PROJECT SUMMARY Rapid advances over the past decade have generated novel technologies to image tissue at both ultrastructural resolution and in three dimensional volumes. Such technologies have provided new ability to probe the ultrastructure of cells and tissues and have thus been a boon for both cell biologists and neurobiologists. One such technique is Serial Block Face Scanning Electron Microscopy (SBFSEM), which consists of an ultramicrotome mounted within the chamber of a scanning electron microscope. In SBFSEM, samples are prepared, stained and mounted in resin as they would be for traditional transmission electron microscopy (TEM). However, instead of the labor- and time-intensive process of creating, collecting, imaging and registering images from ultra-thin sections (~40nm) in TEM, the resin- embedded tissue blocks are inserted into the SBFSEM chamber, the block face is imaged by collecting the back-scattered electrons, the upper-most surface of the block-face is removed by the ultramicrotome, and without displacing the resin block, another image of the block-face is obtained. Repeating this process allows the rapid capture of hundreds to thousands of serial images that have near-TEM resolution (1-5 nm in the x-y axis, depending on the SBFSEM make and model) and are captured in register. Large volumes of three-dimensional data that previously took months or years to obtain and assemble can now be produced in a day with SBFSEM. A group of highly productive biomedical researchers at Virginia Tech have identified this methodology as a necessary component of their NIH- funded research projects. Because no SBFSEM instrument is present at Virginia Tech, these groups have thus far outsourced the generation of SBFSEM datasets to Renovo Neural, Inc. However, outsourcing SBFSEM dataset generation is expensive and slow, which ultimately impedes progress on these investigators' NIH-funded research projects. For this reason, these researchers are requesting funds to purchase a Thermo Fisher Apreo VolumeScope SEM for Virginia Tech. This instrument would be installed at the Virginia Tech Fralin Biomedical Research Institute (FBRI), a world-class biomedical research institute, where the majority of the Major Users identified in this proposal are located. Furthermore, leadership at FBRI is committed to financially support an imaging facility that houses the Thermo Fisher Apreo VolumeScope SEM.