Substance P activates osteoclast formation and osteoclastic bone resorption through the neurokinin-1 receptor

Axons containing substance P (SP) serve bone tissue, however, the role of S P in bone metabolism, particularly on osteoclastic bone resorption, is unkn own. Therefore, we examined the distribution of neurokinin l-receptors (NK1 -R), which have a high affinity to SP, in rat osteoclasts in vivo, and inve stigated the effects of SP on osteoclast formation and osteoclastic bone re sorption in vitro. Using electron microscopy, immunoreactive products of NK 1-R were seen in the plasma membrane and cytoplasm of osteoclasts, and were also observed in preosteoclast-like cells. Cell suspensions containing ost eoclasts were prepared from neonatal rats and cultured on ivory slices. The addition of 10(-10)-10(-6)M SP caused the number of mono- and multi-nuclea ted tartrate-resistant acid phosphatase positive (TRAP(+)) cells to increas e. The increase in TRAP(+) cells with the addition of 10(-8) M SP was inhib ited by treatment with the SP receptor antagonist. In cultures on glass cov erslips, time-lapse studies show that SP induced cell spreading within 5 mi n and maintained the spreading. The number of resorption pits excavated by the osteoclasts and the resorption area per osteoclast increased in a 48-ho ur incubation with 10(-8) M SP. These results suggest that SP stimulates os teoclast formation and activates osteoclastic bone resorption through NK1-R .