[Osteoclasts and tartrate-resistant acid phosphatase-positive mononuclear cells in the mouse femur: a histochemical study].

Osteoclasts contain tartrate-resistant acid phosphatase (TRAP). To understand the role of osteoclasts in trabecular bone formation, the distal spongiosa of the femurs from 1, 2, 4, 8, 16, and 24 week-old mice were histochemically examined in methacrylate sections stained with an azo-dye method for TRAP. For quantitative evaluations, the surface density of trabecular bones, length of the spongy bones, numerical density of TRAP-positive cells (osteoclasts and mononuclear cells), proportions of the trabecular bone surface covered with osteoclasts, numerical density of osteoclasts on the trabecular bone surface, size of osteoclasts, and distribution of TRAP-positive mononuclear cells in the bone marrow were examined. In conclusion, the results indicate that 1) in the spongiosa, osteoclasts are distributed numerously at the ossification front along the epiphyseal cartilage, junction between the primary and secondary spongiosas, and diaphyseal end of trabecular bones for modeling of the spongiosa, 2) osteoclasts function independently from osteoblasts at the ossification front and the diaphyseal end of trabecular bones, 3) spongiosa changes the amount of trabecular bones through the bone formation-resorption equivalent stage, bone formation dominant stage, and bone resorption dominant stage, 4) TRAP-positive mononuclear cells, probable preosteoclasts, are distributed in the bone marrow, and 5) TRAP-positive mononuclear cells appear frequently in the marrow around osteoclasts, suggesting that osteoclast activity produces a differentiation or migration factor for preosteoclasts.