OPTOMOTOR BEHAVIOUR IN XENOPVS LAEVIS TADPOLES AS A MEASURE OF THE EFFECT OF GRAVITY ON VISUAL AND VESTIBULAR NEURAL INTEGRATION

摘要

The ability of aquatic vertebrates to maintain their position requires integration of visual and vestibular sensory information. To understand better how aquatic animals integrate such information, we measured the optomotor behaviour of Xenopus laevistadpoles raised in growth chambers in microgravity (<10~9-3)g), normal gravity (1g), hypergravity (3g) and on a slowly rotating clinostat (simulated microgravity). The goal of this research was to determine how development in an altered gravitational force field affects the visual- and vestibular-dependcnt behaviour of tadpoles. This research represents the first tinne that the optomotor behaviour of an organism raised from fertilization in microgravfiy has been tested. Significant differences were observed in the optomotor behaviour among the four gravity treatments. When first exposed to normal gravity, the microgravity-raised tadpoles exhibited the strongest (or most positive) optomotor behaviour, while the 3g centrifuge tadpoles showed no optomotor response. Some abnormal behaviours (such as erratic swimming, lying motionless and abnormal swimming posture) were observed in the tadpoles raised in altered gravity on the initial day of testing. One day later, the tadpoles raised in hypergravity didnot differ significantly in their optomotor behaviour from control tadpoles raised in normal gravity. However, tadpoles raised in microgravity still displayed an exaggerated optomotor response. One week after the tadpoles had been introduced to normal gravity, there was no longer a significant difference in optomotor behaviour among the different gravity treatments. This convergence of optomotor behaviour by tadpoles from the different treatments reflects the acclimation of their vestibular systems tonormal gravity.