Strength of the efferent olivocochlear system modifies the normal activity of a central auditory nuclei

DI GUILMI M; BOERO L; GOMEZ CASATI ME; ELGOYHEN AB

Congreso; XXX Congreso Anual de la Sociedad Argentina de Investigación en Neurociencia; 2015

The auditory system in many mammals is immature at birth but precisely organized in adults. Spontaneous activity in the inner ear comes into play to guide this process. This activity is modulated by an efferent pathway that descends from the brain. In this work, we used a mouse model with enhanced medial efferent activity (Chrna9L9?T, KI) to understand the role of the olivocochlear efferent system in the correct establishment of auditory circuits.We measured auditory brainstem responses, which represents synchronized activity of neurons along the auditory pathway. Wave I amplitude (activity of cochlear nerve fibers) was the same for WT and KI. However, wave III (activity of synapses within the MNTB) was smaller in the KI suggesting a central dysfunction. In order to analyze this functional observation, we studied the underlying mechanism on brain slices containing the medial nucleus of the trapezoid body (MNTB). Several electrophysiological properties measured in current-clamp (resting membrane potential, input resistance, action potential amplitude, number of spikes during a current pulse injection) and in voltage-clamp mode (Ih current) were topographically organized along a medio-lateral axis in WT. However, these tonotopic differences were abolished in the KI. Our preliminary data suggest that the efferent pathway could be involved in the refinement of the tonotopic map along the auditory pathway.