Abstract: Objective To observe the possible loss and recovery of ribbon synapses in the cochlea of guinea pigs repeatedly exposed to low-intensity noise. Methods Guinea pigs were exposed to 95 dB sound pressure level of white noise for 4 hours per day, continuously for 7 days. The animals were then divided into three groups, and respectively named group 1DPN(1 day post-noise), 1WPN(1 week post-noise), and 1MPN(1 month post-noise), with each group containing 10 guinea pigs. Audiological examinations(auditory brainstem response)and immunofluorescence staining were performed,and the number of ribbon synapses were counted by observing double staining results of C-terminal-binding protein 2 and postsynaptic density protein 95 labeling. Results After long-term low-intensity noise exposure, the auditory brainstem responsethreshold of group 1DPN significantly increased(P<0.05)compared to the control group. No apparent changes in hair cell shape, arrangement, or number were observed, but the number of ribbon synapses was statistically significant(P<0.05). With the extension of time after leaving the noisy environment, the ABR threshold and number of synapses recovered gradually. Conclusion Repeated exposure to long-term, low-intensity noise can cause hearing loss, which is reversible after leaving the noisy environment. Reduction in the number of inner hair cell ribbon synapses caused by long-term low-intensity noise exposure can restore partially while in a noise-free environment.

Key words: Ribbon synapse, Auditory brainstem response, Low intensity noise