Fig. 1. Double labeling of TMRD and peripherin distinguished the adult-like innervation pattern of the type I and type II SGN afferent neurite projections within the P6 mouse cochlea. Maximum intensity projection of confocal images demonstrate the independent labeling of the type I and type II SGN by TMRD (red) and peripherin immunofluorescence (green), respectively. TMRD-labeled fibers in the intraganglionic spiral bundles, running around the perimeter of Rosenthal's canal, are consistent with TMRD also labeling the efferent fibers at this mature stage (see Fig. 6). The SGN cell bodies and their associated neurites innervating the hair cells are shown in whole mounts (A) and in cross sections (B,C). (A) Overview of basal turn of the cochlea. (B,C) Details of the sensory hair cell region and the spiral ganglion in the mid-turn of the cochlea. (B) TMRD-labeled neurites innervating the inner hair cells at inner spiral plexus, with additional neurites extending towards outer hair cells. The type I fibers traveled above the peripherin-expressing type II fibers. The latter bypassed the IHC region and traveled along the basilar membrane to form three rows of outer spiral bundles, which innervated the OHCs. (C) TMRD and peripherin immunofluorescence labeled the type I and type II SGNs, respectively. TMRD-labeled neurons were distributed throughout the ganglion, while peripherin-labeled neurons were found close to the intraganglionic spiral bundles. Scale bars: 50 µm in A; 10 µm in B,C. igsb, intraganglionic spiral bundles; ihc, inner hair cells; isp, inner spiral plexus; ohc, outer hair cells; osb, outer spiral bundles.