nAChR subunit contributions to nicotine dependent behaviors

描述（由申请人提供）：尽管许多吸烟者报告想要戒烟，但很少有人能够通过传统的医学疗法戒烟。今年5月，辉瑞公司获得了FDA批准上市其戒烟药物varenicline，这是一种部分激动剂，据称对含有烟碱乙酰胆碱受体（¿2* nachr）具有选择性。越来越多的数据表明，¿2* nachr是尼古丁相关多巴胺（DA）释放和尼古丁主要强化效应所必需的。最近，人们认为¿2* nachr在调节条件强化（CR）中的作用；也就是说，与初级强化物（如尼古丁）配对的线索对行为（如吸烟）具有控制作用。本实验的主要目的是确定被a- concontoxin MII敏感性分解的¿2*nAChRs亚类是否在调节尼古丁的主要奖励效应和尼古丁增强CR的能力方面存在差异。与a- concontoxin MII （a-CMII）不敏感的a4¿2*nAChRs一样，a-CMII敏感的a4¿2*nAChRs也调节尼古丁刺激的DA释放。a6¿2¿3*nAChRs主要表达于儿茶酚胺能神经元，在纹状体DA末端高度富集，在尼古丁强化中的作用尚不清楚。尽管a4亚基与尼古丁奖励的贡献密切相关，但迄今为止还没有研究特别质疑a4亚基是否需要尼古丁奖励。这些研究的具体目的1是确定哪些nAChR亚基与¿2结合对于尼古丁的奖励效应是必要的，这是由无偏倚尼古丁条件位置偏好（CPP）测量的。实验1将测试¿3和a4 nAChR亚基敲除小鼠尼古丁CPP水平的改变。研究表明，腹侧被盖区（VTA）输注二氢- β -红血碱（DH¿E），一种选择性的¿2* nachr拮抗剂，阻断尼古丁的自我给药。VTA内输注a-CMII将决定VTA水平的MII敏感受体是否为尼古丁CPP所必需。这些实验的具体目的2将确定a- cmii敏感和不敏感的¿2*nAChRs亚类是否在调节基线CR和先前慢性尼古丁增强CR的能力方面存在差异。具有不同尼古丁暴露史的¿3和a4基因敲除小鼠将接受巴普lovan歧视性方法训练，然后通过条件强化物获得新的反应。DA投射到伏隔核（NAc）核心对基线CR的调节至关重要。尽管调节尼古丁介导的CR促进的系统是未知的，Aim 2的第二个实验将使用a- concontoxin MII和DH¿E的壳内输注来测试伏隔核不同水平的¿2* nachr是否调节尼古丁刺激的CR升高，这些实验将开始确定支持尼古丁相关的CR增强的系统，并在此过程中确定尼古丁戒烟的行为相关目标。含有尼古丁乙酰胆碱受体的¿2亚基（¿2*nAChR）对尼古丁具有最高的亲和力，在大脑中表达最广泛。辉瑞公司最近获得了美国食品药品监督管理局和欧盟委员会的批准，可以销售其戒烟药物varenicline。varenicline是一种化合物，可以降低这些受体的活性，而这些受体对尼古丁依赖很重要。尽管varenicline的长期疗效是之前批准的治疗方法的两倍，但针对支持尼古丁依赖的特定行为的治疗方法应该1)减少副作用，2)在更广泛的吸烟者中改善戒烟效果。在确定¿2* nachr可以被a- concontoxin敏感性分解，这涉及到尼古丁的奖励效应调节和尼古丁增强对行为的控制能力，拟议的实验将为尼古丁戒烟治疗确定新的，更具选择性的目标。

DESCRIPTION (provided by applicant): Though many smokers report wanting to quit, very few are able to do so with traditional medical therapies. In May of this year, Pfizer received FDA approval to market its smoking cessation drug, varenicline, a partial agonist with purported selectivity for the ¿2 containing nicotinic acetylcholine receptors (¿2*nAChRs). An accumulation of data indicates that the ¿2*nAChRs are necessary for nicotine associated dopamine (DA) release and for the primary reinforcing effects of nicotine. The ¿2*nAChRs have more recently been implicated for their role in regulating conditioned reinforcement (CR); that is to say, the control that cues paired with a primary reinforcer, such as nicotine, have over behaviors, such as smoking. The primary goal of the proposed experiments is to determine whether subclasses of ¿2*nAChRs, broken down by a-conotoxin MII sensitivity, differentially regulate nicotine's primary rewarding effects versus nicotine's ability to enhance CR. Like the a-conotoxin MII (a-CMII) insensitive a4¿2*nAChRs, the a-CMII sensitive, a6¿2¿3*nAChRs, also modulate nicotine-stimulated DA release. Chiefly expressed in catecholaminergic neurons and highly enriched at striatal DA terminals, the role of a6¿2¿3*nAChRs in nicotine reinforcement is not known. Although the a4 subunit is highly implicated for its contributions to nicotine reward, no studies to date have specifically questioned whether the a4 subunits are required for nicotine reward. Specific Aim 1 of these studies is to identify which nAChR subunits in combination with ¿2 are necessary for the rewarding effects of nicotine as measured by non-biased nicotine conditioned place preference (CPP). Experiment 1 will test ¿3 and a4 nAChR subunit knockout mice for altered levels of nicotine CPP. Studies have shown that ventral tegmental area (VTA)-infusion of dihydro-beta-erythroidine (DH¿E), a selective antagonist of the ¿2*nAChRs, blocks nicotine self administration. Intra-VTA infusion of a-CMII will determine whether MII sensitive receptors at the level of the VTA are required for nicotine CPP. Specific Aim 2 of these experiments will determine whether a-CMII sensitive and insensitive subclasses of ¿2*nAChRs differentially regulate baseline CR and the ability of prior chronic nicotine to enhance CR. ¿3 and a4 knockout mice with different histories of nicotine exposure will undergo Pavlovian discriminative approach training followed by acquisition of a new response with a conditioned reinforcer. DA projections to the nucleus accumbens (NAc) core are critical for regulation of CR at baseline. Although the systems that regulate nicotine-mediated facilitation of CR are unknown, nucleus accumbens shell DA is essential for psychostimulant enhancement of CR. The 2nd experiment of Aim 2 will use intra-shell infusion of a-conotoxin MII and DH¿E to test whether different ¿2*nAChRs at the level of the accumbens regulate nicotine stimulated elevations of CR. These experiments will begin to identify the systems that support nicotine associated enhancement of CR and in doing so will identify behaviorally relevant targets for nicotine cessation. Project De RRATIVE The ¿2 subunit containing nicotinic acetylcholine receptors (¿2*nAChR) have the highest affinity for nicotine and are the most widely expressed in the brain. Pfizer has recently received FDA and European Commission approval to market its smoking cessation drug, varenicline, a compound that reduces activity of these receptors that are important for nicotine dependence. Though varenicline's long-term success is double that of previously approved therapies, treatments that are targeted against specific behaviors that support nicotine dependence ought to 1) lead to fewer side effects and 2) improve outcomes for smoking cessation in a greater diversity of smokers. In determining that ¿2*nAChRs can be broken down by a-conotoxin sensitivity in regard to regulation of nicotine's rewarding effects versus nicotine's ability to enhance the control that cues have over behavior, the proposed experiments will identify novel, more selective targets for nicotine cessation therapy.