Osteoclasts are multinucleated cells that resorb bone. Although osteoclasts originate from the monocyte/macrophage lineage, osteoclast precursors are not well characterized in vivo. The relationship between proliferation and differentiation of osteoclast precursors is examined in this study using murine macrophage cultures treated with macrophage colony-stimulating factor (M-CSF) and receptor activator of NF-κB (RANK) ligand (RANKL). Cell cycle–arrested quiescent osteoclast precursors (QuOPs) were identified as the committed osteoclast precursors in vitro. In vivo experiments show that QuOPs survive for several weeks and differentiate into osteoclasts in response to M-CSF and RANKL. Administration of 5-fluorouracil to mice induces myelosuppression, but QuOPs survive and differentiate into osteoclasts in response to an active vitamin D3 analogue given to those mice. Mononuclear cells expressing c-Fms and RANK but not Ki67 are detected along bone surfaces in the vicinity of osteoblasts in RANKL-deficient mice. These results suggest that QuOPs preexist at the site of osteoclastogenesis and that osteoblasts are important for maintenance of QuOPs.

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The present study investigated the effect on certain physical properties of adding various amounts of hydroxyapatite (HAP) to chitosan sol. Also investigated were connective tissue reactions to a composite membrane that is being developed for possible use in guided tissue regeneration and for the limitation of HA particle migration at sites of implantation. The physical properties evaluated were shrinkage, tensile strength, hardness, calcium ion release, and morphology. Assessment of physical properties indicated that a ratio of HA to chitosan sol of 4/11 by weight is optimal in the preparation of the composite membrane. Subperiosteal implantation of the membranes over rat calvaria revealed that the membranes were well tolerated, with fibrous encapsulation and occasional areas of osteogenesis. Increasing the hydroxyapatite content seems to enhance membrane degradation.

Membranes made of 65, 70, 80, 94, and 100% deacetylated chitin (chitosan) were implanted subperiosteally over the calvaria of 100 rats. Reactions were studied at 1, 2, 4, and 8 weeks after implantation. Membranes prepared with 65, 70, and 80% deacetylated chitin initially elicited marked inflammatory reactions that subsided in time with granulation tissue formation and osteogenesis. Osteocalcin-positive cells were detected immunohistochemically in the granulation tissue. On the other hand, membranes made of 94% deacetylated chitin and chitosan showed mild inflammation and minimal osteogenesis. The results indicate that membranes made of 65, 70, and 80% deacetylated chitin enhance osteogenesis at the site of their implantation. However, the initially severe inflammatory reaction associated with these materials needs to be controlled before the materials would be suitable for clinical application.

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In 4-day-old etiolated rice seedlings, 3 mm of the coleoptile tip did mainly perceive the photostimulus to cause the phytochromedependent inhibition of coleoptile elongation. At this age, cell elongation occurred most in the middle portion of coleoptiles in the dark, and was reversibly controlled by a brief exposure of the tip to red and far-red light. Thus, the photopercep tive site was evidently separated from the growing zone in intact rice coleoptiles.The red-light-induced inhibition of coleoptile elongation was nullified by the removal of tip followed by the exogenous application of IAA. The sensitivity of thus treated coleoptiles to IAA was gradually lost during intervening darkness between the irradiation and the decapitation, and a 50% loss was obtained at ca. 6th hour at 26°C. Polar auxin transport from coleoptile tips was remarkably prevented at the period between, at least, 2nd and 4th hour after red irradiation, and it recovered to the level of dark control by the 6th hour. Far-red light given immediately after red irradiation reversed the yield of diffusible auxin up to that of far-red control.1. 2.3.

A new self-hardening paste was made by using a combination of chitosan, hydroxyapatite (HA) granules, ZnO, and CaO. The sol was made by dissolving 0.1 g of chitosan in a solution of 0.1 g malic acid and 2.0 mL physiological saline solution. Mixed with 0.03 g of CaO and 0.04 g of ZnO powders was 2.77 g (55 wt %) of HA granules which had a homogeneous pore distribution and a porosity of 35-48%. The size of the granules was set for 0.1-0.3 mm. Kneading and setting of the paste generated a little amount of heat (32.8 degrees C) as compared with the heat produced by polymethyl-methacrylate (PMMA) bone cement (114.5 degrees C). The pH value of chitosan-HA-hardened composite after setting was nearly equal to that of human plasma (pH 7.4), while that of PMMA bone cement maintained an acid pH of 4.7. Hydroxyapatite granules less than 0.1 mm, 0.1-0.3 mm, or 0.3-0.6 mm were set using chitosan sol. The size of the granules did not influence the compressive strength of the set chitosan-HA-hardened composite. The greatest compressive strength of chitosan-HA-hardened composite was obtained by using 55 wt % of HA granules. The strength of the chitosan-HA-hardened composite was comparable to that of the cancellous bone derived from tibial eminentia, but was considerably lower than that of the PMMA bone cement.