PROJECT SUMMARY Central Nervous System disorders have proven to be among the most difficult of diseases to treat and have placed an enormous burden on society. A major contributing factor to this situation is that currently we often cannot distinguish between normal and pathological states since we do not possess even a basic 'ground truth' map of how neurons and other cells are arranged at the nanoscale level for representative pieces of neuronal tissue. Extensive efforts are underway to build these fine scale structural maps of mammalian brains with the hope that these will lead to an understanding of the how brain ultimately functions and how best to target therapeutics. However the problem is immense as a single cubic mm of brain tissue contains about 100,000 neurons and roughly a billion synaptic connections. The overwhelming majority of these structural details are too small to be resolved with even the best optical microscopes and current super resolution approaches lack the necessary throughput. We propose to meet this challenge by developing an ultra-high speed Serial Two-Photon Tomography system that combines high speed resonant scanning with TissueVision's novel multi-focal microscopy and which will be able to quickly image 3D volumes of neuronal tissue with sub-micron resolution. With our collaborators at MIT in the Ed Boyden group, we will apply this system to study the CNS cytoarchitecture at the nanoscopic level by using a new technique the Boyden lab has developed called Expansion Microscopy (ExM) that physically expands tissue up to 20-fold to provide an effective nanoscale (~25nm) view into the structure of macroscopic portions of the CNS. For this project, we have put together a world class team of experts from TissueVision and MIT who have deep expertise with optics and neuroscience as well as a successful track record of commercializing biomedical imaging systems for the neuroscience market. While our focus here is on nanoscale imaging of CNS tissues, the device we will develop will represent a major tool for a variety of brain mapping efforts including whole brain neuronal circuit analysis and mesoscale mapping efforts.