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Early Development of Gravity-Sensing Organs in MicrogravityMost animals have organs that sense gravity. These organs use dense stones (called otoliths or statoconia), which rest on the sensitive hairs of specialized gravity- and motion-sensing cells. The weight of the stones bends the hairs in the direction of gravitational pull. The cells in turn send a coded representation of the gravity or motion stimulus to the central nervous system. Previous experiments, in which the eggs or larvae of a marine mollusk (Aplysia californica, the sea hare) were raised on a centrifuge, demonstrated that the size of the stones (or test mass) was reduced in a graded manner as the gravity field was increased. This suggests that some control mechanism was acting to normalize the weight of the stones. The experiments described here were designed to test the hypothesis that, during their initial development, the mass of the stones is regulated to achieve a desired weight. If this is the case, we would expect a larger-than-normal otolith would develop in animals reared in the weightlessness of space. To test this, freshwater snails and swordtail fish were studied after spaceflight. The snails mated in space, and the stones (statoconia) in their statocysts developed in microgravity. Pre-mated adult female swordtail fish were flown on the Space Shuttle, and the developing larvae were collected after landing. Juvenile fish, where the larval development had taken place on the ground, were also flown. In snails that developed in space, the total volume of statoconia forming the test mass was 50% greater than in size-matched snails reared in functionally identical equipment on the ground. In the swordtail fish, the size of otoliths was compared between ground- and flight-reared larvae of the same size. For later-stage larvae, the growth of the otolith was significantly greater in the flight-reared fish. However, juvenile fish showed no significant difference in otolith size between flight- and ground-reared fish. Thus, it appears that fish and snails reared in space do produce larger-than-normal otoliths (or their analogs), apparently in an attempt to compensate for the reduced weight of the stones in space. The fish data suggest that there is a critical period during which altered gravity can affect the size of the test mass, since the larval, but not the juvenile, fish showed the changes.
Document ID
20030068205
Document Type
Other
Authors
Wiederhold, Michael L. (Texas Univ. Health Science Center San Antonio, TX, United States)
Gao, Wenyuan (Texas Univ. Health Science Center San Antonio, TX, United States)
Harrison, Jeffrey L. (Texas Univ. Health Science Center San Antonio, TX, United States)
Parker, Kevin A. (Texas Univ. Health Science Center San Antonio, TX, United States)
Date Acquired
September 7, 2013
Publication Date
January 1, 2003
Publication Information
Publication: The Neurolab Spacelab Mission: Neuroscience Research in Space: Results from the STS-90, Neurolab Spacelab Mission
Subject Category
Aerospace Medicine
Funding Number(s)
CONTRACT_GRANT: NSF IBN-95-29136
CONTRACT_GRANT: NAG2-950
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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IDRelationTitle20030068190Analytic PrimaryThe Neurolab Spacelab Mission: Neuroscience Research in Space: Results from the STS-90, Neurolab Spacelab Mission