Ultrastructure of basal cell adenoma in the parotid gland

Basal cell adenoma of the parotid gland was studied with electron microscopy. The cells constituting this tumor were divided into three types of epithelial cells; ductal, myoepithelial, and squamous cells. The ductal cells, which were polygonal and cuboidal in shape, formed a sometimes distinct lumen. Glycogen were recognized in the cytoplasm of these cells. The myoepithelial cells appeared as plasmacytoid cells which contained abundant microfilaments. The squamous cells were characterized by the presence of well-developed tonofilaments and desmosomes. However, no secretory cells could be found, although small, electron dense granules were detected in the cytoplasm of the ductal cells. The granules were unlike secretory granules in their size, number and location. In consideration of the presence of secretory and myoepithelial cells, we reviewed previously reported literature and discussed the identification of secretory granules. From our and other reported results, we tentatively concluded that the electron dense granules described as secretory granules are not intrinsic secretory granules. Further, we suggested that the cell types and the histogenesis of basal cell adenoma are analogous to those of both pleomorphic and clear cell adenomas.     

The effects of ductal obstruction on the acinar cells of the parotid of cat

Twenty-nine parotids ligated for between 1 and 365 days were examined by light and electron microscopy. Major changes in the acini were seen at 4 days and included vacuolation, disintegration, extravasation, apoptosis, phagy and a reduction in number and size of secretory granules. There was a further reduction in secretory granules from 7 to 12 days, but acinar cells persisted even up to 365 days, some contained a luminal concentration of small secretory granules and occasionally acinar cells of a similar appearance to normal were found. These findings contrast with a reported absence of acinar cells from the obstructed parotid of rat and show that parotid acinar cells are able to persist and retain an appearance indicative of secretory activity.     

Ultrastructural immunocytochemical localization of secretory proteins in autophagic vacuoles of parotid acinar cells of starved rats

Previous studies have shown that reduction of mastication has marked effects on the structure and biochemistry of the rat parotid gland. Acute starvation results in the formation in the acinar cells of large autophagic vacuoles which contain lysosomal hydrolases and within which secretory granules appear to undergo degradation. In this study we used electron microscopic immunocytochemistry and antibodies to two secretory proteins, alpha-amylase and B1-immunoreactive protein, to determine whether secretory proteins are present in autophagic vacuoles of parotid acinar cells of starved rats. Small vacuoles were observed after 24-h starvation; they increased in size and number up to 72-h starvation. Both secretory proteins were present in the secretory granules and in the dense content of the autophagic vacuoles, as shown by immunogold labelling. The lighter matrix of the vacuoles was unlabelled. These findings confirm that secretory granules may fuse with lysosomal structures, where their content of secretory proteins is presumably degraded. Thus, the rat parotid appears to be similar to other secretory cells in which cellular levels of stored secretory proteins may be regulated by the process of crinophagy.     

Ultrastructural immunocytochemical localization of secretory proteins in autophagic vacuoles of parotid acinar cells of starved rats

Previous studies have shown that reduction of mastication has marked effects on the structure and biochemistry of the rat parotid gland. Acute starvation results in the formation in the acinar cells of large autophagic vacuoles which contain lysosomal hydrolases and within which secretory granules appear to undergo degradation. In this study we used electron microscopic immunocytochemistry and antibodies to two secretory proteins, oamylase and Brimmunoreactive protein, to determine whether secretory proteins are present in autophagic vacuoles of parotid acinar cells of starved rats. Small vacuoles were observed after 24-h starvation; they increased in size and number up to 72-h starvation. Both secretory proteins were present in the secretory granules and in the dense content of the autophagic vacuoles, as shown by immunogold labelling. The lighter matrix of the vacuoles was unlabelled. These findings confirm that secretory granules may fuse with lysosomal structures, where their content of secretory proteins is presumably degraded. Thus, the rat parotid appears to be similar to other secretory cells in which cellular levels of stored secretory proteins may be regulated by the process of crinophagy.     

Effects of 5-fluorouracil on protein synthesis and secretion of the rat parotid gland

100 mg/kg of FU were injected intraperitoneally once daily for three days. Animals were anaesthetized with 50 mg/kg of sodium pentobarbital before cannulation of the parotid duct. The total volume, amylase and protein content of the saliva were determined after stimulation with either 5 mg/kg pilocarpine or 5 mg/kg isoproterenol in FU-treated, pair-fed, and control animals. Saliva from FU-treated animals was significantly lower (p < 0.05) in volume, amylase and protein content than that of both control groups. SDS, anionic and cationic gel electrophoresis of parotid saliva revealed no qualitative changes in the types of proteins secreted. FU reduced the total glandular amylase per unit DNA in both unstimulated and isoproterenol-stimulated parotids (p < 0.05). Decreased protein synthesis may be the mechanism underlying the depleted secretory protein stores because the contents of isolated secretory granules from experimental glands contained less radiolabelled protein than those of either control group, and whole-gland homogenates had marked reductions in the activities of three lysosomal enzymes and in total RNA content. The secretory granules of experimental animals contained less labelled protein than those of controls, but experimental animals secreted a greater proportion of their total glandular radiolabelled secretory protein into saliva relative to amylase, suggesting that newly synthesized secretory proteins were preferentially secreted.     

Fine morphological studies on the connective tissue core and the epithelial cells of the lingual papillae in Mogella wogura wogura

The three-dimensional structure of the connective tissue core (CTC) of each type of lingual papillae of Mogella wogura wogura was studied by scanning electron microscopy after removal of the epithelial cell layer and compared with the results obtained from light microscopy as well as transmission electron microscopy. Filiform papillae are densely distributed on the dorsal surface of the anterior part of the tongue. They were conical in shape and their connective tissue cores (CTCs) resembled wooden spoons at the tip of the tongue, while they were flower-shaped (Lysichiton camtschatense) at the middle part of the tongue. Fungiform papillae which had a round depression on the top were distributed sporadically among the filiform papillae, and contained columnar CTC with several plane striations running longitudinally along the lateral surface. A pair of vallate papillae was located at the boundary between the anterior and posterior tongue. Their CTC were flower shaped closely resembling a carnation. Giant conical papillae occupied the posterior marginal region of the tongue. These papillae contained much smaller conical CTC similar to the outer form. Light and transmission electron microscopic observations of the dorsal lingual epithelium revealed three different regions: anterior region to the filiform papillae, posterior to the papillae and interpapillary region. In the intermediate layers between the germinal layer and the surface layer of the anterior region to the filiform papillae, a large number of keratohyaline granules was observed, but the cornified layer was obscured. In the posterior region, keratohyaline granules were fewer in number and the cornified layer was clear and thick. In the interpapillary region, keratohyaline granules were few and a thin cornified layer was recognized. At higher magnification, small sized keratohyaline granules contained a large number of free ribosomes, suggesting a close relationship between the two. Odland bodies were found only on the interpapillary region.     

Acinic cell carcinoma arising in the glossopalatine glands: a report of two cases with electron microscopic observations

Two cases of acinic cell carcinoma arising in the glossopalatine glands were examined with the electron microscope by means of conventional thin sectioning and freeze-fracturing. Light and electron microscopic observation revealed that the tumors consisted of three types of cells: serous-type, ductlike, and vacuolated cells. Serous-type cells had numerous secretory granules, some of which were discharged into the intercellular spaces. Ductlike cells were smaller, usually lacked secretory granules, and were similar to intercalated duct cells. Vacuolated cells had electron-opaque vacuoles in the cytoplasm. Our findings supported the hypothesis that acinic cell carcinoma may represent a neoplasm of multipotential duct cells which have differentiated mainly into granulated serous cells. Freeze-fracture images of this tumor revealed that tight junctions were composed of ten or more interlinked strands with elongation of basal frontier strands. These findings suggested that the junctional morphology of the tumor resembled that of developing salivary glands and was associated with the degree of cellular differentiation.     

Immunocytochemical localization of mK1, a true tissue kallikrein,in the mouse parotid gland: sexual dimorphism and effects of castration and hypophysectomy

In the normal parotid glands of mice at 12 weeks of age, mK1, a true tissue kallikrein, was detected at the apical rim of the striated ducts (SDs). Sexual dimorphism in the immunostaining intensity in parotid glands was seen, i.e., immunostaining was more intense in males than in females. Under electron microscopy, secretory granules, being small in size, and condensed at the subluminal cytoplasm, were labeled with immunogold particles showing the presence of mK1. These secretory granules were rather abundant and large in males. Castration in males reduced the immunoreactivity of mK1 in the SD cells because of a decrease in the number and size of secretory granules as revealed by electron microscopy. Hypophysectomy in male mice resulted in considerable loss of immunoreactivity for mK1, which was characterized under electron microscopy by complete disappearance or significant reduction of secretory granules in many SD cells. These results suggest that mK1 expression in the SD cells of murine parotid glands is regulated by pituitary-dependent hormones, and sexual dimorphism of mK1 expression is regulated by androgens.     

Intracellular elemental concentrations in resting and secreting rat parotid glands

Electron probe x-ray micro-analysis was used to study the elemental concentration changes that occur during pilocarpine-stimulated saliva secretion. Quantitative x-ray micro-analysis of elemental concentrations in intracellular compartments of rat parotid glands stimulated in vivo with pilocarpine showed that Na concentration was significantly increased, while K concentration was significantly reduced. The magnitude of these changes was consistent with values obtained in other tissues with the x-ray micro-analysis method, and in the same tissue with other experimental methods. Comparisons with results from studies utilizing dispersed acini suggest that acinar dispersion procedures may affect intracellular elemental concentrations. Total electrolyte concentrations in cytoplasm and secretory granules were estimated to increase on a dry-weight basis following pilocarpine stimulation. The former change is consistent with the notion of a transcellular route of salivary fluid flow, while the latter change may be important in the exocytosis of secretory granules.     

婴儿色素性神经外胚瘤的组织病理及超微结构观察

作者对３例婴儿色素性神经外胚瘤进行了超微结构和免疫组化等研究，结果表明，肿瘤呈局部浸润性生长，并主要由神经母细胞样小细胞和含色素细胞组成；超微结构示小细胞胞浆内含膜性分泌颗粒，花环状多聚核糖体，可见核分裂相，色素细胞含大量黑色素体和微丝；免疫组化结果显示两种瘤细胞对ＮＳＥ及Ｖｉｍｅｎｔ均呈阳性反应，而Ｓ－１００蛋白阴性，表明该肿瘤细胞较幼稚且生长活跃，提示其有复发和恶变的潜能。本文还对肿瘤细胞和胚胎眼杯细胞的同源性进行了讨论。     

The Ultrastructure of leukocyte emigration through the sulcular epithelium in the beagle dog

An electron microscopic investigation of chronically inflamed beagle gingiva has been carried out in order to gain some insight into the pathogenesis of gingival destruction. Chronically inflamed sulcular epithelium was characterized by the presence of numerous polymorphonuclear neutrophilic leukocytes within the intercellular spaces. Many neutrophils were observed to have disrupted cell membranes with a consequent extrusion of cytoplasmic contents including lysosomal granules. The emigration of neutrophils through the epithelium was coincident with a marked decrease in epithelial cell-to-cell contacts such as desmosomes and tight junctions. In addition, the affected intercellular spaces were usually dilated and contained glycogen, granular precipitate and free lysosomal particles. The epithelial cells of inflamed sulcular epithelium contained altered tonofibrils. increased amounts of glycogen and accumulations of lipid droplets. It is suggested that the emigration of large numbers of neutrophils in response to chemotactic stimuli originating from the sulcus may damage the normal cell-to-cell relationship of the sulcular epithelium resulting in altered cell differentiation and widened intercellular spaces.     

Repeated androgen and thyroid hormone injection modulates the morphology of hormone-responsive duct cells in the mouse parotid gland

When the parotid glands of normal male and female ICR mice (12 weeks of age) were examined under a light microscope, no granular cells were seen in the duct system. However, transmission electron microscopy revealed that, in both sexes, many striated duct cells contained a few electron-dense secretory granules in their subluminal cytoplasm and had formed so-called granular striated tubules (GSTs) in some of the striated duct segments. These secretory granules were not large enough to be visible with a light microscope. Fully fledged granular cells, containing large secretory granules visible with a light microscope, could be induced in the GST segments of the glands of males by injection with 5α-dihydrotestosterone (DHT), triiodothyronine (T₃), and dexamethasone (Dex), given alone or in combination every other day for 2 weeks. Dex alone showed no effect on the GSTs in this study. Both DHT and T₃, either individually or with Dex, were moderately effective, inducing a few scattered fully fledged granular cells. A stronger effect was detected after concomitant injection of DHT and T₃, with or without Dex, with more abundant fully developed granular cells appearing in the GST segments. Electron microscopy revealed that these granular cells had abundant large secretory granules in their apical two-thirds, a basal nucleus, and modest basal infoldings. By contrast, the effect of the same hormones was very weak in the glands of females, and even the concomitant injection of DHT and T₃, with or without Dex, rarely induced fully fledged granular cells. These results indicate a close similarity between the ductal systems of the major salivary glands of the mouse, in terms of some of the striated duct segments containing secretory granules, being under the same multihormonal regulation, and being sexually dimorphic.     

Effects of clonidine on the calcium content and morphology of rat salivary glands

These effects were examined with and without pretreatment of animals with reserpine and the adrenergic antagonists prazosin (₁), yohimbine (₂) and propranolol (β). The effects of clonidine on glandular concentrations of norepinephrine and dopamine also were examined. These effects were compared with those of xylazine, a presynaptic ₂-adrenergic agonist. A single, high dose of clonidine followed by an overnight fast caused marked increases in calcium content and acinar secretory granules in the submandibular and sublingual glands, similar to those caused by reserpine. However, the calcium content of the parotid gland was not altered by clonidine. although there seemed to be a modest increase in acinar secretory granules. The clonidine-induced increase in submandibular calcium content could not be attributed to any adrenergic receptor activity since it was not blocked by either - or β-adrenergic antagonists. Unlike reserpine, clonidine did not affect catecholamine concentrations in the parotid and submandibular glands. Pretreatment with reserpine did not significantly alter the clonidine-induced increase in submandibular calcium content. It is likely that the greater accumulation of acinar secretory granules is related to the increased calcium stores of the glands in clonidine- and/or reserpine-treated rats. The large differences in calcium content among the three glands might be attributable, in part, to differences in the calcium-binding capacity of their secretory granules. Possible mechanisms for the clonidine effects on salivary-gland calcium include disturbances in membrane-associated pools or gating mechanisms for calcium, which need further study.     

Parotid secretory granules: crossroads of secretory pathways and protein storage

Saliva plays an important role in digestion, host defense, and lubrication. The parotid gland contributes a variety of secretory proteins-including amylase, proline-rich proteins, and parotid secretory protein (PSP)-to these functions. The regulated secretion of salivary proteins ensures the availability of the correct mix of salivary proteins when needed. In addition, the major salivary glands are targets for gene therapy protocols aimed at targeting therapeutic proteins either to the oral cavity or to circulation. To be successful, such protocols must be based on a solid understanding of protein trafficking in salivary gland cells. In this paper, model systems available to study the secretion of salivary proteins are reviewed. Parotid secretory proteins are stored in large dense-core secretory granules that undergo stimulated secretion in response to extracellular stimulation. Secretory proteins that are not stored in large secretory granules are secreted by either the minor regulated secretory pathway, constitutive secretory pathways (apical or basolateral), or the constitutive-like secretory pathway. It is proposed that the maturing secretory granules act as a distribution center for secretory proteins in salivary acinar cells. Protein distribution or sorting is thought to involve their selective retention during secretory granule maturation. Unlike regulated secretory proteins in other cell types, salivary proteins do not exhibit calcium-induced aggregation. Instead, sulfated proteoglycans play a role in the storage of secretory proteins in parotid acinar cells. This work suggests that unique sorting and retention mechanisms are responsible for the distribution of secretory proteins to different secretory pathways from the maturing secretory granules in parotid acinar cells.     

Effects of colchicine on periodontal ligament fibroblasts of the mouse

The effects of colchicine administration on the ultrastructure aad function of periodontal ligament fibroblasts was studied in young mice as a further attempt to document the microtubule-dependent nature of collagen secretory granule translocation.
Disruption of the normal appearance of the Golgi complex was an early response to colchicine administration. This change was visible at the light microscopic level. At the electron microscopic level it was observed that Golgi saccules were dispersed and that Golgi cisternae were shorter and reduced in number. Microtubules were absent. Dense granules accumulated in a juxtanuclear region of cytoplasm previously occupied by the normal Golgi complex. Lipid droplets and autophagosomes were increased in number. Intermediate filaments (10 nm diameter) formed perinuclear fascicles several hours after colchicine treatment.
These results as well as the recently published report (Cho & Garant 1981d) support the concept that microtubules play an important role in the normal organization of the Golgi complex and in the translocation of secretory granules to the fibroblast cell surface.     

Architecture of minor salivary gland duct/lymphoid follicle associations and possible antigen-recognition sites in the monkey Macaca fascicularis

In Macaca fascicularis, lymphoid follicles with germinal centres related to minor salivary gland ducts are frequently found in the mucosa of lips, cheeks and the soft palate. Three semi-three-dimensional reconstructions, each based on 3 sets of 230-300 serial Epon sections, of such duct/follicle-assemblies (2 in the soft palate and 1 in the lip) and electron microscopic observations were made. These revealed that (1) these structures were about 0.05-0.1 mm3 in size, (2) they were found preferentially at sites where small interlobular ducts fused to form a pelvis-like basin from which blind duct portions protruded into the surrounding lymphoid tissue and (3) they often included a germinal centre which partly embraced blind ducts. The walls of such blind ducts were heavily infiltrated by lymphocytes and in part blast-forming T-cells. Portions of the walls of interlobular and main secretory ducts, passing directly or peripherally through follicles, were also infiltrated with lymphocytes. The duct lumen within the follicles contained clusters of Gram-negative bacteria, probably rods. Based on these findings, it is argued that gland duct/follicle assemblies represent physiological entities, either formed and re-formed temporarily or of long-standing nature, which may provide the locus (i.e. tonsillar microcrypt-like pouches) and the structural matrix necessary for local antigen recognition. The antigens (bacteria, macromolecules in salivary fluid, etc.) might enter the above structure by way of the secretory ducts. Such matrices may also exist in man.     

Morphologic changes in the granular convoluted tubule cells of the mouse submandibular gland following hypophysectomy and hormonal replacement

 Morphological changes in the granular convoluted tubule (GCT) cells of the male mouse submandibular gland (SMG) were examined following hypophysectomy and hormonal replacement. Semithin sections stained with Heidenhain's iron hematoxylin showed that hypophysectomy severely regressed the GCT phenotype. Although only a few dispersed cells containing secretory granules were observed in the GCT segments under a light microscope, electron microscopy revealed that many regressed cells continued to constitutively elaborate apical secretory granules (although they were very small) and contained a euchromatic nucleus at the center of the cell, poor rough endoplasmic reticulum (RER) and Golgi apparatus in the perinuclear region, and well-developed basal infoldings. These findings suggest that hypophysectomy resulted in atrophy of GCT cells, but that they retained evidence of being secretory cells. 5α-Dihydrotestosterone (DHT); 3,5,3′-triiodo-l-thyronine (T₃); and dexamethasone (Dex) each enhanced the GCT phenotype of hypophysectomized males to some degree. Combined hormonal replacement with DHT + T₃ in hypophysectomized males restored a nearly normal male GCT phenotype with a full complement of secretory granules and rare basal infoldings, whereas T₃ alone induced a normal female-like GCT phenotype, with considerably abundant secretory granules and the usual short basal infoldings, in hypophysectomized male glands. Furthermore, Dex was found to synergistically enlarge secretory granules when administered with T₃ and/or DHT, although it was only weakly effective in enhancing the GCT phenotype when used alone. Taken together, the above findings confirmed that the GCT phenotype of the mouse SMG is regulated by the synergistic action of pituitary-dependent hormones. Received: October 1, 2001 / Accepted: May 13, 2002     

Liquid-diet-induced alterations of rat parotid acinar cells studied by electron microscopy and enzyme cytochemistry

After 1 day on liquid diet, the acinar cells were filled with secretory granules, and gland amylase content was approx. 50 per cent greater than chow-fed controls. After 3 days, the number of secretory granules was reduced, and amylase levels had fallen to 50 per cent of controls. Altered or degenerating secretory granules and autophagic vacuoles containing rough endoplasmic reticulum, secretory granules and mitochondria were observed with increasing frequency during the 1st week. These structures were cytochemically reactive for trimetaphosphatase, a lysosomal hydrolase. Concomitantly, macrophages invaded the acinar parenchyma and phagocytosed the degenerating acinar cell components. Lipid droplets and large aggregates of glycogen particles were present in the acinar cells after 7–10 days. After 3 weeks, the acinar cells were considerably reduced in size and contained few secretory granules, but their structure appeared otherwise normal. These results indicate that the acinar-cell lysosomal system and invading macrophages, as in other experimental conditions, play an important role in the parotid-gland atrophy induced by liquid diet.     

Ultrastructural bases for the synthesis of ribosomal RNA in the nuclei of the parotid gland. The role of intranuclear bodies

Identification and numerations on electron microscopic samples of rat parotid glands revealed an unexpected high frequency of nuclear bodies in acini and in striated ducts. Three different morphological types of nuclear bodies were identified: type I corresponded to a circular outline of finely fibrillar or granular bodies. Type II exhibited an outer fibrillar cortex surrounding a central lucent core. Type III possessed a thick granular or fibrillar cortex surrounding dense granules. Type IV nuclear bodies appeared to be circumscribed by a thick lamellar cortex and contained dense and heavy stained granules. The biochemical content of the nuclear bodies mostly corresponds to proteins and it was possible to demonstrate slight quantities of RNA. Recent studies seem to confer to some of those nuclear bodies a possible role in RNA processing or transport. It is however peculiar to find nuclear bodies in striated ducts which are not involved in active protein synthesis as the acini.