Morphology and metabolism of otoconia of guinea pig

Abstract

Morphology and metabolism of the otoconia were studied by scanning electron microscope and x-ray microanalyzer. The experimental animals (albino guinea pig) were divided into two groups. The first group served as control and the second group were treated with streptomycin sulfate (SM). In control animals, the shape of the otoconial crystal of the utricular macula was cylindrical with two pointed ends. In this group, unusual otoconia were also observed in the deep layer of the otoconial crystalline layer. Furthermore, some decrease in number of otoconia was noted in 40% of this group. All of SM administrated animals showed marked reduction of otoconia. This indicates that SM disturbs the metabolism of the otoconia. Two months after cessation of SM injection, it was found that the otoconia on the otochnial membrane increased in number, suggesting regeneration of the otoconia. There were small granules observed on the surface of the otoconial membrane and also on the other side of the otoconial membrane which faces the sensory epithelia. These granules contained certain amount of calcium. These findings suggest that the small granules are a precursor of the otoconia. Numerous granular substances were observed on the surface of the sensory epithelia. It was also found that these granular substances were transformed into the otolithic crystal. There were many protrusions from the surface of the supporting cells surrounding the sensory hair cells. These protrusions and granular substances contained some amount of calcium. Some specimens were also freeze-cracked and observed in the same way. In the cracked specimens, small granules were found in some cells and these granules also contained some amount of calcium. Therefore, it is suggested that precursors of otoconia may be secreted from the supporting cells. On the surface of the perimacular dark cells, numerous otoconia were observed. They appeared fragmented and shrunken. Their surface was irregular like a pumice stone. These deformed otoconia contained smaller amount of calicium than the normal. The author found new mesh-like substances on the surface of the dark cells. These substances were various in shape and had many micropores. It was concluded that the calcium ions are actively absorbed by dark cells and the mesh-like substance is an organic matrix of the otoconia.