title: Locomotor corollary activation of trigeminal motoneurons: coupling of discrete motor behaviors.
abstract: During motor behavior, corollary discharges of the underlying motor commands inform sensory-motor systems about impending or ongoing movements. These signals generally limit the impact of self-generated sensory stimuli but also induce motor reactions that stabilize sensory perception. Here, we demonstrate in isolated preparations of Xenopus laevis tadpoles that locomotor corollary discharge provokes a retraction of the mechanoreceptive tentacles during fictive swimming. In the absence of sensory feedback, these signals activate a cluster of trigeminal motoneurons that cause a contraction of the tentacle muscle. This corollary discharge encodes duration and strength of locomotor activity, thereby ensuring a reliable coupling between locomotion and tentacle motion. The strict phase coupling between the trigeminal and spinal motor activity, present in many cases, suggests that the respective corollary discharge is causally related to the ongoing locomotor output and derives at least in part from the spinal central pattern generator; however, additional contributions from midbrain and/or hindbrain locomotor centers are likely. The swimming-related retraction might protect the touch-receptive Merkel cells on the tentacle from sensory over-stimulation and damage and/or reduce the hydrodynamic drag. The intrinsic nature of the coupling of tentacle retraction to locomotion is an excellent example of a context-dependent, direct link between otherwise discrete motor behaviors.
authors.affiliation: Department Biology II, Ludwig-Maximilians-University Munich, 82152 Planegg, Germany Graduate School of Systemic Neurosciences, Ludwig-Maximilians-University Munich, 82152 Planegg, Germany.
authors.forename: Sara
authors.initials: S
authors.lastname: Hänzi
authors.affiliation: Department Biology II, Ludwig-Maximilians-University Munich, 82152 Planegg, Germany Graduate School of Systemic Neurosciences, Ludwig-Maximilians-University Munich, 82152 Planegg, Germany.
authors.forename: Roberto
authors.initials: R
authors.lastname: Banchi
authors.affiliation: Department Biology II, Ludwig-Maximilians-University Munich, 82152 Planegg, Germany b.chagnaud@lmu.de.
authors.forename: Hans
authors.initials: H
authors.lastname: Straka
authors.affiliation: Department Biology II, Ludwig-Maximilians-University Munich, 82152 Planegg, Germany b.chagnaud@lmu.de.
authors.forename: Boris P
authors.initials: BP
authors.lastname: Chagnaud
mesh_terms: D000818:Animals; D066298:In Vitro Techniques; D007814:Larva / Q000502:physiology; D008124:Locomotion / Q000502:physiology*; D008465:Mechanoreceptors / Q000502:physiology; D009046:Motor Neurons / Q000502:physiology*; D009119:Muscle Contraction; D013116:Spinal Cord / Q000502:physiology; D014276:Trigeminal Nerve / Q000166:cytology / Q000502:physiology*; D014982:Xenopus laevis / Q000502:physiology*
keywords: Corollary discharge; Efference copy; Spinal locomotion; Trigeminal nerve; Xenopus laevis