Mucous Tubules Research Articles

Capybara (Hydrochoerus hydrochaeris) Salivary Glands Morphology.

Morphological studies concerning salivary glands have emerged as an exciting tool to understand feeding habits. In this sense, this study aimed to describe capybara salivary glands morphology to understand potential morphological associations to this species feeding habits. Macroscopic dissections and microscopic analyses were performed on eight specimens. The findings indicate that capybaras have three pairs of major (parotid, mandibular and sublingual) and two pairs of minors (dorsal and ventral buccal) salivary glands. The parotid gland, the largest, is irregularly shaped, forming small macroscopic lobes. The mandibular gland is rounded and found syntopically alongside the mandible angle and arranged medially to the ventral projection of the parotid gland. The sublingual gland is a compact elongated and semicircular mass. The dorsal and ventral buccal glands are located in the buccal portion of the buccinator muscle. Histologically, the parotid and mandibular glands are composed of serous acini, while the sublingual and buccal (dorsal and ventral) glands consist of mucous tubules containing serous demi-lunes at their periphery. Capybara salivary glands reveal morphological associations with a predominantly herbivorous diet. The parotid gland, for example, notably developed in size and volume, suggests a specialisation for increased saliva production, necessary for chewing, forming the food bolus, swallowing fibrous foods, and protecting the oral cavity ecosystem.

Lingual Ultrastructural and Histochemical Study in the Patagonian Mara (Rodentia: Caviidae, Dolichotis patagonum) in Relation to Other Hystricomorphs.

The study describes the ultrastructure of the tongue in the Patagonian mara (Dolichotis patagonum) using light and scanning electron microscopy. Histochemical methods were used for evaluation of lingual salivary glands. The tongue is divided into a small and rounded apex, a narrow corpus, and a significantly wider radix, with a well-developed lingual prominence. The tip of the apex is free of papillae. The caudal part of the apex and the corpus are covered by filiform papillae. Round fungiform papillae are scattered among them. Papillae on the narrow stalk are conical. The radix contains caudally bent papillae forming wide flat prominences, slender, hook shaped filiform papillae, foliate papillae, and two oval vallate papillae. Taste buds were found on the lateral sides of the foliate and vallate papillae. Purely serous salivary glands are beneath the vallate and foliate papillae. Serous acini and mucous tubules are in the lingual radix. The Patagonian mara is the only hystricomorph rodent with described hyaline cartilage strengthening the lingual radix. Some typical signs of adaptation to herbivorous diet were found. The structure of the tongue is adapted to grass-feeding, as grasses form the main component of their diet.

Reactivity of human labial glands in response to cevimeline treatment.

Among the pathologies affecting the salivary glands, the Sjögren's syndrome (SS), an autoimmune disease, causes progressive destruction of the glandular tissue. The effect of SS is particularly evident on the labial glands and the morphological analysis of these minor glands is considered useful for diagnosis. Cevimeline hydrochloride (SNI), a selective muscarinic agonist drug, is one of the elective treatments for the hyposalivation due to SS, acting not only on major salivary glands, but also on labial glands since their secretion is primarily under parasympathetic control. Aim of this study is to describe the morphology of human labial glands treated with SNI by light, transmission, and high-resolution scanning electron microscopy. Moreover, a morphometric analysis was applied to the light and transmission electron microscopy micrographs to obtain data that were then compared with analogous data collected on control and carbachol-treated labial glands. Following SNI administration, the mucous tubules exhibited enlarged lumina, which were filled with a dense mucous secretion. Occasionally, small broken debris of the cells were retrieved into the lumen. In the mucous secretory cells, some mucous droplets fused to form a large vacuole-like structure. Similarly, the seromucous acini showed both dilated lumina and canaliculi. These above reported signs of secretion were confirmed through morphometric analysis and a milder action of SNI than carbachol on labial parenchyma was observed. This study confirmed that SNI also evoked secretion on labial glands and that its effect is more physiologic than that of the pan-muscarinic agonists.

Morphofunctional changes in the heart and lung tissues of dogs for isoniazid poisoning

The article presents the results of macroscopic, histological and histochemical studies of the heart and lungs of dogs for isoniazid poisoning. A pathoanatomical section of 19 carcasses of dogs of different ages and breeds was performed; heart and lung fragments were selected for morphological examination. Heart and lung samples were fixed in 10 % aqueous formalin neutral solution, Carnua and Buen fluids. Dehydration was carried out in ethanol of increasing concentration and embedded in paraffin. The sections were made on a MC-2 microtome 7 μm thick, stained with hematoxylin and eosin, using the McManus and Brasche technique. Made histopreparations were examined under a Leica DM 2500 light microscope (Switzerland), photo-fixation was performed with a Leica DFC450C using Leica Application Suite Version 4.4 software. The results of morphohistochemical studies have shown that in acute poisoning of dogs with isoniazid in the heart prevailed acute disorders of the vascular circulation, manifested by a sharp expansion and destruction of the walls of the venous vessels, plasmorrhagia, microtromb of the capillaries and spasm of the arterioles, which led to the development of swelling, caused acute decrease of protein synthesation function of muscle fibers and dystrophic-necrobiotic changes of cardiomyocytes. It was noted, in the lungs of dogs on the background of acute congestive hyperemia, diapedesis of erythrocytes and accumulation of transudate in the lumen of the alveoli, foci of emphysema and bronchiectasis with rupture of the epithelial layer of the mucous membrane, elastic skeleton and muscular tubules of bronchial tubules that indicated the violation of gas exchange and the development of anoxemia. It is known that spontaneous isoniazid poisoning in dogs leads to an acute course and often fatal consequences. In the comprehensive study of the effects of chemicals on the body, and in particular isoniazid on the body of dogs, toxicological and pathomorphological studies are of great importance. The use of morphological and histochemical methods will reveal some of the mechanisms of intoxication.

Detection of an Intermediate Filament Protein in the Pancreas and Mandibular Salivary Gland of the Goat (Capra hircus): An Immunocytochemical Study

The centroacinar cells (CACs) are a specialized ductal pancreatic cell. Recently, it has been revealed that such cells showed a progenitor function in the pancreas of adult mouse and zebrafish. However, no information about its occurrence in other exocrine glands specially in farm animals. Cytokeratins immunohistochemistry was used to detect ductal segments of the submandibular glands and the pancreas including CACs in human and rat. In the present study, the detection of cytokeratins in the normal goat pancreas (a serous type gland) and mandibular salivary gland (a mixed type gland, consisted of mucous tubules capped with serous demilunes) was investigated using a standard immunoperoxidase technique on paraffin sections. In the goat pancreas and mandibular salivary gland, cytokeratins were found in all duct cells including the CACs of the pancreas. Interestingly in the mandibular salivary glands, some immunoreacted cells with immunopositive cytoplasmic extensions were frequently observed between the cytoplasm of the mucous cells, especially near the lumina of the mucous tubules. We postulate that these cells could be centroacinar- like cells. Therefore, from these findings, it can be concluded that these cells could provide a supportive cytoskeleton to maintain cellular shape and avoid the collapse of the mucous cells during mucous secretion. Additionally, a regenerative function for such cells could be hypothesized. Furthermore, the keratin demonstration could be used as a marker for ductal cells and is a useful aid in the detection of lesions derived from gland ductal cells in goat. Further research is necessary to investigate the expression of keratins in caprine glandular tumors as well as the regenerative ability of these centroacinar- like cells in goat mandibular salivary glands injury.

Use of diatom life-forms and ecological guilds to assess pesticide contamination in rivers: Lotic mesocosm approaches

The persistence of pesticides in the environment and their effects are a cause of concern to more and more people, and so in 2009 the French government announced plans to reduce pesticide use in agriculture over the next 10 years. Water managers are to monitor the beneficial impact of this reduction on aquatic environments. It has been suggested that diatoms may be good indicators of pesticides, and more particularly of herbicides, in water. Diatoms have been routinely used to assess organic and nutrient pollution for more than 10 years. The general approach is to develop a diatom-based tool to assess pesticide contamination. Diatom indices are usually based on specific pollution sensitivity. Other metrics, such as life-forms, ecological guilds, or cell size offer other advantages. For instance, the relationships between trends in these metrics and environmental gradients are more robust, and make it easier to establish ecological hypotheses. We have therefore opted for this approach. To develop such a tool, outdoor, lotic mesocosm experiments lasting about 2 months were conducted from 2006 to 2008. Herbicides (diuron) and fungicides (azoxystrobin, tebuconazole) were tested at environmental concentrations (sum of pesticides concentrations from 1.11 to 3.01 μg L −1 for chronic pollutions and from 20.25 to 29.50 μg L −1 for short-term acute pollutions). Diatom communities in artificial channels were analyzed by light microscopy using standard European methods. The various parameters structuring diatom communities were assessed, and colonization time appeared to be the most important. However, pesticide contamination was the second most important, and had a more significant impact on the composition of ecological guilds than on species composition. Some metrics did not display any significant trends (benthic/planktonic, colonial, pedunculate, pioneer), but others looked promising for use in pesticide contamination assessment: the abundances of motile guild, low-profile guild and mucous tubule diatoms all increased in contaminated channels, whereas high-profile diatoms showed the opposite trend. Some possible explanations, such as a protective effect of the exopolysaccharide matrix, can be advanced: diatoms living inside a mucous tubule may be shielded from dissolved pesticides, as are motile diatoms, which have a micro-habitat preference for thick matrices which also allows them to withstand higher levels of water contamination. In the same way, high-profile guild diatoms are exposed to dissolved pesticides to a greater extent, and this could explain their lower abundance in contaminated channels.

Oral glands in dipsadine “goo-eater” snakes: Morphology and histochemistry of the infralabial glands in Atractus reticulatus, Dipsas indica, and Sibynomorphus mikanii

Although snake infralabial glands are generally constituted of mucous cells, among dipsadines, they are much more developed and predominantly serous in nature, possibly due to the peculiar feeding habits of some species of this group, the “goo-eaters”, which feed on soft and viscous invertebrates. We compared the morphology and histochemistry of the infralabial glands of three goo-eater species of Southeast Brazil, Atractus reticulatus, Dipsas indica and Sibynomorphus mikanii. In A. reticulatus the glands are formed by mixed acini composed of mucous and seromucous cells and in D. indica, they are composed of mucous tubules and seromucous acini. In S. mikanii the glands are organized in seromucous acini; mucous cells are restricted to the gland anterior region and to the duct lining epithelium. Ultrastructurally, secretory granule electron density varies from low to moderate, depending on their mucous or seromucous nature. The results indicate a large morphological and histochemical variation in the infralabial glands, probably reflecting differences in the secretion chemical composition and in feeding specialization among the three species. The protein content in the secretory cells can be related with the presence of toxins that can be used in chemical prey immobilization or detaching of snails from their shells.

Effect of thyroidectomy on the histology of rat sublingual gland.

This study was carried out to investigate the effect of thyroidectomy on the histology of rat sublingual gland. Twenty-eight male Wistar albino rats, aged 4 weeks and weighing between 45-55 g, were used. The rats were divided into two experimental groups (control and thyroidectomy), each containing 14 animals. Total thyroidectomy of rats was performed under ether anesthesia in thyroidectomy group. The rats in the control group were sham operated without having the thyroidectomy. Seven rats randomly selected from both groups were fixed using the perfusion fixation technique 2 and 6 weeks after thyroidectomy, and their sublingual glands were harvested for histological investigation. No histological difference was observed between the two groups 2 weeks after thyroidectomy. However, 6 weeks after thyroidectomy considerable cytoplasmic vacuolization of the epithelial cells of the mucous tubules was seen in the thyroidectomy group compared to the controls. Enlargement of mucous tubules was also observed, and the lumina in most of the tubules was quite dilated. In the stroma surrounding the parenchymal tissues, increased lipid tissue mass was observed. In addition, increased connective tissue mass and mononuclear cell infiltrations were evident. Furthermore, the number of mast cells was significantly higher in the thyroidectomy group than in the controls 6 weeks after thyroidectomy. It was concluded that the thyroid gland and hormones might have an influence on the histology of the sublingual gland.

ON THE RICTAL STRUCTURES OF SOME SNAKES

I describe structures around the corner of the mouth of some snakes. Anilius has a large serous superior rictal gland lateral to the quadrato-maxillary ligament and a large serous inferior rictal gland. Other rictal structures of henophidian grade snakes are mesial to the ligament. Cylindrophis has a medium superior rictal gland and a large inferior gland. Two uropeltines have a large superior rictal gland opening into a rictal bulb with thick folded walls. Xenopeltis has a large superior rictal gland opening by three ducts into a thick walled rictal pocket. Aspidites, Calabaria, Exiliboa, Loxocemus, Tropidophis, and Ungaliophis have a rictal pocket into which open glands that may be mucous or serous. Candoia has glands opening around, but not into, a rictal pocket. Bolyerines show no evidence of differentiated rictal structures. Pareas has a superior rictal gland with serous tubules leading to mucous tubules; supralabial gland lobules also have serous leading to mucous tubules and, from about midway forwards, these lobules form a double row; there is no evidence of a dental gland. Two xenodermatines have supralabial serous tubules leading to mucous tubules, but no evidence of alternating mucous and serous cords. I discuss some alternative evolutionary interpretations.

Immunoelectron microscopic identification of lysozyme-expressing cells in human labial salivary glands.

Although human labial gland secretions contain serous components such as the bactericidal enzyme, lysozyme, the presence of serous cells in this gland has yet to be clearly visualized under the electron microscope. The present study identifies lysozyme-expressing cells of the labial glands using microwave-fixed, Epon-Araldite-embedded specimens, which showed excellent preservation of both ultrastructural detail and antigenicity for post-embedding immunogold labeling of lysozyme. Ultrastructurally, all of the secretory cells of the glands appeared to be a mucous-type and have a serial maturation relationship, consistent with a previous report by TANDLER et al. (1969a): their secretory granules were electron-lucent and exhibited reactivity for mucus staining by the periodic acid-thiocarbohydrazide-silver proteinate (PA-TCH-SP) method. We classified them into two immature types (I, II) and two mature types (I, II). Their distinctive features were the following: 1) relatively small (0.5-1 microm) secretory granules and well-developed basal rough endoplasmic reticulum for the immature types; 2) larger (1-2 microm) secretory granules and well-developed Golgi apparatus, which showed intense PA-TCH-SP reactivity in the 2-3 trans-cisterns, for the mature types; 3) few secretory granules in the immature type I; and 4) the darkest appearance for the mature type II. Immunogold labeling with anti-lysozyme showed specific labeling of the two immature-type cells, in which gold particles were found mainly over the secretory granules and Golgi apparatus, and moderately over the rough endoplasmic reticulum. In the secretory granules, the labeling was distributed throughout the contents and was present even if they showed strong PA-TCH-SP reactivity; in the Golgi area, it was seen over the stacked cisternae, trans-Golgi networks, and condensing vacuoles. No specific labeling was seen in the mature-type cells or in the duct cells. These immature- and mature-type cells were almost equivalent to the "serous demilune or acinus" and "mucous tubule" cells, respectively, at the light-microscopic level. These results indicate that the traditional "immature mucous-type cells" of the human labial glands produce lysozyme and should be classified as seromucous cells.

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

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. 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. 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. 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.

Different glycoconjugates in the submucosal glands of the supraglottis and subglottis. Lectin histochemistry study in the hamster.

A lectin histochemistry study was performed in the supraglottic and subglottic regions of 10 hamsters. The submucosal glands were observed by light microscopy. The supraglottic submucosal glands presented numerous mucous tubules but on the other hand, the subglottic submucosal glands had serous tubules which finished at the distal portion in serous acini. The results suggest that the distribution of fucosylated-mucin and serum-type glycoproteins between the supra- and subglottic submucosal glands suggest a different viscosity and function of the mucus.

Cellular distribution of prolactin receptors in human digestive tissues.

In the present study we analyzed the expression of prolactin receptors (PRLR) in human digestive tissues by immunohistochemistry. PRLR immunoreactivity was primarily localized in the cytoplasm. However, in some organs (liver and salivary glands) a nuclear positivity was also found. The liver was used as control and showed a diffuse immunostaining in the parenchymal cells. In the gastrointestinal tract, PRLR immunoreactivity was observed in the mucosa, muscularis layer, and nervous plexuses. The more intense immunostaining in the mucosa of the different segments was as follows: esophagus, superficial layers of the stratified squamous epithelium and mucous glands; stomach, parietal cells; small intestine, absorptive and Paneth cells; and colon, surface epithelium and superficial half of the crypts of Lieberkühn. In the salivary glands, immunoreactivity was strong in the mucous tubules, moderate in the ducts, and weak in the serous cells. Endocrine pancreas showed a more intense immunoreactivity than the pancreatic acini. By serial sections of the islets of Langerhans we showed that immunostaining was confined to B cells. These findings demonstrate the widespread distribution of PRLR in human digestive tissues and its localization both in cytoplasms and nuclei.

Ultrastructure and histochemistry of human anterior lingual salivary glands (glands of Blandin and Nuhn).

Specimens of human anterior lingual salivary glands obtained by surgery and by dissection of cadavers were studied ultrastructurally and histochemically. 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 means. Formalin-fixed cadaver specimens were subjected to a battery of tests for glycoconjugates. 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 typical 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 glycoproteins. Contrary to previously published reports, we could find no differences in the ratio of mucous to seromucous cells along the anterior-posterior 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 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. 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 function(s) of these organs remains unknown.

Morphological and histochemical study of human submucosal laryngeal glands

The respiratory submucosal glands are a major source of secretions in the airway. Human submucosal laryngeal glands have been scarcely studied, with no works existing about their ultrastructure and histochemistry. Samples of epiglottis, ventricle, false vocal folds and true vocal folds were fixed in 10% buffered formalin for histochemical study with conventional and carbohydrate lectin histochemistry. Other samples were fixed in 2.5% glutaraldehyde and conventionally processed for transmission electron microscopy. The human submucosal laryngeal glands are composed of serious tubules; mucous tubules; collector duct; and final portion of this duct. The serous cells showed sialosulphomucins and affinity for WGA and Con-A lectins. With a previous treatment with neuraminidase, they also labelled with PNA. The mucous cells contained sialosulphomucins and showed affinity for WGA and DBA lectins in the samples proceeding from blood group A, and for WGA, UEA-I and LTA with those from blood group O. Ultrastructurally, the serous cells presented a wide variety of granules, cells in which seromucous granules predominated. The mucous cells presented larger-sized granules which were very electron-lucent. The collector duct was composed of mitochondria-rich cells and basal cells. A cell which we have termed "intermediate" was identified in the transition zone between the mucous tubules and the collector duct, and in the final portion of the collector duct. It had morphological characteristics as if it were a transition between a goblet cell and collector duct cell. Some nerve endings with cholinergic and peptidergic vesicles were found among the myoepithelial cells. These glands presented some histological differences from the bronchial glands, the mucous secretion was related to the blood group antigens, and the serous cells showed a wide variability in their secretory granules, many of them being of a seromucous type.

ヒト気管腺の加齢による変化

The histochemical and ultrastructural differences between young and aged human tracheal glands were studied. The materials were obtained at necropsy or during surgical procedures of the larynx and trachea. In human tracheal gland, remarkable differences between young (10 to 21-year-old) and aged (61 to 81-year-old) ones were especially seen in serous cells. Mucosubstances of young tracheal serous cells were classified as serum glycoprotein types, but those of the aged cells were mainly mucin types. Ultrastructurally, young tracheal serous cells contained homogeneously electron dense or biphasic secretory granules. On the other hand, the aged cells contained not only homogeneous electron dense granules but also multiform ones, hiphasic or electron lucent, resembling mucous cell granules. In aged human tracheal serous cells, alterations of histochemical and ultrastructural properties of secretory materials reflected depression of host defence mechanism of the trachea. By these results, the reason why various airway deseases increase with aging could be explained. In aged human, in addition, oncocytes were found within the mucous tubule and they occasion ally contained secretory granules. Although appearance of oncocytes in the tracheal gland was closely related with aging, this phenomenon seemed not to directly participate in depres sion of the defence mechanism.

Ultrastructure of the ferret sublingual gland.

The sublingual glands of 2 male and 2 female adult ferrets were examined using electron microscopy. The secretory end piece consisted of mucous tubules, serous and mixed acini. The mucous cells showed two different types of granules. The serous cells contained electron-dense secretory granules. The duct system entirely comprised excretory ducts.

Ultrastructural observations on human sublingual gland.

That part of the human sublingual gland that corresponds in morphology to the conventional description of this organ presented in most histology texts (probably the major sublingual gland, in contradistinction to the aggregated small glands that compose the minor sublingual glands) was studied by electron microscopy. The gland is mixed, with slightly more mucous elements than seromucous ones. The mucous cells are arranged in tubules that usually are capped by seromucous demilunes. Seromucous cells also form occasional acini or may be scattered in the walls of the mucous tubules. The appearance of the mucous cells varies with the stage of the secretory cycle that they may be in. Their secretory droplets increase in number and progressively compress cytoplasmic organelles. Filamentous bodies also may be present. Based on secretory-granule substructure, four different kinds of seromucous cells can be recognized; these may be a morphological expression of asynchronous synthesis of different secretory proteins. The duct system is an abbreviated one compared to the other major salivary glands. The first duct segments, into which the mucous tubules drain, are similar to intercalated ducts. Larger ducts contain mitochondria-rich cells but lack the basal striations that characterize striated ducts. The paucity of typical striated ducts may be correlated with the elaboration of sodium-rich saliva by the human sublingual gland.

Carbonic anhydrase in the rat salivary glands: distribution and ultrastructural localization.

Rat salivary glands were studied by Hanson's method to specify the ultrastructural localization of carbonic anhydrase (CA). Two different procedures were used: 1) The embedding of the tissues in water-soluble resins, followed by the incubation of the resin sections on the medium. 2) The embedding in epon-araldite of previously incubated frozen sections. Light and electron microscopy were used to observe the distribution and the ultrastructural localization of the cobalt precipitate. In parotid and mandibular glands, CA was localized in the secretion granules and the hyaloplasma of the secretory endpieces. The enzyme was also detected on the basal and lateral membranes of the striated duct cells in the three glands. In the convoluted granular duct cells of the mandibular gland CA was found in the hyaloplasma only. In the sublingual gland, CA was localized in the hyaloplasma of the serous crescents and no activity was detected in the mucous tubules. As regards the localization of the enzyme in the granules of the secretory endpieces of parotid and mandibular glands, it appears that CA has to be considered as a secretory product of these cells; this localization is consistent with the presence of the enzyme in rat saliva.

Intercellular junctions in upper airway submucosal glands of the rat: a tracer and freeze fracture study.

The structure of intercellular tight junctions of rat airway submucosal glands was examined by freeze fracture techniques and their permeability assessed by the use of colloidal lanthanum. The submucosal glands were organized into three distinct regions: a) serous tubules and b) mucous tubules lined, respectively, by serous and mucous cells, and c) ducts lined by cuboidal epithelial cells, containing few secretory granules, and some ciliated cells. The mean number of parallel fibrils constituting the tight junctions between serous cells was 3.6 +/- 0.4, which was significantly smaller than those between any of the other cell types. Colloidal lanthanum permeated the tight junctions between serous cells up to the level of the acinar lumen. There was a progressive increase in the mean number of parallel fibrils of tight junctions between mucous (5.1 +/- 0.6), ductal (5.4 +/- 0.5), and ciliated cells (8.5 +/- 0.7); none of these junctions was permeated by colloidal lanthanum. These results imply that tight junctions between serous cells are more permeable to small water-soluble solutes than those present in the more proximal portions of the gland. Gap junctions were observed between serous cells and between mucous cells, suggesting that these secretory cells may be electotronically and metabolically coupled.