The Tangential Nucleus Controls a Gravito-inertial Vestibulo-ocular Reflex

Background: Although adult vertebrates sense changes in head position by using two classes of accelerometer, at larval stages zebrafish lack functional semicircular canals and rely exclusively on their otolithic organs to transduce vestibular information. Results: Despite this limitation, we find that larval zebrafish perform an effective vestibulo-ocular reflex (VOR) that serves to stabilize gaze in response to pitch and roll tilts. By using single-cell electroporations and targeted laser ablations, we identified a specific class of central vestibular neurons, located in the tangential nucleus, that are essential for the utricle-dependent VOR. Tangential nucleus neurons project contralaterally to extraocular motoneurons and in addition to multiple sites within the reticulospinal complex. Conclusions: We propose that tangential neurons function as a broadband inertial accelerometer, processing utricular acceleration signals to control the activity of extraocular and postural neurons, thus completing a fundamental three-neuron circuit responsible for gaze stabilization.