Subcutaneous Basic FGF-Injection Accelerates the Development of Mandibular Condyle of Newborn Mice during Lactation Period

Abstract

To elucidate the effect of local bFGF administration, we administered a total of 0.3μg rhbFGF was to the left mandibular condyle by three injections of 0.1μl bFGF solution for 3 days after birth. The contralateral condyles with three injections of 0.1μl physiologic saline served as controls. Serial sections including the widest condyle were evaluated with H-E staining and immunostaining for PCNA. The maximum width of condyle, proliferative zone thickness, proliferative zone thickness ratio and proliferating index were analyzed using image analysis software after digital image capture of H-E stained sections. All condyles were composed of fibrous, proliferative, maturation and hypertrophic cell zones without significant abnormal findings. Experimental condyles demonstrated a markedly thickened proliferative zone compared with that of the controls at 1 day after the injection. At 4 and 7 days, chondrocytes and hypertrophic chondrocytes of the experiments increased in thickness. However, at 14 days after the injection, both the controls and experiments showed similar features with an upward shift of ossification front and active formation of bone trabeculae. Morphometrically, all values of experiments were significantly higher than those of the controls. Especially at 4 days after the final injection, proliferative zone thickness and proliferative index values of the experiment reached a peak and were nearly 1.6-fold higher than those of the control, which were statistically significant compared to other experimental groups. Despite the short half-life of rhbFGF, its effect seems to be prolonged by synergic actions of growth factors such as bFGF or TGF beta1. In conclusion, we showed that local administration of bFGF was feasible for accelerating mesenchymal cell proliferation of mandibular condyles of newborn mice in the lactation period after birth.