title: Functional subpopulations of V3 interneurons in the mature mouse spinal cord.
abstract: V3 interneurons (INs) are a major group of excitatory commissural interneurons in the spinal cord, and they are essential for producing a stable and robust locomotor rhythm. V3 INs are generated from the ventral-most progenitor domain, p3, but migrate dorsally and laterally during postmitotic development. At birth, they are located in distinctive clusters in the ventral horn and deep dorsal horn. To assess the heterogeneity of this genetically identified group of spinal INs, we combined patch-clamp recording and anatomical tracing with cluster analysis. We examined electrophysiological and morphological properties of mature V3 INs identified by their expression of tdTomato fluorescent proteins in Sim1(Cre/+); Rosa(floxstop26TdTom) mice. We identified two V3 subpopulations with distinct intrinsic properties and spatial distribution patterns. Ventral V3 INs, primarily located in lamina VIII, possess a few branching processes and were capable of generating rapid tonic firing spikes. By contrast, dorsal V3 INs exhibited a more complex morphology and relatively slow average spike frequency with strong adaptation, and they also displayed large sag voltages and post-inhibitory rebound potentials. Our data suggested that hyperpolarization-activated cation channel currents and T-type calcium channel currents may account for some of the membrane properties of V3 INs. Finally, we observed that ventral and dorsal V3 INs were active in different ways during running and swimming, indicating that ventral V3 INs may act as premotor neurons and dorsal V3 INs as relay neurons mediating sensory inputs. Together, we detected two physiologically and topographically distinct subgroups of V3 INs, each likely playing different roles in locomotor activities.
authors.affiliation: Departments of Medical Neuroscience, and Mathematics and Statistics, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada, and Molecular Neurobiology Laboratory, the Salk Institute for Biological Studies, La Jolla, California 92037.
authors.forename: Joanna
authors.initials: J
authors.lastname: Borowska
authors.forename: Christopher T
authors.initials: CT
authors.lastname: Jones
authors.forename: Han
authors.initials: H
authors.lastname: Zhang
authors.forename: Jake
authors.initials: J
authors.lastname: Blacklaws
authors.forename: Martyn
authors.initials: M
authors.lastname: Goulding
authors.forename: Ying
authors.initials: Y
authors.lastname: Zhang
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D000831:Animals, Newborn; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics; D001562:Benzimidazoles / Q000494:pharmacology; D002317:Cardiovascular Agents / Q000494:pharmacology; D016000:Cluster Analysis; D003521:Cyclopropanes / Q000494:pharmacology; D004558:Electric Stimulation; D066298:In Vitro Techniques; D007395:Interneurons / Q000145:classification* / Q000502:physiology*; D051379:Mice; D008822:Mice, Transgenic; D009043:Motor Activity / Q000187:drug effects; D009281:Naphthalenes / Q000494:pharmacology; D009532:Nickel / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D016760:Proto-Oncogene Proteins c-fos / Q000494:pharmacology; D011743:Pyrimidines / Q000494:pharmacology; D022661:RNA, Untranslated / Q000235:genetics; D012097:Repressor Proteins / Q000235:genetics; D013116:Spinal Cord / Q000166:cytology*; D018709:Statistics, Nonparametric
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D001562:Benzimidazoles; D002317:Cardiovascular Agents; D003521:Cyclopropanes; D009281:Naphthalenes; D009532:Nickel; D016760:Proto-Oncogene Proteins c-fos; D011743:Pyrimidines; D022661:RNA, Untranslated; D012097:Repressor Proteins; C110853:Gt(ROSA)26Sor non-coding RNA, mouse; C101750:Sim1 protein, mouse; C484287:NNC 55-0396; C082246:ICI D2788