Cochlear aging after synaptopathic noise: age-noise interactions in hair cell loss and axonal degeneration.
Level 5 - mechanism / opinion, no new human data
Animal model (mouse) study of acoustic trauma and aging
PubMed 42378959 · doi:10.1016/j.heares.2026.109726
What was done
CBA/CaJ mice were exposed to an 8–16 kHz noise stimulus designed to cause an immediate 50% loss of inner hair cell synapses without substantial acute recovery. Noise-exposed and unexposed control mice were followed across survival times of 1 month, 6 months, 1 year, or 2 years. Using immunostaining and machine-learning pipelines, researchers quantified hair cells, synaptic ribbons, auditory-nerve fiber (ANF) peripheral axons, efferent fibers, ANF myelination, and nodal/heminodal structures.
What was found
The initial 50% ribbon loss persisted without recovery from 1 month to 1 year, with modest additional loss at 2 years. Peripheral axon loss was delayed, not exceeding age-matched controls until 6 months, and remaining only half of ribbon loss even at 2 years. Surviving ANFs retained spike-generator heminode structures despite synaptic disconnection. Inner hair cells in noise-exposed ears showed enhanced basal degeneration at later ages, and non-nodal myelin gaps increased with age in both groups.
Why it matters
Demonstrating that auditory-nerve peripheral axons persist for long periods after noise-induced synaptopathy indicates an extended temporal window for potential regenerative therapies.
Limits
The study was conducted exclusively in mice (CBA/CaJ), which limits direct extrapolation to human cochlear pathophysiology. Exact sample sizes per group were not reported in the abstract. Functional auditory assessments (e.g., ABR thresholds or wave I amplitudes) were not included in the abstract.
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