Project Summary/Abstract In response to RFA-MH-20-555, this Instrumentation grant application requests NIMH funds to purchase a customized state-of-the-art light-sheet fluorescence microscope system from the 3i Corporation (Intelligent Imaging Innovations, Inc.). The system has a unique custom-designed stage for imaging large cleared brain samples from mice, rats and non-human primates. This instrumentation will allow for high-speed, three-dimensional imaging of whole rodent brains and large non-human primate and human brain samples at single cell resolution. Our team has the required expertise. We have combined whole brain clearing and light sheet imaging to improve localization and quantification of virally mapped neurons across the entire mouse brain. Available turnkey imaging systems sold by LaVision/Miltenyi and Zeiss are not capable of large brain sample imaging. Our proposed 3i system has large sample imaging capability, superior automated performance and superior analysis capability based on hardware and software improvements developed by the 3i Corporation. Quantitative comparisons of connection patterns will be achieved with our analysis pipeline using automated quantification of brain wide fluorescent labeling, which allows for rapid quantification and analysis. We foresee that this enhanced microscope will allow us to effectively perform 3-D large scale neural circuit mapping in mouse, rat and monkey brain samples to better achieve the goals of our research projects funded by 9 active NIMH grant awards and 14 other NIH grant awards at UCI. This proposed instrument will be located at and managed by the core facility of the newly established UCI Center for Neural Circuit Mapping. We request funds to purchase the customized light-sheet microscope system. The UCI Center for Neural Circuit Mapping will ensure that the instrument is covered under full service contract through the estimated 5 years of instrument lifetime. Institutional commitment of the UCI School of Medicine will cover maintenance and software upgrade needs throughout the instrument lifetime. This new imaging system will significantly enhance data acquisition for our ongoing NIH- funded basic and translational research programs, which address the areas of high priority to NIMH.