Low-invasive, wide-field, and cellular resolution two-photon imaging of neural population activity in brainstem and nucleus tractus solitarii

Abstract

SummaryBrain-viscera communication is thought to play a crucial role in regulating mental health, with the vagus nerve being a key structure mediating this interaction. Clinically, artificial vagus nerve stimulation (VNS) is used to treat various neuropsychiatric disorders, highlighting the importance of vagal afferent fibers in regulating emotion. The nucleus tractus solitarii (NTS) is a brainstem structure proposed to receive direct signals from vagal afferents and relay them to the brain emotional regulatory networks. Direct evidence for this network is limited, however, due to the anatomic complexity and difficulty accessing the deep-brain NTS region in living animals. Here, to investigate this further, we developed a wide-field and deep-brain two-photon imaging method using a prism-based optical interface enabling the identification of cellular-resolution neural activities of the NTS while keeping the cerebellum, which covers the NTS, intact. This method allowed us to evaluate how NTS neurons respond to VNS and the gastrointestinal hormone cholecystokinin-8, suggesting its usefulness for investigating the role of the vagus-NTS pathway in regulating emotion.