Fig. 6. TMRD, peripherin and ChAT labeling in the mouse organ of Corti between P0 and P6. Single confocal optical sections overlaid with (A-C,G-I,M-O) and without (D-F,J-L,P-R) transmitted-light images demonstrate the relationship between the labeled afferent and efferent nerve fibers and the cellular structures in the organ of Corti. (A-F) P0 organ of Corti showing peripherin- (green, type II SGNs) and TMRD- (red, type I SGNs) labeled neurites innervate both the IHCs and OHCs; no significant ChAT labeling was detected. (A,D) Peripherin-labeled type II neurites branch to innervate the IHCs, with primary neurite processes passing along the basilar membrane to innervate the three rows of OHCs. (B,E) Type I SGN fiber terminals make close contact with the basal and lateral membrane of the IHCs. (G-L) P3 organ of Corti shows both TMRD and peripherin labeling in the three rows of outer spiral bundles (OSBs); TMRD and ChAT labeling, but not peripherin labeling in the inner spiral plexus (ISP) under the IHCs. (G,J) Peripherin labeling is now absent under the IHCs. (H,K) TMRD labeling is more restricted to the basolateral region of the IHCs compared with P0 (see B,E). (I,L) Weak ChAT signal in the ISP. (M-R) Adult-like primary auditory afferent innervation pattern in the P6 organ of Corti with increased efferent nerve fiber labeling. (M,P) Peripherin-labeled neurites, as for P3, confined to the OSBs. (N,Q) TMRD-labeled neurites are predominantly found under the IHCs, while only minimal labeling was detected in the OSBs. Some TMRD-labeling would be attributed to efferent nerve fibers. (O,R) ChAT immunolabeling in both the ISP and OSBs. Scale bar: 10 µm. bm, basilar membrane; dc, Deiters' cell; isp, inner spral plexus; osb, outer spiral bundle; PPH, peripherin; SGNI, type I spiral ganglion neurons; SGNII, type II spiral ganglion neurons.