The origin of efferent fibers to the inner ear in a turtle (Terrapene ornata). A horseradish peroxidase study.

The origin of efferent acoustic and vestibular fibers was determined in the turtle Terrapene ornata. After injection of an aqueous solution of horseradish peroxidase (HRP) into either the cochlear duct or into the ampullae of the horizontal and anterior semicircular canals, neurons in the medullary reticular formation were labeled by the reaction production of retrogradely transported HRP. These neurons were located bilaterally in the medial reticular nucleus. The majority were found ipsilateral to the injection site. There was no demonstrable difference in size, shape, and labeling pattern between efferent acoustic and efferent vestibular neurons. The crossed component component of efferent acoustic fibers, however, was rather sparsely developed.