Cochlear histopathology in macaques after noise-induced temporary threshold shifts

Area of Science:

• Otoacoustic emissions
• Auditory neuroscience
• Hearing research

Background:

• Temporary noise-induced hearing loss was once thought benign.
• Recent studies link temporary threshold shifts to lasting cochlear damage, including cochlear synaptopathy.
• Primate auditory systems show higher noise resistance, making their response to noise exposure less understood.

Purpose of the Study:

• To investigate the long-term effects of noise exposure causing temporary hearing loss on cochlear histopathology in macaque monkeys.
• To understand the cochlear sequelae of temporary threshold shifts in nonhuman primates.

Main Methods:

• Macaque monkeys were exposed to 120 dB SPL noise for 4 hours.
• Cochlear histopathology was assessed at 2 and 10 months post-exposure.
• Evaluated hair cell integrity, inner hair cell synapses, and efferent innervation.

Main Results:

• No significant loss of hair cells, inner hair cell synapses, or cholinergic efferent innervation was found at 2 and 10 months post-exposure.
• Enlargement of synaptic ribbons in both inner and outer hair cells was observed.
• Transient loss of outer hair cell ribbons was also noted.

Conclusions:

• Single noise exposures causing temporary threshold shifts did not lead to significant hair cell or synapse loss in macaques.
• Chronic enlargement of hair cell ribbons suggests a potential long-term adaptation or consequence of noise exposure.
• Findings provide insights into the variable susceptibility and cochlear effects of noise exposure in nonhuman primates.