101
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Effects of the histamine (H)3 receptor antagonist ABT-239 on acute and repeated nicotine locomotor responses in rats. Pharmacol Rep 2011; 63:1553-9. [DOI: 10.1016/s1734-1140(11)70720-4] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2011] [Revised: 08/01/2011] [Indexed: 11/22/2022]
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102
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Hone AJ, Meyer EL, McIntyre M, McIntosh JM. Nicotinic acetylcholine receptors in dorsal root ganglion neurons include the α6β4* subtype. FASEB J 2011; 26:917-26. [PMID: 22024738 DOI: 10.1096/fj.11-195883] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The α6-containing nicotinic acetylcholine receptors (nAChRs) have recently been implicated in diseases of the central nervous system (CNS), including Parkinson's disease and substance abuse. In contrast, little is known about the role of α6* nAChRs in the peripheral nervous system (where the asterisk denotes the possible presence of additional subunits). Dorsal root ganglia (DRG) neurons are known to express nAChRs with a pharmacology consistent with an α7, α3β4*, and α4β2* composition. Here we present evidence that DRG neurons also express α6* nAChRs. We used RT-PCR to show the presence of α6 subunit transcripts and patch-clamp electrophysiology together with subtype-selective α-conotoxins to pharmacologically characterize the nAChRs in rat DRG neurons. α-Conotoxin BuIA (500 nM) blocked acetylcholine-gated currents (I(ACh)) by 90.3 ± 3.0%; the recovery from blockade was very slow, indicating a predominance of α(x)β4* nAChRs. Perfusion with either 300 nM BuIA[T5A;P6O] or 200 nM MII[E11A], α-conotoxins that target the α6β4* subtype, blocked I(ACh) by 49.3 ± 5 and 46.7 ± 8%, respectively. In these neurons, I(ACh) was relatively insensitive to 200 nM ArIB[V11L;V16D] (9.4±2.0% blockade) or 500 nM PnIA (23.0±4% blockade), α-conotoxins that target α7 and α3β2*/α6β2* nAChRs, respectively. We conclude that α6β4* nAChRs are among the subtypes expressed by DRG, and to our knowledge, this is the first demonstration of α6β4* in neurons outside the CNS.
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Affiliation(s)
- Arik J Hone
- Interdepartmental Program in Neuroscience, University of Utah, Salt Lake City, Utah, USA
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103
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Paolini M, De Biasi M. Mechanistic insights into nicotine withdrawal. Biochem Pharmacol 2011; 82:996-1007. [PMID: 21782803 PMCID: PMC3312005 DOI: 10.1016/j.bcp.2011.07.075] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2011] [Revised: 07/03/2011] [Accepted: 07/05/2011] [Indexed: 12/20/2022]
Abstract
Smoking is responsible for over 400,000 premature deaths in the United States every year, making it the leading cause of preventable death. In addition, smoking-related illness leads to billions of dollars in healthcare expenditures and lost productivity annually. The public is increasingly aware that successfully abstaining from smoking at any age can add years to one's life and reduce many of the harmful effects of smoking. Although the majority of smokers desire to quit, only a small fraction of attempts to quit are actually successful. The symptoms associated with nicotine withdrawal are a primary deterrent to cessation and they need to be quelled to avoid early relapse. This review will focus on the neuroadaptations caused by chronic nicotine exposure and discuss how those changes lead to a withdrawal syndrome upon smoking cessation. Besides examining how nicotine usurps the endogenous reward system, we will discuss how the habenula is part of a circuit that plays a critical role in the aversive effects of high nicotine doses and nicotine withdrawal. We will also provide an updated summary of the role of various nicotinic receptor subtypes in the mechanisms of withdrawal. This growing knowledge provides mechanistic insights into current and future smoking cessation therapies.
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Affiliation(s)
- Michael Paolini
- Department of Neuroscience, Baylor College of Medicine, Houston, TX, 77030, USA
- Center on Addiction, Learning, Memory, Baylor College of Medicine, Houston, TX, 77030, USA
| | - Mariella De Biasi
- Department of Neuroscience, Baylor College of Medicine, Houston, TX, 77030, USA
- Center on Addiction, Learning, Memory, Baylor College of Medicine, Houston, TX, 77030, USA
- Program in Translational Biology and Molecular Medicine, Baylor College of Medicine, Houston, TX, 77030, USA
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104
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Pérez-Alvarez A, Hernández-Vivanco A, McIntosh JM, Albillos A. Native α6β4* nicotinic receptors control exocytosis in human chromaffin cells of the adrenal gland. FASEB J 2011; 26:346-54. [PMID: 21917987 DOI: 10.1096/fj.11-190223] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
In the present study, we have electrophysiologically characterized native nicotinic acetylcholine receptors (nAChRs) in human chromaffin cells of the adrenal gland as well as their contribution to the exocytotic process. α-Conotoxin AuIB blocked by 14 ± 1% the acetylcholine (ACh)-induced nicotinic current. α-Conotoxin MII (α-Ctx MII) exhibited an almost full blockade of the nicotinic current at nanomolar concentrations (IC(50)=21.6 nM). The α6*-preferring α-Ctx MII mutant analogs, α-Ctx MII[H9A,L15A] and α-Ctx MII[S4A,E11A,L15A], blocked nAChR currents with an IC(50) of 217.8 and 33 nM, respectively. These data reveal that nAChRs in these cells include the α6* subtype. The washout of the blockade exerted by α-conotoxin BuIA (α-Ctx BuIA; 1 μM) on ACh-evoked currents was slight and slow, arguing in favor of the presence of a β4 subunit in the nAChR composition. Exocytosis was almost fully blocked by 1 μM α-Ctx MII, its mutant analogs, or α-Ctx BuIA. Finally, the fluorescent analog Alexa Fluor 546-BuIA showed distinct staining in these cells. Our results reveal that α6β4* nAChRs are expressed and contribute to exocytosis in human chromaffin cells of the adrenal gland, the main source of adrenaline under stressful situations.
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Affiliation(s)
- Alberto Pérez-Alvarez
- Departamento de Farmacología y Terapéutica, Universidad Autónoma de Madrid, Madrid, Spain.
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105
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Progress and challenges in the study of α6-containing nicotinic acetylcholine receptors. Biochem Pharmacol 2011; 82:862-72. [PMID: 21736871 DOI: 10.1016/j.bcp.2011.06.022] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2011] [Revised: 06/15/2011] [Accepted: 06/15/2011] [Indexed: 11/22/2022]
Abstract
Recent progress has been made in the understanding of the anatomical distribution, composition, and physiological role of nicotinic acetylcholine receptors containing the α6 subunit. Extensive study by many researchers has indicated that a collection of α6-containing receptors representing a nicotinic sub-family is relevant in preclinical models of nicotine self-administration and locomotor activity. Due to a number of technical difficulties, the state of the art of in vitro model systems expressing α6-containing receptors has lagged behind the state of knowledge of native α6 nAChR subunit composition. Several techniques, such as the expression of chimeric and concatameric α6 subunit constructs in oocytes and mammalian cell lines have been employed to overcome these obstacles. There remains a need for other critical tools, such as selective small molecules and radioligands, to advance the field of research and to allow the discovery and development of potential therapeutics targeting α6-containing receptors for smoking cessation, Parkinson's disease and other disorders.
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106
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Role of α6 nicotinic receptors in CNS dopaminergic function: relevance to addiction and neurological disorders. Biochem Pharmacol 2011; 82:873-82. [PMID: 21684266 DOI: 10.1016/j.bcp.2011.06.001] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2011] [Revised: 06/01/2011] [Accepted: 06/02/2011] [Indexed: 11/23/2022]
Abstract
Although a relative newcomer to the nicotinic acetylcholine receptor (nAChR) family, substantial evidence suggests that α6 containing nAChRs play a key role in CNS function. This subtype is unique in its relatively restricted localization to the visual system and catecholaminergic pathways. These latter include the mesolimbic and nigrostriatal dopaminergic systems, which may account for the involvement of α6 containing nAChRs in the rewarding properties of nicotine and in movement. Here, we review the literature on the role of α6 containing nAChRs with a focus on the striatum and nucleus accumbens. This includes molecular, electrophysiological and behavioral studies in control and lesioned animal models, as well as in different genetic models. Converging evidence suggest that the major α6 containing nAChRs subtypes in the nigrostriatal and mesolimbic dopamine system are the α6β2β3 and α6α4β2β3 nAChR populations. They appear to have a dominant role in regulating dopamine release, with consequent effects on nAChR-modulated dopaminergic functions such as reinforcement and motor behavior. Altogether these data suggest that drugs directed to α6 containing nAChRs may be of benefit for the treatment of addiction and for neurological disorders with locomotor deficits such as Parkinson's disease.
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107
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The necessity of α4* nicotinic receptors in nicotine-driven behaviors: dissociation between reinforcing and motor effects of nicotine. Neuropsychopharmacology 2011; 36:1505-17. [PMID: 21430644 PMCID: PMC3096818 DOI: 10.1038/npp.2011.35] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Here we utilize a mouse line with a targeted deletion of the α4 subunit (α4-/- mice), to investigate the role of α4* nAChRs in reinforcing and locomotor effects of nicotine. Within a conditioned place preference paradigm, both α4-/- mice and wild-type (WT) littermates showed a similar place preference to nicotine (0.5 mg/kg i.p.) conditioning. When assessed for operant intravenous self-administration of nicotine (0.05 mg/kg/infusion), α4-/- mice did not differ from their WT littermates in self-administration behavior. To further examine a modulatory role for α4* nAChRs in the reinforcing effects of nicotine, a transgenic mouse with a point mutation of the α4 subunit (α4-S248F) that renders increased sensitivity to low dose nicotine, was assessed for nicotine self-administration over a range of doses. At higher doses examined (0.05 and 0.07 mg/kg/infusion) there was no difference in intravenous nicotine self-administration; however, when mice were offered a lower dose of nicotine (0.03 mg/kg/infusion), α4-S248F mice showed greater nicotine intake than controls. Acute administration of 0.5 mg/kg nicotine caused significant locomotor depression in WT mice but α4-/- mice instead showed significant hyperactivity. Following chronic, intermittent administration of this dose of nicotine only WT mice displayed significant tolerance. Analogous experiments utilizing administration of the nicotinic antagonist mecamylamine in WT mice confirmed a dissociation between the putative nicotinic receptor subtypes required for mediating psychomotor and reinforcing effects of nicotine. These data demonstrate a necessary role for α4* nAChRs in the locomotor depressant effect of nicotine but not the reinforcing effects that support ongoing self-administration of nicotine.
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108
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Characterizing functional α6β2 nicotinic acetylcholine receptors in vitro: mutant β2 subunits improve membrane expression, and fluorescent proteins reveal responsive cells. Biochem Pharmacol 2011; 82:852-61. [PMID: 21609715 DOI: 10.1016/j.bcp.2011.05.005] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2011] [Revised: 05/06/2011] [Accepted: 05/09/2011] [Indexed: 01/09/2023]
Abstract
α6* nicotinic acetylcholine receptors (nAChRs) are highly expressed in mesostriatal and nigrostriatal dopaminergic systems, and participate in motor control, reward, and learning and memory. In vitro functional expression of α6* nAChRs is essential for full pharmacological characterization of these receptors and for drug screening, but has been challenging. We expressed eGFP-tagged-α6 and β2 nAChR subunits in Neuro-2a cells, leading to functional channels. Inward currents were elicited with 300 μM ACh in 26% (5/19) of cells with evenly expressed α6-eGFP in cytoplasm and periphery. We dramatically increased chances of detecting functional α6-eGFPβ2 nAChRs by (i) introducing two endoplasmic reticulum (ER) export-enhancing mutations into β2 subunits, and (ii) choosing cells with abundant Sec24D-mCherry-labeled ER exit sites. Both manipulations also modestly increased α6-eGFPβ2 nAChR current amplitude. α6-eGFPβ2 nAChRs were also activated by nicotine and by TC-2403. The α6-eGFPβ2 currents were desensitized by 1μM nicotine, blocked by α-conotoxin MII, partially inhibited by dihydro-β-erythroidine, and potentiated by extracellular Ca(2+). Single-channel recordings showed that α6-eGFPβ2 nAChRs had similar single-channel conductance to, but longer open time than, α4-eGFPβ2 nAChRs. These methods provide avenues for developing cell lines expressing subtypes of α6* nAChRs for both pharmacological study and drug screening.
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109
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Midde NM, Gomez AM, Harrod SB, Zhu J. Genetically expressed HIV-1 viral proteins attenuate nicotine-induced behavioral sensitization and alter mesocorticolimbic ERK and CREB signaling in rats. Pharmacol Biochem Behav 2011; 98:587-97. [PMID: 21420997 DOI: 10.1016/j.pbb.2011.03.013] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/18/2010] [Revised: 03/07/2011] [Accepted: 03/12/2011] [Indexed: 12/29/2022]
Abstract
The prevalence of tobacco smoking in HIV-1 positive individuals is 3-fold greater than that in the HIV-1 negative population; however, whether HIV-1 viral proteins and nicotine together produce molecular changes in mesolimbic structures that mediate psychomotor behavior has not been studied. This study determined whether HIV-1 viral proteins changed nicotine-induced behavioral sensitization in HIV-1 transgenic (HIV-1Tg) rats. Further, we examined cAMP response element binding protein (CREB) and extracellular regulated kinase (ERK1/2) signaling in the prefrontal cortex (PFC), nucleus accumbens (NAc) and ventral tegmental area (VTA). HIV-1Tg rats exhibited a transient decrease of activity during habituation, but showed attenuated nicotine (0.35mg/kg, s.c.)-induced behavioral sensitization compared to Fisher 344 (F344) rats. The basal levels of phosphorylated CREB and ERK2 were lower in the PFC of HIV-1Tg rats, but not in the NAc and VTA, relative to the controls. In the nicotine-treated groups, the levels of phosphorylated CREB and ERK2 in the PFC were increased in HIV-1Tg rats, but decreased in F344 animals. Moreover, repeated nicotine administration reduced phosphorylated ERK2 in the VTA of HIV-1Tg rats and in the NAc of F344 rats, but had no effect on phosphorylated CREB, indicating a region-specific change of intracellular signaling. These results demonstrate that HIV-1 viral proteins produce differences in basal and nicotine-induced alterations in CREB and ERK signaling that may contribute to the alteration in psychomotor sensitization. Thus, HIV-1 positive smokers are possibly more vulnerable to alterations in CREB and ERK signaling and this has implications for motivated behavior, including tobacco smoking, in HIV-1 positive individuals who self-administer nicotine.
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Affiliation(s)
- Narasimha M Midde
- Department of Pharmaceutical and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Columbia, SC 29208, USA
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110
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Rahman S. Brain nicotinic receptors as emerging targets for drug addiction: neurobiology to translational research. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2011; 98:349-65. [PMID: 21199776 DOI: 10.1016/b978-0-12-385506-0.00008-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Drug addiction, a chronic relapsing disorder, is a serious public health problem around the world. A growing body of preclinical and clinical evidence suggests that mammalian brain nicotinic acetylcholine receptors (nAChRs), the heterogeneous family of ion channels, play a pivotal role in drug addiction, including nicotine and alcohol dependence. As a result, there is an increasing interest in developing nAChR-based therapies for the treatment of addictive disorders. The current review summarizes the important preclinical and clinical data, demonstrating the ability of nAChR ligands to modulate nicotine and alcohol-induced biobehavioral and neurochemical changes in laboratory animals and humans. Recent studies suggest that partial agonists and antagonists at nAChRs have therapeutic potential for the management of nicotine and alcohol dependence. The complexity of nAChRs and their regulation for the development of nAChR-based drug candidates as novel pharmacotherapy for other addictive disorders will also be discussed. Taken together, this review will provide new insights into nAChR-based compounds and offer innovative translational strategies for combating drug addictive disorders.
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Affiliation(s)
- Shafiqur Rahman
- Department of Pharmaceutical Sciences, College of Pharmacy, South Dakota State University, Brookings, South Dakota, USA
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111
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Azarn L, Maskos U, Changeux JP, Dowell CD, Christensen S, Biasi MD, McIntosh JM. α‐Conotoxin BuIA[T5A;P6O]: a novel ligand that discriminates between 06 β4 and 0:6 β2 nicotinic acetylcholine receptors and blocks nicotine‐stimulated norepinephrine release. FASEB J 2010. [DOI: 10.1096/fj.10.166272] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Layla Azarn
- Department of BiologyUniversity of Utah, Salt Lake City Utah USA
| | - Uwe Maskos
- Unité Neurobiologie Intégrative des Systèmes Cholinergiques, Institut Pasteur Paris France
| | - Jean-Pierre Changeux
- Unité Neurobiologie Intégrative des Systèmes Cholinergiques, Institut Pasteur Paris France
| | - Cheryl D. Dowell
- Department of BiologyUniversity of Utah, Salt Lake City Utah USA
| | - Sean Christensen
- Department of BiologyUniversity of Utah, Salt Lake City Utah USA
| | - Mariella De Biasi
- Department of Neuroscience and Graduate Program in Translational Biology and Molecular MedicineBaylor College of Medicine Houston Texas USA
| | - J. Michael McIntosh
- Department of BiologyUniversity of Utah, Salt Lake City Utah USA
- Department of PsychiatryUniversity of Utah, Salt Lake City Utah USA
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112
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Turner JR, Castellano LM, Blendy JA. Parallel anxiolytic-like effects and upregulation of neuronal nicotinic acetylcholine receptors following chronic nicotine and varenicline. Nicotine Tob Res 2010; 13:41-6. [PMID: 21097981 DOI: 10.1093/ntr/ntq206] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
INTRODUCTION Clinical and preclinical studies suggest that regulation of nicotinic acetylcholine receptors (nAChR) maybe involved in the etiology of withdrawal symptoms. METHODS We evaluated heteromeric nAChR regulation via [³H]epibatidine binding following cessation of chronic nicotine or varenicline treatment. Animals were concurrently tested in the marble-burying test to evaluate treatment-related effects. RESULTS We found that both nicotine (18 mg/kg/day, free base) and varenicline (1.8 mg/kg/day) chronically administered for 14 days upregulated nAChRs significantly in the cortex, hippocampus, striatum, and thalamus. The duration of upregulation (up to 72 hr) was both drug and region specific. In addition to nAChR upregulation, chronic administration of both nicotine and varenicline had anxiolytic-like effects in the marble-burying test. This effect was maintained for 48 hr following cessation of varenicline but was absent 24 hr following cessation from nicotine. Additionally, marble-burying behavior positively correlated to the regulation of cortical nAChRs following cessation of either treatment. CONCLUSIONS Varenicline has been shown to be an efficacious smoking cessation aid, with a proposed mechanism of action that includes modulation of dopamine release in reward areas of the brain. Our studies show that varenicline elicits both anxiolytic effects in the marble-burying test as well as region- and time-specific receptor upregulation. These findings suggest receptor upregulation as a mechanism for its efficacy as a smoking cessation therapy.
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Affiliation(s)
- Jill R Turner
- Department of Pharmacology, University of Pennsylvania, Philadelphia, PA, USA
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113
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Berrendero F, Robledo P, Trigo JM, Martín-García E, Maldonado R. Neurobiological mechanisms involved in nicotine dependence and reward: participation of the endogenous opioid system. Neurosci Biobehav Rev 2010; 35:220-31. [PMID: 20170672 PMCID: PMC2908214 DOI: 10.1016/j.neubiorev.2010.02.006] [Citation(s) in RCA: 101] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2009] [Revised: 02/08/2010] [Accepted: 02/09/2010] [Indexed: 01/07/2023]
Abstract
Nicotine is the primary component of tobacco that maintains the smoking habit and develops addiction. The adaptive changes of nicotinic acetylcholine receptors produced by repeated exposure to nicotine play a crucial role in the establishment of dependence. However, other neurochemical systems also participate in the addictive effects of nicotine including glutamate, cannabinoids, GABA and opioids. This review will cover the involvement of these neurotransmitters in nicotine addictive properties, with a special emphasis on the endogenous opioid system. Thus, endogenous enkephalins and beta-endorphins acting on mu-opioid receptors are involved in nicotine-rewarding effects, whereas opioid peptides derived from prodynorphin participate in nicotine aversive responses. An up-regulation of mu-opioid receptors has been reported after chronic nicotine treatment that could counteract the development of nicotine tolerance, whereas the down-regulation induced on kappa-opioid receptors seems to facilitate nicotine tolerance. Endogenous enkephalins acting on mu-opioid receptors also play a role in the development of physical dependence to nicotine. In agreement with these actions of the endogenous opioid system, the opioid antagonist naltrexone has shown to be effective for smoking cessation in certain sub-populations of smokers.
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Affiliation(s)
- Fernando Berrendero
- Laboratory of Neuropharmacology, Department of Experimental and Health Sciences, University Pompeu Fabra, PRBB, C/Doctor Aiguader 88, 08003 Barcelona, Spain
| | - Patricia Robledo
- Laboratory of Neuropharmacology, Department of Experimental and Health Sciences, University Pompeu Fabra, PRBB, C/Doctor Aiguader 88, 08003 Barcelona, Spain
- Municipal Institute of Medical Research (IMIM), Barcelona, Spain
| | - José Manuel Trigo
- Laboratory of Neuropharmacology, Department of Experimental and Health Sciences, University Pompeu Fabra, PRBB, C/Doctor Aiguader 88, 08003 Barcelona, Spain
| | - Elena Martín-García
- Laboratory of Neuropharmacology, Department of Experimental and Health Sciences, University Pompeu Fabra, PRBB, C/Doctor Aiguader 88, 08003 Barcelona, Spain
| | - Rafael Maldonado
- Laboratory of Neuropharmacology, Department of Experimental and Health Sciences, University Pompeu Fabra, PRBB, C/Doctor Aiguader 88, 08003 Barcelona, Spain
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114
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Kuryatov A, Lindstrom J. Expression of functional human α6β2β3* acetylcholine receptors in Xenopus laevis oocytes achieved through subunit chimeras and concatamers. Mol Pharmacol 2010; 79:126-40. [PMID: 20923852 DOI: 10.1124/mol.110.066159] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
α6β2β3* acetylcholine receptors (AChRs) on dopaminergic neurons are important targets for drugs to treat nicotine addiction and Parkinson's disease. However, it has not been possible to efficiently express functional α6β2β3* AChRs in oocytes or transfected cells. α6/α3 subunit chimeras permit expression of functional AChRs and reveal that parts of the α6 M1 transmembrane domain and large cytoplasmic domain impair assembly. Concatameric subunits permit assembly of functional α6β2β3* AChRs with defined subunit compositions and subunit orders. Assembly of accessory subunits is limiting in formation of mature AChRs. A single linker between the β3 accessory subunit and an α4 or α6 subunit is sufficient to permit assembly of complex β3-(α4β2)(α6β2) or β3-(α6β2)(α4β2) AChRs. Concatameric pentamers such as β3-α6-β2-α4-β2 have been functionally characterized. α6β2β3* AChRs are sensitive to activation by drugs used for smoking cessation therapy (nicotine, varenicline, and cytisine) and by sazetidine. All these are partial agonists. (α6β2)(α4β2)β3 AChRs are most sensitive to agonists. (α6β2)₂β3 AChRs have the greatest Ca²+ permeability. (α4β2)(α6β2)β3 AChRs are most efficiently transported to the cell surface, whereas (α6β2)₂β3 AChRs are the least efficiently transported. Dopaminergic neurons may have special chaperones for assembling accessory subunits with α6 subunits and for transporting (α6β2)₂β3 AChRs to the cell surface. Concatameric pentamers and pentamers formed from combinations of trimers, dimers, and monomers exhibit similar properties, indicating that the linkers between subunits do not alter their functional properties. For the first time, these concatamers allow analysis of functional properties of α6β2β3* AChRs. These concatamers should enable selection of drugs specific for α6β2β3* AChRs.
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Affiliation(s)
- Alexandre Kuryatov
- Department of Neuroscience, Medical School of the University of Pennsylvania, Philadelphia, PA 19104, USA
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115
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Azam L, Maskos U, Changeux JP, Dowell CD, Christensen S, De Biasi M, McIntosh JM. α-Conotoxin BuIA[T5A;P6O]: a novel ligand that discriminates between α6ß4 and α6ß2 nicotinic acetylcholine receptors and blocks nicotine-stimulated norepinephrine release. FASEB J 2010; 24:5113-23. [PMID: 20739611 DOI: 10.1096/fj.10-166272] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
α6* (asterisk indicates the presence of additional subunits) nicotinic acetylcholine receptors (nAChRs) are broadly implicated in catecholamine-dependent disorders that involve attention, motor movement, and nicotine self-administration. Different molecular forms of α6 nAChRs mediate catecholamine release, but receptor differentiation is greatly hampered by a paucity of subtype selective ligands. α-Conotoxins are nAChR-targeted peptides used by Conus species to incapacitate prey. We hypothesized that distinct conotoxin-binding kinetics could be exploited to develop a series of selective probes to enable study of native receptor subtypes. Proline6 of α-conotoxin BuIA was found to be critical for nAChR selectivity; substitution of proline6 with 4-hydroyxproline increased the IC(50) by 2800-fold at α6/α3β2β3 but only by 6-fold at α6/α3β4 nAChRs (to 1300 and 12 nM, respectively). We used conotoxin probes together with subunit-null mice to interrogate nAChR subtypes that modulate hippocampal norepinephrine release. Release was abolished in α6-null mutant mice. α-Conotoxin BuIA[T5A;P6O] partially blocked norepinephrine release in wild-type controls but failed to block release in β4(-/-) mice. In contrast, BuIA[T5A;P6O] failed to block dopamine release in the wild-type striatum known to contain α6β2* nAChRs. BuIA[T5A;P6O] is a novel ligand for distinguishing between closely related α6* nAChRs; α6β4* nAChRs modulate norepinephrine release in hippocampus but not dopamine release in striatum.
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Affiliation(s)
- Layla Azam
- Department of Biology, University of Utah, Salt Lake City, UT 84112, USA.
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116
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Changeux JP. Nicotine addiction and nicotinic receptors: lessons from genetically modified mice. Nat Rev Neurosci 2010; 11:389-401. [PMID: 20485364 DOI: 10.1038/nrn2849] [Citation(s) in RCA: 333] [Impact Index Per Article: 23.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The past decades have seen a revolution in our understanding of brain diseases and in particular of drug addiction. This has been largely due to the identification of neurotransmitter receptors and the development of animal models, which together have enabled the investigation of brain functions from the molecular to the cognitive level. Tobacco smoking, the principal - yet avoidable - cause of lung cancer is associated with nicotine addiction. Recent studies in mice involving deletion and replacement of nicotinic acetylcholine receptor subunits have begun to identify the molecular mechanisms underlying nicotine addiction and might offer new therapeutic strategies to treat this addiction.
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Affiliation(s)
- Jean-Pierre Changeux
- Collge de France and the Institut Pasteur CNRS URA 2182, 25 rue du Dr Roux, 75015 Paris, France.
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