[Changes in morphology and calcium content of otoconia in rats after 120 d tail-suspension]

The morphology and calcium content of otoconia in rats after long term (120 d) tail-suspension were studied using scanning electron microscopy (SEM) and X-ray microanalysis, respectively. The results showed that after 120 d simulated weightlessness otoconia were round, irregularly shaped, or with fissures, and there were rough and fine granular or small globular substances on the surface. X-ray microanalysis showed that the calcium content in the otoconia of both utricule and saccule was significantly decreased in the 120 d tail-suspended rats than that in control (P < 0.01). These results suggest that a long term(120 d) simulation of the headward distribution of blood volume and hindlimb underloading effect induced by weightlessness may cause the morphological changes and lower calcium content of the otoconia. Finally, the possible mechanism and the physiologic meaning of these findings are discussed.