乙酰胆碱参与情绪调控的神经环路机制研究

It has been hypothesized that acetylcholine (ACh) elevation in the brain may result in major depression disorder (MDD), also known simply as depression. And it was recently discovered that blocking ACh degradation solely in the hippocampus can lead to depression-like behaviors. Nevertheless, the cholinergic circuitry involved in MDD remains unknown. We thus seek to understand whether the cholinergic pathway from the medial septal nucleus (MS) and vertical limb of the diagonal band (VDB) in the basal forebrain to the hippocampus plays a critical role in mood control related to MDD. In the current project, we intend to make use of optogenetics and designer receptors exclusively activated by designer drugs (DREADDs) to control MS/VDB cholinergic neurons precisely, adopting a combination of techniques including electrophysiology, behavioral tests, confocal microscopy and single cell RNA-seq to address five major issues. Firstly, we will confirm whether increasing ACh in the hippocampus is sufficient to induce depression. Secondly, we will find out whether there is a causal link between ACh increase and memory impairment accompanied with depression. Thirdly, we will examine what malfunctions are caused by abnormal ACh increase in the hippocampus and figure out what subtypes of ACh receptors and local microcircuits mediate the effects of ACh on hippocampal functions relevant to MDD. Fourthly, we are going to determine the identity and molecular markers of MS/VDB cholinergic neurons in response to stress. Lastly, we will explore potential strategies to rescue MDD phenotype, based on interference of the cholinergic pathway from the MS/VDB to the hippocampus. Furthermore, we will compare these methods and identify their underlying mechanisms. These results may help us to better understand the causes of MDD and to develop better treatments for MDD.

整体目标：阐明胆碱能系统对情绪调控的神经环路机制，进而揭示胆碱能神经回路异常与抑郁样行为的关系。本项目拟以胆碱能神经元特异标记的转基因小鼠为研究对象，运用光遗传学、化学遗传学方法精确操控胆碱能神经元活动，并整合电生理、动物行为、单细胞转录组测序等技术研究：（1）胆碱能神经系统通过调节海马的生理特性进而影响情绪的神经环路机制；（2）直接参与情绪调节的胆碱能神经元的亚型和特异标记分子；（3）通过调控胆碱能神经通路挽救抑郁样行为表型的干预机制。本研究将阐明：（1）大脑内乙酰胆碱水平升高导致抑郁症状的致病机理；（2）理解相关神经回路如基底前脑内侧隔核和斜角带垂直支（MS/VDB）投射到海马的胆碱能通路的结构、信息处理与调节规律。本研究将在分子、细胞、环路和整体等不同层面理解乙酰胆碱能神经元调控情绪的新机制，将为寻找针对抑郁症的干预靶点提供新研究思路和实验支撑，因而具有重要的科学、临床和经济价值。

现代社会竞争激烈，人们压力倍增，长期处于应激状态使得抑郁症高发，抑郁症是一种以长期情绪低落等情绪障碍为主的精神疾病，并引起记忆力减退等系列认知障碍，其发病原因复杂，致病机制目前尚不完全清楚，抑郁症的神经认知障碍与胆碱能系统紊乱密切相关，而海马是脑中情绪情感及学习记忆等活动的关键脑区。本课题围绕抑郁症发病的机制，从胆碱能投射到海马的环路和海马本身参与认知活动的规律两方面进行研究。通过光遗传学和化学遗传学方法精确操控特定类型神经元亚型，整合电生理学、动物行为学、形态学等多种分析手段，直接观测投射到海马的胆碱能神经激活所导致的行为结果，发现MS/DBB-vSub 胆碱能神经环路兴奋性升高会激活vSub 锥体神经元从而诱发动物出现焦虑、抑郁样症状。通过化学遗传结合注射药物等手段阻断mAChRs受体的功能同时记录电生理和行为学的结果，看到可以逆转由 ACh 水平上调诱发的焦虑、抑郁样症状和神经元活性的变化。在海马相关的学习和情绪神经环路和分子机制方面，本项目发现海马DG中PV中间神经元的激活足以介导运动逆转精神分裂的表型；响海马记忆编码的倒摄抑制的作用强度，是由海马齿状回的GluN2A/GluN2B比值升高决定的；LTP是海马长时记忆形成的重要机制，LTP反转的易感性在成体新生神经元成熟的过程中逐渐增加，且其原因是NR2A相对表达量的增加。本项目从分子、细胞、环路和整体等不同层面深入、准确地阐明在完整大脑结构中 MS/VDB-海马胆碱能通路与抑郁发生发展的关系和作用机制，同时对海马相关的神经环路和调节学习记忆的分子机制进行研究，为解析情绪情感关键脑区海马的功能提供了新思路和理论基础。本项目研究成果共发表3篇高水平论文，其中一篇发表在cell report，两外两篇发表在Frontiers in Cell and Developmental Biology。