Calcitonin gene-related peptide in the efferent system of the inner ear. A review

Many calcitonin gene-related peptide-like immunoreactive (CGRP-IR) fibers were found in the vestibular end-organs and the cochlea of rats. CGRP-IR fibers in the vestibular end-organs originated in the bilateral cell groups dorsolateral to the genu of the facial nerve. These fibers formed a fiber plexus at the base of the sensory epithelia in the maculae of the otolith organs and the ampullae of the semicircular canals, and formed synaptic contacts with the nerve chalice on type I vestibular sensory cells. CGRP-IR fibers in the cochlea originated in the ipsilateral lateral superior olivary nucleus. Most of them existed in the inner spiral bundle under the inner hair cells, and formed synaptic contacts with afferent terminals on the inner hair cells. These findings suggest a postsynaptic modulation of CGRP on the vestibular and cochlear information at the level of type I vestibular sensory cells and the inner hair cells.