Cellular and circuit mechanisms of the therapeutic action of inhaled nitrous oxide in rodent models of chronic stress

This administrative supplement request is submitted in support of R35GM151160-01, a project focused on elucidating the cellular and circuit mechanisms by which inhaled nitrous oxide exerts rapid antidepressant effects in rodent models of chronic stress. The parent award received a highly favorable impact score (20), reflecting its innovative use of in vivo imaging in awake, behaving mice to study the actions of the world's oldest anesthetic. To date, we have performed over 600 in vivo imaging experiments revealing that nitrous oxide rapidly activates deep-layer excitatory pyramidal neurons, particularly layer 5 (L5) neurons in the prefrontal cortex. Using Cre-driver lines and chemogenetic tools, we have demonstrated that L5 neurons are both necessary and sufficient for mediating nitrous oxide's antidepressant-like effects. These neurons are also modulated by serotonergic psychedelics via 5HT-2A receptors, suggesting a potential shared mechanism between anesthetics and psychedelics. To understand how L5 neurons engage downstream mood-related circuits—such as the striatum, nucleus accumbens, thalamus, hypothalamus, amygdala, and ventral tegmental area—we require high- resolution anatomical imaging of both input and output projections. Toward this goal, we have strategically acquired approximately 60% (~$120,000) of a modular confocal microscope system. However, the lab currently lacks access to a functional fluorescence microscope for fixed-tissue analysis. With this supplement request, we seek $82,086 to complete the system, enabling four-channel high-speed acquisition and large-scale tiled reconstructions essential for circuit mapping. The completed system will significantly enhance the R35-funded research by allowing precise anatomical visualization of the circuits underlying nitrous oxide's therapeutic effects and will further support related mechanistic studies of rapid-acting antidepressants.