On the fine structure of the parotid gland of tufted capuchin monkey, Cebus apella

The parotid gland of the tufted capuchin monkey (Cebus apella) was examined by scanning and transmission electron microscopy. In general the ultrastructural morphology of this gland appears similar to that described in spider and squirrel monkeys. This study has established that the gland is serous. Acinar cells, which contain a well developed granular endoplasmic reticulum and a prominent GOLGI complex, produce a single secretory material. Myoepithelial cells are present around acini and around intercalated ducts. The intercalated ducts, which are composed of cells that show no evidence of secretory activity, lead into striated ducts.     

Fine structure of the mandibular gland of the Djungarian hamster (Phodopus sungarus)

The mandibular gland of the Djungarian hamster was examined by light microscopy, and transmission and scanning electron microscopies. Its acinar cells reacted with periodic acid-Schiff (PAS) and were weakly stained with alcian blue (AB). There were intercellular canaliculi between the acinar cells. These cells therefore appeared to be seromucous. The acinar epithelium was composed of light cells containing various spherical secretory granules. The granular cells of the mandibular gland possessed many acidophilic granules exhibiting a positive reaction to PAS stain. They were frequently observed at the junction of the acini and intercalated ducts in all mandibular glands examined. All of these cells were light and contained secretory granules of varying size and density. The intercalated ducts consisted exclusively of light cells possessing a few round granules of high density in the apical region. The striated ducts were comprised of two portions--a secretory portion and a typical striated portion without secretory granules. The secretory portion consisted of light, dark and specifically light epithelial cells containing acidophilic granules, which exhibited a strongly positive PAS reaction. The epithelium of typically striated portions was composed of light and dark cells containing fine vacuoles in the apical region. The mandibular gland of the Djungarian hamster revealed no histological differences between sexes.     

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 postfixation, 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.     

Expression of transforming growth factor beta 1 in the submandibular gland of the rat

We employed immunocytochemical and in situ hybridization techniques to study the expression of transforming growth factor beta 1 (TGF-beta 1) in rat submandibular gland. Immunoreactivity for TGF-beta 1 was observed in the cells of granular convoluted tubules (GCTs), striated ducts, and excretory ducts, whereas it was absent in the intercalated ducts and secretory acini in both male and female rats. Immunoelectron microscopy revealed the ultrastructural localization of TGF-beta 1 in the secretory granules of GCT cells. On the other hand, signals for rat TGF-beta 1 mRNA were abundant in the GCT and striated duct cells but were lacking in the excretory duct cells. These results provided evidence for the production of TGF-beta 1 in the GCTs and striated ducts of rat submandibular gland.     

Cytodifferentiation of striated duct cells and secretory cells of the convoluted granular tubules of the rat submandibular gland.

The structural and functional development of the striated ducts and convoluted granular tubules (CGT) of the rat submandibular gland (SMG) were studied by electron microscopy and alkaline protease chemistry. Development of the SMG was followed from 14 days of gestation through 30 weeks of age. The specialized morphology of the basal aspect of the striated duct cells arises from cellular extensions which are first seen at 20 days of gestation. These processes elongate and intertwine with similar processes from adjacent cells, and as the cells enlarge the processes are compressed together giving the appearance of "infolding" of the basal plasma membrane. Mitochondria migrate to the basal part of the cell and are seen in close relationship to the cellular extensions throughout the development of these cells. Development of the striated duct is complete by one week after birth. The CGT develop from the proximal portions of intralobular striated ducts. At one week after birth, cells of the proximal striated duct demonstrate apical vacuoles. By two weeks after birth these vacuoles are replaced by distinct zymogen-like granules. There is a progressive accumulation of large numbers of secretory granules in the CGT cells as the animals age. However, rough endoplasmic reticulum is a relatively inconspicuous cellular component throughout development. The accumulation of alkaline protease activity in the gland closely parallels the pattern of granule accumulation.     

Subcellular localization of epidermal growth factor in human submandibular gland

Epidermal growth factor in human submandibular gland was localized at the subcellular level by means of an immunogold staining method. Labelling was observed in serous acini and ducts. In the acini, gold particles were found within secretory granules, indicating that the growth factor is released into the saliva through granule exocytosis. In the ductal system, the most intense reactivity was revealed in the principal cells of striated ducts. In these cells, an abundant population of small cytoplasmic vesicles was specifically stained. Immunoreactive vesicles were found both apically and basally, suggesting that ductal cells can release their products not only into the saliva but also into the interstitium.     

Exogenous thyroid hormone affects myoepithelium and proliferation in the developing rat parotid gland

Abstract

In the mature rat parotid gland, myoepithelial cells (MEC) invest intercalated ducts, but not acini. During postnatal development, however, these cells differentiate around both intercalated ducts and acini, then translocate to only intercalated ducts during weaning. Previously, we found that thyroxine (T₄) accelerates translocation of cells with small secretory granules from acini into intercalated ducts and the number of apoptotic cells increased tremendously with high doses. We present here additional analysis of the effects of T₄ on developing rat parotid gland, namely, the distribution of MEC and the proliferation of parenchymal cells. Beginning at age four days, pups were given daily subcutaneous injections of low, medium, and high doses of T₄ or vehicle or no injection. At ages 4, 7, 10, and 15 days, glands were excised and processed for light microscopy. Sections were double-immunostained with antibodies against proliferating cell nuclear antigen (PCNA) and actin, and counterstained with hematoxylin. Proliferative activity was assessed via PCNA histochemistry and MEC were identified using actin histochemistry. MEC in the T₄ groups invested mostly acini at 15 days in vehicle/normal glands and mostly intercalated ducts after 10 days in the T₄ groups. The proliferative activity of acinar cells and MEC in vehicle/normal glands declined progressively with age and T₄ increased the rate of this decline in the MEC in a dose-dependent manner. We conclude that T₄ accelerates the translocation of MEC from acini to intercalated ducts and that an important mechanism is the more rapid decline in the proliferative activity of MEC than in acinar cells in the T₄ groups. Some of the decline in the proliferative activity of all cells in the high and medium dose T₄ groups after seven days may have been due to dose-related thyroxine toxicity.     

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.     

Immunohistochemistry of carbonic anhydrase isozymes VI and II during development of the rat salivary glands

 Secreted carbonic anhydrase (isozyme VI; CA VI) was localized by immunohistochemistry in the developing postnatal rat submandibular and parotid glands using a specific monoclonal antibody to the rat enzyme. CA VI immunostaining was not detectable in the glands before birth. In the submandibular gland, granular immunostaining for CA VI was detectable in several terminal tubule cells of 1-day-old rats. At 1 week, the CA VI-positive cells were located at the periphery of the terminal tubules and appeared to be budding off the tubules. These cellular buds gradually increased, and, by 4 weeks, formed acini. CA VI was also detected in the duct lumen from day 1. The immunostaining in the parotid gland was detected sporadically in the acinar cells at 2 or 3 weeks. By 4 weeks, when the gland was almost indistinguishable from the adult one, the number of positive acinar cells had increased. Their number, however, was far smaller than in the adult gland, and the enzyme could not be detected in the duct lumen. CA II was also localized using specific antibodies to the rat isozyme. CA II was detectable in the inter- and intralobular striated ducts at 2 weeks after birth in the submandibular gland and at 3 weeks in the parotid gland. These results suggset that CA VI is secreted into saliva from soon after birth and that CA II appears in parallel with the functional maturation of the ducts. In addition, CA II was transiently expressed by the cellular buds of the submandibular gland at 2 and 3 weeks. Accepted: 7 January 1998     

Structural features of the submandibular salivary gland of gnotobiotic rats

The submandibular salivary gland was histochemically and electron microscopically studied in gnotobiotic and conventional Wistar rats at the age of 15 days--10 months. By the first month of age, the submandibular salivary glands in both groups of animals complete differentiation of their acini, and the gland, according to the type of its secretion, becomes seromucous with predominance of albuminous component in it. Succinate dehydrogenase activity and nonspecific esterase predominate in epithelium of the excretory ducts. At the second month of life some signs of moreasing ductal part of the gland appear in the gnotobiotic rats. This part greatly increases by the 4th--10th month of life, mainly at the expense of twisted granular sections. This increase in number and volume of the twisted granular ducts results in compressing acini and in ultrastructural disorders of granulocytes, with destruction of some mitochondria, increasing number of lysosomes, decreasing size and alterations in character of secretory granules, in structural disorders of the laminar complex. All these manifest depressing secretory function of granulocytes in the gland of gnotobiotic animals.     

Ultrastructure of the submandibular gland in the rabbit

The secretory endpieces of the rabbit submandibular gland are unusual in that they consist of seromucous acini (not demilunes) that empty into serous tubules that in turn drain into intercalated ducts. Seromucous granules consist of a moderately dense spherule in a fibrillogranular matrix. Serous granules contain a feltwork of filaments, which are liberated as a tangled skein during exocytosis. Peculiar granulated cells that have secretory granules of complex morphology are present at each end of the serous tubules. Intercalated ducts are, cytologically speaking, relatively simple, but the duct cells may contain a few oblong secretory granules. Striated ducts are typical in structure, although postfixation with ferrocyanide-reduced osmium reveals significant amounts of glycogen in the basal processes. Modified mitochondria are present in striated duct cells, but their frequency varies from rabbit to rabbit. Such mitochondria contain either an array of parallel, rigid cristae linked by intermembranous bridges, or a bundle of helical filaments within an expanded crista. Interspersed with the striated duct cells, especially near the duct origin, are some highly vacuolated cells with sparse mitochondria. Excretory ducts consisting of stratified columnar (sometimes pseudostratified) epithelium often show bleb formation of the luminal surface of the tall cells.     

Ultrastructural aspects of cat submandibular glands

Submandibular glands of five adult female cats were examined by conventional electron microscopic techniques. All gland acini are mucous secreting and each acinus is capped with mucous secreting demilunar cells. Secretory product of demilunar cells is more electron lucent than that of acinar cells. The demilunes show intercellular tissue spaces and intercellular canaliculi whereas similar specializations are absent between acinar cells. Mitochondria and arrays of granular endoplasmic reticulum are more numerous in demilunar cells than in acinar cells. In acinar and demilunar cells secretory droplets first appear as enlarged Golgi saccules which subsequently become closely related to cisternae of the granular endoplasmic reticulum. Filamentous structures, interpreted as mucin molecules, are present in secretory droplets of acinar cells. Intercalated ducts are short, consisting of several junctional cells between acini and striated ducts. Striated ducts are long and tortuous and contain light cells, dark cells and basal cells. Light cells contain numerous membrane bound granules in their distal ends whereas dark cells show electron lucent vesicles in the same position. Basal cells contain a paucity of organelles and membrane plications but exhibit hemidesmosomes along their basal plasma membranes. Myoepithelial cells are abundant in relation to acinar and demilunar cells. Nerve terminals are present in some instances between acinar cells or between acinar and myoepithelial cells.     

An enzyme histochemical and biochemical study of the activity of three oxidative enzymes in the developing rat parotid gland

Information on ductal differentiation in the developing rat parotid gland is sparse. One of the main functions of the striated and excretory ducts in this gland is the selective exchange of electrolytes from the primary fluid secreted by the acini. These ducts are rich in a number of enzymes involved in this task, suggesting that they might be useful as markers of ductal differentiation. The objective of this investigation was to delineate the developmental changes in activity of three of these, cytochrome C oxidase (CCO), succinate dehydrogenase (SDH), nicotinamide adenine phosphate dinucleotide (reduced form)-dehydrogenase (NADPH-DH). Histochemical localization of all three enzymes in fresh frozen sections was complemented by biochemical assays of CCO and SDH and cytochemical localization of CCO. Biochemically, CCO- and SDH-specific activity in gland homogenates increased progressively after birth, reaching adult levels at 21-28 days. Histochemically, deposits of reaction products of all three enzymes increased more in the striated and excretory ducts, especially in their basal cytoplasm, than in other glandular structures between 19 days in utero and 28 days after birth. During the same age span, the mitochondria in the striated and excretory ducts increased markedly in both number and size, migrated to a mostly basal location, and increased from many to virtually all showing strong cytochemical CCO reactions. These histochemical and cytochemical patterns of changes in enzyme activity at the cellular level accounted for the overall increases in CCO and SDH seen in the biochemical assays. Only the SDH histochemical reaction was consistently weak in the acini and intercalated ducts, and thus provided the most contrast with the progressively stronger reactions in the larger ducts. We conclude that of the three enzymes evaluated in these experiments, SDH is the best marker of the functional differentiation of the striated and excretory ducts in the developing rat parotid gland.     

An enzyme histochemical and biochemical study of the activity of three oxidative enzymes in the developing rat parotid gland

Information on ductal differentiation in the developing rat parotid gland is sparse. One of the main functions of the striated and excretory ducts in this gland is the selective exchange of electrolytes from the primary fluid secreted by the acini. These ducts are rich in a number of enzymes involved in this task, suggesting that they might be useful as markers of ductal differentiation. The objective of this investigation was to delineate the developmental changes in activity of three of these, cytochrome C oxidase (CCO), succinate dehydrogenase (SDH), nicotinamide adenine phosphate dinucleotide (reduced form)-dehydrogenase (NADPH-DH). Histochemical localization of all three enzymes in fresh frozen sections was complemented by biochemical assays of CCO and SDH and cytochemical localization of CCO. Biochemically, CCO- and SDH-specific activity in gland homogenates increased progressively after birth, reaching adult levels at 21-28 days. Histochemically, deposits of reaction products of all three enzymes increased more in the striated and excretory ducts, especially in their basal cytoplasm, than in other glandular structures between 19 days in utero and 28 days after birth. During the same age span, the mitochondria in the striated and excretory ducts increased markedly in both number and size, migrated to a mostly basal location, and increased from many to virtually all showing strong cytochemical CCO reactions. These histochemical and cytochemical patterns of changes in enzyme activity at the cellular level accounted for the overall increases in CCO and SDH seen in the biochemical assays. Only the SDH histochemical reaction was consistently weak in the acini and intercalated ducts, and thus provided the most contrast with the progressively stronger reactions in the larger ducts. We conclude that of the three enzymes evaluated in these experiments, SDH is the best marker of the functional differentiation of the striated and excretory ducts in the developing rat parotid gland.     

Elafin expression in human fetal and adult submandibular glands

Elafin, a bifunctional protein, has the NH(2)-terminal domain functions as a transglutaminase substrate for crosslinking to lysine-containing proteins and the COOH-terminal whey acidic protein domain as a potent anti-elastase. Human fetal submandibular glands (n=100) and adult submandibular glands (n=10) were used to elucidate the expression pattern of elafin in the developmental processes of human submandibular gland by immunohistochemistry, in situ hybridization, and western blot analysis. Elafin mRNA was expressed both in the gland epithelium and intralobular mesenchymal tissue of fetal submandibular gland in an early developmental stage (10-18 weeks) and an early intermediate developmental stage (EIDS; 19-24 weeks). The elafin antigen was also found in the intralobular mesenchyme of submandibular gland in the same stages. Thereafter, elafin was transitionally expressed in the ducts and acini of submandibular glands. In the late intermediate developmental stage (LIDS; 25-32 weeks) and the late developmental stage (LDS; 33-40 weeks), elafin became markedly positive in the excretory and striated ducts but weakly positive in the intralobular mesenchymal tissue. The elafin was heavily present in the excretory and striated ducts of adult submandibular gland, while it was sparse in the intralobular mesenchymal tissues. Western blot analysis showed the protein extracts from submandibular glands of EIDS, LIDS, and LDS, adult submandibular gland, fetal tissues (8 weeks), and adult parotid saliva migrated into multiple bands, about 25, 50, 65, and 140 kDa, which were higher than the putative size of elafin protein, 12 kDa. These data suggest that elafin, anti-elastase, is an essential component highly utilized during the morphogenetic processes of fetal salivary gland development and continuously plays a role for the protection of the tubuloalveolar structures of adult salivary gland.     

Ultrastructure of bovine parotid glands

Bovine parotid glands exhibit outstanding structural differences when compared with those of non-ruminant mammals. The acini are tortuous, branched and lined with cells of different heights, imparting a scalloped appearance to acinar lumina. Numerous microvilli, ca. 1.5 μ in length, extend into the lumina and intercellular canaliculi. Intercellular canaliculi measure ca. 3 μ in diameter and interweave in close association with intercellular tissue spaces. Intercellular tissue spaces are separated from the extraacinar spaces across a basal lamina only, whereas junctional complexes guard canaliculi from direct continuity with tissue spaces and/or extraacinar spaces. Flattened cytoplasmic lamellae extend from adjacent acinar cells and loosely interdigitate with one another across the tissue spaces. Acinar cells contain more mitochondria and less granular endoplasmic reticulum than parotid glands of non-ruminant mammals. Two types of secretory material, in the form of inclusions which vary in size and electron density, are present in the acinar cells. Intercalated ducts connect acini with striated ducts which in turn, empty into collecting ducts located between gland lobules. In terms of frequency of “basal infoldings” and numbers of mitochondria, striated ducts of calf parotid glands are not as well developed as those of certain other salivary glands. Myoepithelial cells are most often present at junctions of acini and intercalated ducts where they may attach to both acinar and ductal epithelium. Nerve “terminals” were not observed on the epithelial side of basement membranes in relation to the secretory cells.     

Ultrastructure and complex carbohydrate ultracytochemistry of the cat parotid gland

The structure and glycoconjugate content of the cat parotid gland were analyzed at electron microscopic level by applying morphological techniques and three ultrastructural histochemical methods - HID-TCH-SP, LID-TCH-SP and PA-TCH-SP. This gland appeared as a typical salivary gland composed of acinar secretory cells, intercalated ducts, striated ducts and excretory ducts. The most common configuration of secretory granules consisted of a dense core surrounded by a variable electron-lucent halo. All ductal segments were characterized by the presence of different cell populations and small apical granules greatly different from those localized in the acinar cells. By using HID-TCH-SP we were able to demonstrate that in a few acinar cells there are sulphated sites, whereas PA-TCH-SP staining revealed the presence of vic-glycol radicals in all acinar cells preferentially located on the halo of secretory granules.     

Fetoacinar pancreatic protein in the developing human pancreas

The distribution of the 110-kilodalton fetoacinar pancreatic (FAP) protein was examined in 56 pancreases obtained from human embryos and fetuses (ranging 6 from weeks of gestation to full term) and 10 normal adult pancreases. This recently discovered protein is a concanavalin-A-binding glycoprotein that is specific for acinar cells of the pancreas. Using a murine monoclonal antibody for either immunoperoxidase or immunofluorescence procedures, FAP-protein expression was not found in embryos at less than 9 weeks of gestation. At 9-10 weeks, a clear staining was observed in the terminal portions of dilated buds in primitive pancreatic tubular structures (i.e., the site of the first development of the future acinus). At 11-12 weeks, acinar structuration began, and FAP-protein expression increased as shown by the higher number of stained acini and the greater staining intensity. Maximal expression occurred at 15-22 weeks and then gradually decreased; from 28 to 32 weeks until full term, the pancreas was almost negative for this protein. In the adult pancreases, the protein was either absent or only present in acinar cells surrounding the islets of Langerhans. The pancreatic ducts and endocrine cells remained negative throughout gestation and in adults. FAP-protein thus appears to be a marker of acinar-cell differentiation. Its function remains unknown at present. Its close association with the growth and development of the pancreas together with the fact that, in a previous study, it was found to be re-expressed in pancreatitis and in cancer, suggest that it may play a role in developmental regenerative and neoplastic processes in the pancreas.     

Early markers of regeneration following ductal ligation in rat submandibular gland

Rat submandibular glands can recover their function and secretory protein content following ductal ligation-induced atrophy. Morphological studies have established that following ligation, deligation of the gland allows the regeneration of new salivary gland tissue. However, little is known about changes happening during early regeneration following intra-oral duct ligation, which does not damage the parasympathetic nerves. Glands that had been 2 weeks ligated or 2 weeks ligated + 3 days deligated were compared. Tissue was prepared for histological, immunohistochemical (SMG-B and Ki-67) and immunocytochemical analyses (smooth muscle actin, aquaporin 5). Haematoxylin and eosin staining of deligated glands showed that some acini regained their cytoplasmic volume; moreover, the loss of Alcian blue/periodic acid-Schiff’s staining from the lumen of ducts suggested successful deligation. The deligated gland was characterized by atypical acinar-ductal branched structures, which were less frequent in the ligated gland and rarely seen in normal unoperated tissue. Myoepithelial cells were also investigated since changes in their morphology reflected changes in the acini morphology not readily detected by conventional staining. Actin staining revealed the presence of some shrunken acini in the atrophic tissue, whereas they had regained their normal morphology in the deligated gland suggesting that the acini were recovering. Some acini during deligation regained aquaporin 5 expression, which had decreased during atrophy. SMG-B protein, located in the pro-acinar cell during gland development and usually found in the intercalated duct cells in the adult, was detected in the newly formed acini of the deligated gland. This study suggests that morphological markers of regeneration appear as early as 3 days following ligation removal. The authors thank the Wellcome Trust for funding.