Morphological Tracing and Functional Identification of Monosynaptic Connections in the Brain: A Comprehensive Guide
Yuanyuan Li1,2,3 · Yuanyuan Fang1,2,3,5 · Kaiyuan Li1,2,3 · Hongbin Yang1,2,3 · Shumin Duan2,3,4 · Li Sun1,2,31 Afliated Mental Health Center and Hangzhou Seventh People’s Hospital and School of Brain Science and Brain Medicine, Zhejiang University School of Medicine, Hangzhou 310058, China
2 Liangzhu Laboratory, MOE Frontier Science Center for Brain Science and Brain-machine Integration, State Key Laboratory of Brain-machine Intelligence, Zhejiang University, Hangzhou 311121, China
3 NHC and CAMS Key Laboratory of Medical Neurobiology, Zhejiang University, Hangzhou 310058, China
4 Department of Neurobiology and Department of Neurology of the Second Afliated Hospital, Zhejiang University School of Medicine, Hangzhou 310058, China
5 Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100005, China
Abstract
Behavioral studies play a crucial role in unraveling the mechanisms underlying brain function. Recent advances in optogenetics, neuronal typing and labeling, and circuit tracing have facilitated the dissection of the neural circuitry involved in various important behaviors. The identification of monosynaptic connections, both upstream and downstream of specific neurons, serves as the foundation for understanding complex neural circuits and studying behavioral mechanisms. However, the practical implementation and mechanistic understanding of monosynaptic connection tracing techniques and functional identification remain challenging, particularly for inexperienced researchers. Improper application of these methods and misinterpretation of results can impede experimental progress and lead to erroneous conclusions. In this paper, we present a comprehensive description of the principles, specific operational details, and key steps involved in tracing anterograde and retrograde monosynaptic connections. We outline the process of functionally identifying monosynaptic connections through the integration of optogenetics and electrophysiological techniques, providing practical guidance for researchers.
Keywords
Trans-monosynaptic; Retrograde; Anterograde; Viral tool; Neural circuit; Optogenetics; Electrophysiology
