Three-Photon Microscope for Fluorescence and Phosphorescence Lifetime Imaging - Project Summary/Abstract This application requests funds for purchase of a three-photon microscopy system with fluorescence and phosphorescence intensity and lifetime imaging capabilities that will constitute a shared facility in the Neurophotonics Center at the Boston University (BU). Three-photon microscopy is becoming an important tool for biomedical research, providing the ability to image intact brain tissue to depths of up to >1.2 mm, with sub- micron resolution. We have assembled an outstanding broadly based group of NIMH- and other NIH-funded Users from multiple departments at BU with a major focus on using model organisms to understand how neuronal circuits control behavior. On the pre-clinical side, our Users study how these circuits go awry in neuropsychiatric and neurological disease. We expect the User base to grow, as new projects get funded, and as we attract additional investigators. The proposed research projects require deep penetration of light in tissue, a requirement that will be addressed by the proposed state-of-the-art three-photon microscopy multi-user facility. The requested system was chosen because it allows versatile imaging of deep brain’s structure and function under in vivo conditions, supports three-photon Fluorescent Lifetime Imaging Microscopy (3p-FLIM) and three-photon Phosphorescence Lifetime Imaging Microscopy (3PLM), has high image quality and is compatible with the existing software and hardware platforms at the Center. Administratively, the proposed instrument will be part of the Neurophotonics Center. The Center provides comprehensive imaging facilities for users at BU and the greater Boston area, with established infrastructure for resource administration, recharge mechanisms, and User training. The proposed three-photon instrument is complementary to the existing neuroimaging modalities at the Center such as two-photon and confocal microscopes and will provide an essential and central component of BU’s investment in neuroscience, neuroimaging and neuroengineering. Further, the proposed facility will serve as a collaboration vehicle strengthening multidisciplinary ties across BU’s departments and between the Charles River campus and School of Medicine. In summary, the proposed cutting-edge three-photon microscopy facility will provide NIH-funded investigators at BU with an essential tool to study the intricate pathways involved in deep brain function, features of neuropsychiatric and neurological disease progression, disease diagnosis and treatment. These studies will impact our understanding of normal and pathological brain function, opening new avenues for treatment and prevention of human disease. The proposed facility is also expected to play a significant role in the training and teaching efforts at BU.