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At least 595 records · Page 33Linked to original sources
PubMed1991

Vacuoles and vesicles in the rat junctional epithelium: a study with serial ultrathin sections.

To investigate whether the electron-lucent structures resembling vesicles and vacuoles in the rat molar junctional epithelium (JE) are in fact intracellular or extracellular, a study using serial ultrathin sections was carried out. In one series of experiments, the animals were not treated before the tissues were conventionally fixed; in another, anesthetized animals were administered horseradish peroxidase 20 min before the tissues were fixed. A large number of electron-lucent structures resembling vesicles and vacuoles were detected in both the peripheral and central cytoplasm of the JE localized at enamel and connective tissue sites. These were 70 to 800 nm in diameter and had a lucency similar to that of the extracellular space in untreated specimens fixed with conventional fixative. Serial ultrathin sectioning revealed that the electron-lucent structures gradually became part of the extracellular space in the following sections. There were also found in the middle portion of the cytoplasm in specimens pretreated with horseradish peroxidase. Numerous vacuole-like structures containing peroxidase-positive materials were found to be contiguous with the extracellular space. A small number of vesicles, also containing peroxidase-positive materials, did not appear in the previous or following sections. These results indicate that almost all electron-lucent structures resembling vesicles and vacuoles in the JE are located at the end of a long infolding, and are still in contact with the extracellular space.

Animals↗
PubMed1992

Osmolality and nonsynaptic epileptiform bursts in rat CA1 and dentate gyrus.

In several clinical situations, such as hyposmolar states and hypoxia-ischemia, reductions in the size of the extracellular space are associated with increased seizure susceptibility. Nonsynaptic interactions provide a likely means of mediating the effect of extracellular space on seizure susceptibility. Synchronous bursting of CA1 hippocampal neurons occurs via nonsynaptic mechanisms in solutions containing very low [Ca2+] and excitatory amino acid antagonists. We tested the hypothesis that lowering the osmolality of the extracellular medium could induce nonsynaptic bursting in the dentate gyrus, even though it is normally resistant to this treatment. Extracellular field potentials were recorded in the dentate gyrus and CA1 area of rat hippocampal slices. In the low-[Ca2+] solution with normal osmolality, bursts of population spikes were recorded from the dentate gyrus in only 7% of the slices, but solutions with decreased osmolality induced bursting in 63%. Corresponding values for the CA1 area were 60 and 73%, respectively. Mannitol, which reversed the hyposmolar state, abolished bursting in both regions. This study demonstrates that reducing the size of the extracellular space by lowering extracellular osmolality can transform a seizure-resistant area into one that exhibits robust epileptiform activity.

Action Potentials↗
PubMed1982

[Study of the brain capillaries and their surrounding tissues at various stages of development in mice (author's transl)].

The development of the brain capillaries and their surrounding tissues from fetuses to adult mice were studied ultrastructurally. 1. The intracerebral blood vessels on day 10 of gestation showed sinusoid characteristics. 2. The interendothelial junctional complex on day 15 of gestation showed the zonula occludens like in the case of adult. 3. The anlage of pericyte was observed already on day 15 of gestation. 4. The endothelium decreased prominently in its complexity and thickness till the 8th day of age. 5. Sprouting of the intracerebral capillaries were observed on the 8th day of age. 6. The BM-material was observed continuously near the corresponding plasma membranes of the endothelium on the first day of age. The perivascular clefts surrounding the blood vessels were partly open and had direct contact with the extracellular space till 8 days of age. 7. The large extracellular space which was observed from the fetuses to the first day of age became remarkably narrower after 4 days and it was observed that there were interrelations between the development of neuropils and narrowing of the extracellular space. This study shows that several capillaries with different permeabilities coexist over a long period of time in the cereberum. The latter seems to play an important role in the formation of the blood-brain barrier.

Animals↗
PubMed2000

Directed spatial potassium redistribution in rat neocortex.

The functional role of the glial network as a draining system for extracellular potassium (spatial buffer) was investigated in rat neocortical brain slices. After electrical stimulation, extracellular space volume decreased in the middle cortical layers and increased in the upper cortical layers, confirming predictions for a spatial buffer. The widening of extracellular space was associated with an increase in extracellular potassium. The data suggested a delayed redistribution of potassium from middle to superficial cortical layers. Interruption of gap junctions abolished the widening of extracellular space. The data show that a multicellular directed network connected by gap junctions participates in maintaining potassium homeostasis in brain.

Animals↗
PubMed1985

Diffusion coefficients of neurotransmitters and their metabolites in brain extracellular fluid space.

Diffusion coefficients of catecholamine neurotransmitters, their metabolites and related species was measured in brain extracellular fluid using in vivo voltammetric techniques. Nanoliter volumes of the species were pressure-ejected into the rat caudate nucleus and their concentration profiles were determined at nearby voltammetric detector electrodes. Thorough testing was carried out to show that the present methodology gave results which agreed with brain diffusion coefficients measured previously by ion-selective microelectrode techniques. All of the species which are anionic at pH 7.4 have brain diffusion coefficients about one-third of their solution counterparts in accord with earlier studies of diffusion in tortuous media. However, the brain diffusion coefficients of all the cation species are about three-times slower than those of the anions. This phenomenon is believed to be caused by ion binding with the polyanionic glycosaminoglycans and related species in brain tissue. In vitro model experiments lend support to this interpretation. This new information on biogenic amines and their metabolites provides meaningful predictions of the spatio-temporal concentration distribution of these species in the extracellular fluid.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1994

Morphology of non-vascular intracerebral fluid spaces.

In the electron microscope the value for the extracellular space (ECS) in the mammalian CNS was suggested of several percent to about one third dependent on the method how it was evaluated. Since von Harreveld introduced 1965 cryofixation to estimate the extension of the ECS, the method has been never applied in brain edema research. We carried out improved low temperature methods to measure the extracellular space of the mammalian CNS in physiological conditions. Small samples of brain tissue were cryofixed by slam freezing on a precooled metal mirror and substituted with ethanol at -95 degrees C over 17 hours. The embedding procedure was carried out at -22 degrees C with LR-White under UV-irradiation. ECS was measured computer assisted with Bioquant Software. The values for the ECS of the cryofixed normal rat brain were more than twice compared to the usual transmission electron microscopy (16.3% to 7.4%, p < 0.01) and close to those estimated by von Harreveld (18.1-25.5%, 1965). It was interesting that the data obtained in cryofixed normal rat brain correspond to the extension measured in rat brain with irradiation edema, which was conventionally treated for EM. Greater variance of ECS in cryofixed brain (16.3% +/- 3.4) demonstrate that it is far more variable than expected. This data correspond closely to the in vivo ECS. The morphological evaluation of brain edema should be revised under this premise.

Animals↗
PubMed1983

Diffusion in the slice microenvironment and implications for physiological studies.

The brain cell microenvironment includes the extracellular space surrounding the cell together with the cellular elements that define the space. The dense packing of cells in the mammalian nervous system ensures that the extracellular space is narrow but highly complex in geometry. Recent studies with ion-selective micropipettes have revealed that the cerebellar slice can support changes in [K+]o that resemble those seen in the intact preparation. In the slice, [K+]o responses of individual cells can even be resolved. Studies with iontophoretic techniques and quantitative analysis in the slice have shown that the extracellular space has diffusion properties, characterized by a volume fraction and a tortuosity, that are very similar to those seen in the intact animal. These data confirm that the microenvironment in the slice is comparable to that in the intact animal. The diffusion parameters can be used to make predictions about the time necessary for substances to diffuse into slices under various conditions. Such estimates, together with other studies, indicate that it is probably inadvisable to use slices with thicknesses in excess of 300--400 micrometers, and that the bathing conditions can be critical in maintaining slice viability.

Animals↗
PubMed1987

Extra-axonal environment and fibre directionality in the early development of the chick embryo optic chiasm: a light and scanning electron microscopic study.

The events that occur during the early development of the optic chiasm of the chick embryo have been studied by light and scanning electron microscopy. In developmental stages previous to the arrival of the first optic fibres in the floor of the diencephalon, as well as during the arrival of the leading fibres, extracellular spaces can be seen in the diencephalon ventral wall. These spaces are defined by external cell prolongations which end in a foot-shaped formation. During stages 25 and 26 a prechiasmic degenerative centre appears in the area immediately rostral to the early chiasm, leading to a notable degree of disorganization in the diencephalon wall. This centre appears to be related to the reorganization of the system of external cell processes and extracellular spaces which become progressively more irregularly distributed, coinciding with the arrival of the first optic fibre fascicles to the midline of the floor of the diencephalon. The optic fibre fascicles change their latero-medial directionality in the medial-most regions of the ventral diencephalon, where their course becomes rostrocaudal. This reorientation of the optic fibres seems to be mediated by primitive glial cells which first appear in the ventrorostral region of the early chiasm (previously occupied by the system of external cell processes and extracellular spaces) in stage 26, increasing in number from this stage on. The morphology of the primitive glial cells is laminar in nature and the cells are seen to be densely packed together with no large extracellular spaces between them.

Animals↗
PubMed1979

The extracellular compartments of frog skeletal muscle.

1. Detailed studies of solute efflux from frog sartorius muscle and single muscle fibres were carried out in order to characterize a 'special region' (Harris, 1963) in the extracellular space of muscle and determine whether this 'special region' is the sarcoplasmic reticulum. 2. The efflux of radioactive Na, Cl, glusose, 3-O-methylglucose, xylose, glycine, leucine, cycloleucine, Rb, K, inulin (mol. wt. 5000) and dextran (mol. wt. 17,000) from previously loaded muscles was studied. In all cases except dextran the curve had three components, a rapid (A) component which could be equated with efflux from the extracellular space proper, a slow (C) component representing cellular solute and an intermediate (B) component. The distribution space for the B component was 8% of muscle volume in summer frogs and 12% in winter frogs and appeared to be equal for all compounds studied. We tested the hypothesis that the B component originated from the sarcoplasmic reticulum. 3. The C component was missing from the dextran curves. Both dextran and inulin entered the compartment of origin of the B component (compartment B) to the same extent as small molecules. 4. For all compounds studies, the efflux rate constant for the A component could be predicted from the diffusion coefficient. For the B component the efflux rate constant was 6--10 times slower than that for the A component but was still proportional to the diffusion coefficient for the solute in question. 5. When Na and sucrose efflux from single fibres was followed, a B component was usually observed. The average distribution space for this component was small, averaging 1.5% of fibre volume. There was no difference between the average efflux rate constants for Na and sucrose. 6. In an appendix, the constraints placed on the properties of a hypothetical channel between the sarcoplasmic reticulum and the T-system by the linear electrical parameters of frog skeletal muscle are derived. It is shown that the conductance of such a channel must be less than 0.06 x 10(-3) mohs/cm2 of fibre membrane. 7. The conductance between compartment B and the extracellular space can be calculated from the efflux rate constants for Na, K and Cl. The value obtained was 5 x 10(-3) mhos/cm2 of fibre membrane or 100 times the limiting value for the conductance of the T-SR junction. 8. The finding that there is a B component in the efflux curves for large molecular weight substances like inulin and dextran and the small size of the B component in efflux curves from single muscle fibres indicate that the 'speical region' of the extra-cellular space of frog muscle is not the sarcoplasmic reticulum. This conclusion is confirmed by a calculation of the conductance between the B compartment and the extracellular space. The value obtained is incompatible with predicted electrical properteis of the SR-T-tubule junction...

Animals↗
PubMed1985

Tomographic mapping of brain intracellular pH and extracellular water space in stroke patients.

Functional images of regional intracellular pH (pHi) and of fractional volume of extracellular water (FVECW) were obtained in 10 patients with recent hemispheric infarction (between 10 and 19 days after onset of symptoms) using positron emission tomography (PET). The volume of extracellular water relative to that of total water was evaluated in each pixel of the PET scan 7-8 h after injection of 76Br. The pHi image was calculated from the data obtained after injection of [11C]5,5-dimethyl-2,4-oxazolidinedione and from the FVECW image. Regional CBF, oxygen extraction, and oxygen metabolism were also measured in the same patients. In normal hemisphere, mean +/- SD values for FVECW and pHi were 0.12 +/- 0.01 and 6.86 +/- 0.11, respectively. FVECW was increased in the infarcted area in most patients. pHi was increased in the infarct in seven patients and unchanged in three. The increase in pHi was not correlated with changes in FVECW, CBF, or CMRO2, but there was a significant correlation with the decrease in oxygen extraction fraction in the same region. Thus, the decreased H+ content in the infarcted area was correlated with the occurrence of perfusion in excess of metabolic demand. An alkaline shift in pHi enhances the glycolysis rate and could explain why the glucose metabolism is less affected than the oxygen metabolism in recent cerebral infarction. The pHi measured in the infarct could represent mainly the pHi of phagocytic cells that use aerobic glycolysis to synthesize hydrogen peroxide.

Adult↗
PubMedDate not supplied

Light-induced changes of extracellular ions and volume in the isolated chick retina-pigment epithelium preparation.

To better understand the mechanisms of extracellular space volume regulation and their possible effects on retinal function, light-induced changes in the concentrations of the principal extracellular ions (Na+, K+, Ca2+, and Cl-) were measured with ion-sensitive microelectrodes in the chick retina-pigment epithelium-choroid preparation. Changes of extracellular space volume were assessed by measuring the concentration of an impermeant marker, tetramethylammonium. In the inner retina, transient ON/OFF Na+ decrease was about twice as large as K+ increase, and the charge difference was compensated by a decrease in Cl- concentration. The ion changes were accompanied by extracellular space-volume decreases here. In the subretinal space, [Na+]o increase was about twice as large as K+ decrease, yet [Cl-]o, also decreased; this was accompanied by a sustained extracellular space-volume increase. The ionic changes in the inner retina are consistent with a model of extracellular space-volume regulation which assumes that neuronal depolarization causes net uptake of NaCl, cell swelling, and extracellular space shrinkage. However, to prevent the apparent violation of electroneutrality in the subretinal space, our simple model should be expanded to include the involvement of unidentified anion(s). Substantial changes in the subretinal space volume may influence interaction between the neural retina and pigment epithelium. Among ionic changes, only the light-induced [K+]o decrease around the photoreceptors and the [Ca2+]o increase near the photoreceptor bodies and synaptic terminals are large enough (-25% and 7.5%, respectively) to be likely candidates for integrated intercellular signaling.

Animals↗
PubMed1987

Myocardial capillaries in the fetal and the neonatal rat: a morphometric analysis of the maturing myocardial capillary bed.

Developing myocardial capillaries from 16-day-gestation fetus to adult undergo several morphological changes including a thinning of the lateral extensions of the capillary endothelial cells, the formation of a basal lamina, and an increase in the number of plasmalemmal vesicles. A decrease in the extracellular space, an increase in the number of capillaries, and a decrease in the capillary diameter were also observed during the developmental period. In view of these ultrastructural changes, a morphometric analysis was made on the developing myocardial wall to demonstrate specific quantitative changes. The volumes which were occupied by capillary endothelial cells, capillary lumina, extracellular space, and myocardial myocytes within a reference volume of myocardium were measured; and we found that 8% of the reference myocardial volume was occupied by capillary endothelial cells, 85% was occupied by myocardial myocytes, 4% was occupied by capillary lumina, and, except for a significant change in extracellular space at 16 days gestation, 3% was occupied by extracellular space. Each volume ratio was found to be nearly constant throughout the studied period. In contrast to this constancy in the volume ratios, other parameters which were measured demonstrated significant changes during the developmental period studied. These overall changes include a 135% increase in capillary density, a 63% increase in luminal surface area of capillary endothelial cells, a 24% decrease in capillary diameter, a 12% decrease in diffusion distance, and a 35% decrease in the diameter of the erythrocyte population.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗