Sympathectomy was carried out in 4-week-old Sprague-Dawley rats by unilateral surgical removal of the superior cervical ganglion. Sham-treated rats served as controls. All rats were injected with tetracycline hydrochloride at surgery as well as 36 hr prior to sacrifice. Rats were killed at 7, 14, or 21 days following sympathectomy. Mandibular periosteal and endosteal surfaces were analyzed by fluorochrome morphometry. Osteoclasts were identified by acid phosphatase staining, and incisor and molar root sockets were analyzed morphometrically. Following sympathectomy, periosteal and endosteal apposition as well as the rate of mineralization were significantly lower. At the same time, a significant increase in the number of osteoclasts per socket as well as in active and inactive bone resorption surfaces was also seen. All parameters, however, returned to normal values 2-3 weeks after sympathectomy. The data provide the first direct quantitative evidence that sympathetic neurons modulate bone resorption and bone remodeling in vivo.

Sympathectomy was carried out in rats by injections of guanethidine-sulfate from birth to 14 days of age. At 45 days of age, the activity of osteoblastic cells was monitored by 3H-proline autoradiography. Effectiveness of sympathectomy was verified by light-microscopic examination of superior cervical and celiac ganglia. Grain counts over periosteal osteoblasts of the femoral diaphysis and osteoblasts mesial to the first molar in the mandible demonstrated a significant reduced uptake of 3H-proline in the sympathectomized rats. The data provide direct evidence of sympathetic influence on osteoblastic activity and suggest that sympathectomy may result in the loss of a trophic influence which is important in the regulation of osteogenesis.

Osteoblastic activity in the rat femur was assessed following sympathectomy by injections of guanethidine sulfate from birth to 14 days of age. At ages 30, 45 and 90 days, osteogenesis was monitored by quantitative autoradiography using ³H-proline. Grain counts over periosteal osteoblasts of the femoral diaphysis showed a significant reduction in the uptake of ³H -proline in sympathectomized rats. The results indicate that the sympathetic innervation of bone influences osteoblastic activity and provide support for a role of the autonomic nervous system in the regulation of bone formation.

No abstract

In vivo effects of fibroblast growth factor (FGF) on osteogenesis were evaluated in the chick embryo. Autoradiographic studies of Η-proline labeling over bone matrix indicated that 24 h after treatment on day 11, FGF stimulated osteogenic cell proliferation, while inhibiting the production of bone matrix collagen. However, 4 days after multiple doses of FGF, the large pool of newly formed osteogenic and chondrogenic cells expressed their function with the increased formation of matrix. The data provide in vivo evidence of the effects of exogenous FGF on osteogenesis and also point to a possible role for FGF both in embryonic osteogenesis and in fracture repair.