This study was aimed at investigating the morphological change and plasticity of the cupula and other vestibular cells in a model of mechanical rupture of the membranous labyrinth.
Ten bullfrogs were used as study subjects. As in our previous reports, mechanical rupturing was accomplished by inserting a fine needle into the center of the saccule. The morphological change of the vestibular organs originated in an inflammatory change, and/or mixture of endolymph and perilymph which might be caused by rupturing. The vestibular membranous labyrinths were sectioned on 1-28 days after insult, and the degrees of cupula change were observed with the stereoscopic microscope. After the fixation and preparation of specimens for transmission electron microscopy (TEM), the ampullary and utricular sensory epithelium and ampullary dark cells were evaluated and compared with cupular changes. As controls, the vestibular organs on the opposite side were observed.
Sensory epithelia and dark cells were impaired in the early stage, and those tended to recover thereafter. Morphologically, the epithelia recovered in 14 days after the insult, whereas dark cells needed 28 days for recovery. The cupulae did not change significantly within 3 days after insults. In the lateral semicircular canals, the cupulae were highly affected, and those of the posterior semicircular canals were less affected. As for the dark cells, there were no obvious differences between each canal.
Morphological variations and possibilities of plasticity were seen in the vestibular organs with TEM observations, however, no obvious relationship between changes in the cupulae and vestibular cells was found. It is considered that the time lag of the damage development and recovery phase in each cell and cupula are responsible for this phenomenon. The change and plasticity of the cupula might be influenced by not only the anatomical features of the canals but also the degree of ampullary epithelial change.
