Morphologic diversity of the minor salivary glands of the rat: fertile ground for studies in gene function and proteomics

In this article the locations and histologic and ultrastructural features of all of the minor salivary glands of the rat are presented; similarities and differences among them are highlighted. These glands are almost as diverse morphologically as the major salivary glands of the rat. The acini of von Ebner's glands are serous; those of the anterior and posterior buccal glands and minor sublingual glands are mucous; and those of the glossopalatal, palatal, and Weber's glands are mucous with serous demilunes. The anterior buccal, minor sublingual and von Ebner's glands have striated and stratified columnar ducts, while only the minor sublingual and von Ebner's glands have intercalated ducts. The glossopalatal, palatal, posterior buccal and Weber's glands have none of these ducts; the tubulo-acini drain abruptly into short terminal ducts composed of stratified squamous epithelium. All of the mucous acini react with an antibody to a mucin (Muc19) of the rat major sublingual gland, but in some of the glands the reaction varies in intensity among the acinar cells. Ultrastructurally, the mucous secretory granules of the anterior buccal, glossopalatal, palatal and Weber's glands are biphasic, while those of the minor sublingual and posterior buccal glands are monophasic. Although there is a considerable body of literature concerning the development, innervation, physiology and proteomics of von Ebner's glands, investigation of the other minor salivary glands of the rat ranges from modest to nearly nonexistent.     

Expression and localization of immunoreactive-sialomucin complex (Muc4) in salivary glands

Sialomucin Complex (SMC; Muc4) is a heterodimeric glycoprotein consisting of two subunits, the mucin component ASGP-1 and the transmembrane subunit ASGP-2. Northern blot and immunoblot analyses demonstrated the presence of SMC/Muc4 in submaxillary, sublingual and parotid salivary glands of the rat. Immunocytochemical staining of SMC using monoclonal antisera raised against ASGP-2 and glycosylated ASGP-1 on paraffin-embedded sections of parotid, submaxillary and sublingual tissues was performed to examine the localization of the mucin in the major rat salivary glands. Histological and immunocytochemical staining of cell markers showed that the salivary glands consisted of varying numbers of serous and mucous acini which are drained by ducts. Parotid glands were composed almost entirely of serous acini, sublingual glands were mainly mucous in composition and a mixture of serous and mucous acini were present in submaxillary glands. Since immunoreactive (ir)-SMC was specifically localized to the serous cells, staining was most abundant in parotid glands, intermediate levels in submaxillary glands and least in sublingual glands. Ir-SMC in sublingual glands was localized to caps of cells around mucous acini, known as serous demilunes, which are also present in submaxillary glands. Immunocytochemical staining of SMC in human parotid glands was localized to epithelial cells of serous acini and ducts. However, the staining pattern of epithelial cells was heterogeneous, with ir-SMC present in some acinar and ductal epithelial cells but not in others. This report provides a map of normal ir-SMC/Muc4 distribution in parotid, submaxillary and sublingual glands which can be used for the study of SMC/Muc4 expression in salivary gland tumors.     

A high resolution sem study of human minor salivary glands

By SEM we have investigated the human minor salivary glands using the NaOH method for the visualization of endpieces and myoepithelial cells, and the osmium maceration technique that reveals membranous intracellular structures. With the former method all minor glands, including the posterior deep (Ebner's) lingual glands, consist of tubules sometimes dilated into alveoli, while true acini of the kind observed in human major salivary glands, are absent. Tubules of the posterior deep lingual gland exhibit stellate myoepitelial cells that leave a substantial part of the secretory cells uncovered. The latter cells, at variance with serous cells of major glands, do not show basal folds. In contrast, tubules of the other minor glands, like the mucous ones of major glands, are covered almost completely by band-like myoepithelial cells. The osmium maceration method clearly demonstrates that posterior deep lingual glands are serous in character and that all the other minor glands, together with the predominant mucous cells, possess a variable number of seromucous cells that, despite variations among individuals, increase in order from palatine and posterior superficial lingual (Weber's), to minor sublingual, labial, anterior lingual (Blandin and Nuhn's), and buccal glands.     

SD大鼠和Beagle犬大唾液腺的形态学观察

目的-研究及观察SD大鼠和Beagle犬大唾液腺正常比较组织学.方法-SD大鼠和Beagle犬三对大唾液腺剖取后进行石蜡切片、HE染色和PAS染色,光学显微镜观察.结果-SD大鼠腮腺是纯浆液腺,Beagle犬腮腺属混合腺,以浆液性腺泡为主,偶见小的粘液细胞群.SD大鼠的下颌下腺属于以浆液腺泡为主的混合腺,Beagle犬的下颌下腺属于以粘液腺泡为主的混合腺.SD大鼠与Beagle犬的舌下腺均为粘液性腺泡为主的混合腺.Beagle犬的眶腺亦是以纯粘液性腺泡为主的混合腺结构.     

Immunohistochemical distribution of calcitonin gene-related peptide in nerve fibres of the anterior buccal gland of the rat

Summary Calcitonin gene-related peptide immunoreactive (CGRP-IR) nerves in rat were studied as to their distribution and origin in anterior buccal glands, which are unique minor mucous salivary glands in the rat. A moderate number of CGRP-IR nerve fibres were located, mostly perivascularly and around intralobular ducts, but they were also found around acini. The latter fibres were mainly of sensory origin, as suggested by their disappearance after denervation of the ophthalmic and maxillary branches of the trigeminal nerve. On the contrary, CGRP-IR nerves around interlobular ducts and some of those in a perivascular location remained both after sensory denervation and after extirpation of the sympathetic superior cervical ganglion. Whether these fibres originate in dorsal root ganglia C₃−C₄ or represent parasympathetic fibres is not known. Based on the present data and the previous findings showing a regulatory role of CGRP both on blood and salivary flow, it is possible that CGRP in sensory, and possibly also in parasympathetic nerves, participates in the regulation of reflex blood flow and salivary secretion in the anterior buccal gland of the rat.     

The distribution and origin of nerve fibers immunoreactive for substance P and neurokinin A in the anterior buccal gland of the rat

The distribution and origin of substance P (SP) and neurokinin A (NKA) were studied in rat in the anterior buccal glands, which are minor mucous salivary glands. Indirect immunofluorescence staining showed moderate SP and NKA innervation of salivary acini and interlobular ducts, whereas blood vessels were more sparsely innervated, and there were few nerve fibers in the stroma and around the intralobular ducts. About 10%–20% of the trigeminal ganglion cells showed equally strong immunoreactivity to both SP and NKA. Unilateral denervation of the branches of the trigeminal nerve caused complete disappearance of the stromal fibers and greatly reduced the number of all other SP-immunoreactive and NKA-immunoreactive nerve fibers. In the superior cervical ganglia, SP and NKA immunoreactivity was restricted to small intensely fluorescent cells; SP and NKA immunoreactivity was absent from principal ganglionic cells, and thus sympathectomy had no any effect on the number or distribution of fibers immunoreactive for SP and NKA in the anterior buccal glands. The fibers remaining after sensory denervation could have been of parasympathetic origin, indicating a dual origin of nerves immunoreactive for SP and NKA in these glands. The present data demonstrate that the major part of the glandular SP and NKA innervation in the minor salivary glands derives from the trigeminal ganglia. The distribution of the peripheral nerve fibers indicates that they may play a role in the delivery of potent neuropeptides involved in the vascular, secretory, and motor (myoepithelial cells) functions of salivary glands.     

Microstereological and histochemical studies of the salivary glands of the giant rat (Cricetomys gambianus, waterhouse)

The histology and histochemistry of the parotid, submandibular and sublingual glands were studied. The submandibular gland contained only serous acini as in the guinea pig, but unlike in many other mammals. The parotid gland contained only serous acini while the sublingual gland was mixed, mucous acini being the predominant secretory tissue interspersed by a few serous acini. Serous demilunes also commonly formed caps on the mucous acini. The ducts of the gland contributed over 30% of the volume of the submandibular gland, while those of the parotid and sublingual glands formed about 12 and 10% of the gland, respectively. The secretions of the parotid gland, as judged by histochemical methods, contained neutral mucins and some sialomucins. Neutral mucins, sulphomucins and sialomucins were detected in both the submandibular gland and sublingual gland.     

Morphology,histochemistry and physiology of the major salivary glands in the echidna Tachyglossus aculeatus (Monotremata)

The three major salivary glands of the monotreme echidna are described. The parotid is a typical serous gland with tubulo-acinar secretory endpieces and a well-developed system of striated ducts. The mandibular gland, although light microscopically resembling a mucous gland, secretes very little glycoprotein. Its cells are packed instead with serous granules, resembling in fine structure the “bull's eye” granules in the mandibular gland of the European hedgehog Erinaceus europaeus. The sublingual glands secrete an extremely viscous mucous saliva. Expulsion of this saliva through the narrow ducts is probably aided by contraction of the extensive myoepithelial sheaths surrounding the secretory tubules. Application of the glyoxylic acid induced fluorescence method failed to demonstrate adrenergic innervation in any of the glands.     

A histochemical study of catecholamines and cholinesterases in the autonomic nerves of the human minor salivary glands

Synopsis The cholinergic and adrenergic innervation of human minor sublingual buccal and labial salivary glands has been studied with histochemical techniques for localizing acetylcholinesterase and catecholamines. A rich cholinergic innervation was observed around the acini, blood vessels and some ducts of the three glands.The adrenrgic innervation, however, was virtually absent from the parenchyma although present around the blood vessels, in marked contrast to the dense parenchymal adrenergic innervation observed in the human parotid and submandibular glands. These results suggest that the autonomic nervous mechanism which regulates salivary secretion is more elaborate in the major than in the minor salivary glands.     

Histology and mucosubstance histochemistry of ferret lingual glands.

The histology and mucosubstance histochemistry of the ferret lingual glands were studied. Both serous and mucous minor salivary glands were present in the posterior part of the tongue. In serous glands, acinar cells and a very few cells of the excretory ducts contained granules which gave reactions for neutral mucopolysaccharides only. The mucous glands, including the duct system, contained mainly weakly sulphated acidic mucin, some neutral mucin but no carboxylated mucin. Occasional goblet cells were present in the excretory ducts of both serous and mucous glands. They contained weakly sulphated mucin.     

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.     

Adrenergic innervation of the salivary glands in the rat

Summary The adrenergic innervation of the major salivary glands in the rat has been studied by a specific histochemical method for the visualization of the adrenergic transmitter. Adrenergic varicose nerve fibres were found, located in a typical adrenergic ground plexus closely surrounding the serous acini of the submaxillary and parotid glands, but not the acini of the mainly mucous sublingual gland. The ducts were found to be completely devoid of adrenergic innervation. Arterioles and venules in the stroma of all three glands and certain very small vessels, possibly the sphincters of arterio-venous anastomoses, were also richly innervated by adrenergic vasomotor fibres. The relationship of the adrenergic nerve fibres to the different functional units of the gland parenchyma is discussed.The investigation has been supported by a research grant (B 66–257) from the Swedish Medical Research Council and by a Public Health Service Research Grant (NB 05236-01) from the National Institute of Neurological Diseases and Blindness.     

The sympathetic and parasympathetic nature of neuropeptide Y-immunoreactive nerve fibres in the major salivary glands of the rat

Summary The distribution and origin of neuropeptide Y in the major salivary glands of the rat was studied by indirect immunofluorescence technique. Numerous nerve fibres immunoreactive for the peptide were seen in the parotid and sublingual glands. Most of the fibres were located around blood vessels and salivary acini. In the submandibular gland the number of immunoreactive nerve fibres around the acini was lower in comparison with that in the parotid and sublingual glands. Some immunoreactive nerve fibres were also found around or along intra- and interlobular ducts in all major salivary glands.A large number of the neuropeptide-containing neuronal cell bodies and nerve fibres were detected in the sympathetic superior cervical ganglion. Sympathetic postganglionic nerve trunks of this ganglion contained numerous immunoreactive nerve fibres as well. A subpopulation of the neuronal cell bodies in the submandibular ganglion were immunoreactive to neuropeptide Y.Both uni- and bilateral superior cervical ganglionectomies caused a significant decrease in the number of immunoreactive nerve fibres around the blood vessels in all the major salivary glands. However, these denervations did not affect the density of nerve fibres around the acini and ducts. On the contrary, unilateral parasympathetic denervation by sectioning the auriculotemporal nerve reduced the fibres around the secretory acini in the parotid gland remarkably, while only a minor reduction in the density of immunoreactive fibres associated with the blood vessels of the gland was detected. Unilateral electrocoagulation of the trigeminal nerve branches caused no detectable change in the density of immunoreactive nerve fibres in any of the major salivary glands.On the basis of the present findings it is concluded that neuropeptide Y-reactive nerve fibres present in all major salivary glands around the blood vessels seem to be mainly sympathetic, whereas those around the acini and ducts seems to be of parasympathetic origin.     

Immunocytochemical localization of PTHrP in human and rat salivary glands

Parathyroid hormone-related protein (PTHrP) was isolated from tumours and is thought to represent the main factor responsible for humoral hypercalcaemia, which accompanies neoplastic diseases. At present, the protein is known to reside in multiple tissues and organs of both humans and animals. Our study was aimed at demonstrating the presence of PTHrP in normal salivary glands (parotid and submandibular) of rats and humans. Application of immunocytochemical techniques permitted to document the presence of PTHrP in the human and in the rat salivary glands. In all cases, an intense reaction was observed in intra- and interlobular ducts. In rat salivary glands, PTHrP was also present in cells of mucous acini. In our opinion, the presence of PTHrP in the ducts indicates participation of the protein in electrolyte transport across the epithelial cells. The positive reaction noted in mucous acini of rat salivary glands may indicate accessory role of PTHrP in the secretory processes in the glands.     

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

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

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.     

Immunolocalization of PTHrP in the sublingual glands of three mammals

The present study deals with immunohistochemical localization of PTHrP in sublingual glands of white mouse, bank vole, and common vole. PTHrP immunoreactivity was observed in epithelial cells of striated, interlobular and main excretory ducts of the salivary glands in all the three animal species tested. However, we found no positive reaction for PTHrP in epithelial cells of the intercalated ducts. In striated duct cells, the reaction intensity was species-dependent. In bank vole and common vole, the reaction was very strong, while in white mouse very weak. In the remaining segments of excretory ducts (interlobular and main excretory duct) we found no species-related differences in the reaction intensity or character. Myoepithelial cells surrounding ducts and mucous tubules with serous demilunes in sublingual glands were also PTHrP-negative in all the three animal species tested.     

Cloning and characterization of a novel animal lectin expressed in the rat sublingual gland.

We cloned a rat gene that is expressed primarily in the sublingual gland and named the predicted 503 amino-acid protein SLAMP (sublingual acinar membrane protein). SLAMP has 63% homology with human ERGIC-53-like protein, a member of the family of animal L-type lectins. Using a cDNA probe for SLAMP mRNA and rabbit antisera against SLAMP, we examined the expression and localization of SLAMP in major rat organs and tissues. With both Northern and Western blot analyses, abundant expression of SLAMP was demonstrated predominantly in the sublingual gland, with single sizes of the mRNA and protein 1.8 kb and 50 kDa, respectively, but not in other organs or tissues, including the parotid and submandibular glands. With immunohistochemistry, SLAMP was localized to the mucous acinar cells, but not to the serous demilunes or the duct system. With immunoelectron microscopy, SLAMP was localized predominantly to regions corresponding to the ER-Golgi intermediate compartment. Besides the sublingual gland, SLAMP immunoreactivity was also demonstrated in mucous cells of the minor salivary glands in oral cavity and of Brunner's glands in the duodenum. These results suggested that rat SLAMP plays a specific role in the early secretory pathway of glycoproteins in specific types of mucous cells.