Nicotine-Mediated behavioral Consequences of Nicotinic Receptor Upregulation

描述（由申请人提供）：长期暴露于烟草烟雾每年导致约500万人死亡，使吸烟引起的健康并发症成为世界上可预防死亡的主要原因。尼古丁，烟草的成瘾成分，结合并激活神经元烟碱乙酰胆碱受体（nAChR），配体门控阳离子通道，通常由内源性神经递质乙酰胆碱激活。尼古丁通过激活中皮质边缘奖赏回路的腹侧被盖区（VTA）内的神经元引发依赖，最终驱动丘脑核内多巴胺（DA）的释放，这一现象与尼古丁的奖赏或强化价值广泛相关。多种nAChR亚基基因在腹侧被盖区DA能投射神经元和GABA能中间神经元中表达，但腹侧被盖区中含有α 4和β 2亚基的nAChR的激活对于尼古丁的奖励特性最为关键。暴露于慢性尼古丁功能上调nAChR在不同的大脑区域，虽然这种上调的行为后果是未知的。在中脑中，含有α 4亚基的nAChR在GABA能神经元而不是DA能神经元中选择性上调。这项R21提案的目标是深入了解这种神经元亚型选择性功能性上调α 4亚基如何影响尼古丁奖励行为。具体目标一将使用病毒介导的基因递送来选择性地在小鼠的VTA GABA能神经元中表达功能获得性α 4亚基，并与对照动物相比测量尼古丁介导的奖励行为。具体目标二将使用免疫组织化学和生物物理方法来确定尼古丁如何增加GABA能神经元的激活，从而影响腹侧被盖区DA能神经元的活性。这些研究的结果不仅有助于确定GABA能神经元在尼古丁奖赏中的作用，而且还应该揭示nAChR上调的行为后果。

DESCRIPTION (provided by applicant): Chronic exposure to tobacco smoke accounts for ~5 million deaths per year making health complications from smoking the primary cause of preventable mortality in the world. Nicotine, the addictive component of tobacco, binds to and activates neuronal nicotinic acetylcholine receptors (nAChRs), ligand-gated cation channels that are normally activated by the endogenous neurotransmitter, acetylcholine. Nicotine initiates dependence by activating neurons within the ventral tegmental area (VTA) of the mesocorticolimbic reward circuitry, ultimately driving the release of dopamine (DA) within the nucleus accumbens, a phenomenon widely associated with the rewarding or reinforcing value of nicotine. A large variety of nAChR subunit genes are expressed in both VTA DAergic projection neurons and GABAergic interneurons but activation of nAChRs containing alpha4 and beta2 subunits in the VTA are most critical for the rewarding properties of nicotine. Exposure to chronic nicotine functionally upregulates nAChRs in various brain regions although the behavioral consequence of this upregulation is unknown. In the midbrain, nAChRs containing the alpha4 subunit are selectively upregulated in GABAergic neurons but not DAergic neurons. The goal of this R21 proposal is to gain insight into how this neuronal subtype selective functional upregulation of the alpha4 subunit affects nicotine reward behavior. Specific aim one will use viral-mediated gene delivery to selectively express gain-of-function alpha4 subunits in VTA GABAergic neurons of mice and measure nicotine-mediated reward behavior compared to control animals. Specific aim two will use immunohistochemical and biophysical approaches to determine how increased activation of GABAergic neurons by nicotine affects VTA DAergic neuron activity. The results from these studies will not only help define the role of GABAergic neurons in nicotine reward, but should also unmask behavioral consequences of nAChR upregulation.