A Molecular Analysis of the Gateway Hypothesis in Mice

描述（由申请人提供）：研究的总体目标是从分子角度检验一种流行病学假设，即网关假设。该假说描述了使用一类药物（如香烟（尼古丁））先于使用其他药物（如可卡因）的步骤顺序。我们建议在分子水平上使用小鼠模型来测试网关假说。我们的方法进一步基于成瘾与长期记忆共享分子步骤和分子逻辑的证据。我们将解决四个具体目标：(1)在行为和转录水平上确定网关假说预测的尼古丁和可卡因之间是否存在顺序，该顺序是单向的（从尼古丁到可卡因）还是双向的（从可卡因到尼古丁），以及尼古丁是否也可以增强对可卡因以外的滥用药物的反应，如吗啡。(2)为了确定尼古丁诱导动物接受可卡因效应的分子机制，我们建议使用基因芯片分析选择的目标区域来调查纹状体，特别是伏隔核和杏仁核的mRNA模式。我们将使用药理学分析来剖析可能介导启动效应的任何可能的信号转导途径，并通过转基因小鼠来探索从筛选中出现的一些选定的候选基因。(3)为了确定可能有助于维持门户效应的分子机制，我们将使用染色质免疫沉淀法研究聚焦于FosB和c-Fos启动子的持续组蛋白乙酰化。(4)为了从行为和分子角度描述青少年药物暴露的性质和后果，我们将在目标1-3 (a)中对青少年小鼠进行重复实验，将这些结果与成年小鼠进行比较，并(b)对预先暴露于尼古丁或可卡因的成年小鼠进行实验，以确定青少年药物暴露对成年后对相同或不同药物的药物反应的影响。试点研究的初步结果支持拟议的方法。除了测试某些理解成瘾的基本假设外，这些分子见解还有两个潜在的用途：(1)它们可能为成瘾治疗提供新的分子靶点；(2)它们可能提供关于人群药物行为的新假设，可在流行病学数据中进一步探索。药物滥用是这个国家最重要的公共卫生问题之一。药物滥用始于青春期，使用一种合法药物，酒精或烟草（尼古丁）；那些使用其中一种药物的人有更大的风险发展到使用非法药物，如大麻或可卡因。那些在青春期开始吸烟的人成年后继续吸烟的可能性比那些在晚年开始吸烟的人更大，并且更有可能经历吸烟带来的不良健康后果。该研究旨在通过小鼠模型阐明从尼古丁到可卡因的药物使用过程中的生物学机制。这项研究的发现可能使开发新的药物来预防和治疗药物滥用成为可能。

DESCRIPTION (provided by applicant): The overall goal of the research is to test an epidemiological hypothesis, the Gateway Hypothesis, in molecular terms. The hypothesis describes the sequence of steps whereby use of one class of drug, e.g. cigarettes (nicotine), precedes the use of other drugs, such as cocaine. We propose to test the Gateway Hypothesis at the molecular level using a mouse model. Our approach is further based on the evidence that addiction shares molecular steps and molecular logic with long-term memory. We will address four specific aims: (1) To determine on a behavioral and transcriptional level whether there is the sequential order between nicotine and cocaine predicted by the Gateway Hypothesis, whether this sequence is unidirectional (from nicotine to cocaine) or bidirectional (from cocaine to nicotine), and whether nicotine can also enhance the response to drugs of abuse other that cocaine, such as morphine. (2) To determine the molecular mechanisms by which nicotine primes an animal to the effects of cocaine, we propose to use gene-chip analysis to selected target regions to survey patterns of mRNA in the striatum, particularly the nucleus accumbens, and the amygdala. We will use pharmacological analysis to dissect any possible signal transduction pathway that may mediate the priming effects, and genetically modified mice to explore some of the selected candidate genes emerging from the screen. (3) To identify molecular mechanisms that might contribute to maintaining the gateway effect, we will examine persistent histone acetylation focusing on promoters of FosB and c-Fos, using chromatin immunoprecipitation assays. (4) To characterize the nature and consequences of adolescent drug exposure in both behavioral and molecular terms, we will replicate selected experiments outlined in Aims 1-3 (a) on adolescent mice to compare these results to those obtained on adults, and (b) on adult mice preexposed to nicotine or cocaine to identify the consequences of adolescent drug exposure for drug responses in adulthood to the same or different drugs. Preliminary results from pilot studies support the proposed approach. In addition to testing certain fundamental hypotheses for understanding addiction, these molecular insights are potentially useful for two reasons: (1) They may provide new molecular targets for the treatment of addiction; (2) They are likely to provide new hypotheses about drug behavior in human populations that can be further explored in epidemiological data. Drug abuse represents one of the most important public health issues in the nation. Drug abuse begins in adolescence, with the use of one of the legal drugs, alcohol or tobacco (nicotine); those who use one of these drugs are at much greater risk of progressing to the use of illicit drugs, such as marijuana or cocaine. Those who start smoking in adolescence are much more likely to continue smoking as adults and to experience the adverse health consequences of smoking than individuals who start smoking later in life. The proposed research aims to elucidate the biological mechanisms that underlie the progression in drug use from nicotine to cocaine by using a mouse model. The findings of the research may make it possible to develop new drugs to prevent and treat substance abuse.