Nerve innervations in the human adult and fetal parotid duct

The human adult parotid duct is the longest of all major salivary gland ducts, approximately 6-8 cm in length. Its unique structure extends over the masseter muscle, penetrates through the buccinator muscle and opens into the oral cavity. Salivary secretion is under basic control of the sympathetic and parasympathetic divisions of the autonomic nervous system. Scarce reporting on the parotid duct nerve distribution led us to this study; to investigate the nervous distribution in the human adult and fetal parotid ducts using an antibody against protein gene product 9.5 (PGP9.5), a molecular marker for nerve cells and fibers. In order to identify the nerve fibers distributed throughout the parotid duct and confirm them to be part of the autonomic nervous system, we stained adult parotid ducts with tyrosine hydroxylase (TH) and choline acetyltransferase (ChAT) for observation. PGP9.5 staining of the parotid duct’s inside wall where it traverses over the masseter prior to penetrating the buccinator revealed a dense concentration of nerve fibers in the area. Staining revealed both sympathetic and parasympathetic nerve fibers in the same area, with the majority of the sympathetic nerve fibers surrounding blood vessels. However, the section of the duct penetrating the buccinator showed less concentration of nerve fibers in both adult and fetal specimens. The difference in the nerve distribution of the parotid duct suggests its direct association with the salivary transport function of the duct. PGP9.5 expression in fetuses over five months of age further suggests that the nerve distribution in the human parotid duct is fully established at six months of gestation.