Efferent innervation of the cochlea.

The origin of the efferent innervation of the cochlea was investigated in the guinea pigs. Horseradish peroxidase (HRP) was injected into the cochlea and transported to the brainstem by retrograde axonal transport of the efferent fibers, showing the origin of the crossed an uncrossed olivocochlear bundles of Rasmussen. HRP-labeled neurons were found in various nuclei of the superior olivary complex bilaterally. Ipsilateral to the injected cochlea ther were three times more cells than on the contralateral side. About 40% of the total number of labeled neurons, a remarkable quantity, occurred in the ipsilateral lateral superior olivary nucleus. Moreover, extraolivary origin of the efferent innervation of the cochlea could be demonstrated bilaterally in the ventral nucleus of the lateral lemniscus.