Appearance Of Secretory Granules Research Articles

New insights into sexually dimorphic skin glands of anurans: The structure and ultrastructure of the mental and lateral glands in Hypsiboas punctatus (Amphibia: Anura: Hylidae)

Many anuran species are characterized by sexually dimorphic skin glands. These glands often are concentrated on specific areas, such as the mental region, flanks, or the nuptial pads. We studied the histology and histochemistry of mental and lateral glands in Hypsiboas punctatus, and compared them to skin from other body regions. We describe four types of dermal glands, two types of mucous and two types of serous glands. The mucous glands are formed by a single layered epithelium. The mucocytes surrounding a central lumen are filled with polyhedral granules. Ordinary mucous glands are small sized glands with cubical epithelium, mucoid content, and small granules. Specialized mucous glands are characterized by a larger size, a columnar epithelium, a proteinaceous content and larger granules. Both types of serous glands are syncytial and share some structural features including size, shape, and morphology of secretory granules. However, ordinary and specialized serous glands differ in their histochemical properties, size and appearance of secretory granules, and glandular outlets. The specialized type of mucous glands in H. punctatus resembles most SDSGs described in anurans, whereas the presence of specialized serous glands that are sexually dimorphic is less common. Both specialized glands occur only in mental and lateral regions of males, whereas ordinary mucous and ordinary serous glands occur in males and females.

Immunocytochemical localization of chromogranin A and secretogranin II in female rat gonadotropes.

Ultrastructures of pituitary gonadotropes are known to show a prominent sex-related difference: typical male rat gonadotropes contain both large- and small-sized granules, whereas typical female rat gonadotropes appear to exhibit uniformly small-sized granules. Our preceding studies have demonstrated that two representative granins, chromogranin A (CgA) and secretogranin II (SgII), are separately localized to each type of granule in male rat gonadotropes. To clarify whether or not there is a certain relationship between granin proteins and characteristic features of secretory granules in female rat gonadotropes, we examined the expression levels and immunocytochemical localizations of CgA and SgII in the cells. Northern blot and immunoblot analyses demonstrated that both CgA and SgII were synthesized and stored in the female pituitary, although the amount of CgA was much lower in the female than that in the male pituitary. Immunocytochemical observations clarified that gonadotropes in the female pituitary possessed intermediate secretory granules containing both CgA and SgII, in addition to solely CgA-positive and SgII-positive ones. However, secretory granules containing CgA in the female gonadotropes were much smaller in size and appeared less frequently than those in the male cells, whereas no sexual difference was discerned in SgII-positive granules. Moreover, the size and appearance of CgA-positive secretory granules varied depending on stages of the estrous cycle. These findings suggest that the size and appearance of secretory granules containing CgA are closely associated with the expression and storage levels of CgA in the pituitary.

Ultrastructural studies of endocrine-like cells in the fundic gastric mucosa of the bullfrog, Rana catesbeiana

This study is concerned with electron-microscopic observations on endocrine or paracrine cells in the fundic gastric mucosa of the bullfrog. Also, an attempt was made to identify the histamine-releasing cells involved in the secretagogue response. At least three distinct endocrine-like cell types were found. The classification is based on the appearance of secretory granules and other organelles, and the relationship of endocrine-like cells with other cells in the tissue. The amphibian endocrine-like cells resemble the ECL, D and EC cells of mammals. Type-I (ECL) cells showed degranulation after repeated stimulation with tetragastrin (TG), acetylcholine (ACh) and K+ depolarizing solution, all of which release histamine.

β-adrenergic stimulation of mouse parotid gland: Amylase activity and secretory granules during isoproterenol-induced mitosis

1. 1. This paper examines the mitotic activity of parotid glands of groups of mice sacrificed at 1 hr-intervals between 26 and 36 hr after being injected with dl-isoproterenol (IPR, 1 μmol/g, single dose, i.p.). 2. 2. Maximal mitotic activity occurs 35 hr after IPR injection; there is a concomitant rise of amylase activity (64% over control). 3. 3. Mitotic cells showed increased number of secretory granules ( N) with regard to interphasic cells. However, the increment of N is paralleled by an increment of the cell section area ( A); the N A ratio is thus maintained around 0.45 throughout. 4. 4. These findings suggest that during IPR-induced mitosis of mice parotid cells there is not a blockade of the biosynthetic pathways which lead to the appearance of secretory granules in the cell cytoplasm.

Fine Structural Classification and Comparative Distribution of Endocrine Cells in Normal Human Large Intestine

Rectosigmoid- or colonoscopy biopsies were performed at different levels of the large intestine of 16 adult subjects free from major intestinal disease. Tissue specimens were subsequently examined by electron microscopy. Four different endocrine cell types could be distinguished on the basis of the shape and ultrastructural appearance of secretory granules, of their silver affinity, and of their morphometry. Type I cells (enterochromaffin cells, 60.5%) were argentaffin and presented granules with widely different morphologies, which could correspond to several subtypes. The three other cell types were nonargentaffin. Type II (21.3%) contained granules with a diameter distribution peak of 200 to 300 nm. Type III cells, rare (3.2%), were characterized by small and infrequent granules with a diameter distribution peak of 150 to 200 nm. Type IV cells (7.4%) were characterized by large and round granules with a diameter distribution peak of 300 to 400 nm and resembled the "L cell" of the small intestine. The most endocrine cell-rich portion of the colon was the rectum (179 of 618 cells examined). Type I cells represented approximately 73% of the endocrine cell population from the cecum to the descending colon and decreased to 42% in the rectum. Both the absolute number and the percentage of type II cells increased from the cecum (8%) to the rectum (31%). Type IV cells also increased in the rectum both in absolute number and percentage (14%). The absolute number of type III cells was too small to enable significant differences to be observed.

Quail Rathke's pouch differentiation an electron microscopic study.

Adenohypophyseal region of quail embryo has been examined by electron microscopy from stage 12 to stage 21 of Zacchei (1961). The Seessel's pouch develops prior to the early stages of adenohypophysis formation, then regresses while Rathke's pouch proliferates and differentiates. From Rathke's pouch formation by stage 12 (48 h of incubation) until appearance of the first secretory granules by stage 21 (6 days of incubation), there are no major ultrastructural modifications in adenohypophyseal cells. Mitochondria, Golgi vesicles, polysomic ribosomes, pinocytotic vesicles, and mitotic figures become more numerous while nucleocytoplasmic ratio and the number of ribosomes and lipid droplets decreases. The major change is the appearance of secretory granules by day 6 of incubation. This phenomenon occurs at the same time as in chick embryo, despite an incubation period shorter for quail than for chick. Mitotic figures are mainly distributed near the pouch lumen, while secretory granules are first located in the peripheral cells of the cephalic part of pars distalis primordium. The hypothetical role of mesenchyme and vascularization is discussed.

Ontogeny of neurophysin in the rat pituitary gland. An electron microscope immunohistochemical study

The ontogenic development of neurophysin has not been investigated so far. To study this problem, electron microscopic immunohistochemistry was performed on ultrathin sections of the posterior pituitary of foetal and newborn rats. A concomitant appearance of secretory granules and neurophysin was first noted in the posterior pituitary of 18-day-old foetus. Neurophysin was detected only in the secretory granules, all of which were labelled. The number of granules (75–110 nm in diameter) as well as the intensity of the reaction for neurophysin increased as the foetus became older. In the newborn rat, the secretory granules were more numerous and showed a strong neurophysin positive reaction. The results support the hypothesis that neurophysin is an essential component for the formation of the secretory granules in the hypothalamoneurohypophysial system.

Maturation and Differentiation of Cultured Fetal Stomach

Gastric mucosa of fetal rats undergoes striking developmental changes during the last few days of gestation in utero. To investigate some aspects of this process, gastric explants from 18-day fetuses (4 days before birth) were maintained in organ culture for 3 days, then assessed by light and electron microscopy. The epithelia from base line uncultured stomachs were stratified and morphologically undifferentiated. During culture in basic medium (Leibovitz L 15), modest maturation of antral and fundic architecture occurred, characterized by epithelial invagination to produce small pit-glands. Secretory granules appeared in occasional epithelial cells, and cytochemistry indicated that most were mucous granules. Addition of pentagastrin (10(-9) to 2 X 10(-7) M) did not induce further morphological maturation in this system. However, addition of cortisol (10(-6) to 10(-5) M) resulted in a marked, dose-related increase of pit-gland formation and of cytological differentiation (appearance of secretory granules). This cortisol-induced architectural maturation was completely inhibited by the mold metabolite cytochalasin B (10(-5) M). The results indicate that fetal gastric maturation can be partially reproduced by culture in chemically defined media, and also suggest that corticosteroids may plan an important role in gastric organogenesis.

A light and electron microscopic study of Rathke's pouch in fetal rabbits

Rathke's pouch, the anlage of the adenohypophysis, has been studied in fetal rabbits with the light and electron microscope from its first appearance on the tenth day of gestation until the sixteenth day when secretory granules are observed in some of the cells of the pars distalis portion of the pouch. The pouch is considered undifferentiated from the tenth through fifteenth day since secretory granules were not observed within any of its cells during this period. The secretory granules observed for the first time on the sixteenth day of gestation within cells of the pars distalis closely resemble those found in basophils in the adult rabbit pars distalis. The cytologic development of the partes intermedia and tuberalis is essentially identical to that of the pars distalis from the tenth to fifteenth day of gestation. Rathke's pouch at ten days is a single-layered epithelium composed of a single cell type characterized by a high nuclear-cytoplasmic ratio, irregular contours, and very few organelles except for an abundance of ribosomes. Lipoprotein inclusions are common near the luminal surface from ten to twelve days but diminish thereafter. In specific regions of the pouch large, polymorphic structures are observed located intra- and extra-cellularly. These are tentatively designated “odd bodies.” A striking feature of the pouch at ten and eleven days are large, extracellular spaces across which processes of the pouch cells contact one another. Cell processes also extend between the pouch and adjacent neural tube and notochord. The extracellular spaces gradually diminish from the twelfth to fourteenth day as the number of cells increases. Organelles increase gradually during this period though the cells are still not richly endowed. At fifteen days (the day preceding the appearance of secretory granules and mesenchymal infiltration) the entire cell population of Rathke's pouch undergoes a radical change. The cells appear swollen, electron lucent, and organelles are diminished in quantity. The extracellular spaces are almost completely obliterated. These changes in the cytology at fifteen days are considered a normal prelude to further cyto-differentiation which is evident in the pars distalis at sixteen days and later.