Distribution of Substance P Immunoreactive Nerve Fibers in the Tracheal Submucosal Gland of Cats

Immunohistochemistry combined with electron microscopy was employed to investigate the distribution of substance P—immunoreactive (SP-IR) nerve fibers in the tracheal submucosal gland of cats. The SP-IR nerve fibers were found to form a network around the glands. Numerous varicosities were also detected within the basement membrane of the acini and secretory tubules. All the intraglandular varicosities showed close spatial contact with serous cells, mucous cells, and myoepithelial cells. Our findings suggest that substance P—induced mucus secretion from tracheal submucosal glands in cats may be caused not only by a glandular contractile response of myoepithelial cells, but also by direct stimulation to both serous and mucous cells.