Abstract
On Earth, signals from otolith organs can be interpreted either as linear motion or as tilt with respect to gravity. In microgravity, static tilt will no longer give rise to changes in otolith activity. However, linear acceleration as well as angular acceleration stimulates the otolith organ. Therefore, during adaptation to microgravity, otolith-mediated response such as eye movements would alter. Flatfish provide a natural model for the study of adaptive changes in the vestibulo-ocular reflex. During metamorphosis, vestibular and oculomotor coordinate of flatfish displaced 90 degrees about the longitudinal body axis. Therefore, it is expected that microgravity induce the sensory mismatch in adult flatfish. In this study, we analyzed the eye movements for body tilting in normal flatfish and in unilaterally otolith removed flatfish. The eye movements for body tilting along the different body axis were video-recorded. The vertical and torsional eye rotations were calculated from the images digitized by computer.In normal flatfish, the properties of vertical and torsional eye movements for body tilt were almost the same as that in goldfish. After removal of left utricular otolith, the amplitude of vertical eye movements decreased. Especially for 180 degrees tilting, the vertical eye movements almost disappeared. These results suggested that utricular otolith play some roll in flatfish. [J Physiol Sci. 2008;58 Suppl:S110]
