Medial olivocochlear strength influences auditory brainstem response development in mice

The medial olivocochlear efferent system has been proposed to influence the maturation of auditory circuits during early postnatal development. Here, we examined the acquisition of auditory evoked responses in mice with absent α9α10 nicotinic cholinergic receptor activity (α9 knock-out mice; α9KO) or enhanced medial olivocochlear function (α9 knock-in mice; α9KI). Auditory brainstem responses were evaluated throughout juvenile postnatal development. Enhanced medial olivocochlear activity accelerated the onset and early maturation of auditory function, whereas its absence delayed these developmental processes. Despite this accelerated maturation, α9KI mice exhibited reduced auditory brainstem response wave amplitudes later in development, resembling the deficits observed in α9KO mice. Thus, enhanced and absent medial olivocochlear activity produced opposing effects on the timing of auditory maturation but converged on reduced response wave amplitudes later in development. Together, these findings suggest that appropriate levels of medial olivocochlear activity are required for normal maturation of the auditory system.