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SPACEFLIGHT-INDUCED CHANGES IN TIBIAL BONE FORMATION IN THE MOUSE M.L. Simons^1,2ё R.E. Thacker³, Y. Yuan³, T.A. Bateman³. ¹Mechanical Engineering Department, University of Colorado.  NSF REU Program, Clemson University, Clemson, SC.  ³Department of Bioengineering, Clemson University, Clemson, SC.

   The purpose of this study was to investigate the effects of micro-gravity on murine skeletal development, representing the first examination of spaceflight’s effect on mouse bone.  This was part of a larger study, in which female C57BL/6J mice, aged 64 days were divided into Animal Enclosure Module ground control (AEM) and Space Flight (SF) groups.  SF animals were exposed to microgravity for approximately 11 days and 17 hours aboard the Space Shuttle Endeavour (STS-108/UF-1).  Calcein, a fluorescent bone marker was injected (20mg/kg) one day prior to launch to allow visualization of bone formed during flight. 
   Following the shuttle flight, both AEM control and SF animals were sacrificed.  To observe effects on bone formation between AEM and SF groups, the left tibia were embedded in Epoxide epoxy (Buehler, Lake Bluff, IL), cured, and sectioned at the tibiofibular junction.  Polished samples were then viewed and photomicrographs taken at 10x magnification.  Sections were imaged using an AxioCam MRc(Zeiss) at 16.7x and imported into SigmaScan Pro version 5.0 (Jandel Scientific Software, SanRafael, CA) to observe the effects.  Bone Formation Area (BF.Ar) and Active Mineralizing Perimeter (AM.Pm) were measured and Mineral Apposition Rate (MAR) was calculated for both the periosteal and endocortical surfaces [MAR = BF.Ar/(AM.Pm/13 days)].
   There was no difference found in the BF.Ar, MAR, or the AM.Pm for the periosteal surface.  On the endocortical surface the SF group had a BF.Ar decrease of 36 % (p = 0.02) compared to the AEM controls.  SF did not change AM.Pm at the endocortical surface, however, it did decrease MAR 33% (p = 0.03) in relation to the ground controls.  These findings indicate that spaceflight does have a direct effect on the amount of bone mineralized on the endocortical surface of the mouse tibia after exposure to 12-days of spaceflight. 

(Supported by: Amgen Inc., NSF REU Program, NASA/SC EPSCoR)