Molecular Mechanisms of Nicotine Addiction and Extinction

描述(由申请人提供)：首席研究员的长期目标是确定尼古丁成瘾/依赖的分子机制。尼古丁成瘾的一个显著方面是，通常与尼古丁有关的暗示对吸烟者的渴望和复发施加了强有力的控制。尽管已有一些研究尝试通过消除线索来帮助戒烟，但对线索控制机制的缺乏阻碍了这方面的进展。这项拟议的研究旨在阐明在小鼠的位置条件反射范式中线索控制尼古丁成瘾消失的分子机制。这个R01应用测试了一个总体假设，即沿中皮质边缘多巴胺系统的cGMP依赖的蛋白激酶亚型II(PKG-II)是小鼠尼古丁诱导的条件性位置偏爱(CPP)消失率的决定因素。我们已发表的研究和初步研究表明，a)尼古丁可升高纹状体(伏隔核和尾壳核)中cGMP的浓度；b)尼古丁可上调伏隔核和VTA中的PKG活性，这两个区域分别代表中皮质边缘多巴胺途径的靶点和来源；c)尼古丁导致纹状体(包括伏隔核)中一种PKG底物的磷酸化；d)在戒毒试验的头几天，小鼠的尼古丁CPP增强并随后消失，以及e)在PKG II基因敲除(KO)小鼠中，尼古丁CPP的消失加速。这项拟议的研究依赖于对小鼠大脑中PKG水平的遗传操作。具体目标1将检验这一假设，即决定尼古丁CPP消退速度的是PKG-II水平，而不是PKG-I水平。将使用PKG-I和PKG-II野生型(WT)、杂合子(HT)和KO小鼠。此外，我们还将确定PKG亚型在尼古丁CPP消退过程中发挥作用的确切行为过程，以及PKG亚型在其他成瘾物质消退线索控制过程中所起的一般作用。特定目标2将确定PKG可能调节尼古丁CPP消退的特定脑区(S)。我们将使用慢病毒载体局部恢复PKG-II(或PKG-I)KO小鼠。此外，我们还将沿着中皮质边缘多巴胺通路，将尼古丁CPP在消退过程中的维持与选定脑区的PKG活性联系起来。拟议的研究结果意义重大，因为它将提供证据，可用于为吸烟者设计治疗方案。在特定的大脑基因座识别PKG亚型，与尼古丁成瘾的线索控制有关，将是增强我们微调分子靶标以防止线索触发的吸烟复发和加速戒烟的能力的重要一步。如果这种激酶被证明对其他成瘾物质在灭绝过程中的线索控制很重要，这些研究的结果将对治疗其他形式的成瘾的线索触发的复发具有更广泛的影响。最近的估计表明，全世界约有13亿烟民，每年有500万人死于烟草使用。目前可用的治疗方法在帮助戒烟方面并不有效，部分原因是尼古丁成瘾戒除的确切神经机制仍然知之甚少。拟议的研究旨在填补这一知识空白。

DESCRIPTION (provided by applicant): The long-term objective of the principal investigator is to ascertain the molecular mechanisms underlying nicotine addiction/dependence. One salient aspect of nicotine addiction is that cues that are usually associated with nicotine exert a powerful control over craving and relapse in smokers. Although some attempts have been made to implement cue extinction to aid smoking cessation, lack of knowledge regarding the mechanisms of cue control of smoking has hampered progress. The proposed studies are designed to elucidate the molecular mechanisms underlying extinction of cue control of nicotine addiction in the place conditioning paradigm in mice. This R01 application tests the overall hypothesis that cGMP-dependent protein kinase subtype II (PKG-II), in regions along the mesocorticolimbic dopamine system, is a determinant of the rate of extinction of nicotine-induced conditioned place preference (CPP) in mice. Our published and preliminary studies show that a) nicotine elevates the concentration of cGMP in the striatum (nucleus accumbens and caudate-putamen), b) nicotine can up-regulate PKG activity in the nucleus accumbens and the VTA, which represent a target and the origin of the mesocorticolimbic dopamine pathway, respectively, c) nicotine causes phosphorylation of a PKG substrate in the striatum (including the nucleus accumbens), d) mice exhibit intensified nicotine CPP on the first few drug-free test days and extinction thereafter, and e) extinction of nicotine CPP is accelerated in PKG-II knockout (KO) mice. The proposed studies rely on genetic manipulation of PKG levels in the mouse brain. Specific Aim 1 will test the hypothesis that the level of PKG-II, but not PKG-I, determines the rate of extinction of nicotine CPP. PKG-I and PKG-II wild-type (WT), heterozygous (HT), and KO mice will be employed. Moreover, we will determine the exact behavioral processes in which PKG subtypes play a role during extinction of nicotine CPP and the general role played by PKG subtypes in extinction of cue control by other addictive substances. Specific Aim 2 will identify the specific brain region(s) in which PKG may act to regulate extinction of nicotine CPP. We will use a lentiviral vector to locally restore PKG-II (or PKG-I) in PKG-II (or PKG-I) KO mice. Moreover, we will correlate maintenance of nicotine CPP during extinction with PKG activities in selected brain regions along the mesocorticolimbic dopamine pathway. The outcome of the proposed studies is significant, as it will provide evidence that can be used to devise therapeutic options for smokers. Identification of a PKG subtype in specific brain loci, in connection with cue control of nicotine addiction, would be an important step toward enhancing our ability to fine-tune molecular targets to prevent cue-triggered smoking relapse and accelerate extinction. If this kinase turns out to be important for cue control of other addictive substances during extinction, the outcome of these studies will have a much broader implication for treatment of cue-triggered relapses in other forms of addiction. Recent estimates indicate that there are approximately 1.3 billion smokers world-wide and 5 million deaths are attributable to tobacco use annually. Currently available therapies are not effective in aiding cessation, partly because the exact neuronal mechanisms underlying extinction of nicotine addiction are still poorly understood. The proposed studies are designed to fill in this knowledge gap.