Connections of Purkinje cell axons of lobule X with vestibulocerebellar neurons projecting to lobule X or IX in the rat.

Connections of Purkinje cell axons of lobule X (nodulus) with vestibulocerebellar neurons projecting to lobule X or IX (uvula) were revealed in the rat. Purkinje cell axons were anterogradely labeled with biotinylated dextran (BD) injected into sublobule Xa while vestibular neurons were retrogradely labeled with cholera toxin subunit B (CTB) injected into sublobule Xa or IXc. Labeled terminals of Purkinje cell axons of lobule X were numerous in the superior vestibular nucleus (SV), medial parts of the parvocellular (MVpc) and the caudal part (MVc) of the medial vestibular nucleus (MV), and group y. These subdivisions of the vestibular nuclei contained many neurons projecting to lobule X or IX. Lobule-X-projecting and lobule-IX-projecting neurons were in contact with terminals of Purkinje cell axons of lobule X in the MVpc and MVc. They were distributed dorsally to medially in medial parts of the MVpc and MVc. The present study suggests that Purkinje cells in lobule X regulate the output of a population of lobule-X-projecting or lobule-IX-projecting neurons of the MVpc and MVc.