The effect of developmental stage on the mouse response to induced osteopenia

This dissertation concerns the dependence of spaceflight-induced and simulated spaceflight-induced changes in the skeletal system on the developmental state of the mouse. In order to investigate this subject, general characteristics such as animal mass and metabolism are considered together with specific investigations of the skeletal system itself and the related immune system. The hypothesis that the level of development will impact skeletal response to spaceflight or spaceflight simulations is supported by initial investigations in which age, sex and strain of the mice are varied. The research focuses on the tail-suspension model for spaceflight, but pivotal insight is a careful investigation of provided by a second model for skeletal degeneration and a careful investigation of mouse bone and immune system development. The dissertation provides evidence for a direct relationship between the developmental state of the animal and skeletal effects of suspension. The skeletal formation rate is seen to rapidly plateau by six months of age in mice; thereafter, a near steady-state in terms of peripheral bone structural, compositional and geometric parameters is maintained until the second year, during which an endogenous "osteon-based osteoporosis" apparently develops. These findings also establish the first set of data investigating the utility of the mouse skeleton as an animal model for bone changes.