Validity of Ewald's law in the horizontal semicircular canals and the vestibular nuclei: electron microscopic observation and quantitative [14C]-2-deoxy-D-glucose study.

Two series of experiments were performed by using a total of 36 guinea pigs. The 1st series was to compare the influence of rotatostimulation on the bilateral cristae ampullare. After repeating the rotatostimulation with the cupulometric mode (the terminal turning velocity: 450 degrees/sec) for 48 hr, ultrastructural changes of sensory cells were found in 9 of 17 animals with transmission electron microscopy. They showed stronger influences on the ampullopetal flow side with the exception of one animal. In the 2nd series, the difference in excitability between the bilateral vestibular nuclei was investigated on 6 guinea pigs which were exposed to the clockwise constant angular acceleration of 1 degree/sec2 for 8 min. The autoradiographic study with [14C]-2-deoxy-D-glucose (the 2-DG) revealed that the rotation-induced glucose uptake was increased significantly in the superior and the medial vestibular nuclei of the ampulloptal flow side. The results of the two series of experiments suggest the predominance of the ampullopetal effect not only in the horizontal semicircular canals but also in the vestibular nuclei.