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做到这一点。今年5月，辉瑞获得了FDA的批准，可以销售其戒烟药物varenicline，这是一种部分激动剂，据称对含有烟碱型乙酰胆碱受体(？2*nAChRs)的部分激动剂具有选择性。数据的积累表明，2*nAChRs是尼古丁相关多巴胺(DA)释放和尼古丁的主要强化作用所必需的。2*nAChRs最近被认为是因为它们在调节条件性强化(CR)中的作用；也就是说，信号与主要增强剂(如尼古丁)配对的控制对行为的控制，如吸烟。拟议实验的主要目标是确定被a-芋螺毒素MII敏感性分解的2*nAChRs亚类是否对尼古丁的主要奖励效应与尼古丁增强CR的能力进行不同的调节。与a-芋螺毒素MII(a-CMII)不敏感的a4？2*nAChRs一样，a-CMII敏感的a6？2？3*nAChRs也调节尼古丁刺激的DA释放。主要在儿茶酚胺能神经元中表达，在纹状体DA终末高度表达，其在尼古丁强化中的作用尚不清楚。尽管A4亚基对尼古丁奖赏的贡献被高度怀疑，但到目前为止还没有研究明确质疑A4亚基是否对尼古丁奖赏是必需的。这些研究的具体目的1是确定哪些nAChR亚基与？2结合是尼古丁的奖赏效应所必需的，这是通过无偏见尼古丁条件性位置偏爱(CPP)来衡量的。实验1将测试3和A4 nAChR亚单位基因敲除小鼠尼古丁CPP水平的变化。研究表明，腹侧被盖区(VTA)--注射二氢β-红景天碱(DHE)--一种选择性的nAChRs拮抗剂，可以阻断尼古丁的自身给药。VTA内注入a-CMII将确定尼古丁CPP是否需要VTA水平的MII敏感受体。这些实验的具体目标2将确定a-CMII敏感和不敏感的2*nAChRs亚类是否对基线CR和先前慢性尼古丁增强CR的能力有不同的调节作用。有不同尼古丁暴露史的3号和A4号基因敲除小鼠将接受巴甫洛夫鉴别方法训练，然后用条件增强剂获得新的反应。DA向伏核(NAC)核心的投射对基线时CR的调节至关重要。虽然调控尼古丁介导的CR易化的系统尚不清楚，但伏隔核壳DA对于增强CR的精神刺激性至关重要。AIM 2的第二个实验将使用壳内注射a-芋螺毒素MII和DHE来测试伏隔水平上不同的2*nAChRs是否调节尼古丁刺激的CR升高。这些实验将开始识别支持尼古丁相关的CR增强的系统，并在这样做的过程中识别与行为相关的尼古丁戒断目标。Project de RATIVE是含有烟碱型乙酰胆碱受体(2*nAChR)的2亚基，对尼古丁的亲和力最高，在大脑中表达最广泛。辉瑞最近获得了FDA和欧盟委员会的批准，可以销售其戒烟药物varenicline，一种降低这些受体活性的化合物，这些受体对尼古丁依赖非常重要。尽管varenicline的长期成功是之前批准的疗法的两倍，但针对支持尼古丁依赖的特定行为的治疗应该1)减少副作用，2)在更多不同的吸烟者中改善戒烟结果。在确定与尼古丁的奖赏效应的调节和尼古丁增强对行为的控制的尼古丁的敏感性有关的2*nAChRs可以被a-芋螺毒素敏感性所分解时，拟议的实验将确定尼古丁戒断治疗的新的、更具选择性的靶点。

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.