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Page 188 of 547-
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.
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Fine structure of ependymal cysts in and around the area postrema of the rat.
Peculiar cells forming cysts were observed in the area postrema and sometimes also in the choroid plexus and the tela chorioidea near the area postrema, and were studied in detail by electron microscopy. The cytological features of the cyst cell and its junctional relationship to neighboring cells imply that cyst cells are derived from ependymal and choroid epithelial cells. The cyst cells usually contact directly the perivascular spaces of postremal, choroidal or pial capillaries, where the cytoplasm is often considerably attenuated. The cystic lumen is commonly filled with a flocculent material. The limiting membrane of the cystic lumen, which frequently bears cilia and microvilli, has the same thickness as the surface cell membrane. In many cases the cyst is surrounded by the cytoplasm of a single cell. In some cases, however, two cells participating in the formation of the cyst, although one is only a slender process and joined by a zonula occludens with the main cyst cell. Horseradish peroxidase (HRP) injected into the cerebrospinal fluid (CSF) space failed to enter the cystic lumen. A possible significance of the cyst in relation to the CSF and blood circulation was considered.
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Responses of pineal photoreceptors in the brook and rainbow trout.
Electron microscopy of the pineal receptor cells in light- and dark-adapted brook trout, Salvelinus fontinalis and the rainbow trout, Salmo gairdneri, revealed no significant differences in the tubular and filamentous elements of the inner segment, neck and supranuclear regions. However, changes in synaptic relations between the photoreceptor and nerve cell were induced by light and darkness. In the light-adapted state, the synaptic relationship between axon terminals and photoreceptor basal processes predominates, while in darkness the synapses between photoreceptor basal processes and ganglion cell dendrites are more prominent. Further, in darkness, the photoreceptor basal processes show a number of synaptic vesicles and synaptic ribbons. These findings suggest that the sensory function of the fish pineal is enhanced during darkness but inhibited by light, and that the synaptic relationships are involved in the control of sensory activity in the pineal photoreceptor and ganglion cells. These results corroborate those of electrophysiological studies in that the maximal spontaneous discharge frequency of the ganglion cells occurs in the dark, and it also shows a burst when light is removed. The "typical" chemical synapse between the axon terminal and the photoreceptor basal process in light seems to function as an inhibitor.
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Ultrastructural investigation of ACTH immunoreactivity in arcuate and supraoptic nuclei of the rat.
Fine structural localization of an ACTH-like substance was obtained in neurons of the rat arcuate nucleus using immuno-electron microscopy, whereas it could not be confirmed that ACTH-containing cell bodies are present in the supraoptic nucleus. The immunoreactive cells of the arcuate nucleus appeared to be more numerous than the unreactive neurons. Immunostaining was carried out before embedding in resin. Empty vesicles of irregular shape were found in dendrites of immunoreactive arcuate neurons, but their significance and nature remain enigmatic. The reaction product was distributed uniformly throughout the cytoplasm of the ACTH-positive cells, except that the mitochondria, rough endoplasmic reticulum and Golgi vesicles and cisternae were devoid of PAP molecules. This distribution differed from the localization reported in ACTH-secreting cells of the rat anterior pituitary, where the reaction product was found in the rough endoplasmic reticulum and Golgi complex as well as in secretory granules.
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[Ultrastructural organization of the mammalian pineal body during postnatal ontogenesis].
Ultrastructural organization of the components composing the mammal pineal gland is analyzed on the basis of literature data and personal observations. Variations in the form, size and ultrastructural organization of the cellular elements in the pineal gland--pinealocytes, interstitial and glial cells--are discussed. The problem of dark and light pinealocytes is considered as a part of a general biological problem on the presence of dark and light cells as a reflection of the law on "intermittent activity of functional structures". An attention is paid to the organization of the microcirculatory bed and pericapillary space to the peculiarities of the secretory process in the organ. Dynamic changes in the cytologic organization of pinealocytes and other components of the organ in the postnatal ontogenesis are presented in detales.
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Functional morphology of the pineal gland in young chickens.
One and two-month-old chickens were killed at mid light and mid dark under the experimental photoperiod (LD 12: 12). The pineal glands of the young chickens are composed of parenchymal cells and large follicles, presenting a tubulofollicular arrangement. The sensory-like pinealocytes are pear-shaped and have a cilium with 9 + 0 axial configuration projecting into the lumen. Their cytoplasm has cell organelles, small granulated vesicles about 100 nm in diameter and synaptic ribbons. The concentric lamellar complexes like myelin sheaths are frequently observed in the follicular lumen. The secretory-like supporting cells have irregular-shaped microvilli and some granulated vesicles about 200 nm in diameter in the vicinity of the apical surfaces. Occasionally, a few nerve cells are found in the pineal parenchyma. It was found that the sensory-like pinealocytes of the young chickens have many mitochondria, well-developed Golgi complexes and large lysosomes in solid type in the light period, whereas they have a few cell organelles and somewhat smaller rod-like lysosomes with some vacuoles in the dark period. On the other hand, the sensory-like pinealocytes have more synaptic ribbons in the dark period than in the light period.
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Ultrastructure of the pineal gland of the fox.
The ultrastructure of the pineal gland of the fox was examined and compared with that of other mammals. The pineal gland of the fox is composed of two different populations of pinealocytes (I and II). The pinealocytes I were distributed homogeneously throughout the parenchyma, while pinealocytes II were located generally near blood vessels. A Golgi apparatus, granular endoplasmic reticulum, mitochondria, lysosomes, centrioles, and cilia were present in both cell populations. A characteristic feature of pinealocytes I was the presence of dense-core vesicles, presumably of Golgi origin; whereas glycogen deposits and pigment granules were common features of pinealocytes II. In addition to the pinealocytes, the parenchyma contained fibrous astrocytes. The capillaries of the pineal gland of the fox consisted of a nonfenestrated endothelium. Numerous never fibers, presumably adrenergic, were observed throughout the parenchyma.
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[Epiphyseal epithelium of pigeons under natural conditions and in vitro. Ultrastructure and histochemical evidence of hydroxyindoles in the receptor line cells].
An electron microscopic study of the pineal organ of the pigeon was conducted under natural conditions and after short in vitro incubation or culture. Two cell types could be identified in the epithelium: receptor line cells (RLC) and interstitial cells of the ependymal type. Good preservation of the cells' fine structure could be observed whatever the different incubation times used. RLC display cytological features reflecting the existence of a protein secretory process and of regression of the photoreceptor structures (secretory rudimentary photoreceptor cells). The use of the Falck-Hillarp technique together with specific inhibition of tryptophan hydroxylase enabled to demonstration of the storage of 5-hydroxytryptophan/serotonin in RLC. In contrast with other birds, no catecholamine containing nerve fibers could be observed by histofluorescence.
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A light and electron microscopic study of the pineal body of the nutria (Myocastor coypus).
Light and electron microscopic studies of the nutria (Myocastor coypus) pineal gland revealed pinealocytes interspersed among glial, vascular, and neuronal elements. Each pinealocyte possessed a single process that terminated within the parenchyma near the perivascular region. The eccentrically located nucleus in these cells contained euchromatic chromatin, a prominent nucleolus, and a highly infolded nuclear envelope. The cytoplasm was rich in mitochondria, Golgi complexes, and glycogen particles. The smooth endoplasmic reticulum (SER) was better developed thant he rough endoplasmic reticulum (RER) and polyribosomes were not abundant. Long profiles of subsurface cisterns constituted prominent cytoplasmic features, and these were most conspicuous in the regions of soma-somatic apposition. The bulbous endings of the pinealocyte processes were filled with clear, round, secretory vesicles. Dense-cored vesicles were rarely observed. Glia reminiscent of protoplasmic astrocytes displayed cytoplasmic processes that enveloped blood vessels, invested the pineal periphery, and intervened among the pinealocytes. They thus seemed to form a barrier between the meningeal capsule and vascular space on the one hand and the parenchyma on the other.