Project Summary/Abstract We are requesting funds to support the purchase of an ASI Dual Selective Plane Illumination Microcopy for Cleared Tissue (ct-dSPIM) Microscope System. This instrument will be housed within the Neuroscience Microscopy Core (NMC) at the University of North Carolina (UNC) School of Medicine. The mandate of this core facility is to provide a full spectrum of advanced systems for cellular and molecular imaging of fixed and live samples, to implement new imaging technologies, and to offer training, consultation, data analysis, image processing, and centralized technical expertise to support the imaging needs of UNC and other researchers. High-resolution imaging to discriminate between cells in closely-packed regions of the brain is an essential service provided by the center. The NMC currently does not support a light-sheet microscope. Multiple competitive demos with NMC samples have determined that the requested ct-dSPIM system is best suited for imaging iDISCO-cleared mouse brain tissue at high-resolution. The requested system is complementary to the current LaVision Lightsheet microscope, which is currently limited by lower-resolution hardware capabilities (see Letter of Support from Dr. Ariel). The need for this instrument is demonstrated in this application with multiple diverse NIMH supported projects in fields including; Neurobiology, Genetics, Pathology, Psychology, Cell Biology, Developmental Biology, and Cancer Biology. We describe 10 NIMH-funded projects that require the use of high-resolution xy and optical sectioning provided by the ASI ct-dSPIM, in order to distinguish fine cellular features with high spatial resolution within large densely packed volumes (e.g., extended circuitry throughout an adult mouse brain, in densely packed regions of a mouse embryonic brain, and for detailed imaging of large human brain tissue) and require imaging of large tissues in their original full 3D context. Since the NMC commenced operations 18 years ago, it has become an integral part of the medical research community, currently supporting over 60 NIH-funded research projects. Acquisition of an ASI Dual Selective Plane Illumination Microcopy for Cleared Tissue (ct-dSPIM) Microscope System is an essential addition to the repertoire of instrumentation available to NMIH-funded investigators in order to not only maintain the current high-level of critical support for NIMH-funded projects, but also to enhance their research by providing modern imaging capabilities.