Area Postrema Neurons that Mediate Nausea-Associated Behaviors

Project Summary Nausea is an unpleasant sensation of visceral malaise, with underlying molecular and neuronal pathways remaining mysterious. Current anti-nausea medications display variable success across patient cohorts, with nausea being the major reason why cancer patients cannot adhere to treatment regimens. New strategies for nausea intervention are needed, and may be enabled by a mechanistic understanding of how the sensation of nausea arises. Classical studies involving brain lesion and stimulation revealed a tiny brain structure termed the area postrema that mediates nausea responses to several visceral threats. The area postrema is a circumventricular organ containing brain-resident sensory neurons that are anatomically poised to receive inputs from both circulating factors and vagal afferents. However, the diversity of area postrema cell types and receptors was previously uncharted. In preliminary data, we built an area postrema cell atlas through single-nucleus RNA sequencing, revealing four excitatory and three inhibitory neuron types. Transcriptome analysis revealed signature genes expressed in different neuronal clusters, as well as many cell surface receptors that guide cellular responses. We generated Cre knock-in mice for genetic access to various area postrema neurons, and adapted approaches for cell-specific chemogenetics, optogenetics, ablation, imaging, and anatomical mapping. We found two excitatory neuron types (clusters 2 and 4) that provide powerful aversion teaching signals, and one (cluster 1) that does not. In Aim 1, we will use genetic tools to ask whether cell clusters 2 and 4, and the receptors they express, mediate behavioral responses to a panel of nausea-inducing stimuli. In Aim 2, we will measure the responses of cell clusters 2 and 4 to humoral factors, genetically defined vagal afferents, and various nausea- inducing stimuli. In Aim 3 we will investigate the roles of newly charted inhibitory neurons in the area postrema, which project locally and are excellent candidates to suppress nausea or other area postrema-mediated behaviors. Together, these experiments will reveal the basic organization of area postrema circuitry, and provide a framework towards understanding and therapeutically controlling nausea.