Dye labeling of afferent and efferent fiber to the organ of Corti after central applications to cochlear nuclei (NeuroVue Orange, red) and crossing efferent fibers (NeuroVue Maroon, green). Whole mounted in glycerol and viewed within 1 h after mounting. (a, b) Single and (c, d) double labeling of afferents (red) and efferents (green) to the organ of Corti of a newborn mouse. Labeled spiral ganglion neurons (SG) send radial fibers (RF) to reach the IHC region with few fibers expanding to OHC. Efferents form intraganglionic spiral bundle (IGSB), join radial fibers and reach to IHC but only rarely to OHC. Bar = 100 μm in (a, b, d) 10 μm in (c). Modified after [23, 29]