Receptor organs for detecting gravity are called otocysts in invertebrates, and otolithic organs in vertebrates. They are pouches that contain dense masses of calcified crystals called otoconia; the action of gravity on these masses, overlying specialized mechanosensory cells, provides a signal for determining the normal earth-vertical direction. The otoconia have remarkably specific mineral chemistry and crystalline structure in different animals, and pilot studies suggest that these features may vary somewhat under different gravitational conditions. The flight of Neurolab provides a unique opportunity to examine the development of these gravitational sensing accessories in the absence of normal gravity. Ground-based studies using electron microscopy and atomic-force microscopy provide data on the sizes, weights, and mineral composition of the otoconia during normal development. Results will be important for understanding development of the vestibular system, for considering calcium homeostasis in general, and may have some impact on biomaterials studies. Contribution to this project represents the NSF Biological Sciences Directorate's participation in the NASA/Interagency Neurolab activity on the space shuttle orbiter, which in turn is part of Decade of the Brain activities.
