Aging Effect on the Morphology of the Otoconia Using Scanning Electron Microscopy / 대한이비인후과학회지

ABSTRACT

BACKGROUND AND OBJECTIVES: Displaced otoconia in the semicircular canal from senile otoconial degeneration have been believed as a major cause of benign paroxysmal positional vertigo (BPPV). The otoconia are mainly composed of calcium carbonate, and thus they are susceptible to chemical deformation during the usual process of scanning electron microscopy (SEM). The aims of this study were to present an optimal protocol of otoconial preparation for SEM and to investigate the change of otoconial morphology due to aging. SUBJECTS AND METHOD: The macula in mice were dissected free from the temporal bone and were divided into three groups using different fixatives and buffers 2.5% glutaraldehyde in phosphate buffer, 2.5% glutaraldehyde in cacodylate buffer and 70% acetone. The duration of storage in buffer differed for each group, and SEM was used to examine the morphology. After the optimal processing protocol was made, we analysed the difference in the otoconial morphology in younger and older rats. RESULTS: The otoconia with shorter storage duration in phosphate buffer had more clear surface, while longer exposures resulted in coarse surface and fused otoconia. The otoconia stored in cacodylate buffer had smooth surface and showed grossly normal morphology regardless of exposure time. The otoconia fixed in acetone had irregular surface and was easily displaced. In older rats, the bodies of many otoconia were pitted, fissured, penetrated and eventually broken into several fragments. The size variation of utricular otoconia was greater in older rats. The giant otoconia were discovered frequently on the outer margin of utricular macula in older rats. The weakened or linked filaments that were cut in the older group were frequently observed. CONCLUSION: The appropriate processing for SEM is needed to observe the intact otoconial morphology. Older rats showed more degeneration of otoconia and linked filaments. This study for morphologic changes of senile otoconia is expected to be helpful in understanding the etiology of BPPV and aging effect.