Figure 8.

Local delivery of D-JNKI-1 into the scala tympani protected against acoustic trauma-induced hair cell loss. A, B, Scanning electron micrographs of areas of acoustic trauma damage in cochleae from the same noise exposed animal. In the damaged area of the contralateral unperfused cochleae, the most severe damage was observed in the row of IHCs (I) and the first row of OHCs (O), with a gradation of damage in the second and the third rows of OHCs (A). Note that direct delivery of 10 μm D-JNKI-1 into the scala tympani of the cochlea effectively prevented acoustic trauma-induced hair cell loss (B). Scale bar, 15μm. C, D, Quantitative analysis of hair cell damage consisted of counting all hair cells along the entire length of the cochlear ducts. Cochleograms represent the mean survival of hair cells as the function of the distance from the apex (in millimeters) in contralateral unperfused cochleae (C; n = 3) and in the 10μm D-JNKI-1-perfused cochleae (D; n = 3) of the same animals. Noise exposure caused a narrow band of hair cell trauma in the cochlea located 14–16 mm from the apex of the cochlea. Ninety-one percent of the IHCs (white circles) and 43% of the OHCs were lost from this area by 30 d after the initial acoustic trauma in the unprotected cochleae (C). Note the typical gradient of loss from the first row (black circles) to the second (dark gray circles) and third (light gray circles) rows of OHCs. In contrast, only 6% OHCs and 11.9% IHCs were lost as a consequence of acoustic trauma if cochleae that were treated with local application of a 10 μm solution of D-JNKI-1 (D).