Resistance to noise and cochlear efferent system

The cochlear efferent system appears to play a protective role with respect to noise-induced damage. The present study aimed to evaluate the possible role of both crossed and uncrossed olivocochlear bundles in the acquired resistance to noise, as assessed by auditory brainstem responses (ABR) measurement. A unilateral vestibular neurectomy was performed by a retrosigmoid approach in order to interrupt the entire efferent projections to the guinea pig cochlea of the same side. The animals were then exposed to an octave band noise, centred at 4 kHz, 85 dB SPL, for 10 consecutive days, 6 hours on/18 hours off. No differences were seen in the percentage of outer and inner hair cell loss between the two groups of ears. However, the de-efferented ears did not show recovery from the hearing loss during conditioning noise exposure in comparison with the contralateral normal ears. These results suggest that the efferent system could play a role in the development of resistance to noise. © 2005 Taylor & Francis.