Task Progress:
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The specific aim and project remain as originally proposed. A No Cost Extension was requested because we have finally found access to the Focused Ion Beam and Scanning Electron Microscope (dual beam) configuration needed to validate our hypothesis. Images have been acquired, and new imaging sessions are scheduled. Although delayed, we have made significant progress and are on course to successful complete the project.
Specific Aim: Is the structure of inner ear otoconia remodeled by the intensity and duration of gravity loading? To answer this question we will determine the structural integrity of otoconia as a result of short- and long-duration exposure to altered gravity conditions. Mammals possess a highly conserved and elaborate gravitoinertial sensing system in the inner ear, comprised of two otolith organs, the utricle and saccule, using biomineral crystalline deposits of calcium carbonate (CaCO3) called otoconia. Otoconia formation begins during embryogenesis and is completed in early postembryonic stages. The calcium-containing part of the otoconia forms the outer layer, and it has the capacity to turn over. In weightlessness, it is argued the organism counters the loss of the gravity vector by increasing CaCO3 production and deposition onto existing otoconia, in an attempt to restore correct biomechanical interaction between movement and neural sensation. In hypergravity, it is argued the opposite occurs and the otoconia lose mass.
Results and Progress
The entire sample populations are now tabulated into two groups: 1) samples completely analyzed and 2) samples that will be either scanned using the standard SEM or milled using the focus ion beam/SEM instrument. It was necessary to refrain from imaging all the samples using the standard protocol of sputter-coating to the samples. This thin layer of conductive material might be inappropriate for the FIB technique, and thus samples were held in reserve. We now have images of otoconia from FIB. I am not satisfied with the results so far, and I am confident that with a slower milling technique we will be able to visualize the outer shell and inner organic core of the otoconia. This will be particularly desired for the flight otoconia where it appears a deposition has resulted from the weightlessness exposure.
FIB imaging results obtained from FEI dual beam FIB/SEM show the focused ion beam can directly modify or "mill" the otoconia surface with nanometer precision. We are gaining experience in this technique and specifically we must carefully control the energy and intensity of the ion beam to create a clear cross-sectional image of the otoconia and reveal the inorganic layers and the boundary interface between the outer shell and inner organic core matrix. To conclude the study we will characterize using FIB/SEM technique the otoconia from control mice and the experimental (micro-G and hyper-G mice).
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Abstracts for Journals and Proceedings
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Boyle R, Varelas J. "Influence of duration and magnitude of gravity loading on mouse inner ear otoconia." 2012 NASA Human Research Program Investigators’ Workshop, Houston, TX, February 14-16, 2012. 2012 NASA Human Research Program Investigators’ Workshop, Houston, TX, February 14-16, 2012. , Feb-2012
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Abstracts for Journals and Proceedings
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Boyle R. "Inner ear otoconia response in mice to micro- and hyper-gravity." 1st Annual International Space Station (ISS) Research and Development Conference, Denver, CO, June 26-28, 2012. 1st Annual International Space Station (ISS) Research and Development Conference, Denver, CO, June 26-28, 2012. , Jun-2012
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Abstracts for Journals and Proceedings
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Boyle R, Popova Y, Varelas J, Kondrachuk A, Balaban P. "Influence of magnitude and time course of altered gravity on the vestibular system in fish, snails, and mice." Society for Neuroscience 2012, New Orleans, LA, October 13-17, 2012. Program#/Poster#: 574.08/HH20. Abstract available at: http://www.abstractsonline.com/Plan/ViewAbstract.aspx?sKey=5353275c-c339-4b52-b456-feb5782bb6b9&cKey=f383c367-adab-46db-83b3-9a868587ca0a&mKey=70007181-01c9-4de9-a0a2-eebfa14cd9f1 ; accessed 6/12/2013. , Oct-2012
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Abstracts for Journals and Proceedings
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Boyle R, Popova Y, Varelas J, Kondrachuk A, Balaban P. "Influence of magnitude and time course of altered gravity on the vestibular system in vertebrates." 2013 NASA Human Research Program Investigators’ Workshop, Galveston, TX, February 12-14, 2013. 2013 NASA Human Research Program Investigators’ Workshop, Galveston, TX, February 12-14, 2013. , Feb-2013
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Abstracts for Journals and Proceedings
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Boyle R, Popova Y, Varelas J, Kondrachuk A, Balaban P. "Influence of magnitude and time course of altered gravity on the vestibular system in fish, snails, and mice." To be presented at the 19th IAA Humans in Space Symposium, Cologne, Germany, July 7-13, 2013. 19th IAA Humans in Space Symposium, Cologne, Germany, July 7-13, 2013. Submitted and accepted but PI's participation in the congress and presentation of this research is prevented due to the "sequestration." , Jul-2013
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