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Noise-induced Cochlear Synaptopathy with and Without Sensory Cell Loss
Katharine A Fernandez1, Dan Guo1, Steven Micucci2
1Eaton-Peabody Laboratories, Massachusetts Eye & Ear, Boston, MA 02114, USA; Department of Otolaryngology-Head & Neck Surgery, Harvard Medical School, Boston, MA 02115, USA.
Neuroscience
|December 31, 2019
Summary
Noise-induced cochlear synaptopathy, or synapse loss, can occur without sensory hair cell damage. Varying noise exposure levels and durations reveals complex injury patterns affecting neural responses.
Area of Science:
- Neuroscience
- Otolaryngology
- Audiology
Background:
- Noise exposure causes hearing loss through hair cell damage.
- Cochlear synaptic loss precedes hair cell loss in some noise exposures.
- Understanding noise dose effects on cochlear synaptopathy is crucial.
Purpose of the Study:
- To investigate how cochlear synaptopathy and its mechanisms change with varying noise exposure doses.
- To assess the relationship between noise dose, synaptic loss, and hair cell injury.
Main Methods:
- Exposed adult CBA/CaJ mice to a range of noise levels (85-112 dB SPL) and durations (15 min to 8 h).
- Measured cochlear physiologic (thresholds, neural responses) and histologic (hair cell, synapse loss) outcomes.
- Analyzed data based on noise dose, exposure duration, and resulting injury patterns.
Main Results:
- Noise exposure caused temporary and permanent threshold shifts.
- Synapse loss occurred early and did not directly correlate with threshold shifts.
- Outer hair cell loss was observed at high noise doses, while inner hair cell loss was minimal.
- Synapse loss peaked around 50% and declined with permanent hair cell injury.
- Persistent neural response declines occurred with synaptopathy; exaggerated declines with outer hair cell injury.
Conclusions:
- Cochlear synaptopathy can occur independently of sensory hair cell loss.
- Noise dose and patterns of cellular injury dictate the extent and outcome of synaptopathy.
- Synaptopathy influences neural response deficits, with outer hair cell damage exacerbating these effects.
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