Synaptic mechanisms underlying the rapid antidepressant actions of scopolamine

描述（由申请人提供）：重度抑郁症（MDD）是世界上最普遍和最令人衰弱的疾病之一，影响约17%的人口，造成巨大的个人和经济负担。目前可用药物的局限性突出了重度抑郁症的影响，包括低反应率、治疗耐药性和治疗滞后（几周到几个月）。这些数据突出了对更有效和更快速的抗抑郁药的主要未满足需求。最近的研究表明，单次低剂量东莨菪碱（一种毒蕈碱受体拮抗剂）对治疗耐药患者产生快速和持久的抗抑郁作用。这种快速作用的机制与典型的单胺再摄取抑制剂完全不同，是过去60年来抑郁症领域最重要的发现之一。东莨菪碱快速抗抑郁作用的机制尚未确定，目前的应用解决了这个问题。初步研究发现，东莨菪碱能快速刺激哺乳动物rapamycin complex 1靶点（mTORC1），使PFC神经元棘数和功能迅速增加，并在啮齿动物模型中产生快速的抗抑郁行为反应。此外，东莨菪碱的作用被雷帕霉素阻断，表明需要mTORC1。基于这些发现，我们假设东莨菪碱的快速抗抑郁作用是由于mTORC1的刺激和PFC突触连通性的增加，通过谷氨酸的爆发和脑源性神经营养因子（BDNF）的释放而发生。本申请描述了一种综合的多学科方法，包括分子、生化、电生理、形态学、光遗传学和行为学研究来检验这一假设。目的1将描述东莨菪碱刺激mTORC1、脊柱密度和行为反应的时间过程和区域定位，并使用药理学、病毒载体和突变小鼠方法的组合来确认mTORC1和BDNF的必要性。东莨菪碱可以迅速逆转由慢性压力引起的突触和行为缺陷的假设也将得到验证。目的2将确定谷氨酸- ampa受体传递的作用，这涉及BDNF-mTORC1信号和突触形成的活性依赖性刺激，使用微透析和选择性抑制剂。微输注和光遗传学方法将用于测试谷氨酸在PFC亚区传递的作用，并确定快速抗抑郁反应的靶电路。Aim 3将测试谷氨酸爆发是否通过位于GABA中间神经元上的M1受体发生，从而导致谷氨酸传递的去抑制，使用细胞特异性病毒表达的floxed shRNA， M1缺失突变体和细胞特异性Cre小鼠。东莨菪碱信号通路的表征将确定速效抗抑郁药的基本机制和更安全的速效药物的新靶点。

DESCRIPTION (provided by applicant): Major depressive disorder (MDD) is one of the most prevalent and debilitating illnesses world wide, affecting ~17 percent of the population and causing enormous personal and economic burden. The impact of MDD is underscored by the limitations of currently available medications, including low response rates, treatment resistance, and therapeutic time-lag (weeks to months). These data highlight a major unmet need for more efficacious and faster-acting antidepressants. Recent studies demonstrate that a single low dose of scopolamine, a muscarinic receptor antagonist, produces rapid and long-lasting antidepressant actions in treatment resistant patients. This rapid action, by a mechanism completely different from typical monoamine reuptake inhibitors, represents one of the most significant findings in the field of depression over the past 60 years. The mechanisms underlying the rapid antidepressant actions of scopolamine have not been identified, and the current application addresses this issue. Preliminary studies have found that scopolamine rapidly stimulates the mammalian target of rapamycin complex 1 (mTORC1), a pathway involved in synaptic protein synthesis, rapidly increases spine number and function of PFC neurons, and produces rapid antidepressant behavioral responses in rodent models. Moreover, the actions of scopolamine are blocked by rapamycin, demonstrating a requirement for mTORC1. Based on these findings, we hypothesize that the rapid antidepressant actions of scopolamine result from stimulation of mTORC1 and increased synaptic connectivity in PFC that occur via a burst of glutamate and release of brain derived neurotrophic factor (BDNF). This application describes an integrated multidisciplinary approach, including molecular, biochemical, electrophysiological, morphological, optogenetic, and behavioral studies to test this hypothesis. Aim 1 will characterize the time course and regional localization of scopolamine-stimulation of mTORC1, spine density, and behavioral responses, and confirm the requirement for mTORC1 and BDNF using a combination of pharmacological, viral vector, and mutant mouse approaches. The hypothesis that scopolamine can rapidly reverse the synaptic and behavioral deficits caused by chronic stress will also be tested. Aim 2 will determine the role of glutamate-AMPA receptor transmission, which has been implicated in activity-dependent stimulation of BDNF-mTORC1 signaling and synapse formation, using microdialysis and selective inhibitors. Microinfusions and optogenetic approaches will be used to test the role of glutamate transmission in subregions of PFC and to identify target circuits that underlie rapid antidepressant responses. Aim 3 will test if the glutamate burst occurs via muscarinic-1 (M1) receptors located on GABA interneurons, resulting in disinhibition of glutamate transmission, using cell specific virally expressed floxed shRNA, M1 deletion mutants, and cell specific Cre mice. Characterization of the signaling pathways for scopolamine will identify fundamental mechanisms for rapid acting antidepressants and novel targets for safer, rapid-acting agents.