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Updated: May 8, 2026
08:25
Immunolabeling and Counting Ribbon Synapses in Young Adult and Aged Gerbil Cochleae
Published on: April 21, 2022
Age-related cochlear synaptopathy: an early-onset contributor to auditory functional decline
Yevgeniya Sergeyenko1, Kumud Lall, M Charles Liberman
1Department of Audiology, Massachusetts Eye and Ear Infirmary, Boston, MA, USA.
Summary
Age-related hearing loss in mice shows significant cochlear synaptic and neural degeneration, even with normal hearing thresholds. This progressive damage occurs before changes in hair cells, impacting auditory function.
Area of Science:
- Neuroscience
- Auditory Neuroscience
- Gerontology
Background:
- Aging listeners often struggle with speech comprehension in noisy environments.
- Central and cognitive factors are typically implicated in age-related auditory decline when peripheral hearing is normal.
- Previous research indicated cochlear afferent synaptic loss and nerve degeneration in noise-exposed ears with normal thresholds.
Purpose of the Study:
- To investigate age-related cochlear synaptic and neural degeneration in mice without prior noise exposure.
- To correlate structural changes with auditory function across the lifespan.
- To identify potential non-invasive biomarkers for age-related auditory changes.
Main Methods:
- Assessed cochlear hair cell and neuronal function using distortion product otoacoustic emissions and auditory brainstem responses.
- Quantified hair cells, cochlear neurons, and synaptic structures (presynaptic ribbons, postsynaptic glutamate receptors) via microscopy.
- Examined cochlear tissue from mice aged 4 to 144 weeks.
Main Results:
- Significant cochlear synaptic loss was observed progressively from youth to old age, present throughout the cochlea.
- This synaptic degeneration preceded age-related changes in hearing thresholds and hair cell counts.
- Cochlear nerve loss was found to parallel synaptic loss, with a delay of several months.
Conclusions:
- Age-related cochlear synaptic and neural degeneration occurs independently of noise exposure and hair cell loss.
- This "hidden hearing loss" may underlie age-related difficulties in understanding speech.
- Auditory brainstem responses may offer non-invasive insights into cochlear synaptopathy, aiding clinical translation.
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