RT Journal Article SR Electronic T1 Optical clearing of living brains with MAGICAL to extend in vivo imaging JF bioRxiv FD Cold Spring Harbor Laboratory SP 507426 DO 10.1101/507426 A1 Kouichirou Iijima A1 Takuto Oshima A1 Ryosuke Kawakami A1 Tomomi Nemoto YR 2019 UL http://biorxiv.org/content/early/2019/01/09/507426.abstract AB To understand brain functions, it is important to observe directly how multiple neural circuits are performing in living brains. However, due to tissue opaqueness, observable depth and spatiotemporal resolution are severely degraded in vivo. Here, we propose an optical brain clearing method for in vivo fluorescence microscopy, termed MAGICAL (Magical Additive Glycerol Improves Clear Alive Luminance). MAGICAL enabled two-photon microscopy to capture vivid images with fast speed, at cortical layer V and hippocampal CA1 in vivo. Moreover, MAGICAL promoted conventional confocal microscopy to visualize finer neuronal structures including synaptic boutons and spines in unprecedented deep regions, without intensive illumination leading to phototoxic effects. Fluorescence Emission Spectrum Transmissive Analysis (FESTA) showed that MAGICAL improved in vivo transmittance of shorter wavelength light, which is vulnerable to optical scattering thus unsuited for in vivo microscopy. These results suggest that MAGICAL would transparentize living brains via scattering reduction.