https://www.selleckchem.com/products/Semagacestat(LY450139).html The vagus nerve plays a pivotal role in communication between the brain and peripheral organs involved in the sensory detection and the autonomic control of visceral activity. While the lack of appropriate experimental techniques to manipulate the physiological activity of the vagus nerve has been a long-standing problem, recent advancements in optogenetic tools, including viral vectors and photostimulation devices, during the late 2010s have begun to overcome this technical hurdle. Furthermore, identifying promoters for expressing transgenes in a cell-type-specific subpopulation of vagal neurons enables the selective photoactivation of afferent/efferent vagal neurons and specific visceral organ-innervating vagal neurons. In this chapter, we describe recent optogenetic approaches to study vagus nerve physiology and describe how these approaches have provided novel findings on the roles of vagus nerve signals in the cardiac, respiratory, and gastrointestinal systems. Compared with studies of the central nervous system, there are still few insights into vagus nerve physiology. Further studies with optogenetic tools will be useful for understanding the fundamental characteristics of vagus nerve signals transferred throughout the body.Using an optogenetic approach, we analyzed a local neuron network of the respiratory center in the medulla of a brainstem-spinal cord preparation isolated from neonatal rat. We developed a transgenic (Tg) rat line in which Phox2b-positive cells expressed archaerhodopsin-3 (Arch) or one of the step-function channelrhodopsin variants (ChRFR) under the control of Phox2b promoter-enhancer regions. Then, in en bloc preparations from 0- to 2-day-old Tg neonatal rats, we analyzed membrane potential changes of medullary respiratory-related neurons in response to photostimulation of the rostral ventral medulla. The photostimulation-induced inhibition or facilitation of the respiratory