The Effects of Strial and Synaptic Degeneration on Age-Related Hearing Loss Using the Mongolian Gerbil as a Model

Age-related hearing loss, also known as presbycusis, is a complex condition affecting many people, with its underlying causes involving various parts of the hearing system. This research investigated how two specific changes inside the inner ear (cochlea) contribute to this hearing loss, using the Mongolian gerbil as a model known for similar age-related hearing issues. The study focused on the loss of connections (ribbon synapses) between inner hair cells and the auditory nerve, which are vital for sending sound information to the brain, and the breakdown (degeneration) of the stria vascularis, a tissue essential for maintaining the inner ear's fluid composition needed for hearing. Key findings revealed that synapse loss was most prominent on the modiolar side of the inner hair cells within the high-frequency hearing region, potentially affecting how sounds above the hearing threshold are processed. Degeneration of the stria vascularis was most severe in certain cell layers and particularly noticeable in the cochlea's apex and base (low and high-frequency regions). Furthermore, the severity of this strial degeneration, especially in the base, correlated with the degree of hearing loss. Overall, this research deepens our understanding of the mechanisms behind age-related hearing loss, highlighting the roles of both synapse loss and stria vascularis degeneration. It emphasizes the multifaceted nature of this condition and the need for further research to develop effective treatments.