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Noise-induced cochlear synaptopathy in rhesus monkeys (Macaca mulatta)
M D Valero1, J A Burton2, S N Hauser2
1Eaton-Peabody Laboratories, Massachusetts Eye and Ear Infirmary, Boston, MA 02114, USA; Department of Otolaryngology, Harvard Medical School, Boston, MA 02115, USA.
Hearing Research
|July 18, 2017
Summary
Noise-induced cochlear synaptopathy, a loss of auditory nerve fiber synapses, occurred in non-human primates. This damage impacts hearing-in-noise and temporal processing, even with temporary threshold shifts.
Area of Science:
- Neuroscience
- Auditory Neuroscience
- Ototoxicology
Background:
- Cochlear synaptopathy, damage to synapses between auditory nerve fibers (ANFs) and inner hair cells (IHCs), can be caused by noise, aging, or ototoxicity.
- While rodents show significant synapse loss after noise exposure, non-human primates' susceptibility to synaptopathy is less understood.
- A non-human primate model is crucial for developing diagnostics and therapeutics for hearing loss.
Purpose of the Study:
- To investigate cochlear innervation and the effects of acoustic overexposure in rhesus macaques.
- To establish a non-human primate model for studying noise-induced cochlear synaptopathy.
Main Methods:
- Young adult rhesus macaques were exposed to narrow-band noise (2 kHz) for 4 hours at various sound pressure levels.
- Cochlear function was assessed using auditory brainstem responses (ABRs) and otoacoustic emissions (OAEs) for up to 8 weeks post-exposure.
Main Results:
- Moderate synapse loss (12-27%) occurred after temporary threshold shifts (TTS), with minimal hair cell damage.
- Severe synapse loss (50-75%) was observed in IHCs following permanent threshold shifts (PTS) and significant hair cell loss.
- Primates required higher noise levels for PTS than rodents, indicating greater resistance to hair cell loss.
Conclusions:
- Noise-induced cochlear synaptopathy occurs in non-human primates, similar to rodents.
- Synaptopathy can precede significant hair cell loss, potentially explaining hearing-in-noise deficits.
- Rhesus macaques provide a valuable model for studying synaptopathy and developing interventions for hearing loss.
