Fig. 5. Three-dimensional reconstruction of the afferent innervation in the organ of Corti at P3 and P6 in mice. Spatial resolution of the pathways for TMRD- (red) and peripherin- (green) labeled type I and type II neurites, respectively, under the hair cells. (A-C) At P3, both types of afferent nerve fibers were found under the OHCs, but their labeling was independent. TMRD labeling was found in the inner spiral plexus (ISP), forming a calyceal innervation to IHCs. In the outer spiral bundles (OSB) under the OHC, TMRD-labeled neurites were located above peripherin-immunopositive type II neurites in the hair cell region and osseous spiral lamina. (D-F) At P6, TMRD-labeled nerve fibers were largely confined to the ISP, with limited residual projection to the first row of OHCs. At this age, peripherin-labeled neurites formed three prominent rows of OSBs innervating the OHCs, after passing close to the basilar membrane below TMRD-labeled neurites. Scale bars: 10 µm. isp, inner spral plexus; osb, outer spiral bundle; osl, osseous spiral lamina; SGNI, type I spiral ganglion neurons; SGNII, type II spiral ganglion neurons.