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Found: 5 467
Page 168 of 547-
Localization of microfilaments in prolactin cells of the rat anterior pituitary gland.
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Subsurface cisterns in paraventricular nuclei of the hypothalamus of the rat.
Structures identified as subsurface cisterns (SSC's) were found in neurons of the paraventricular nuclei of the rat hypothalamus. They appeared as cytoplasmic organelles consisting most often of stacks of parallel cisterns apposed to the neuronal plasmalemma. These SSC's were located in the interneurons of the parvocellular system, but not in neurosecretory cells and glial cells. SSC's were seen at zones of cytoplasm apposed to neuronal or glial cell processes, showing in some instances specific relationships with synaptic areas. The morphological features of these SSC's are described, and their possible functional significance is briefly discussed.
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Studies on the dense-core vesicles in the ontogenesis of locus coeruleus. II. Method of statistical reconstruction of the diameter distribution of the dense-core vesicles.
A statistical method for reconstruction of the distribution of the diameters of spheres according to their planar image obtained from ultrathin sections, is proposed. The method can be applied for casses when the thickness of the section is commensurate with the diameter of the spheric objects studied. The formulae worked out in the work are based on the assumption that the diameters of the spheres are with discrete distribution in geometric order. The method is elaborated in connection with the problem of the changes in the diameters of the dense-core vesicles in monoaminergic structures during development.
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The retrograde intraaxonal transport of horseradish peroxidase in the chick visual system: a light and electron microscopic study.
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Circadian rhythm in the number of granulated vesicles in the pinealocytes of mice. Effects of sympathectomy and melatonin treatment.
Adult, Charles River CD-1, male mice were housed in an environmental control chamber under strict conditions of controlled light (12D/12L) and temperature. The mice were sacrificed at various times throughout the twenty-four hour clock and their pineals prepared routinely for electron microscopy. The number of dense-cored or granulated vesicles present in the polar terminals of pinealocytes were quantitated in thin cross sections through pericapillary areas. A distinct circadian rhythm was observed in the number of granulated vesicles with a three- to four-fold difference between late photoperiod maximum and late dark period minimum. The rhythm was abolished by bilateral superior cervical ganglionectomy. These results are consistent with the hypothesis that the granulated vesicles are synthesized and stored in the pinealocytic cytoplasm during the photoperiod under the tropic influence of norepinephrine, and are released during the dark period when melatonin synthesis is greatest. Melatonin, administered as daily intraperitoneal doses of 50 microgram over a period of five days, was observed to increase markedly the number of pinealocytic granulated vesicles during the light period, but led during the dark period to a decrease in their numbers to levels below that of diluent-treated controls. It may be that melatonin stimulates the synthesis and/or release of granulated vesicles which represent the packaged form of a major secretory product.
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Optic tract cells projecting to the retina in the teleost, Pantodon buchholzi.
Horseradish peroxidase was employed to trace retino-fugal and retino-petal connections in the teleost fish, Pantodon buchholzi. Most of the reciprocal connections found were within the range also observed in previously studied species of teleosts. Of particular interest is the discovery of cells located within the optic tract and projecting to the retina. These neurons were investigated electron microscopically.
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On the intracerebral locus for androgenization of female rats.
Comparison of control and androgenized rats has revealed that many nerve terminals ending on arcuate nerve cells of rats treated neonatally with testosterone phenylpropionate show a decrease in dense-core vesicles, and an increase in the number of clear vesicles and of vesicles that exhibit various degrees of electron density. The same changes were observed in nerve terminals ending on preoptic neurons of rats androgenized neonatally. These findings are discussed in view of the intracerebral locus for androgenization of female rats.
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Intracellular transport and packaging of prolactin: a quantitative electron microscope autoradiographic study of mammotrophs dissociated from rat pituitaries.
Dispersed pituitary cells prepared from estrogen-treated female rats were subjected to pulse labeling with [3H]leucine (5 min) followed by a chase incubation (up to 3 h) in order to study intracellular transport of PRL in mammotrophs. Sites of synthesis, rates of transport, and sites of packaging and storage of PRL were determined by quantitative electron microscopic autoradiography. Results of grain counts show that label is initially (end of pulse) distributed randomly over the rough endoplasmic reticulum (ER), but rapidly (5--15 min of chase) moves to the stacked Golgi cisternae where concentration into secretion granules takes place. The label moves successively from small (Type I) immature granules (15--55 min of chase) to large (Types II and III) polymorphic granules (55--115 min) in the Golgi region, to rounded or ovoid mature (Type IV) granules (55--185 min) usually found in the peripheral cytoplasm, indicating that these types of granules represent successive stages in granule concentration and assembly. Analysis of the relative grain density (percentage of total grains/percentage of total area) confirmed that there was progressive concentration (up to 20--150 times) along the transport route with the concentration lowest in the ER, higher in the Golgi, and highest in immature and mature secretion granules. These data indicate that synthesis of PRL occurs randomly in the ER, transport to the Golgi occurs rapidly (within 5--10 min), and is completed rapidly (90% within 15--20 min), and concentration into granules and aggregation of small granules into larger forms also occurs rapidly (by 15--20 min), but goes on over a prolonged period of time (up to 3 h). Use of dispersed cells has allowed a more precise determination of the location and kinetics of steps in the intracellular processing of PRL than has been possible previously using other systems.
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The osmotically sensitive potassium and sodium compartments of synaptosomes.
1. Synaptosomes are pinched-off nerve terminals whose components can be liberated by osmotic ;shock'. A synaptosome preparation run through a Sephadex column that was eluted with an iso-osmotic solution retained its small ions, whereas when the column was eluted hypo-osmotically the small ions were lost. In this way the osmotically sensitive Na(+) and K(+) of synaptosomes were measured. Measurements of the lactate dehydrogenase occluded within the synaptosome were also made. The release of osmotically sensitive Na(+) and K(+) and occluded lactate dehydrogenase had similar characteristics with respect to the degree of osmotic ;shock' necessary and the action of lytic agents. 2. The distribution of osmotically sensitive Na(+), K(+) and occluded lactate dehydrogenase in the subfractions of a crude mitochondrial preparation was examined. The synaptosome fraction was the richest source of these constituents. 3. On standing at 5 degrees in iso-osmotic solution Na(+) and K(+) were lost from synaptosomes, whereas the amount of occluded lactate dehydrogenase remained stable, suggesting that the synaptosome membrane retained its integrity but that Na(+) and K(+) diffused through it out of the osmotically sensitive compartment. 4. The uptake of Na(+) and K(+) into the osmotically sensitive compartment was examined. At 5 degrees the rates of uptake of Na(+) and K(+) were found to be equal to the rates of loss of these ions when correction to a uniform concentration gradient had been made. K(+) travelled across the membrane slightly faster than Na(+), the rate of K(+) movement being about 1.0mumuequiv.cm.(-2)sec.(-1) under a concentration gradient of 0.1m. Active transport is not thought to contribute to the ion movements under the conditions used. 5. The amount of K(+) taken up into the osmotically sensitive compartment as a function of the external concentration was examined. Since the uncharged molecule d-[(14)C]galactose distributes across the synaptosome membrane similarly to K(+) there is not thought to be a synaptosomal trans-membrane potential. The volume of the osmotically sensitive compartment was measured by this method and found to agree with estimates of the synaptosomal volume made from morphological studies. In media of low ionic strength synaptosomes exhibit a Donnan effect. 6. It is concluded from these studies that the osmotically sensitive compartment represents the inner volume of the synaptosome, which is completely separated from the outside environment by a diffusion barrier having many of the general properties of a biological membrane.
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TrkB receptor ligands promote activity-dependent inhibitory synaptogenesis.
Organotypic cerebellar cultures derived from newborn mice were simultaneously exposed to activity-blocking agents and neurotrophins for 2 weeks. Activity-blocked explants treated with the TrkB receptor ligands BDNF and neurotrophin-4 (NT-4) developed a full complement of Purkinje cell inhibitory axosomatic synapses, as defined ultrastructurally, and displayed control spontaneous cortical discharge rates after recovery from activity blockade. Otherwise untreated activity-blocked cultures and activity-blocked cultures exposed to the TrkC receptor ligand NT-3 had reduced inhibitory synapse development and persistent cortical hyperactivity after recovery. The added TrkB receptor ligands did not induce axonal sprouting to account for increased inhibitory synaptogenesis. Addition of neurotrophins to untreated cerebellar cultures did not increase the complement of Purkinje cell axosomatic synapses. Exposure of cerebellar cultures to a combination of antibodies to BDNF and NT-4 resulted in reduced inhibitory synapse formation, similar to the effects of activity blockade, indicating the necessity for endogenous neurotrophins for development of the full complement of inhibitory synapses in the presence of neuronal activity. Application of antibodies to BDNF and NT-4 to cerebellar explants exposed to picrotoxin to increase neuronal activity prevented the hyperinnervation of Purkinje cell somata by inhibitory terminals characteristic of cultures exposed to picrotoxin alone. These results are consistent with the concept that TrkB receptor ligands promote inhibitory synaptogenesis. The ability of neurotrophins to substitute for neuronal activity in encouraging development of inhibitory synapses may have therapeutic implications.