Stabilization of Gaze during Early Xenopus Development by Swimming-Related Utricular Signals

• Published in: Current biology 2020-02, Vol.30 (4), p.746-753.e4
• Main Authors: Lambert, François M., Bacqué-Cazenave, Julien, Le Seach, Anne, Arama, Jessica, Courtand, Gilles, Tagliabue, Michele, Eskiizmirliler, Selim, Straka, Hans, Beraneck, Mathieu
• Format: Article
• Language: English
• Subjects: Age Factors; Animals; Biomechanical Phenomena; Fixation, Ocular; gaze stabilization; Head - physiology; kinematics; Larva - growth & development; Larva - physiology; Life Sciences; locomotion; Neurobiology; Neurons and Cognition; otolith organ; Reflex, Vestibulo-Ocular; Saccule and Utricle - physiology; semicircular canal; Swimming; vestibular system; vestibulo-ocular reflex; xenopus; Xenopus laevis - growth & development; Xenopus laevis - physiology
• ISSN: 0960-9822; 1879-0445
• DOI: 10.1016/j.cub.2019.12.047

Locomotor maturation requires concurrent gaze stabilization improvement for maintaining visual acuity [1, 2]. The capacity to stabilize gaze, in particular in small aquatic vertebrates where coordinated locomotor activity appears very early, is determined by assembly and functional maturation of inner ear structures and associated sensory-motor circuitries [3–7]. Whereas utriculo-ocular reflexes become functional immediately after hatching [8, 9], semicircular canal-dependent vestibulo-ocular reflexes (VORs) appear later [10]. Thus, small semicircular canals are unable to detect swimming-related head oscillations, despite the fact that corresponding acceleration components are well-suited to trigger an angular VOR [11]. This leaves the utricle as the sole vestibular origin for swimming-related compensatory eye movements [12, 13]. We report a remarkable ontogenetic plasticity of swimming-related head kinematics and vestibular end organ recruitment in Xenopus tadpoles with beneficial consequences for gaze-stabilization. Swimming of older larvae generates sinusoidal head undulations with small, similar curvature angles on the left and right side that optimally activate horizontal semicircular canals. Young larvae swimming causes left-right head undulations with narrow curvatures and strong, bilaterally dissimilar centripetal acceleration components well suited to activate utricular hair cells and to substitute the absent semicircular canal function at this stage. The capacity of utricular signals to supplant semicircular canal function was confirmed by recordings of eye movements and extraocular motoneurons during off-center rotations in control and semicircular canal-deficient tadpoles. Strong alternating curvature angles and thus linear acceleration profiles during swimming in young larvae therefore represents a technically elegant solution to compensate for the incapacity of small semicircular canals to detect angular acceleration components. [Display omitted] •Xenopus larvae elicit compensatory, gaze-stabilizing eye movements at all stages•Swimming in young larvae causes stronger head curvatures and linear acceleration•Utricular signals during swimming triggers adequate eye movements in young larvae•Stage-specific locomotor profiles differentially activate vestibular end organs Lambert, Bacqué-Cazenave, et al. report that swimming in young Xenopus larvae generates substantial linear acceleration components, which supplant the incapacity of small semicircu