title: Effect of tail suspension (or simulated weightlessness) on the lumbar intervertebral disc: study of proteoglycans and collagen.
abstract: METHODS
  An experiment to measure the proteoglycan and collagen content of the lumbar intervertebral discs of rats that had been tail-suspended for up to 4 weeks.
  
  
  OBJECTIVE
  To determine the effect of tensile force (or simulated weightlessness) on the intervertebral disc.
  
  
  BACKGROUND
  During space flight the intervertebral disc experiences low compressive force (because of so-called "weightlessness"), which, in turn, produces, among other things, low hydrostatic pressure acting on the disc cells. Although disc cells respond (in vitro) to changes in hydrostatic pressure, it is unclear what effect low levels of hydrostatic pressure have in vivo and whether they lead to a degenerative catabolic process. The rat tail-suspension model is appropriate for studying the effects of tensile force on the disc. The disc (especially the anulus) is subjected to tension during various body movements (e.g., bending stretches the posterior anulus, and twisting tensions the whole anulus).
  
  
  METHODS
  Thirty-two Sprague-Dawley rats were tail-suspended for either 2 weeks (16 rats) or 4 weeks (16 rats). Sixteen other rats were left unsuspended for 4 weeks; these were used as controls. At the end of 2 or 4 weeks, as appropriate, the rats were killed and their lumbar spines were removed. In each rat the six lumbar discs were bisected and the discs (anulus and nucleus together) were carefully removed. The six lumbar discs from one rat were pooled with the six lumbar discs of a second matching rat (i.e., from the same group) to give one sample. The disc samples were then assessed using enzyme-linked immunosorbent assays.
  
  
  RESULTS
  There was a 35% statistically significant decrease in proteoglycan content going from the control group down to the 4-week group, but no significant differences between the control group and the 2-week group or between the 2-week group and the 4-week group. There were no statistically significant differences between the three groups for collagen I or collagen II.
  
  
  CONCLUSIONS
  These findings clearly establish a link between decreased proteoglycan content and tension on the disc, as modeled by the tail-suspended rat.
authors.affiliation: Emory University School of Medicine, Veterans Affairs Medical Center, Department of Biology, Emory University, Atlanta, Georgia, USA. William_Hutton@Emory.org
authors.forename: William C
authors.initials: WC
authors.lastname: Hutton
authors.forename: S Tim
authors.initials: ST
authors.lastname: Yoon
authors.forename: William A
authors.initials: WA
authors.lastname: Elmer
authors.forename: Jun
authors.initials: J
authors.lastname: Li
authors.forename: Hideki
authors.initials: H
authors.lastname: Murakami
authors.forename: Akihito
authors.initials: A
authors.lastname: Minamide
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Akamaru
mesh_terms: D000818:Animals; D003094:Collagen / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay; D019417:Hindlimb Suspension; D007403:Intervertebral Disc / Q000378:metabolism*; D008159:Lumbar Vertebrae / Q000378:metabolism*; D011509:Proteoglycans / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D018474:Weightlessness Simulation
chemical_list: D011509:Proteoglycans; D003094:Collagen