Distribution of substance P and neurokinin-1 receptors in the peri-implant epithelium around titanium dental implants in rats

We examined the distribution of substance P and neurokinin-1 (NK1) receptors and substance-P-containing nerve fibers in the peri-implant mucosa around titanium dental implants in rats. Immunohistochemistry and immunocytochemistry revealed that substance-P-immunoreactive nerve fibers abundantly innervated the peri-implant epithelium (PIE) compared with other epithelia of the peri-implant mucosa. NK1 receptor mRNA and protein expression in the peri-implant mucosa were confirmed by reverse transcription with the polymerase chain reaction and immunoblotting. Immunoelectron microscopy revealed that NK1 receptor immunoreactivity was preferentially localized in peri-implant epithelial cells. NK1-receptor-positive products were found on the plasma membrane and in vesicles and granules in PIE cells. Neutrophils and intraepithelial nerve axons in the PIE were positive for the NK1 receptor. NK1 receptor immunoreactivity was also detected in endothelial cells, fibroblasts, and nerve fibers in the connective tissue beneath the PIE. These findings suggest that peri-implant tissue receives sensory information through regenerated nerves expressing substance P and the NK1 receptor. In the peri-implant mucosa, the substance P/NK1 receptor system may play a role in pain transmission, the endocytosis of neutrophils, the extravasation of crevicular fluid, and the migration of macrophages and neutrophils in response to neurogenic inflammation, as in healthy gingiva.