Innervation of the human tubarial gland compared with the major salivary glands; immunohistochemical study for neurochemical substances.

The tubarial gland is a potential salivary organ in humans. In this study, the innervation of the tubarial gland was examined using immunohistochemistry for protein gene product 9.5 (PGP 9.5), dopamine β-hydroxylase (DBH), choline acetyltransferase (ChAT), and vasoactive intestinal polypeptide (VIP). PGP 9.5-positive nerve fibers displayed thick and slender shapes around the mucous and serous acinar cells, respectively, in the tubarial gland. Both mucous and serous acinar cells were enclosed by thick and fine PGP 9.5-positive nerve fibers in major salivary glands. Other neurochemical substances were usually present in fine and varicose nerve fibers in glandular acini. DBH-positive nerve fibers were infrequent, and VIP-positive nerve fibers were rich in the tubarial gland, compared with submandibular and parotid glands. In the tubarial gland, the acinar cells were enclosed by a few DBH-positive nerve fibers and many ChAT- and VIP-positive nerve fibers. Serous acini had sparse DBH-positive nerve fibers and dense VIP-positive nerve fibers in the tubarial gland compared with submandibular and parotid glands. The parasympathetic ganglion probably sends the ChAT- and VIP-positive nerve fibers to the tubarial gland. Acetylcholine and VIP in the gland may contribute the immune system by regulating moisture, ciliary movement, and immune proteins in the respiratory tract.