[Brain stem neurons of the guinea pig that form projections into the ampullae of the anterior, lateral and posterior semicircular canals].

Brain stem neurons projecting to the ampullae of anterior, lateral and posterior semicircular canals (vestibular efferent neurons) were identified in guinea pigs using, retrograde labelling with horseradish peroxidase. Two groups of such neurons located bilaterally dorsal and ventral to the facial nerve trajectory were classified. A dorsal group contained vestibular efferent neurons to all three canals; these units were located at all the levels of the subependymal granular layer of the floor of the 4th ventricle lateral to the facial nerve genu and abducens nerve nucleus. Vestibular efferent neurons of the ventral group were distributed within different parts of parvocellular and rostral part of the caudal pontine reticular nucleus. Heterogeneity of organization of the vestibular efferent system of semicircular canal ampullae according to cell location and their morphological characteristics are discussed.