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Alegre-Zurano L, Caceres-Rodriguez A, Berbegal-Sáez P, Lassalle O, Manzoni O, Valverde O. Cocaine-induced loss of LTD and social impairments are restored by fatty acid amide hydrolase inhibition. Sci Rep 2023; 13:18229. [PMID: 37880305 PMCID: PMC10600200 DOI: 10.1038/s41598-023-45476-7] [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: 08/04/2023] [Accepted: 10/19/2023] [Indexed: 10/27/2023] Open
Abstract
A single dose of cocaine abolishes endocannabinoid-mediated long-term depression (eCB-LTD) in the nucleus accumbens (NAc) within 24 h of administration. However, it is uncertain whether this altered neuroplasticity entails a behavioral deficit. As previously reported, after a single dose of cocaine (20 mg/kg), mice displayed impaired eCB-LTD in the NAc. Such cocaine-induced neuroplastic impairment was accompanied by an altered preference for saccharin and social interactions and a reduction in mRNA levels of the anandamide-catabolizing enzyme NAPE-PLD. The pharmacological increase of anandamide through the fatty acid amide hydrolase (FAAH) inhibitor URB597 (1 mg/kg) reversed the cocaine-induced loss of eCB-LTD in the NAc and restored normal social interaction in cocaine-exposed mice, but it did not affect saccharin preference. Overall, this research underlines the neuroplastic and behavioral alterations occurring after the initial use of cocaine and suggests a potential role for anandamide.
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Affiliation(s)
- Laia Alegre-Zurano
- Neurobiology of Behaviour Research Group (GReNeC-NeuroBio), Department of Medicine and Life Sciences, Universitat Pompeu Fabra, C/ Dr Aiguader, 88, 08003, Barcelona, Spain
| | | | - Paula Berbegal-Sáez
- Neurobiology of Behaviour Research Group (GReNeC-NeuroBio), Department of Medicine and Life Sciences, Universitat Pompeu Fabra, C/ Dr Aiguader, 88, 08003, Barcelona, Spain
| | - Olivier Lassalle
- INMED, INSERM U1249, Marseille, France
- Aix-Marseille University, Marseille, France
| | - Olivier Manzoni
- INMED, INSERM U1249, Marseille, France
- Aix-Marseille University, Marseille, France
| | - Olga Valverde
- Neurobiology of Behaviour Research Group (GReNeC-NeuroBio), Department of Medicine and Life Sciences, Universitat Pompeu Fabra, C/ Dr Aiguader, 88, 08003, Barcelona, Spain.
- Neuroscience Research Program, IMIM-Hospital Del Mar Research Institute, Barcelona, Spain.
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Neutral CB1 Receptor Antagonists as Pharmacotherapies for Substance Use Disorders: Rationale, Evidence, and Challenge. Cells 2022; 11:cells11203262. [PMID: 36291128 PMCID: PMC9600259 DOI: 10.3390/cells11203262] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2022] [Revised: 10/03/2022] [Accepted: 10/10/2022] [Indexed: 11/17/2022] Open
Abstract
Cannabinoid receptor 1 (CB1R) has been one of the major targets in medication development for treating substance use disorders (SUDs). Early studies indicated that rimonabant, a selective CB1R antagonist with an inverse agonist profile, was highly promising as a therapeutic for SUDs. However, its adverse side effects, such as depression and suicidality, led to its withdrawal from clinical trials worldwide in 2008. Consequently, much research interest shifted to developing neutral CB1R antagonists based on the recognition that rimonabant’s side effects may be related to its inverse agonist profile. In this article, we first review rimonabant’s research background as a potential pharmacotherapy for SUDs. Then, we discuss the possible mechanisms underlying its therapeutic anti-addictive effects versus its adverse effects. Lastly, we discuss the rationale for developing neutral CB1R antagonists as potential treatments for SUDs, the supporting evidence in recent research, and the challenges of this strategy. We conclude that developing neutral CB1R antagonists without inverse agonist profile may represent attractive strategies for the treatment of SUDs.
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On the Biomedical Properties of Endocannabinoid Degradation and Reuptake Inhibitors: Pre-clinical and Clinical Evidence. Neurotox Res 2021; 39:2072-2097. [PMID: 34741755 DOI: 10.1007/s12640-021-00424-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2021] [Revised: 09/14/2021] [Accepted: 09/28/2021] [Indexed: 10/19/2022]
Abstract
The endocannabinoid system (ECS) is composed of endogenous cannabinoids; components involved in their synthesis, transport, and degradation; and an expansive variety of cannabinoid receptors. Hypofunction or deregulation of the ECS is related to pathological conditions. Consequently, endogenous enhancement of endocannabinoid levels and/or regulation of their metabolism represent promising therapeutic approaches. Several major strategies have been suggested for the modulation of the ECS: (1) blocking endocannabinoids degradation, (2) inhibition of endocannabinoid cellular uptake, and (3) pharmacological modulation of cannabinoid receptors as potential therapeutic targets. Here, we focused in this review on degradation/reuptake inhibitors over cannabinoid receptor modulators in order to provide an updated synopsis of contemporary evidence advancing mechanisms of endocannabinoids as pharmacological tools with therapeutic properties for the treatment of several disorders. For this purpose, we revisited the available literature and reported the latest advances regarding the biomedical properties of fatty acid amide hydrolase and monoacylglycerol lipase inhibitors in pre-clinical and clinical studies. We also highlighted anandamide and 2-arachidonoylglycerol reuptake inhibitors with promising results in pre-clinical studies using in vitro and animal models as an outlook for future research in clinical trials.
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Humburg BA, Jordan CJ, Zhang H, Shen H, Han X, Bi G, Hempel B, Galaj E, Baumann MH, Xi Z. Optogenetic brain-stimulation reward: A new procedure to re-evaluate the rewarding versus aversive effects of cannabinoids in dopamine transporter-Cre mice. Addict Biol 2021; 26:e13005. [PMID: 33538103 DOI: 10.1111/adb.13005] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2020] [Revised: 12/04/2020] [Accepted: 01/09/2021] [Indexed: 12/12/2022]
Abstract
Despite extensive research, the rewarding effects of cannabinoids are still debated. Here, we used a newly established animal procedure called optogenetic intracranial self-stimulation (ICSS) (oICSS) to re-examine the abuse potential of cannabinoids in mice. A specific adeno-associated viral vector carrying a channelrhodopsin gene was microinjected into the ventral tegmental area (VTA) to express light-sensitive channelrhodopsin in dopamine (DA) neurons of transgenic dopamine transporter (DAT)-Cre mice. Optogenetic stimulation of VTA DA neurons was highly reinforcing and produced a classical "sigmoidal"-shaped stimulation-response curve dependent upon the laser pulse frequency. Systemic administration of cocaine dose-dependently enhanced oICSS and shifted stimulation-response curves upward, in a way similar to previously observed effects of cocaine on electrical ICSS. In contrast, Δ9 -tetrahydrocannabinol (Δ9 -THC), but not cannabidiol, dose-dependently decreased oICSS responding and shifted oICSS curves downward. WIN55,212-2 and ACEA, two synthetic cannabinoids often used in laboratory settings, also produced dose-dependent reductions in oICSS. We then examined several new synthetic cannabinoids, which are used recreationally. XLR-11 produced a cocaine-like increase, AM-2201 produced a Δ9 -THC-like reduction, while 5F-AMB had no effect on oICSS responding. Immunohistochemistry and RNAscope in situ hybridization assays indicated that CB1 Rs are expressed mainly in VTA GABA and glutamate neurons, while CB2 Rs are expressed mainly in VTA DA neurons. Together, these findings suggest that most cannabinoids are not reward enhancing, but rather reward attenuating or aversive in mice. Activation of CB1 R and/or CB2 R in different populations of neurons in the brain may underlie the observed actions.
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Affiliation(s)
- Bree A. Humburg
- Addiction Biology Unit, Molecular Targets and Medications Discovery, Intramural Research Program National Institute on Drug Abuse Baltimore Maryland USA
| | - Chloe J. Jordan
- Addiction Biology Unit, Molecular Targets and Medications Discovery, Intramural Research Program National Institute on Drug Abuse Baltimore Maryland USA
| | - Hai‐Ying Zhang
- Addiction Biology Unit, Molecular Targets and Medications Discovery, Intramural Research Program National Institute on Drug Abuse Baltimore Maryland USA
| | - Hui Shen
- Synaptic Plasticity Section, Intramural Research Program National Institute on Drug Abuse Baltimore Maryland USA
| | - Xiao Han
- Addiction Biology Unit, Molecular Targets and Medications Discovery, Intramural Research Program National Institute on Drug Abuse Baltimore Maryland USA
| | - Guo‐Hua Bi
- Addiction Biology Unit, Molecular Targets and Medications Discovery, Intramural Research Program National Institute on Drug Abuse Baltimore Maryland USA
| | - Briana Hempel
- Addiction Biology Unit, Molecular Targets and Medications Discovery, Intramural Research Program National Institute on Drug Abuse Baltimore Maryland USA
| | - Ewa Galaj
- Addiction Biology Unit, Molecular Targets and Medications Discovery, Intramural Research Program National Institute on Drug Abuse Baltimore Maryland USA
| | - Michael H. Baumann
- Designer Drug Research Unit, Intramural Research Program National Institute on Drug Abuse Baltimore Maryland USA
| | - Zheng‐Xiong Xi
- Addiction Biology Unit, Molecular Targets and Medications Discovery, Intramural Research Program National Institute on Drug Abuse Baltimore Maryland USA
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Abstract
Substance use disorder (SUD) is a major public health crisis worldwide, and effective treatment options are limited. During the past 2 decades, researchers have investigated the impact of a variety of pharmacological approaches to treat SUD, one of which is the use of medical cannabis or cannabinoids. Significant progress was made with the discovery of rimonabant, a selective CB1 receptor (CB1R) antagonist (also an inverse agonist), as a promising therapeutic for SUDs and obesity. However, serious adverse effects such as depression and suicidality led to the withdrawal of rimonabant (and almost all other CB1R antagonists/inverse agonists) from clinical trials worldwide in 2008. Since then, much research interest has shifted to other cannabinoid-based strategies, such as peripheral CB1R antagonists/inverse agonists, neutral CB1R antagonists, allosteric CB1R modulators, CB2R agonists, fatty acid amide hydrolase (FAAH) inhibitors, monoacylglycerol lipase (MAGL) inhibitors, fatty acid binding protein (FABP) inhibitors, or nonaddictive phytocannabinoids with CB1R or CB2R-binding profiles, as new therapeutics for SUDs. In this article, we first review recent progress in research regarding the endocannabinoid systems, cannabis reward versus aversion, and the underlying receptor mechanisms. We then review recent progress in cannabinoid-based medication development for the treatment of SUDs. As evidence continues to accumulate, neutral CB1R antagonists (such as AM4113), CB2R agonists (JWH133, Xie2-64), and nonselective phytocannabinoids (cannabidiol, β-caryophyllene, ∆9-tetrahydrocannabivarin) have shown great therapeutic potential for SUDs, as shown in experimental animals. Several cannabinoid-based medications (e.g., dronabinol, nabilone, PF-04457845) that entered clinical trials have shown promising results in reducing withdrawal symptoms in cannabis and opioid users.
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Affiliation(s)
- Ewa Galaj
- Addiction Biology Unit, Molecular Targets and Medication Discoveries Branch, Intramural Research Program, National Institute on Drug Abuse, Baltimore, MD, 21224, USA
| | - Zheng-Xiong Xi
- Addiction Biology Unit, Molecular Targets and Medication Discoveries Branch, Intramural Research Program, National Institute on Drug Abuse, Baltimore, MD, 21224, USA.
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Spiller KJ, Bi GH, He Y, Galaj E, Gardner EL, Xi ZX. Cannabinoid CB 1 and CB 2 receptor mechanisms underlie cannabis reward and aversion in rats. Br J Pharmacol 2019; 176:1268-1281. [PMID: 30767215 DOI: 10.1111/bph.14625] [Citation(s) in RCA: 44] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2018] [Revised: 12/11/2018] [Accepted: 01/30/2019] [Indexed: 01/24/2023] Open
Abstract
BACKGROUND AND PURPOSE Endocannabinoids are critically involved in brain reward functions, mediated by activation of CB1 receptors, reflecting their high density in the brain. However, the recent discovery of CB2 receptors in the brain, particularly in the midbrain dopamine neurons, has challenged this view and inspired us to re-examine the roles of both CB1 and CB2 receptors in the effects of cannabis. EXPERIMENTAL APPROACH In the present study, we used the electrical intracranial self-stimulation paradigm to evaluate the effects of various cannabinoid drugs on brain reward in laboratory rats and the roles of CB1 and CB2 receptors activation in brain reward function(s). KEY RESULTS Two mixed CB1 / CB2 receptor agonists, Δ9 -tetrahydrocannabinol (Δ9 -THC) and WIN55,212-2, produced biphasic effects-mild enhancement of brain-stimulation reward (BSR) at low doses but inhibition at higher doses. Pretreatment with a CB1 receptor antagonist (AM251) attenuated the low dose-enhanced BSR, while a CB2 receptor antagonist (AM630) attenuated high dose-inhibited BSR. To confirm these opposing effects, rats were treated with selective CB1 and CB2 receptor agonists. These compounds produced significant BSR enhancement and inhibition, respectively. CONCLUSIONS AND IMPLICATIONS CB1 receptor activation produced reinforcing effects, whereas CB2 receptor activation was aversive. The subjective effects of cannabis depend on the balance of these opposing effects. These findings not only explain previous conflicting results in animal models of addiction but also explain why cannabis can be either rewarding or aversive in humans, as expression of CB1 and CB2 receptors may differ in the brains of different subjects.
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Affiliation(s)
- Krista J Spiller
- Department of Pathology and Laboratory Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Guo-Hua Bi
- Molecular Targets and Medications Discovery Branch, Intramural Research Program, National Institute on Drug Abuse, Baltimore, Maryland, USA
| | - Yi He
- Molecular Targets and Medications Discovery Branch, Intramural Research Program, National Institute on Drug Abuse, Baltimore, Maryland, USA
| | - Ewa Galaj
- Molecular Targets and Medications Discovery Branch, Intramural Research Program, National Institute on Drug Abuse, Baltimore, Maryland, USA
| | - Eliot L Gardner
- Molecular Targets and Medications Discovery Branch, Intramural Research Program, National Institute on Drug Abuse, Baltimore, Maryland, USA
| | - Zheng-Xiong Xi
- Molecular Targets and Medications Discovery Branch, Intramural Research Program, National Institute on Drug Abuse, Baltimore, Maryland, USA
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7
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Freels TG, Lester DB, Cook MN. Arachidonoyl serotonin (AA-5-HT) modulates general fear-like behavior and inhibits mesolimbic dopamine release. Behav Brain Res 2019; 362:140-151. [DOI: 10.1016/j.bbr.2019.01.010] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2018] [Revised: 01/08/2019] [Accepted: 01/08/2019] [Indexed: 01/02/2023]
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Scherma M, Masia P, Satta V, Fratta W, Fadda P, Tanda G. Brain activity of anandamide: a rewarding bliss? Acta Pharmacol Sin 2019; 40:309-323. [PMID: 30050084 DOI: 10.1038/s41401-018-0075-x] [Citation(s) in RCA: 42] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2018] [Accepted: 05/20/2018] [Indexed: 12/11/2022] Open
Abstract
Anandamide is a lipid mediator that acts as an endogenous ligand of CB1 receptors. These receptors are also the primary molecular target responsible for the pharmacological effects of Δ9-tetrahydrocannabinol, the psychoactive ingredient in Cannabis sativa. Several studies demonstrate that anandamide exerts an overall modulatory effect on the brain reward circuitry. Several reports suggest its involvement in the addiction-producing actions of other abused drugs, and it can also act as a behavioral reinforcer in animal models of drug abuse. Importantly, all these effects of anandamide appear to be potentiated by pharmacological inhibition of its metabolic degradation. Enhanced brain levels of anandamide after treatment with inhibitors of fatty acid amide hydrolase, the main enzyme responsible for its degradation, seem to affect the rewarding and reinforcing actions of many drugs of abuse. In this review, we will provide an overview from a preclinical perspective of the current state of knowledge regarding the behavioral pharmacology of anandamide, with a particular emphasis on its motivational/reinforcing properties. We will also discuss how modulation of anandamide levels through inhibition of enzymatic metabolic pathways could provide a basis for developing new pharmaco-therapeutic tools for the treatment of substance use disorders.
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Wenzel JM, Cheer JF. Endocannabinoid Regulation of Reward and Reinforcement through Interaction with Dopamine and Endogenous Opioid Signaling. Neuropsychopharmacology 2018; 43:103-115. [PMID: 28653666 PMCID: PMC5719091 DOI: 10.1038/npp.2017.126] [Citation(s) in RCA: 83] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/19/2017] [Revised: 06/01/2017] [Accepted: 06/08/2017] [Indexed: 12/11/2022]
Abstract
The endocannabinoid system (eCB) is implicated in the mediation of both reward and reinforcement. This is evidenced by the ability of exogenous cannabinoid drugs to produce hedonia and maintain self-administration in both human and animal subjects. eCBs similarly facilitate behaviors motivated by reward through interaction with the mesolimbic dopamine (DA) and endogenous opioid systems. Indeed, eCB signaling in the ventral tegmental area stimulates activation of midbrain DA cells and promotes DA release in terminal regions such as the nucleus accumbens (NAc). DA transmission mediates several aspects of reinforced behavior, such as motivation, incentive salience, and cost-benefit calculations. However, much research suggests that endogenous opioid signaling underlies the hedonic aspects of reward. eCBs and their receptors functionally interact with opioid systems within the NAc to support reward, most likely through augmenting DA release. This review explores the interaction of these systems as it relates to reward and reinforcement and examines current literature regarding their role in food reward.
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Affiliation(s)
- J M Wenzel
- Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, MD, USA
| | - J F Cheer
- Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, MD, USA,Department of Psychiatry, University of Maryland School of Medicine, Baltimore, MD, USA,Program in Neuroscience, University of Maryland School of Medicine, Baltimore, MD, USA,Department of Anatomy and Neurobiology, Department of Psychiatry, Graduate Program in Neuroscience, University of Maryland School of Medicine, HSF I, Room 280J, 20 Penn Street, Baltimore, MD 21201, USA, Tel: +1 410 7060112, Fax: +1 410 7062512, E-mail:
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10
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Han X, He Y, Bi GH, Zhang HY, Song R, Liu QR, Egan JM, Gardner EL, Li J, Xi ZX. CB1 Receptor Activation on VgluT2-Expressing Glutamatergic Neurons Underlies Δ 9-Tetrahydrocannabinol (Δ 9-THC)-Induced Aversive Effects in Mice. Sci Rep 2017; 7:12315. [PMID: 28951549 PMCID: PMC5614984 DOI: 10.1038/s41598-017-12399-z] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2017] [Accepted: 09/08/2017] [Indexed: 11/09/2022] Open
Abstract
Cannabis can be rewarding or aversive. Cannabis reward is believed to be mediated by activation of cannabinoid CB1 receptors (CB1Rs) on GABAergic neurons that disinhibit dopaminergic neurons in the ventral tegmental area (VTA). However, little is known about the mechanisms underlying cannabis aversion in rodents. In the present study, CB1Rs are found not only on VTA GABAergic neurons, but also on VTA glutamatergic neurons that express vesicular glutamate transporter 2 (VgluT2). We then used Cre-Loxp transgenic technology to selectively delete CB1Rs in VgluT2-expressing glutamatergic neurons (VgluT2-CB1−/−) and Cre-dependent viral vector to express light-sensitive channelrhodopsin-2 into VTA glutamatergic neurons. We found that photoactivation of VTA glutamatergic neurons produced robust intracranial self-stimulation (ICSS) behavior, which was dose-dependently blocked by DA receptor antagonists, but enhanced by cocaine. In contrast, Δ9-tetrahydrocannabinol (Δ9-THC), the major psychoactive component of cannabis, produced dose-dependent conditioned place aversion and a reduction in the above optical ICSS in VgluT2-cre control mice, but not in VgluT2-CB1−/− mice. These findings suggest that activation of CB1Rs in VgluT2-expressing glutamate neurons produces aversive effects that might explain why cannabinoid is not rewarding in rodents and might also account for individual differences in the hedonic effects of cannabis in humans.
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Affiliation(s)
- Xiao Han
- Molecular Targets and Medications Discovery Branch, Intramural Research Program, National Institute on Drug Abuse, Baltimore, MD, 21224, USA.,Beijing Institute of Pharmacology and Toxicology, Beijing, 100850, China
| | - Yi He
- Molecular Targets and Medications Discovery Branch, Intramural Research Program, National Institute on Drug Abuse, Baltimore, MD, 21224, USA
| | - Guo-Hua Bi
- Molecular Targets and Medications Discovery Branch, Intramural Research Program, National Institute on Drug Abuse, Baltimore, MD, 21224, USA
| | - Hai-Ying Zhang
- Molecular Targets and Medications Discovery Branch, Intramural Research Program, National Institute on Drug Abuse, Baltimore, MD, 21224, USA
| | - Rui Song
- Beijing Institute of Pharmacology and Toxicology, Beijing, 100850, China
| | - Qing-Rong Liu
- Laboratory of Clinical Investigation, Intramural Research Program, National Institute on Aging, Baltimore, MD, 21224, USA
| | - Josephine M Egan
- Laboratory of Clinical Investigation, Intramural Research Program, National Institute on Aging, Baltimore, MD, 21224, USA
| | - Eliot L Gardner
- Molecular Targets and Medications Discovery Branch, Intramural Research Program, National Institute on Drug Abuse, Baltimore, MD, 21224, USA
| | - Jing Li
- Beijing Institute of Pharmacology and Toxicology, Beijing, 100850, China.
| | - Zheng-Xiong Xi
- Molecular Targets and Medications Discovery Branch, Intramural Research Program, National Institute on Drug Abuse, Baltimore, MD, 21224, USA.
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Preclinical studies on the reinforcing effects of cannabinoids. A tribute to the scientific research of Dr. Steve Goldberg. Psychopharmacology (Berl) 2016; 233:1845-66. [PMID: 27026633 PMCID: PMC5073892 DOI: 10.1007/s00213-016-4244-7] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/11/2015] [Accepted: 02/09/2016] [Indexed: 11/27/2022]
Abstract
RATIONALE The reinforcing effects of most abused drugs have been consistently demonstrated and studied in animal models, although those of marijuana were not, until the demonstration 15 years ago that delta-9-tetrahydrocannabinol (THC) could serve as a reinforcer in self-administration (SA) procedures in squirrel monkeys. Until then, those effects were inferred using indirect assessments. OBJECTIVES The aim of this manuscript is to review the primary preclinical procedures used to indirectly and directly infer reinforcing effects of cannabinoid drugs. METHODS Results will be reviewed from studies of cannabinoid discrimination, intracranial self-stimulation (ICSS), conditioned place preference (CPP), as well as change in levels of dopamine assessed in brain areas related to reinforcement, and finally from self-administration procedures. For each procedure, an evaluation will be made of the predictive validity in detecting the potential abuse liability of cannabinoids based on seminal papers, with the addition of selected reports from more recent years especially those from Dr. Goldberg's research group. RESULTS AND CONCLUSIONS ICSS and CPP do not provide consistent results for the assessment of potential for abuse of cannabinoids. However, drug discrimination and neurochemistry procedures appear to detect potential for abuse of cannabinoids, as well as several novel "designer cannabinoid drugs." Though after 15 years transfer of the self-administration model of marijuana abuse from squirrel monkeys to other species remains somewhat problematic, studies with the former species have substantially advanced the field, and several reports have been published with consistent self-administration of cannabinoid agonists in rodents.
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Hernandez G, Cheer JF. To Act or Not to Act: Endocannabinoid/Dopamine Interactions in Decision-Making. Front Behav Neurosci 2015; 9:336. [PMID: 26733830 PMCID: PMC4681836 DOI: 10.3389/fnbeh.2015.00336] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2015] [Accepted: 11/19/2015] [Indexed: 12/11/2022] Open
Abstract
Decision-making is an ethologically adaptive construct that is impaired in multiple psychiatric disorders. Activity within the mesocorticolimbic dopamine system has been traditionally associated with decision-making. The endocannabinoid system through its actions on inhibitory and excitatory synapses modulates dopamine activity and decision-making. The aim of this brief review is to present a synopsis of available data obtained when the endocannabinoid system is manipulated and dopamine activity recorded. To this end, we review research using different behavioral paradigms to provide further insight into how this ubiquitous signaling system biases dopamine-related behaviors to regulate decision-making.
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Affiliation(s)
- Giovanni Hernandez
- Faculté de Pharmacie, Université de Montréal Montréal, Quebec, QC, Canada
| | - Joseph F Cheer
- Department of Anatomy and Neurobiology, University of Maryland School of MedicineBaltimore, Maryland, MD, USA; Department of Psychiatry, University of Maryland School of MedicineBaltimore, Maryland, MD, USA
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13
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Grim TW, Wiebelhaus JM, Negus SS, Lichtman AH, Lichtman AH. Effects of acute and repeated dosing of the synthetic cannabinoid CP55,940 on intracranial self-stimulation in mice. Drug Alcohol Depend 2015; 150:31-7. [PMID: 25772438 PMCID: PMC4601922 DOI: 10.1016/j.drugalcdep.2015.01.022] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/21/2014] [Revised: 01/19/2015] [Accepted: 01/21/2015] [Indexed: 01/19/2023]
Abstract
BACKGROUND Synthetic cannabinoids have emerged as a significant public health concern. To increase the knowledge of how these molecules interact on brain reward processes, we investigated the effects of CP55,940, a high efficacy synthetic CB1 receptor agonist, in a frequency-rate intracranial self-stimulation (ICSS) procedure. METHODS The impact of acute and repeated administration (seven days) of CP55,940 on operant responding for electrical brain stimulation of the medial forebrain bundle was investigated in C57BL/6J mice. RESULTS CP55,940 attenuated ICSS in a dose-related fashion (ED50 (95% C.L.)=0.15 (0.12-0.18)mg/kg). This effect was blocked by the CB1 receptor antagonist rimonabant. Tolerance developed quickly, though not completely, to the rate-decreasing effects of CP55,940 (0.3mg/kg). Abrupt discontinuation of drug did not alter baseline responding for up to seven days. Moreover, rimonabant (10mg/kg) challenge did not alter ICSS responding in mice treated repeatedly with CP55,940. CONCLUSIONS The finding that CP55,940 reduced ICSS in mice with no evidence of facilitation at any dose is consistent with synthetic cannabinoid effects on ICSS in rats. CP55,940-induced ICSS depression was mediated through a CB1 receptor mechanism. Additionally, tolerance and dependence following repeated CP55,940 administration were dissociable. Thus, CP55,940 does not produce reward-like effects in ICSS under these conditions.
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Affiliation(s)
| | | | | | | | - Aron H Lichtman
- Department of Pharmacology and Toxicology, Medical College of Virginia Campus, Virginia Commonwealth University, PO Box 980613, Richmond, 23298-0613, VA U.S.A
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Gamage TF, Ignatowska-Jankowska BM, Muldoon PP, Cravatt BF, Damaj MI, Lichtman AH. Differential effects of endocannabinoid catabolic inhibitors on morphine withdrawal in mice. Drug Alcohol Depend 2015; 146:7-16. [PMID: 25479915 PMCID: PMC4295928 DOI: 10.1016/j.drugalcdep.2014.11.015] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/20/2014] [Revised: 11/16/2014] [Accepted: 11/16/2014] [Indexed: 02/07/2023]
Abstract
BACKGROUND Inhibition of endocannabinoid catabolic enzymes fatty acid amide hydrolase (FAAH) and/or monoacylglycerol lipase (MAGL) reduces somatic morphine withdrawal signs, but its effects on aversive aspects of withdrawal are unknown. The present study investigated whether Δ(9)-tetrahydrocannabinol (THC), the MAGL inhibitor JZL184, the FAAH inhibitor PF-3845, or the dual FAAH/MAGL inhibitor SA-57 would reduce acquisition of morphine withdrawal-induced conditioned place avoidance (CPA) and jumping. METHODS Mice were implanted with placebo or 75 mg morphine pellets, 48 h later injected with naloxone or saline and placed in the conditioning apparatus, and assessed for CPA at 72 h. Subjects were also observed for jumping behavior following naloxone challenge. RESULTS Naloxone (0.056 mg/kg) produced robust CPA in morphine-pelleted, but not placebo-pelleted, mice. Morphine pretreatment prevented the occurrence of withdrawal CPA and withdrawal jumping, while clonidine (an α2 adrenergic receptor agonist) only blocked withdrawal CPA. THC, JZL184, and SA-57 significantly reduced the percentage of mice that jumped during the conditioning session, but did not affect acquisition of withdrawal CPA. PF-3845 did not reduce morphine withdrawal CPA or jumping. Finally, neither THC nor the endocannabinoid catabolic enzyme inhibitors in non-dependent mice elicited a conditioned place preference or aversion. CONCLUSIONS These findings suggest that inhibiting endocannabinoid catabolic enzymes reduces somatic morphine withdrawal signs, but not aversive aspects as inferred in the CPA paradigm. The observation that non-dependent mice administered inhibitors of endocannabinoid degradation did not display place preferences is consistent with the idea that that endocannabinoid catabolic enzymes might be targeted therapeutically, with reduced risk of abuse.
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Affiliation(s)
- Thomas F. Gamage
- Department of Pharmacology and Toxicology, Medical College of Virginia Campus, Virginia Commonwealth University, Kontos Medical Sciences Building, 1217 East Marshall Street, Richmond, VA, 23298
| | - Bogna M. Ignatowska-Jankowska
- Department of Pharmacology and Toxicology, Medical College of Virginia Campus, Virginia Commonwealth University, Kontos Medical Sciences Building, 1217 East Marshall Street, Richmond, VA, 23298
| | - Pretal P. Muldoon
- Department of Pharmacology and Toxicology, Medical College of Virginia Campus, Virginia Commonwealth University, Kontos Medical Sciences Building, 1217 East Marshall Street, Richmond, VA, 23298
| | - Benjamin F. Cravatt
- The Skaggs Institute for Chemical Biology and Department of Chemical Physiology, The Scripps Research Institute, 10550 N. Torrey Pines Rd. La Jolla, CA 92037
| | - M. Imad Damaj
- Department of Pharmacology and Toxicology, Medical College of Virginia Campus, Virginia Commonwealth University, Kontos Medical Sciences Building, 1217 East Marshall Street, Richmond, VA, 23298
| | - Aron H. Lichtman
- Department of Pharmacology and Toxicology, Medical College of Virginia Campus, Virginia Commonwealth University, Kontos Medical Sciences Building, 1217 East Marshall Street, Richmond, VA, 23298
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15
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Wiebelhaus JM, Grim TW, Owens RA, Lazenka MF, Sim-Selley LJ, Abdullah RA, Niphakis MJ, Vann RE, Cravatt BF, Wiley JL, Negus SS, Lichtman AH. Δ9-tetrahydrocannabinol and endocannabinoid degradative enzyme inhibitors attenuate intracranial self-stimulation in mice. J Pharmacol Exp Ther 2014; 352:195-207. [PMID: 25398241 DOI: 10.1124/jpet.114.218677] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
A growing body of evidence implicates endogenous cannabinoids as modulators of the mesolimbic dopamine system and motivated behavior. Paradoxically, the reinforcing effects of Δ(9)-tetrahydrocannabinol (THC), the primary psychoactive constituent of cannabis, have been difficult to detect in preclinical rodent models. In this study, we investigated the impact of THC and inhibitors of the endocannabinoid hydrolytic enzymes fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) on operant responding for electrical stimulation of the medial forebrain bundle [intracranial self-stimulation (ICSS)], which is known to activate the mesolimbic dopamine system. These drugs were also tested in assays of operant responding for food reinforcement and spontaneous locomotor activity. THC and the MAGL inhibitor JZL184 (4-[bis(1,3-benzodioxol-5-yl)hydroxymethyl]-1-piperidinecarboxylic acid 4-nitrophenyl ester) attenuated operant responding for ICSS and food, and also reduced spontaneous locomotor activity. In contrast, the FAAH inhibitor PF-3845 (N-3-pyridinyl-4-[[3-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenyl]methyl]-1-piperidinecarboxamide) was largely without effect in these assays. Consistent with previous studies showing that combined inhibition of FAAH and MAGL produces a substantially greater cannabimimetic profile than single enzyme inhibition, the dual FAAH-MAGL inhibitor SA-57 (4-[2-(4-chlorophenyl)ethyl]-1-piperidinecarboxylic acid 2-(methylamino)-2-oxoethyl ester) produced a similar magnitude of ICSS depression as that produced by THC. ICSS attenuation by JZL184 was associated with increased brain levels of 2-arachidonoylglycerol (2-AG), whereas peak effects of SA-57 were associated with increased levels of both N-arachidonoylethanolamine (anandamide) and 2-AG. The cannabinoid receptor type 1 receptor antagonist rimonabant, but not the cannabinoid receptor type 2 receptor antagonist SR144528, blocked the attenuating effects of THC, JZL184, and SA-57 on ICSS. Thus, THC, MAGL inhibition, and dual FAAH-MAGL inhibition not only reduce ICSS, but also decrease other reinforced and nonreinforced behaviors.
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Affiliation(s)
- Jason M Wiebelhaus
- Department of Pharmacology and Toxicology, Virginia Commonwealth University School of Medicine, Richmond, Virginia (J.M.W., T.W.G., R.A.O., M.F.L., L.J.S.-S., R.A.A., R.E.V., S.S.N., A.H.L.); Skaggs Institute for Chemical Biology and Department of Chemical Physiology, Scripps Research Institute, La Jolla, California (M.J.N., B.F.C.); and RTI International, Research Triangle Park, North Carolina (J.L.W.)
| | - Travis W Grim
- Department of Pharmacology and Toxicology, Virginia Commonwealth University School of Medicine, Richmond, Virginia (J.M.W., T.W.G., R.A.O., M.F.L., L.J.S.-S., R.A.A., R.E.V., S.S.N., A.H.L.); Skaggs Institute for Chemical Biology and Department of Chemical Physiology, Scripps Research Institute, La Jolla, California (M.J.N., B.F.C.); and RTI International, Research Triangle Park, North Carolina (J.L.W.)
| | - Robert A Owens
- Department of Pharmacology and Toxicology, Virginia Commonwealth University School of Medicine, Richmond, Virginia (J.M.W., T.W.G., R.A.O., M.F.L., L.J.S.-S., R.A.A., R.E.V., S.S.N., A.H.L.); Skaggs Institute for Chemical Biology and Department of Chemical Physiology, Scripps Research Institute, La Jolla, California (M.J.N., B.F.C.); and RTI International, Research Triangle Park, North Carolina (J.L.W.)
| | - Matthew F Lazenka
- Department of Pharmacology and Toxicology, Virginia Commonwealth University School of Medicine, Richmond, Virginia (J.M.W., T.W.G., R.A.O., M.F.L., L.J.S.-S., R.A.A., R.E.V., S.S.N., A.H.L.); Skaggs Institute for Chemical Biology and Department of Chemical Physiology, Scripps Research Institute, La Jolla, California (M.J.N., B.F.C.); and RTI International, Research Triangle Park, North Carolina (J.L.W.)
| | - Laura J Sim-Selley
- Department of Pharmacology and Toxicology, Virginia Commonwealth University School of Medicine, Richmond, Virginia (J.M.W., T.W.G., R.A.O., M.F.L., L.J.S.-S., R.A.A., R.E.V., S.S.N., A.H.L.); Skaggs Institute for Chemical Biology and Department of Chemical Physiology, Scripps Research Institute, La Jolla, California (M.J.N., B.F.C.); and RTI International, Research Triangle Park, North Carolina (J.L.W.)
| | - Rehab A Abdullah
- Department of Pharmacology and Toxicology, Virginia Commonwealth University School of Medicine, Richmond, Virginia (J.M.W., T.W.G., R.A.O., M.F.L., L.J.S.-S., R.A.A., R.E.V., S.S.N., A.H.L.); Skaggs Institute for Chemical Biology and Department of Chemical Physiology, Scripps Research Institute, La Jolla, California (M.J.N., B.F.C.); and RTI International, Research Triangle Park, North Carolina (J.L.W.)
| | - Micah J Niphakis
- Department of Pharmacology and Toxicology, Virginia Commonwealth University School of Medicine, Richmond, Virginia (J.M.W., T.W.G., R.A.O., M.F.L., L.J.S.-S., R.A.A., R.E.V., S.S.N., A.H.L.); Skaggs Institute for Chemical Biology and Department of Chemical Physiology, Scripps Research Institute, La Jolla, California (M.J.N., B.F.C.); and RTI International, Research Triangle Park, North Carolina (J.L.W.)
| | - Robert E Vann
- Department of Pharmacology and Toxicology, Virginia Commonwealth University School of Medicine, Richmond, Virginia (J.M.W., T.W.G., R.A.O., M.F.L., L.J.S.-S., R.A.A., R.E.V., S.S.N., A.H.L.); Skaggs Institute for Chemical Biology and Department of Chemical Physiology, Scripps Research Institute, La Jolla, California (M.J.N., B.F.C.); and RTI International, Research Triangle Park, North Carolina (J.L.W.)
| | - Benjamin F Cravatt
- Department of Pharmacology and Toxicology, Virginia Commonwealth University School of Medicine, Richmond, Virginia (J.M.W., T.W.G., R.A.O., M.F.L., L.J.S.-S., R.A.A., R.E.V., S.S.N., A.H.L.); Skaggs Institute for Chemical Biology and Department of Chemical Physiology, Scripps Research Institute, La Jolla, California (M.J.N., B.F.C.); and RTI International, Research Triangle Park, North Carolina (J.L.W.)
| | - Jenny L Wiley
- Department of Pharmacology and Toxicology, Virginia Commonwealth University School of Medicine, Richmond, Virginia (J.M.W., T.W.G., R.A.O., M.F.L., L.J.S.-S., R.A.A., R.E.V., S.S.N., A.H.L.); Skaggs Institute for Chemical Biology and Department of Chemical Physiology, Scripps Research Institute, La Jolla, California (M.J.N., B.F.C.); and RTI International, Research Triangle Park, North Carolina (J.L.W.)
| | - S Stevens Negus
- Department of Pharmacology and Toxicology, Virginia Commonwealth University School of Medicine, Richmond, Virginia (J.M.W., T.W.G., R.A.O., M.F.L., L.J.S.-S., R.A.A., R.E.V., S.S.N., A.H.L.); Skaggs Institute for Chemical Biology and Department of Chemical Physiology, Scripps Research Institute, La Jolla, California (M.J.N., B.F.C.); and RTI International, Research Triangle Park, North Carolina (J.L.W.)
| | - Aron H Lichtman
- Department of Pharmacology and Toxicology, Virginia Commonwealth University School of Medicine, Richmond, Virginia (J.M.W., T.W.G., R.A.O., M.F.L., L.J.S.-S., R.A.A., R.E.V., S.S.N., A.H.L.); Skaggs Institute for Chemical Biology and Department of Chemical Physiology, Scripps Research Institute, La Jolla, California (M.J.N., B.F.C.); and RTI International, Research Triangle Park, North Carolina (J.L.W.)
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Abstract
Intracranial self-stimulation (ICSS) is a behavioral procedure in which operant responding is maintained by pulses of electrical brain stimulation. In research to study abuse-related drug effects, ICSS relies on electrode placements that target the medial forebrain bundle at the level of the lateral hypothalamus, and experimental sessions manipulate frequency or amplitude of stimulation to engender a wide range of baseline response rates or response probabilities. Under these conditions, drug-induced increases in low rates/probabilities of responding maintained by low frequencies/amplitudes of stimulation are interpreted as an abuse-related effect. Conversely, drug-induced decreases in high rates/probabilities of responding maintained by high frequencies/amplitudes of stimulation can be interpreted as an abuse-limiting effect. Overall abuse potential can be inferred from the relative expression of abuse-related and abuse-limiting effects. The sensitivity and selectivity of ICSS to detect abuse potential of many classes of abused drugs is similar to the sensitivity and selectivity of drug self-administration procedures. Moreover, similar to progressive-ratio drug self-administration procedures, ICSS data can be used to rank the relative abuse potential of different drugs. Strengths of ICSS in comparison with drug self-administration include 1) potential for simultaneous evaluation of both abuse-related and abuse-limiting effects, 2) flexibility for use with various routes of drug administration or drug vehicles, 3) utility for studies in drug-naive subjects as well as in subjects with controlled levels of prior drug exposure, and 4) utility for studies of drug time course. Taken together, these considerations suggest that ICSS can make significant contributions to the practice of abuse potential testing.
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Affiliation(s)
- S Stevens Negus
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, Virginia
| | - Laurence L Miller
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, Virginia
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17
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Hillard CJ, Liu QS. Endocannabinoid signaling in the etiology and treatment of major depressive illness. Curr Pharm Des 2014; 20:3795-811. [PMID: 24180398 PMCID: PMC4002665 DOI: 10.2174/13816128113196660735] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2013] [Accepted: 10/23/2013] [Indexed: 12/28/2022]
Abstract
The purpose of this review is to examine human and preclinical data that are relevant to the following hypotheses. The first hypothesis is that deficient CB1R-mediated signaling results in symptoms that mimic those seen in depression. The second hypothesis is that activation of CB1R-mediated signaling results in behavioral, endocrine and other effects that are similar to those produced by currently used antidepressants. The third hypothesis is that conventional antidepressant therapies act through enhanced CB1R mediated signaling. Together the available data indicate that activators of CB1R signaling, particularly inhibitors of fatty acid amide hydrolase, should be considered for clinical trials for the treatment of depression.
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MESH Headings
- Animals
- Antidepressive Agents/pharmacology
- Antidepressive Agents/therapeutic use
- Brain/drug effects
- Brain/enzymology
- Brain/metabolism
- Brain/pathology
- Cannabis
- Depressive Disorder, Major/drug therapy
- Depressive Disorder, Major/etiology
- Depressive Disorder, Major/genetics
- Depressive Disorder, Major/pathology
- Disease Models, Animal
- Endocannabinoids/genetics
- Endocannabinoids/metabolism
- Humans
- Magnetic Resonance Imaging
- Neurogenesis/drug effects
- Polymorphism, Genetic
- Receptor, Cannabinoid, CB1/genetics
- Receptor, Cannabinoid, CB1/metabolism
- Signal Transduction/drug effects
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Affiliation(s)
| | - Qing-song Liu
- Neuroscience Research Center, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226.
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18
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Panagis G, Mackey B, Vlachou S. Cannabinoid Regulation of Brain Reward Processing with an Emphasis on the Role of CB1 Receptors: A Step Back into the Future. Front Psychiatry 2014; 5:92. [PMID: 25132823 PMCID: PMC4117180 DOI: 10.3389/fpsyt.2014.00092] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/20/2014] [Accepted: 07/16/2014] [Indexed: 01/17/2023] Open
Abstract
Over the last decades, the endocannabinoid system has been implicated in a large variety of functions, including a crucial modulation of brain-reward circuits and the regulation of motivational processes. Importantly, behavioral studies have shown that cannabinoid compounds activate brain reward mechanisms and circuits in a similar manner to other drugs of abuse, such as nicotine, alcohol, cocaine, and heroin, although the conditions under which cannabinoids exert their rewarding effects may be more limited. Furthermore, there is evidence on the involvement of the endocannabinoid system in the regulation of cue- and drug-induced relapsing phenomena in animal models. The aim of this review is to briefly present the available data obtained using diverse behavioral experimental approaches in experimental animals, namely, the intracranial self-stimulation paradigm, the self-administration procedure, the conditioned place preference procedure, and the reinstatement of drug-seeking behavior procedure, to provide a comprehensive picture of the current status of what is known about the endocannabinoid system mechanisms that underlie modification of brain-reward processes. Emphasis is placed on the effects of cannabinoid 1 (CB1) receptor agonists, antagonists, and endocannabinoid modulators. Further, the role of CB1 receptors in reward processes is investigated through presentation of respective genetic ablation studies in mice. The vast majority of studies in the existing literature suggest that the endocannabinoid system plays a major role in modulating motivation and reward processes. However, much remains to be done before we fully understand these interactions. Further research in the future will shed more light on these processes and, thus, could lead to the development of potential pharmacotherapies designed to treat reward-dysfunction-related disorders.
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Affiliation(s)
- George Panagis
- Laboratory of Behavioral Neuroscience, Department of Psychology, School of Social Sciences, University of Crete , Rethymno , Greece
| | - Brian Mackey
- Laboratory of Behavioural Neuroscience, School of Nursing and Human Sciences, Faculty of Science and Health, Dublin City University , Dublin , Ireland
| | - Styliani Vlachou
- Laboratory of Behavioural Neuroscience, School of Nursing and Human Sciences, Faculty of Science and Health, Dublin City University , Dublin , Ireland
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19
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Panlilio LV, Justinova Z, Goldberg SR. Inhibition of FAAH and activation of PPAR: new approaches to the treatment of cognitive dysfunction and drug addiction. Pharmacol Ther 2013; 138:84-102. [PMID: 23333350 DOI: 10.1016/j.pharmthera.2013.01.003] [Citation(s) in RCA: 69] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2012] [Accepted: 12/21/2012] [Indexed: 12/16/2022]
Abstract
Enhancing the effects of endogenously-released cannabinoid ligands in the brain might provide therapeutic effects more safely and effectively than administering drugs that act directly at the cannabinoid receptor. Inhibitors of fatty acid amide hydrolase (FAAH) prevent the breakdown of endogenous ligands for cannabinoid receptors and peroxisome proliferator-activated receptors (PPAR), prolonging and enhancing the effects of these ligands when they are naturally released. This review considers recent research on the effects of FAAH inhibitors and PPAR activators in animal models of addiction and cognition (specifically learning and memory). These studies show that FAAH inhibitors can produce potentially therapeutic effects, some through cannabinoid receptors and some through PPAR. These effects include enhancing certain forms of learning, counteracting the rewarding effects of nicotine and alcohol, relieving symptoms of withdrawal from cannabis and other drugs, and protecting against relapse-like reinstatement of drug self-administration. Since FAAH inhibition might have a wide range of therapeutic actions but might also share some of the adverse effects of cannabis, it is noteworthy that at least one FAAH-inhibiting drug (URB597) has been found to have potentially beneficial effects but no indication of liability for abuse or dependence. Although these areas of research are new, the preliminary evidence indicates that they might lead to improved therapeutic interventions and a better understanding of the brain mechanisms underlying addiction and memory.
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Affiliation(s)
- Leigh V Panlilio
- Preclinical Pharmacology Section, Behavioral Neuroscience Research Branch, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Department of Health and Human Services, Baltimore, MD 21224, USA
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20
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Oleson EB, Cheer JF. Paradoxical effects of the endocannabinoid uptake inhibitor VDM11 on accumbal neural encoding of reward predictive cues. Synapse 2012; 66:984-8. [PMID: 22807176 PMCID: PMC3440520 DOI: 10.1002/syn.21587] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2012] [Revised: 06/13/2012] [Accepted: 07/12/2012] [Indexed: 11/08/2022]
Abstract
A growing body of evidence implicates the endocannabinoid (eCB) system in brain reward function. Previous studies show that antagonizing eCB transmission decreases reward-directed behavior and nucleus accumbens (NAc) encoding of reward predictive cues. We, therefore, hypothesized that elevating eCB levels would uniformly facilitate NAc neural encoding of reward predictive cues and reward-directed behavior. Contrary to our expectations, the eCB transport uptake inhibitor, VDM11, dose dependently decreased both measures.
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Affiliation(s)
- Erik B. Oleson
- Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, Maryland 21201
| | - Joseph F. Cheer
- Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, Maryland 21201
- Department of Psychiatry, University of Maryland School of Medicine, Baltimore, Maryland 21201
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21
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Marco EM, Laviola G. The endocannabinoid system in the regulation of emotions throughout lifespan: a discussion on therapeutic perspectives. J Psychopharmacol 2012; 26:150-63. [PMID: 21693551 DOI: 10.1177/0269881111408459] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Alterations in emotion regulation processes may form the basis of psychopathologies. The endocannabinoid (eCB) system, composed of endogenous ligands, the enzymatic machinery in charge of their metabolism and the specific metabotropic receptors, has emerged as a major neuromodulatory system critically involved in the control of emotional homeostasis and stress responsiveness. Data from animal models indicate that the eCB system plays a key role in brain development, and is probably involved in the control of emotional states from early developmental stages. The present review summarizes the latest information on the role of the eCB system in emotionality and anxiety-related disorders throughout the lifespan. Putative therapeutic strategies based on the pharmacological modulation of this system will be discussed. Given the fact that the pharmacological modulation of the eCB system has recently arisen as a promising strategy in the management of anxiety and mood disorders, the potential efficacy of this pharmacological approach (i.e. blockers of the catabolic pathway) will be discussed, as well as pharmacological alternatives such as modulators of cannabinoid receptors other than the classical CB1 receptor, or administration of other plant-derived compounds (e.g. cannabidiol).
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Affiliation(s)
- Eva M Marco
- Department of Animal Physiology (Animal Physiology II), Faculty of Biological Sciences, Complutense University of Madrid, Madrid, Spain.
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22
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López-Moreno JA, Echeverry-Alzate V, Bühler KM. The genetic basis of the endocannabinoid system and drug addiction in humans. J Psychopharmacol 2012; 26:133-43. [PMID: 21937688 DOI: 10.1177/0269881111416689] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The cannabinoid receptor (CNR1) and the fatty acid amide hydrolase (FAAH) genes are located on chromosomes 6 and 1 in the 6q15 and 1p33 cytogenetic bands, respectively. CNR1 encodes a seven-transmembrane domain protein of 472 amino acids, whereas FAAH encodes one transmembrane domain of 579 amino acids. Several mutations found in these genes lead to altered mRNA stability and transcription rate or a reduction of the activity of the encoded protein. Increasing evidence shows that these functional mutations are related to dependence upon cocaine, alcohol, marijuana, heroin, nicotine and other drugs. One of the most compelling associations is with the C385A single nucleotide polymorphism (SNP), which is found in the FAAH gene. For all of the genetic polymorphisms reviewed here, it is difficult to form overall conclusions due to the high diversity of population samples being studied, ethnicity, the use of volunteers, heterogeneity of the recruitment criteria and the drug addiction phenotype studied. Care should be taken when generalizing the results from different studies. However, many works have repeatedly associated polymorphisms in the CNR1 and FAAH genes with drug-related behaviours; this suggests that these genes should be examined in further genetic studies focusing on drug addiction and other psychiatric disorders.
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Hernandez G, Bernstein D, Schoenbaum G, Cheer JF. Contrasting Effects of Lithium Chloride and CB1 Receptor Blockade on Enduring Changes in the Valuation of Reward. Front Behav Neurosci 2011; 5:53. [PMID: 21922005 PMCID: PMC3167146 DOI: 10.3389/fnbeh.2011.00053] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2011] [Accepted: 08/13/2011] [Indexed: 01/16/2023] Open
Abstract
When an organism responds for a reward, its learned behavior can be characterized as goal-directed or habitual based on whether or not it is susceptible to reward devaluation. Here, we evaluated whether instrumental responding for brain stimulation reward (BSR) can be devalued using a paradigm traditionally used for natural rewards. Rats were trained to lever press for BSR; afterward, BSR was paired with either lithium chloride (LiCl, 5 mg/kg, i.p.), a pro-emetic, or AM251, a CB1 receptor antagonist (3 mg/kg, i.p.) or the vehicle of these compounds. Pairings of BSR with these compounds and their vehicles were performed in a novel environment so that only unconditional effects of BSR would be affected by the pharmacological manipulations. Subsequently, in a probe test, all rats were returned in the drug-free state to the boxes where they had received training and instrumental responding was reassessed in the absence of BSR delivery. When compared to control, LiCl produced a significant decrease in the number of responses during the test session, whereas AM251 did not. These results show that instrumental responding for BSR is susceptible to devaluation, in accord with the proposal that this behavior is supported at least in part by associations between the response and the rewarding outcome. Further, they suggest that reward modulation observed in studies involving the use of CB1 receptor antagonists arises from changes in the organism’s motivation rather than drug-induced changes in the intrinsic value of reward.
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Serrano A, Parsons LH. Endocannabinoid influence in drug reinforcement, dependence and addiction-related behaviors. Pharmacol Ther 2011; 132:215-41. [PMID: 21798285 DOI: 10.1016/j.pharmthera.2011.06.005] [Citation(s) in RCA: 140] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2011] [Accepted: 06/17/2011] [Indexed: 12/12/2022]
Abstract
The endogenous cannabinoid system is an important regulatory system involved in physiological homeostasis. Endocannabinoid signaling is known to modulate neural development, immune function, metabolism, synaptic plasticity and emotional state. Accumulating evidence also implicates brain endocannabinoid signaling in the etiology of drug addiction which is characterized by compulsive drug seeking, loss of control in limiting drug intake, emergence of a negative emotional state in the absence of drug use and a persistent vulnerability toward relapse to drug use during protracted abstinence. In this review we discuss the effects of drug intake on brain endocannabinoid signaling, evidence implicating the endocannabinoid system in the motivation for drug consumption, and drug-induced alterations in endocannabinoid function that may contribute to various aspects of addiction including dysregulated synaptic plasticity, increased stress responsivity, negative affective states, drug craving and relapse to drug taking. Current knowledge of genetic variants in endocannabinoid signaling associated with addiction is also discussed.
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Affiliation(s)
- Antonia Serrano
- Committee on the Neurobiology of Addictive Disorders, The Scripps Research Institute, La Jolla, CA 92037, USA
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26
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Fokos S, Panagis G. Effects of delta9-tetrahydrocannabinol on reward and anxiety in rats exposed to chronic unpredictable stress. J Psychopharmacol 2010; 24:767-77. [PMID: 19406854 DOI: 10.1177/0269881109104904] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Although cannabis derivatives produce clear subjective motivational responses in humans leading to drug-seeking behaviour, the reinforcing attributes of these subjective effects are difficult to define in experimental animals. The aim of this study was to examine how exposure to chronic unpredictable stress (CUS) will affect reward function and anxiety after acute administration of Delta(9)-tetrahydrocannabinol (Delta(9)-THC) in rats. Male rats were exposed to either 10 days of CUS or no stressor. Alterations in brain reward function were assessed with the intracranial self-stimulation (ICSS) paradigm, and anxiety responses were measured with the elevated plus maze. CUS did not affect baseline brain stimulation reward thresholds. Delta(9)-THC did not exhibit reinforcing actions in the ICSS paradigm neither in nonstressed nor in stressed animals. More importantly, in nonstressed animals, both the low and the high dose of Delta(9)-THC exerted anxiolytic-like effects. In stressed animals, however, only the high dose of THC induced an anxiolytic-like response, whereas the low dose induced anxiogenic effects. The present results provide clear evidence for an anxiolytic effect of Delta(9)-THC both in stressed and in nonstressed animals, and indicate that environmental conditions, such as stressful experiences, do not alter the behavioural effects of Delta( 9)-THC in the ICSS paradigm.
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Affiliation(s)
- S Fokos
- Laboratory of Behavioral Neuroscience, Department of Psychology, School of Social Sciences, University of Crete, Crete, Greece
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D'Souza MS, Markou A. Neural substrates of psychostimulant withdrawal-induced anhedonia. Curr Top Behav Neurosci 2010; 3:119-178. [PMID: 21161752 DOI: 10.1007/7854_2009_20] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Psychostimulant drugs have powerful reinforcing and hedonic properties and are frequently abused. Cessation of psychostimulant administration results in a withdrawal syndrome characterized by anhedonia (i.e., an inability to experience pleasure). In humans, psychostimulant withdrawal-induced anhedonia can be debilitating and has been hypothesized to play an important role in relapse to drug use. Hence, understanding the neural substrates involved in psychostimulant withdrawal-induced anhedonia is essential. In this review, we first summarize the theoretical perspectives of psychostimulant withdrawal-induced anhedonia. Experimental procedures and measures used to assess anhedonia in experimental animals are also discussed. The review then focuses on neural substrates hypothesized to play an important role in anhedonia experienced after termination of psychostimulant administration, such as with cocaine, amphetamine-like drugs, and nicotine. Both neural substrates that have been extensively investigated and some that need further evaluation with respect to psychostimulant withdrawal-induced anhedonia are reviewed. In the context of reviewing the various neurosubstrates of psychostimulant withdrawal, we also discuss pharmacological medications that have been used to treat psychostimulant withdrawal in humans. This literature review indicates that great progress has been made in understanding the neural substrates of anhedonia associated with psychostimulant withdrawal. These advances in our understanding of the neurobiology of anhedonia may also shed light on the neurobiology of nondrug-induced anhedonia, such as that seen as a core symptom of depression and a negative symptom of schizophrenia.
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Affiliation(s)
- Manoranjan S D'Souza
- Department of Psychiatry, University of California, San Diego, La Jolla, CA 92093, USA
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Giuffrida A, McMahon LR. In vivo pharmacology of endocannabinoids and their metabolic inhibitors: therapeutic implications in Parkinson's disease and abuse liability. Prostaglandins Other Lipid Mediat 2009; 91:90-103. [PMID: 19523530 DOI: 10.1016/j.prostaglandins.2009.05.004] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2009] [Revised: 05/19/2009] [Accepted: 05/26/2009] [Indexed: 01/03/2023]
Abstract
This review focuses on the behavioral pharmacology of endogenous cannabinoids (endocannabinoids) and indirect-acting cannabinoid agonists that elevate endocannabinoid tone by inhibiting the activity of metabolic enzymes. Similarities and differences between prototype cannabinoid agonists, endocannabinoids and inhibitors of endocannabinoid metabolism are discussed in the context of endocannabinoid pharmacokinetics in vivo. The distribution and function of cannabinoid and non-CB(1)/CB(2) receptors are also covered, with emphasis on their role in disorders characterized by dopamine dysfunction, such as drug abuse and Parkinson's disease. Finally, evidence is presented to suggest that FAAH inhibitors lack the abuse liability associated with CB(1) agonists, although they may modify the addictive properties of other drugs, such as alcohol.
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Affiliation(s)
- Andrea Giuffrida
- Department of Pharmacology, University of Texas Health Science Center, San Antonio, TX 78229, USA.
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Mavrikaki M, Nomikos GG, Panagis G. Effects of mood stabilizers on brain reward processes in rats: studies using the intracranial self-stimulation paradigm. Eur Neuropsychopharmacol 2009; 19:205-14. [PMID: 19110403 DOI: 10.1016/j.euroneuro.2008.11.002] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/23/2008] [Revised: 11/05/2008] [Accepted: 11/12/2008] [Indexed: 12/19/2022]
Abstract
Bipolar disorder is characterized by dysregulated motivation and increased hedonistic drive. d-Amphetamine induces manic symptoms in humans and exacerbates mania in bipolar disorder patients, effects that are counteracted by mood stabilizers. We utilized intracranial self-stimulation (ICSS) to examine how lithium (LiCl), valproate (VPA) or their combination that is commonly used in the clinic affect brain reward function in rats, and how these drugs affect d-amphetamine's reward-facilitating effects. Acute intraperitoneal (i.p.) administration of LiCl (100, 200 mg/kg), VPA (400 mg/kg) or combined administration of subthreshold doses of LiCl (50 mg/kg) and VPA (200 mg/kg) increased ICSS thresholds. LiCl (100 mg/kg) and combined administration of LiCl and VPA (50 and 200 mg/kg), but not VPA alone (200, 400 mg/kg), attenuated d-amphetamine's reward-facilitating effects. These results suggest that ICSS combined with d-amphetamine constitutes a useful model to explore the elation and increased hedonistic drive observed in bipolar patients and ultimately help to identify novel pharmacotherapies for bipolar disorder.
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Affiliation(s)
- Maria Mavrikaki
- University of Crete, School of Social Sciences, Department of Psychology, Laboratory of Behavioral Neuroscience, 74100 Rethymno, Crete, Greece
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Marco EM, Rubino T, Adriani W, Viveros MP, Parolaro D, Laviola G. Long-term consequences of URB597 administration during adolescence on cannabinoid CB1 receptor binding in brain areas. Brain Res 2009; 1257:25-31. [DOI: 10.1016/j.brainres.2008.12.037] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2008] [Revised: 12/11/2008] [Accepted: 12/14/2008] [Indexed: 11/17/2022]
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Enhancement of endocannabinoid neurotransmission through CB1 cannabinoid receptors counteracts the reinforcing and psychostimulant effects of cocaine. Int J Neuropsychopharmacol 2008; 11:905-23. [PMID: 18377702 DOI: 10.1017/s1461145708008717] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Cannabinoids, in contrast to typical drugs of abuse, have been shown to exert complex effects on behavioural reinforcement and psychomotor function. We have shown that cannabinoid agonists lack reinforcing/rewarding properties in the intracranial self-stimulation (ICSS) paradigm and that the CB1 receptor (CB1R) agonist WIN55,212-2 attenuates the reward-facilitating actions of cocaine. We sought to determine the effects of the endocannabinoid neurotransmission enhancer AM-404 (1, 3, 10, 30 mg/kg) on the changes in ICSS threshold and locomotion elicited by cocaine and extend the study of the effects of WIN55,212-2 (0.3, 1, 3 mg/kg) on cocaine-induced hyperlocomotion. AM-404 did not exhibit reward-facilitating properties, and actually increased self-stimulation threshold at the highest dose. Cocaine significantly reduced self-stimulation threshold, without altering maximal rates of responding. AM-404 (10 mg/kg) attenuated this action of cocaine, an effect which was reversed by pretreatment with the selective CB1R antagonist SR141716A. WIN55,212-2 decreased locomotion at the two highest doses, an effect that was blocked by SR141716A; AM-404 had no effect on locomotion. Cocaine caused a significant, dose-dependent increase in locomotion, which was reduced by WIN55,212-2 and AM-404. SR141716A blocked the effects of WIN55,212-2 and AM-404 on cocaine-induced hyperlocomotion. SR141716A alone had no effect on ICSS threshold or locomotion. These results indicate that cannabinoids may interfere with brain reward systems responsible for the expression of acute reinforcing/rewarding properties of cocaine, and provide further evidence that the cannabinoid system could be explored as a potential drug discovery target for the treatment of psychostimulant addiction and pathological states associated with psychomotor overexcitability.
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Abstract
The identification of the cannabinoid receptor type 1 (CB1 receptor) was the milestone discovery in the elucidation of the behavioural and emotional responses induced by the Cannabis sativa constituent Delta(9)-tetrahydrocannabinol. The subsequent years have established the existence of the endocannabinoid system. The early view relating this system to emotional responses is reflected by the fact that N-arachidonoyl ethanolamine, the pioneer endocannabinoid, was named anandamide after the Sanskrit word 'ananda', meaning 'bliss'. However, the emotional responses to cannabinoids are not always pleasant and delightful. Rather, anxiety and panic may also occur after activation of CB1 receptors. The present review discusses three properties of the endocannabinoid system as an attempt to understand these diverse effects. First, this system typically functions 'on-demand', depending on environmental stimuli and on the emotional state of the organism. Second, it has a wide neuro-anatomical distribution, modulating brain regions with different functions in responses to aversive stimuli. Third, endocannabinoids regulate the release of other neurotransmitters that may have even opposing functions, such as GABA and glutamate. Further understanding of the temporal, spatial and functional characteristics of this system is necessary to clarify its role in emotional responses and will promote advances in its therapeutic exploitation.
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Affiliation(s)
- Fabrício A Moreira
- Department of Physiological Chemistry, Johannes Gutenberg University Mainz, Duesbergweg 6, 55099 Mainz, Germany.
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Di Marzo V. Targeting the endocannabinoid system: to enhance or reduce? Nat Rev Drug Discov 2008; 7:438-55. [PMID: 18446159 DOI: 10.1038/nrd2553] [Citation(s) in RCA: 612] [Impact Index Per Article: 38.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
As our understanding of the endocannabinoids improves, so does the awareness of their complexity. During pathological states, the levels of these mediators in tissues change, and their effects vary from those of protective endogenous compounds to those of dysregulated signals. These observations led to the discovery of compounds that either prolong the lifespan of endocannabinoids or tone down their action for the potential future treatment of pain, affective and neurodegenerative disorders, gastrointestinal inflammation, obesity and metabolic dysfunctions, cardiovascular conditions and liver diseases. When moving to the clinic, however, the pleiotropic nature of endocannabinoid functions will require careful judgement in the choice of patients and stage of the disorder for treatment.
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Affiliation(s)
- Vincenzo Di Marzo
- Endocannabinoid Research Group, Institute of Biomolecular Chemistry, National Research Council (CNR), Via Campi Flegrei 34, 80078, Pozzuoli, Naples, Italy.
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Boutrel B. A neuropeptide-centric view of psychostimulant addiction. Br J Pharmacol 2008; 154:343-57. [PMID: 18414383 PMCID: PMC2442449 DOI: 10.1038/bjp.2008.133] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2008] [Revised: 03/14/2008] [Accepted: 03/14/2008] [Indexed: 11/08/2022] Open
Abstract
Drugs of abuse all share common properties classically observed in human beings and laboratory animals. They enhance neural firing and dopamine tone within the nucleus accumbens and produce progressively greater drug-induced motor responses defined as behavioural sensitization. They produce conditioned place preference, a behavioural model of incentive motivation, which highlights the role of environmental cues in drug addiction. They increase brain reward function as seen by a lowering of intracranial self-stimulation thresholds. And last but not least, they are self-administered, and sometimes even abused, and can trigger reinstatement of drug-seeking behaviour in animals extinguished from drug self-administration. It has long been considered that the reinforcing properties of virtually all drugs of abuse, more specifically psychostimulants, are primarily dependent on activation of the mesolimbic dopamine system. However, recent evidence raises the importance of dopamine-independent mechanisms in reward-related behaviours. The overwhelming body of evidence that indicates a critical role for the mesolimbic dopamine system in the reinforcing effect of psychostimulants should not mask the key contribution of other modulatory systems in the brain. This review summarizes the complex and subtle role of several neuropeptidergic systems in various aspects of addictive behaviours observed in laboratory animals exposed to psychostimulants. A special emphasis is given to the cannabinoid, opioid, nociceptin/orphanin FQ, corticotropin-releasing factor and hypocretin/orexin systems. The relevance of these systems viewed as potential therapeutic targets for drug addiction is discussed in the light of their narrow pharmacological profile and their effectiveness in preventing drug addiction at doses usually not accompanied by severe side effects.
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Affiliation(s)
- B Boutrel
- Center for Psychiatric Neuroscience and Division of Child and Adolescent Psychiatry, Department of Psychiatry, Lausanne University Hospital, Site de Cery, Prilly, Switzerland.
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Abstract
Food, drugs and brain stimulation can serve as strong rewarding stimuli and are all believed to activate common brain circuits that evolved in mammals to favour fitness and survival. For decades, endogenous dopaminergic and opioid systems have been considered the most important systems in mediating brain reward processes. Recent evidence suggests that the endogenous cannabinoid (endocannabinoid) system also has an important role in signalling of rewarding events. First, CB(1) receptors are found in brain areas involved in reward processes, such as the dopaminergic mesolimbic system. Second, activation of CB(1) receptors by plant-derived, synthetic or endogenous CB(1) receptor agonists stimulates dopaminergic neurotransmission, produces rewarding effects and increases rewarding effects of abused drugs and food. Third, pharmacological or genetic blockade of CB(1) receptors prevents activation of dopaminergic neurotransmission by several addictive drugs and reduces rewarding effects of food and these drugs. Fourth, brain levels of the endocannabinoids anandamide and 2-arachidonoylglycerol are altered by activation of reward processes. However, the intrinsic activity of the endocannabinoid system does not appear to play a facilitatory role in brain stimulation reward and some evidence suggests it may even oppose it. The influence of the endocannabinoid system on brain reward processes may depend on the degree of activation of the different brain areas involved and might represent a mechanism for fine-tuning dopaminergic activity. Although involvement of the various components of the endocannabinoid system may differ depending on the type of rewarding event investigated, this system appears to play a major role in modulating reward processes.
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Tanda G. Modulation of the endocannabinoid system: therapeutic potential against cocaine dependence. Pharmacol Res 2007; 56:406-17. [PMID: 17945506 DOI: 10.1016/j.phrs.2007.09.001] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/30/2007] [Accepted: 09/05/2007] [Indexed: 02/03/2023]
Abstract
Dependence on cocaine is still a main unresolved medical and social concern, and in spite of research efforts, no pharmacological therapy against cocaine dependence is yet available. Recent studies have shown that the endocannabinoid system participates in specific stages and aspects of drug dependence in general, and some of this evidence suggests an involvement of the cannabinoid system in cocaine effects. For example, cocaine administration has been shown to alter brain endocannabinoid levels, and the endocannabinoid system has been involved in long-term modifications of brain processes that might play a role in neuro/behavioral effects of psychostimulant drugs like cocaine. Human studies show that marijuana dependence is frequently associated with cocaine dependence, and that the cannabinoid receptor CNR1 gene polymorphism might be related to cocaine addiction. This article will review the main papers in the field showing how a modulation of different components of the cannabinoid system might interact with some of the neurobiological/behavioral effects of cocaine related to its reinforcing effects, evaluated in preclinical models or in clinical settings. The goal of this review will be to provide insights into the complex picture of cocaine abuse and addiction, and to extrapolate from such endocannabinoid-cocaine interactions useful information to test the therapeutic potential of cannabinoid ligands and endocannabinoid-level enhancers against cocaine dependence for future preclinical/clinical trials.
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Affiliation(s)
- Gianluigi Tanda
- Psychobiology Section, Medications Discovery Research Branch, National Institute on Drug Abuse, National Institutes of Health, Department of Health and Human Services, Baltimore, MD 21224, USA.
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Vlachou S, Nomikos GG, Stephens DN, Panagis G. Lack of evidence for appetitive effects of Delta 9-tetrahydrocannabinol in the intracranial self-stimulation and conditioned place preference procedures in rodents. Behav Pharmacol 2007; 18:311-9. [PMID: 17551324 DOI: 10.1097/fbp.0b013e3282186cf2] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Data on the ability of Delta 9-tetrahydrocannabinol (THC) to modify reward processes in experimental animals are inconsistent. This study examined the effects of Delta 9-THC on brain reward function using the rate-frequency curve shift paradigm of intracranial self-stimulation (ICSS) and the conditioned place preference (CPP) paradigm. In ICSS tests, rats were implanted with electrodes into the medial forebrain bundle. After brain stimulation reward thresholds stabilized, rats received intraperitoneal injections of Delta 9-THC (0, 0.5, 1 and 2 mg/kg) or the CB1 receptor antagonist SR141716A (0, 0.02 mg/kg) and Delta 9-THC (0, 2 mg/kg). The two highest doses of Delta 9-THC significantly increased the threshold ICSS frequency. SR141716A reversed the action of Delta 9-THC (2 mg/kg), without affecting reward thresholds by itself. In the CPP test, mice received intraperitoneal injections of Delta 9-THC (0, 1 or 3 mg/kg). Delta 9-THC showed neither statistically significant preference nor aversion in either of the doses tested. These findings indicate that Delta 9-THC, in contrast to other drugs of abuse, does not facilitate ICSS or support CPP under the present experimental conditions, but rather has a dose-dependent inhibitory influence on ICSS.
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Affiliation(s)
- Styliani Vlachou
- Laboratory of Behavioral Neuroscience, Department of Psychology, School of Social Sciences, University of Crete, Rethymnon, Crete, Greece
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