral oxycodone self-administration leads to features of opioid misuse in male and female mice. Addict Biol 2023; 28:e13253. [PMID: 36577735 DOI: 10.1111/adb.13253] [Citation(s) in RCA: 13] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2022] [Revised: 10/19/2022] [Accepted: 10/21/2022] [Indexed: 11/18/2022]
Abstract
Use of prescription opioids, particularly oxycodone, is an initiating factor driving the current opioid epidemic. There are several challenges with modelling oxycodone abuse. First, prescription opioids including oxycodone are orally self-administered and have different pharmacokinetics and dynamics than morphine or fentanyl, which have been more commonly used in rodent research. This oral route of administration determines the pharmacokinetic profile, which then influences the establishment of drug-reinforcement associations in animals. Moreover, the pattern of intake and the environment in which addictive drugs are self-administered are critical determinants of the levels of drug intake, of behavioural sensitization and of propensity to relapse behaviour. These are all important considerations when modelling prescription opioid use, which is characterized by continuous drug access in familiar environments. Thus, to model features of prescription opioid use and the transition to abuse, we designed an oral, homecage-based oxycodone self-administration paradigm. Mice voluntarily self-administer oxycodone in this paradigm without any taste modification such as sweeteners, and the majority exhibit preference for oxycodone, escalation of intake, physical signs of dependence and reinstatement of seeking after withdrawal. In addition, a subset of animals demonstrate drug taking that is resistant to aversive consequences. This model is therefore translationally relevant and useful for studying the neurobiological substrates of prescription opioid abuse.
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Affiliation(s)
- Richard A Slivicki
- Washington University Pain Center, Department of Anesthesiology, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Tom Earnest
- Washington University Pain Center, Department of Anesthesiology, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Yu-Hsuan Chang
- Washington University Pain Center, Department of Anesthesiology, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Rajesh Pareta
- Washington University Pain Center, Department of Anesthesiology, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Eric Casey
- Department of Psychiatry, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Jun-Nan Li
- Washington University Pain Center, Department of Anesthesiology, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Jessica Tooley
- Washington University Pain Center, Department of Anesthesiology, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Kavitha Abiraman
- Washington University Pain Center, Department of Anesthesiology, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Yvan M Vachez
- Washington University Pain Center, Department of Anesthesiology, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Drew K Wolf
- Washington University Pain Center, Department of Anesthesiology, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Jason T Sackey
- Washington University Pain Center, Department of Anesthesiology, Washington University in St. Louis, St. Louis, Missouri, USA
| | | | | | - Robert W Gereau
- Washington University Pain Center, Department of Anesthesiology, Washington University in St. Louis, St. Louis, Missouri, USA.,Department of Neuroscience, Washington University in St. Louis, St. Louis, Missouri, USA.,Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Bryan A Copits
- Washington University Pain Center, Department of Anesthesiology, Washington University in St. Louis, St. Louis, Missouri, USA.,Department of Neuroscience, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Alexxai V Kravitz
- Washington University Pain Center, Department of Anesthesiology, Washington University in St. Louis, St. Louis, Missouri, USA.,Department of Psychiatry, Washington University in St. Louis, St. Louis, Missouri, USA.,Department of Neuroscience, Washington University in St. Louis, St. Louis, Missouri, USA.,Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Meaghan C Creed
- Washington University Pain Center, Department of Anesthesiology, Washington University in St. Louis, St. Louis, Missouri, USA.,Department of Psychiatry, Washington University in St. Louis, St. Louis, Missouri, USA.,Department of Neuroscience, Washington University in St. Louis, St. Louis, Missouri, USA.,Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri, USA
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12
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Franco D, Wulff AB, Lobo MK, Fox ME. Chronic Physical and Vicarious Psychosocial Stress Alter Fentanyl Consumption and Nucleus Accumbens Rho GTPases in Male and Female C57BL/6 Mice. Front Behav Neurosci 2022; 16:821080. [PMID: 35221946 PMCID: PMC8867005 DOI: 10.3389/fnbeh.2022.821080] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2021] [Accepted: 01/20/2022] [Indexed: 12/16/2022] Open
Abstract
Chronic stress can increase the risk of developing a substance use disorder in vulnerable individuals. Numerous models have been developed to probe the underlying neurobiological mechanisms, however, most prior work has been restricted to male rodents, conducted only in rats, or introduces physical injury that can complicate opioid studies. Here we sought to establish how chronic psychosocial stress influences fentanyl consumption in male and female C57BL/6 mice. We used chronic social defeat stress (CSDS), or the modified vicarious chronic witness defeat stress (CWDS), and used social interaction to stratify mice as stress-susceptible or resilient. We then subjected mice to a 15 days fentanyl drinking paradigm in the home cage that consisted of alternating forced and choice periods with increasing fentanyl concentrations. Male mice susceptible to either CWDS or CSDS consumed more fentanyl relative to unstressed mice. CWDS-susceptible female mice did not differ from unstressed mice during the forced periods, but showed increased preference for fentanyl over time. We also found decreased expression of nucleus accumbens Rho GTPases in male, but not female mice following stress and fentanyl drinking. We also compare fentanyl drinking behavior in mice that had free access to plain water throughout. Our results indicate that stress-sensitized fentanyl consumption is dependent on both sex and behavioral outcomes to stress.
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Affiliation(s)
- Daniela Franco
- Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, MD, United States
| | - Andreas B. Wulff
- Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, MD, United States
| | - Mary Kay Lobo
- Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, MD, United States
| | - Megan E. Fox
- Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, MD, United States,Department of Anesthesiology and Perioperative Medicine, Penn State College of Medicine, Hershey, PA, United States,*Correspondence: Megan E. Fox,
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13
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Nicolas C, Zlebnik NE, Farokhnia M, Leggio L, Ikemoto S, Shaham Y. Sex Differences in Opioid and Psychostimulant Craving and Relapse: A Critical Review. Pharmacol Rev 2022; 74:119-140. [PMID: 34987089 PMCID: PMC11060335 DOI: 10.1124/pharmrev.121.000367] [Citation(s) in RCA: 61] [Impact Index Per Article: 30.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2021] [Accepted: 08/15/2021] [Indexed: 01/11/2023] Open
Abstract
A widely held dogma in the preclinical addiction field is that females are more vulnerable than males to drug craving and relapse. Here, we first review clinical studies on sex differences in psychostimulant and opioid craving and relapse. Next, we review preclinical studies on sex differences in psychostimulant and opioid reinstatement of drug seeking after extinction of drug self-administration, and incubation of drug craving (time-dependent increase in drug seeking during abstinence). We also discuss ovarian hormones' role in relapse and craving in humans and animal models and speculate on brain mechanisms underlying their role in cocaine craving and relapse in rodent models. Finally, we discuss imaging studies on brain responses to cocaine cues and stress in men and women.The results of the clinical studies reviewed do not appear to support the notion that women are more vulnerable to psychostimulant and opioid craving and relapse. However, this conclusion is tentative because most of the studies reviewed were correlational, not sufficiently powered, and not a priori designed to detect sex differences. Additionally, imaging studies suggest sex differences in brain responses to cocaine cues and stress. The results of the preclinical studies reviewed provide evidence for sex differences in stress-induced reinstatement and incubation of cocaine craving but not cue- or cocaine-induced reinstatement of cocaine seeking. These sex differences are modulated in part by ovarian hormones. In contrast, the available data do not support the notion of sex differences in craving and relapse/reinstatement for methamphetamine or opioids in rodent models. SIGNIFICANCE STATEMENT: This systematic review summarizes clinical and preclinical studies on sex differences in psychostimulant and opioid craving and relapse. Results of the clinical studies reviewed do not appear to support the notion that women are more vulnerable to psychostimulant and opioid craving and relapse. Results of preclinical studies reviewed provide evidence for sex differences in reinstatement and incubation of cocaine seeking but not for reinstatement or incubation of methamphetamine or opioid seeking.
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Affiliation(s)
- Céline Nicolas
- Neurocentre Magendie, University of Bordeaux, Bordeaux, France (C.N.); Department of Anatomy & Neurobiology, University of Maryland School of Medicine, Baltimore, MD, Present address: Division of Biomedical Sciences, University of California Riverside, School of Medicine, Riverside, CA (N.E.Z.); Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Baltimore, MD (M.F., L.L., S.I., Y.S.); and Division of Intramural Clinical and Biological Research, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD (M.F., L.L.)
| | - Natalie E Zlebnik
- Neurocentre Magendie, University of Bordeaux, Bordeaux, France (C.N.); Department of Anatomy & Neurobiology, University of Maryland School of Medicine, Baltimore, MD, Present address: Division of Biomedical Sciences, University of California Riverside, School of Medicine, Riverside, CA (N.E.Z.); Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Baltimore, MD (M.F., L.L., S.I., Y.S.); and Division of Intramural Clinical and Biological Research, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD (M.F., L.L.)
| | - Mehdi Farokhnia
- Neurocentre Magendie, University of Bordeaux, Bordeaux, France (C.N.); Department of Anatomy & Neurobiology, University of Maryland School of Medicine, Baltimore, MD, Present address: Division of Biomedical Sciences, University of California Riverside, School of Medicine, Riverside, CA (N.E.Z.); Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Baltimore, MD (M.F., L.L., S.I., Y.S.); and Division of Intramural Clinical and Biological Research, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD (M.F., L.L.)
| | - Lorenzo Leggio
- Neurocentre Magendie, University of Bordeaux, Bordeaux, France (C.N.); Department of Anatomy & Neurobiology, University of Maryland School of Medicine, Baltimore, MD, Present address: Division of Biomedical Sciences, University of California Riverside, School of Medicine, Riverside, CA (N.E.Z.); Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Baltimore, MD (M.F., L.L., S.I., Y.S.); and Division of Intramural Clinical and Biological Research, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD (M.F., L.L.)
| | - Satoshi Ikemoto
- Neurocentre Magendie, University of Bordeaux, Bordeaux, France (C.N.); Department of Anatomy & Neurobiology, University of Maryland School of Medicine, Baltimore, MD, Present address: Division of Biomedical Sciences, University of California Riverside, School of Medicine, Riverside, CA (N.E.Z.); Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Baltimore, MD (M.F., L.L., S.I., Y.S.); and Division of Intramural Clinical and Biological Research, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD (M.F., L.L.)
| | - Yavin Shaham
- Neurocentre Magendie, University of Bordeaux, Bordeaux, France (C.N.); Department of Anatomy & Neurobiology, University of Maryland School of Medicine, Baltimore, MD, Present address: Division of Biomedical Sciences, University of California Riverside, School of Medicine, Riverside, CA (N.E.Z.); Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Baltimore, MD (M.F., L.L., S.I., Y.S.); and Division of Intramural Clinical and Biological Research, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD (M.F., L.L.)
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14
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Abstract
Animal models of addictive behaviors are useful for uncovering neural mechanisms involved in the development of dependence and for identifying risk factors for drug abuse. One such risk factor is biological sex, which strongly moderates drug self-administration behavior in rodents. Female rodents are more likely to acquire drug self-administration behaviors, consume higher amounts of drug, and reinstate drug-seeking behavior more readily. Despite this female vulnerability, preclinical addiction research has largely been done in male animals. The study of sex differences in rodent models of addictive behavior is increasing, however, as more investigators are choosing to include both male and female animals in experiments. This commentary is meant to serve as an introductory guide for preclinical investigators new to the study of sex differences in addiction. We provide an overview of self-administration models, a broad view of female versus male self-administration behaviors, and suggestions for study design and implementation. Inclusion of female subjects in preclinical addiction research is timely, as problem drug and alcohol use in women is increasing. With proper attention, design, and analysis, the study of sex differences in addiction has the potential to uncover novel neural mechanisms and lead to greater translational success for addiction research. © 2021 Wiley Periodicals LLC.
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Affiliation(s)
- Anna K. Radke
- Department of Psychology and Center for Neuroscience and Behavior, Miami University, Oxford, Ohio
| | - Elizabeth A. Sneddon
- Department of Psychology and Center for Neuroscience and Behavior, Miami University, Oxford, Ohio
| | - Sean C. Monroe
- Department of Psychology and Center for Neuroscience and Behavior, Miami University, Oxford, Ohio
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15
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Monroe SC, Radke AK. Aversion-resistant fentanyl self-administration in mice. Psychopharmacology (Berl) 2021; 238:699-710. [PMID: 33226446 PMCID: PMC7914171 DOI: 10.1007/s00213-020-05722-6] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/08/2020] [Accepted: 11/13/2020] [Indexed: 12/28/2022]
Abstract
RATIONALE Animal models of compulsive drug use that continues despite negative consequences can be used to investigate the neural mechanisms of addiction. However, models of punished or aversion-resistant opioid self-administration are notably lacking. OBJECTIVES We sought to develop an aversion-resistant, oral fentanyl self-administration paradigm. METHODS In Experiment 1, C57BL/6J male and female, adult mice consumed fentanyl (10 μg/mL) in a two-bottle drinking in the dark task and escalating concentrations of quinine were added to the bottles. In Experiment 2, mice were trained to administer oral fentanyl (10 μg/mL) in an operant response task. Quinine was next added to the fentanyl solution in escalating concentrations. In Experiment 3, mice were trained to respond for oral fentanyl or fentanyl adulterated with 500 μM quinine on every session. In Experiment 4, mice were trained to respond for a 1% sucrose solution before introduction of quinine. RESULTS Quinine reduced two-bottle choice consumption in males but not in females. Both sexes demonstrated the ability to detect the selected concentrations of quinine in fentanyl. In the operant chamber, mice responded robustly for oral fentanyl but introduction of quinine at any stage of training was insufficient to reduce responding. In contrast, quinine reduced responding for sucrose at concentrations above 250 μM. CONCLUSIONS Mice will respond for and consume oral fentanyl in both a two-bottle choice and an operant response task. Quinine is detectable in fentanyl but mice will continue to respond for and consume fentanyl with quinine in both paradigms. These data support the use of these models in behavioral studies of compulsive-like opioid use.
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Affiliation(s)
| | - Anna K. Radke
- Correspondence to: Anna K. Radke, PhD, 90 N Patterson Ave, Oxford, OH, USA 45056,
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16
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Doyle MA, Mazei-Robison MS. Opioid-Induced Molecular and Cellular Plasticity of Ventral Tegmental Area Dopamine Neurons. Cold Spring Harb Perspect Med 2021; 11:cshperspect.a039362. [PMID: 31964652 PMCID: PMC7371531 DOI: 10.1101/cshperspect.a039362] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Opioid drugs are highly valued as potent analgesics; however, there are significant risks associated with long-term use because of their abuse liability. Opioids cause changes in ventral tegmental area (VTA) gene expression and cell activity that have been linked to addiction-related behaviors in rodent models. Here, we focus on VTA dopamine (DA) neurons and review the cellular, structural, and synaptic plasticity changes induced by acute and chronic opioid exposure. We also discuss many avenues for future research including determination of whether opioid neuroadaptations are specific for subpopulations of VTA DA neurons. A better understanding of the molecular adaptations within the cells and circuits that drive opioid abuse is crucial for the development of better treatments for substance use disorders and to create novel, safer pain-relieving therapeutics.
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Bakhti-Suroosh A, Towers EB, Lynch WJ. A buprenorphine-validated rat model of opioid use disorder optimized to study sex differences in vulnerability to relapse. Psychopharmacology (Berl) 2021; 238:1029-1046. [PMID: 33404740 PMCID: PMC7786148 DOI: 10.1007/s00213-020-05750-2] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/13/2020] [Accepted: 12/08/2020] [Indexed: 12/13/2022]
Abstract
RATIONALE Opioid use disorder (OUD) is a major epidemic in the USA. Despite evidence indicating that OUD may be particularly severe for women, preclinical models have yet to establish sex as a major factor in OUD. OBJECTIVES Here, we examined sex differences in vulnerability to relapse following intermittent access fentanyl self-administration and protracted abstinence and used buprenorphine, the FDA-approved treatment for OUD, to test the validity of our model. METHODS Following acquisition of fentanyl self-administration under one of two training conditions, male and female rats were given extended, 24-h/day access to fentanyl (0.25 μg/kg/infusion, 10 days) using an intermittent access procedure. Vulnerability to relapse was assessed using an extinction/cue-induced reinstatement procedure following 14 days of abstinence; buprenorphine (0 or 3 mg/kg/day) was administered throughout abstinence. RESULTS Levels of drug-seeking were high following extended-access fentanyl self-administration and abstinence; buprenorphine markedly decreased drug-seeking supporting the validity of our relapse model. Females self-administered more fentanyl and responded at higher levels during subsequent extinction testing. Buprenorphine was effective in both sexes and eliminated sex and estrous phase differences in drug-seeking. Interestingly, the inclusion of a time-out during training had a major impact on later fentanyl self-administration in females, but not males, indicating that the initial exposure conditions can persistently impact vulnerability in females. CONCLUSIONS These findings demonstrate the utility of this rat model for determining sex and hormonal influences on the development and treatment of OUD.
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Affiliation(s)
- Anousheh Bakhti-Suroosh
- Department of Psychiatry and Neurobehavioral Sciences, University of Virginia, P.O. Box 801402, Charlottesville, VA 22904 USA
| | - Eleanor Blair Towers
- Department of Psychiatry and Neurobehavioral Sciences, University of Virginia, P.O. Box 801402, Charlottesville, VA 22904 USA
| | - Wendy J. Lynch
- Department of Psychiatry and Neurobehavioral Sciences, University of Virginia, P.O. Box 801402, Charlottesville, VA 22904 USA
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