Peripherin immunolabelled type II spiral ganglion neurons (SGNs) are absent at the apex of the cochlea and between P1 and P7 their number reduces in the middle and basal regions. (A-I) Single plane confocal images of β-tubulin (green) and peripherin (red) double immunolabeling of SGNs in the most apical region (apex) (A,D,G), and in the middle (B,E,H) and basal (C,F,I) turns in sectioned cochleae from P1 (A-C), P7 (D-E) and P21 (G-I) mice. Marked areas are shown in insets and detail β-tubulin and peripherin immunolabeling of SGNs. β-Tubulin and peripherin double immunolabeled type II SGNs are absent from the apex of P1 (A), P7 (D) and P21 (G) mouse cochleae. Many of these double-immunolabeled type II SGNs are present in the middle and basal turns in P1 cochlea (B,C); however, this number is reduced in P7 (E,F) and P21 (H,I) cochleae. The level of β-tubulin expression in the type II SGN soma appears reduced in P7 and P21 cochleae, resulting in relatively stronger red signal (peripherin channel). Scale bars: 50 μm.