Experimental protocol. Mice underwent hindlimb-unloading (HLU) for 7 days, received whole-body irradiation at a single dose of 50 cGy, then HLU for an additional 7 days and were then sacrificed for tissue isolation at days 4 and 30 after the combined treatments. Radiation was delivered as a fully modulated beam of 150 MeV protons to give a broad energy distribution similar to a solar particle event (SPE) and galactic cosmic ray (GCR) radiation spectrum.