Serous, seromucous, and special serous cells in salivary glands

Expression of muscarinic receptor subtypes in salivary glands of rats, sheep and man

In rat parotid, submandibular and sublingual glands and in ovine parotid and in human labial glands, the expression of muscarinic receptor subtypes was examined by immunoblotting and immunohistochemistry. Functional correlates were searched for in rat salivary glands. In the rat submandibular and sublingual glandular tissues clear signals of muscarinic M1 and M5 receptors could be detected in the immunoblotting and vague bands for muscarinic M3 and, in particular for, M4 receptors. The rat parotid gland differed. In this gland, the signal was less obvious for the muscarinic M1 receptor, and further, muscarinic M4 receptors appeared more strongly marked than in the submandibular glands. The results from the immunohistochemistry could be interpreted as the muscarinic M4 receptors are located on nerve fibres, since the outer layer of lobuli were densely stained. Intraglandular vessels in the rat submandibular and parotid glands showed expression of M3 receptors. In contrast to the parotid gland, the submandibular vessels also expressed M1 and M2 receptors. Occasionally M5 receptors appeared in the arteries and veins also. The functional studies in the rat confirmed muscarinic M1 receptor mediated secretion in the submandibular gland. Since the M1 receptor blockade did not affect submandibular blood flow, indirect vascular effects could not in total explain the secretory inhibition. Also in the human labial glands, muscarinic M1, M3 and M5 receptors occurred. No or low amounts of muscarinic M2 and M4 receptors could be detected. In patients with Sjögren-like symptoms an up-regulation of M3, M4 and M5 receptors was apparent in the labial glands. In ovine parotid glands all receptors could be detected, but constantly with vague bands for muscarinic M2 receptors. In conclusion, muscarinic M1 receptors seem to be expressed in seromucous/mucous glands. A secretory effect by muscarinic M5 receptors is not to be excluded, since they were expressed in all the glands examined. However, other functions, such as promotion of inflammation, cell growth and proliferation are possible as well.

Three-dimensional characteristics of submandibular salivary gland of ageing rats: an HRSEM study

The characteristics of the submandibular glands of ageing Wistar rats were studied using light and high-resolution scanning electron microscopy (HRSEM) methods. For light microscopy, the samples were fixed in Bouin solution and embedded in paraffin. Sections were stained with hematoxilin-eosin and Azo-Carmin. For conventional scanning electron microscopy, the tissues were fixed in modified Karnovsky solution, and treated with NaOH solution for 3-4 days. The O-D-O method was used for HRSEM. The samples were fixed in 2% osmium tetroxide, macerated in diluted osmium and dehydrated in an increasing series of ethanol. The samples were dried in a critical point dryer, coated with gold-palladium and examined in a Hitachi high-resolution scanning electron microscope, S-900. The results showed that submandibular glands with lobules are separated by connective tissue septum. The acinar formations and the ducts, revealing the serous and mucous cells were observed. After fracture in liquid nitrogen and treatment with NaOH solution to remove the cellular components, the original disposition of the collagen bundles fibers were revealed corresponding to the round, oval or irregular acinar and ductal structures. In the cytoplasm, organelles such as mitochondria, rough endoplasmic reticulum, Golgi apparatus and serous and mucous secretory granules were observed localized in the apical portion in three-dimensional HRSEM images. The serous secretory granules presented different sizes and shapes showing the modifications which occurred in the ageing rats. The striated duct cells revealed the presence of the secretory cells and mitochondria in parallel disposition. The mitochondrial cristae were noted in three-dimensional aspects. The lumen presented numerous cytoplasmic microprojections. The lumen of excretor ducts are covered by polygonal epithelial cells containing numerous microplicae.

Menkes protein localization in rat parotid acinar cells

The aim was to study the subcellular localization of the Menkes protein (MNK; ATP7A) in the rat parotid acinar cell. MNK protein is a copper transporting P-type ATPase whose absence or dysfunction causes a fatal neurodegenerative disorder, MNK disease. Rat parotid glands were fixed and low-temperature embedded in Lowicryl K4M resin, and ultrathin sections were prepared for immunocytochemical analysis. Immunolocalization of MNK was demonstrated mainly over the trans Golgi network (TGN) area. Immature and mature secretory granules were also labelled, indicating that MNK protein could be involved here in copper secretion from acinar cells into saliva, consistent with a proposed cariostatic role for copper.

Electron microscopic immunogold localization of salivary mucins MG1 and MG2 in human submandibular and sublingual glands

The human salivary mucins MG1 and MG2 are well characterized biochemically and functionally. However, there is disagreement regarding their cellular and glandular sources. The aim of this study was to define the localization and distribution of these two mucins in human salivary glands using a postembedding immunogold labeling method. Normal salivary glands obtained at surgery were fixed in 3% paraformaldehyde-0.1% glutaraldehyde and embedded in Lowicryl K4M or LR Gold resin. Thin sections were labeled with rabbit antibodies to MG1 or to an N-terminal synthetic peptide of MG2, followed by gold-labeled goat anti-rabbit IgG. The granules of all mucous cells of the submandibular and sublingual glands were intensely reactive with anti-MG1. No reaction was detected in serous cells. With anti-MG2, the granules of both mucous and serous cells showed reactivity. The labeling was variable in both cell types, with mucous cells exhibiting a stronger reaction in some glands and serous cells in others. In serous granules, the electron-lucent regions were more reactive than the dense cores. Intercalated duct cells near the acini displayed both MG1 and MG2 reactivity in their apical granules. In addition, the basal and lateral membranes of intercalated duct cells were labeled with anti-MG2. These results confirm those of earlier studies on MG1 localization in mucous cells and suggest that MG2 is produced by both mucous and serous cells. They also indicate differences in protein expression patterns among salivary serous cells.

Histochemical and ultrastructural study of the chicken salivary palatine glands

Salivary glands are a good model to investigate the relationship between cell secretion and glandular structure. Most studies of this organ deal with mammals, but we are interested in a morphofunctional characterization of these glands in poultry in relation with particular feeding habits. For this purpose, conventional and lectin histochemical methods as well as ultrastructural methods have been applied to the chicken lateral and medial palatine salivary glands. It was found that periodic acid-Schiff (PAS)-positive, alcianophilic, and metachromatic or orthochromatic cells were present with a more homogeneous distribution pattern in lateral glands than in medial palatine glands. Lectin staining depended on the lectin type that was applied, but also on the glandular part both in lateral and medial glands. Ultrastructural studies showed cytoplasmic membranous structures with a scattered granular or filamentous content depending on the secretory cell. In conclusion, morphofunctional characteristics of salivary glands of chicken suggest that their products are involved in lubrication and humidification of food ingested, and probably in protection of the oral surface, as has been previously described for other animals showing similar histochemical staining patterns.

Histology, histochemistry and fine structure of the lacrimal and nictitans gland in the South American armadillo Chaetophractus villosus (Xenarthra, Mammalia)

The anatomical, histological, histochemical and ultrastructural characteristics of the lacrimal gland (LG) and nictitans gland (NG) of the armadillo Chaetophractus villosus were described. The histochemical and histological features of both glands in male and female adult animals were compared. The tissues were processed with conventional techniques for light and transmission electron microscopy. Fixed specimens were submitted to a battery of tests for glycans, glycosaminglycans, glycoconjugates, proteins, and lipids. The LG of the armadillo may be considered within the set of glandulae lacrimales superior in which primates, carnivores, perisodactyls and artiodactyls are included. The localization of the NG was similar to that of other mammals. Lacrimal and NG were histologically and histochemically identical. The secretory endpieces consisted of three cell types: (1) Mucous cells (MC) with different types of mucous secretory granules with neutral and sialic acid-containing glycoconjugates (GCs). (2)Seromucous cells (SMC) showing a variety of moderately electron dense secretory granules with flocculent material with carboxylated acidic, neutral, and sialic acid-containing GCs. Intercellular canaliculi with junctional complexes and basolateral intercellular spaces were frequent. (3) Serous cells (SC) with electron dense secretory granules. Histochemically, they showed the strongest reaction for proteins and neutral, weakly acid and carboxylated acidic GCs. The epithelium of the intra- and inter-lobular excretory ducts showed secretory activity, junctional complexes, and wide basolateral intercellular spaces with lateral folds. The endpieces and ducts were surrounded by myoepithelial cells. The stroma was characterized by fenestrated endothelium, unmyelinated axons, and abundant plasma cells. MC, SMC, and the duct system were richly innervated by hypolemmal nerve terminals.

Fine structure of the 7 postnatal days Calomys callosus palatine salivary glands

The aim of this study has been to determine the ultrastructural characteristics of the minor palatine salivary glands on the seventh day of development and to demonstrate wether their secretion is mucous, serous or seromucous by light, transmission and scanning electron microscopy. This study has shown that the palatine gland acinar cells are predominantly mucous with some serous units. These cells contain electron dense (serous) and low electron dense (mucous) granules in the apical portions. The cytoplasmatic organelles like mitochondria, Golgi apparatus and rough endoplasmic reticulum are localized in a supranuclear portion. We could also observe the flattened myoepithelial cells surrounding the basal part of the acini with myofilaments, Golgi apparatus and mitochondria. Desmosomal junctions and membrane interdigitations are present between the acinar and the myoepithelial cells. A basal lamina, divided in two layers, an electron dense and an electron lucent is present between the glandular stroma which is composed of dense connective tissue and the endpieces.

Acinar phenotypes in salivary pleomorphic adenoma: unusual differentiation or disordered functional activity?

To explain the occurrence in salivary pleomorphic adenoma of structures with an arrangement and appearance of tumour cells resembling acini, two tumours showing such structures and, for comparison, a tumour showing goblet cells were examined with the use of histochemistry and immunocytochemistry for constituents of the salivary secretory process. One tumour consisted mainly of slightly granular cells with an acinar arrangement, which contained neutral and carboxylated glycoproteins, -SH groups and cytoplasmic epithelial membrane antigen. The second tumour showed a minor component of structures resembling mucous acini, which contained neutral and carboxylated glycoproteins, -SS- groups and fucoglycoconjugates. The goblet cells of the third tumour contained sulphated glycoproteins and were associated with cystic lumina. Acinar phenotypes in salivary pleomorphic adenoma could reflect either an unusual line of differentiation or luminal cells with increased synthesis and/or retention of variably mature glycoproteins different from those of goblet cells. Disordered secretion and externalization of glycoproteins are possible factors influencing phenotypes in this tumour.

Subcellular localization of epidermal growth factor in human parotid gland

The intracellular distribution of epidermal growth factor was investigated in human parotid gland by immunogold cytochemistry at the electron-microscopy level. Epidermal growth factor immunoreactivity was demonstrated in both acini and ducts. In acinar cells, secretory granules appeared moderately stained, clearly indicating that parotid gland contributes to salivary epidermal growth factor through granule exocytosis. In ductal cells, gold particles were found to decorate numerous cytoplasmic vesicles, particularly abundant in striated duct cells. Since epidermal growth factor reactive vesicles were seen not only at the cellular apex, but nearby lateral plasma membranes as well, it leads to the hypothesis that epidermal growth factor may be discharged both apically into the saliva, and basally into the interstitium.

Ultrastructure of submucosal glands in human anterior middle nasal turbinates

The abundant glands situated in the lamina propria of the human anterior middle nasal turbinate were complex tubules that consist of serous, seromucous, and mucous cells, either singly or in combination. Serous granules were homogeneously dense, but could have a small lighter core. Seromucous granules had a dense rim and a large compartment of appreciably lighter density. Gradation between serous and seromucous granules made precise identification of these secretory cell types difficult. Mucous cells were of conventional morphology. The secretory tubules, which possessed a complement of myoepithelial cells, gradually transformed into ducts or the changeover was relatively sudden. The ductular portions of the tubules consisted either of tall prismatic cells or of shorter columnar cells, both of which lacked secretory granules, but had many mitochondria in their supranuclear cytoplasm. In many cases the ducts, for most of their length, consisted of secretory cells. These glands clearly participate in the elaboration of the glycoconjugate coat that serves to protect the nasal mucosa and keeps it from drying out.

Characterisation of glycoconjugate sugar residues in the vomeronasal organ of the armadillo Chaetophractus villosus (Mammalia, Xenarthra)

Conventional carbohydrate histochemistry and the binding patterns of 21 lectins were analysed to characterise the glycoconjugate content in the components of the vomeronasal organ of the armadillo Chaetophractus villosus. The mucomicrovillous complex of the sensory epithelium bound most of the lectins studied. No reaction was observed with Con A, PSA, S-Con A and SBA, and the sustentacular cells were-stained with UEA-I, DSL, LEL, STL and Con A. The vomeronasal receptor neurons were labelled with S-WGA, WGA, PNA, UEA-I, STL, Con A, S-Con A, ECL and RCA120. The basal cell layer reacted with S-WGA, WGA, LCA, UEA-I, DSL, LEL, STL, Con A, JAC and VVA. The nonsensory epithelium exhibited a differential staining in relation to the different components. The mucociliary complex stained with ECL, DBA, JAC, RCA120, STL, LCA, PHA-E, PHA-L, LEL, BSL-I and VVA. However, SJA and UEA-I stained the mucus complex lining a subpopulation of columnar cells. The cytoplasm and cell membranes of columnar cells was labelled with DBA, DSL and LCA. The apical region of these cells exhibited moderate reactivity with LEL and SJA. None of the lectins bound specifically to secretory granules of the nonsecretory cells. Basal cells of the nonsensory epithelium were labelled with DSL, LEL, LCA, BSL-I and STL. The vomeronasal glands showed a positive reaction with WGA, DSL, LEL, LCA, DBA, PNA, RCA120 and SBA. Subpopulations of acinar cells were observed with ECL, S-WGA, Con A, S-Con A and DBA. PNA and RCA120 stained the cells lining the glandular ducts. In comparison with previous results obtained in the olfactory mucosa of the same group of armadillos, the carbohydrate composition of the vomeronasal organ sensory epithelium differed from the olfactory sensory epithelium. This is probably related to the different nature of molecules involved in the perireceptor processes.

Morphological features of the minor salivary glands

The minor salivary glands are important components of the oral cavity, present in most parts of the mouth, and their secretions directly bathe the tissues. Individual glands are usually in the submucosa between muscle fibres, and consist of groups of secretory endpieces made up of mucous acinar cells and serous or seromucous demilune cells. The ductal systems comprise intercalated ducts, intralobular ducts usually lacking basal striations, and excretory ducts opening directly through the mucosa Minor glands secrete highly glycosylated mucins, containing blood group determinants, and probably active in tissue lubrication and bacterial aggregation. They also secrete several antimicrobial proteins and immunoglobulins, and the lingual serous (von Ebner's) glands secrete digestive enzymes and proteins with possible taste perception functions. Minor gland morphology and function can conveniently be studied in the rat. There are substantial differences between major and minor salivary glands, as well as among the minor glands, in the nature and composition of their mucous and serous secretory products. The role of minor salivary glands in the function and defence of the oral cavity may be better understood as a result of new physiological and molecular methods applicable to samples of limited size and availability.

Ultrastructure of the binary parotid glands in the free-tailed bat, Tadarida thersites. II. Accessory parotid gland

BACKGROUND

Many bat species have an extra set of major salivary glands. In some species, the accessory glands are quite similar to the principal one, but in others they may be radically different. Accessory glands usually are associated with the submandibular gland, but the free-tailed bat, Tadarida thersites, also has an accessory parotid gland. In the present study, we compared the accessory parotid gland with its principal counterpart.

METHODS

Salivary glands were removed from two specimens of free-tailed bats, one of each sex, that had been live-trapped in western Kenya and immersion-fixed in a specially formulated mixture designed for field fixation. Once back in the laboratory, the tissue was further prepared for electron microscopy by conventional means.

RESULTS

The secretory endpieces consist of serous tubules composed of typical serous cells that contain numerous dense granules. In contrast, the intralobular duct system shows a radical departure from normal. These ducts are enormous in caliber, their lumina measuring greater than 100 microm in diameter. They appear to arise by amalgamation of the homologues of intercalated and striated ducts into macroducts. The walls of the macroducts consist of intermingled patches of simple cuboidal and simple columnar epithelia that occasionally include a tuft cell and are underlaid by an almost continuous layer of myoepithelium. A few cells have some modified basal striations, but most cells display a cytological organization that differs radically from either of their two putative ancestral cell types. Both tall and short epithelial macroduct cells have a paranuclear collection of ovate mitochondria and aggregates of what presumably are peroxisomes. Macroduct cells in both the female and male are pervaded by a system of tubular smooth endoplasmic reticulum (SER). In the female, the SER gives rise to membranous whorls that consist of numerous plies. As the macroducts approach their termini, a single row of small dense secretory granules appears just beneath their luminal surface. At the lobular periphery, the ducts taper down to become excretory ducts of normal dimensions.

CONCLUSIONS

An accessory parotid gland occurs in T. thersites, but apparently is absent in the related species, T. brasiliensis. The ultrastructural data are consistent with a possible steroidogenic function, although other features of the gland might relate to the elaboration of a secretory product associated with feeding on chitinous beetles. The macroducts conceivably function as reservoirs of preformed saliva.

Ultrastructure of the unusual accessory submandibular gland in the fringe-lipped bat, Trachops cirrhosus

BACKGROUND

The phyllostomid fringe-lipped bat, Trachops cirrhosus, is sui generis (in a family of ca. 138 species) in that it subsists in part on tropical frogs. These amphibians frequently possess highly toxic integument. We examined the salivary glands of this bat to determine if these glands could be the source of protective factors that permit consumption of seemingly unsavory prey. The parotid and principal salivary glands of this bat are similar to homologous glands in other phyllostomids, but the accessory submandibular gland is unique.

METHODS

The accessory submandibular glands of live-trapped T. cirrhosus were fixed and processed for transmission electron microscopy by conventional means.

RESULTS

The accessory submandibular gland consists of follicles and ducts. The principal cells of the follicular walls have an abundance of rough endoplasmic reticulum (RER), free ribosomes, and extensive Golgi apparatuses. Typically, these cells have relatively few serous secretory granules. The ells contain collections of peculiar lipid droplets, and some of their mitochondria have dense crystalloids within expanded cristae. A layer of irregular, moderately dense bodies lies immediately subjacent to the luminal plasmalemma; it is not clear if these structures are endocytotic or exocytotic. Clusters of mucous cells, some of which have a single, hugely distended RER cisterna, are ensconced in the follicular walls; mucus from these cells reaches the lumen via intercellular canaliculi. Ducts progress from simple cuboidal to simple columnar epithelium. They lack basal striations, and their constituent cells contain relatively few mitochondria. Follicles and ducts have numerous myoepithelial cells at their periphery, and both are heavily innervated by hypolemmal nerve terminals.

CONCLUSIONS

The unusual accessory submandibular gland in T. cirrhosus documents the extreme modifications in gland histology and in cell ultrastructure that have occurred in mammalian families. The cells composing the follicle walls and ducts bear little similarity to typical acinar or duct cells. Duplication of the submandibular gland in some bat lineages might be the key innovation underlying such plasticity. The heavy innervation of both follicles and ducts also implies that these structures are sensitive to and capable of responding to various inputs, perhaps including dietary factors.

Ultrastructure of bovine von Ebner's salivary glands

Bovine von Ebner's glands were studied by electron microscopy. The gland consists of tubulo-alveolar adenomeres which open into an abbreviated duct system. The cells of the secretory acini show many morphological features typical of serous cells and contain numerous granules with a complex substructure. Short intercalated ducts connect the acini with excretory ducts which are lined with bistratified epithelium. The striated ducts are absent. The von Ebner's gland morphology was compared with that of the same gland in other species of mammals and with the ultrastructure of the major bovine salivary glands.

Mucous droplets with multiple membranes in the accessory submandibular glands of long-winged bats

BACKGROUND

Certain species of bats possess two sets of submandibular glands, namely, principal and accessory. The ultrastructure and histochemistry of the accessory submandibular gland was examined in three species of long-winged bats.

METHODS

Specimens of Miniopterus schreibersi and M. magnator were live-trapped in Thailand, and of M. inflatus were live-trapped in Kenya. For electron microscopy, accessory submandibular lands were initially fixed in triple aldehyde-DMSO, postfixed in osmium tetroxide, and embedded in Epon-Maraglas. A portion of the glands collected in Thailand (M. schreibersi and M. magnator) was fixed in buffered formalin and embedded in paraffin. Sections of the latter material were subjected to a battery of histochemical tests for glycoconjugates.

RESULTS

Although in all three species the accessory submandibular glands have normal histological structure, the glands in two, M. schreibersi and M. magnator, were distinguished by possessing mucous droplets of unusual morphology. These droplets, whose identity as mucous was confirmed by histochemical tests for glygoconjugates, are delimited by manifold membranes: up to 10 in M. schreibersi and fewer, but still multiple, in M. magnator. In both species, the entire array of surface membranes may fold inward in the fashion of mitochondrial cristae, forming packets of membranes, many of which have the spurious appearance of floating free in the droplet matrix. These multipartite limiting membranes appear to originate simply by Golgi saccules and moderately large, flattened Golgi vesicles repeatedly wrapping themselves around the surface of nascent mucous droplets. During exocytosis, the outermost membrane of each mucous droplet contacts the luminal membrane, this barrier ruptures, then the remainder of the droplet--multiple membranes and matrix--either flow into the lumen or are cast out in toto. In either case, a great deal of membrane phospholipid is added to the saliva. This salivary lipid may permit these bats to consume insects that normally are able to repel predators with chemical defenses that make them unpalatable. The third species that we studied, M. inflatus, has mucous droplets of normal appearance, i.e., they have only one limiting membrane.

CONCLUSIONS

The varying structure of mucous secretory products among the species of Miniopterus provides important clues as to the evolution of this genus as well as to the evolution of secretory cells in general.