Substance P immunoreactive sensory axons as a subset of the total axonal population in the maxillary sinus of the rabbit: A characterization of normal and infected mucosa

Substance P (SP), one of the neuropeptides released from sensory nerves, is thought to mediate neurogenic inflammation. Although SP immunoreactive axo ne have been described in the sinus mucosa, no attempt has been made to cha racterize SP fibers as a subset of all axons present in the sinus mucosa. I n addition, no study to date has characterized the changes in infected sinu s mucosa. The maxillary sinus mucosa of New Zealand white rabbits was harve sted from control animals and in animals with induced maxillary sinusitis. Immunohistochemical staining of the sinus mucosa for both Protein Gene Prod uct 9.5 (PGP), a nonspecific marker for all nerves, and for SP was performe d on 11 animals: 3 controls and 8 infected. In sinus mucosa from the contro l rabbits, <50% of all axons labeled by PGP were immunoreactive for SP. In infected mucosa, the absolute number of axons found by PGP staining decreas ed and nearly all of these remaining fibers were also immunoreactive for SP . We conclude that the phenotypical labeling of nerve fibers seen in normal mucosa is altered by bacterial-induced infection.