Abstract Neuropeptides have a critical role in modulating sleep and wakefulness and offer unique opportunities to treat sleep disorders. Among them, Neuropeptide S shows outstanding features: i) Administration of NPS increases wakefulness and reduces anxiety; ii) Neuropeptide S knockout mice show display increased NREM and anxiety; iii) Mutations of the NPS receptor that give rise to overactive signaling result in short sleep in humans and mice; iv) Expression of NPS is restricted to a few thousand neurons distributed across five main clusters in the basomedial amygdala, dorsomedial thalamus, Kolliker-Fuse/parabrachial area, pericoerulear region and nucleus incertus. These regions have been directly or indirectly associated with arousal and anxiety, but the detailed mechanisms as to how the modulate sleep architecture are unknown. We have recently generated a new line of mice expressing cre recombinase under the control of the endogenous NPS gene promoter (NPS-IRES-cre mice). Here we propose to use these mice and a combination of circuit mapping tools to decipher the mechanisms by which NPS modulates sleep/wake cycle. First, we will use viral-mediated tracing to determine if the five clusters of NPS+ neurons are interconnected, and their anatomical relationship with known arousal circuits. In a second aim, we will use fiber photometry to determine the activity profiles of the five clusters of NPS cells across the sleep/wake cycle and in response to stress and positive emotional stimuli. We will also determine which arousal circuits are activated by optogenetic stimulation of NPS, and which circuits activate NPS neurons. We will also assess whether NPS stimulation affects locomotor activity, anxiety, core body temperature and other physiological variables that may confound the arousal effect. In aim 3, we will test whether individual clusters of NPS neurons are necessary for NPS’s effects on sleep by using opto and chemogenetic inhibition. Finally, we will use a CRISPR-based approach to introduce NPS gene mutations in individual NPS+ cell clusters and determine whether NPS release in these brain regions is essential to control sleep/wake architecture and anxiety behaviors. The results from these experiments will shed new light into the function of NPS and NPS+ neurons, as well as the interconnection between them and arousal circuits. These data may lead to improved treatments of neuropsychiatric disorders associated with imbalances in arousal systems.