The purpose of this review is to provide an overview of the differences in parenchymal structures that occur between the parotid and sublingual salivary glands of the rat from prior to birth to old age. Although the mature rat parotid gland is classified as serous, mucous cells have been identified in the acini during the early postnatal period. Mucous cells contained secretory granules including mucins and secretory proteins common to those of serous granules. Moreover, these cells morphologically showed transformation from mucous to serous type, and lack of apoptosis. When these findings are considered together, they suggest the possibility that mucous cells are converted into serous cells. Many myoepithelial cells around the acini were observed during the early postnatal period, whereas the mature rat parotid gland showed hardly any myoepithelial cells around the acini, but had such cells investing the intercalated ducts. The main reason for the disappearance of myoepithelial cells surrounding the acini during postnatal development is not apoptosis, but rather the large difference in cell number between myoepithelial cells and acinar cells, because the rate of proliferation of acinar cells declined more slowly than that of myoepithelial cells. Transient cells also occurred in the sublingual gland acini during the perinatal period, but these transformed into mucous cells, the opposite of transient cells in the developing parotid gland.
The submandibular gland (SMG) of the fetal mouse is useful for understanding the epithelial-mesenchymal interactions required for branching morphogenesis (BrM), which entails cleft formation and stalk elongation. We found that specific signaling pathways activated by growth factors or integrins regulate the processes of cleft formation and stalk elongation. Western blot analysis showed that epidermal growth factor (EGF) strongly stimulated the phosphorylation of extracellular signal-regulated kinase-1/2 (ERK-1/2) and weakly stimulated the phosphorylation of phospholipase Cγ1 (PLCγ1) and phosphatidylinositol-3 kinase (PI3K) in cultured E14 SMG. Meanwhile, fibroblast growth factor (FGF) 7 and FGF10 stimulated the phosphorylation of both PLCγ1 and PI3K, but elicited only minimal phosphorylation of ERK-1/2. Morphological studies revealed that EGF induced cleft formation of epithelial endpieces of mesenchyme-free SMG and that FGF7 stimulated both cleft formation and stalk elongation, whereas FGF10 induced only stalk elongation. U0126 (a MEK inhibitor) completely blocked cleft formation, while U73122 (a PLCγ1 inhibitor) suppressed stalk elongation. These results suggest that EGF stimulates cleft formation by activation of ERK1/2 and that FGF7 stimulates both cleft formation and stalk elongation by activation of PLCγ1 and partial activation of ERK1/2, and that FGF10 stimulates stalk elongation mainly by activation of PLCγ1. GoH3, a neutralizing antibody against the α6 integrin subunit, caused a slight increase over basal levels of ERK1/2 phosphorylation in cultured E14 SMG, but it had no discernible effect on EGF-induced phosphorylation. Based on these new findings regarding the effects of α6 integrin on growth factor receptor signals, we discuss the regulation of salivary gland development.
Imaging analysis using multiphoton microscopy revealed that rat parotid ductal cells exhibit spontaneous Ca2+ oscillations in the absence of calcium mobilizing agonist stimulation. This spontaneous Ca2+ release was first observed during the monitoring of Ca2+ transients during continuous perfusion at 37°C, and the protocol for cell preparation was modified to allow consistent observation of spontaneous oscillations. Spontaneous Ca2+ oscillations were completely blocked by application of the purinergic receptor inhibitors PPADS and suramin. Simultaneous observation of fura-2 fluorescence and differential interference contrast (DIC) images showed that spontaneous elevations in intracellular Ca2+ concentration ( [Ca2+] i) were well correlated with changes in the shape of ductal cells. Using a plasma membrane fluorescence probe we found that the changes in DIC images reflected spontaneous cell swelling of ductal cells. The present findings suggest the possibility that purinergic receptors mediate spontaneous Ca2+ oscillations in parotid ductal cells and regulate electrolyte reabsorption from the primary saliva under resting conditions. Cell swelling concomitant with a spontaneous increase in [Ca2+] i was an unexpected result because an agonist-induced increase in [Ca2+] i has been shown to induce cell shrinkage in ductal cells. When spontaneous Ca2+ release was compared to the carbachol-induced Ca2+ response, there were significant differences in the speed of Ca2+ elevation and duration of the Ca2+ response. Our data suggest that the different patterns of Ca2+ responses in parotid ducts might activate different ion channels and/or ion transporters and cause opposite cell shape changes.
Aquaporin-6 (AQP6) is a unique member of the family of AQP water channels and is involved in anion permeability. AQP6 was initially discovered in the cytoplasm of kidney cells as a kidney-specific AQP; however, subsequent studies revealed that the brain, inner ear, vestibular and intestines also express AQP6. Recently, we demonstrated that reactivity with an AQP6 antibody was observed in rat parotid granule membranes using immunohistochemistry. Those findings suggest that AQP6 participates as an anion channel in parotid secretory granule membranes. Here, we review the role of AQP6 in organelle membranes and introduce our challenge to elucidate the specific function of AQP6 in rat parotid granule osmoregulation.
While physiological pain (nociceptive pain) has a protective role in warning of potential tissue damage in response to a variety of noxious stimuli, pathological pain (neuropathic and inflammatory pain) serves no such meaningful purpose. Injury/inflammation in the peripheral tissue that innervates the trigeminal nerve may also alter the properties of trigeminal somatic sensory pathways, causing behavioral hypersensitivity (e. g., pathological pain) and induce pain abnormality caused by noxious stimulation (hyperalgesia) or normally innocuous stimulation (allodynia). These hypersensitivities to nociception are caused by changes in the excitability of trigeminal ganglion neurons (peripheral sensitization), which alter sensory information processing in spinal trigeminal spinal subnucleus caudalis (SpVc)/upper cervical spinal cord (C1-2) neurons (central sensitization). More is being learned about the activation of peripheral and central glia that play an important role in creating and maintaining pathological pain. This review therefore focuses on the possible sites for sensitization of nociceptive signaling through pain pathways that contribute to trigeminal pathological pain and also discuss potential therapeutic targets in neuron-glial interactions for preventing trigeminal neuropathic and inflammatory pain.
Salivary glands are intimately connected with the entire body via the nervous system and blood vessels, yet few studies have documented the effects of the salivary glands on the health of the whole body, although saliva has often been reported to possibly contain promising biomarkers of systemic disease states, including cancer. We therefore propose that the investigation of the effects of the salivary gland on the whole body and vice versa could introduce a new field of study, i.e., “salivary gland and health medicine.” This review examines data from novel studies on “salivary gland and health medicine” that were carried out by 3 different research groups.
The sense of taste has been evaluated mostly by investigating the taste perception threshold of taste solutions; however, few studies have examined the spread of taste in terms of the masticatory process. We examined the factors related with the number of chewing strokes for recognizing taste. Forty-three subjects without missing teeth were instructed to chew food samples made from 3% agarose containing 2 or 5% sucrose. The number of chewing strokes needed to recognize sweetness in either a partial area or the whole area of the tongue was counted using electromyography. In addition, masticatory performance, salivary flow rate, maximum bite force and scores of oral health related to quality of life (Oral Health Impact Profile, OHIP) were assessed. Male subjects exhibited a larger number of chewing strokes to recognize taste than female subjects for the 5% sucrose sample. The number of necessary chewing strokes for the taste recognition in the whole area was larger than that in a partial area of the tongue. Moreover, some relationships between the count and experimental conditions were found, such as masticatory performance (Spearman’s correlation coefficient by rank test: rs=0.49), salivary flow rate (rs=−0.53), maximum bite force (rs=−0.43) and scores of OHIP (rs=0.44—0.66). The findings suggest that the number of chewing strokes for recognizing sweetness might be affected by the aesthetic feeling against the teeth and oral conditions.
Objective: Tobacco, which annually kills 4.9 million people worldwide at present, is estimated to take 10 million lives every year by 2020 and India has been cited as the country with highest incidence. Multiple studies have been done to study the effects of tobacco on soft tissue with very few on hard tissues. So, in this study we evaluated the effects of tobacco on teeth by determining the weight % of various ions. Material & Methods: This preliminary study was designed including various categories according to habits. The samples of teeth were analyzed under the advanced SEM-Energy Dispersive Analysis of X-rays to examine the change in ionic composition of enamel in tobacco users and non-users. Results: Increase in weight % of ions like Sulphur (S), Magnesium (Mg) and Aluminium (Al) was noted depending on the habit. The weight % of these ions was highest in category II with a mixed habit of gutka, kharra, tobacco lime quid and smoking as compared to other groups. The weight % of these ions was also significantly more in category III and IV as compared to category I of unstained teeth. Conclusion: The results showed that there is a chemical alteration induced by tobacco in teeth, i. e., increase in levels of Al, S, Mg. It is postulated that this may result in the increase of these ions in saliva in due course of time. Ions like Al and S are known to make a cell more prone towards carcinogenesis. So, increase in concentration of these ions in saliva may make a cell prone towards carcinogens.
We previously isolated 40 predominant strains of bacteria, the characteristics of which resembled Wolinella (presently Campylobacter), among 422 isolates from seven human periodontal pockets; however, at that time, exact identification was not possible by conventional microbiological and biochemical tests because the criteria were ambiguous. Therefore, in the present study we aimed to clarify the classifications of the 17 representative strains by polymerase chain reaction (PCR) using a species-specific primer, 16S rDNA sequence similarity, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), and Western immunoblotting. We also aimed to describe each strain’s biochemical characteristics in detail. All of the 17 isolates studied were asaccharolytic, positive in nitrate reduction and arylsulfatase activity, negative in catalase and urease, and produced succinate as an end product of formate and fumarate for growth. Of the 17, 13 strains were identified as C. rectus, and 4 were oxidase negative strains (C. gracilis). Three of the C. gracilis strains were cocobacilli, which were morphologically different from the previously established strains. Evidence suggests that Campylobacter isolates from periodontal pockets in our previous work may be primarily C. rectus and secondarily C. gracilis.
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