Morphological and histochemical changes in the secretory granules of mucous cells in the early postnatal mouse parotid gland

Confocal laser scanning microscopic analysis of ectopic sublingual gland-like tissue inside the hamster submandibular gland

Based on its histochemical properties, the secretory portion of the hamster submandibular gland has been classified as seromucous cells. The presence of endogenous peroxidase (PO) reaction was shown in the nuclear envelope, cisternae of endoplasmic reticulum and Golgi apparatus. The 3,3'-diaminobenzidene, tetrahydrochloride (DAB) method revealed bipartite secretory granules containing a PO-positive dense core surrounded by a less dense halo in these cells. In the present investigation, serous and mucous-like cells were found in resin-embedded semi-thin sections of the DAB-reacted hamster submandibular gland. These sections were already on glass slides for routine light microscopic observations, therefore electron microscopic analysis could be unrealizable. We then used reflectance-mode confocal laser scanning microscopy to visualize additional sites of PO activity as detected in these sections. Using this approach, we found mucous cells with PO activity-negative secretory granules and seromucous cells with PO activity-positive spot-like secretory granules of the regular sublingual gland most frequently adjacent to the serous cells with typical electron-dense secretory granules. These cells clearly differ from the seromucous cells with bipartite secretory granules and the granular duct cells with typical electron-dense secretory granules of the hamster submandibular gland. Additionally, secretory endpieces of the ectopic sublingual gland-like tissue empty into the duct of the hamster submandibular gland lobule. Thus, our findings suggest that a mass of sublingual gland tissue extends into the hamster submandibular gland during its development, and PO may be synthesized and secreted into the same duct.

Chronic alcohol consumption promotes alterations on salivary gland regeneration process

The aim of this study is to investigate the histological effect of alcohol ingestion on the regeneration of the submandibular gland (SMG) in rats. Twelve 60-day-old male Wistar rats were randomized into two experimental groups. Test group (TG) animals ingested 40° GL of alcohol for 45 days before surgery, being its concentration gradually increased 10° GL/week for 4 weeks to achieve the final concentration of 40° GL. The control group (CG) received water during the whole experimental period. One-third of the left SMG lobe was removed. Three and seven days after, the whole gland was excised and analyzed. In the TG, the inflammatory process was pronounced when comparing the CG on day 3. The inverse aspect was observed on day 7, associated with an advanced parenchyma development. Changes in laminin expression and glycoproteins production were observed in the TG, causing advanced morphogenesis and delay in cytodifferentiation during the salivary gland regeneration, probably due to alcohol effects. Animals who received ethanol showed alterations in the pattern of glandular regeneration.

Effects of exogenous thyroid hormone on the postnatal morphogenesis of the rat parotid gland

Administration of thyroid hormone has been shown to accelerate the early postnatal development of the rat parotid gland, but these studies have dwelt almost entirely on biochemical changes. The objective of this study was to describe the effects of exogenous thyroid hormone on morphologic aspects of the developing parotid gland, in particular the transient appearance of scattered mucous cells in this otherwise serous gland. Pups were given a daily subcutaneous injection of thyroxine (T(4)) of 0.1, 0.5, or 5.0 microg/g body weight, vehicle only (injection control), or no injection (normal control) beginning at 4 days, and killed for the collection of blood and parotid glands at intervals through 15 days. The serum was analyzed for T(4) and the glands were examined by light and electron microscopy. The results indicated that both serum T(4) and the pace of gland development were proportional to the dose of T(4). In particular, T(4) accelerated decreases in acinar size and gland area occupied by stroma and translocation of a subset of cells with small secretory granules, deeply stained with periodic acid-Schiff, from acini to intercalated ducts. However, the chronology of mucous cell disappearance was indifferent to treatment. In addition, signs of toxicity, including slower gain in body weight and greatly increased apoptosis and vacuoles in the glands, occurred with the higher doses of T(4).

Granule types and their morphological changes in terminal cluster and acinar cells in the late pre- and early postnatal rat sublingual gland

The developmental characteristics of serous cells appearing in the rat sublingual gland from the late prenatal to the early postnatal period were investigated in this study. Particular attention was paid to the morphological changes observed in the secretory granules at the histochemical and ultrastructural level. On prenatal day 18, granules with homogeneous high electron density (Type I granules), and mottled granules (Type II granules) with heterogeneous electron density appeared in the narrow luminar cytoplasm of cells constituting the terminal clusters. On prenatal day 19, these granules decreased in number and were replaced by bipartite granules (Type III granules) composed of a highly electron-dense core and a more electron-lucent rim. Pronase treatment almost completely digested the Type I and II granules and the electron-dense core of the Type III granules, although some of the Type I and II granules in serous demilunes at a later stage were insufficiently digested. On prenatal day 19.5, homogeneous granules of low electron density (Type IV granules) appeared in the terminal clusters and acini, and increased in number daily, making up 92.8% of the total granules on postnatal day 28. The granule morphology on electron microscopy, Alcian blue, and periodic acid-Schiff staining strongly suggested that Type I and II granules were serous granules, Type IV granules were mucous granules, and Type III granules were transforming-type granules. None of the secretory cells showed chromatin condensation, which is a characteristic of apoptosis. These findings suggest that the developing rat sublingual gland from the late prenatal to early postnatal period has numerous serous granules in the terminal clusters and acini, and that the majority of granules are replaced by mucous granules through transforming-type granules. In addition, because apoptotic figures of secretory cells could not be detected, it appears that most of the serous cells in the developing rat sublingual gland might have changed to mucous cells.

Ontogeny of plasma cells in the early rat yolk sac

The present study investigated the development of plasma cells in the early rat yolk sac (days 10-16 of gestation) by light microscopy, transmission electron microscopy, immunoelectron microscopy, and indirect immunofluoresce techniques. Cells delineating the morphology of plasma cells in the yolk sac were observed as early as 12 days of embryonic life. As for positive immune staining for the intra-cytoplasmic immunoglobulin (Ig) production (IgA, IgM and IgG), the intensity of the immune staining was very weak on days 10 and 11 of gestation, while it turned very dense on day 12 of gestation. At 14 days of gestation, the number of positive cells was markedly reduced. Immunoelectron microscopy visualized products of the immune reaction in cisterns of the rough endoplasmic reticulum. Conventional electron microscopic examination of 12, 13, and 16-day yolk sacs confirmed the development and differentiation of plasma cells with their well-known ultrastructural features, making this the first study to demonstrate these in the early rat yolk sac. The development of plasma cells in the early yolk sac implies the ability of the yolk sac to effect a humoral immune response at this stage of fetal life. The probable role of plasma cells in the yolk sac is also discussed.

Developmental changes in the fine structure and histochemical properties of mucous cells in the parotid gland of the infant Japanese macaque

Mucous cells have been known to occur in the terminal portions of the parotid gland in a few species of mammals during a limited period of their development. The aim of this study was to examine the occurrence and features of mucous cells in the parotid gland of the infant Japanese macaque. Light microscopy revealed that mucous cells in the macaque parotid gland were present in the terminal clusters and acini at postnatal day 15, were less prevalent at day 30, and continued to decrease in number over 3 months. Mucous cells were no longer recognized in the parotid gland in 6-month-old macaques. Electron microscopy showed that the mucous cells contained electron-lucent secretory granules and bipartite or tripartite secretory granules. By 3 months of age, there was a scarcity of mucous cells and a concomitant increase in transitional cells. These transitional cells were intermediate in structure between mucous and serous cells, and contained three types of granules: electron-lucent, bipartite or tripartite, and electron-dense. None of the cells showed apoptotic figures. Lectin histochemistry indicated that the mucous cells in the early postnatal period had sugar residues identical in nature to those seen in the granules from mature serous cells in the glands of 3-month-old macaques. Immunohistochemistry using an antibody against human alpha-amylase showed a weakly positive reactivity in the secretory granules of the mucous cells, starting from day 15. In the transitional cells, the electron-dense granules showed a stronger immunoreactivity than either the electron-lucent granules or the heterogeneously structured granules. These results suggest that the secretory granules of mucous cells have characteristics in common with those of serous cells, and that during the transitional period the mucous granules change from the initial electron-lucent to hetorogenous forms, finally becoming the electron-dense granules. The mucous cells in the parotid gland of the juvenile Japanese macaque are therefore suggested to be converted into serous cells.