Brainstem connections of the anterior and posterior parts of the saccule in the guinea pig.

Studies on specific brainstem connections of the saccule are scanty, present notable divergences, have never concerned the guinea pig, and have not considered separately the two branches of its innervation. In this study, the central connections of the entire saccule and of anterior or posterior parts of the epithelium were investigated in the guinea pig, using horseradish peroxidase (HRP). HRP was deposited on the saccular epithelium and associated with surgical section of the inferior or superior division of the VIII nerve in order to study the connections of specific parts of the saccule. The whole organ was found to project to the ipsilateral side, principally to the lateral part of the lateral vestibular nucleus (LVN) and to the gamma group. The posterior part of the saccule projects also to the gamma group and to a lesser extent to the LVN, the anterior part projects to the LVN but not to the gamma group. In all cases, labelled efferent cells were seen located bilaterally between the genu of the VII nerve and the medial vestibular nucleus (MVN).