The medial efferent system during development of the auditory pathway

CASTAGNA, VC; BOERO, L; DI GUILMI, MN; ELGOYHEN, AB; GOMEZ CASATI, ME

Congreso; Congreso de la Sociedad Argentina de Neurociencias; 2020

The auditory system of many mammals develops after birth. It is known that before theonset of hearing inner hair cells (IHCs) of the cochlea are innervated by neurons of theafferent system and transiently by neurons of the medial olivocochlear (MOC) system.During this period, IHCs exhibit spontaneous periodic depolarization patterns, thatproduce the release of the neurotransmitter, glutamate. These events inducestereotyped bursts of action potentials that are transmitted to the auditory circuits in thebrain and promote physiological maturation and the proper establishment of thetonotopic map. The transient efferent innervation to IHCs of the cochlea has beenproposed as a modulator of this activity. In this work, we sought to understand thefunction of this transient synapse during the beginning of hearing. We used a previouslyreported genetically modified mice carrying an α9 cholinergic receptor subunit pointmutation that leads to enhanced responses to MOC activity. First, we analyze the onsetof hearing and we found that these knock-in gain of function animals start to hear a daybefore than wild types, which means that the MOC system might be involved in cochleardevelopment. Second, we observed that the maturation of the auditory system is aprocess that occurs from the periphery towards the higher nuclei. Finally, we evidencedthat afferent synapse formation begins as a multiple innervation and then, a 'prune' andrefinement of these synapses occurs.