SUPRANUCLEAR EFFERENT SYNAPSES ON OUTER HAIR-CELLS AND DEITERS CELLS IN THE HUMAN ORGAN OF CORTI

Synaptophysin immunoreactivity and transmission electron microscopy have demonstrated vesiculated nerve endings synapsing on the supranuclear zone of outer hair cells and also of Deiters' cells in the human organ of Corti. These fibers seem similar to supranuclear fibers, apparently derived from the olivocochlear efferent system, which have been described in the animal. However, these endings were found throughout the cochlea in the human whereas in the animal such fibers were limited to the apical cochlea. Although such fibers have been demonstrated among supporting cells by immunohistochemical techniques, this is the first demonstration by transmission electron microscopy of morphology consistent with a chemical synapse between such fibers and Deiters' cells. Although the role of such fibers is unknown, neurophysiologic evidence suggests that they may modify the micromechanics of the outer hair cell. The function of neural innervation of Deiters' cells is speculative.