ASGSB 2003 Annual Meeting Abstracts


Expression of CalBindin in sensory cells of the labyrinth in tadpoles (Xenopus laevis) after a space flight and its relation to the extent of the static vestibuloocular reflex. E. Horn1, D. Husson2, C. Dournon3, S. Böser1, and L. Gualandris-Parisot2. 1Gravitational Physiology, University, Ulm, Germany; 2Centre de Biologie du Développement, University Paul Sabatier, Toulouse, France; 3EA 3442 Genetic, Signaling, Differentiation., University Henri Poincaré, Nancy, France.

The calcium-buffering protein CalBindin is common in sensory cells including vestibular hair cells. Studies in the chick provided evidence for its involvement in otoconia formation. We studied its expression in vestibular sensory cells in tapoles (Xenopus laevis) after exposure to microgravity and, in addition, focused our interest on correlations with the extent of the static vestibuloocular reflex (rVOR) which is usually modified by a 9- to 10-day period of gravity deprivation. - METHODS: Xenopus tadpoles were deprived from gravity for 9.5 days during the French Soyuz taxi flight Andromède to the International Space Station (October 21-31, 2001). At onset of microgravity, tadpoles were at stages 27 and 45. After the mission, each tadpole was tested first for its rVOR and, thereafter, fixed for the immunocytochemical stains for CalBindin. - RESULTS: Despite of the low number of animals, CalBindin expression in macula cells revealed no sensitivity to microgravity exposure in both young and old tadpoles. In particular, within the utricular and saccular macula, numbers and sizes of CalBindin stained cells were as large as those recorded from the ground controls. In contrast, the rVOR of 0g-tadpoles with upward bended tail was depressed in both young and old tadpoles, but not affected or augmented in 0g-animals with normal tail in the young and the old group, respectively. The behavioral data were never significantly correlated with the CalBindin data recorded from the macular hair cells. - CONCLUSIONS: (1) In constrast to observations in other vertebrate animals, expression of CalBindin in labyrinthine hair cells of Xenopus is insensitive to gravity deprivation. (2) Microgravity-induced modifications of the rVOR are not caused by the status of maturation of utricular and saccular hair cells.


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