中枢5-羟色胺能神经元在全脑投射广泛，参与调控情绪、认知、学习、记忆等生理过程，其功能异常与焦虑、抑郁和创伤后应激等精神类疾病相关。由于缺乏有效神经元稀疏标记工具，无法对特定5-羟色胺能神经元的全脑精细投射及功能进行精确研究。本项目将利用我们在嗜神经病毒改造和神经环路示踪的优势, 1）开发基于全新Split-Cre狂犬病毒和CRE依赖光遗传及化学遗传原件AAV病毒的稀疏标记系统；2）利用上述病毒逆行稀疏标记同时投射听觉皮层和杏仁核的5-羟色胺能神经元，结合fMOST对稀疏标记神经元进行全脑三维重构和单神经元追踪成像；3）结合化学遗传学和行为学实验，揭示稀疏标记的5-羟色胺能神经元在声音条件性恐惧记忆中的功能; 4）结合光遗传、双光子成像和电生理对稀疏标记的神经元进行功能分析。该稀疏标记系统将为解析单神经元水平全脑投射提供有效的示踪工具，也将为精细水平探究特定神经环路功能提供有力的调控病毒工

Central serotoninergic neurons project widely in whole brain and play multiple physiological functions including emotion，cognition, learning and memory, of which the dysfunction is correlated with many psychological symptoms like anxiety, depression as well as posttraumatic stress disorder and so on. Due to the lack of effective sparse labeling tool , we cannot yet perform accurate research on precise projection of central serotoninergic neurons in whole brain and their specific functions. In current project, based on our expertise on neurotropic virus engineering and neural circuit tracing, we are planning to: 1) develop novel sparse neuron labeling system based on Split-Cre rabies virus and Cre-depedent optogenetic/ chemogenetic tools AAV virus; 2) sparsely label central serotonergic neurons simultaneously projecting to auditory cortex and amygdala, image and track their projection in whole brain using fMOST; 3) explore the function of labeled serotonergic neurons in tone conditioned fear memory through chemogenetic manipulation; 4) carry out further functional studies on sparsely labeled serotonergic neurons by behavioral test, optogenetical manipulation, two-photon microscopic imaging and electrophysiology. The sparse labeling system will provide powerful tracing virus tool for exploring whole brain projection of single neuron at precise resolution and provide promising regulatable virus for functional studies of specific neural circuit on fine level.