Understanding the roles of the efferent system after acoustic trauma

GOMEZ CASATI ME; ELGOYHEN AB

Congreso; XXVIII Congreso Anual de la Sociedad Argentina de Investigación en Neurociencia; 2012

Understanding the roles of the efferent system after acoustic trauma. Maria Eugenia Gómez-Casati and Ana Belén Elgoyhen. Tercera Cátedra de Farmacología. Facultad de Medicina, UBA. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular (INGEBI).   The transduction of sound is inhibited by efferent cholinergic neurons projecting from the brainstem and synapsing directly on hair cells. Efferent innervation undergoes extensive modification early in development, i.e. shortly after the onset of hearing in mice (P11), synaptic contacts between efferent fibers and inner hair cells (IHCs) are lost. However, it is not clear if efferent synapses are modified by age, hearing loss or both. Here, we tested how efferent innervation is rewired after noise trauma. We evaluated if exposure to loud sounds (1-16 kHz, 100 dB SPL, 30min) in mature animals can trigger a re-innervation. We used confocal immunohistochemistry to visualize efferent nerve terminals and found disorganized efferent terminals after acoustic trauma comparing to controls. We measured auditory brainstem responses (ABR), which reflect synchronized discharges from neurons along the auditory pathway and distortion product otoacoustic emissions (DPOAEs), to test outer hair cells function. After acoustic trauma, animals showed large ABRs and DPOAEs threshold shifts. Suprathreshold ABR amplitudes were reduced, even in animals with almost normal threshold sensitivity. These findings will contribute to the understanding of how normal hair cell function is affected by acoustic trauma and the role of the efferent system.