Effects of housing density on mouse physiology and behavior in the NASA Animal Enclosure Module simulators

Space flight studies using the Animal Enclosure Module (AEM) make it possible to investigate the role of microgravity on animal physiology and behavior. In this study, we compared the health and well-being of mice housed at different densities in AEM simulators (AEMS), to vivarium shoebox (control) cages (VSBC). A stress assessment battery (SAB) of measures was developed to evaluate mouse health and well-being, and to determine if any of the population sizes resulted in a stressful environment. The SAB was based, in part, on recommendations of a NASA Workshop on Rodent Cage Sizing. It includes: 1) General assessment of appearance, 2) Behavioral assessment (video), 3) Food and water consumption, 4) Body weight changes, 5) Thymus, adrenal, spleen, heart and kidney weights, 6) Plasma corticosterone concentration, 7) Total plasma protein concentration, 8) Total blood leukocyte count, 9) Differential leukocyte count: neutrophil/lymphocyte ratio; eosinophil count, 10) Gastric histology.