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At least 1,621 records · Page 90Linked to original sources
PubMed2004

[Reliable parameters for assessing the birefringence of retinal nerve fiber layer under various conditions of corneal birefringence].

PURPOSE: To find a reliable parameter for the assessment of parafoveal nerve fiber layer using scanning laser polarimetry. METHODS: The retinal nerve fiber layer was imaged using a Nerve Fiber Analyzer II (NFA II) along the parafoveal circle with a 90-pixel diameter in 4 dilated eyes of 4 normal subjects. The average thickness was measured in the superior(S), temporal(T), inferior(I), and nasal(N) quadrants. The image was obtained by means of a laser beam passing through 4 different locations in the cornea: the center, 2 mm temporal from the center, 2 mm lower temporal from the center, and 2 mm lower from the center. RESULTS: The circumference profile of the nerve fiber layer around the fovea showed a biphasic pattern similar to that obtained around the optic disc. However, the peaks of the pattern varied according to the corneal location through which the laser beam passed. Accordingly, the average thickness of the nerve fiber layer in each quadrant showed great fluctuation when using a displaced laser beam. The coefficient of variance was large (0.265-0.313) for the nerve fiber layer thickness itself; however, it was far less for the ratio of the nerve fiber layer thickness in the opposite direction, such as temporal-to-nasal (0.082) or superior-to-inferior (0.089). CONCLUSIONS: Although the measurement of the retinal nerve fiber thickness itself depends largely on the location in the birefringent cornea through which the laser beam passes, the ratios of nerve fiber layer thickness such as temporal-to-nasal or superior-to-inferior are reliable and show less fluctuation in the measured values.

Adolescent↗
PubMedDate not supplied

Diffusive boundary layer development above a sediment-water interface.

A model to estimate the entry length to a fully developed diffusive boundary layer above a sediment bed, such as those found in lakes, reservoirs, rivers, and estuaries, is presented. The model is used to determine how the length of a sediment bed in mass-transfer experiments influences the measured vertical diffusive flux at the sediment-water interface. A nondimensional local mass flux is introduced in the form of a Sherwood number (Sh) and expressed as a function of both the distance from the leading edge of the sediment bed (x) and the Schmidt number (Sc). Similarly, a mean Sherwood number (Sh(ave)) for a sediment bed of length (L) is introduced. The diffusive boundary layer grows with distance, and its thickness depends on the Schmidt number (i.e., the diffusive boundary layer gets thicker and develops more quickly as the Schmidt number decreases). For Schmidt numbers greater than or equal to 100, the diffusive boundary layer begins to develop slowly but is fully developed when the nondimensional horizontal coordinate (x+) is approximately 1000. The Sherwood number is largest (i.e., infinity) near the leading edge of the sediment bed (i.e., at x = 0), decreases as the distance from the bed increases, and, finally, approaches a constant value for a fully developed diffusive boundary layer (Sh(infinity)). In this paper, the distance to a fully developed diffusive boundary layer (L99) and the required length of a sediment bed are related explicitly to Sc, sheer velocity (U*), and the relative errors of local or average Sherwood numbers (Sh or Sh(ave), respectively) against the Sherwood number for the fully developed diffusive boundary layer (Sh(infinity)). The lengths L99 and L decrease as the Schmidt number increases and become independent of the Schmidt number when Sc is greater than 1000. A longer sediment bed is needed when the shear velocity or the Schmidt number is small (e.g., L99 and L approximately 1.0 m and 8.0 m, respectively, for Sc = 500, U* = 0.1 cm/s, and a 3% acceptable error). Experimental studies may not be able to meet these requirements and an adjustment of measured mass-transfer rates at a sediment-water interface may be necessary. The magnitude of that adjustment is up to 50%. Its dependence on the Schmidt number, shear velocity, and bed length is given in this paper.

Diffusion↗
PubMed1992

A comparison of a new two-layer anatomic repair to the traditional shouldice herniorrhaphy.

Since 1976, the Shouldice repair has been the herniorrhaphy of choice at the Veterans Administration Medical Center, Augusta, Georgia. The authors previously reported their experience with this technique, and their recurrence rate of 1.8 per cent was consistent with the experience of the Shouldice clinic. It is often difficult to obtain adequate tissue for a four-layer repair in patients with recurrent hernias or in those patients with large direct or indirect inguinal hernias. In these instances, a two-layer running closure similar to the Shouldice was performed, but the shelving edge of the inguinal ligament was sewn to the conjoined area in one layer and then the fascia of the internal oblique to the inguinal ligament in the second layer. To obtain an estimate of the recurrence rate with this modification, the authors reviewed their herniorrhaphy experience from 1984 to 1988. During this period, 420 herniorrhaphies were performed. Two hundred twenty-six patients were available for follow-up. Of this group, 154 patients had a traditional four-layer Shouldice repair; there were two recurrences in this group (1.2%). Seventy-two patients underwent the described two-layer repair; there were no documented recurrences in this group. Based on this experience, the authors believe that the described running two-layer herniorrhaphy is a valuable alternative when the tissue is inadequate to allow a traditional Shouldice repair. This procedure has now become the authors' method of choice for the majority of repairs.

Follow-Up Studies↗
PubMedDate not supplied

Does Bowman's layer determine the biomechanical properties of the cornea?

BACKGROUND: Bowman's layer is believed to be the stabilizing element of corneal curvature due to its assumed mechanical stiffness. METHODS: Uniaxial stress-strain analysis was performed in paired corneal strips to compare the contribution from Bowman's layer. Two central strips were taken from each cornea and Bowman's layer was removed from one of them with the excimer laser. RESULTS: Pairwise comparison yielded no statistical difference in elastic or viscoelastic properties according to presence or absence of Bowman's layer. At a strain of 2%, the stress was measured to be (5.06 +/- 2.01) x 10(3) N/m2 with Bowman's layer and (4.72 +/- 1.3) x 10(3) N/m2 without Bowman's layer. Also, the two relaxation times did not differ significantly. CONCLUSIONS: These findings imply that Bowman's layer does not contribute significantly to mechanical stability within the cornea.

Aged↗
PubMed1991

[Retinal nerve fiber layer photography in retinal vein occlusion].

In six eyes we found typical signs that could serve as criteria for the differentiation of ischemic from non-ischemic retinal branch vein occlusion. Perimetry showed a mean defect (in the affected area) of more than 10 dB in eyes with defects in the retinal nerve fiber layer in contrast with 5 dB on one eye without nerve fiber defects. Secondly, fluorescein angiography showed ischemic areas in all eyes examined with localized defects in the photographs of the retinal nerve fiber layer. Damage of the retinal nerve fiber layer was observed before capillary obliteration could be detected by fluorescein angiography. Thirdly, semiquantitative optic disc morphometry demonstrated that using the difference between pallor and excavation as the only sign in ascending optic atrophy is not always useful. Fourthly, photography of the retinal nerve fiber layer showed that there is no correlation between the extension of the ischemic area and the sector angle of the defect of the retinal nerve fiber layer. Photography of the retinal nerve fiber layer can differentiative ischemic from non-ischemic retinal branch vein occlusion because of the qualitative detection of localized retinal nerve fiber layer defects. Consequently, this method is not only of great clinical importance for the diagnosis of different optic lesions, but is also useful for the prognosis and management of occlusion of the retinal branch vein.

Female↗
PubMedDate not supplied

[Focus on the smear layer in 1990].

The smear layer is a debris-ladden layer, adhering firmly to the hard tissues of the tooth. It plays a major role in the different adhesive systems. An update of the recent knowledge on smear layer will be done in this article. When the carious lesion is removed, a microscopic debris-ladden layer forms at the level on the enamel and the dentine. This layer of materials is extremely adherent to the dental structure, and will come in between the hard dental tissues and the filling materials. In this article different studies were reviewed on the formation, structure and physiology of the smear layer. Consequences of this smear layer's removal on the pulp are discussed. A small study of different adhesive systems is conducted.

Adhesives↗
PubMedDate not supplied

[Appraisal of the status of metabolism in myocardial layers in acute left-ventricular insufficiency using data from radionuclide examination methods].

Experiments were conducted on 35 mongrel dogs. It was demonstrated in series I experiments that exclusion of a 14.5% myocardial area from the heart mass induces acute left-ventricular insufficiency manifested by authentic decrease of the cardiac ejection and left-ventricular output index and a 22% increase of pressure in the left atrium and pulmonary artery. The left-ventricular coronary blood flow and the blood flow in the myocardial layers of the right and left ventricles and in the interventricular septum increased significantly as compared to the control values. Distal to the area of the necrosis, however, the layer-by-layer flow of the blood in the left ventricle had a marked tendency to increase. In series II experiments, in myocardial necrosis the volume load, which was equal to one half and one initial circulation volume, mobilized the heart contractile activity, which led to increase of the coronary blood flow which was less than the initial level in series I experiments. Analysis of layer-by-layer blood flow after a volume load equal to one initial circulation volume showed it to be markedly increased in all layers of the left-ventricular anterior wall above and below the necrotic area, in the left-ventricular posterior wall, in the interventricular septum, and in the right-ventricular anterior wall. The increase of 201Tl-chloride accumulation in the myocardial layers under the studied conditions is evidently linked with activation of metabolic processes responsible for increase of heart contractile activity and, consequently, for increased uptake of 201Tl from circulation by the intact cardiomyocytes rather than with change in redistribution of the blood flow and its increase.

Animals↗
PubMed1988

Chemical composition of the yeast ascospore wall. The second outer layer consists of chitosan.

In a preceding paper (Briza, P., Winkler, G., Kalchhauser, H., and Breitenbach, M. (1986) J. Biol. Chem. 261, 4288-4294), we reported the presence of dityrosine in the outer layers of yeast ascospore walls. Both outer layers seen in electron micrographs of yeast ascospore walls are sporulation-specific. Here we show that the second of these two outer layers consists of chitosan. In intact spores, it is shielded from staining with primulin by the outermost layer. However, in purified spore walls, the second layer is brightly stained by primulin, and hydrolysates of such preparations contain about 10% glucosamine relative to spore wall dry weight. The spore wall material staining with primulin is resistant to chitinase, but readily degraded by treatment with HNO2. Acetylation prior to HNO2 treatment completely prevents its degradation. A partial acid hydrolysate of spore walls contains predominantly soluble poly-beta-(1,4)-glucosamine as determined by 13C NMR spectroscopy. By these criteria, the glucosamine polymer of yeast ascospore walls is chitosan. As spore walls treated with alkali lack the inner layers but contain chitosan and as chitosan is not exposed at the surface of the spore, we conclude that it is localized in the second outer layer of the spore wall.

Chitin↗
PubMed1988

Development of cell density gradients in the retinal ganglion cell layer of marsupials.

An area centralis and visual streak, specializations of high cell density in the mammalian retinal ganglion cell layer, develop from a more uniform cell distribution. In the wallaby and kangaroo, this transition is first seen 60 days postnatally. Total live cell numbers in this layer fall by approximately one-third as these specializations start to appear and dying cells are seen. However, dying cells have already become concentrated at the retinal rim prior to the emergence of live cell density gradients. Our results suggest that cell death may partially sculpt patterns of live cells, particularly by lowering densities around the entire far periphery. Studies of cell division demonstrate that ganglion cells are generated and enter the ganglion cell layer before the area centralis and visual streak are formed. However, cell addition to the inner and outer nuclear layers continues as cell density gradients become apparent in the ganglion cell layer. Furthermore, this late cell generation ceases first in areas adjacent to the presumptive area centralis. The differential distribution of such prolonged cell addition to the inner and outer nuclear layers may result in an asymmetric expansion of the retina. This process would partially explain the changing topography of cells in the ganglion cell layer. Mathematical analysis of patterns of overall retinal growth support this interpretation.

Animals↗
PubMed1988

The projection from the superficial to the deep layers of the superior colliculus: an intracellular horseradish peroxidase injection study in the hamster.

Intracellular recording and horseradish peroxidase (HRP) injection techniques were employed to examine the projections of superficial layer [stratum griseum superficiale (SGS) and stratum opticum (SO)] superior collicular (SC) neurons in the hamster that sent axon collaterals into the deep laminae (those ventral to the SO) of this structure. Sixty-nine neurons were studied, selected from a sample of over 185 HRP-filled superficial layer cells on the basis of having heavily stained axons. Of the 69 cells included in the study, 43.4% (n = 30) sent at least one axon collateral to the deep laminae. Not all cell types in the superficial layers contributed equally to this interlaminar projection: 78.6% (n = 11) of the recovered wide-field vertical cells, 55.0% (n = 11) of the narrow-field vertical cells, 16.7% (n = 2) of the stellate cells, 40.0% (n = 2) of the marginal cells, 18.2% (n = 2) of the horizontal cells, and 28.6% (n = 2) of neurons we could not classify on the basis of their somadendritic morphology projected to the deep layers. Within a given cell class, there were no significant morphological or physiological differences between the neurons that possessed deep axon collaterals and those that did not. The deep axon collaterals of most of the interlaminar projection neurons were restricted to the stratum griseum intermediate (SGI). In this layer, the largest segment of the axon arbor was located lateral to a projection line that was orthogonal to the SC surface and that passed through the soma of the cell in question. These results, along with those of a previous study (Mooney et al., 1984), which demonstrated that the dendrites of deep layer cells may extend through the SO and into the SGS, indicate that there is an extensive anatomical substrate by which sensory information may be communicated from superficial to deep layer SC neurons.

Animals↗
PubMed1987

A Golgi study of the sixth layer of the cerebral cortex. III. Neuronal changes during normal and abnormal cortical folding.

During normal development in the cat Layer VI cortical neurons, including pyramidal cells, fusiform neurons, inverted pyramidal cells and bipolar neurons located in the gyral regions retain the vertical orientation characteristic of earlier developmental stages. However, Layer VI pyramidal neurons and the subtypes in the sulcal zones develop long horizontal basilar dendrites which seem to form dendritic bundles with those of neighbouring pyramidal cells; in addition, fusiform neurons and bipolar cells are tangentially orientated and horizontal pyramidal neurons appear in place of inverted pyramidal cells in the gyral and intermediate regions. In human cortical malformations, neurons of the external cellular layer (Layers V and VI) in lissencephaly are vertically arranged, but Layer VI neurons in polymicrogyria are tangentially orientated when located in microsulci. These features suggest that neuronal changes occur in Layer VI neurons as a consequence of cortical folding and that cortical folding determines the cellular shape of Layer VI neurons in normal as well as in abnormal development of the cerebral cortex.

Animals↗
PubMed1981

Light-induced changes in energy metabolites, guanine nucleotides, and guanylate cyclase within frog retinal layers.

Freeze-dried sections were prepared from retinas of frogs which were dark-adapted or exposed to varying periods of light. Samples of the discrete layers were dissected, weighed, and analyzed for energy metabolites, guanylate compounds, and the enzyme guanylate cyclase. ATP and P-creatine were measured in both dark- and light-adapted retinas. There was a gradient in ATP and P-creatine levels in dark-adapted retinas, with the lower concentrations in the photoreceptors, and increasing concentrations in the inner retina. After light adaptation, concentrations increased, an observation which supports the concept that transmitter release occurs in the dark and ceases in the light. The sum of GTP plus GDP, GDP, and cyclic GMP were analyzed in dark-adapted retinas and after exposure to 2 min or 2 h of room light. GDP was rather uniformly distributed in the retinal layers, was increased by 2 min of light in all layers but the outer nuclear, and remained elevated at 2 h in the inner retina. GTP values showed a marked localization in the outer nuclear layer, which increased after 2 min or 2 h of illumination; in all other layers GTP was decreased by light. Cyclic GMP in the dark was highest in the photoreceptor cells, decreasing to one-third after 2 min of light; there were significant increases in the outer plexiform and inner nuclear layers at this time. Cyclic GMP remained low in the photoreceptor cells even after 2 h of light, while the inner layers returned to dark values. Guanylate cyclase, like cyclic GMP, was largely confined to the photoreceptor cells and showed a maximal increase after 2 min of light exposure.

Adenosine Triphosphate↗
PubMed1983

[An electron microscope study of the inner circular layer and related interstitial Cajal cells of the small intestine of the hedgehog (Erinaceus europaeus) during its annual cycle].

The inner portion of the circular layer (the special layer) of the small intestine of the hedgehog (Erinaceus europaeus) and its related interstitial cells of Cajal (ICC) were studied by electron microscopy for the first time in the literature. Hedgehogs were studied in active conditions, during hibernation and at arousal. The structure of the inner portion of the circular layer of the hedgehog is similar to that observed in other mammals a special layer formed by thin muscle cells may be recognized; a plexus muscularis profundus (PMP) and ICC are localized between this layer and the outer portion of the circular layer; the PMP is rich in varicosities with many synaptic vesicles (both small agranular and large granular vesicles); most varicosities are in close contact with the ICC; the ICC are closely resembling those described for man, since they have several cytological features very similar to those of smooth muscle cells. During hibernation glycogen particles and caveolae are very numerous and the Golgi apparatus is poorly developed both in the ICC and in the smooth muscle cells of the special layer; in the PMP the synaptic vesicles, especially the large granular ones, are greatly reduced in number. At the beginning of arousal the glycogen particles disappear; at the end of arousal the caveolae are as numerous and the Golgi apparatus as large as in the active conditions both in ICC and in smooth muscle cells. The synaptic vesicles, following the gradual increase of body temperature, become numerous and at the end of arousal their number is similar to or greater than in active conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1981

In vitro analysis of the contributions of adherent cell layer and recharging population to hemopoietic cell proliferation in long-term bone marrow cultures.

Cell proliferation in long-term suspension cultures of mouse bone marrow was studied. Bone marrow cells were maintained on irradiated or conventional non-irradiated semiallogeneic adherent feeder layers and the origin of the proliferating cells was investigated by using the unique T6 chromosome marker. In cultures containing irradiated feeder layers total cell numbers were less at the first week after "recharging," but the levels soon reached those of conventional non-irradiated cultures. At the first weeks after recharging, proliferating cells, maintained on conventional non-irradiated feeder layers, originated mainly from the adherent layer. The contribution of the recharging population to the proliferating cell population increased with time. In contrast, the proliferating cells grown on irradiated adherent layers originated mainly from recharging population from the first week after recharging. The origin of the nonadherent CFUs and their development in F1 hybrid mice and mice of syngeneic strains was also examined. The pluripotent stem cells grown on non-irradiated feeder layers were derived mainly from the adherent layer.

Animals↗
PubMed1995

The thickness of the mucus layer in different segments of the rat intestine.

The thickness of the pre-epithelial mucus layer has been measured in different gut segments of rats kept under normal (ad libitum) feeding conditions, and after 48 h of fasting, using cryostat sections and celloidin stabilization from samples containing luminal contents. The mucus layer of the stomach, duodenum, jejunum, ileum, caecum, proximal colon, colon transversum, distal colon and rectum was studied in five groups of male rats (10, 40, 70 and 150 days of age, and older). Under ad libitum feeding conditions, a distinct and continuous mucus layer, with a thickness of more than 3 microns, was only observed in the colon transversum, in the distal colon, in the rectum and in the stomach. No pre-epithelial mucus layer was observed in the duodenum and jejunum where the glycocalix from the apical membrane of the superficial cells appeared to be in a direct contact with the luminal ingesta. In the ileum, caecum and the proximal colon, the surface epithelium of the mucosa was only partly covered by a mucus layer of highly variable thickness. After 48 h of fasting, a mucus layer of 28.8 +/- 25.6 microns and 93.3 +/- 59.4 microns thickness, respectively, was found in the duodenum and jejunum of adult rats, but no increase in the thickness of the mucus layer was observed in the rat hind gut.

Aging↗
PubMed1995

Two-layer repair of the transversalis fascia is sufficient for inguinal hernia repair.

The Shouldice four-layer repair is considered to be the gold standard procedure for repair of inguinal hernia with low recurrence rates around 1%. Tension-free two-layer repair of the transversalis fascia may be all that is required to avoid recurrence. We compared the early recurrence rate after two-layer repair of the transversalis fascia or the standard four-layer Shouldice technique in a randomised study of elective inguinal herniorrhaphy. In 48 patients (53 repairs) who had a two-layer transversalis fascia repair, there was one recurrence (2%) in the first 12 months after operation, though there was one more recurrence within 36 months (total 4%). In 39 patients who had a four-layer Shouldice repair (42 repairs), there was no recurrence at 12 months but at 36 months two recurrences (5%) were found. We conclude that a two-layer repair of the transversalis fascia is anatomically correct, physiologically sound and can provide equivalent results to the standard Shouldice repair for inguinal hernia.

Adult↗
PubMed1994

Antiproliferative lymphokine production by human peripheral blood lymphocytes and lymph node lymphocytes detected by a modified double layer soft agarose clonogenic assay.

The double layer soft agarose clonogenic assay using colony formation of target cells as an endpoint was adapted for the detection of antiproliferative lymphokine production from peripheral blood lymphocytes (PBL) and lymph node lymphocytes (LNL). The colony formation of cervical cancer cell lines, HeLa, CAC-1, and TMCC, in the upper layers was significantly inhibited by the inclusion of either PBL or LNL pretreated with PHA in the lower layers. Without stimulation by PHA, neither resident PBL nor LNL exhibited antiproliferative activity on the tumor cells in the upper layers. The antiproliferative activity against target cells increased in relation to the density of lymphocytes in the lower layers, and was dependent on protein synthesis by lymphocytes. Since the cell to cell contact between the effector cells and target cells is not possible in this assay, the reduction of colony formation should be attributed to soluble factor(s) that were secreted from the lymphocytes. Additionally, an antibody against IFN-gamma neutralized most of the antiproliferative activity, and equivalent levels of IFN-gamma were found to be present in the supernatant of PBL and LNL lower layers by a radioimmunoassay. The double layer soft agarose assay system should thus serve as a useful method for studying antiproliferative lymphokine production by lymphocytes.

Animals↗
PubMed1993

Mechanism of closure of experimental excision-wounds in the bare upper layer of the chick blastoderm.

The closure of experimental excision-wounds in the upper layer of the gastrulating chick blastoderm was studied by time-lapse videography and videomicrography and by light microscopy, transmission electron microscopy and scanning electron microscopy. One experimental excision-wound was made in the upper layer of stages 4V to 6V blastoderms (Vakaet, Arch. Biol. (Liège) 81:387-426, 1970), in the proamnion where no middle layer cells are present. The deep layer was previously discarded, so that the wounds were made in the bare upper layer. They closed within 2 to 6 hours and further development was normal by in vitro standards. With videography, global movements of the upper layer towards the wound were observed. With videomicrography, the wound submarginal region cells were seen to move like sheep in a flock: individual cells in different directions, the whole flock towards the wound. During closure the shape of the wound edge was irregular. The structure of the epithelium of the wound submarginal region was unchanged throughout closure: a pseudostratified columnar epithelium in which cell divisions occur at its dorsal side and are parallel to its surface. The basal lamina was absent below the edge of the wounds. We propose that the cells of the upper layer are mobile against one another and are not confined to a specific part of the basal lamina. During wound closure the movements of the cells on the basal lamina would be driven by mitotic pressure. This is the horizontal pressure exerted by the addition of daughter cells and their parting during anaphase and telophase.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗