Project summary| Over 50 million people suffer from epilepsy worldwide resulting in massive health, social, and economic burdens. While there is a growing need for improved anti-epileptic treatments, many of the current options are ineffective and are coupled with harrowing side effects such as depression, nausea, and fatigue. Chronic vagus nerve stimulation (VNS), in which an electrical implant stimulates the vagus nerve, can effectively treat epilepsy and is one of the few alternatives for drug-resistant patients. Although it is widely believed that wake promoting vagal subsets are responsible for the anti-epileptic effects, the identity, number, and valence of these subsets remains unknown. Existing literature and ongoing studies in our own lab suggest that Neuropeptide Y Receptor 2 neurons of the vagus sense hypoxia in the lung and promote wakefulness via dopaminergic neurons of the NTS. Interestingly, literature also suggests that Glucagon-like Peptide 1 Receptor neurons innervating the stomach may promote sleep following a meal. This proposal aims to couple recent genetic advances in targeting these functionally distinct subsets with in vivo optical recording of neuronal activity and optogenetic circuit manipulation. Specifically, hypoxia and food intake paradigms will be used to examine the state under which each neuronal subset is engaged using fiber-photometry and genetically encoded calcium sensors. It also aims to examine the capacity of each subset to promote wakefulness and attenuate seizures using optogenetic stimulation with channelrhodopsins and fiberoptic implants. The findings will provide fundamental insight into the efficacy of VNS and will provide a framework for future therapeutic innovation.