title: Nuclear morphometric analysis of osteoblast precursor cells in periodontal ligament, SL-3 rats.
abstract: Five small (55 days old, 196 +/- 5 g) (mean +/- SE) and five large (83 days old, 382 +/- 4 g) Sprague-Dawley strain, specific pathogen-free rats were exposed to a 7-day spaceflight and 12-h postflight recovery period. As measured in 3-micron sections, periodontal ligament (PDL) fibroblastlike cells were classified according to nuclear size: A + A' (40-79), B (80-119), C (120-169), and D (greater than or equal to 170 microns 3). Since the histogenesis sequence is A----A'----C----D----osteoblast, the relative incidence of A + A' to C + D is an osteogenic index. No difference in A + A' or C + D cells in small rats may reflect partial recovery of preosteoblast formation (A----C) during the 12-h postflight period. Large flight rats demonstrated increased numbers of A + A', indicating an inhibition of preosteoblast formation (A----C). At least in the older group, a 7-day flight is adequate to reduce PDL osteogenic potential (inhibition in PDL osteoblast differentiation and/or specific attrition of C + D cells) that does not recover by 12-h postflight.
mesh_terms: D000818:Animals; D001835:Body Weight; D002453:Cell Cycle; D002467:Cell Nucleus / Q000648:ultrastructure*; D008297:Male; D010006:Osteoblasts / Q000648:ultrastructure*; D010513:Periodontal Ligament / Q000166:cytology / Q000648:ultrastructure*; D051381:Rats; D011919:Rats, Inbred Strains; D013026:Space Flight