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1.
Glutamate is the main excitatory amino acid, but its presence in the extracellular milieu has deleterious consequences. It
may induce excitotoxicity and also compete with cystine for the use of the cystine–glutamate exchanger, blocking glutathione
neosynthesis and inducing an oxidative stress-induced cell death. Both mechanisms are critical in the brain where up to 20%
of total body oxygen consumption occurs. In normal conditions, the astrocytes ensure that extracellular concentration of glutamate
is kept in the micromolar range, thanks to their coexpression of high-affinity glutamate transporters (EAATs) and glutamine
synthetase (GS). Their protective function is nevertheless sensitive to situations such as oxidative stress or inflammatory
processes. On the other hand, macrophages and microglia do not express EAATs and GS in physiological conditions and are the
principal effector cells of brain inflammation. Since the late 1990s, a number of studies have now shown that both microglia
and macrophages display inducible EAAT and GS expression, but the precise significance of this still remains poorly understood.
Brain macrophages and microglia are sister cells but yet display differences. Both are highly sensitive to their microenvironment
and can perform a variety of functions that may oppose each other. However, in the very particular environment of the healthy
brain, they are maintained in a repressed state. The aim of this review is to present the current state of knowledge on brain
macrophages and microglial cells activation, in order to help clarify their role in the regulation of glutamate under pathological
conditions as well as its outcome. 相似文献
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Criteria for the cytologic diagnosis of microinvasive adenocarcinoma of the cervix have not been previously established. Such cytologic criteria were evolved through the detailed analysis of cervical smears from 40 histologically confirmed cases. The cellular features of cervical adenocarcinoma in situ (AIS) were always associated with microinvasion. Syncytia of glandular cells, small cells in very crowded sheets and papillary groupings of cells, when seen in conjunction with AIS, were suggestive of microinvasion. Dissociation of cells was common. Nuclear pleomorphism with an irregular chromatin pattern and inconspicuous-to-prominent nucleoli was frequently present. In some cases, a tumor diathesis was seen in the smear background. Using these criteria, our predictive accuracy for diagnosing microinvasive cervical adenocarcinoma is improving steadily and now approaches 50%. Ongoing investigation of these cases must include a diagnostic come biopsy to further improve the predictive accuracy for this lesion. 相似文献
5.
Dr. Vladimir K. Chetverukhin Michael A. Belenky Audrey L. Polenov 《Cell and tissue research》1986,243(3):649-654
Summary The median eminence (ME) of the adult frog, Rana temporaria, was studied by means of electron microscopy including quantitative electron-microscopic autoradiography. In frogs captured in May and June numerous peptidergic neurosecretory fibres extending via the internal zone to the pars nervosa display large swellings containing few granules, mitochondria, neurotubules and cisternae of the smooth endoplasmic reticulum. In addition, few secretory globules up to 1.5 m in diameter occur in these varicosities. In animals collected during the autumn period many of these neurosecretory swellings filled with neurosecretory granules and polymorphic inclusions resemble Herring bodies. Three types of granule-containing neurosecretory fibres were observed in the external zone (EZ) of the ME of adult R. temporaria. Peptidergic A1- and A2-type fibres are characterized by granules 150–220 nm and 100–160 nm in diameter, respectively. Monoaminergic fibres of type B with granules approximately 100 nm in diameter represent 50% of all neurosecretory elements in the EZ of the frog ME; 12% of the total number of granule-bearing axons in the EZ actively taking up radiolabelled 5-hydroxytryptophan are thought to be serotoninergic terminals. Neurosecretory terminals of all types and glial vascular endfeet establish direct contacts with the perivascular space of the primary portal capillaries. Some neurosecretory terminals are separated from the lumen of the third ventricle by a thin cytoplasmic lamella of tanycytes. The possible physiological significance of this structural pattern is discussed. 相似文献
6.
Serial sections of the rectal valve in Aphelenchoides blastophthorus Franklin and the oesophago-intestinal valve in Thornenema wickeni Yeates were examined electron microscopically. Each valve when closed appears as a convoluted path of closely apposed (10 nm) pairs of three-layered cell membranes. Both valves serve to stop intestinal leakage, open briefly and rapidly by forcible dilatation and are closed by pressure from surrounding tissues, helped perhaps by intermolecular forces. 相似文献
7.
1. As early as 1hr. after the intraperitoneal administration of tannic acid to rats, it could be demonstrated in the liver. At 3hr. the nuclear fraction contained the largest amount of tannic acid. 2. Nuclear RNA synthesis was inhibited in vivo 2hr. after the administration of tannic acid. Induction by cortisol of tryptophan pyrrolase was 90% inhibited at 24hr. 3. Incorporation of [1-(14)C]leucine into protein by liver slices from treated rats was decreased by 50% after 24hr. Its incorporation into postmitochondrial supernatant from treated animals was not inhibited. Incorporation into slices and postmitochondrial supernatants were inhibited in vitro by tannic acid. 4. The sequence of events: concentration of tannic acid in nuclei, inhibition of nuclear RNA synthesis, inhibition of protein synthesis and production of necrosis, is discussed. 相似文献
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Properties of the transport systems for amino acids in Pseudomonas aeruginosa were investigated. Exogenous (14)C-labeled amino acids were shown to equilibrate with the internal native amino acid pool prior to incorporation into protein. When added at low external concentrations, the majority of the amino acids examined entered the protein of the cell unaltered. The rates of amino acid transport, established at low concentrations with 18 commonly occurring amino acids, varied as much as 40-fold. The transport process became saturated at high external amino acid concentrations, was temperature-sensitive, and was inhibited by sodium azide and iodoacetamide. Intracellular to extracellular amino acid ratios of 100- to 300-fold were maintained during exponential growth of the population in a glucose minimal medium. When the medium became depleted of glucose, neither extracellular nor intracellular amino acids could be detected. 相似文献
10.
The accumulation and behavior of various amino acids in the pool of Pseudomonas aeruginosa (ATCC 9027) were investigated. Patterns of pool formation and maintenance varied with different amino acids tested and were dependent, to a considerable extent, upon the ability of the organism to catabolize the particular amino acid. The establishment of steady-state amino acid pool levels depended upon the activity of the amino acid permease involved and upon the rate of protein synthesis. The presence of a relatively large specific amino acid pool did not affect the formation of a pool of a structurally different amino acid, and a preformed steady-state pool was not displaced by structurally unrelated amino acids. Steady-state amino acid pools decreased rapidly in the presence of inhibitors of energy metabolism and at 0 C. Steady-state internal amino acid pools were found to be in equilibrium with the corresponding external amino acid, present at low levels. A multiplicity of proline pools was demonstrated. 相似文献