Synapses from medial olivocochlear branches in the inferior vestibular nucleus

Olivocochlear neurons are auditory efferent neurons that convey information from the brainstem to the auditory periphery. With light and electron microscopy, using mice, we studied the central branches of medial olivocochlear neurons that are given off to the inferior vestibular nucleus. At the level of the electron microscope, the branches form synapses. The synapses are asymmetric with round vesicles, suggesting that they are excitatory. The synapses are formed mainly onto neuronal dendrites. These dendrites have a large range of diameters, and they may emanate from several types of target neurons. These results indicate that the inferior vestibular nucleus is an integrating center for vestibular, auditory, and other types of information, but the results do not fit with current theories about the function of the olivocochlear system.