Electron microscopic study of bone surface changes during aging. The loss of cellular control and biofeedback.

An electron microscopic study was made to determine (1) the effects of aging on periosteal and endosteal bone surfaces and (2) whether the membrane-like arrangement of osteoblasts at bone surfaces was retained during aging. Short-lived BNL inbred Swiss albino mice 5 to 130 weeks of age were perfused with glutaraldehyde. Femoral samples were taken and fixed in cold glutaraldehyde, decalcified in EDTA, and postfixed in OsO4. Epon sections were cut and stained with uranyl acetate and lead citrate. In young mice, during bone formation a zone of osteoid was observed while the preosseous zone above consisted of young collagen fibers in formation. The osteoblasts formed a tight membrane-like structure at all bone surfaces. Where bone formation did not occur, single and multiple osmiophilic laminae were observed. With increasing age collagen formation became diminished as did the width of the preosseous and osteoid zones. Subsequently, the zones disappeared. Increased surface structural complexity was seen in some areas, while other areas revealed simplification with advancing age. This depended upon the net accretionary or resorptive activity at a given surface. The membrane-like arrangement of osteogenic cells was lost in 104-week-old animals, exposing bone surfaces to physio-chemical changes not under cellular control and biofeedback.