Frequency-specific and level-dependent alteration in cochlear nucleus following prolonged moderate noise exposure

Moderate noise exposure is increasingly recognized as a potential risk factor for inducing subtle auditory plasticity. To date, its effects on the cochlear nucleus (CN), the first central relay of auditory input, remain poorly understood. To investigate how prolonged exposure to a moderate-level pure tone (65 dB SPL for 1 h, TE₆₅) alters neuronal receptive fields and auditory responses in the CN, extracellular recordings were obtained before, immediately after and up to 6 h following exposure in 33 female mice. We found that TE₆₅ produced robust, frequency-specific changes in CN. Response thresholds increased and spike activity decreased at the exposure frequency and at higher frequencies, indicating neural suppression, whereas thresholds decreased and responses increased at lower neighbouring frequencies, indicating hyperactivity. These effects were most prominent at low to moderate sound levels near threshold. Receptive-field alterations showed partial recovery within 6 h, with significantly greater recovery in animals placed in an acoustically enriched environment. These findings demonstrate rapid reorganization of CN receptive fields following moderate noise exposure, suggesting contributions from both altered peripheral input and intrinsic CN circuitry, and highlighting the importance of post-exposure acoustic environment in functional recovery.