[Vestibular efferent neurons of the guinea pig forming projections into the saccule]

Abstract

The distribution of vestibular efferent neurons projecting to the saccule and efferent neurons transmitting axons to the acoustic nerve (cochlear efferent neurons) has been studied in guinea pig by comparison using the method of retrograde axonal transport of horseradish peroxidase. The saccular efferent neurons are revealed bilaterally in the subendymal granular fundus of the fourth ventricle of the brain and more laterally of the facial nerve genu, ipsilaterally in the small-celled reticular nucleus as well as in nuclei of the supraolivary complex: nucleus of lateral oliva and lateral nucleus of the trapezoid body. The cochlear efferent neurons are localized ipsilaterally in the reticular caudal nucleus of the bridge in the anteroventral cochlear nucleus and in nuclei of lateral and medial olivae. In the medial nucleus of the trapezoid body such neurons are found contralaterally. Thus, the regions of the vestibular saccular efferent neurons are partially overlapped with such of the cochlear efferent units. Possible participation of the vestibular efferent neurons of the saccule in the mechanism of the acoustic perception is discussed.