Project summary Nausea is an unpleasant sensation of visceral malaise often accompanied by an involuntary urge to vomit. Nausea responses to toxin ingestion and infection are evolutionarily beneficial survival behaviors that avoid or expel toxins which may cause peripheral tissue damage. However, the sensation of nausea can also be maladaptive, as many treatments for cancer, diabetes, and other illnesses induce nausea as a major side effect, while current anti-emetic drugs have only limited efficacy. Known as the “chemoreceptors trigger zone” for nausea, the area postrema is a brain circumventricular sensory organ critical for nausea and vomiting. Neurons in the area postrema occupy a unique anatomical location with a deficient blood-brain barrier, and can be regulated by inputs from both the humoral routes and the gastrointestinal tract. However, little is known about how area postrema neurons contribute to the mechanisms of nausea and its related aversive behaviors. Using single-nucleus RNA-sequencing combined with genetic and behavioral studies, we have recently discovered a population of the area postrema neurons that, in response to emetic cues, induce nausea-associated aversive behaviors in mice. Here, I propose a multi-tiered approach, based on these preliminary findings, to investigate the humoral and vagal inputs to the chemosensory circuit of the area postrema and how they contribute to nausea. First, I will identify humoral cues that act through the area postrema aversion-promoting excitatory neuron types by testing a panel of nausea-inducing or anorexigenic humoral stimuli (Aim 1). Next, I will map and identify vagal inputs to the genetically defined area postrema excitatory neuron types using viral tracing and channelrhodopsin-assisted circuit mapping techniques (Aim 2). These experiments will reveal how vagal inputs and humoral cues can regulate the functions of the area postrema neurons which mediate nausea-associated aversive behaviors. Following this training, I will be poised to transition to the R00 phase of my career and establish a unique independent research program incorporating targeted cell-type manipulation in vomiting animal models (Aim 3). These studies will elucidate the cellular and neural mechanisms nausea and may guide the design of novel anti-emetic therapies. Central to this proposal is the mentorship of Dr. Stephen Liberles, an expert in internal sensations, Dr. Brad Lowell, an expert in functional circuit mapping, Dr. Frank Reimann, an expert in gut hormone signaling, Dr. Chenghua Gu, a leader in blood-brain barrier mechanisms, and Dr. Charles Horn, an expert in vomiting models and nausea physiology. They will provide career guidance and help me achieve my training goals. In my application I have outlined a comprehensive plan for acquiring the conceptual, technical, and professional skills that will enable my transition to an independent research position.