title: Separate microcircuit modules of distinct v2a interneurons and motoneurons control the speed of locomotion.
abstract: Spinal circuits generate locomotion with variable speed as circumstances demand. These circuits have been assumed to convey equal and uniform excitation to all motoneurons whose input resistance dictates their activation sequence. However, the precise connectivity pattern between excitatory premotor circuits and the different motoneuron types has remained unclear. Here, we generate a connectivity map in adult zebrafish between the V2a excitatory interneurons and slow, intermediate, and fast motoneurons. We show that the locomotor network does not consist of a uniform circuit as previously assumed. Instead, it can be deconstructed into three separate microcircuit modules with distinct V2a interneuron subclasses driving slow, intermediate, or fast motoneurons. This modular design enables the increase of locomotor speed by sequentially adding microcircuit layers from slow to intermediate and fast. Thus, this principle of organization of vertebrate spinal circuits represents an intrinsic mechanism to increase the locomotor speed by incrementally engaging different motor units.
authors.affiliation: Department of Neuroscience, Karolinska Institute, 171 77 Stockholm, Sweden.
authors.forename: Konstantinos
authors.initials: K
authors.lastname: Ampatzis
authors.affiliation: Department of Neuroscience, Karolinska Institute, 171 77 Stockholm, Sweden.
authors.forename: Jianren
authors.initials: J
authors.lastname: Song
authors.affiliation: Department of Neuroscience, Karolinska Institute, 171 77 Stockholm, Sweden.
authors.forename: Jessica
authors.initials: J
authors.lastname: Ausborn
authors.affiliation: Department of Neuroscience, Karolinska Institute, 171 77 Stockholm, Sweden. Electronic address: Abdel.ElManira@ki.se.
authors.forename: Abdeljabbar
authors.initials: A
authors.lastname: El Manira
mesh_terms: D000054:Acceleration; D000200:Action Potentials / Q000502:physiology; D000818:Animals; D007395:Interneurons / Q000502:physiology*; D008124:Locomotion / Q000502:physiology*; D009046:Motor Neurons / Q000502:physiology*; D009415:Nerve Net / Q000166:cytology* / Q000502:physiology; D013116:Spinal Cord / Q000166:cytology* / Q000502:physiology; D015027:Zebrafish