FIG. 4.

Synaptic degeneration in noise-exposed ears is seen as loss, disorganization, and dysmorphology of synaptic ribbons. Confocal images of the IHC area in control (A–C) and noise-exposed (D–F) ears immunostained for synaptic ribbons (anti-CtBP2, red) and ANF terminals (anti-NF, green; C, F only). The exposed ear was harvested 10 days after the 106-dB octave-band noise. For both ears, images were obtained from the 22-kHz region of the cochlea. A, D Maximum projections in the x–y-plane (see Fig. 1) from image stacks focused through the entire synaptic regions of seven to eight adjacent IHCs: Their nuclei stain faintly with anti-CtBP2. Arrowheads in D indicate abnormally large ribbons in the exposed ear. B, E The image stacks from A and D are rotated to view as y–z projections, i.e. as a cross section through the sensory epithelium (Fig. 1). A dotted line in B divides “modiolar” and “pillar” sides of the IHCs. C, F Same image stack as B, E, but with the green (anti-NF) channel added. Arrowheads in F indicate abnormally large CtBP2-positive puncta at circumnuclear locations where ANF terminals are not found. Scale bar in C applies to all panels.