On ground preflight studies on skeletal muscle from mice kept in the Mouse Drawer System (MDS)

The Mouse Drawer System (MDS) has been developed to individually accommodate mice on board the International Space Station. MDS size is 110 x 118 mm (floor area) and 85 mm height, which is several fold smaller than standard laboratory cages, and may affect mouse activity. The study was aimed at establish the effects of 20-day housing in MDS on 2-month-old male mice compared to age-matched controls individually housed in normal cages. After 20 days, body weight of MDS mice (n = 3) decreased by about 12% whereas that of controls (n = 3) increased by about 4.4%. The mean cross sectional area of EDL and soleus muscle fibers of MDS mice was slightly lower than that of controls. SDS-PAGE analysis of myosin heavy chain (MyHC) composition shows that type 2B MyHC was slightly reduced in MDS EDL compared to control. Expression of the activity-dependent gene PGC-1α and of IGF-1 isoforms was up-regulated in MDS soleus, whereas that of chloride channel-1 was unchanged. Expression of ubiquitin-ligases and autophagic genes was only slightly modified. The study shows that short-term housing in the MDS payload produces adaptive changes on hind limb skeletal muscle properties, known to disappear in prolonged housing.