A. Schematic for the activation of an inducible ChR2-tdTomato or ChR2-EYFP gene targeted to the Rosa26 locus using Gad2Cre. B. Image of the Gad2Cre/Ai27 mouse cerebellum in a parasagittal plane, showing tdTomato (red) counterstained with Nissl fluorescence (green). DCN, deep cerebellar nuclei; VN, vestibular nuclei. C. Confocal images of boxed area C of the cerebellar cortex in B, showing strong ChR2-tdTomato fluorescence in both somas and dendrites of PCs (C1), Nissl staining with green fluorescent dye (C2), and their overlay (C3). GL, granular layer; ML, molecular layer; PCL, Purkinje cell layer. D. Confocal image of a DCN region in B (boxed area D) in a Z-stack (10.5 μm, D1) and in a single optical section (0.5 μm, D2), showing that cells are heavily innervated by ChR2-positive fibers. Scale bar: 500 μm in B, 25 μm in C, and 15 μm in D.