Hair cells in the adult mammalian cochlea cannot spontaneously regenerate after damage resulting in the permanency of hearing loss. Stem cells have been found to be present in the cochlea of young rodents; however, there has been little evidence for their existence into adulthood. We used nestin-CreERT2/tdTomato-reporter mice to trace the lineage of putative nestin-expressing cells and their progeny in the cochleae of adult mice. Nestin, an intermediate filament found in neural progenitor cells during early development and adulthood, is regarded as a multi-potent and neural stem cell marker. Other investigators have reported its presence in postnatal and young adult rodents; however, there are discrepancies amongst these reports. Using lineage tracing, we documented a robust population of tdTomato-expressing cells and evaluated these cells at a series of adult time points. Upon activation of the nestin promoter, tdTomato was observed just below and medial to the inner hair cell layer. All cells co-localized with the stem cell and cochlear-supporting-cell marker Sox2 as well as the supporting cell and Schwann cell marker Sox10; however, they did not co-localize with the Schwann cell marker Krox20, spiral ganglion marker NF200, or GFAP-expressing supporting cell marker. The cellular identity of this unique population of tdTomato-expressing cells in the adult cochlea of nestin-CreERT2/tdTomato mice remains unclear however these cells may represent a type of supporting cell on the neural aspect of the inner hair cell layer.

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Objective Evaluate the effects of α‐difluoromethylornithine (DFMO) on hearing thresholds as part of a randomized, double‐blind, placebo‐controlled trial. Methods Subjects were randomized and assigned to the control (placebo) or experimental (DFMO) group. DFMO or placebo were administered orally (500 mg/m2/day) for up to 5 years. Results Subjects taking DFMO had, on average, increased hearing thresholds from baseline across the frequency range compared to subjects in the control group. Statistical analysis revealed this was significant in the lower frequency range. Conclusions This randomized controlled trial revealed the presence of increased hearing thresholds associated with long‐term DFMO use. As a whole, DFMO may help prevent and treat certain types of cancers; however, it can result in some degree of hearing loss even when administered at low doses. This study further highlights the importance of closely monitoring hearing thresholds in subjects taking DFMO. Laryngoscope, 133:676–682, 2023