On the ultrastructure of the parotid and submandibular gland of the mongoose Herpestes edwardsi (Viverridae) (author's transl)

The parotid and submandibular glands of the mongoose are described. Essential differences between the 2 glands were recognized in the acini; however, the intra- and interlobular ducts are built up similarly. The parotid gland is acinar. Its secretory cells are filled with distinct types of granula, which show a considerable variation of size and structure of their secretory material. Organelles are found sparsely. The submandibular gland, however, is tubuloacinar. Its tubuli are capped with cells which belong to the demilunes of v. EBNER, but because of their pale granules they occupy an exceptional position. As the acinar cells of the parotid gland, they form intercellular canaliculi by their plasmalemmata. In the secretory cells of the tubules an intimate contact between the rER and the granules is observed. The intralobular duct surface is built up by an onelayered epithelial cell formation. The cytoplasm of the intercalated duct cells is rich in bundles of filaments, and these cells contain mitochondria with a particular dense matrix. Some microvilli cover the apical surface. In the cells of the striated ducts several populations of granules differing in size and electron density are found. The material of the dense granules shows a marginal plate-like condensation, sometimes it cristallizes. It is supposed that they were released by an apocrine extrusion mechanism. Terminal axons innervate the acini, the duct cells, and also the myoepithelial cells. The findings are compared with the well-known morphology of the salivary glands of the cat.     

Ultrastructure of the anterior buccal gland of the rat

The anterior buccal gland of the rat is a mucous salivary gland which develops as a branch of the main (Stensen's) duct of the serous parotid gland, a few mm from its oral orifice. The purpose of the present study was to further characterize the mature gland by means of electron microscopy and the histochemical demonstration of myoepithelial cells. The tubuloacini were found to have intercellular extensions (canaliculi) of the lumina, prominent Golgi complexes, and mucous secretory granules with a biphasic substructure. Discharge was by exocytosis of individual granules. The tubuloacini joined directly to striated ducts; no intercalated ducts were seen. First-order excretory ducts had larger lumina and shorter columnar cells, with fewer mitochondria and basal infoldings, than the striated ducts. Myoepithelial cells invested the tubuloacini but not the ducts. The anterior buccal gland has several features that are unusual for a minor salivary gland of mucous type, and which are usually associated with serous glands such as the parotid. It should provide a particularly interesting model for investigating factors which control the differentiation of secretory and myoepithelial cells, and the glycosylation of polypeptides to form mucous secretory products.     

Immunohistochemical and Immunocytochemical Localization of Amylase in Rat Parotid Glands and von Ebner's Glands by Ion Etching-Immunoscanning Electron Microscopy

The distribution of amylase in rat parotid glands and von Ebner's glands was examined using ion etching-immunoscanning electron microscopy, which enables both light and electron microscopic observations of identical semi-thin resin sections immunolabeled with anti-α-amylase and immunogold in association with silver enhancement. At the light microscopic level, most acinar secretory granules (SG) and striated duct secretions of parotid glands were strongly stained dark brown. In von Ebner's glands, acinar SG and duct secretions were weakly to strongly stained light to dark brown. At the electron microscopic level, labeling was observed as bright gold-silver particles. The labeling intensity of acinar SG of parotid glands was higher than that of von Ebner's glands. In parotid glands, weak labeling of SG in transitional cells between acini and intercalated ducts, very weak labeling of SG in intercalated ducts, and strong labeling of striated duct secretions were observed. In von Ebner's glands, the secretions and some SG of interlobular ducts were strongly labeled compared to those of intralobular ducts and SG of acini. Less amylase was synthesized in von Ebner's acini compared to parotid acini, whereas von Ebner's ducts may secrete significantly more amylase to modify saliva than parotid ducts.     

Ultrastructure and histochemistry of human anterior lingual salivary glands (glands of blandin and nuhn)

Background: Speciamens of human anterior lingual salivary glans obtained by surgery and by dissection of cadavers were studied ultrastructurally and histochemically. Methods: Specimens were obtained by surgery for ultrastructural study. Other specimens for histochemistry were obtained by dissection of fresh cadavers. Tissues for electron microscopy were fixed and processed by conventional mesns. Formalin-fixed cadaver specimens were subjected to a battery of tests for glycoconjugates. Results: The anterior lingual salivary glands are composed predominantly of mucous tubules (which come in two distinct sizes: large and small), seromucous demilunes, and rare seromucous acini. Regardless of tubule size, mucous cells are typically in appearance and, like mucous cells in other human salivary glands, contain filamentous bodies. Histochemically, the larger tubules contain neutral glycoproteins, low concentrations of sialoglycoproteins, and large amounts of sulfated glycoproteins. The small mucous tubules contain neutral glycoproteins, much sialoglycoprotein, and relatively small amounts of sulfated glycoprotein. The seromucous cells, whether demilunar or acinar, are identical. They contain numerous secretory granules, which show a spectrum of internal patterns from one individual to another. These cells have considerable concentrations of neutral- and sialoglycoproteins and lower concentrations of sulfated gly-coproteins. Countrary to previously published reports, we could find no differences in the ratio of mucous to seromucous cells along the anteriorposterior lingual axis: there was no gradient of seromucous cells in our specimens. The ducts in the anterior lingual salivary glands are not precise counterparts of those in the major salivary glands, since the former have no capsules, hence lack lobulation. Without these familiar structural landmarks, the only duct that can be identified with certainty is the intercalated duct, and then only if it is in continuity with or lies close to a secretory endpiece. Such ducts consist of simple cuboidal epithelium of prosaic appearance. The ductular epithelium gradually thickens and gives rise to what appear to be excretory ducts consisting of columnar cells with few mitochondria. Scattered within the walls of the walls of the larger ducts are patches of typical striated ducts wherein the taller cells display basal striations resulting from highly folded basal plasma membranes and numerous, vertically oriented, virgulate mitochondria. In other atypical regions of the excretory duct, basal cells may have a primary cilium that juts into the intercellular space. Conclusions: There is a high degree of structural variability in human anterior lingual salivary glands. Because of the technical difficulties in collecting pristine saliva from these glands, the precise functions(s) of these organs remains unknown. © 1994 Wiley-Liss, Inc.     

Ultrastructure of the principal and accessory submandibular glands of the common vampire bat

The principal and accessory submandibular glands of the common vampire bat, Desmodus rotundus, were examined by electron microscopy. The secretory endpieces of the principal gland consist of serous tubules capped at their blind ends by mucous acini. The substructure of the mucous droplets and of the serous granules varies according to the mode of specimen preparation. With ferrocyanide-reduced osmium postfixation, the mucous droplets are moderately dense and homogeneous; the serous granules often have a polygonal outline and their matrix shows clefts in which bundles of wavy filaments may be present. With conventional osmium postifixation, the mucous droplets have a finely fibrillogranular matrix; the serous granules are homogeneously dense. Mucous cells additionally contain many small, dense granules that may be small peroxisomes, as well as aggregates of 10-nm cytofilaments. Intercalated duct cells are relatively unspecialized. Striated ducts are characterized by highly folded basal membranes and vertically oriented mitochondria. Luminal surfaces of all of the secretory and duct cells have numerous microvilli, culminating in a brush borderlike affair in the striated ducts. The accessory gland has secretory endpieces consisting of mucous acini with small mucous demilunes. The acinar mucous droplets contain a large dense region; the lucent portion has punctate densities. Demilune mucous droplets lack a dense region and consist of a light matrix in which fine fibrillogranular material is suspended. A ring of junctional cells, identifiable by their complex secretory granules, separates the mucous acini from the intercalated ducts. The intercalated ducts lack specialized structure. Striated ducts resemble their counterparts in the principal gland. As in the principal gland, all luminal surfaces are covered by an array of microvilli. At least some of the features of the principal and accessory submandibular glands of the vampire bat may be structural adaptations to the exigencies posed by the exclusively sanguivorous diet of these animals and its attendant extremely high intake of sodium chloride.     

Localization of sodium pump sites in cat salivary glands.

1. Cat submandibular glands were perfused with Locke solution containing [3H]ouabain. In some experiments additional medium was given by retrograde intraductal injection. 2. [3H]ouabain binding sites were localized by light microscopical autoradiography and the findings compared with the electron micrographs. 3. The cells of the striated ducts were heavily labelled with [3H]ouabain, predominantly in the contraluminal parts. 4. At the acinar level moderate amounts of [3H]ouabain were found in relation to the plasma membranes of the demilunar cells. The central acinar cells were found to be virtually devoid of [3H]ouabain. 5. Electron microscopy revealed that the demilunar cells possessed long, tortuous intercellular spaces separated from the secretory canaliculi by junctional complexes. In contrast, the membranes between adjacent central acinar cells were fairly straight. 6. It is concluded that the striated ducts play a dominant role in the ductal reabsorption of sodium, and that the transport is probably mediated by a (Na+ + K+)-activated ATPase. The findings on the acinar level are in agreement with the view that the primary saliva is formed predominantly by the demilunar cells. The role of a (Na+ + K+)-activated ATPase in this process is unclear.     

Ultrastructure of baboon parotid gland

The parotid gland of the olive baboon, Papio anubis, was examined by electron microscopy. The acini are all serous in nature, and consist of pyramidal cells with abundant secretory granules of varying size. These granules consist of a dense matrix in which a denser spherule or lenticular body is present. Granules linked by a short isthmus are observed in the apical cytoplasm, and granules in the process of discharging their contents to the acinar lumen may be connected to the luminal plasma membrane by a neck-like protrusion. Intercalated duct cells contain granules reminiscent of those found in the rat submandibular acinar cells. The striated ducts consist of tall cells interloked in a complex fashion near their bases, with numerous vertically-oriented mitochondria lodged in their basal crenulations. Small vesicles whose contents vary in density are present in the apical cytoplasm as are large deposits of lipofuscin. The striated duct cells display a proclivity for ballooning into the duct lumen. Excretory ducts consist of simple to pseudostratified columnar epithelium, and lack basal striations or apical blebs.     

An unusual parotid gland in the tent-building bat,Uroderma bilobatum: Possible correlation of interspecific ultrastructural differences with differences in salivary pH and buffering capacity

The tent-building bat, Uroderma bilobatum, is a small, frugivorous phyllostomid bat with a broad neotropical distribution. Generally found in humid forest, this bat lives in small groups that create daytime “roosts” from large leaves of a variety of tropical plants. Fruit eating engenders a variety of ecological and physiological challenges for bats, some of which could require adaptive features in their salivary glands. The parotid salivary glands of Uroderma bilobatum were prepared for transmission electron microscopy by using methods that have become standard for field work. The parotid gland is extremely unusual in structure. Although the secretory endpieces still produce serous granules with a complex substructure, they are modified into quasi striated ducts. Their basal folds, which are extensive, occasionally harbor some vertically oriented mitochondria, imparting a resemblance to striated ducts. Other evidence for the endpiece origin of these parenchymal components is a well-developed system of intercellular canaliculi, structures that never occur in bona fide striated ducts. The long but sparse intercalated ducts consist of two types of cells, each of which elaborates a modest number of secretory granules of differing substructure. Striated ducts are of conventional morphology, except that a few dark cells shaped like wine glasses are present in their walls. The striated duct cells produce no secretory granules, but their apical cytoplasm may contain some small, empty vesicles. Capillaries lie in longitudinal grooves in the base of the duct cells, an arrangement that might enhance electrolyte exchange. Excretory ducts consist of simple cuboidal epithelium composed of cytologically unspecialized cells that sometimes includes a dark cell. It was concluded that salivary glands could have a major role in adapting species to acquire nutrients from marginal sources, such as tropical fruits, which have a low protein and sodium content. The unusual parotid acinar cells in Uroderma bilobatum are discussed in the context of salivary pH and buffering capacity. Comparisons are made with four other bat species, including an insectivorous species with a salivary pH > 8.0 and a very high buffering capacity, an intermediate species, and a fruit bat with acidic-stimulated saliva and very low buffering capability. Such interspecific comparisons provide a foundation for hypothesizing that ultrastructural features of the acinar cell basolateral membranes and intercellular canaliculi correlate with differences involving Na⁺/H⁺ exchangers and release of HCO₃⁻ and, thus, are associated with the species differences that are important to diet and nutrient acquisition. Anat. Rec. 252:290–300, 1998. © 1998 Wiley-Liss, Inc.     

Endocytosis of parotid salivary proteins by striated duct cells in streptozotocin-diabetic rats

Salivary gland striated duct cells play an important role in the modification of primary saliva by secretion and reabsorption of electrolytes, and secretion of glycoproteins. Recent observations have shown that in the rat parotid gland these cells are able to internalize exogenous proteins, e.g., horseradish peroxidase and ferritin, from the ductal lumen. In rats made diabetic by injection of streptozotocin, dense vacuoles and crystalloids are present in the apical cytoplasm of parotid striated duct cells. In this study we utilized electron microscopic immunocytochemistry to determine if these vacuoles and crystalloids contain acinar secretory proteins. At various times after induction of diabetes by streptozotocin (65 mg/kg), the parotid glands were fixed in a glutaraldehyde-formaldehyde mixture, postfixed in OsO4, and embedded in epoxy resin. Thin sections were immunolabeled with antibodies to protein B1 (Ball et al., 1988) and alpha-amylase (Baum et al., 1982) using a modification of the Protein A-gold technique (Bendayan and Duhr, 1986). With antibody to B1, label was localized in the secretory granules of acinar and intercalated duct cells of both normal and diabetic rats. In striated duct cells of diabetic rats, label was present over the electron-dense vacuoles but not over the crystalloids. Since crystalloids appear to form within the vacuoles, their lack of reactivity may indicate degradation of the internalized protein. The same distribution of label was found with antibody to amylase except for the intercalated duct granules, which were unlabeled in both control and diabetic animals. These results demonstrate that striated duct cells take up salivary proteins from the lumen and that the endocytosis of some secretory proteins from the saliva may be a significant function of these cells in certain pathological conditions.     

Expression patterns of tight junction proteins in porcine major salivary glands: a comparison study with human and murine glands

Tight junction (TJ) proteins play a dynamic role in paracellular fluid transport in salivary gland epithelia. Most TJ studies are carried out in mice and rats. However, the morphology of rodent salivary glands differs from that of human glands. This study aimed to compare the histological features and the expression pattern of TJ proteins in porcine salivary glands with those of human and mouse. The results showed that porcine parotid glands were pure serous glands. Submandibular glands (SMGs) were serous acinar cell‐predominated mixed glands, whereas sublingual glands were mucous acinar cell‐predominated. Human SMGs were mixed glands containing fewer mucous cells than porcine SMGs, whereas the acinar cells of murine SMGs are seromucous. The histological features of the duct system in the porcine and human SMGs were similar and included intercalated, striated and excretory ducts, but the murine SMG contained a specific structure, the granular convoluted tubule. TJ proteins, including claudin‐1 to claudin‐12, occludin and zonula occludin‐1 (ZO‐1), were detected in the porcine major salivary glands and human SMGs by RT‐PCR; however, claudin‐6, claudin‐9 and claudin‐11 were not detected in the murine SMG. As shown by immunofluorescence, claudin‐1, claudin‐3, claudin‐4, occludin and ZO‐1 were distributed in both acinar and ductal cells in the porcine and human SMGs, whereas claudin‐1 and claudin‐3 were mainly present in acinar cells, and claudin‐4 was mainly distributed in ductal cells in the murine SMG. In addition, 3D images showed that the TJ proteins arranged in a honeycomb‐like structure on the luminal surface of the ducts, whereas their arrangements in acini were irregular in porcine SMGs. In summary, the expression pattern of TJ proteins in salivary glands is similar between human and miniature pig, which may be a candidate animal for studies on salivary gland TJ function.     

Histochemical analyses of glycoconjugates and antimicrobial substances in goat labial glands

Saliva is known to protect the oral cavity and contains glycoproteins and antimicrobial substances. The distribution of these salivary secretions was studied in the labial glands of the Japanese miniature (Shiba) goat using lectin histochemical and immunohistochemical methods. The mucous acinar cells of the labial glands exhibited glycoconjugates with different saccharide residues, such as GalNAcα1-3GalNAc, Galβ1-4GalNAc, β-d-GlcNAc and sialic acid linked to α2-6Gal/GalNAc. Furthermore, α-d-Man, α-l-Fuc, α-d-GalNAc, β-d-Gal and sialic acid residues were present, in particular, in the serous demilunar cells. Antimicrobial substances (lysozyme, IgA, lactoferrin and β-defensin) were shown to be mainly immunolocalized in the serous demilunes and duct cells. The results obtained are discussed with regard to the functional role of labial glands. The secretory compounds demonstrated may play an important role in the maintenance of oral health with regard to saliva.     

Distribution of dendritic cells in normal human salivary glands

Dendritic cells (DC) are believed to contribute to development of autoimmune sialadenitis, but little is known about their distribution in normal salivary glands. In this study, DC were identified and their distribution was determined in normal human parotid and submandibular glands. For light microscopy, salivary gland sections were stained with H&E or immunocytochemically using antibodies to DC markers. Transmission electron microscopy (TEM) was used to evaluate the ultrastructural characteristics of DC. In H&E sections, elongated, irregularly shaped nuclei were occasionally seen in the striated and excretory duct epithelium. Immunolabeling with anti-HLA-DR, anti-CD11c and anti-S100 revealed DC with numerous processes extending between ductal epithelial cells, often close to the lumen. Morphometric analyses indicated that HLA-DR-positive DC occupied approximately 4-11% of the duct wall volume. Similar reactive cells were present in acini, intercalated ducts and interstitial tissues. TEM observations revealed cells with indented nuclei containing dense chromatin, pale cytoplasm with few organelles, and lacking junctional attachments to adjacent cells. These results indicate that DC are abundant constituents of normal human salivary glands. Their location within ductal and acinar epithelium suggests a role in responding to foreign antigens and/or maintaining immunological tolerance to salivary proteins.     

Ultrastructure of the cat sublingual gland

The sublingual gland of the cat consists primarily of branched secretory tubules that open into an abbreviated duct system. The simple epithelium that composes the secretory tubules consists of an admixture of mucous and serous cells, with the former predominating. Some secretory tubules are capped by a serous demilune. Regardless of position, almost all serous cells have prominent basal folds and border on at least one intercellular canaliculus as well as on the tubule lumen. Serous cells possess an extensive array of irregular, distended cisternae of rough-surfaced endoplasmic reticulum that frequently contain dense intracisternal granules. Serous granules are relatively few in number and rarely show evidence of substructure. Mucous cells, which lack basal folds, contain an apical mass of secretory material in the form of partially fused droplets. The duct system is somewhat less ordered than in most major salivary glands; secretory tubules empty into structures resembling intercalated ducts or may be in direct continuity with ducts intermediate in morphology between intercalated and excretory ducts. The absence of striated ducts noted in this study may be correlated with the high sodium content of cat sublingual saliva. The main excretory duct of the sublingual gland closely resembles that of the cat submandibular gland in terms of morphology, but exhibits little of the transport functions reported in the latter duct.     

Freeze-fracture and lead ion tracer evidence for a paracellular fluid secretory pathway in rat parotid glands

The morphology and permeability of tight junctions of the three major epithelial constituents of rat parotid gland-acinus, intercalated duct, and striated duct-have been examined ultrastructurally. Acinar and intercalated duct junctions (including those surrounding intercellular canaliculi) averaged two to three sealing strands, whereas striated duct junctions had five to eight sealing strands. When the permeability of the junctional complex was probed by means of a recently devised lead ion tracer technique, acinar junctions were found to be very permeable, intercalated duct junctions were somewhat permeable, and striated duct junctions were essentially impermeable to the tracer. Thus, by both morphological and tracer-permeability criteria, acinar tight junctions appear to be "leaky." These data provide strong evidence that, in rat parotid glands, a potential paracellular secretory pathway exists in the acinar region for the transepithelial passage of fluid.     

Ultrastructure of the sublingual gland in the African multimammate rodent

The sublingual gland of Praomys natalensis, an African rodent that is phenotypically and cytogenetically intermediate to mice and rats, is a mixed gland, consisting of mucous acini that are capped by serous demilunes, of intercalated ducts, and of some short striated ducts that quickly become excretory ducts. The mucous cells are typical in appearance, with lucent granules that contain an assortment of scattered vermiform or particulate densities. The serous cells display an array of secretory granules with a highly unusual substructure. Rather than a pattern based on the manner in which light and dark regions are disposed in their matrix, these granules contain packets--some furled, some flat--of membranes that exhibit a pronounced axial periodicity of approximately 5 nm. Intercalated ducts are simple in structure, with no obvious morphological specializations. Striated ducts resemble those in the salivary glands of less exotic rodents, but they and the excretory ducts often have clusters of cytoplasmic crystalloids consisting of linear densities that intersect at right angles and that have a periodicity in both directions of approximately 12 nm.     

An immunohistochemical study of normal human neonate and adult parotid gland tissue. Detection of lysozyme, lactoferrin, a1-antichymotrypsin, a1-antitrypsin and carcinoembryonic antigen

The immunohistochemical detection and distribution of lysozyme (Ly), Lactoferrin (Lf), a1-Antichymotrypsin (a1-AChy), a1-Antitrypsin (a1-AT) and Carcinoembryonic antigen (CEA) were studied in neonate and adult parotid gland tissue, using the peroxidase-antiperoxidase (PAP) method. Ly stain in neonates extended into acini, intercalated ducts and occasional cells of large ducts, whereas in adults Ly was usually confined to the intercalated ducts. The distribution pattern of Lf in neonates varied considerably between individual glands showing three staining patterns. Most of the intercalated ducts, some groups of acini and rare striated duct cells were positive for Lf in adults. a1-AChy and a1-AT in neonates were positive mainly in the large ducts, whereas staining for a1-AChy and a1-AT in adults frequently extended into some intercalated duct cells, although less intensively. Finally, CEA in neonates was localized in the lumina and luminal membranes of the acini, in intercalated ducts, and less frequently in the large ducts. In adults CEA was present predominantly in the lumina and luminal membranes of the intercalated duct cells. These differences may suggest an immunohistochemical postnatal differentiation of the parotid gland.     

Ultrastructure of the anterior medial glands of the rat nasal septum

The anterior medial glands lying in the submucosa of the rat nasal septum were studied by light and electron microscopy. The glands consist of a single long duct, which is studded with numerous solitary acinar formations connected perpendicularly to the main duct by short intercalated ducts. Proximal acini (those furthest from the stoma of the main duct) consist of typical serous cells with many dense secretory granules and an extensive rough endoplasmic reticulum. The most distal acini consist of cells whose major feature is the enwrapment of each mitochondrion by a cisternal profile of rough endoplasmic reticulum. Myoepithelial cells are absent from proximal acini, but are abundant on distal acini. Intracellular nerve terminals are extremely common, particularly in distal acini. The main ducts resemble, to a degree, the striated ducts of salivary glands.     

Histology and ultrastructure of the pig parotid gland

Parotid glands of adult pigs were studied by light and electron microscopy. The parenchyma consists of acini, intercalated ducts, striated ducts, and excretory ducts. Acini had little affinity for periodic acid-Schiff and were alcian blue-negative at pH 2.6 or 0.5. These results indicate a paucity of neutral mucins and an absence of sialo- and sulfomucins. Histologically, acinar cells had vacuoles which corresponded ultrastructurally to large electron-lucent secretory granules. The latter contained electron-dense bodies and lipid droplets. Acinar cells differed histochemically and ultrastructurally from typical serous cells and were classified as special serous. Intercalated duct cells near acini contained electron-dense secretory granules and numerous microfilaments. Cells in distal segments lacked secretory granules. Striated ducts were lined by two types of columnar epithelial cells, light cells and dark cells. Light cells were characterized by numerous infoldings of the basal plasma membrane, mitochondria between the infoldings, and electron-lucent vesicles in the apical cytoplasm. The mitochondria contained tubular cristae. Dark cells were characterized by an abundance of microfilaments and numerous infranuclear processes which extended to the basement membrane. Excretory ducts, in addition to light and dark cells, also contained basal cells and goblet cells. Mitochondria in the light cells had flattened rather than tubular cristae. The pig parotid is a unique salivary gland and the most atypical mammalian parotid gland studied thus far. Mitochondria with tubular cristae and vacuolated special serous cells with lipid in the secretory granules are hallmarks of the pig parotid.