Acute consequences of a unilateral VIIIth nerve transection on vestibulo-ocular and optokinetic reflexes in Xenopus laev
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Acute consequences of a unilateral VIIIth nerve transection on vestibulo‑ocular and optokinetic reflexes in Xenopus laevis tadpoles Parthena Soupiadou1,2 · Clayton Gordy1,2 · Michael Forsthofer1,2 · Rosario Sanchez‑Gonzalez1 · Hans Straka1 Received: 10 June 2020 / Revised: 28 August 2020 / Accepted: 29 August 2020 © The Author(s) 2020
Abstract Loss of peripheral vestibular function provokes severe impairments of gaze and posture stabilization in humans and animals. However, relatively little is known about the extent of the instantaneous deficits. This is mostly due to the fact that in humans a spontaneous loss often goes unnoticed initially and targeted lesions in animals are performed under deep anesthesia, which prevents immediate evaluation of behavioral deficits. Here, we use isolated preparations of Xenopus laevis tadpoles with functionally intact vestibulo-ocular (VOR) and optokinetic reflexes (OKR) to evaluate the acute consequences of unilateral VIIIth nerve sections. Such in vitro preparations allow lesions to be performed in the absence of anesthetics with the advantage to instantly evaluate behavioral deficits. Eye movements, evoked by horizontal sinusoidal head/table rotation in darkness and in light, became reduced by 30% immediately after the lesion and were diminished by 50% at 1.5 h postlesion. In contrast, the sinusoidal horizontal OKR, evoked by large-field visual scene motion, remained unaltered instantaneously but was reduced by more than 50% from 1.5 h postlesion onwards. The further impairment of the VOR beyond the instantaneous effect, along with the delayed decrease of OKR performance, suggests that the immediate impact of the sensory loss is superseded by secondary consequences. These potentially involve homeostatic neuronal plasticity among shared VOROKR neuronal elements that are triggered by the ongoing asymmetric activity. Provided that this assumption is correct, a rehabilitative reduction of the vestibular asymmetry might restrict the extent of the secondary detrimental effect evoked by the principal peripheral impairment. Keywords Vestibulo-ocular reflex · Semicircular canal · Extraocular motoneurons · Eye movements · Unilateral labyrinthectomy · Homeostatic plasticity · Optokinetic reflex
Introduction Unilateral loss of peripheral vestibular function causes severe and incapacitating symptoms [1]. These emerging deficits derive from either an impairment of inner ear structures or are commonly observed following damage to the statoacoustic (VIIIth) nerve. Well characterized impairments Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00415-020-10205-x) contains supplementary material, which is available to authorized users. * Hans Straka [email protected] 1
Department Biology II, Ludwig-Maximilians-University Munich, Großhaderner Str. 2, 82152 Planegg, Germany
Graduate School of Systemic Neurosciences, Ludwig-Maximilians-University Munich, Großhaderner Str. 2, 82152 Planegg, Germany
2
of this nerve, s
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