| dc.description.abstract | As the focus shifts to potential Lunar and Mars missions, there are many aspects of the
space environment that are still unknown, one of those being radiation exposure. There are many
radiation studies examining the effects of acute, high dose radiation on bone; however, it has been
discovered that the total exposure astronauts will experience will be much lower than the doses
these studies have utilized. The purpose of this study was to determine the effect of a continuous,
low-dose irradiation exposure on bone at various time points. Sixty-six male C57Bl/6 mice, aged
47-49 weeks, were placed in the continuous radiation field for either four, twelve, or twenty-eight
days. The radiation field was created by locating four activated ^60Co wires emitting gamma
radiation around a mouse rack in a lead-shielded room. At a dose rate of 6.49 mGy/day, the total
cumulative dose was approximately 25.6 mGy for four days, 77.88 mGy for 12 days, and 181.72
mGy for 28 days. Fluorochrome calcein labels were injected to obtain bone formation rate post
termination. DXA scans were performed prior to radiation exposure and again just before
termination to determine bone mineral density and body composition. At termination, tibiae and
femurs were collected from all animals for histomorphometry assessments. Also, osteocyte
apoptosis was quantified in cancellous bone via staining for Annexin V. Continuous radiation
exposure at this low dose rate did not have any impact on total body bone mineral density, lean
mass, fat mass, and percent fat at any time point. There were also no differences in cortical or
cancellous bone formation rate at any time point in radiation-exposed mice vs. control animals.
Also, bone volume and trabecular microarchitecture were not affected by radiation at any time
point. Osteoid and osteoclast surfaces were not different after radiation at any time point, nor were
there any differences in osteocyte apoptosis at any time point examined. These results are quite
different from those seen after acute, high-dose radiation exposures, after which decreased bone
volume, depressed bone formation rate, and increased osteoclast surface are often observed. This
data begins to elucidate a time course of continuous low dose radiation impacts on bone, similar
to radiation that might be experienced during transit to Mars and alludes to the potential that it may
not be deleterious to bone health, as previously assumed. | en |
