Session: 5

PS5-04 | The medial olivocochlear system alters the development of the auditory pathway.

Valeria Castagna

Laboratorio de Fisiología Auditiva/Instituto de Farmacología/Universidad de Buenos Aires

The auditory system of many mammals develops after birth. Before the onset of hearing, inner hair cells (IHC) are innervated by auditory nerve fibers and transiently by neurons of the medial olivocochlear (MOC) system. During this period, IHCs exhibit periodic depolarization patterns inducing stereotyped bursts of action potentials that are transmitted to the auditory circuits in the brain and promote neuronal survival, physiological maturation, and the proper establishment of the tonotopic map. It has been proposed that the MOC system may be a modulator of this activity. In addition, it has an important role in the protection from noise-induced hearing loss in adult rodents. Here, we evaluated the function of this transient synapse and the consequences of an early acoustic exposure during this critical period by using mice with genetic enhancement or ablation of MOC activity. We found that mice with enhanced MOC function have an earlier onset of hearing compared to mice with normal MOC synapses. In contrast, a delay was observed in mice with no MOC activity, suggesting that cochlear maturation is slowed in the absence of pre-hearing efferent modulation. Moreover, we observed that the maturation of the auditory system begins in the periphery and continues after the onset of hearing. Exposure to loud noise at this early stage, produced an alteration in the auditory sensitivity in mice with normal MOC while no changes were observed in those with enhanced function.