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Ashok AH, Mizuno Y, Howes OD. Tobacco smoking and dopaminergic function in humans: a meta-analysis of molecular imaging studies. Psychopharmacology (Berl) 2019; 236:1119-1129. [PMID: 30887059 PMCID: PMC6591186 DOI: 10.1007/s00213-019-05196-1] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/06/2018] [Accepted: 02/07/2019] [Indexed: 12/21/2022]
Abstract
RATIONALE About 1.1 billion people smoke tobacco globally and tobacco-related health care costs 1.8% of GDP in many countries. The majority of people are unable to quit smoking despite pharmacological intervention, highlighting the need to understand the pathophysiology associated with tobacco smoking to aid the development of new therapeutics. The reinforcing effects of tobacco smoking are thought to be mediated by the dopamine system. However, the nature of dopamine dysfunction seen in smokers is unclear. OBJECTIVE To determine the nature and robustness of the evidence for dopaminergic alterations in smokers. METHODS The entire MEDLINE, EMBASE, and PsycINFO databases were searched for studies from inception date to November 18, 2018. In vivo human molecular imaging studies of dopamine measures (dopamine synthesis or release capacity, transporter levels, receptor levels) in tobacco smokers were selected. Demographic, clinical, and imaging measures were extracted from each study and meta-analyses, and sensitivity analyses were conducted. RESULTS Fourteen studies met inclusion criteria comprising a total sample of 219 tobacco smokers and 297 controls. The meta-analysis showed a significant reduction in dopamine transporter availability in the smokers relative to controls with an effect size of - 0.72 ([95% CI, - 1.38 to - 0.05], p = 0.03). However, there was no difference in D2/3 receptor availability in smokers relative to controls (d = -0.16 ([95% CI, - 0.42 to 0.1], p = 0.23). There were insufficient studies for meta-analysis of other measures. However, findings from the published studies indicated blunted dopamine release and lower D1 receptor availability, while findings for dopamine synthesis capacity were inconsistent. CONCLUSION Our data indicate that striatal dopamine transporter availability is lower but D2/3 receptors are unaltered in smokers relative to controls. We discuss the putative mechanisms underlying this and their implications.
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Affiliation(s)
- Abhishekh H. Ashok
- Psychiatric Imaging Group, MRC London Institute of Medical Sciences Centre (LMS), Du Cane Road, London, W12 0NN UK ,Psychiatric Imaging Group, Faculty of Medicine, Imperial College London, Institute of Clinical Sciences (ICS), Du Cane Road, London, UK ,Department of Psychosis Studies, Institute of Psychiatry, Psychology & Neuroscience, King’s College London, 16 De Crespigny Park, London, SE5 8AB UK
| | - Yuya Mizuno
- Department of Psychosis Studies, Institute of Psychiatry, Psychology & Neuroscience, King’s College London, 16 De Crespigny Park, London, SE5 8AB UK ,Department of Neuropsychiatry, Keio University School of Medicine, Tokyo, Japan
| | - Oliver D. Howes
- Psychiatric Imaging Group, MRC London Institute of Medical Sciences Centre (LMS), Du Cane Road, London, W12 0NN UK ,Psychiatric Imaging Group, Faculty of Medicine, Imperial College London, Institute of Clinical Sciences (ICS), Du Cane Road, London, UK ,Department of Psychosis Studies, Institute of Psychiatry, Psychology & Neuroscience, King’s College London, 16 De Crespigny Park, London, SE5 8AB UK
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Cahill K, Lindson‐Hawley N, Thomas KH, Fanshawe TR, Lancaster T. Nicotine receptor partial agonists for smoking cessation. Cochrane Database Syst Rev 2016; 2016:CD006103. [PMID: 27158893 PMCID: PMC6464943 DOI: 10.1002/14651858.cd006103.pub7] [Citation(s) in RCA: 190] [Impact Index Per Article: 23.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
BACKGROUND Nicotine receptor partial agonists may help people to stop smoking by a combination of maintaining moderate levels of dopamine to counteract withdrawal symptoms (acting as an agonist) and reducing smoking satisfaction (acting as an antagonist). OBJECTIVES To review the efficacy of nicotine receptor partial agonists, including varenicline and cytisine, for smoking cessation. SEARCH METHODS We searched the Cochrane Tobacco Addiction Group's specialised register for trials, using the terms ('cytisine' or 'Tabex' or 'dianicline' or 'varenicline' or 'nicotine receptor partial agonist') in the title or abstract, or as keywords. The register is compiled from searches of MEDLINE, EMBASE, and PsycINFO using MeSH terms and free text to identify controlled trials of interventions for smoking cessation and prevention. We contacted authors of trial reports for additional information where necessary. The latest update of the specialised register was in May 2015, although we have included a few key trials published after this date. We also searched online clinical trials registers. SELECTION CRITERIA We included randomised controlled trials which compared the treatment drug with placebo. We also included comparisons with bupropion and nicotine patches where available. We excluded trials which did not report a minimum follow-up period of six months from start of treatment. DATA COLLECTION AND ANALYSIS We extracted data on the type of participants, the dose and duration of treatment, the outcome measures, the randomisation procedure, concealment of allocation, and completeness of follow-up.The main outcome measured was abstinence from smoking at longest follow-up. We used the most rigorous definition of abstinence, and preferred biochemically validated rates where they were reported. Where appropriate we pooled risk ratios (RRs), using the Mantel-Haenszel fixed-effect model. MAIN RESULTS Two trials of cytisine (937 people) found that more participants taking cytisine stopped smoking compared with placebo at longest follow-up, with a pooled risk ratio (RR) of 3.98 (95% confidence interval (CI) 2.01 to 7.87; low-quality evidence). One recent trial comparing cytisine with NRT in 1310 people found a benefit for cytisine at six months (RR 1.43, 95% CI 1.13 to 1.80).One trial of dianicline (602 people) failed to find evidence that it was effective (RR 1.20, 95% CI 0.82 to 1.75). This drug is no longer in development.We identified 39 trials that tested varenicline, 27 of which contributed to the primary analysis (varenicline versus placebo). Five of these trials also included a bupropion treatment arm. Eight trials compared varenicline with nicotine replacement therapy (NRT). Nine studies tested variations in varenicline dosage, and 13 tested usage in disease-specific subgroups of patients. The included studies covered 25,290 participants, 11,801 of whom used varenicline.The pooled RR for continuous or sustained abstinence at six months or longer for varenicline at standard dosage versus placebo was 2.24 (95% CI 2.06 to 2.43; 27 trials, 12,625 people; high-quality evidence). Varenicline at lower or variable doses was also shown to be effective, with an RR of 2.08 (95% CI 1.56 to 2.78; 4 trials, 1266 people). The pooled RR for varenicline versus bupropion at six months was 1.39 (95% CI 1.25 to 1.54; 5 trials, 5877 people; high-quality evidence). The RR for varenicline versus NRT for abstinence at 24 weeks was 1.25 (95% CI 1.14 to 1.37; 8 trials, 6264 people; moderate-quality evidence). Four trials which tested the use of varenicline beyond the 12-week standard regimen found the drug to be well-tolerated during long-term use. The number needed to treat with varenicline for an additional beneficial outcome, based on the weighted mean control rate, is 11 (95% CI 9 to 13). The most commonly reported adverse effect of varenicline was nausea, which was mostly at mild to moderate levels and usually subsided over time. Our analysis of reported serious adverse events occurring during or after active treatment suggests there may be a 25% increase in the chance of SAEs among people using varenicline (RR 1.25; 95% CI 1.04 to 1.49; 29 trials, 15,370 people; high-quality evidence). These events include comorbidities such as infections, cancers and injuries, and most were considered by the trialists to be unrelated to the treatments. There is also evidence of higher losses to follow-up in the control groups compared with the intervention groups, leading to a likely underascertainment of the true rate of SAEs among the controls. Early concerns about a possible association between varenicline and depressed mood, agitation, and suicidal behaviour or ideation led to the addition of a boxed warning to the labelling in 2008. However, subsequent observational cohort studies and meta-analyses have not confirmed these fears, and the findings of the EAGLES trial do not support a causal link between varenicline and neuropsychiatric disorders, including suicidal ideation and suicidal behaviour. The evidence is not conclusive, however, in people with past or current psychiatric disorders. Concerns have also been raised that varenicline may slightly increase cardiovascular events in people already at increased risk of those illnesses. Current evidence neither supports nor refutes such an association, but we await the findings of the CATS trial, which should establish whether or not this is a valid concern. AUTHORS' CONCLUSIONS Cytisine increases the chances of quitting, although absolute quit rates were modest in two recent trials. Varenicline at standard dose increased the chances of successful long-term smoking cessation between two- and three-fold compared with pharmacologically unassisted quit attempts. Lower dose regimens also conferred benefits for cessation, while reducing the incidence of adverse events. More participants quit successfully with varenicline than with bupropion or with NRT. Limited evidence suggests that varenicline may have a role to play in relapse prevention. The most frequently recorded adverse effect of varenicline is nausea, but mostly at mild to moderate levels and tending to subside over time. Early reports of possible links to suicidal ideation and behaviour have not been confirmed by current research.Future trials of cytisine may test extended regimens and more intensive behavioural support.
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Affiliation(s)
- Kate Cahill
- University of OxfordNuffield Department of Primary Care Health SciencesRadcliffe Observatory QuarterWoodstock RoadOxfordUKOX2 6GG
| | - Nicola Lindson‐Hawley
- University of OxfordNuffield Department of Primary Care Health SciencesRadcliffe Observatory QuarterWoodstock RoadOxfordUKOX2 6GG
| | - Kyla H Thomas
- University of BristolSchool of Social and Community MedicineCanynge Hall39 Whatley RoadBristolUKBS8 2PS
| | - Thomas R Fanshawe
- University of OxfordNuffield Department of Primary Care Health SciencesRadcliffe Observatory QuarterWoodstock RoadOxfordUKOX2 6GG
| | - Tim Lancaster
- University of OxfordNuffield Department of Primary Care Health SciencesRadcliffe Observatory QuarterWoodstock RoadOxfordUKOX2 6GG
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Protracted treatment with MDMA induces heteromeric nicotinic receptor up-regulation in the rat brain: an autoradiography study. Prog Neuropsychopharmacol Biol Psychiatry 2014; 53:1-8. [PMID: 24614096 DOI: 10.1016/j.pnpbp.2014.02.014] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/13/2014] [Revised: 02/10/2014] [Accepted: 02/26/2014] [Indexed: 11/23/2022]
Abstract
Previous studies indicate that 3,4-methylenedioxy-methamphetamine (MDMA, ecstasy) can induce a heteromeric nicotinic acetylcholine receptor (nAChR, mainly of α4β2 subtype) up-regulation. In this study we treated male Sprague-Dawley rats twice-daily for 10 days with either saline or MDMA (7 mg/kg) and sacrificed them the day after to perform [(125)I]Epibatidine binding autoradiograms on serial coronal slices. MDMA induced significant increases in nAChR density in the substantia nigra, ventral tegmental area, nucleus accumbens, olfactory tubercle, anterior caudate-putamen, somatosensory, motor, auditory and retrosplenial cortex, laterodorsal thalamus nuclei, amygdala, postsubiculum and pontine nuclei. These increases ranged from 3% (retrosplenial cortex) to 30 and 34% (amygdala and substantia nigra). No increased α4 subunit immunoreactivity was found in up-regulated areas compared with saline-treated rats, suggesting a post-translational mechanism as occurs with nicotine. The heteromeric nAChR up-regulation in certain areas could account, at least in part, for the reinforcing, sensitizing and psychiatric disorders observed after long-term consumption of MDMA.
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Abstract
Varenicline is a selective alpha(4)beta(2) nicotinic acetylcholine receptor partial agonist and the first non-nicotine-containing medication developed with the sole purpose of treating nicotine addiction. To date, four published clinical trials have demonstrated the efficacy and safety of varenicline for smoking cessation in healthy adults who were ready to make a quit attempt. One additional trial found that extended use of varenicline effectively reduced relapse to smoking. One trial to date published as a poster documented the 1-year safety of the drug. Varenicline was more efficacious than bupropion 24 weeks after randomization to a 12-week treatment course and 1 year after randomization in an identical trial. It has no contraindications except hypersensitivity and is well tolerated. This article reviews the available information on varenicline and discusses its clinical use.
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Affiliation(s)
- Serena Tonstad
- Ullevål University Hospital, Department of Preventive Cardiology N-0407 Oslo, Norway.
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Ciudad-Roberts A, Camarasa J, Pubill D, Escubedo E. Heteromeric nicotinic receptors are involved in the sensitization and addictive properties of MDMA in mice. Prog Neuropsychopharmacol Biol Psychiatry 2013; 44:201-9. [PMID: 23466442 DOI: 10.1016/j.pnpbp.2013.02.013] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/02/2012] [Revised: 01/30/2013] [Accepted: 02/21/2013] [Indexed: 12/12/2022]
Abstract
We have investigated the effect of nicotinic receptor ligands in the behavioral sensitization (hyperlocomotion) and rewarding properties (conditioned place preference paradigm, CPP) of 3,4-methylenedioxy-methamphetamine (MDMA) in mice. Each animal received intraperitoneal pretreatment with either saline, dihydro-β-erythroidine (DHβE, 1 mg/kg) or varenicline (VAR, 0.3 mg/kg), 15 min prior to subcutaneous saline or MDMA (5 mg/kg), for 10 consecutive days. On day 1, both DHβE and VAR inhibited the MDMA-induced hyperlocomotion. After 10 days of treatment, MDMA induced a hyperlocomotion that was not reduced (rather enhanced) in antagonist-pretreated animals. This early hyperlocomotion was accompanied by a significant increase in heteromeric nicotinic receptors in cortex that was not blocked by DHβE or VAR. Behavioral sensitization to MDMA was highest 2 weeks after the discontinuation of MDMA treatment. This additional increase in sensitivity was prevented in animals pretreated with DHβE or VAR. At this time, MDMA-treated mice showed a significant increase in heteromeric receptors in cortex that was prevented by DHβE and VAR. An involvement of α7 nicotinic receptors in this effect is ruled out. MDMA (10 mg/kg) induced positive CPP that was abolished by DHβE (2 mg/kg) and VAR (2 mg/kg). Moreover, chronic nicotine pretreatment (2 mg/kg, ip, b.i.d., for 14 days) caused MDMA, administered at a low dose (3 mg/kg), to induce CPP, which would otherwise not occur. Finally, present results point out that heteromeric nicotinic receptors are involved in locomotor sensitization and addictive potential induced by MDMA. Thus, varenicline might be a useful drug to treat both tobacco and MDMA abuse at once.
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Affiliation(s)
- Andrés Ciudad-Roberts
- Department of Pharmacology and Therapeutic Chemistry (Pharmacology Section), Institute of Biomedicine (IBUB), University of Barcelona, Barcelona, Spain
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Pubill D, Garcia-Ratés S, Camarasa J, Escubedo E. 3,4-Methylenedioxy-methamphetamine induces in vivo regional up-regulation of central nicotinic receptors in rats and potentiates the regulatory effects of nicotine on these receptors. Neurotoxicology 2012; 35:41-9. [PMID: 23261423 DOI: 10.1016/j.neuro.2012.11.008] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2012] [Revised: 11/19/2012] [Accepted: 11/22/2012] [Indexed: 12/01/2022]
Abstract
Nicotine (NIC), the main psychostimulant compound of smoked tobacco, exerts its effects through activation of central nicotinic acetylcholine receptors (nAChR), which become up-regulated after chronic administration. Recent work has demonstrated that the recreational drug 3,4-methylenedioxy-methamphetamine (MDMA) has affinity for nAChR and also induces up-regulation of nAChR in PC 12 cells. Tobacco and MDMA are often consumed together. In the present work we studied the in vivo effect of a classic chronic dosing schedule of MDMA in rats, alone or combined with a chronic schedule of NIC, on the density of nAChR and on serotonin reuptake transporters. MDMA induced significant decreases in [(3)H]paroxetine binding in the cortex and hippocampus measured 24h after the last dose and these decreases were not modified by the association with NIC. In the prefrontal cortex, NIC and MDMA each induced significant increases in [(3)H]epibatidine binding (29.5 and 34.6%, respectively) with respect to saline-treated rats, and these increases were significantly potentiated (up to 72.1%) when the two drugs were associated. Also in this area, [(3)H]methyllycaconitine binding was increased a 42.1% with NIC+MDMA but not when they were given alone. In the hippocampus, MDMA potentiated the α7 regulatory effects of NIC (raising a 25.5% increase to 52.5%) but alone was devoid of effect. MDMA had no effect on heteromeric nAChR in striatum and a coronal section of the midbrain containing superior colliculi, geniculate nuclei, substantia nigra and ventral tegmental area. Specific immunoprecipitation of solubilised receptors suggests that the up-regulated heteromeric nAChRs contain α4 and β2 subunits. Western blots with specific α4 and α7 antibodies showed no significant differences between the groups, indicating that, as reported for nicotine, up-regulation caused by MDMA is due to post-translational events rather than increased receptor synthesis.
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Affiliation(s)
- David Pubill
- Unitat de Farmacologia i Farmacognòsia, Facultat de Farmàcia, Nucli Universitari de Pedralbes, Universitat de Barcelona, Institut de Biomedicina de la UB (IBUB), 08028 Barcelona, Spain.
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Abstract
BACKGROUND Nicotine receptor partial agonists may help people to stop smoking by a combination of maintaining moderate levels of dopamine to counteract withdrawal symptoms (acting as an agonist) and reducing smoking satisfaction (acting as an antagonist). OBJECTIVES The primary objective of this review is to assess the efficacy and tolerability of nicotine receptor partial agonists, including cytisine, dianicline and varenicline for smoking cessation. SEARCH METHODS We searched the Cochrane Tobacco Addiction Group's specialised register for trials, using the terms ('cytisine' or 'Tabex' or 'dianicline' or 'varenicline' or 'nicotine receptor partial agonist') in the title or abstract, or as keywords. The register is compiled from searches of MEDLINE, EMBASE, PsycINFO and Web of Science using MeSH terms and free text to identify controlled trials of interventions for smoking cessation and prevention. We contacted authors of trial reports for additional information where necessary. The latest update of the specialised register was in December 2011. We also searched online clinical trials registers. SELECTION CRITERIA We included randomized controlled trials which compared the treatment drug with placebo. We also included comparisons with bupropion and nicotine patches where available. We excluded trials which did not report a minimum follow-up period of six months from start of treatment. DATA COLLECTION AND ANALYSIS We extracted data on the type of participants, the dose and duration of treatment, the outcome measures, the randomization procedure, concealment of allocation, and completeness of follow-up.The main outcome measured was abstinence from smoking at longest follow-up. We used the most rigorous definition of abstinence, and preferred biochemically validated rates where they were reported. Where appropriate we pooled risk ratios (RRs), using the Mantel-Haenszel fixed-effect model. MAIN RESULTS Two recent cytisine trials (937 people) found that more participants taking cytisine stopped smoking compared with placebo at longest follow-up, with a pooled RR of 3.98 (95% confidence interval (CI) 2.01 to 7.87). One trial of dianicline (602 people) failed to find evidence that it was effective (RR 1.20, 95% CI 0.82 to 1.75). Fifteen trials compared varenicline with placebo for smoking cessation; three of these also included a bupropion treatment arm. We also found one open-label trial comparing varenicline plus counselling with counselling alone. We found one relapse prevention trial, comparing varenicline with placebo, and two open-label trials comparing varenicline with nicotine replacement therapy (NRT). We also include one trial in which all the participants were given varenicline, but received behavioural support either online or by phone calls, or by both methods. This trial is not included in the analyses, but contributes to the data on safety and tolerability. The included studies covered 12,223 participants, 8100 of whom used varenicline.The pooled RR for continuous or sustained abstinence at six months or longer for varenicline at standard dosage versus placebo was 2.27 (95% CI 2.02 to 2.55; 14 trials, 6166 people, excluding one trial evaluating long term safety). Varenicline at lower or variable doses was also shown to be effective, with an RR of 2.09 (95% CI 1.56 to 2.78; 4 trials, 1272 people). The pooled RR for varenicline versus bupropion at one year was 1.52 (95% CI 1.22 to 1.88; 3 trials, 1622 people). The RR for varenicline versus NRT for point prevalence abstinence at 24 weeks was 1.13 (95% CI 0.94 to 1.35; 2 trials, 778 people). The two trials which tested the use of varenicline beyond the 12-week standard regimen found the drug to be well-tolerated during long-term use. The main adverse effect of varenicline was nausea, which was mostly at mild to moderate levels and usually subsided over time. A meta-analysis of reported serious adverse events occurring during or after active treatment and not necessarily considered attributable to treatment suggests there may be a one-third increase in the chance of severe adverse effects among people using varenicline (RR 1.36; 95% CI 1.04 to 1.79; 17 trials, 7725 people), but this finding needs to be tested further. Post-marketing safety data have raised questions about a possible association between varenicline and depressed mood, agitation, and suicidal behaviour or ideation. The labelling of varenicline was amended in 2008, and the manufacturers produced a Medication Guide. Thus far, surveillance reports and secondary analyses of trial data are inconclusive, but the possibility of a link between varenicline and serious psychiatric or cardiovascular events cannot be ruled out. AUTHORS' CONCLUSIONS Cytisine increases the chances of quitting, although absolute quit rates were modest in two recent trials. Varenicline at standard dose increased the chances of successful long-term smoking cessation between two- and threefold compared with pharmacologically unassisted quit attempts. Lower dose regimens also conferred benefits for cessation, while reducing the incidence of adverse events. More participants quit successfully with varenicline than with bupropion. Two open-label trials of varenicline versus NRT suggested a modest benefit of varenicline but confidence intervals did not rule out equivalence. Limited evidence suggests that varenicline may have a role to play in relapse prevention. The main adverse effect of varenicline is nausea, but mostly at mild to moderate levels and tending to subside over time. Possible links with serious adverse events, including serious psychiatric or cardiovascular events, cannot be ruled out.Future trials of cytisine may test extended regimens and more intensive behavioural support. There is a need for further trials of the efficacy of varenicline treatment extended beyond 12 weeks.
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Affiliation(s)
- Kate Cahill
- Department of Primary Care Health Sciences, University of Oxford, Oxford, UK.
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Moore SJ, Throesch BT, Murphy GG. Of mice and intrinsic excitability: genetic background affects the size of the postburst afterhyperpolarization in CA1 pyramidal neurons. J Neurophysiol 2011; 106:1570-80. [PMID: 21697442 DOI: 10.1152/jn.00257.2011] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
As the use of genetically engineered mice has become increasingly prevalent in neurobiological research, evidence has steadily accumulated that substantial differences exist between strains. Although a number of studies have reported effects of genetic background on behavior, few have focused on differences in neurophysiology. The postburst afterhyperpolarization (AHP) is an important determinant of intrinsic neuronal excitability and has been suggested to play a critical role in the cellular mechanisms underlying learning and memory. Using whole cell current-clamp recordings of CA1 pyramidal neurons, we examined the magnitude of different phases of the AHP (peak, medium, and slow) in two commonly used genetic backgrounds, C57BL/6 (B6) and 129SvEv (129), as well as in an F2 hybrid B6:129 background (F2). We found that neurons from B6 and F2 animals exhibited a significantly larger AHP compared with 129 animals and that this difference was consistent across all phases. Furthermore, our recordings revealed a marked dichotomy in the shape of the AHP waveform, which was independent of genetic background. Approximately 60% of cells exhibited an AHP with a sharp transition between the peak AHP and medium AHP, whereas the remaining 40% exhibited a more gradual transition. Our data add to the growing body of work suggesting that genetic background can affect neuronal function as well as behavior. In addition, these results highlight the innate heterogeneity of CA1 pyramidal neurons, even within a single genetic background. These differences should be taken into consideration during the analysis and comparison of experimental results.
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Affiliation(s)
- Shannon J Moore
- Molecular & Behavioral Neuroscience Institute, University of Michigan, Ann Arbor, MI 48109-2200, USA
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Abstract
BACKGROUND Nicotine receptor partial agonists may help people to stop smoking by a combination of maintaining moderate levels of dopamine to counteract withdrawal symptoms (acting as an agonist) and reducing smoking satisfaction (acting as an antagonist). Varenicline was developed as a nicotine receptor partial agonist from cytisine, a drug widely used in central and eastern Europe for smoking cessation. The first trial reports of varenicline were released in 2006, and further trials have now been published or are currently underway. OBJECTIVES The primary objective of this review is to assess the efficacy and tolerability of nicotine receptor partial agonists, including varenicline and cytisine, for smoking cessation. SEARCH STRATEGY We searched the Cochrane Tobacco Addiction Group's specialised register for trials, using the terms ('varenicline' or 'cytisine' or 'Tabex' or 'nicotine receptor partial agonist') and 'smoking' in the title or abstract, or as keywords. We also searched MEDLINE, EMBASE, PsycINFO and CINAHL using MeSH terms and free text, and we contacted authors of trial reports for additional information where necessary. The latest search was in September 2010. SELECTION CRITERIA We included randomized controlled trials which compared the treatment drug with placebo. We also included comparisons with bupropion and nicotine patches where available. We excluded trials which did not report a minimum follow-up period of six months from start of treatment. DATA COLLECTION AND ANALYSIS We extracted data on the type of participants, the dose and duration of treatment, the outcome measures, the randomization procedure, concealment of allocation, and completeness of follow up.The main outcome measured was abstinence from smoking after at least six months from the beginning of treatment. We used the most rigorous definition of abstinence, and preferred biochemically validated rates where they were reported. Where appropriate we performed meta-analysis to produce a risk ratio, using the Mantel-Haenszel fixed-effect model. MAIN RESULTS We found 11 trials of varenicline compared with placebo for smoking cessation; three of these included a bupropion experimental arm. We also found one relapse prevention trial, comparing varenicline with placebo, and two open-label trials comparing varenicline with nicotine replacement therapy (NRT). We also include one trial in which all the participants were given varenicline, but received behavioural support either online or by phone calls, or by both methods. This trial is not included in the analyses, but contributes to the data on safety and tolerability. The included studies covered >10,300 participants, 6892 of whom used varenicline. We identified one trial of cytisine (Tabex) for inclusion.The pooled risk ratio (RR) (10 trials, 4443 people, excluding one trial evaluating long term safety) for continuous abstinence at six months or longer for varenicline at standard dosage versus placebo was 2.31 (95% confidence interval [CI] 2.01 to 2.66). Varenicline at lower or variable doses was also shown to be effective, with an RR of 2.09 (95% CI 1.56 to 2.78; 4 trials, 1272 people). The pooled RR for varenicline versus bupropion at one year was 1.52 (95% CI 1.22 to 1.88; 3 trials, 1622 people). The RR for varenicline versus NRT for point prevalence abstinence at 24 weeks was 1.13 (95% CI 0.94 to 1.35; 2 trials, 778 people). The two trials which tested the use of varenicline beyond the 12-week standard regimen found the drug to be well-tolerated during long-term use. The main adverse effect of varenicline was nausea, which was mostly at mild to moderate levels and usually subsided over time. Post-marketing safety data raised questions about a possible association between varenicline and depressed mood, agitation, and suicidal behaviour or ideation. The labelling of varenicline was amended in 2008, and the manufacturers produced a Medication Guide. Thus far, surveillance reports and secondary analyses of trial data lend little support to a causal relationship.The one cytisine trial included in this review found that more participants taking cytisine stopped smoking compared with placebo at two-year follow up, with an RR of 1.61 (95% CI 1.24 to 2.08). AUTHORS' CONCLUSIONS Varenicline at standard dose increased the chances of successful long-term smoking cessation between two- and threefold compared with pharmacologically unassisted quit attempts. Lower dose regimens also conferred benefits for cessation, while reducing the incidence of adverse events. More participants quit successfully with varenicline than with bupropion. Two open-label trials of varenicline versus NRT suggested a modest benefit of varenicline but confidence intervals did not rule out equivalence. Limited evidence suggests that varenicline may have a role to play in relapse prevention. The main adverse effect of varenicline is nausea, but mostly at mild to moderate levels and tending to subside over time. Possible links with serious adverse events, including depressed mood, agitation and suicidal thoughts, have been reported but are so far not substantiated.There is a need for further independent community-based trials of varenicline, to test its efficacy and safety in smokers with varying co-morbidities and risk patterns. There is a need for further trials of the efficacy of treatment extended beyond 12 weeks. Cytisine may also increase the chances of quitting, but the evidence at present is inconclusive.
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Affiliation(s)
- Kate Cahill
- Department of Primary Health Care, University of Oxford, Rosemary Rue Building, Old Road Campus, Oxford, UK, OX3 7LF
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Abstract
BACKGROUND Nicotine receptor partial agonists may help people to stop smoking by a combination of maintaining moderate levels of dopamine to counteract withdrawal symptoms (acting as an agonist) and reducing smoking satisfaction (acting as an antagonist). Varenicline was developed as a nicotine receptor partial agonist from cytisine, a drug widely used in central and eastern Europe for smoking cessation. The first trial reports of varenicline were released in 2006, and further trials have now been published or are currently underway. OBJECTIVES The primary objective of this review is to assess the efficacy and tolerability of nicotine receptor partial agonists, including varenicline and cytisine, for smoking cessation. SEARCH STRATEGY We searched the Cochrane Tobacco Addiction Group's specialised register for trials, using the terms ('varenicline' or 'cytisine' or 'Tabex' or 'nicotine receptor partial agonist') and 'smoking' in the title or abstract, or as keywords. We also searched MEDLINE, EMBASE, PsycINFO and CINAHL using MeSH terms and free text, and we contacted authors of trial reports for additional information where necessary. The latest search was in September 2010. SELECTION CRITERIA We included randomized controlled trials which compared the treatment drug with placebo. We also included comparisons with bupropion and nicotine patches where available. We excluded trials which did not report a minimum follow-up period of six months from start of treatment. DATA COLLECTION AND ANALYSIS We extracted data on the type of participants, the dose and duration of treatment, the outcome measures, the randomization procedure, concealment of allocation, and completeness of follow up.The main outcome measured was abstinence from smoking after at least six months from the beginning of treatment. We used the most rigorous definition of abstinence, and preferred biochemically validated rates where they were reported. Where appropriate we performed meta-analysis to produce a risk ratio, using the Mantel-Haenszel fixed-effect model. MAIN RESULTS We found 11 trials of varenicline compared with placebo for smoking cessation; three of these included a bupropion experimental arm. We also found one relapse prevention trial, comparing varenicline with placebo, and two open-label trials comparing varenicline with nicotine replacement therapy (NRT). We also include one trial in which all the participants were given varenicline, but received behavioural support either online or by phone calls, or by both methods. This trial is not included in the analyses, but contributes to the data on safety and tolerability. The included studies covered >10,300 participants, 6892 of whom used varenicline. We identified one trial of cytisine (Tabex) for inclusion.The pooled risk ratio (RR) (10 trials, 4443 people, excluding one trial evaluating long term safety) for continuous abstinence at six months or longer for varenicline at standard dosage versus placebo was 2.31 (95% confidence interval [CI] 2.01 to 2.66). Varenicline at lower or variable doses was also shown to be effective, with an RR of 2.09 (95% CI 1.56 to 2.78; 4 trials, 1272 people). The pooled RR for varenicline versus bupropion at one year was 1.52 (95% CI 1.22 to 1.88; 3 trials, 1622 people). The RR for varenicline versus NRT for point prevalence abstinence at 24 weeks was 1.13 (95% CI 0.94 to 1.35; 2 trials, 778 people). The two trials which tested the use of varenicline beyond the 12-week standard regimen found the drug to be well-tolerated during long-term use. The main adverse effect of varenicline was nausea, which was mostly at mild to moderate levels and usually subsided over time. Post-marketing safety data raised questions about a possible association between varenicline and depressed mood, agitation, and suicidal behaviour or ideation. The labelling of varenicline was amended in 2008, and the manufacturers produced a Medication Guide. Thus far, surveillance reports and secondary analyses of trial data lend little support to a causal relationship.The one cytisine trial included in this review found that more participants taking cytisine stopped smoking compared with placebo at two-year follow up, with an RR of 1.61 (95% CI 1.24 to 2.08). AUTHORS' CONCLUSIONS Varenicline at standard dose increased the chances of successful long-term smoking cessation between two- and threefold compared with pharmacologically unassisted quit attempts. Lower dose regimens also conferred benefits for cessation, while reducing the incidence of adverse events. More participants quit successfully with varenicline than with bupropion. Two open-label trials of varenicline versus NRT suggested a modest benefit of varenicline but confidence intervals did not rule out equivalence. Limited evidence suggests that varenicline may have a role to play in relapse prevention. The main adverse effect of varenicline is nausea, but mostly at mild to moderate levels and tending to subside over time. Possible links with serious adverse events, including depressed mood, agitation and suicidal thoughts, have been reported but are so far not substantiated.There is a need for further independent community-based trials of varenicline, to test its efficacy and safety in smokers with varying co-morbidities and risk patterns. There is a need for further trials of the efficacy of treatment extended beyond 12 weeks. Cytisine may also increase the chances of quitting, but the evidence at present is inconclusive.
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Affiliation(s)
- Kate Cahill
- Department of Primary Health Care, University of Oxford, Rosemary Rue Building, Old Road Campus, Oxford, UK, OX3 7LF
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11
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Gahring LC, Rogers SW. Nicotinic receptor subunit alpha5 modifies assembly, up-regulation, and response to pro-inflammatory cytokines. J Biol Chem 2010; 285:26049-57. [PMID: 20566638 DOI: 10.1074/jbc.m110.105346] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In the mammalian brain high affinity nicotine-binding sites are composed of at least the alpha4 and beta2 subunits. Additional nicotinic acetylcholine receptor subunits that are often co-expressed with alpha4+beta2 include alpha5. The introduction of alpha5 into 293 cells expressing alpha4+beta2 strongly favors assembly of alpha4+alpha5+beta2 receptors, increases constitutive ligand binding density as measured using [(3)H]epibatidine, but reduces the magnitude of up-regulation in response to chronic nicotine. In contrast, when beta4 is substituted for beta2, alpha5 interferes with the assembly of these receptors, demonstrating an important role for the beta subunit in this process. When cells co-express alpha4+alpha5+beta2+beta4, over 50% of the subunit associations include all four subunits, but they fail to be detected using [(3)H]epibatidine binding. However, complexes of alpha4+alpha5+beta2 do preferentially emerge from these subunit mixtures, and these mixtures bind ligand. In previous studies of alpha4+beta2+beta4 co-expression by 293 cells, the inflammatory cytokines IL-1beta and TNFalpha influenced the outcome of receptor assembly (Gahring, L. C., Days, E. L., Kaasch, T., González de Mendoza, M., Owen, L., Persiyanov, K., and Rogers, S. W. (2005) J. Neuroimmunol. 166, 88-101). When alpha5 is included in this subunit mixture, and cells are exposed to either inflammatory cytokine, subunit association is no longer altered. These findings suggest that alpha5 is an influential modulator of alpha4+beta2 nicotinic acetylcholine receptor assembly and stabilizes their expression in response to fluctuations in external conditions.
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Affiliation(s)
- Lorise C Gahring
- Salt Lake City Veterans Affairs-Geriatrics Research, Education and Clinical Center, University of Utah, Salt Lake City, Utah 84132, USA
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12
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Scherma M, Panlilio LV, Fadda P, Fattore L, Gamaleddin I, Le Foll B, Justinová Z, Mikics E, Haller J, Medalie J, Stroik J, Barnes C, Yasar S, Tanda G, Piomelli D, Fratta W, Goldberg SR. Inhibition of anandamide hydrolysis by cyclohexyl carbamic acid 3'-carbamoyl-3-yl ester (URB597) reverses abuse-related behavioral and neurochemical effects of nicotine in rats. J Pharmacol Exp Ther 2008; 327:482-90. [PMID: 18725543 PMCID: PMC2663803 DOI: 10.1124/jpet.108.142224] [Citation(s) in RCA: 106] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Emerging evidence suggests that the rewarding, abuse-related effects of nicotine are modulated by the endocannabinoid system of the brain. For example, pharmacological blockade or genetic deletion of cannabinoid CB(1) receptors can reduce or eliminate many abuse-related behavioral and neurochemical effects of nicotine. Furthermore, doses of Delta(9)-tetrahydrocannabinol and nicotine that are ineffective when given alone can induce conditioned place preference when given together. These previous studies have used systemically administered CB(1) receptor agonists and antagonists and gene deletion techniques, which affect cannabinoid CB(1) receptors throughout the brain. A more functionally selective way to alter endocannabinoid activity is to inhibit fatty acid amide hydrolase (FAAH), thereby magnifying and prolonging the effects of the endocannabinoid anandamide only when and where it is synthesized and released on demand. Here, we combined behavioral and neurochemical approaches to evaluate whether the FAAH inhibitor URB597 (cyclohexyl carbamic acid 3'-carbamoyl-3-yl ester) could alter the abuse-related effects of nicotine in rats. We found that URB597, at a dose (0.3 mg/kg) that had no behavioral effects by itself, prevented development of nicotine-induced conditioned place preference (CPP) and acquisition of nicotine self-administration. URB597 also reduced nicotine-induced reinstatement in both CPP and self-administration models of relapse. Furthermore, in vivo microdialysis showed that URB597 reduced nicotine-induced dopamine elevations in the nucleus accumbens shell, the terminal area of the brain's mesolimbic reward system. These findings suggest that FAAH inhibition can counteract the addictive properties of nicotine and that FAAH may serve as a new target for development of medications for treatment of tobacco dependence.
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Affiliation(s)
- Maria Scherma
- Preclinical Pharmacology Section, National Institute on Drug Abuse, Intramural Research Program, National Institutes of Health, Department of Health and Human Services, Baltimore, MD 21224, USA
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13
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Scherma M, Fadda P, Le Foll B, Forget B, Fratta W, Goldberg SR, Tanda G. The endocannabinoid system: a new molecular target for the treatment of tobacco addiction. CNS & NEUROLOGICAL DISORDERS DRUG TARGETS 2008; 7:468-81. [PMID: 19128204 PMCID: PMC3821699 DOI: 10.2174/187152708786927859] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Tobacco addiction is one of the leading preventable causes of mortality in the world and nicotine appears to be the main critical psychoactive component in establishing and maintaining tobacco dependence. Several lines of evidence suggest that the rewarding effects of nicotine, which underlie its abuse potential, can be modulated by manipulating the endocannabinoid system. For example, pharmacological blockade or genetic deletion of cannabinoid CB(1) receptors reduces or eliminates many behavioral and neurochemical effects of nicotine that are related to its addictive potential. This review will focus on the recently published literature about the role of the endocannabinoid system in nicotine addiction and on the endocannabinoid system as a novel molecular target for the discovery of medications for tobacco dependence.
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Affiliation(s)
- Maria Scherma
- 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, USA
- B.B. Brodie Department of Neuroscience, University of Cagliari, Italy
| | - Paola Fadda
- B.B. Brodie Department of Neuroscience, University of Cagliari, Italy
| | - Bernard Le Foll
- Translational Addiction Research Laboratory, Centre for Addiction and Mental Health, and University of Toronto, Toronto, Canada
| | - Benoit Forget
- Translational Addiction Research Laboratory, Centre for Addiction and Mental Health, and University of Toronto, Toronto, Canada
| | - Walter Fratta
- B.B. Brodie Department of Neuroscience, University of Cagliari, Italy
| | - Steven R. Goldberg
- 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, USA
| | - Gianluigi Tanda
- Psychobiology Section, Medications Discovery Research Branch, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Department of Health and Human Services, Baltimore, MD, USA
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14
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Abstract
BACKGROUND Nicotine receptor partial agonists may help people to stop smoking by a combination of maintaining moderate levels of dopamine to counteract withdrawal symptoms (acting as an agonist) and reducing smoking satisfaction (acting as an antagonist). Varenicline was developed as a nicotine receptor partial agonist from cytisine, a drug widely used in central and eastern Europe for smoking cessation. The first trial reports of varenicline were released in 2006, and further trials have now been published or are currently are underway. OBJECTIVES The primary objective of this review is to assess the efficacy and tolerability of nicotine receptor partial agonists, including varenicline and cytisine, for smoking cessation. SEARCH STRATEGY We searched the Cochrane Tobacco Addiction Group's specialised register for trials, using the terms ('varenicline' or 'cytisine' or 'Tabex' or 'nicotine receptor partial agonist') and 'smoking' in the title or abstract, or as keywords. We also searched MEDLINE, EMBASE, PsycINFO and CINAHL using MeSH terms and free text, and we contacted authors of trial reports for additional information where necessary. The latest search was in March 2008. SELECTION CRITERIA We included randomized controlled trials which compared the treatment drug with placebo. We also included comparisons with bupropion and nicotine patches where available. We excluded trials which did not report a minimum follow-up period of six months from start of treatment. DATA COLLECTION AND ANALYSIS We extracted data in duplicate on the type of participants, the dose and duration of treatment, the outcome measures, the randomization procedure, concealment of allocation, and completeness of follow up. The main outcome measured was abstinence from smoking after at least six months from the beginning of treatment. We used the most rigorous definition of abstinence, and preferred biochemically validated rates where they were reported. Where appropriate we performed meta-analysis to produce a risk ratio, using the Mantel-Haenszel fixed-effect model. MAIN RESULTS We found seven trials of varenicline compared with placebo for smoking cessation; three of these also included a bupropion experimental arm. We found one relapse prevention trial, comparing varenicline with placebo. We also found one open-label trial comparing varenicline with nicotine replacement therapy. The nine trials covered 7267 participants, 4744 of whom used varenicline. We identified one trial of cytisine (Tabex) for inclusion. The pooled risk ratio (RR) for continuous abstinence at six months or longer for varenicline versus placebo was 2.33 (95% confidence interval [CI] 1.95 to 2.80). The pooled RR for varenicline versus bupropion at one year was 1.52 (95% CI 1.22 to 1.88). The RR for varenicline versus NRT at one year was 1.31 (95% CI 1.01 to 1.71). The two trials which tested the use of varenicline beyond the 12-week standard regimen found the drug to be well-tolerated during long-term use. The main adverse effect of varenicline was nausea, which was mostly at mild to moderate levels and usually subsided over time. Post-marketing safety data suggest that varenicline may be associated with depressed mood, agitation, and suicidal behaviour or ideation. The labelling of varenicline has been amended, and the FDA is conducting a safety review. The one cytisine trial included in this review found that more participants taking cytisine stopped smoking compared with placebo at two-year follow up, with an RR of 1.61 (95% CI 1.24 to 2.08). AUTHORS' CONCLUSIONS Varenicline increased the chances of successful long-term smoking cessation between two- and threefold compared with pharmacologically unassisted quit attempts. More participants quit successfully with varenicline than with bupropion. One open-label trial of varenicline versus nicotine replacement therapy demonstrated a modest benefit of varenicline. The effectiveness of varenicline as an aid to relapse prevention has not been clearly established. The main adverse effect of varenicline is nausea, but mostly at mild to moderate levels and tending to subside over time. Possible links with serious adverse events, including depressed mood, agitation and suicidal thoughts, are currently under review. There is a need for independent community-based trials of varenicline, to test its efficacy and safety in smokers with varying co-morbidities and risk patterns. There is a need for further trials of the efficacy of treatment extended beyond 12 weeks. Cytisine may also increase the chances of quitting, but the evidence at present is inconclusive.
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Affiliation(s)
- Kate Cahill
- Department of Primary Health Care, University of Oxford, Rosemary Rue Building, Old Road Campus, Oxford, UK, OX3 7LF.
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15
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Abstract
Varenicline, a partial agonist of alpha(4)beta(2) nicotinic acetylcholine receptors, is the most recently approved drug for smoking cessation. This paper reviews the outcomes of Phase 2 and Phase 3 clinical trials that assess the efficacy of varenicline in comparison to placebo and other smoking cessation pharmacotherapies, ie, sustained-release bupropion (bupropion SR) and nicotine transdermal patch. Varenicline has higher abstinence rates than placebo and the alternative active treatments at the end of standard regimen treatment periods. Significantly higher abstinence rates were also found with varenicline in comparison to both placebo and bupropion SR at the end of a 40-week non-treatment follow-up period. Varenicline typically tripled the abstinence rates compared with placebo. In addition, varenicline reduced craving and withdrawal symptoms as well as some of the positive experiences associated with smoking to a greater extent than placebo, bupropion SR, and nicotine replacement therapy (NRT). These findings are consistent with the proposed agonist/antagonist effects of varenicline. Preliminary studies assessing individual variables such as smoking dependency level and smoking reinforcement types provide justification to examine further the effects of varenicline according to these individual factors. Outcomes from such research could improve our understanding of varenicline's mechanism of action and could ultimately help clinicians to develop individualized smoking cessation programs. Also, given varenicline's ability to reduce the reward from smoking, it might be helpful to use it before cessation to motivate or prepare smokers for a quit attempt.
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Affiliation(s)
- Karl Fagerström
- Smokers Information Centre, Fagerström Consulting AB Berga Alle 1, 25452 Helsingborg, Sweden.
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16
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Ochoa ELM, Lasalde-Dominicci J. Cognitive deficits in schizophrenia: focus on neuronal nicotinic acetylcholine receptors and smoking. Cell Mol Neurobiol 2008; 27:609-39. [PMID: 17554626 PMCID: PMC4676572 DOI: 10.1007/s10571-007-9149-x] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2006] [Accepted: 04/13/2007] [Indexed: 02/08/2023]
Abstract
Patients with schizophrenia present with deficits in specific areas of cognition. These are quantifiable by neuropsychological testing and can be clinically observable as negative signs. Concomitantly, they self-administer nicotine in the form of cigarette smoking. Nicotine dependence is more prevalent in this patient population when compared to other psychiatric conditions or to non-mentally ill people. The target for nicotine is the neuronal nicotinic acetylcholine receptor (nAChR). There is ample evidence that these receptors are involved in normal cognitive operations within the brain. This review describes neuronal nAChR structure and function, focusing on both cholinergic agonist-induced nAChR desensitization and nAChR up-regulation. The several mechanisms proposed for the nAChR up-regulation are examined in detail. Desensitization and up-regulation of nAChRs may be relevant to the physiopathology of schizophrenia. The participation of several subtypes of neuronal nAChRs in the cognitive processing of non-mentally ill persons and schizophrenic patients is reviewed. The role of smoking is then examined as a possible cognitive remediator in this psychiatric condition. Finally, pharmacological strategies focused on neuronal nAChRs are discussed as possible therapeutic avenues that may ameliorate the cognitive deficits of schizophrenia.
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Affiliation(s)
- Enrique L. M. Ochoa
- Department of Psychiatry, University of California at Davis, 2230 Stockton Boulevard, Sacramento, CA 95817, USA
| | - Jose Lasalde-Dominicci
- Department of Biology, University of Puerto Rico, Río Piedras Campus, P.O. Box 23360, San Juan 00931-3360, Puerto Rico
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17
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Abstract
Varenicline is the first pharmacological aid for smoking cessation treatment to be approved in almost a decade. Varenicline is an alpha4beta2 nicotinic acetylcholine receptor partial agonist. It may assist those who wish to quit smoking by producing partial activation at nicotinic receptors to ease craving and withdrawal symptoms; and by simultaneously blocking the effects of nicotine from cigarettes smoked, thereby reducing the satisfaction of continued smoking. The effectiveness of varenicline as an aid for smoking cessation has been demonstrated in several clinical trials versus placebo and sustained release bupropion. In addition, varenicline is well tolerated and has an acceptable safety profile. As an aid for smoking cessation, varenicline offers progress in the treatment of tobacco dependence.
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Affiliation(s)
- Elbert D Glover
- University of Maryland College Park School of Public Health, Department of Public & Community Health, College Park, MD 20742, USA.
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18
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Rose JE. Multiple brain pathways and receptors underlying tobacco addiction. Biochem Pharmacol 2007; 74:1263-70. [PMID: 17826746 DOI: 10.1016/j.bcp.2007.07.039] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2007] [Revised: 07/26/2007] [Accepted: 07/26/2007] [Indexed: 01/16/2023]
Abstract
Over the last 20 years much progress has been made in understanding the pharmacologic basis of tobacco addiction. In particular, the role of nicotine in reinforcing smoking behavior has been studied from a variety of perspectives. This article discusses two important aspects of this topic: (1) brain pathways underlying tobacco addiction; and (2) the actions of nicotine at nicotinic cholinergic receptors. Recent evidence will be reviewed indicating that nicotine reinforces smoking behavior by acting on more than one subtype of nicotinic receptor. Similarly, the role of several brain pathways in tobacco addiction will be considered. Tobacco addiction may thus be seen as a complex neuropsychopharmacological disorder; further progress in smoking cessation treatment may require that we address the multiple molecular and brain components of this addiction.
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Affiliation(s)
- Jed E Rose
- Center for Nicotine and Smoking Cessation Research, Duke University Medical Center, Durham, NC 27705, USA.
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19
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Maskos U. Emerging concepts: novel integration of in vivo approaches to localize the function of nicotinic receptors. J Neurochem 2007; 100:596-602. [PMID: 17116233 DOI: 10.1111/j.1471-4159.2006.04224.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Nicotinic acetylcholine receptors (nAChRs) are important targets of the neuromodulator acetylcholine (ACh) and the drug nicotine. The role of their different subunits has been analysed for a decade by the creation of knock-out (KO) mice using homologous recombination. This technique shows that a given subunit is necessary for a given function. However, for ubiquitously expressed genes, it cannot demonstrate the localization for a given subunit in which its expression is sufficient, especially for behavioural phenotypes. Sufficient in this context means that the brain region requiring the expression of the gene product has been localized. Novel strategies have therefore been developed to re-express, region specifically, nAChR subunits on a KO background using lentiviral vectors. Localized regeneration of fully functional high-affinity nAChRs in defined brain regions has proven that these receptors are sufficient to restore a variety of functions: nicotine-induced dopamine release, nicotine self-administration in mice, dopamine neuron firing patterns, and exploratory and locomotor behaviours in a sequential locomotor task testing executive function were thus defined as depending exclusively on the 'knock-back' of beta2*-nAChRs into the ventral tegmental area. These analyses highlight the important role of endogenous cholinergic regulation of a variety of functions. The novel integrated use of restricted re-expressed nAChR subunits with in vivo electrophysiology and automated quantitative behavioural analysis enables the further analysis of defined neuronal circuits in nicotine addiction and higher cognitive function.
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Affiliation(s)
- Uwe Maskos
- Récepteurs et Cognition, CNRS URA 2182, Institut Pasteur, Paris, France.
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20
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Abstract
BACKGROUND Nicotine receptor partial agonists may help smokers to quit by a combination of maintaining moderate levels of dopamine to counteract withdrawal symptoms (acting as an agonist) and reducing smoking satisfaction (acting as an antagonist). Varenicline was developed as a nicotine receptor partial agonist from cytisine, a drug widely used in central and eastern Europe for smoking cessation. The first trial reports of varenicline were released in 2006, and further trials are underway. OBJECTIVES The primary objective of this review is to assess the efficacy and tolerability of nicotine receptor partial agonists, including varenicline and cytisine, for smoking cessation. SEARCH STRATEGY We searched the Cochrane Tobacco Addiction Group's specialised register for trials, using the terms ('varenicline' or 'cytisine' or 'Tabex' or 'nicotine receptor partial agonist') and 'smoking' in the title or abstract, or as keywords. We also searched MEDLINE, EMBASE, PsycINFO and CINAHL using MeSH terms and free text, and we contacted authors of trial reports for additional information where necessary. The last search was in October 2006. SELECTION CRITERIA We included randomized controlled trials which compared the treatment drug with placebo. We also included comparisons with bupropion where available. We excluded trials which did not report a minimum follow-up period of six months from start of treatment. DATA COLLECTION AND ANALYSIS We extracted data in duplicate on the type of participants, the dose and duration of treatment, the outcome measures, the randomization procedure, concealment of allocation, and completeness of follow up. The main outcome measured was abstinence from smoking after at least six months from the beginning of treatment. We used the most rigorous definition of abstinence, and preferred biochemically validated rates where they were reported. Where appropriate we performed meta-analysis using the Mantel-Haenszel fixed-effect model. MAIN RESULTS We found five trials of varenicline compared with placebo for smoking cessation; three of these also included a bupropion experimental arm. We also found one relapse prevention trial, comparing varenicline with placebo. The six trials covered 4924 participants, 2451 of whom used varenicline. We identified one trial of cytisine (Tabex) for inclusion. The pooled odds ratio (OR) for continuous abstinence at 12 months for varenicline versus placebo was 3.22 (95% confidence interval [CI] 2.43 to 4.27). The pooled OR for varenicline versus bupropion was 1.66 (95% CI 1.28 to 2.16). The main adverse effect of varenicline was nausea, which was mostly at mild to moderate levels and usually subsided over time. The two trials which tested the use of varenicline beyond the 12-week standard regimen found the drug to be well-tolerated and effective during long-term use. The one cytisine trial included in this review found that more participants taking cytisine stopped smoking compared with placebo at two-year follow up, with an OR of 1.77 (95% CI 1.30 to 2.40). AUTHORS' CONCLUSIONS Varenicline increased the odds of successful long-term smoking cessation approximately threefold compared with pharmacologically unassisted quit attempts. In trials reported so far, more participants quit successfully with varenicline than with bupropion. The effectiveness of varenicline as an aid to relapse prevention has not been clearly established. The main adverse effect of varenciline is nausea, but this is mostly at mild to moderate levels and tends to reduce with habituation. There is a need for independent trials of varenicline versus placebo, to test the early findings. There is also a need for direct comparisons with nicotine replacement therapy, and for further trials with bupropion, to establish the relative efficacy of the treatments.Cytisine may also increase the chances of quitting, but the evidence at present is inconclusive.
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Affiliation(s)
- K Cahill
- Department of Primary Health Care, Old Road Campus, University of Oxford, Oxford, UK, OX3 7LF.
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21
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Brody AL, Mandelkern MA, London ED, Olmstead RE, Farahi J, Scheibal D, Jou J, Allen V, Tiongson E, Chefer SI, Koren AO, Mukhin AG. Cigarette smoking saturates brain alpha 4 beta 2 nicotinic acetylcholine receptors. ACTA ACUST UNITED AC 2006; 63:907-15. [PMID: 16894067 PMCID: PMC2773659 DOI: 10.1001/archpsyc.63.8.907] [Citation(s) in RCA: 265] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
CONTEXT 2-[18F]fluoro-3-(2(S)-azetidinylmethoxy) pyridine (2-F-A-85380, abbreviated as 2-FA) is a recently developed radioligand that allows for visualization of brain alpha 4 beta 2* nicotinic acetylcholine receptors (nAChRs) with positron emission tomography (PET) scanning in humans. OBJECTIVE To determine the effect of cigarette smoking on alpha 4 beta 2* nAChR occupancy in tobacco-dependent smokers. DESIGN Fourteen 2-FA PET scanning sessions were performed. During the PET scanning sessions, subjects smoked 1 of 5 amounts (none, 1 puff, 3 puffs, 1 full cigarette, or to satiety [2(1/2) to 3 cigarettes]). SETTING Academic brain imaging center. PARTICIPANTS Eleven tobacco-dependent smokers (paid volunteers). Main Outcome Measure Dose-dependent effect of smoking on occupancy of alpha 4 beta 2* nAChRs, as measured with 2-FA and PET in nAChR-rich brain regions. RESULTS Smoking 0.13 (1 to 2 puffs) of a cigarette resulted in 50% occupancy of alpha 4 beta 2* nAChRs for 3.1 hours after smoking. Smoking a full cigarette (or more) resulted in more than 88% receptor occupancy and was accompanied by a reduction in cigarette craving. A venous plasma nicotine concentration of 0.87 ng/mL (roughly 1/25th of the level achieved in typical daily smokers) was associated with 50% occupancy of alpha 4 beta 2* nAChRs. CONCLUSIONS Cigarette smoking in amounts used by typical daily smokers leads to nearly complete occupancy of alpha 4 beta 2* nAChRs, indicating that tobacco-dependent smokers maintain alpha 4 beta 2* nAChR saturation throughout the day. Because prolonged binding of nicotine to alpha 4 beta 2* nAChRs is associated with desensitization of these receptors, the extent of receptor occupancy found herein suggests that smoking may lead to withdrawal alleviation by maintaining nAChRs in the desensitized state.
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Affiliation(s)
- Arthur L Brody
- Department of Psychiatry and Biobehavioral Sciences, University of California, Los Angeles, CA 90095, USA.
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Millan MJ. Multi-target strategies for the improved treatment of depressive states: Conceptual foundations and neuronal substrates, drug discovery and therapeutic application. Pharmacol Ther 2006; 110:135-370. [PMID: 16522330 DOI: 10.1016/j.pharmthera.2005.11.006] [Citation(s) in RCA: 389] [Impact Index Per Article: 21.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2005] [Accepted: 11/28/2005] [Indexed: 12/20/2022]
Abstract
Major depression is a debilitating and recurrent disorder with a substantial lifetime risk and a high social cost. Depressed patients generally display co-morbid symptoms, and depression frequently accompanies other serious disorders. Currently available drugs display limited efficacy and a pronounced delay to onset of action, and all provoke distressing side effects. Cloning of the human genome has fuelled expectations that symptomatic treatment may soon become more rapid and effective, and that depressive states may ultimately be "prevented" or "cured". In pursuing these objectives, in particular for genome-derived, non-monoaminergic targets, "specificity" of drug actions is often emphasized. That is, priority is afforded to agents that interact exclusively with a single site hypothesized as critically involved in the pathogenesis and/or control of depression. Certain highly selective drugs may prove effective, and they remain indispensable in the experimental (and clinical) evaluation of the significance of novel mechanisms. However, by analogy to other multifactorial disorders, "multi-target" agents may be better adapted to the improved treatment of depressive states. Support for this contention is garnered from a broad palette of observations, ranging from mechanisms of action of adjunctive drug combinations and electroconvulsive therapy to "network theory" analysis of the etiology and management of depressive states. The review also outlines opportunities to be exploited, and challenges to be addressed, in the discovery and characterization of drugs recognizing multiple targets. Finally, a diversity of multi-target strategies is proposed for the more efficacious and rapid control of core and co-morbid symptoms of depression, together with improved tolerance relative to currently available agents.
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Affiliation(s)
- Mark J Millan
- Institut de Recherches Servier, Centre de Recherches de Croissy, Psychopharmacology Department, 125, Chemin de Ronde, 78290-Croissy/Seine, France.
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Bertrand D. The possible contribution of neuronal nicotinic acetylcholine receptors in depression. DIALOGUES IN CLINICAL NEUROSCIENCE 2005. [PMID: 16156379 PMCID: PMC3181734 DOI: 10.31887/dcns.2005.7.3/dbertrand] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Although tobacco use and smoking were introduced long ago, it was only recently that the nicotine contained in the tobacco leaves was recognized as an addictive substance acting on the central nervous system (CNS). However, even prior to this recognition, several studies have reported an association between smoking and psychiatric disorders. One of the many observations was that smoking cessation is accompanied by a marked increase in the probability of major depression. In parallel with the discovery of the neuronal nicotinic acetylcholine receptors and their extensive expression in the CNS, this association sheds new light on the influence of cholinergic transmission in depression. In this article, we examine the various modes of action of nicotine in the CNS and discuss the mechanisms by which this alkaloid can prevent or precipitate mood disorders, and the possibility of discovering new therapeutic avenues for the treatment of depression.
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Affiliation(s)
- Daniel Bertrand
- Department of Neuroscience, Medical Faculty, Geneva University Hospitals, Geneva, Switzerland
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Perry EK, Perry RH. Neurochemistry of consciousness: cholinergic pathologies in the human brain. PROGRESS IN BRAIN RESEARCH 2004; 145:287-99. [PMID: 14650923 DOI: 10.1016/s0079-6123(03)45020-6] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/11/2023]
Affiliation(s)
- Elaine K Perry
- MRC Building, Newcastle General Hospital, Westgate Road, Newcastle upon Tyne NE4 6BE, UK.
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