Feasibility of a Short-Arm Centrifuge for Mouse Hypergravity Experiments

Abstract

To elucidate the pure impact of microgravity on small mammals despite uncontrolled factors that exist in the International Space Station, it is necessary to construct a 1 g environment in space. The Japan Aerospace Exploration Agency has developed a novel mouse habitat cage unit that can be installed in the Cell Biology Experiment Facility in the Kibo module of the International Space Station. The Cell Biology Experiment Facility has a short-arm centrifuge to produce artificial 1 g gravity in space for mouse experiments. However, the gravitational gradient formed inside the rearing cage is larger when the radius of gyration is shorter; this may have some impact on mice. Accordingly, biological responses to hypergravity induced by a short-arm centrifuge were examined and compared with those induced by a long-arm centrifuge. Hypergravity induced a significant Fos expression in the central nervous system, a suppression of body mass growth, an acute and transient reduction in food intake, and impaired vestibulomotor coordination. There was no difference in these responses between mice raised in a short-arm centrifuge and those in a long-arm centrifuge. These results demonstrate the feasibility of using a short-arm centrifuge for mouse experiments.

The vestibular system is critical for the changes in muscle and bone induced by hypergravity in mice

“…As we recently reported, the trunk became flat and the tail went up at the onset of 2 g environment in mice, although these postural changes were not observed in VL mice during centrifugal acceleration or exposure to 2 g (Morita et al. ). In our preliminary study, the trunk of mice became flat immediately after 3 g centrifugation in mice with sham surgery, and the mice kept the flat posture for 4–7 h. On the other hand, the posture did not change during 3 g centrifugation in mice with VL.…”

“…; Morita et al. ). Briefly, 6‐week‐old mice were anesthetized using 2% isoflurane, and the malleus, anvil, and stapes were removed through the outer ear.…”

“…; Morita et al. ), in which mice with complete VL continued to turn around under warm water, but mice with incomplete VL did not. The surgery was performed bilaterally at the same time.…”

“…Vestibular lesion (VL) was induced in mice according to the method described previously (Abe et al 2010;Morita et al 2015). Briefly, 6-week-old mice were anesthetized using 2% isoflurane, and the malleus, anvil, and stapes were removed through the outer ear.…”

“…The parameters of cautery technique were with the aim of inducing vestibular hair cell lesions and destroying the vestibular epithelium in histological sections of the cochleo-vestibular organ. The effectiveness of the VL procedure was checked by swimming test, as described previously (Abe et al 2010;Morita et al 2015), in which mice with complete VL continued to turn around under warm water, but mice with incomplete VL did not. The surgery was performed bilaterally at the same time.…”