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Studies with electron microscopic autoradiography of thyroxine 125 I in organotypic cultures of the CNS. II. Sites of cellular localization of thyroxine 125 I.
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[Differentiation and reactions of the neurohypophyseal pituicytes in conditions of whole-body irradiation].
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Ultrastructure of circulatory changes in the pars distalis of the hypophysis of hepatectomized mice.
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Synaptic vesicles of inhibitory and excitatory TERMINALS IN THE CEREBELLUM.
Populations of synaptic vesicles within cerebellar terminals considered excitatory or inhibitory on the basis of physiological evidence differ with respect to size and shape. Size rather than shape appears to be the main morphological difference between these populations. Elongation of vesicles is depenident on fixation with aldehyde fixatives, and both size and elongation change with age mainly during maturation.
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Electron microscopic study of the substantia nigra and the strio-nigral projection in the rat.
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Inverse behaviour of "synaptic" ribbon and spherule numbers in the pineal gland of male guinea-pigs exposed to continuous illumination.
There is increasing evidence that pineal "synaptic" ribbons are a heterogeneous population of organelles. In addition to "synaptic" ribbons (SR) sensu stricto, which consist of an electron-dense rod surrounded by electron-lucent vesicles, "synaptic" spherules (SS) exist, the electron-dense core of which is round and much wider than that of the SR. In the guinea-pig SR and SS numbers exhibit an inverse day/night rhythmicity. To gain more insight into the functional significance of SR and SS, guinea-pigs were exposed to continuous illumination for approximately 4 months (LL) and the respective structures in the pineal gland were quantitated under the electron microscope and compared with control animals kept under a lighting regimen of 12 h light and 12 h dark. It was found that SR numbers increase following LL whereas SS numbers decrease. The proximal, intermediate and distal parts of the dumbbell-shaped organ respond differently. The increase in SR numbers is significant in the distal and intermediate regions only, whereas the decrease in SS numbers is significant in the proximal and the intermediate regions only. Within each pineal region analyses of parenchymal subareas measuring 65 microns by 65 microns exhibit an inverse correlation of SR and SS numbers indicating that there are parenchymal domains in which either SR or SS predominate. Morphometric analyses of a number of pinealocytic parameters reveal minor differences between different pineal regions and that exposure to LL does not strikingly affect the pinealocyte perikarya. By contrast, the numbers of pinealocyte processes increase significantly after LL in the distal and intermediate, but not the proximal region of the pineal gland.(ABSTRACT TRUNCATED AT 250 WORDS)
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Morphologic evidence of photoreceptor differentiation of pinealocytes in the neonatal rat.
The pineal body and the retina of the neonatal Sprague-Dawley rat were studied by light and electron microscopy, and the morphologic differentiation of the parenchymal cells of the pineal body was compared with that of the developing photoreceptor cells of the retina. Between the ages of 4 and 12 days after birth, some of the developing pinealocytes were observed to become elongated and polarized, with their nuclei located at one pole. "Synaptic" ribbons were observed within the cell body. At the opposite pole the cells developed elongated cell processes that initially contained microtubules and ribosomes. These cell processes projected into luminal spaces and were attached by structures resembling zonulae adherentes to the adjacent cells. Extending from the tips of the cell processes, cilia with a 9 + 0 arrangement were observed. Lamellated and vesicular membranes were noted at the tips of the cilia. Such morphologic differentiation, however, could be observed only in rats younger than 17 days. Comparison of the morphologic features of the neonatal pinealocytes with those of the developing retinal photoreceptor cells showed much similarity. It is suggested that the pinealocytes of the neonatal rat undergo "photoreceptor-like" differentiation during a transient neonatal period. Such morphologic differentiation may provide an explanation for light-induced biochemical changes described in neonatal rats whose eyes had been enucleated.
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The formation and maturation of synapses in the visual cortex of the rat. I. Qualitative analysis.
Synapse formation and maturation were examined in the visual cortex of albino rats from birth to maturity. During the first few days of postnatal life, synapses were sparsely scattered in the subplate zone and in layer I. They appeared immature as judged by the irregular shapes of the presynaptic and postsynaptic profiles, the relatively poorly defined membrane specializations and the presence of only a few synaptic vesicles in the presynaptic structures. As the neuropil matured, synapses were observed throughout the cortex, showing increased thickening of the membrane specializations and more vesicles. However, it was not until the end of the fourth postnatal week that they appeared qualitatively indistinguishable from synapses identified in the adult material. A feature characteristic of the developing visual cortex was the presence of vacant membrane specializations that resembled type I postsynaptic densities. These specializations, which were located either opposite extracellular space or opposite another neuronal process, were only evident during the initial stages of synaptogenesis and their frequency decreased as the number of synapses increased. In addition, transitional forms between these densities and true type I synapses were identified during the first two postnatal weeks. Structures that resembled vacant postsynaptic densities typical of type II synapses were not observed. The earliest identified forms of type II synaptic contacts identified consisted of two profiles that exhibited symmetrical membrane specializations and cleft material. Based on these observations, a scheme has been proposed for the formation of type I and type II synapses in the visual cortex of the rat.
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Scanning electron microscopical investigation of the larval development and the morphological differentiation of the paraventricular organ (PVO) of the South African clawed toad Xenopus laevis Daudin.
The development and the differentiation of the surface of the paraventricular organ (PVO) in tadpoles of the South African Clawed Toad Xenopus laevis Daudin from stages 46 to 66 and one adult animal was studied by means of light microscopy, scanning and transmission electron microscopy. At the light microscopical level, the PVO is visible from stage 46 on. From stage 48 on the organ is divided into two parts, a narrow rostral one and a more flattened and broad caudal one. From stage 58 on the rostral part of the PVO lies in the sulcus organi paraventricularis similar to the caudal part which lies in the sulcus lateralis infundibuli. The position of the PVO on both sides of the third ventricle is unchanged over all stages studied. The growth of the organ is finished at stage 65. The structure of the surface of the rostral and the caudal part of the organ differs up to the stage of 57. From stage 58 on the surfaces of the two parts of the PVO assimilate by developing a network of fibers which is orientated transversally. The different cell types of the PVO which can be seen at the level of transmission electron microscopy are fully developed at stage 57 but their position does not correspond to that of the adult animal. There is no difference between the right and left half of the organ in all groups studied.
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Changes induced by 6-hydroxydopamine in the paraventricular nucleus. A correlated fluorescence microscopic/electron microscopic evaluation.
Remodelling of catecholaminergic (CA) fibers after cerebral intraventricular 6-hydroxydopamine (6-OH-DA) administration was evaluated quantitatively in the paraventricular nucleus ( PAR) of young adult rats, using fluorescence microscopy (FM) and electron microscopy (EM). Fluorescent CA varicosities and CA boutons (marked with 5-OH-DA) were counted after survival periods of 4, 21, 56 or 180 days. Four days after 6-OH-DA treatment, the number of fluorescent varicosities dropped to 45% of control numbers but was restored to 79% of control values by 180 days. In the EM study, marked boutons had dropped more dramatically: to 12% of control numbers, after 4 days and 54% by 180 days post-neurotoxin. These data provide strong evidence that substantial but incomplete restoration of CA terminals occurred in PAR. It is of interest that, in all survival intervals, percentage reductions in numbers of CA terminals were more extreme when EM was used for quantification. Nevertheless, the trends indicating partial restoration of terminal numbers with time were parallel in the FM and EM studies. Structures identified as CA growth cones in PAR contained a feltwork of fine filaments together with mitochondria, granular vesicles (often with electron-dense cores marked by the 5-OH-DA label), vacuoles and smooth-surfaced reticulum. The presence of growth cones, some of which persisted 11 months after neurotoxin administration, further supports the inference that a regenerative response of CA elements was evoked in PAR by the 6-OH-DA treatment.