Dark Secretory Granules Research Articles

The lack of terminal tubule cells in the submandibular gland of mice deficient in submandibular gland protein C.

The submandibular gland (SMG) of newborn mice has no mature acini but has the rudiments of acini called terminal tubules (TT). The TT are composed of TT cells with dark secretory granules and proacinar cells with lighter secretory granules, the latter being considered the immediate precursor of mature acinar cells. TT cells contain a specific secretory protein, submandibular gland protein C (SMGC) and they decrease in number postnatally at a higher rate in males than in females. In the present study, in order to clarify the biological roles of TT cells and their secretory product SMGC, we generated a knockout (KO) mouse strain deficient in SMGC. The KO mice of both sexes grew normally, had normal reproductive capacity and had normal acinar and duct systems in the SMG in adult ages. However, through the neonatal and early postnatal stages, the KO mice were deficient not only in the production of SMGC but also in TT cells. With electron microscopy of the SMG of newborn KO mice, TT cells with characteristic granules were absent and replaced by undifferentiated ductal cells, whereas proacinar cells were normal. These results suggested that the absence of SMGC inhibits the development of TT cells and that the absence of SMGC and TT cells has no notable influence on the postnatal development of the acinar and duct systems in the SMG.

The ultrastructure of taste buds in the newborn cat

Tichy, F.: The Ultrastructure of Taste Buds in the Newborn Pig. ACta 'vet. Brno, 61,1992: 171-177. . . Taste buds localized on circumvallate papillae of the porcine tongue were in­ vestigated for the occurrence of dark, light and receptor cells and the stage of their differentiation, the morphology of the taste pore area, the occurrence and distriou­ tion of intragemmal nerve endings and the way in which these are connected with each cell type. It was observed that, as early as two days after birth, the porcine taste buds included all three cell types. These were elongated towards the taste pore. Their apical parts, however, did not come up to level with the epithelial surface nor were they shaped into microvilli typical of the bud ultrastructure described in adult animals of other mammalian species. The cytoplasm of the dark cells had only a low amount of dark secretory granules and the receptor cells showed only oc­ casional occurrence of dark vesicles. The dark, light and receptor cells were con­ nected with nerve fibres and the way of contact was different in each cell type. Taste bud, taste pore, gustatory nerve. ultrastructure

Ultrastructure of the taste disc in the red-bellied toad Bombina orientalis (Discoglossidae, Salientia)

The taste disc of the red-bellied toad Bombina orientalis (Discoglossidae) has been investigated by light and electron microscopy and compared with that of Rana pipiens (Ranidae). Unlike the frog, B. orientalis possesses a disc-shaped tongue that cannot be ejected for capture of prey. The taste discs are located on the top of fungiform papillae. They are smaller than those in Ranidae, and are not surrounded by a ring of ciliated cells. Ultrastructurally, five types of cells can be identified (mucus cells, wing cells, sensory cells, and both Merkel cell-like basal cells and undifferentiated basal cells). Mucus cells are the main secretory cells of the taste disc and occupy most of the surface area. Their basal processes do not synapse on nerve fibers. Wing cells have sheet-like apical processes and envelop the mucus cells. They contain lysosomes and multivesicular bodies. Two types of sensory cells reach the surface of the taste disc; apically, they are distinguished by either a brush-like arrangement of microvilli or a rod-like protrusion. They are invaginated into lateral folds of mucus cells and wing cells. In contrast to the situation in R. pipiens, sensory cells of B. orientalis do not contain dark secretory granules in the perinuclear region. Synaptic connections occur between sensory cells (presynaptic sites) and nerve fibers. Merkel cell-like basal cells do not synapse onto sensory cells, but synapse-like connections exist between Merkel cell-like basal cells (presynaptic site) and nerve fibers.

Light- and electron-microscopic immunocytochemistry of a molluscan insulin-related peptide in the central nervous system of Planorbarius corneus

Two groups of cerebral dorsal cells of the pulmonate snail Planorbarius corneus stain positively with antisera raised against synthetic fragments of the B- and C-chain of the molluscan pro-insulin-related prohormone, proMIP-I, of another pulmonate snail, Lymnaea stagnalis. At the light-microscopic level the somata of the dorsal cells and their axons and neurohemal axon terminals in the periphery of the paired median lip nerves are immunoreactive with both antisera. Furthermore, the canopy cells in the lateral lobes of the cerebral ganglia are positive. In addition, MIPB-immunoreactive neurons are found in most other ganglia of the central nervous system. At the ultrastructural level, pale and dark secretory granules are found in somata and axon terminals of the dorsal cells. Dark granules are about 4 times as immunoreactive to both antisera as pale granules. Release of anti-MIPB- and anti-MIPC-immunopositive contents of the secretory granules by exocytosis is apparent in material treated according to the tannic acid method. It is concluded that the dorsal and canopy cells synthesize a molluscan insulin-related peptide that is packed in the cell body into secretory granules and that is subsequently transported to the neurohemal axon terminals and released into the hemolymph by exocytosis. Thus, MIP seems to act as a neurhormone on peripheral targets. On the basis of the analogy between the dorsal cells and the MIP-producing cells in L. stagnalis, it is proposed that the dorsal cells of P. corneus are involved in the control of body growth and associated processes.

Influence of Lactation on Morphometric and Secretory Variables in Pancreatic β-Cell of Mildly Diabetic Rats

In nondiabetic rats, lactation accelerates the restoration of pancreatic beta-cell function after the period of increased secretory activity associated with pregnancy. To investigate whether a comparable situation prevails in mildly diabetic animals, streptozocin (22.5 mg/kg body wt) was administered to female rats at the onset of pregnancy. Plasma glucose and insulin concentrations, content and release of insulin in isolated islets, total mass and volume density of both the endocrine pancreas and granulated beta-cells, and ultrastructural prevalence of light and dark secretory granules were measured on the 20th day of pregnancy and in lactating and nonlactating animals 20 days after delivery. In the mildly diabetic animals, the changes in endocrine pancreatic function normally associated with pregnancy and lactation were greatly attenuated, albeit not completely eliminated. We propose that the increased biosynthetic and secretory activity imposed on surviving beta-cells after streptozocin administration tends to mask the adaptative changes in beta-cell function otherwise seen during the postpartum and lactation period.

Brain lesions and short-term endocrine effects of monosodium L-glutamate in goldfish, Carassius auratus.

Monosodium L-glutamate (MSG) was injected intraperitoneally into goldfish at a dosage of 2.5 mg/g body weight. At 24 h post-injection there was a marked hypertrophy and edema in the region of the nucleus lateralis tuberis (NLT) from the anterior margin of the pituitary stalk through to the posterior end of the NLT, irrespective of the sex of the goldfish. A similar hypertrophy and edema occurred ventral to the anterior commissure in the preoptic region in the anterior-ventral nucleus preopticus periventricularis (NPP). At 6 h post-injection a slight vacuolization was evident in these two regions, and at two days the hypertrophy and edema had abated from the extent observed at 24 h post-injection. At five and eight days post-injection only necrotic cells were found in the affected NLT region, but only a small band of necrotic cells was evident in the anterior-ventral preoptic region. No other brain lesions were evident. Serum levels of gonadotropin (GtH) were increased at 6 h, 24 h, and two days after treatment with MSG, but were similar to control values at five, seven and eight days after MSG in male and female goldfish. Exocytosis of small dark secretory granules in gonadotrophs was evident at 24 h after MSG in a fish with a somewhat greater increase in serum GtH than usually found. The time course of increased serum GtH levels postinjection of MSG is consistent with the observed time course of hypertrophy and atrophy of NLT neurons; the increase in serum levels of GtH is interpreted to reflect a stimulation of release of GtH-releasing factor from neurons in the NLT. Electron microscope investigation indicates that prolactin cells have increased secretory and synthetic activity from 24 h through to seven days post-injection of MSG. The mechanism for stimulation of the prolactin cells by MSG is not known. No other changes in activity of adenohypophysial secretory cells were found.

Ultrastructure of the middle ear mucosa.

Histologic studies of recent years have definitely concluded that the epithelium of the middle ear is a modified respiratory epithelium with ciliated and secretory cells, including goblet cells. These cells, like the ciliated cells, are developd from the basal cell and are just ordinary secretory cells completely filled with secretory granules. For different reasons it is postulated, that the dark secretory granules are prestages of the actual secretory product presenting as light granules and that dark and light granules do not represent different secretory capacities of the cell. The subepithelial layer which consists of loose connective tissue is a structure of just as great importance as the epithelial layer.

Ultrastructure of the middle-ear mucosa in secretory otitis media. I. Serous effusion.

Mucosal biopsies from the middle ear of patients with secretory otitis media and serous effusion were studied by electron microscopy. This confirmed that the effusion is produced by active secretion from an epithelium without signs of degeneration: Two types of secretory cell were demonstrated: one with mucigen-like granules and one with dark secretory granules and apocrine secretion, possibly serous-secreting. Compared with the normal middle ear mucosa, the number of secretory cells had increased while the number of ciliated cells had decreased. There were signs of ciliated cells being transformed into secretory cells.

Cytological Events Associated with the Secretory Process in the Rabbit Oviduct

The structure of and the cytological changes which take place in the epithelium of the rabbit oviduct during the reproductive cycle have been studied by techniques of light and electron microscopy. The pseudostratified columnar epithelium consists of 2 cell types: ciliated and secretory. Ciliated cells predominate in the infundibulum, and make up approximately half of the highly folded epithelium of the ampulla and isthmus. The more electron-dense secretory cells in the precoitus oviduct contain an abundance of free ribosomes and rough endoplasmic reticulum, a well developed Golgi complex, and many dark secretory granules in the apical portions. The apices of these cells commonly extend beyond the level of adjacent ciliated cells, and occasionally discharge their secretion granules. Oviducts of one rabbit at each of 13, 24, 48, 72, 108 hr and 10 and 14 days postcoitum were utilized in this study. After coitus, when the ova and early cleavage stages are passing down the oviduct, the secretory cells assume a goblet shape, with many electronlucent granules massed in the apical portion of the cell. These granules are discharged, usually with their encompassing membranes, between 24 and 72 hr postcoitum. Histochemical tests indicate that the secretory material is a muco- or glycoprotein or an acid mucopolysaccharide. Subsequent to the discharge of the electron-lucent granules, the secretory cells become elongated, but persist and take part in the ensuing secretory cycle. The sequestration of the secretory material takes place continuously during the reproductive cycle in the saccules of the Golgi complex. The contribution of the endoplasmic reticulum and the Golgi complex to the secretion granules and the role of the secretion in the reproductive process is discussed. From the time of the discovery of the oviduct by Fallopio in 1561 until the early 1900’s, the fallopian tube was considered merely as a conduit for the passage of sperm and ova, with no physiologic or metabolic functions. Although several early histological investigations were made on oviducts of various mammals (Guerriero, 1929; Moreaux, 1913; Novak and Everett, 1928), little correlation was made between anatomy and function. Only recently have detailed studies been made of the epithelium and of its secretions in an effort to elucidate oviductal functions.

Functional morphology of the pars intermedia of the rat hypophysis as revealed with the electron microscope. II. Correlation of the pars intermedia with the hypophyseo-adrenal axis.

The pars intermedia of the hypophysis of normal and experimental rats was studied by electron microscopy. Observations of the hypophysis at various intervals following formalin induced stress or adrenalectomy indicate the existence of a functional relationship between the posterior lobe, the pars intermedia, and the adrenal cortex. Glandular cells of the normal pars intermedia are divided into two types, i. e., the light and dark cells. The former type dominates in number and is characterized by a large amount of cytoplasm filled with clear vesicles 250–350 mμ in diameter. Dark secretory granules smaller than 300 mμ are few in number and restricted to the Golgi region. After a single injection of formalin, the clear vesicles of the light cell dimmish and dark secretory granules varying in opacity increase in number. Transition from dark granules to clear vesicles is suggested. Three to five days after adrenalectomy, the light cells contain an abundance of moderately dense vesicles which are smaller than the larger more electron lucent vesicles of the normal light cells. The moderately dense vesicles are about 200 mμ in diameter and are extremely abundant filling the entire cytoplasm of the light cells 7 days after adrenalectomy. Bundles of unmyelinated nerve fibers are often observed in the pars intermedia, and a typical neuroglandular synapse was found in the pars intermedia of a sham-operated animal suggesting neural control of the secretion process of pars intermedia cells.