Pre-exposure to Lower-Level Noise Mitigates Cochlear Synaptic Loss Induced by High-Level Noise

Abstract

The auditory sensory organs appear to be less damaged by exposure to high-level noise that is presented after exposure to non-traumatizing low-level noise. This phenomenon is known as the toughening or conditioning effect. Functionally, it is manifested by a reduced threshold shift, and morphologically by a reduced hair cell loss. However, it remains unclear whether prior exposure to toughening noise can mitigate the synaptic loss induced by exposure to damaging noise. Since the cochlear afferent synapse between the inner hair cells and primary auditory neurons has been identified as a novel site involved in noise-induced cochlear damage, we were interested in assessing whether this synapse can be toughened. In the present study, the synaptic loss was induced by a damaging noise exposure (106 dB SPL) and compared across Guinea pigs who had and had not been previously exposed to a toughening noise (85 dB SPL). Results revealed that the toughening noise heavily reduced the synaptic loss observed 1 day after exposure to the damaging noise. Although it was significant, the protective effect of the toughening noise on permanent synaptic loss was much smaller. Compared with cases in the control group without noise exposure, coding deficits were seen in both toughened groups, as reflected in the compound action potential (CAP) by signals with amplitude modulation. In general, the pre-exposure to the toughening noise resulted in a significantly reduced synaptic loss by the high-level noise. However, this morphological protection was not accompanied by a robust functional benefit.

Molecular Behavior of HMGB1 in the Cochlea Following Noise Exposure and in vitro

“…Stimulus generation and biosignal acquisition were conducted processed by using the RZ6 BioAMP Processor (TDT System III; Tucker-Davis Technologies, Alachua, FL, United States). Parameters were similar to those used in our previous study (Fan et al, 2020;Zhang et al, 2020). Briefly, the signal of acoustic stimuli is TB for 10 ms at 0.5 ms rise/fall time, and 21.1/s stimulation rate, starting from 90 to 0 dB SPL in decreasing steps of 5 or 10 dB.…”

A survey of protocols from 54 infant and toddler neuroimaging research labs

“…Sudden changes from relative quiet to loud, unfamiliar sounds disrupt the auditory system’s natural ability to adapt to slowly increasing sounds, a process that protects hearing in the context of high sound levels ( Fuchs and Lauer, 2019 ). Preliminary research in non-human animals suggests that prior exposure to loud but non-damaging sound levels may reduce loss of cochlear synapses following damaging sound level exposure ( Fan et al, 2020 ). One area of further study could involve utilizing the auditory system’s natural protective processes to improve scan success.…”

A survey of protocols from 54 infant and toddler neuroimaging research labs

“…Sudden changes from relative quiet to loud, unfamiliar sounds disrupt the auditory system's natural ability to adapt to slowly increasing sounds, a process that protects hearing in the context of high sound levels (Fuchs & Lauer, 2019). Preliminary research in non-human animals suggests that prior exposure to loud but nondamaging sound levels may reduce loss of cochlear synapses following damaging sound level exposure (Fan et al, 2020). One area of further study could involve utilizing the auditory system's natural protective processes to improve scan success.…”