Marked depression or arrest of bone formation has been associated with space
flight and simulated weightlessness. The mechanism of this suppression of osteo-
genesis is unclear, but probably involves altered induction. Data indicate that
nuclear volume frequency distributions are an effective means of assaying pre-
osteoblast differentiation in a population of connective tissue cells. Thus,
the objective of this experiment was to determine whether space flight would
alter cellular induction in the fibroblast-like cells in the rat periodontal
ligament (PDL).
PDL, the osteogenic interface between tooth and bone, was morphometrically
analyzed. The region studied was a 300 µm length of midroot PDL on the medial
aspect of the medial root of the maxillary first molars. Volumes for 100 nuclei
from throughout the width of the PDL were determined, and frequency distri-
butions of nuclear volume for each group were calculated. Studies were conducted
on rats sacrificed at recovery and six and 29 days postflight.
Immediately postflight, PDL width and total cell number were decreased. Fre-
quency distributions of nuclear volume revealed that presumptive preosteoblasts
(nuclei ³ 130 µm-3) were particularly depressed. Compared to vivarium controls,
frequency distributions of nuclear volume revealed a relative increase in smaller
nuclei (² 80 µmÐ3) at the expense of these larger nuclei. No significant differ-
ences in interzone mean nuclear volumes were observed for the groups sacrificed
at six and twenty-nine days postflight. This study suggests that depleted numbers
of preosteoblasts may be an important factor in the arrest of bone formation
during weightlessness. Data are consistent with either a defect in proliferation
and/or differentiation. Additional cell kinetic studies utilizing 3H-thymidine
are needed to define the mechanism of this important aerospace problem.
Roberts, W.E. and P.G. Mozsary: Effects of Weightlessness on Osteoblast Differentiation
in Rat Molar Periodontium. Proceedings of the Aerospace Medical Association
Meeting, San Antonio, Tex., May 3-6, 1981, pp. 114-115.
Roberts, W.E. et al.: Nuclear Volume Assay of Osteogenic Potential in Ulna
Primary Spongiosa of Rats Flown in Space for 18.5 Days. Anatomical Record, vol.
214, 1986, p. 109A.
Roberts, W.E. et al.: Quantitative Analysis of Selected Bone Parameters: Supplemental
Report 1: Effects of Weightlessness on Osteoblast. Final Reports of U.S. Rat
Experiments Flown on the Soviet Satellite Cosmos 1129. M.R. Heinrich and K.A.
Souza, eds., NASA TM-81289, 1981, pp. 127-148.
Roberts, W.E. et al.: Suppression of Osteoblast Differentiation During Weightlessness.
Physiologist, supl., vol. 24, 1981, pp. S75-S76.
¥ = publication of related ground-based study