title: Distribution and Structure of Synapses on Medial Vestibular Nuclear Neurons Targeted by Cerebellar Flocculus Purkinje Cells and Vestibular Nerve in Mice: Light and Electron Microscopy Studies.
abstract: Adaptations of vestibulo-ocular and optokinetic response eye movements have been studied as an experimental model of cerebellum-dependent motor learning. Several previous physiological and pharmacological studies have consistently suggested that the cerebellar flocculus (FL) Purkinje cells (P-cells) and the medial vestibular nucleus (MVN) neurons targeted by FL (FL-targeted MVN neurons) may respectively maintain the memory traces of short- and long-term adaptation. To study the basic structures of the FL-MVN synapses by light microscopy (LM) and electron microscopy (EM), we injected green florescence protein (GFP)-expressing lentivirus into FL to anterogradely label the FL P-cell axons in C57BL/6J mice. The FL P-cell axonal boutons were distributed in the magnocellular MVN and in the border region of parvocellular MVN and prepositus hypoglossi (PrH). In the magnocellular MVN, the FL-P cell axons mainly terminated on somata and proximal dendrites. On the other hand, in the parvocellular MVN/PrH, the FL P-cell axonal synaptic boutons mainly terminated on the relatively small-diameter (< 1 μm) distal dendrites of MVN neurons, forming symmetrical synapses. The majority of such parvocellular MVN/PrH neurons were determined to be glutamatergic by immunocytochemistry and in-situ hybridization of GFP expressing transgenic mice. To further examine the spatial relationship between the synapses of FL P-cells and those of vestibular nerve on the neurons of the parvocellular MVN/PrH, we added injections of biotinylated dextran amine into the semicircular canal and anterogradely labeled vestibular nerve axons in some mice. The MVN dendrites receiving the FL P-cell axonal synaptic boutons often closely apposed vestibular nerve synaptic boutons in both LM and EM studies. Such a partial overlap of synaptic boutons of FL P-cell axons with those of vestibular nerve axons in the distal dendrites of MVN neurons suggests that inhibitory synapses of FL P-cells may influence the function of neighboring excitatory synapses of vestibular nerve in the parvocellular MVN/PrH neurons.
authors.affiliation: Laboratory for Motor Learning Control, Riken Brain Science Institute, Hirosawa 2-1, Wako, Saitama, 351-0198, Japan.
authors.forename: Hitomi
authors.initials: H
authors.lastname: Matsuno
authors.affiliation: Laboratory for Motor Learning Control, Riken Brain Science Institute, Hirosawa 2-1, Wako, Saitama, 351-0198, Japan.
authors.forename: Moeko
authors.initials: M
authors.lastname: Kudoh
authors.affiliation: Laboratory for Molecular Analysis of Higher Brain Function, RIKEN Brain Science Institute, Hirosawa 2-1, Wako, Saitama, 351-0198, Japan.
authors.forename: Akiya
authors.initials: A
authors.lastname: Watakabe
authors.affiliation: Laboratory for Molecular Analysis of Higher Brain Function, RIKEN Brain Science Institute, Hirosawa 2-1, Wako, Saitama, 351-0198, Japan.
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Yamamori
authors.affiliation: Division of Cerebral Structure, National Institute for Physiological Sciences, 5-1 Higashiyama, Myodaiji, Okazaki, Aichi, 444-8787, Japan.
authors.forename: Ryuichi
authors.initials: R
authors.lastname: Shigemoto
authors.affiliation: Laboratory for Motor Learning Control, Riken Brain Science Institute, Hirosawa 2-1, Wako, Saitama, 351-0198, Japan.
authors.forename: Soichi
authors.initials: S
authors.lastname: Nagao
mesh_terms: D000818:Animals; D001369:Axons / Q000378:metabolism; D008027:Light; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008854:Microscopy, Electron; D011689:Purkinje Cells / Q000166:cytology* / Q000648:ultrastructure*; D013569:Synapses / Q000378:metabolism*; D014725:Vestibular Nerve / Q000166:cytology* / Q000648:ultrastructure*