Medial Olivocochlear System in noise and age related hearing loss

GOMEZ CASATI, ME

Buenos Aires

Simposio; Second International Hearing Research symposium; 2019

IHear Project, Germany.

Age-related hearing loss is the most common cause of hearing loss. It first affects the ability to understand speech, particularly in background noise and even when cochlear thresholds are normal. It has been suggested that cochlear synaptopathy is the earliest contributor to age-related auditory function decline.We characterize age-related cochlear synaptic degeneration and hair cell loss in mice with enhanced a9a10 cholinergic nicotinic receptors (nAChRs) activity never exposed to high-level noise. Cochlear function was assessed via distortion product otoacoustic emissions and auditory brainstem responses. Immunostained cochlear whole mounts were analyzed by confocal microscopy to quantify hair cells, auditory neurons, presynaptic ribbons and postsynaptic glutamate receptors. Cochlear synaptic loss is seen throughout the aged cochlea together with some loss of outer hair cells. Notably, enhancement of the medial olivocochlear reflex by increasing the a9a10 nAChR activity reduced age-related cochlear synaptopathy and outer hair cell loss, suggesting that efferents are important for long-term maintenance of inner ear function in mice. Our results suggest that efferent reflex strength might be an important marker for age-related hearing loss.