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

Brain-viscera communication plays 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 signals from vagal afferents and relay them to brain networks for emotion regulation. However, due to the anatomical complexity and difficulty in accessing the deep-brain NTS region in living animals, the mechanisms remain unclear. Here, we developed a wide-field and deep-brain two-photon imaging method using a double-prism based optical interface. This approach enables the identification of cellular-resolution neural activities in the NTS while preserving the cerebellum, which covers the NTS and is important for emotion regulation, intact. We systematically evaluated how NTS neurons respond to VNS and a gastrointestinal hormone, suggesting the usefulness of this method for investigating the role of the vagus-NTS pathway in vivo.