immunolabeling-counting-ribbon-synapses-young-adult-aged-gerbil

Immunolabeling and Counting Ribbon Synapses in Young Adult and Aged Gerbil Cochleae

The loss of ribbon synapses connecting inner hair cells and afferent auditory nerve fibers is assumed to be one cause of age-related hearing loss. The ...

Carl von Ossietzky University Oldenburg

Loss of inner hair cell-auditory nerve fiber synapses is considered to be an important early stage of neural presbyacusis. Mass potentials, recorded at the cochlear round window, can be used to derive the neural index (NI), a sensitive measure for pharmacologically-induced synapse loss. Here, we investigate the applicability of the NI for measuring age-related auditory synapse loss in young-adult, middle-aged, and old Mongolian gerbils. Synapse loss, which was progressively evident in the 2 aged groups, correlated weakly with NI when measured at a fixed sound level of 60 dB SPL. However, the NI was confounded by decreases in single-unit firing rates at 60 dB SPL. NI at 30 dB above threshold, when firing rates were similar between age groups, did not correlate with synapse loss. Our results show that synapse loss is poorly reflected in the NI of aged gerbils, particularly if further peripheral pathologies are present. The NI may therefore not be a reliable clinical tool to assess synapse loss in aged humans with peripheral hearing loss.

Sonny Bovee

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