New observations on the innervation of striated ducts in submandibular glands of cats, including possible peptidergic nerves

Abstract

The presence of hypolemmal axons between striated duct cells in submandibular glands of cats has been established electron microscopically. Axons were found between "light" cells, between "light" and "dark" cells and between "light" and basal cells. Hypolemmal axons were observed most frequently in the junctional region between striated and intercalary ducts. They were often more common in younger animals. "Dark" cells with numerous processes sometimes appeared to have a special relationship with hypolemmal axons. Most of the hypolemmal axons in striated ducts contained characteristic agranular vesicles of the cholinergic type, about 40 nm in diameter; many of these axons also contained large dense cored vesicles of the peptidergic type, about 100 nm in diameter and possessing a more clear outer halo. No adrenergic axons have been observed beneath the basal lamina of striated ducts, even after use of 5-OHDA. The possibility that some of the hypolemmal axons in striated ducts are peptidergic and their possible functions are discussed. Apart from other activities these axons may have a role in supplying special trophic factors to the cells, helping them in their developmental specialisation and maintaining them in normal condition. An absence of such factors after parasympathetic decentralisation may be responsible for the dramatic atrophic changes in striated duct cells, especially since the atrophy in the gland is not solely due to an absence of acetylcholine activation.