Neurobiological mechanisms of nicotine reinforcement: Role of the nucleus tractus

说明(申请人提供)：尼古丁强化的神经生物学机制：孤束核(NTS)的作用吸烟在发达国家是可预防的死亡和疾病的主要原因，美国每年大约花费1600亿美元来支付由此导致的疾病的直接医疗费用。尼古丁是烟草烟雾中导致烟草成瘾的主要精神活性成分。尼古丁通过刺激烟碱型乙酰胆碱受体(NAChRs)在大脑中发挥作用，nAChRs是由五个离散亚单位组成的五聚体离子通道。我们对吸烟行为理解的一个重大进展是最近发现染色体区域15q25上的A3/a5/？4nAChR亚单位基因簇的遗传变异显著增加了烟草成瘾的风险。有趣的是，A3/a5/？4nAChR亚基在大脑中的表达模式高度受限，孤束核(NTS)是仅有的三个亚基都有强劲表达的大脑区域之一。NTS参与调节摄食、呼吸、内感信息的处理，最近被认为与阿片类奖赏有关，但它在尼古丁强化中的作用在很大程度上仍未被探索。初步数据显示，利多卡因介导的NTS失活显著减少了大鼠静脉注射尼古丁的自我给药(IVSA)。此外，胰高血糖素样肽-1(GLP-1)是在NTS产生的一种神经肽，参与调节内感应激和摄食抑制，是其主要传出系统之一，投射到与药物强化相关的脑区。初步数据显示，急性尼古丁注射后，NTS中的GLP-1神经元被激活。此外，初步研究表明，在缺乏GLP-1受体表达的小鼠中，尼古丁IVSA几乎完全取消。综上所述，这些结果表明，NTS，也许还有GLP-1的传递，在尼古丁强化中起到了调节作用。我们的目标是研究NTS中A3/a5和/或含有A4的nAChRs在尼古丁强化中的作用，以及包含这些亚单位的nAChRs如何调节NTS的神经化学系统，如GLP-1。为了实现这一目标，我们建议使用一种创新的小鼠尼古丁IVSA技术来测试特定基因敲除对意志性尼古丁摄入量的影响。此外，我们计划使用尖端病毒介导的基因转移技术在体内重新表达或沉默靶基因，以及使用免疫化学技术对大脑区域特定的神经元激活进行评估，并利用颅内自我刺激直接询问大鼠和小鼠的奖赏系统。这项提案中概述的实验结果将增加我们对尼古丁成瘾的基本了解，并可能为开发新的戒烟疗法提供令人兴奋的目标。 公共卫生相关性：尼古丁强化的神经生物学机制：孤束核的作用(NTS)估计，到2020年，与烟草相关的疾病将成为全球最大的单一健康问题，每年导致约840万人死亡[12]。这项研究计划旨在更好地了解尼古丁成瘾的基本神经生物学基础。这些实验的结果可能有助于开发戒烟的新疗法。

DESCRIPTION (provided by applicant): Neurobiological mechanisms of nicotine reinforcement: Role of the nucleus tractus solitarius (NTS) Cigarette smoking is a principal cause of preventable death and disease in developed nations, with approximately $160 billion being spent yearly in the United States to cover direct health care costs from resulting diseases. Nicotine is the major psychoactive component of tobacco smoke responsible for tobacco addiction. Nicotine acts in the brain by stimulating nicotinic acetylcholine receptors (nAChRs), which are pentameric ion channels comprised of five discrete subunits. A major advance in our understanding of smoking behavior is the recent finding that genetic variation in the a3/ a5/¿4 nAChR subunit gene cluster on chromosome region 15q25 dramatically increases risk of tobacco addiction. Intriguingly, a3/ a5/¿4 nAChR subunits have a highly-restricted expression pattern in the brain, with the nucleus of the solitary tract (NTS) being one of the only brain regions to display robust expression of all three subunits. The NTS is involved in the regulation of feeding, respiration, processing of interoceptive information, and was recently implicated in opiate reward, yet its role in nicotine reinforcement remains largely unexplored. Preliminary data show that lidocaine-mediated NTS inactivation significantly reduces intravenous nicotine self-administration (IVSA) in rats. Furthermore, glucagon-like peptide-1 (GLP-1), a neuropeptide involved in regulating interoceptive stress and feeding inhibition, is produced in the NTS and represents one of its major efferent systems, projecting to brain regions related to drug reinforcement. Preliminary data show that GLP-1 neurons in the NTS are activated in response to acute nicotine injections. In addition, preliminary studies suggest that nicotine IVSA is almost completely abolished in mice lacking expression of the GLP-1 receptor. Taken together, these results suggest a regulatory role for the NTS, and perhaps GLP-1 transmission, in nicotine reinforcement. We aim to characterize the role of a3/ a5, and/or ¿4 -containing nAChRs in the NTS in nicotine reinforcement and how nAChRs containing these subunits may regulate NTS neurochemical systems such as GLP-1. To achieve this goal we propose to use an innovative mouse nicotine IVSA technique to test the effect of specific gene knockouts on volitional nicotine intake. In addition, we plan to employ cutting-edge viral- mediated gene transfer technologies to re-express or silence target genes in vivo, as well as immunochemical techniques for brain region-specific assessment of neuronal activation, and intracranial self-stimulation for direct inquiry of reward systems in rats and mice. Results from the experiments outlined in this proposal will increase our basic understanding of nicotine addiction, and may provide exciting targets for the development of novel therapeutics for smoking cessation. PUBLIC HEALTH RELEVANCE: Neurobiological mechanisms of nicotine reinforcement: Role of the nucleus tractus solitarius (NTS) Estimates project that by the year 2020, tobacco-related disease will become the largest single health problem world-wide, resulting in approximately 8.4 million deaths annually [12]. This research proposal seeks to provide a better understanding of the fundamental neurobiology underlying nicotine addiction. Results from these experiments may serve to develop novel therapeutics for smoking cessation.