Age dependent development of osteopenia in the long bones of tail-suspended mice

The microgravity, or weightlessness, of space causes measurable bone deterioration in humans and rats. The use of tail-suspension to simulate weightlessness in rats is well-documented. Our studies have focused on mice, as their smaller size suggests more efficient space-based experimentation. Using mice ranging from 1.3-12 months in age, the results of a 2-wk suspension were ascertained through measurement of bone mass and mechanical (3-pt bending) characteristics. Significant differences between tail-suspended (S) and control (C) mice were noted for mice less than 6 months old. Such significance was not observed for the older mice. In addition, for the 1.3 month and 1.7 month old mice, a group of mice were sacrificed (designated PC, or pre-control) with ages matching those of the S mice prior to suspension. These were assayed to determine if the effects of tail-suspension are predominantly on growth-suppression or on bone atrophy. Our results show that tail-suspension effects are best explained by growth-suppression, as both the C and S groups showed growth when compared to the PC groups. 4-wk tail-suspensions of 10 month old mice were implemented to determine if increased suspension time would produce deterioration in older mice. An indication of longer periods of suspension being effective was found, but significant differences like those obtained for younger mice were not seen in the numbers of mice used.