Basal Forebrain Corticopetal GABAergic Neurons and Cortical Arousal

描述(申请人提供)：基底前脑(BF)的结构和功能的完整性是维持行为和脑电(EEG)觉醒的绝对要求。然而，BF调节脑电和神经行为唤醒的机制和底物仍然知之甚少。对相关文献的回顾表明，绝大多数关于BF回路的研究都集中在皮质顶叶胆碱能BF系统在生理(脑电和行为唤醒)和病理生理(神经退行性疾病)调节方面的研究，尽管事实是：1)胆碱能BF系统的损伤对EEG或行为觉醒产生有限的变化；以及2)BF还包含一群皮质投射的GABA能神经元，大致与胆碱能神经元混合。虽然人们已经意识到其他皮质顶叶BF神经递质系统可能在调节皮质回路方面与胆碱能神经元相互作用或并行工作，但GABA能BF神经元，特别是那些投射到皮质的神经元，在这一过程中的贡献在很大程度上仍未被探索。在这项建议中，我们试图确定BF GABA能神经元在体外(细胞)和体内(系统)机制和底物对脑电和行为唤醒(包括睡眠-觉醒周期)的贡献。我们假设BF GABA能群在维持脑电和行为觉醒中起重要作用，这种影响主要是通过皮质投射的GABA能BF神经元而不是投射到其他脑区的BF GABA能中间神经元或BF GABA能神经元介导的，如下丘脑外侧区。然而，鉴于BF内GABA能神经元的多个递质系统和亚群，对BF GABA能神经元，特别是皮质顶叶GABA能神经元在脑电和行为觉醒中的作用的实验解剖已被证明是一个相当大的挑战。因此，我们试图开发和验证新的基于病毒的药物遗传学和条件性启动子特异性转基因表达系统，以通过选择性分离和操纵BF GABA能神经元来验证我们的假设。具体地说，我们将使用所谓的DREADD(由设计药物独占激活的设计者受体)系统来可逆地激活或沉默BF GABA能神经元，包括在体外和体内选择性地操纵皮质投射的BF GABA能神经元。这项实验工作的结果将提供有关产生和维持觉醒所必需的底物的重要信息，并强调BF GABA能神经元在自由行为、不受约束的动物的这些过程中的关键贡献。

DESCRIPTION (provided by applicant): The structural and functional integrity of the basal forebrain (BF) is an absolute requirement for maintaining behavioral and electrographic (EEG) wake. The mechanisms and substrates by which the BF regulates EEG and neurobehavioral arousal remains however poorly understood. A review of the relevant literature reveals that the vast majority of studies on BF circuitry have focused on the corticopetal cholinergic BF system in physiological (EEG and behavioral arousal) and pathophysiological (neurodegenerative disorders) regulation, despite the facts that 1) lesions of the cholinergic BF system produce limited changes in EEG or behavioral wake; and 2) the BF also contains a population of cortically projecting GABAergic neurons that roughly intermingle with the cholinergic neurons. While it has been appreciated for some time that other corticopetal BF neurotransmitter systems may interact or work in parallel with cholinergic neurons in modulating cortical circuitry, the contribution of GABAergic BF neurons, and in particular those projecting to the cortex, to this process remains largely unexplored. In this proposal we seek to determine the in vitro (cellular) and in vivo (system) mechanisms and substrates by which the BF GABAergic neurons contribute to EEG and behavioral arousal, including sleep-wake cycles. We hypothesize that the BF GABAergic population is critically involved in maintaining EEG and behavioral wake and that this influence is mediated primarily by cortically-projecting GABAergic BF neurons and not by BF GABAergic interneurons or BF GABAergic neurons that project to other brain regions, such as the lateral hypothalamus. The experimental dissection of the role of BF GABAergic neurons, and in particular the corticopetal BF GABAergic neurons in EEG and behavioral arousal, has however proven a considerable challenge given the multiple transmitter systems and sub-populations of GABAergic neurons within the BF. We have therefore sought to develop and validate novel viral-based pharmacogenetic and conditional promoter-specific transgene expression systems to test our hypothesis through the selective isolation and manipulation of BF GABAergic neurons. Specifically we will use the so-called DREADD (designer receptors exclusively activated by designer drugs) system to reversibly activate or silence BF GABAergic neurons, including the selective manipulation of cortically-projecting BF GABAergic neurons, both in vitro and in vivo. The results from this experimental work will provide important information regarding the substrates that are necessary to produce and maintain arousal and emphasize the critical contribution of BF GABAergic neurons to these processes in freely behaving, unrestrained animals.