Lectin histochemistry of posterior lingual glands of developing rats.

The posterior lingual glands are classified as Weber and von Ebner glands. Glycans play an important role in salivary glands. Although the distribution of glycans can explain functional diversity and variation, there are many unknowns in the developing rat posterior lingual glands. The purpose of this study was to elucidate the relationship between the development and function of the posterior lingual gland in rats by histochemical analysis using lectins that bind to sugar residues. In adult rats, Arachis hypogaea (PNA), Glycine maximus (SBA), and Triticum vulgaris (WGA) were associated with serous cells and Dolichos biflorus (DBA) with mucous cells. In both Weber's and von Ebner's glands, all 4 lectins were bound to serous cells in early development, but as development progressed, DBA disappeared in serous cells and only the DBA remained in mucous cells. These results suggest that Galß (1,3) > Galß(1,4) > Gal, αGalNAc > αGal > ßGalNAc, NeuAc > (GalNAc)2-3>>>GlcNAc, and GalNAcα(1,3) are present in the early stage of development, but that GalNAcα(1,3) disappear in serous cells and only GalNAcα(1,3) are localized in mucous cells after maturation. These results indicate that Weber glands function as serous glands in the early postnatal stage when von Ebner glands have not matured.

Alterations in the von Ebner's gland secretion and implications for taste sensation in diabetic (db/db) mice.

The taste buds and associated glands, known as von Ebner's glands (VEGs), are involved in and augment gustatory function. The obese diabetic db/db mouse, which has defects in the leptin receptor, displays enhanced neural responses to, and an elevated behavioral preference for, sweet stimuli. However, the effect of diabetes on the morphology of circumvallate papilla (CVP) taste buds and the role of VEGs have not been investigated. The present study aimed to compare the CVP taste buds and VEGs in wildtype (Wt) and type 2 diabetic (db/db) mice. These mice were divided into control and isoproterenol-treated (at 1 h, 2 h, and 4 h after one day of fasting) groups, and were sacrificed for morphometric, immunohistochemical, and ultrastructural analyses. Morphometry revealed no significant difference in papilla size and the number of taste buds in the control and diabetic groups. Detection of PGP 9.5-immunoreactivity revealed nerve fibers in the trench wall of vallate papillae, but no significant differences were detected between groups. α-Amylase immunoreactivity levels in Wt and db/db mice were also similar. However, 1 h after isoproterenol injection, the majority of the VEG secretion of db/db mice was discharged, while the level of α-amylase was restored by 2 h after injection. The effect on α-amylase was in line with the quantitative ultrastructural analysis of the secretory granules. Our findings suggest diabetic metabolic disturbances in db/db mice do not alter the structure or innervation of CVP taste buds. However, the VEG secretory pattern was altered in db/db mice and might disrupt taste sensation.

von Ebner's glands intercalated duct adenocarcinoma with PALB2 gene mutation.

Secretory carcinoma of the salivary glands is a distinct entity with distinct morphologic features, immunohistochemical profile and molecular alterations. It mainly affects middle aged individuals with slight male predominance and parotid gland is the most common site of involvement. Although ETV6-NTRK3 gene fusion is considered pathognomonic for secretory carcinoma, advances in molecular profiling of this tumor have led to the discovery of novel ETV6 fusion partners and gene mutations. Herein, we describe a case of an adenocarcinoma of intercalated duct origin favor secretory carcinoma, in a unique location of von Ebner's glands of mobile tongue in a 40-year-old Caucasian female. Aside from being in a unique location, the tumor showed somatic mutation for PALB2 gene which has not been described so far in secretory carcinoma. Discovery of novel fusions and mutations have therapeutic implications with respect to targeted therapy.

Tight junctions in Gerbil von Ebner's gland: horseradish peroxidase and freeze-fracture studies.

The permeability of tight junctions to horseradish peroxidase (HRP) and the freeze-fracture appearance of junctional structures were investigated in the von Ebner's gland of gerbils. In the tracing study, HRP was either administered topically on the dorsal surface of tongues or injected subepithelially into the connective tissue of vallate papillae for 5-30 min. Lingual tissues containing the von Ebner's gland were sectioned and examined by light and electron microscopy. In von Ebner's glands, the reaction product for HRP was found in the intercellular and interstitial spaces, whereas HRP appeared to penetrate the tight junctions and the reaction product was localized in the lumina of serous acini. In contrast, the staining for HRP that delineated the boundary of epithelial cells was frequently observed in the superficial layers of the lingual epithelium but not the underlying tissues while applying HRP topically. Freeze-fracture replicas of acinar cells revealed that the tight junction had a depth of 0.815 ± 0.023 µm, and 4-6 parallel strands on the protoplasmic fracture face, with a branching network of joining strands with interruptions, interconnections and high linear strand density apically, and corresponding grooves on the extracellular face. Quantitative analyses showed a greater number of strands (7.217 ± 0.326) in gerbils compared to those of acinar cells (3.86 ± 0.22) in mice. These results demonstrate that the tight junctions in the gerbil von Ebner's gland is permeable, and that specific species differences in tight junction structures may be associated with the mechanism for survival in an extremely dry environment.

The role of carbonic anhydrase VI in bitter taste perception: evidence from the Car6⁻/⁻ mouse model.

BACKGROUND: Carbonic anhydrase VI (CA VI) is a secretory isozyme of the α-CA gene family. It is highly expressed in the salivary and mammary glands and secreted into saliva and milk. Although CA VI was first described as a gustatory protein, its exact functional roles have remained enigmatic. Interestingly, polymorphism of the CA6 gene was recently linked to bitter taste perception in humans. In this study, we compared the preference of Car6⁻/⁻ and wild-type mice for different taste modalities in an IntelliCage monitoring environment. Morphologies of taste buds, tongue papillae, and von Ebner's glands were evaluated by light microscopy. Cell proliferation and rate of apoptosis in tongue specimens were examined by Ki67 immunostaining and fluorescent DNA fragmentation staining, respectively. RESULTS: The behavioral follow up of the mice in an IntelliCage system revealed that Car6⁻/⁻ mice preferred 3 µM quinine (bitter) solution, whereas wild type mice preferred water. When the quinine concentration increased, both groups preferentially selected water. Histological analysis, Ki67 immunostaining and detection of apoptosis did not reveal any significant changes between tongue specimens of the knockout and wild type mice. CONCLUSIONS: Our knockout mouse model confirms that CA VI is involved in bitter taste perception. CA VI may be one of the factors which contribute to avoidance of bitter, potentially harmful, substances.

Occurrence of gustducin-immunoreactive cells in von Ebner's glands of guinea pigs.

An immunohistochemical examination of guinea-pig taste buds in vallate papillae revealed gustducin-immunoreactive cells in the area of von Ebner's glands, minor salivary glands. Since there have been no reports describing those cells in these locations for other species, we investigated these glands in order both to localize the cells and compare their immunoreactive characteristics with corresponding cells in the vallate taste buds. The gustducin-immunoreactive cells coincided with cells containing no secretory granules in the end portion of the glands, which was supported by the electron-microscopic immunocytochemistry. Double immunofluorescence microscopy confirmed these cells to be entirely immunopositive to type III inositol 1,4,5-triphosphate receptor (IP3R-3), phospholipase Cß2 (PLCß2), and villin and also partly immunopositive to neuron-specific enolase (NSE) and calbindin D-28K. The gustducin-immunoreactive cells in the vallate taste buds exhibited completely the same immunoreactivities for these five molecules. Accordingly, the present results give credence to a consideration that the gustducin-immunnoreactive cells in both locations are identical in function(s) e.g., chemo-reception.

GLP-1 expression in von Ebner's gland of diabetic rats.

GLP-1, a peptidergic endocrine hormone, which associate with appetite control, glucose homeostasis and satiety. It might play an important role in the gustatory system. We tried to investigate the expression of GLP-1 in von Ebner's gland of diabetic and control rats, and the ultrastructure changes on von Ebner's gland of diabetes rats. GLP-1 expression in von Ebner's gland was evaluated by immunohistochemistry. The number of GLP-1 positive cells in diabetic rat von Ebner's gland was significantly higher than that in normal controls. Electron micrographs showed that a series of pathologic changes in von Ebner's gland of diabetes rats. The results suggest that GLP-1 have some effects within the gustatory systems, and elevated von Ebner's gland GLP-1 expression may be one cause of diabetic taste impairment.

Necessity of the glossopharyngeal nerve in the maintenance of normal intake and ingestive bout size of corn oil by rats.

Recent evidence in the literature suggests that signals carried by the glossopharyngeal nerve (GL), which supplies sensory and parasympathetic innervation of the posterior tongue, might be essential in the maintenance of normal gustatory responses to fat stimuli. Here, we report that GL transection (GLX) significantly decreased corn oil intake and preference in 23-h two-bottle tests relative to sham-operated controls (Sham). Drinking-pattern analysis of corn oil licking revealed that bout size, rather than the number of bouts initiated, was smaller in GLX than Sham rats. We also tested a range of glucose concentrations and found that total licks over daily 23-h sessions significantly decreased in GLX compared with Sham rats, but this difference failed to reach significance when intake or any bout parameter was measured. These results show that the signals in the GL normally contribute to processes involved with corn oil bout termination as opposed to bout initiation. GL-derived signals could potentially provide input to "reward" circuits in the ventral forebrain that could serve to maintain ingestion during a meal or, alternatively, could act at the level of the brain stem to attenuate the inhibitory potency of vagal signals, thus delaying the onset of satiation, or perhaps contribute to a cephalic phase reflex modulation of the gut. Parasympathetic efferents in the GL innervating the von Ebner's glands, which secrete lingual lipase, which is thought to break down corn oil into detectable ligands, could also be playing a role in driving corn oil intake. Whatever the mechanism, an intact GL is clearly necessary in maintaining normal intake of corn oil.

Antioxidant enzyme immunoreactivity in rat von Ebner gland after nickel treatment.

Our study was designed to clarify the role of antioxidant enzymes in the rat von Ebner gland during acute nickel toxicity. After treatment with nickel acetate, we monitored ultrastructural alterations in acinar and ductal cells, immunohistochemical staining for glutathione peroxidase (GPx) and glutathione S-transferases (GST mu and GST pi), and immunoreactivity for malondialdehyde (MDA). Immunoreactivity for MDA was present only in the acinar cells, and it was enhanced at 3 h after Ni treatment. In contrast, immunoreactivities for GPx and GSTs did not change in acinar cells but significantly increased in ductal cells after Ni treatment. Cytoplasmic vacuoles increased in acinar cells at 3 h after Ni treatment, but they almost completely disappeared at 24 h. No morphological changes were observed in taste bud cells from Ni-treated rats. Because lipid peroxidation, as monitored by immunoreactivity for MDA, was only transiently increased in the acinar cells, the enhanced antioxidant enzyme immunoreactivity in ductal cells of the von Ebner gland plays a crucial role in the self-defense system against nickel toxicity in the rat oral cavity.

Ionotropic glutamate receptor expression in preganglionic neurons of the rat inferior salivatory nucleus.

Glutamate receptor (GluR) subunit composition of inferior salivatory nucleus (ISN) neurons was studied by immunohistochemical staining of retrogradely labeled neurons. Preganglionic ISN neurons innervating the von Ebner or parotid salivary glands were labeled by application of a fluorescent tracer to the lingual-tonsilar branch of the glossopharyngeal nerve or the otic ganglion respectively. We used polyclonal antibodies to glutamate receptor subunits NR1, NR2A, NR2B, (NMDA receptor subunits) GluR1, GluR2, GluR3, GluR4 (AMPA receptor subunits), and GluR5-7, KA2 (kainate receptor subunits) to determine their expression in ISN neurons. The distribution of the NMDA, AMPA and kainate receptor subunits in retrogradely labeled ISN neurons innervating the von Ebner and parotid glands was qualitatively similar. The percentage of retrogradley labeled ISN neurons innervating the parotid gland expressing the GluR subunits was always greater than those innervating the von Ebner gland. For both von Ebner and parotid ISN neurons, NR2A subunit staining had the highest expression and the lowest expression of GluR subunit staining was NR2B for von Ebner ISN neurons and GluR1 for parotid ISN neurons. The percentage of NR2B and GluR4 expressing ISN neurons was significantly different between the two glands. The percentage of ISN neurons that expressed GluR receptor subunits ranged widely indicating that the distribution of GluR subunit expression differs amongst the ISN neurons. While ISN preganglionic neurons express all the GluR subunits, differences in the percentage of ISN neurons expression between neurons innervating the von Ebner and parotid glands may relate to the different functional roles of these glands.