activeDISCO enables large-scale exploration of human brain anatomy by light sheet microscopy

Tissue clearing and light microscopy of large human brain specimens remains challenging due to factors including accumulation of pigments and lengthy protocols required to achieve a high level of optical clarity. In this study we present a novel solvent-based clearing protocol capable of clearing intact human brain regions such as the hippocampus and cerebellar hemispheres in around 12 days. We term this protocol “activeDISCO”, as it utilises active dehydration by the ketal 2,2-dimethoxypropane which rapidly reacts with water, therefore expediting the clearing process. We subsequently performed imaging of autofluorescence using meso-aspheric based light sheet microscopy and were able to reconstruct intact brain regions in three dimensions, including high-resolution visualisation of structures such as the dentate gyrus and Horn of Ammon in the hippocampus. This work represents a tool with diverse applications in the fields of neuroscience and medicine; and sets a baseline for further improvements to active dehydration based clearing protocols and imaging possibilities. Chemical dehydration of human brain specimens by 2,2-dimethoxypropane facilitates rapid tissue clearing of large human brain specimens, allowing light sheet microscopy and volumetric reconstruction of regions such as the intact hippocampus.