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Cochlear histopathology in macaques after noise-induced temporary threshold shifts
J A Mondul1, C A Mackey1, A N Conner1
1Vanderbilt Neuroscience Graduate Program, Vanderbilt University, Nashville, TN 37212, USA; Vanderbilt Department of Hearing and Speech Sciences, Vanderbilt University Medical Center, Nashville, TN 37212, USA.
Hearing Research
|March 12, 2026
Summary
Temporary noise-induced hearing loss can cause lasting cochlear damage. In macaques, noise exposure led to enlarged hair cell ribbons, but no loss of hair cells or synapses long-term.
Area of Science:
- Auditory Neuroscience
- Ototoxicology
- Comparative Anatomy
Background:
- Temporary noise-induced threshold shifts were once considered harmless.
- Recent research links these shifts to persistent cochlear histopathology, including cochlear synaptopathy.
- The effects on humans and nonhuman primates, who are more noise-resistant, are not well understood.
Purpose of the Study:
- To investigate the long-term cochlear histopathological effects of noise exposure causing temporary threshold shifts.
- To examine these effects in macaque monkeys, a relevant model for human auditory research.
Main Methods:
- Macaque monkeys were exposed to noise causing temporary threshold shifts.
- Cochlear tissues were analyzed at 2 and 10 months post-exposure.
- Evaluated hair cell counts, inner hair cell synapses, efferent innervation, and hair cell ribbon morphology.
Main Results:
- Cochlear histopathology varied among subjects, mirroring human susceptibility.
- No significant loss of hair cells, inner hair cell synapses, or efferent innervation was observed at 2 or 10 months.
- Significant enlargement of both inner and outer hair cell ribbons was found.
Conclusions:
- Single noise exposures causing temporary threshold shifts did not result in hair cell or synapse loss in macaques at long survival times.
- Enlarged hair cell ribbons suggest a potential underlying cellular adaptation or pathology.
- Findings offer insights into the cochlear consequences of temporary threshold shifts in primates.
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