Study of mouse behavior in different gravity environments.

Many experiments have analyzed the effect of the space environment on various organisms. However, except for the group-rearing of mice in space, there has been little information on the behavior of organisms in response to gravity changes. In this study, we developed a simple Active Inactive Separation (AIS) method to extract activity and inactivity in videos obtained from the habitat cage unit of a space experiment. This method yields an activity ratio as a ratio of 'activity' within the whole. Adaptation to different gravitational conditions from 1g to hypergravity (HG) and from microgravity (MG) to artificial 1g (AG) was analyzed based on the amount of activity to calculate the activity ratio and the active interval. The result for the activity ratios for the ground control experiment using AIS were close to previous studies, so the effectiveness of this method was indicated. In the case of changes in gravity from 1g to HG, the ratio was low at the start of centrifugation, recovered sharply in the first week, and entered a stable period in another week. The trend in the AG and HG was the same; adapting to different gravity environments takes time.

Novel method for evaluating the health condition of mice in space through a video downlink.

Clarification of the criteria for managing animal health is essential to increase the reliability of experiments and ensure transparency in animal welfare. For experiments performed in space, there is no consensus on how to care for animals owing to technical issues, launch mass limitation, and human resources. Some biological processes in mammals, such as musculoskeletal or immune processes, are altered in the space environment, and mice in space can be used to simulate morbid states, such as senescence acceleration. Thus, there is a need to establish a novel evaluation method and evaluation criteria to monitor animal health. Here, we report a novel method to evaluate the health of mice in space through a video downlink in a series of space experiments using the Multiple Artificial-gravity Research System (MARS). This method was found to be more useful in evaluating animal health in space than observations and body weight changes of the same live mice following their return to Earth. We also developed criteria to evaluate health status via a video downlink. These criteria, with "Fur condition" and "Respiratory" as key items, provided information on the daily changes in the health status of mice and helped to identify malfunctions at an early stage. Our method and criteria led to the success of our missions, and they will help establish appropriate rules for space experiments in the future.