title: The effects of hibernation and forced disuse (neurectomy) on bone properties in arctic ground squirrels.
abstract: Bone loss is a well-known medical consequence of disuse such as in long-term space flight. Immobilization in many animals mimics the effects of space flight on bone mineral density. Decreases in metabolism are also thought to contribute to a loss of skeletal mass. Hibernating mammals provide a natural model of disuse and metabolic suppression. Hibernating ground squirrels have been shown to maintain bone strength despite long periods of disuse and decreased metabolism during torpor. This study examined if the lack of bone loss during torpor was a result of the decrease in metabolic rate during torpor or an evolutionary change in these animals affording protection against disuse. We delineated changes in bone density during natural disuse (torpor) and forced disuse (sciatic neurectomy) in the hind limbs of the arctic ground squirrel (AGS) over an entire year. We hypothesized that the animals would be resistant to bone loss due to immobilization and disuse during the winter hibernation season when metabolism is depressed but not the summer active season. This hypothesis was not supported. The animals maintained bone density (dual-energy X-ray absorptiometry) and most bone structural and mechanical properties in both seasons. This was observed in both natural and forced disuse, regardless of the known metabolic rate increase during the summer. However, trabecular bone volume fraction (microcomputed tomography) in the distal femur was lower in neurectomized AGS at the study endpoint. These results demonstrate a need to better understand the relationship between skeletal load (use) and bone density that may lead to therapeutics or strategies to maintain bone density in disuse conditions.
authors.affiliation: Chemistry and Biochemistry Department, Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, Alaska lori.bogren@ucdenver.edu.
authors.forename: Lori K
authors.initials: LK
authors.lastname: Bogren
authors.affiliation: Chemistry and Biochemistry Department, Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, Alaska.
authors.forename: Erin L
authors.initials: EL
authors.lastname: Johnston
authors.affiliation: Chemistry and Biochemistry Department, Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, Alaska.
authors.forename: Zeinab
authors.initials: Z
authors.lastname: Barati
authors.affiliation: Chemistry and Biochemistry Department, Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, Alaska.
authors.forename: Paula A
authors.initials: PA
authors.lastname: Martin
authors.affiliation: Mechanical Engineering Department, Colorado State University, Fort Collins, Colorado.
authors.forename: Samantha J
authors.initials: SJ
authors.lastname: Wojda
authors.affiliation: Department of Biological Sciences, University of Alaska Anchorage, Anchorage, Alaska.
authors.forename: Ian G
authors.initials: IG
authors.lastname: Van Tets
authors.affiliation: Universities Space Research Association, Houston, Texas.
authors.forename: Adrian D
authors.initials: AD
authors.lastname: LeBlanc
authors.affiliation: Mechanical Engineering Department, Colorado State University, Fort Collins, Colorado.
authors.forename: Seth W
authors.initials: SW
authors.lastname: Donahue
authors.affiliation: Chemistry and Biochemistry Department, Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, Alaska.
authors.forename: Kelly L
authors.initials: KL
authors.lastname: Drew
mesh_terms: D000818:Animals; D015519:Bone Density / Q000502:physiology*; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging* / Q000502:physiology*; D006605:Hibernation / Q000502:physiology*; D019417:Hindlimb Suspension / Q000502:physiology*; D008297:Male; D020966:Muscular Disorders, Atrophic / Q000000981:diagnostic imaging; D011859:Radiography; D020426:Sciatic Neuropathy / Q000000981:diagnostic imaging; D012589:Sciuridae; D016474:Weight-Bearing / Q000502:physiology
keywords: Bone density; disuse; hibernation; muscle atrophy; torpor