Mechanisms of recovery from sensory stereocilia after acoustic trauma noise-induced

Abstract

Exposure to excessive noise is the major avoidable cause of permanent hearing impairment worldwide, and is defined as an important public health priority by the World Health Organization. It has been demonstrated in recent studies a systematic incorporation of actin monomers at the tips of stereocilia in mature hair bundles, evidencing what was previously unknown, the existence of a continuous renewal process (turnover) and length adjustment of the stereocilia. The turnover rate of 48 h for this process in mature bundles is of the same order as the recovery time from noiseinduced temporary hearing loss, indicating that the core structure of stereocilia may play an unforeseen part in this recovery. The molecular mechanisms involved in renewal of the stereocilia after acoustic trauma are not fully established, requiring definitions about the spontaneous recovery of stereocilia, the occurrence of intrinsic mechanisms of turnover or the existence of regeneration processes involved in this restoration, culminating in the functional recovery of hearing.PURPOSE: To study the structure and stereocilia function by the ciliary expressions forms of actin (²-actin and F-actin) in cochlear hair cells after acute acoustic trauma and correlated with the mechanisms involved in spontaneous recovery and stereocilia regeneration.MATERIALS AND METHODS: Male albino rats, Wistar, will be exposed to a white noise in the range of 4 kHz with and intensity equal to 110 dB SPL for 72 hours to generate an acoustic trauma. Two situations will be proposed: group 1 (G1) and group 2 (G2). Each situation will have different moments of hearing functional examination by Distortion Product Otoacoustic Emissions (DPOAE) and Auditory Brainstem evoked Response (ABR), in G1, all animals will be exposed to DPOAE and ABR before and after exposure to the noise, and in G2 before and after exposure to the noise and after 5 days of hearing rest. After euthanasia, all the cochleae will be prepared for histological study. TUNEL test will be performed to analyses apoptosis in situ and immunofluorescence will be used to mark the protein beta-actin and F-actin.