Browsing by Author "Dirks, Rachel C."

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    Reduced gravitational loading does not account for the skeletal effect of botulinum toxin-induced muscle inhibition suggesting a direct effect of muscle on bone
    (Elsevier, 2013) Warden, Stuart J.; Galley, Matthew R.; Richard, Jeffrey S.; George, Lydia A.; Dirks, Rachel C.; Guildenbecher, Elizabeth A.; Judd, Ashley M.; Robling, Alexander G.; Fuchs, Robyn K.; Physical Therapy, School of Health and Human Sciences
    Intramuscular injection of botulinum toxin (botox) into rodent hindlimbs has developed as a useful model for exploring muscle-bone interactions. Botox-induced muscle inhibition rapidly induces muscle atrophy and subsequent bone loss, with the latter hypothesized to result from reduced muscular loading of the skeleton. However, botox-induced muscle inhibition also reduces gravitational loading (as evident by reduced ground reaction forces during gait) which may account for its negative skeletal effects. The aim of this study was to investigate the skeletal effect of botox-induced muscle inhibition in cage control and tail suspended mice, with tail suspension being used to control for the reduced gravitational loading associated with botox. Female C57BL/6J mice were injected unilaterally with botox and contralaterally with vehicle, and subsequently exposed to tail suspension or normal cage activities for 6 weeks. Botox-induced muscle inhibition combined with tail suspension had the largest detrimental effect on the skeleton, causing the least gains in midshaft tibial bone mass, cortical area and cortical thickness, greatest gains in midshaft tibial medullary area, and lowest proximal tibial trabecular bone volume fraction. These data indicate botox-induced muscle inhibition has skeletal effects over and above any effect it has in altering gravitational loading, suggesting that muscle has a direct effect on bone. This effect may be relevant in the development of strategies targeting musculoskeletal health.
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    Uphill treadmill running does not induce histopathological changes in the rat Achilles tendon
    (Springer Nature, 2013-03-11) Dirks, Rachel C.; Richard, Jeffrey S.; Fearon, Angela M.; Scott, Alexander; Koch, Lauren G.; Britton, Steven L.; Warden, Stuart J.; Anatomy, Cell Biology and Physiology, School of Medicine
    Background: The purpose of this study was to investigate whether uphill treadmill running in rats created histopathological changes within the Achilles tendon consistent with Achilles tendinosis in humans. Methods: Twenty-six mature rats selectively bred for high-capacity running were divided into run and cage control groups. Run group rats ran on a treadmill at a 15° incline for a maximum duration of 1 hr/d, 5 d/wk for 9 weeks at increasing speeds, while rats in the cage control group maintained normal cage activity. After 9 weeks, Achilles tendons were harvested for histological processing and semi-quantitative histopathological analysis. Results: There were no significant group differences within each of the individual histopathological categories assessed (all p ≥ 0.16) or for total histopathological score (p = 0.14). Conclusions: Uphill treadmill running in rats selectively bred for high-capacity running did not generate Achilles tendon changes consistent with the histopathological presentation of Achilles tendinosis in humans.