Ultrastructure of the cat sublingual gland

Microscopy of the echidna sublingual glands

The secretory units and duct system of the echidna sublingual glands exhibit subtle architectural modifications to accommodate the viscous secretion produced by these glands. The glands are compound tubular glands, the secretory units of which are elongate with open lumina and consist only of mucous cells. Closely packed spindle-shaped myoepithelial cells invest the secretory units, but are absent around the ducts. The branched secretory tubules open into an abbreviated duct system characterized by wide lumina. Striated ducts normally associated with the second portion of the intralobular duct system are absent. The duct system shows the most obvious modification of general salivary gland architecture presumably to accommodate the viscous secretion propelled from the secretory units by surrounding myoepithelial cells.

Interlobular excretory ducts of mammalian salivary glands: structural and histochemical review

In the major salivary glands of mammals, excretory ducts (EDs) succeed striated ducts. They are for the most part interlobular in position, although their proximal portions sometimes are on the periphery of a lobule, where they occasionally retain some of the structural features of striated ducts. Based on a survey of a broad range of mammalian species and glands, the predominant tissue type that composes EDs is pseudostratified epithelium. In some species, there is a progression of epithelial types: the proximal EDs are composed of simple cuboidal or columnar epithelium that, in the excurrent direction, usually gives way to the pseudostratified variety. Secretory granules are visible in the apical cytoplasm of the principal cells of the EDs of only a few species, but histochemistry has shown the presence of a variety of glycoproteins in these cells in a spectrum of species. Moreover, the latter methodology has revealed the presence of a variety of oxidative, acid hydrolytic, and transport enzymes in the EDs, showing that, rather than simply acting as a conduit for saliva, these ducts play a metabolically active role in gland function. It is difficult to describe a "typical" mammalian ED because it can vary along its length and interspecific variation does not follow a phylogenetic pattern. Moreover, in contrast to intercalated and striated ducts, ED cellular features do not exhibit a relationship to diet.

The serous demilune of rat sublingual gland is an artificial structure produced by conventional fixation

The ultrastructure of the secretory end-piece of the rat sublingual gland was examined in samples prepared by rapid freezing and freeze-substitution method, and results were analyzed in combination with 3-D images reconstructed by computer graphics from light micrographs of serial sections. Fixation by rapid freezing followed by freeze-substitution preserved cellular ultrastructures, especially the membrane structure, in perfect condition, and demonstrated the terminal portion of the sublingual gland to be a compound branched tubulo-alveolar gland with serous cells distributed throughout the end-pieces. All the serous cells aligned with mucous cells to surround a common lumen, leaving no demilune structure. In contrast, samples fixed by the conventional immersion method showed distended mucous cells displacing the serous cells toward the basal portion of the acinus to form the demilune structure. The luminal space was also compressed and appeared disconnected from the serous cells. From these observations, the serous demilune that for more than 130 years has been believed to be an actual histological entity was proved to be an artificial structure produced through compression by the hydrated and expanded mucous cells during immersion fixation.

Ultrastructure of Weber's salivary glands of the root of the tongue in the rat

BACKGROUND

The mammalian tongue encompasses several sizeable agglomerations of minor salivary glands. The ultrastructure of the various glands in the body of that organ has already been determined. In contrast, almost nothing is known of the structure of Weber's glands, a collection of salivary glands in the root of the tongue.

METHODS

The entire tongue was extirpated from anesthetized adult male rats that had been perfused with fixative and specimens of tissue that included Weber's glands were dissected from the lingual root. These were prepared for electron microscopic examination by conventional means.

RESULTS

Weber's glands in the rat are mixed glands, consisting of long mucous tubules that often are capped by serous demilunes. There appear to be no ducts per se, the mucous tubules increasing in caliber and approaching the crypts of the dorsal lingual surface while still retaining their mucous secretory character. As these ducts near the surface, their lining changes to stratified squamous epithelium. The mucous cells are cytologically similar to those in the sublingual glands of the same animal. Mucous droplets undergo vertical fusion to form centrally situated intracellular channels through which mucus is exocytosed, much in the same manner as goblet cells. The serous cells, which have all of the hallmarks of protein-secreting cells, probably empty their secretory granules via cellular extensions that directly reach the tubule lumen since there are no intercellular canaliculi between adjacent mucous cells.

CONCLUSIONS

The mucus elaborated by Weber's glands undoubtedly aids in swallowing dry food. We postulate that the serous cells in these glands, as in the more anterior von Ebner's glands, might play a role in the mechanism of taste, especially where posteriorly situated, nonlingual taste buds are concerned.

Ultrastructure of the salivary glands in the midtongue of the common vampire bat, Desmodus rotundus

BACKGROUND

All examined mammals have at least two sets of lingual salivary glands: von Ebner's glands and Weber's glands. A third set, the glands of Blandin and Nuhn, is present in the tongues of some but not all mammals. Vampire bats, Desmodus rotundus, are unusual in that they possess another set of lingual glands, these being in the midtongue region.

METHODS

The anterior half of the tongue was extirpated from several adult vampire bats, dissected, and tissue blocks derived from the midregions of the body of the tongue prepared for transmission electron microscopy by conventional means.

RESULTS

The midlingual glands are in the form of long, tubular secretory endpieces that are succeeded by ducts of simple morphology. In general, the secretory portions consist of two cell types, which may be intermingled in the same tubule or may form tubules that consist wholly of one cell type or the other. Seromucous cells usually have one or several rough endoplasmic reticulum cisternae that are hugely distended by a homogeneously dense material. Their granules have a bizonal substructure: one or several dense bands are embedded in a lighter matrix. Mucous cells are rather typical in structure, but their secretory product is different from run-of-the-mill mucous droplets. These droplets vary in density from cell to cell. In some cells, these droplets have a relatively light matrix; in other cells, the droplet is unusually dense, consisting mainly of a dark, structureless matrix with marginal lenticular lacunae of low density in which some short, irregular filaments are scattered. A rare finding is the presence of ciliated cells intermingled with secretory endpiece cells. The cilia are of conventional morphology. Secretory tubules are succeeded by ducts that resemble intercalated ducts; the epithelium of these ducts gradually increases in height to form a kind of excretory duct, without the intervention of striated ducts. As the ducts approach the lingual surface, the epithelium changes to stratified squamous.

CONCLUSIONS

Saliva produced by the midlingual glands may be an aid in the reciprocal grooming behavior of vampire bats. Based on their morphology, the excurrent ducts may not modify the initial saliva elaborated by these glands and might act simply as pipelines by which the saliva reaches the mouth.

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.

The effects of obstruction and secretory stimulation on microlithiasis in salivary glands of cat: light and electron microscopy

Obstruction and increased secretory activity are considered to be important aetiological factors of salivary microlithiasis, which may itself be an aetiological factor of sialadenitis. However, there is a lack of substantial evidence for the importance of obstruction, and investigations on increased secretory activity used pathological doses of pharmacological agents. Therefore further investigation of these factors is essential. Feline parotid, submandibular and sublingual salivary glands, in which microliths occur normally as in man, were examined after ductal ligation to produce obstruction, electrical stimulation of the glandular nerves to produce increased secretory activity, or both. Microliths were detected in: 0 out of 38 untreated, 1 out of 55 ligated, 2 out of 17 stimulated and 2 out of 17 stimulated ligated submandibular glands; 6 out of 29 untreated, 7 out of 46 ligated, 3 out of 12 stimulated and 4 out of 14 stimulated ligated sublingual glands; and no parotid glands. The chi 2 test confirmed that the experimental procedures did not produce an increased occurrence of microliths. Microliths were detected in parenchymal cells, intercellularly in atrophic parenchyma, intraluminally, interstitially and in macrophages. The present investigation indicates that obstruction and increased secretory activity are not important aetiological factors of salivary microlithiasis.

Ultrastructural localization of microliths in salivary glands of cat

Although microliths occur in normal human salivary glands and may be an aetiological factor of sialadenitis, little is known of their natural history. In an attempt to remedy this, we investigated a large archival collection of normal and experimental feline parotid, submandibular and sublingual salivary glands. In submandibular and sublingual glands, microliths were detected ultrastructurally in: all types of acinar secretory cells; myoepithelial cells; ductal cells; lumina; intercellular spaces; basement membrane; stroma; macrophages; multinuclear giant cells; and neutrophils. Microliths were not detected ultrastructurally in parotid glands. Microliths appear to form in acinar cells during autophagy and in stagnant secretory material in lumina. Microliths appear to be removed by secretion in the saliva, discharge from cells laterally and basally, and engulfment by macrophages. There appears to be a turnover of microliths, which possibly is upset by secretory inactivity with a resulting accumulation that leads to localized obstruction and sialadenitis.

Histochemical and biochemical determination of calcium in salivary glands of cat

Although feline salivary glands have been used in investigations on secretion and microlithiasis and both processes involved calcium, nothing is known about its distribution in these glands. Therefore we have demonstrated the presence of calcium by a histochemical technique using glyoxal bis(2-hydroxyanil) and a biochemical technique using dry ashing. The histochemical technique stained serous acinar cells weakly and rarely found mucous acinar cells strongly in the parotid gland, mucous acinar cells moderately to strongly and serous acinar cells weakly in the sublingual gland, and central and demilunar acinar cells moderately to strongly in the submandibular gland. The biochemical technique revealed less calcium in the parotid than in the submandibular and sublingual glands. Both techniques revealed a decrease of calcium in submandibular and sublingual glands following parasympathetic stimulation. The histochemical distribution of calcium, which corresponds to that of acinar secretory glycoprotein, and the loss of calcium following parasympathetic stimulation, which causes release of secretory granules, indicate the presence of calcium in secretory granules. The concentration of calcium in the different types of acinar cell corresponds to the acidity of the secretory glycoprotein and suggests that calcium is present as a cationic shield to allow the condensation of polyionic glycoprotein in secretory granules.

Microliths in normal salivary glands of cat investigated by light and electron microscopy

This investigation concerns the natural history of microlith in the salivary glands of cat. Microliths were detected in more sublingual than submandibular glands and were almost absent in the parotid. They were found intraparenchymally, intraluminally and interstitially, and ultrastructurally in phagosomes of acinar, ductal and myoepithelial cells, intermixed with the cytoplasm of degenerate acinar cells, and in intraparenchymal macrophages and a multinuclear giant cell. They appear to form in healthy acinar cells during autophagocytosis, and possibly to be discharged luminally, laterally or basally, and to form in the debris of degenerate cells intraparenchymally and intraluminally. They appear to be removed by expulsion in the saliva, scavenging macrophages, and possible eventual degradation in the parenchymal phagosomes. The greater occurrence of microliths in the sublingual gland may relate to a low level of secretory activity, and the near absence of microliths in the parotid to a low level of calcium. The feline salivary glands were found to be an outstanding model for the investigation of microlithiasis.

The effect of sympathectomy on the occurrence of microliths in salivary glands of cat as studied by light and electron microscopy

Parasympathectomy is followed by a greatly increased occurrence of microliths in the feline submandibular gland, which appears to be because of secretory inactivity. The sympathetic nerves are also important in secretory processes, and so feline submandibular, sublingual and parotid glands subjected to postganglionic sympathectomy for periods from 1 day to 1 yr have now been investigated. Microliths were detected in two out of 28 sympathectomized submandibular glands and four out of 27 untreated glands, and in 10 out of 22 sympathectomized sublingual glands and seven out of 19 untreated glands. There were no significant differences between the occurrence of microliths in sympathectomized and untreated glands. Microliths were not detected in any of 29 sympathectomized and 30 untreated parotid glands. The appearance of the sympathectomized glands was similar to that of the untreated glands. The failure of sympathectomy to affect the occurrence of microliths or the appearance of the glands is possibly because of parasympathetic nerve impulses, which produce continuing secretory activity, and also the spontaneous secretion of the sublingual gland. The results support the concept that secretory inactivity is an aetiological factor of microlithiasis.

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.

Ultrastructural and histochemical observations on intracellular and luminal microcalculi in the feline sublingual salivary gland

As the genesis of salivary calculi in man has not been established, the fortuitous observation of microcalculi in sublingual glands of cats prompted this study. Microcalculi were seen occasionally within acinar cells and lumina and macrophages, and rarely interstitially. Microcalculi were stained with the periodic-acid/Schiff technique, and acid-phosphatase activity was associated with intracellular microcalculi. Intracellular microcalculi were seen ultrastructurally in acinar cells in membrane-bound vacuoles that also contained debris and sometimes what appeared to be secretory material. X-ray microanalysis showed the microcalculi to consist of crystals containing calcium and phosphorus. The observations suggest that the microcalculi form within autophagosomes in acinar cells by a precipitation of calcium and phosphorus present in degenerate material, and that the microcalculi eventually enter lumina, where they may be discharged in the saliva or retained and enlarge.

Morphological and biochemical changes in mucous cells of the murine sublingual salivary gland during the carbamylcholine-induced secretory cycle

Changes in these cells have been evaluated over 6 h following cholinergic stimulation. Carbamylcholine administration resulted in the release of almost 50 per cent of secretory material within 15 min, which caused a reduction of 33 per cent in cell size. After 2 h the cells were depleted of secretory material. However, in the second hour the release of secretory material was accompanied by an enlargement of the nucleus, Golgi complexes and rough endoplasmic reticulum (RER), which suggests an elevation of biosynthetic activity. The enlargement of the RER was not the result of an increase in RNA, i.e. in the number of ribosomes, but of dilatation of its cisternal spaces. Before release took place, there was a continuous coalescence of secretory granules. After this extensive fusion, which is probably the result of an altered physiological state of the granule membrane and subsequent water uptake caused by cholinergic stimulation, the viscous mucins could be squeezed out, water transport is likely to assist in this ejection. Refilling of the mucous cells was almost complete within 6 h after stimulation.

Ultrastructure of the parotid gland in the little brown bat

The ultrastructure of the parotid gland was examined in the little brown bat. The seromucous acinar cells contained abundant granules of variable morphology. These granules were characterized by a submembranous dense layer consisting of fine parallel slats. In some bats, the matrix of the granules was structureless, whereas in others it consisted of closely packed but randomly arranged bundles of tubules. The intercalated ducts had a highly developed rough endoplasmic reticulum, often containing large numbers of intracisternal granules. In contrast, only a few secretory granules were present in the supranuclear cytoplasm. The striated ducts, which exhibited the characteristic basal striations consisting of vertically oriented mitochondria and highly folded plasmalemmas, contained numerous small dense granules in a subluminal band. These granules had a paracrystalline substructure with a periodicity of 8 nm. Excretory ducts strongly resembled striated ducts. They showed the same kind of basal striations and about half their constituent cells contained small paracrystalline granules.

Surface architecture of the mucosal epithelium of the cat trachea: I. Cartilaginous portion

The mucosal covering of the cartilaginous portion of the cat trachea was studied by correlated light, transmission-electron, and scanning-electron microscopy. While in some areas the ciliated pseudostratified epithelial lining is fairly smooth in contour, in other areas it contains longitudinally oriented, cilia-lined clefts. Ducts from submucosal glands sometimes open into the base of these clefts, or into funnel-shaped stomata that are lined by either ciliated or microvillus-rich cells. Specialized epithelial cells are occasionally associated with the clefts or with other regions of surface epithelium. In single sections, these cells appear to contain a cilium-lined vacuole, but serial sectioning has demonstrated that these apparent vacuoles actually are long intracellular invaginations in enormously elongated cells that extend longitudinally in the plane of the epithelium. The function of these cells is undetermined. Basal cells are attached to the lamina densa by means of hemidesmosomes that consistently lack peripheral densities; in contrast, the tall columnar cells have no hemidesmosomes.

Ultrastructural localization of complex carbohydrates present in the sublingual gland of rabbits

Stainings with dialized iron (DI), high-iron diamine-thiocarbohydrazide-silver proteinate HID-TCH-SP), tannic acid-uranylacetate (TA-U), tannic acid-ferric chloride (TA-F), and periodate-thiocarbohydrazide-silver proteinate (PA-TCH-SP) were applied to samples of sublingual glands of rabbits. Comparing the results obtained with what had been previously demonstrated biochemically, it is possible to assert that the faintly electron-opaque, granules of the cells of the preterminal tracts contain sulphated glycoconjugates because of the presence of sulphated hexosamines and hexoses, acid glycoconjugates because of the presence of sialic acid and uronic acids, and neutral glycoconjugates because of the presence of hexoses.

The effects of vinblastine on acinar cells of the exorbital lacrimal gland of the rat

The effects of vinblastine treatment on acinar cells of the rat exorbital lacrimal gland were studied by electron microscopy. Experimental animals of both sexes were given single intraperitoneal injections of (1) vinblastine (4 mg/kg body weight) at 1 to 24 h before sacrifice; (2) pilocarpine (20 mg/kg b.w.) for 1 h; or (3) vinblastine for 1 h followed by pilocarpine for 1 h. Vinblastine treatment caused a number of changes including autophagocytosis, formation of intracisternal granules, and alteration of secretory granules. These changes varied in extent and onset between male and female rats. In addition, the Golgi apparatus was reduced in size and dispersed throughout the cytoplasm. Mitotic figures were commonly observed. Moreover, vinblastine inhibited the pilocarpine-stimulated degranulation of the acinar cells. In view of the known anti-microtubular action of vinblastine, these results suggest that microtubules are involved in various aspects of the transport, packaging, and secretion of exportable proteins in the lacrimal gland. Additionally, autophagocytosis and alteration of secretory granules may partially result from the interaction of vinblastine with membranes.