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The Musculoskeletal Effects of Partial Weightbearing in Mice.  E.B. Wagner^1,2, N.P. Granzella³, ¹MIT Department of Aeronautics and Astronautics, ²Harvard-MIT Division of Health Sciences and Technology, Cambridge, MA; ³Pepperdine University, Departments of Social Science and Natural Science, Malibu, CA.

  The effects of partial gravity environments on mammalian physiology are currently poorly characterized. Understanding whether such an environment prevents or reduces the levels of deconditioning seen in microgravity is critical to determining the viability of extended human missions beyond low earth orbit. With a payload of fifteen mice, the Mars Gravity Biosatellite aims to study the effects of, and adaptation to, a 0.38-g environment.

   In preparation for the flight, a ground-based model of partial weightbearing has been developed to study adult mice undergoing reduced musculoskeletal loading. This full-body suspension model allows for manipulation of load levels to simulate various gravitational environments, permitting investigation of how deconditioning scales across the 0-g to 1-g continuum.  

   This novel hardware draws on the heritage of rodent tail suspension and human partial weightbearing studies. It uses spring-suspended forelimb jackets and tail wraps to provide balanced unloading of both the front and hind limbs. Strain gaged animal support flexures, in vivo tibial strain gages, and treadmill-based gait testing enable validation of the musculoskeletal loading environment.

   Adult female BALB/cByJ mice have been successfully supported for periods of up to three weeks in both hypodynamic experiments and fully-weightbearing harnessed controls.  The musculoskeletal effects of partial weightbearing will be quantified using histomorphometry, serum biochemistry, microscale imaging, and biomechanical testing.

(Supported by NASA GSRP NNG 04-GN71H)