Abstract:Objective To demonstrate distinct patterns of cochlear hair cell loss between aging and genetic defects of deafness-associated genes. Methods Vervet monkeys, chinchillas, guinea pigs, Sprague-Dawley rats, CBA/CaJ mice, C57BL/6 mice, DBA/2J mice, and dwarf gray mutant homozygous (dwg/dwg) mice with different ages were used as experimental subjects. The cochlear basilar membranes of all tested animals were prepared as flat surface preparations. All inner and outer hair cells on the cochlear basilar membrane were counted along entire length of the basilar membrane. The hair cell counts were then input into the cochleogram software to generate the averaged cochleogram for each group. Results In natural aging animals, cochlear hair cell loss occurred in the elderly stage. In contrast, in the deaf-related genetic defective animals, cochlear hair cell loss occurred in the younger stage or even in the childhood. The cochlear hair cell loss in natural aging animals was always evenly distributed or expanded from the cochlear apical turn to the basal turn. However, the cochlear hair cell loss in the animals with genetic defects of deafness-associated genes often manifested an extension from the cochlear basal turn to the apical turn. Conclusion The age-related cochlear hair cell loss on elderly animals without deafness-related genetic defects reflects the degenerative lesions caused by real aging, while the age-related cochlear hair cell loss on young animals with deafness-related genetic defects is likely related to the genetic defects of deafness-related genes.
