AAV-Cre-mediated labeling of CST axons in Rosa26-tdTomato reporter mice. A, Coronal brain section of Rosa-tdTomato reporter mouse shows tdTomato⁺ cortical neurons as early as 1 week after AAV-Cre injection (n = 3). A′, Higher-magnification of the boxed areas in A. Schematic representation showing the transverse planes at which the images (C–F) are found in mouse brain and spinal cord. At 2 weeks following intracortical AAV-Cre injection in the Rosa26 reporter mice, tdTomato-labeled axons are seen in (C) motor cortex, (D) brainstem at the level of CST decussation, (E) cervical spinal cord, and (F) lumbar spinal cord. D′, Higher-magnification of the boxed areas in D. F, Low-magnification image of the coronal section at the lumbar level. F′, Higher-magnification of the boxed areas in F. Scale bars: A, C, 1000 μm; D–F, 500 μm.