title: Segmental organization of vestibulospinal inputs to spinal interneurons mediating crossed activation of thoracolumbar motoneurons in the neonatal mouse.
abstract: Vestibulospinal pathways activate contralateral motoneurons (MNs) in the thoracolumbar spinal cord of the neonatal mouse exclusively via axons descending ipsilaterally from the vestibular nuclei via the lateral vestibulospinal tract (LVST; Kasumacic et al., 2010). Here we investigate how transmission from the LVST to contralateral MNs is mediated by descending commissural interneurons (dCINs) in different spinal segments. We test the polysynaptic nature of this crossed projection by assessing LVST-mediated ventral root (VR) response latencies, manipulating synaptic responses pharmacologically, and tracing the pathway transynaptically from hindlimb extensor muscles using rabies virus (RV). Longer response latencies in contralateral than ipsilateral VRs, near-complete abolition of LVST-mediated calcium responses in contralateral MNs by mephenesin, and the absence of transsynaptic RV labeling of contralateral LVST neurons within a monosynaptic time window all indicate an overwhelmingly polysynaptic pathway from the LVST to contralateral MNs. Optical recording of synaptically mediated calcium responses identifies LVST-responsive ipsilateral dCINs that exhibit segmental differences in proportion and dorsoventral distribution. In contrast to thoracic and lower lumbar segments, in which most dCINs are LVST responsive, upper lumbar segments stand out because they contain a much smaller and more ventrally restricted subpopulation of LVST-responsive dCINs. A large proportion of these upper lumbar LVST-responsive dCINs project to contralateral L5, which contains many of the hindlimb extensor MNs activated by the LVST. A selective channeling of LVST inputs through segmentally and dorsoventrally restricted subsets of dCINs provides a mechanism for targeting vestibulospinal signals differentially to contralateral trunk and hindlimb MNs in the mammalian spinal cord.
authors.affiliation: Laboratory of Neural Development and Optical Recording, Department of Physiology, Institute of Basic Medical Sciences, University of Oslo, N-0317 Oslo, Norway.
authors.forename: Nedim
authors.initials: N
authors.lastname: Kasumacic
authors.affiliation: Laboratory of Neural Development and Optical Recording, Department of Physiology, Institute of Basic Medical Sciences, University of Oslo, N-0317 Oslo, Norway.
authors.forename: François M
authors.initials: FM
authors.lastname: Lambert
authors.affiliation: Timone Neurosciences Institute, National Center of Scientific Research and Aix-Marseille University, F-13385 Marseille, France, and.
authors.forename: Patrice
authors.initials: P
authors.lastname: Coulon
authors.affiliation: Timone Neurosciences Institute, National Center of Scientific Research and Aix-Marseille University, F-13385 Marseille, France, and.
authors.forename: Helene
authors.initials: H
authors.lastname: Bras
authors.affiliation: Timone Neurosciences Institute, National Center of Scientific Research and Aix-Marseille University, F-13385 Marseille, France, and.
authors.forename: Laurent
authors.initials: L
authors.lastname: Vinay
authors.affiliation: Laboratory of Neural Development and Optical Recording, Department of Physiology, Institute of Basic Medical Sciences, University of Oslo, N-0317 Oslo, Norway, Norwegian Center for Stem Cell Research, Oslo University Hospital, N-0372 Oslo, Norway, Department of Physiology, School of Medicine, Emory University, Atlanta, Georgia 30322 m-c.perreault@emory.edu joel.glover@medisin.uio.no.
authors.forename: Marie-Claude
authors.initials: MC
authors.lastname: Perreault
authors.affiliation: Laboratory of Neural Development and Optical Recording, Department of Physiology, Institute of Basic Medical Sciences, University of Oslo, N-0317 Oslo, Norway, Norwegian Center for Stem Cell Research, Oslo University Hospital, N-0372 Oslo, Norway, m-c.perreault@emory.edu joel.glover@medisin.uio.no.
authors.forename: Joel C
authors.initials: JC
authors.lastname: Glover
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D005260:Female; D007395:Interneurons / Q000502:physiology*; D008159:Lumbar Vertebrae; D008297:Male; D051379:Mice; D009046:Motor Neurons / Q000502:physiology*; D009434:Neural Pathways / Q000502:physiology; D013116:Spinal Cord / Q000502:physiology*; D013904:Thoracic Vertebrae; D014726:Vestibular Nuclei / Q000502:physiology*
keywords: calcium imaging; commissural interneuron; descending motor pathways; spinal network; supraspinal control; vestibular system