Carlin A. Pinkstaff

The cytology of salivary glands.

Publisher Summary This chapter describes the cytology of salivary glands. The salivary glands are divided into two groups—major and minor. The parotid, submandibular (submaxillary), and sublingual glands are major salivary glands. The gross anatomical relationships of the salivary glands of mammals vary greatly between species. The nature of the secretory products of various salivary glands is widely investigated by histochemical staining methods. Staining methods for mucosubstances demonstrate that gross anatomically comparable glands from different species may secrete entirely different mucosubstances. The chapter discusses the secretory functions of the salivary glands. Salivary glands possess systems that allow these organs to secrete remarkable amounts of proteins, glycoproteins, and water. The secretory capacity of the salivary gland acinar cells has been well investigated, particularly the acinar cells of parotid glands. The synthesis, intracellular transport, storage, and discharge of exportable protein by exocrine-secreting cells are also discussed.

Unique Salivary Glands in Two Genera of Tropical Microchiropteran Bats: An Example of Evolutionary Convergence in Histology and Histochemistry

Submandibular salivary glands were examined in 38 genera of microchiropteran and megachiropteran bats. In species of two of these, Trachops cirrhosus (a Neotropical phyllostomid) and Megaderma lyra and M. spasma (Old World megadermatids), the histology of the accessory submandibular salivary gland was unique among mammals. In both Trachops and Megaderma this gland consists of large, follicle-like structures rather than the usual secretory endpieces. In both genera the secretory cells (except for a few cells in Trachops ) are completely negative to a variety of histochemical staining procedures for glycoproteins, so the secretory product is unknown; in Trachops scattered or clumped mucous cells in the follicular walls contain acidic and neutral glycoproteins. Given the phylogeny of these genera it is likely that this previously unknown histological arrangement evolved independently in each family and thus represents a remarkable example of histological and histochemical convergence. We postulate that the evolution of this unique salivary gland is related to feeding on frogs.

Synthesis and secretion fo mucous glycoprotein by the gill of Mytilus edulis I. Histochemical and chromatographic analysis of [14C]glucosamine bioincorporation

The ability of the isolated gill epithelium of Mytilus edulis to incorporate [14C]glucosamine as a precursor in the biosynthesis and secretion of mucous glycoproteins was investigated. Localization of mucous cells in the gill filament was achieved using histochemical staining techniques. Mucus cells containing neutral and acidic mucins were found in the lateral region, whereas mucus cells containing primarily neutral or sulfated mucins were found in the abfrontal region. Autoradiographic results showed that in both regions, the mucous cells were rich in content of the incorporated radiolabel. The secreted glycoproteins containing the incorporated radiolabel were analyzed by column chromatography using Bio-Gel P-2 and P-6. Two populations of the glycoproteins differing in molecular size were isolated. Upon alkaline reductive borohydride cleavage of the O-glycosidic linkages of the high molecular weight protein, about 70% of the radiolabel and 85% of the carbohydrate content were removed from the protein. The alkaline borohydride cleavage resulted in the formation of at least six oligosaccharide chains of various lengths of sugar units. Gas chromatographic analysis of the carbohydrate composition shows that the glycoproteins contain N-acetylglucosamine, N-acetylgalactosamine, and galactose, fucose, and mannose as the neutral monosaccharides. The above results indicate that the isolated gill epithelium of M. edulis is capable of incorporating [14C]glucosamine in the synthesis of secretable mucin-type glycoproteins.

HISTOCHEMICAL CHARACTERIZATION OF SALIVARY GLAND SECRETION

Publisher Summary This chapter discusses how using histochemical staining methods for mucosubstances can yield information about the nature of the secretory products of salivary glands. The application of histochemical staining methods for carbohydrates to salivary gland tissue sections has yielded considerable information about the nature of salivary gland secretions. However, one must recognize, and work within, the limitations inherent in histochemical methodology. The application of histochemical methods often enables researchers to distinguish differences between salivary glands, or portions of glands, that are indistinguishable when morphological staining methods are used—for example, the anterior and posterior lobes of the rhesus monkey. Phenyl hydrazine pretreatment of sections before staining with the periodic acid–Schiff (PAS) method blocks neutral mucosubstance staining, but PAS-positive acidic mucosubstances are stained.