Figure 1.
Noise-induced functional declines in the young adult CBA/CaJ mouse AN. ABR wave I threshold shifts as a function of frequency showed dynamic alterations Im, and 1 d (D1), 3 d (D3), 7 d (D7), 14 d (D14), and 30 d (D30) after noise exposure. a–c, The mice were exposed to an 8–16 kHz octave-band noise at 100 (a), 106 (b), or 112 (c) dB SPL for 2 h. d, Mean ABR wave I threshold shifts at 11.3 kHz showed >20 dB declines at D3 to D30 after exposure to 106 and 112 dB noise, but recovered rapidly to near-normal levels after a 100 dB SPL exposure. Data from mice of both sexes are included in all physiological studies, as their ABRs are not significantly different before and after noise (data not shown). e–h, There was a marked loss of ribbon synapses under inner hair cells (IHCs) at frequency regions >22.3 kHz at both D1 and D14 after 106 dB SPL noise exposure. Ribbon synapses and IHC nuclei were visualized with anti-CtBP2 antibody (green) in control (e, top) and D1 noise-exposed mice (e, bottom) at the 8 and 45.2 kHz regions. f, Ribbon counts under IHCs revealed a >50% loss of CtBP2+ synapses at the 22.3 kHz and higher-frequency regions at both D1 and D14 after noise exposure. g, An electron micrograph from the 22.6 kHz region reveals vacuole-like spaces filled with debris (*) in the afferent terminal regions under an IHC at D1 after 106 dB exposure. h, An enlarged image of the region, identified by a black arrow in g illustrates two remaining ribbon synapses. i, Staining of hair cells with an antibody to PCP-4 revealed outer hair cell (OHC) losses in higher-frequency regions at D14 after a 106 dB exposure. j, PCP-4+ cell counts document OHC losses at 16 kHz and in higher-frequency regions at D14 after 106 dB noise exposure. k, Wave I amplitudes were reduced at 5.6, 11.3, 16, and 32 kHz at D3 after 106 dB noise exposure (*p < 0.05, **p < 0.01, and ***p < 0.001, Mann–Whitney test; Figure 1-1, exact statistical output). All data were presented as mean ± SEM.