The presence of a calcitonin gene-related peptide in the olivocochlear bundle in rat.

The origins of calcitonin gene-related peptide immunoreactive (CGRPI) fibers in the cochlea were examined in rats. Parasagittal transection of the brain just medial to the principal sensory trigeminal nucleus resulted in the ipsilateral disappearance of CGRPI fibers in the cochlea, indicating that the origins of these fibers lie in the central nervous system. Next, we used a highly sensitive method combining retrograde tracing and immunohistochemistry to identify the origins of the CGRPI fibers in the cochlea. After injection of biotin-wheat germ agglutinin (b-WGA) into the cochlea, CGRPI neurons in the ipsilateral lateral superior olivary nucleus also contained b-WGA granules. These findings indicated that CGRPI efferent fibers are major components of the olivocochlear bundle.