Cochlear Base-Apex Differences in Cell-Death Pathways Following Exposure to Low-Frequency Noise

Abstract

Objective: To determine what death pathways are followed by noise-damaged outer hair cells (OHCs). Methods: Chinchillas were exposed to a 0.5-kHz octave band of noise for 24 h. Administration of trypan blue in vivo was used to stain nuclei in cells with leaky plasma membranes. After removing unbound dye, the cochleae were fixed, plastic- embedded then dissected to obtain flat preparations of the entire organ of Corti (OC). Using morphological criteria, dying and injured OHCs were classified as following an apoptotic or oncotic death pathway, or a pathway that was neither apop- totic nor oncotic. Results: The exposure caused scattered loss of OHCs in the apical OC and, sometimes, focal hair-cell losses in the basal OC. In the apical OC, many dying OHCs appeared to be following a death pathway that was different from apoptosis and oncosis. In the basal OC, oncotic OHCs were found at the edges of focal lesions. Conclusion: The morphological appearance of dying OHCs in the apical OC was distinct from those following an apop- totic or oncotic death pathway, suggesting that these OHCs were following a previously unidentified death pathway.