Meeting Abstract

P2.73  Wednesday, Jan. 5  Cross-sectional Limb Bone Geometry in Mice Bred for High Levels of Voluntary Wheel Running COATS, B.C.*; MIDDLETON, K.M.; KELLY, S.A.; GARLAND, T. Jr.; Cal. State Univ. San Barnardino; Cal. State Univ. San Barnardino; Univ. North Carolina Chapel Hill; Univ. Cal. Riverside britt_coats@yahoo.com

Selection for increased voluntary wheel running in mice has resulted in macro-scale differences in skeletal form. Nonetheless, changes in cross-sectional bone geometry may more accurately reflect the bone’s ability to resist bending and torsion. To examine evolutionary adaptation and plasticity in response to loading, we compared cross-sectional geometry of the femoral mid-shaft in male non-selected control mice, high-runner (HR) mice that had experienced 44 generations of artificial selection, and HR mice expressing the Mini-Muscle (MM) phenotype. Half of each group had wheel access and half did not for 10 weeks. From histological sections, we measured cross-sectional area, cortical and medullary thicknesses, second moments of area, relative ellipticity, and resistance to torsion. Despite no statistical differences among lines or between exercise treatments in cross-sectional area, cross-sectional geometry varied significantly among lines in several biomechanically relevant traits. HR mice had the thinnest cortical bone and the largest medullary diameters, and consequently the highest second moments of area and resistance to torsional loads. The femoral mid-shaft was significantly more elliptical in MM mice, indicating increased resistance to bending resulting from either direct or indirect effects of reduced muscle forces. We conclude that distribution of cortical bone responds both evolutionarily and through phenotypic plasticity to loading environment. Future studies will examine relative rates of bone growth resulting in observed differences. Supported by NSF IOB-0543429 to TG and NIH 1F32AR053008-01 to KMM.