Developmental changes of sugar residues and secretory protein in mucous cells of the early postnatal rat parotid gland.

Mucous cells have been identified in the terminal portions of the early postnatal parotid gland in human and rat, although mature parotid gland acini are composed of serous cells or seromucous cells. Previously, Ikeda et al. demonstrated that mucous cells are present in the rat parotid gland on days 1 to 8 after birth and that the secretory granules within these mucous cells share some histochemical characteristics with mature serous cells. However, it is still not clear whether the mucous cells change into serous cells as the gland develops. The purpose of this study was to determine whether the mucous cells that appear in the early postnatal rat parotid gland change into serous cells. Parotid glands were obtained from male or female Wistar rats (aged 0-14 days and adults). Fixed tissue sections were reacted with soybean agglutinin (SBA) and wheat germ agglutinin (WGA) to detect glycoconjugates, or were stained using an anti-neonatal submandibular gland protein B1 (SMG-B1) antibody to identify serous acinar cells. The sections were observed by transmission electron microscopy. Electron microscopy revealed that cells with characteristics intermediate between those of mucous and serous cells (transitional cells) appeared around day 8 and that the nuclei of these cells did not show chromatin condensation, a characteristic of apoptotic cells. Lectin histochemistry showed that the mucous cells had the same sugar residues as the serous cells, which appeared after day 10. Immunohistochemistry with an anti-SMG-B1 antibody gave a positive reaction not only in the cells with highly electron-dense granules but also in the electron-dense cores of bipartite or tripartite granules in the transitional cells. Cells with morphological characteristics intermediate between those of mucous and serous cells (transitional cells) appearing in the early postnatal rat parotid gland begin to produce B1-immunoreactive protein common to serous acinar cells during development of the gland.     

Differentiation of myoepithelial cells in the developing rat sublingual gland

Sublingual glands of rats were prepared for light and electron microscopy and for the histochemical demonstration of myofibrils and alkaline phosphatase (AkPase) activity. Through 17 days in utero, the epithelial cells of the glandular rudiment are relatively undifferentiated. At 18 days, the inner cells of the terminal buds begin to assemble around a lumen and accumulate secretory granules, while the outer cells flatten and form long processes. At 19 days, many of the outer cells have dilated cisternae of rough endoplasmic reticulum engorged with finely granular material. At 20 days, some of the outer cells have thin bands of microfilaments in their processes, suggesting that they are differentiating into myoepithelial cells (MEC). Though the secretory cells are almost mature at birth, only a few of the MEC have myofibrils detected with an actomyosin reaction, and AkPase activity is very weak. Progressive increases in AkPase activity and in myofibril size and number continue until the acini and intercalated ducts are fully invested with mature MEC at about 14 days after birth. Thus, the MEC and secretory cells begin to differentiate at the same time, but the MEC subsequently differentiate asynchronously with the secretory cells and with each other. Although the sublingual MEC are only partly differentiated in the newborn rat, their overall development occurs somewhat more rapidly than in the adjacent submandibular gland.     

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

It has previously been known that the developing parotid glands in humans and rats contain mucous cells in their terminal clusters and acini, but these cells disappear within a short period of time. Using rat parotid glands, IKEDA and AIYAMA (1997, 1999) suggested that the mucous cells might change into serous cells in the early postnatal period, but it is uncertain whether mucous cells appear only in the developing parotid gland of a few species such as humans and rats, or whether the cell transformation actually occurs. To clarify these points, the present study investigated the developing mouse parotid glands. Light microscopy showed cells with secretory granules that stained extensively with PAS and alcian blue in the terminal clusters of a 1-day-old mouse parotid gland. Mucous cell numbers in the terminal clusters and the acini reached a peak on day 5 and decreased on day 7. By day 10, the mucous cells had disappeared altogether. Thus, the presence of mucous cells in the developing mouse parotid gland was confirmed. Electron microscopy showed granules of low-electron-density and bipartite granules in the mucous cells. Bipartite granules and highly electron-dense granules sometimes co-existed in a single cell. Immuno-electron microscopy revealed a positive reaction for amylase to the low-electron-density granules and the low-electron-density portions of the bipartite granules, in addition to the highly electron-dense granules and the electrondense cores of the bipartite granules. No mucous cells with nuclei displaying characteristics of apoptosis were recognizable. Lectin histochemistry both at the light and electron microscopic levels showed that the secretory granules in the mouse parotid gland mucous cells had sugar residues similar to those of the mature serous granules. These findings demonstrate that mucous cells appear in the early postnatal mouse parotid gland, and that almost all of these cells may be converted into serous cells.     

Changes in the secretory acinar cells of the rat parotid gland during aging

The secretory acinar cells of parotid glands from rats of varying ages have been examined by electron microscopy to determine what age-related changes occur in these cells. The most prominent change noted in these cells is the progressive increase in the amount of lipofuscin granules with age. Lipofuscin granules are membrane-bound structures consisting of lipids, other subcomponents, and a matrix. In addition, these cells contain lipid droplets that are not associated with any other components and tend to accumulate at the base of the cells in older rats. Also, many acinar cells in the glands of old rats contain altered secretory granules which appear to be in the process of degeneration. The accumulation of lipid and degenerating secretory granules appears to be related to the reduced level of cellular secretory activity in the glands of older rats. It is possible that these two types of inclusions contribute to the formation of lipofuscin granules. Lipofuscin and degenerating secretory granules are associated with acid phosphatase, which is demonstrated cytochemically, indicating that these granules are lysosomal structures.     

Transient occurrence of 27 kDa heat-shock protein in the terminal tubule cells during postnatal development of the rat submandibular gland.

It has been suggested that the 27 kDa heat-shock protein (Hsp27) plays a role at crucial cellular checkpoints for proliferation, apoptosis, and differentiation. We examined the immunolocalization of Hsp27 in the rat submandibular gland during postnatal development, wherein acinar cells proliferate and differentiate at earlier postnatal periods. At 2 weeks of age, weak Hsp27 immunoreactivity was distributed diffusely over all gland components. At 3 weeks, Hsp27 immunoreactivity disappeared in most parts of the acini and ducts, but was intensely accumulated in a small cell population located in the acinar center. This population was composed mostly of terminal tubule (TT) type I cells. At 4 weeks, the Hsp27-immunopositive cell population in the acinar center was composed primarily of immature (type II) acinar cells, partly of immature (granulated) intercalated duct (ID) cells, and occasionally of apoptotic cells. After 5 weeks, all acinar components became mature and were no longer immunoreactive for Hsp27. When acinar cell differentiation was accelerated by administration of isoproterenol to 3-week-old rats for 7 days, the number of Hsp27-positive cells was significantly lower than in the control gland at 4 weeks, confirming that Hsp27 expression is downregulated in mature acinar cells. These results suggest that at around 3-4 weeks in postnatal development, the centroacinar TT cells stop proliferating and begin to differentiate into acinar and ID cells, and occasionally undergo apoptosis. Hsp27 is transiently expressed in the centroacinar TT cells during this critical period, and thus may play a role in their differentiation into the immediate descendants.     

Transient expression of a functional serotonin transporter in Merkel cells during late gestation and early postnatal rat development

We and others have previously identified serotonin transporter mRNA throughout the trigeminal system in the whisker region, trigeminal ganglion, trigeminal nucleus and thalamic relay stations. In order to further implicate a role for the serotonin transporter in this sensory system, we have now characterized serotonin transporter gene expression and function in primary cultures from the rat snout, at several stages of gestation. In this study, we have demonstrated a transient expression of serotonin transporter mRNA in quinacrine-positive Merkel cells between embryonic day 16 and postnatal day 5. Peak levels of mRNA occurred at embryonic day 20 and postnatal day 1. Merkel cells in culture exhibited a transient, antidepressant-sensitive [3H]-serotonin uptake, which was maximal at a time in culture corresponding to embryonic day 22 (day of birth). This transient uptake of serotonin suggests a role for this monoamine during a critical time period of the developing trigeminal sensory system. Regulation of extracellular serotonin levels by transporter activity may reflect the specific formation of the merkel cell-sensory neuron complex in an analogous mechanism by which serotonin modulates synaptogenesis in the central nervous system.     

Two types of cation channels in the basolateral cell membrane of human salivary gland acinar cells

Giga-seal patch-clamp single-channel current recording was applied to the basolateral cell membrane of human salivary gland acinar cells. The results indicate that the presence of Ca2+- and voltage-activated K+-channel having a unit conductance of 160 pS and Ca2+-activated Na+ permeable channel, having a unit conductance of 15 pS.     

Clinical pathology in the female rat during the pre- and postnatal period

Clinical pathology parameters are a valuable index relating to the pathophysiological state of an animal and are routinely measured in most toxicological studies. In order to interpret blood data in reproductive studies it is first necessary to know normal background ranges through pregnancy and lactation. The purpose of this study was to generate this database using the Crl:CD VAF/Plus strain of rat as a model. Blood profiles were generated by bleeding time-mated female rats at various intervals during the pre- and postnatal period (days 7,12,15 and 20 of pregnancy, days 4,12,15 and 20 lactation). A routine set of clinical pathology analyses were performed. The haematology results showed that during pregnancy an increase in plasma volume causes a reduction in haemoglobin concentration, RBC and PCV leading to the onset of emergency haematopoiesis and hence an increased reticulocyte count. There was also a decline in circulating WBC, mainly lymphocytes. Both the APTT and PT increased during gestation. With the exception of WBC, the haematology values returned to within normal non-pregnant ranges during lactation. The clinical chemistry results indicated that organ function was changed during gestation and lactation in the dam compared to that of a normal non-pregnant female. These changes were primarily linked to hypertrophy of the liver, changes in hydration and an altered renal threshold.     

Transient occurrence of 27 kDa heat‐shock protein in the terminal tubule cells during postnatal development of the rat submandibular gland

It has been suggested that the 27 kDa heat‐shock protein (Hsp27) plays a role at crucial cellular checkpoints for proliferation, apoptosis, and differentiation. We examined the immunolocalization of Hsp27 in the rat submandibular gland during postnatal development, wherein acinar cells proliferate and differentiate at earlier postnatal periods. At 2 weeks of age, weak Hsp27 immunoreactivity was distributed diffusely over all gland components. At 3 weeks, Hsp27 immunoreactivity disappeared in most parts of the acini and ducts, but was intensely accumulated in a small cell population located in the acinar center. This population was composed mostly of terminal tubule (TT) type I cells. At 4 weeks, the Hsp27‐immunopositive cell population in the acinar center was composed primarily of immature (type II) acinar cells, partly of immature (granulated) intercalated duct (ID) cells, and occasionally of apoptotic cells. After 5 weeks, all acinar components became mature and were no longer immunoreactive for Hsp27. When acinar cell differentiation was accelerated by administration of isoproterenol to 3‐week‐old rats for 7 days, the number of Hsp27‐positive cells was significantly lower than in the control gland at 4 weeks, confirming that Hsp27 expression is downregulated in mature acinar cells. These results suggest that at around 3–4 weeks in postnatal development, the centroacinar TT cells stop proliferating and begin to differentiate into acinar and ID cells, and occasionally undergo apoptosis. Hsp27 is transiently expressed in the centroacinar TT cells during this critical period, and thus may play a role in their differentiation into the immediate descendants. Anat Rec 264:358–366, 2001. © 2001 Wiley‐Liss, Inc.     

Structure and cytochemistry of the acinar cell in the rat maxillary gland

The ultrastructural and cytochemical properties of the maxillary gland were investigated in 24 adult Sprague-Dawley rats of both sexes. The relationship between the interstitial cell and/or excitatory cholinergic terminals with the secretory cell was discussed. The secretory material containing primarily neutral lipids, proteins, carbohydrates and mucosubstances appeared electron-opaque following staining with uranyl acetate and lead citrate. Ruthenium red precipitated strongly on zymogenic granules which showed an increasing affinity for phosphotungstic acid, paralleling a rise in pH towards 7.7. The process of fusion of the plasma membrane with the membrane of secretory granules was observed, although some membrane-bound granules were identified in the acinar and ductal lumina. Intracellular membranous structures were best revealed with phosphotungstic acid at pH 1.0–1.5, whereas ruthenium red reacted primarily with lipid inclusions and tonofilaments. Acid phosphatase activity was predominantly limited to secondary lysosomes and, to a lesser degree, to primary lysosomes and Golgi saccules. The morphological and chemical properties of secondary lysosomes in the secretory cell suggested a pronounced hydrolytic activity related to lipid inclusions and endocytotic vesicles.     

Morphological changes of the myenteric plexus during early postnatal development of the rat

The enteric nervous system needs to adapt itself constantly to the postnatal changes of the developing gut. The aim of this study was to examine the morphological changes between the distal and proximal segments of the gastrointestinal (GI) tract during the first two postnatal weeks. Myenteric plexus from the duodenum, proximal and distal colon of 1‐, 7‐ and 14‐day‐old rat pups was dissected and examined under the scanning electron microscope. Wholemounts from the same regions and postnatal stages were stained with cuprolinic blue. Neuronal numbers per ganglionic area were counted and neuronal sizes were measured. Furthermore, segments of the above‐mentioned areas were embedded in resin and semithin sections were cut. The thickness of the circular and longitudinal muscle layers was measured. The morphology of the myenteric plexus depends on localization as well as on the age of the animal. While in younger animals the myenteric plexus is usually densely packed, the network expands with increasing age. Similarly, the thickness of the circular and the longitudinal muscle layers increases. Nerve cell numbers per ganglionic area increase from duodenum to distal colon and decrease from the 1‐day (P1) to the 14‐day‐old (P14) animal. The longest diameters and the area of the nerve cells decrease from duodenum to distal colon and increase with age of the animal. The intensity of the cuprolinic blue staining varies also according to age and segment of the gut. During the first two postnatal weeks the three‐dimensional architecture of the myenteric plexus as well as the size and densities of the enteric neurons change according to the increasing gut length and the thickness of the muscle layer. The differences between duodenum and colon might reflect the different physiological properties of the proximal and distal gut as well as a varying grade of maturity, which is also supported by a variation in the cuprolinic blue staining intensity. Anat Rec 256:20–28, 1999. © 1999 Wiley‐Liss, Inc.     

Effects of calcitonin on elemental distribution and ultrastructure of rat submandibular gland acinar cells

The effect of calcitonin on rat submandibular gland acinar cells was investigated by X-ray microanalysis and electron microscopy. Calcitonin caused a transient increase of the cellular calcium and magnesium concentration, but did not affect the intracellular concentration of other electrolytes. The relative volume of intracellular mucus increased from 45% in control glands to 72% at 6 h after administration of calcitonin. Calcitonin caused an inhibition of the cellular response of the acinar cells to beta-adrenergic and cholinergic agonists. The changes in elemental composition and ultrastructure of the gland cells are probably due to inhibition of mucus release from the cells.     

Changes in the synapses of rat hippocampus following pre- and postnatal alcohol exposure

Quantitative and qualitative changes in the synapses in stratum lacunosum-moleculare of rat hippocampus following pre- and postnatal alcohol exposure were studied. Dense and lamellar bodies, damaged mitochondria, autophagic vacuoles and dilatated cisterns of the smooth endoplasmic reticulum were seen in axons and dendrites. The enlarged glial processes were also found. The area and the vesicle number of presynaptic terminals were decreased in CA1 and CA3 hippocampal fields, while the vesicle number per area of synaptic contact zones (SCZ) was decreased only in field CA3. The relative and absolute lengths of the SCZ, the total length and total surface of the SCZ were quite differently changed in both fields. The synaptic density was insignificantly increased. The synaptic changes are thought to be due to the impaired development of the pyramidal cell dendrites in the hippocampus and their afferents.