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Embryonic development and secretory differentiation in the pars tuberalis of the mouse hypophysis.
The pars tuberalis (PT) of the mouse, like that of other mammals, consists mainly of glandular cells rich in glycogen and peculiar to this lobe. In the mouse, the glandular cells are characterized by large, dense secretory vesicles (up to 300 nm in diameter), the abundance of which indicates a marked secretory activity. The PT develops from a distinct antero-ventral area of Rathke's pouch. The border between the anlagen of the PT and the pars distalis is formed by Atwell's recessus which represents the access for the vessels afferent to the pars distalis. The pedicle of Rathke's pouch is incorporated into the PT anlage, thus contributing to its formation. The entire PT anlage is characterized by glycogen accumulation from the commencement of its formation and persisting in the adult tuberal lobe. Secretory differentiation of the glandular cells of the PT occurs at day 12 of gestation, preceding that of all other adenohypophysial cell types. The secretory features of these cells (development of ergastoplasm and Golgi apparatus, abundance of dense secretory vesicles) appear at an early stage of the enbryonic life (14 days) comparable to those of mature cells. These results confirm earlier observations in the foetal rat where hypophysial secretion also begins in the PT. The existence of peculiar glandular cells speaks in favour of a specific but still unknown function of the PT during foetal and adult life.
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[Modifications of the adenohypophysis ultrastructures in rodents after total or segmentary irradiation with radiocobalt].
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Fine structure of the mouse anterior pituitary maintained in a short-term incubation system.
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An electron microscopic study of neurons during postnatal development of the rat cerebral cortex.
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Ultrastructural morphology of nontumorous prolactin cells in human pituitaries harboring prolactin-producing adenoma.
To study the effect of hyperprolactinemia on nontumorous prolactin cells, their morphology was investigated by transmission electron microscopy and morphometry in the nontumorous portion of seven human pituitaries containing prolactin-producing adenoma. For cell identification, immunoelectron microscopy was applied using the immunogold labelling method. In five cases, nontumorous prolactin cells demonstrated features of inactivity, whereas in two cases they showed morphological features of active hormone secretion. Our findings are consistent with the view that prolactin regulates its own release from prolactin cells in the anterior pituitary via the short loop negative feedback mechanism. Hyperprolactinemia presumably activates the short loop feedback mechanism resulting in inhibition of nontumorous prolactin cell. However, in two cases, hyperactivity of nontumorous prolactin cells was observed suggesting a dysfunction of the feedback mechanism.
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Recycling of plasmalemma in chick tectal growth cones.
Growth cones from freeze-substituted intact chick optic tectum were analyzed in serial reconstructions of thin-section electron micrographs in order to determine which internal organelles might contribute membrane for plasmalemmal expansion. These growth cones contain numerous stacked and single lumenless membrane-limited disks; the stacks are arrays of single disks interconnected, and possibly organized, by intervening electron-dense cross-links. The single and stacked disks together account for 80% of the total intracellular membrane in the growth cones. Single disks frequently lie close to and occasionally contact the filopodial plasmalemma; regularly spaced electron-dense cross-links also occur at these juxtapositions between single disks and the plasmalemma. Some of the juxtaposed disk membranes contact the growth cone plasmalemma, and images of some of these contacts appear to indicate fusion of the disk membrane with the plasmalemma. When excised optic tecta are exposed to cationized ferritin for various times, ferritin micelles appear sequentially in coated pits, coated vesicles, smooth vesicles, vacuoles, and then in stacked and single disks, including some of those contacting the plasmalemma. Because the cytoplasmic disks filled only at the longest times after exposure to ferritin, the membrane continuities between the disks and the plasmalemma are thought to be indicative of exocytosis rather than endocytosis. We propose, therefore, that components of the plasma membrane are recycled through the stacks of lumenless disks in the chick tectal growth cones; the disks therefore represent a pool of internal membrane waiting to be added to the growth cone plasmalemma that could be used for filopodial extension or neuritic extension.
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Ultrastructure of neuronal cell bodies in the medial cortex of Lacerta galloti.
According to ultrastructure, size, and location within the medial cortex of Lacerta galloti, seven basic kinds of neuronal somata are described in this study. In the outer plexiform layer of the medial cortex only a few somata can be detected. There, moreover some oligodendroglia and microglia cells a few neuronal somata showing conspicuous nuclear invaginations and spongious chromatin (A) can be seen. The granular layer of the medial cortex is formed by up to seven strata of tightly packed neuronal somata in a pattern which resembles that of the profound stratum of the fascia dentata of the mammalian hippocampus. In this layer four neuronal somata can be seen: somata with nuclear invaginations, generally located aside the outer plexiform layer (in the upper stratum) (B); very abundant little neuronal somata with chromatin clumps (C); vertically fusiform shaped neuronal somata with numerous polyribosomes (D); and big neuronal somata with spongious chromatin (E). In the inner plexiform layer, there are a variety of scarce neuronal somata intermingled with ependymal sprouts and fiber tracts running from other cortical areas; two main types are described: big horizontal somata which are almost covered by axonic endings making synapses (F) and somata with dense cytoplasmic matrix and some small nuclear invaginations (G). Location of soma, frequency, and biometric data of them have been used to make a comparison with neuronal types of the medial cortex of Lacerta galloti defined by Golgi impregnations.
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Oestrogen-induced renal carcinogenesis in the hamster: ultrastructural and hormonal studies of the pars intermedia before and after withdrawal of oestrogen.
Long-term oestrogen treatment of male hamster induced renal carcinoma and pituitary enlargement due to hypertrophic and hyperplastic change in the pars intermedia. The latter effect was accompanied by ultrastructural abnormalities in pars intermedia cells and elevation of serum MSH concentration. Oestrogen treatment was stopped after 36 weeks and animals were killed at intervals from 8 to 36 weeks after oestrogen withdrawal. Nearly complete tumour regression occurred during the 36 weeks following cessation of oestrogen and by 28...36 weeks the pars intermedia cells regained normal ultrastructural appearance. However, pituitary enlargement and elevated serum MSH levels persisted throughout the post oestrogen recovery period.
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Effect of acute and repeated immobilization stress on the ultrastructure of neurons of the rat hypothalamic ventromedial nucleus.
The fine structure of neuronal somata of the central subdivision of the hypothalamic ventromedial nucleus (VMN) was studied in acutely and repeatedly immobilized rats. Four categories of neurons were distinguished in control animals based mainly on ultrastructural appearance of rough endoplasmic reticulum (RER): 1. the neurons with longer segments of RER distributed throughout the cytoplasm which, at the same time, clearly dominated in this area, 2. the neurons with RER arranged into several groups located at different sites of the soma, 3. the neurons with only a few of short fragments of RER scattered in the cytoplasm, and 4. the neurons with an extensive parallel system of RER in the cell periphery. After acute stress only three categories were found (the 4th category being absent), whereby the number of the 2nd category of neurons evidently increased. Following repeated immobilization a further category of neurons occurred, which represented 9...11% of the neuronal population and showed a wide variety of RER modifications including whorls. The presented morphological evidence suggest that the central subdivision of rat VMN might be involved in neuroendocrine processes activated during increased pituitary-adrenocortical response under immobilization stress.
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Ependymal astrocytes in the frog cerebellum.
We have examined the ependymal astrocytes of the frog cerebellar cortex in thin sections and freeze-fracture replicas. The somata border the fourth ventricle and give rise to basal processes whose daughter branches cross the molecular layer and terminate as subpial endfeet. Irregular lamellar appendages arise from the basal processes and their branches. In the molecular layer the appendages selectively ensheath apposed parallel fiber boutons and Purkinje cell dendritic spines. Other appendages ramify throughout the neuropil, some contributing to extensive pericapillary sheaths. Freeze-fractured ependymal astrocyte plasma membrane consistently has a greater concentration of intramembranous particles (IMPs) and IMPs of larger mean size than neuronal plasma membrane in the same replicas. Like the astrocytes of the mammalian central nervous system, frog ependymal astrocytes form numerous gap junctions with each other. However, orthogonal arrays of IMPs ("assemblies") were not observed. Ependymal cells in the frog cerebellum combine the morphology, and probably the functions, of both ependymal cells and astrocytes.