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PubMed2000

Synchrotron x-ray study of the smectic layer directional instability

We have investigated the phenomenon of field-induced smectic layer instability, as monitored by synchrotron x-ray scattering. This instability means that, upon application of time-asymmetric electric fields to chiral smectics, the layer direction seems to "rotate" locally around an axis given by the direction of the applied field. For moderate values of field amplitude and asymmetry, domains with a favored layer inclination grow at the expense of unfavored ones, while larger fields and asymmetries generally lead to a chaotic flow behavior. At moderate amplitudes, we have followed the process of the horizontal layer folding (or horizontal chevron domain formation) and the smectic C* layer reorientation of ferroelectric liquid crystals by applying symmetric and asymmetric wave forms, respectively, and performing time resolved x-ray measurements. The studies unambiguously show the formation of a horizontal (in-plane, i.e., in a plane parallel to the cell substrates) chevron domain structure from a nonoriented sample by application of a symmetric electric field of sufficient amplitude. It is then demonstrated that a transition from the horizontal chevron domain structure to an in-plane uniform smectic layer direction takes place on application of asymmetric electric wave forms. Reversal of the field asymmetry reverses the inclination direction and selects the other layer normal direction as the uniform end state. The in-plane smectic layer reorientation process is followed here as it evolves, and analyzed directly by means of x-ray scattering.

Journal Article↗
PubMed2003

Matrix formalism of electromagnetic wave propagation through multiple layers in the near-field region: application to the flat panel display.

We have developed an electromagnetic (EM) wave propagation theory through a single layer and multiple layers in the near-field and far-field regions, and have constructed a matrix formalism in terms of the boundary conditions of the EM waves. From the shielding efficiency (SE) against EM radiation in the near-field region calculated by using the matrix formalism, we propose that the effect of multiple layers yields enhanced shielding capability compared to a single layer with the same total thickness in conducting layers as the multiple layers. We compare the intensities of an EM wave propagating through glass coated with conducting indium tin oxide (ITO) on one side and on both sides, applying it to the electromagnetic interference (EMI) shielding filter in a flat panel display such as a plasma display panel (PDP). From the measured intensities of EMI noise generated by a PDP loaded with ITO coated glass samples, the two-side coated glass shows a lower intensity of EMI noise compared to the one-side coated glass. The result confirms the enhancement of the SE due to the effect of multiple layers, as expected in the matrix formalism of EM wave propagation in the near-field region. In the far-field region, the two-side coated glass with ITO in multiple layers has a higher SE than the one-side coated glass with ITO, when the total thickness of ITO in both cases is the same.

Journal Article↗
PubMed2006

Distinct layered structure with density modulation in solid phase formed from B2 phase of banana molecules.

A unique two-dimensional (2D) long-range structure has been observed in a low-temperature phase X1 for a banana molecule having bromine atom substituted on the central core using synchrotron radiation (SR) x-ray scattering measurements. The X1 phase is formed from the B2 phase with the SmC(A)P(A) structure upon cooling and then shows multiple reflections around the first layer line, which are interpreted as a peculiar frustrated structure with long-range layer modulation order. Furthermore, the observation of a well-defined (100) reflection with a spacing of 171A means that there is the electron density modulation along the layers. By coupling these reflections, a 2D lattice with a=173 A, c=53.4A, and beta=81.1 degrees, is determined where the a axis is parallel to the original layer of the phase. This unique structure with modulation can be interpreted as an undulated layer structure and suggested to be the result from deformation with polarization splay defects periodically occurring along the layer. The angle, beta=81.1 degrees, between a and c axes indicates that the position of splay defects in one layer is staggered from that in the neighboring layer. In other words, the splay defect lines run in a direction tilted by roughly 80 degrees with respect to the a axis.

Journal Article↗
PubMed1983

Effects of inducers on inner and outer gastrula ectoderm layers of Xenopus laevis.

Gastrula ectoderm, isolated from Xenopus laevis, was cultured in Holtfreter solution or modified Leibovitz medium (L-15) by the sandwich-method with or without inducer. The ectoderm (SD cell layers) consisted of two cell sheets, representing a superficial (S) and a deep (D) layer. In the L-15 medium rather than in Holtfreter solution, the two cell layers separate out into distinct cell masses. This difference in cell affinity under certain experimental conditions could indicate that the deep layer contains endodermal cells. However, an endodermal character of the deep layer can be ruled out by induction experiments with vegetalizing factor or dorsal blastopore lip as inducers. Under the influence of vegetalizing factor the outer as well as the inner ectoderm layer differentiated into mesodermal derivatives such as notochord and somites. The results of the experiments with dorsal blastopore lip as inducer indicate that both inner and outer ectoderm layers are responsive to the neural stimulus. The lower neural competence of the outer ectoderm layer observed by several authors in normogenesis is discussed with regard to the hypothesis about short distance diffusion of the neutralizing factor and/or close cell-to-cell contact between inducing tissue and ectodermal target cells.

Animals↗
PubMed1988

Comparison of the activity of circular and longitudinal myometrium from pregnant rats: co-ordination between muscle layers.

1. Contractions and electrical activity were recorded from isolated segments of longitudinal (L) and circular (C) myometrium from rats on gestation days 16-17 and 21 before and during parturition. 2. The segments were arranged so that the activity of the two layers could be monitored simultaneously and independently. 3. Out of the 15 preparations from days 16-17, 13 showed no co-ordination of activity between the layers. In the other two preparations a large contraction of C occasionally initiated a contraction of L. Surgical separation of the layers disrupted the co-ordination and L then developed its independent rhythm. 4. On day 21 before delivery, eight of 10 preparations exhibited 1:1 co-ordination of activity between the two layers, but C did not consistently pace L. The pacing shifted from one layer to the other several times during an experiment. 5. During parturition there was a 1:1 co-ordination of activity in all 10 preparations examined. In nine of these L initiated the activity of the C. Surgical separation of the layers disrupted the co-ordination and C developed its independent rhythm. In one the pacing shifted from one layer to the other several times during the experiment. 6. In all cases where co-ordination between the layers was observed it was myogenic and apparently related to the spread of action potentials between the two muscles.

Animals↗
PubMed2004

Distinct mechanisms of bidirectional activity-dependent synaptic plasticity in superficial and deep layers of rat entorhinal cortex.

The entorhinal cortex plays a key role in processing memory information in the brain; superficial layers relay information to, and deep layers receive information from, the hippocampus. The cellular mechanisms of memory are thought to include a number that produce long-term potentiation (LTP) and depression (LTD) of synaptic strength. Our work presents evidence that LTP and LTD occur simultaneously at memory-relevant synapses. We report here that low frequency stimulation generates NMDA receptor-dependent LTD in Wistar rat superficial (layers II and III), and LTP in the deep entorhinal cortex layers (layers V and VI). LTP in deep layers is masked by simultaneously occurring voltage-gated calcium channel-dependent LTD. Our data support a novel mechanism for the sliding-threshold (BCM) model of synaptic plasticity: The sliding thresholds for induction of LTP and LTD in entorhinal cortex deep layers will be driven by the relative activation state of NMDA receptors and voltage-gated calcium channels. The co-expression of LTD and LTP at presynaptic sites in the entorhinal cortex deep layers reveals an intriguing mechanism for differential processing of synaptic information, which may underlie the vast dynamic capacity for information storage by this cortical structure.

Animals↗
PubMed2006

In vitro evaluation of a closed-bowel technique for one-layer hand-sewn inverting end-to-end jejunojejunosotomy in the horse.

OBJECTIVE: To report a technique for closed-bowel 1-layer inverting end-to-end jejunojejunal anastomosis in horses. STUDY DESIGN: Experimental study. SAMPLE POPULATION: Fresh cadaveric jejunal segments from 12 horses. METHODS: For each bowel segment a 1-layer closed and a 2-layer inverting end-to-end jejunojejunosotomy was created. Anastomosis construction time and anastomotic bursting pressure were measured and compared. RESULTS: Closed-bowel anastomosis was significantly faster to create than a 2-layer technique. Luminal narrowing (<30%) was similar with both techniques and comparable with other inverting techniques. Bursting pressure was significantly higher for the 2-layer technique, although all anastomoses resisted pressures higher than those reported for other jejunojejunal anastomosis techniques. CONCLUSIONS: A 1-layer hand-sewn, closed, inverting jejunojejunosotomy using a modified Doyen clamp was easy and faster to perform, and resulted in functional characteristics similar to, a 2-layer hand-sewn inverting technique. CLINICAL RELEVANCE: A closed, 1-layer inverting technique could be considered for equine jejunal anastomosis but requires in vivo evaluation before recommendation for clinical use.

Anastomosis, Surgical↗
PubMed2001

Variation in the surface layer proteins of Clostridium difficile.

Surface layers (S-layers) form regular crystalline structures on the outermost surface of many bacteria. Clostridium difficile possesses such an S-layer consisting of two protein subunits. Treatment of whole cells of C. difficile with 5 M guanidine hydrochloride revealed two major proteins of different molecular masses characteristic of the S-layer on SDS-PAGE. In this study 25 isolates were investigated. A high degree of variability in the molecular mass of the two S-layer proteins was evident. Molecular masses ranged from 48 to 56 kDa for the heavier protein and from 37 to 45 kDa for the lighter protein. A further protein component of 70 kDa was detectable in all isolates. No cross-reaction was seen between the two major proteins from isolates that produced different S-layer patterns, and most S-layer proteins from isolates with the same or similar banding patterns did not cross-react. The S-layer proteins, when detected by a combination of Coomassie blue staining and immunoblotting, are a useful marker for phenotyping.

Animals↗
PubMed1985

Contraction and cyclic AMP-related relaxation of the intimal and medial smooth muscle layers of pig thoracic aorta.

The contractile responses of an alpha-adrenoceptor agonist, phenylephrine, and of histamine were compared in the intimal and medial smooth muscle layers of the pig aortic arch. Further, the relaxant effects evoked by some compounds influencing the cyclic AMP system were compared in the two muscle layers, as well as their effects on the cyclic AMP content and phosphodiesterase activity. Phenylephrine and histamine induced contraction of the smooth muscle layers. The increase in tension was faster in the intimal than in the medial layer. The alpha-adrenoceptor agonist phenylephrine was a more potent contractile agent in the intimal than in the medial smooth muscle. With histamine, no significant difference in the dose-response curves between the two muscle layers was found. Histamine-contracted muscle preparations were relaxed in a dose-dependent manner by the phosphodiesterase-inhibiting compound 3-isobutyl-1-methylaxanthine (MIX) and by 8-bromo-cyclic AMP. The two substances were more potent relaxants in the medial than in the intimal smooth muscle layer. The content of cyclic AMP in the intimal and the medial smooth muscle was increased by MIX. Isoprenaline had no relaxing effect on the muscle preparations and did not change the content of cyclic AMP. There were no differences in the basal levels of cyclic AMP in the intima and media. Vmax of phosphodiesterase activities differed, however, between the two preparations. This study demonstrates that the intimal layer is characterized by a larger contractile responsiveness to phenylephrine and a lower relaxant response to compounds influencing the cyclic AMP-system than those of the medial layer.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1995

Synaptic integration in layer IV of the ferret striate cortex.

1. Whole-cell patch recording were made with dye-filled electrodes from layer IV in slices of the ferret striate cortex. Projections from the thalamus and layer VI provide most of the extralaminar input to layer IV. Interactions between these two pathways are thought to play a role in the generation of suppressive non-linearities such as end-inhibition. Thus, synaptic responses evoked by stimulating each pathway individually were compared with those produced by activating both projections together. 2. Spiny stellate cells are the majority population in layer IV and were the most frequently patched neurons (n = 23); all fired adapting trains of large, fast action potentials. About half of those tested (n = 13) were progressively inhibited by strengthening the stimulus to layer VI, while the rest became more excited. For the former, the response evoked by stimulating both pathways in coincidence was often more hyperpolarizing than would have been predicted by summing the responses to either projection alone (n = 4). Hence, the inputs from the thalamus and layer VI are integrated by circuits that can produce strong and non-linear inhibition. 3. Recordings from various basket cells, which are inhibitory, have provided a first view of the suppressive circuits in layer IV (n = 5). Two cells were excited by stimulation of both pathways. The remaining three cells were mainly excited by activation of thalamic afferents but were largely inhibited by stimulation of layer VI. Thus, inhibition seen at the level of the spiny stellate cells could result from two mechanisms operating via presynaptic smooth cells: convergent excitation provided by both ascending pathways on the one hand, and a push-pull relationship between pathways on the other.

Animals↗
PubMed2004

Sub- and suprathreshold receptive field properties of pyramidal neurones in layers 5A and 5B of rat somatosensory barrel cortex.

Layer 5 (L5) pyramidal neurones constitute a major sub- and intracortical output of the somatosensory cortex. This layer 5 is segregated into layers 5A and 5B which receive and distribute relatively independent afferent and efferent pathways. We performed in vivo whole-cell recordings from L5 neurones of the somatosensory (barrel) cortex of urethane-anaesthetized rats (aged 27-31 days). By delivering 6 deg single whisker deflections, whisker pad receptive fields were mapped for 16 L5A and 11 L5B neurones located below the layer 4 whisker-barrels. Average resting membrane potentials were -75.6 +/- 1.1 mV, and spontaneous action potential (AP) rates were 0.54 +/- 0.14 APs s(-1). Principal whisker (PW) evoked responses were similar in L5A and L5B neurones, with an average 5.0 +/- 0.6 mV postsynaptic potential (PSP) and 0.12 +/- 0.03 APs per stimulus. The layer 5A sub- and suprathreshold receptive fields (RFs) were more confined to the principle whisker than those of layer 5B. The basal dendritic arbors of layer 5A and 5B cells were located below both layer 4 barrels and septa, and the cell bodies were biased towards the barrel walls. Responses in both L5A and L5B developed slowly, with onset latencies of 10.1 +/- 0.5 ms and peak latencies of 33.9 +/- 3.3 ms. Contralateral multi-whisker stimulation evoked PSPs similar in amplitude to those of PW deflections; whereas, ipsilateral stimulation evoked smaller and longer latency PSPs. We conclude that in L5 a whisker deflection is represented in two ways: focally by L5A pyramids and more diffusely by L5B pyramids as a result of combining different inputs from lemniscal and paralemniscal pathways. The relevant output evoked by a whisker deflection could be the ensemble activity in the anatomically defined cortical modules associated with a single or a few barrel-columns.

Afferent Pathways↗
PubMed1991

Normal contact of elastic spheres with two elastic layers as a model of joint articulation.

An analytical model of two elastic spheres with two elastic layers in normal, frictionless contact is developed which simulates contact of articulating joints, and allows for the calculation of stresses and displacements in the layered region of contact. Using various layer/layer/substrate combinations, the effects of variations in layer and substrate properties are determined in relation to the occurrence of tensile and shear stresses as the source of crack initiation in joint cartilage and bone. Vertical cracking at the cartilage surface and horizontal splitting at the tidemark have been observed in joints with primary osteoarthritis. Deep vertical cracks in the calcified cartilage and underlying bone have been observed in blunt trauma experiments. The current model shows that cartilage stresses for a particular system are a function of the ratio of contact radius to total layer thickness (a/h). Surface tension, which is observed for a/h small, is alleviated as a/h is increased due to increased load, softening and/or thinning of the cartilage layer. Decreases in a/h due to cartilage stiffening lead to increased global compressive stresses and increased incidence of surface tension, consistent with impact-induced surface cracks. Cartilage stresses are not significantly affected by variations in stiffness of the underlying material. Tensile radial strains in the cartilage layer approach one-third of the normal compressive strains, and increase significantly with cartilage softening. For cases where the middle layer stiffness exceeds that of the underlying substrate, tensile stresses occur at the base of the middle layer, consistent with impact induced cracks in the zone of calcified cartilage and subchondral bone. The presence of the superficial tangential zone appears to have little effect on underlying cartilage stresses.

Cartilage, Articular↗
PubMed1993

Paracrystalline surface layers of dairy propionibacteria.

We examined 70 dairy propionibacteria and detected a crystalline surface layer (S-layer) in only 2 organisms (Propionibacterium freudenreichii CNRZ 722 and Propionibacterium jensenii CNRZ 87) by freeze-etching and sodium dodecyl sulfate-polyacrylamide electrophoresis (SDS-PAGE). Both S-layers exhibited oblique (p2) symmetry (a = 9.9 nm; b = 5.4 nm; gamma = 80 degrees) and completely covered the cell surface. Treatment for 15 min at the ambient temperature with 5 M guanidine hydrochloride or acidic conditions (250 mM ammonium acetate, pH 2.7) efficiently extracted the S-layer protein from intact cells of strain CNRZ 722, whereas treatment with 5 M guanidine hydrochloride at 100 degrees C for 15 min was necessary to isolate the S-layer protein of strain CNRZ 87. The precipitates obtained after dialysis of the extracting agents produced no regular patterns. The molecular masses of the two S-layer proteins, as estimated by SDS-PAGE, were 58.5 kDa for the strain CNRZ 722 and 67.3 kDa for the strain CNRZ 87. Mass spectrometry of the isolated S-layer protein of strain CNRZ 722 gave a molecular mass value close to the expected value (56,533 Da). The N-terminal sequences of the two purified S-layer proteins differed, as did their amino acid compositions, except that the same high hydrophobic amino acid content (52%) was observed.

Amino Acid Sequence↗
PubMed1992

S-layer-mediated association of Aeromonas salmonicida with murine macrophages.

The interaction of Aeromonas salmonicida with the murine macrophage (M phi) cell line P388D1 was used as a convenient model to study the involvement of the bacterial crystalline surface array (or A-layer) in the association with M phi s. A-layer-positive (A+) cells readily associated with M phi s in phosphate-buffered saline, whereas A- mutants were unable to do so, even when the bacterium-M phi interaction was forced by centrifugation. M phi s selectively interacted with A+ cells when challenged with mixtures of A+ and excess A- cells. Electron microscopy indicated that in phosphate-buffered saline only A+ bacteria were readily internalized, although by a nonconventional mechanism, suggesting that efficient phagocytosis in the absence of opsonins was A-layer mediated. Latex beads coated with a partially assembled A-layer were more efficiently taken up than uncoated or A-protein-coated beads, indicating that an organized A-layer was essential for M phi uptake. The reduced ability of M phi s plated on a substratum coated with the A-layer to bind A+ bacteria also suggested that association was both A-layer and receptor mediated. In the presence of tissue culture medium, competent M phi s interacted efficiently with A- bacteria and internalized them through conventional phagocytosis. A+ cells were markedly cytotoxic to M phi s, whereas the A-protein or A-layer was not. A- cells were cytotoxic to a lesser extent, suggesting that cytotoxicity was targeted.

Aeromonas↗
PubMed1970

Separation and localization of cell wall layers of a gram-negative bacterium.

The cell envelope of a marine pseudomonad as seen in thin section by electron microscopy has the double-membrane structure typical of other gram-negative bacteria. Cells washed with a solution containing Na(+), K(+), and Mg(++) at their concentrations in the growth medium, when suspended briefly in 0.5 m sucrose, lost 13% of their hexosamine in a form nonsedimentable by centrifugation at 73,000 x g. Since the resulting cells in thin section appeared unchanged, it was concluded that the material released was derived from a nonstaining, loosely bound outer layer. This same layer could be removed from the cells by washing with 0.5 m NaCl. A second nonsedimentable fraction was released after successive suspension of the cells in 0.5 m sucrose. Since this material was released only when the outer double-track structure had broken, it was concluded that it arose from a layer immediately underlying the latter layer. The three layers differed in their content of hexosamine and protein. None of the layers released contained muramic or diaminopimelic acid. The cell form remaining was rod shaped and appeared in thin section to be bounded only by its cytoplasmic membrane. This form contained all the muramic and diaminopimelic acid in the cell. Treatment with lysozyme released the muramic and diaminopimelic acid and converted the rod form to a protoplast, indicating that in the rod form (mureinoplast) a thin layer of peptidoglycan is located on the outside surface of the cytoplasmic membrane. Thus, five separate layers have been detected in the cell envelope of this marine pseudomonad.

Journal Article↗
PubMed1994

Comparative studies of S-layer proteins from Bacillus stearothermophilus strains expressed during growth in continuous culture under oxygen-limited and non-oxygen-limited conditions.

The specific properties of S-layer proteins from three different Bacillus stearothermophilus strains revealing oblique, square, or hexagonal lattice symmetry were preserved during growth in continuous culture on complex medium only under oxygen-limited conditions in which glucose was used as the sole carbon source. When oxygen limitation was relieved, amino acids became metabolized, cell density increased, and different S-layer proteins from wild-type strains became rapidly replaced by a new common type of S-layer protein with an apparent subunit molecular weight of 97,000 which assembled into an identical oblique (p2) lattice type. During switching from wild-type strains to variants, patches of the S-layer lattices characteristics for wild-type strains, granular regions, and areas with oblique lattice symmetry could be observed on the surface of individual cells from all organisms. The granular regions apparently consisted of mixtures of the S-layer proteins from the wild-type strains and the newly synthesized p2 S-layer proteins from the variants. S-layer proteins from wild-type strains possessed identical N-terminal regions but led to quite different cleavage products upon peptide mapping, indicating that they are encoded by different genes. Chemical analysis including N-terminal sequencing and peptide mapping showed that the oblique S-layer lattices synthesized under increased oxygen supply were composed of identical protein species.

Amino Acid Sequence↗
PubMed1977

Effect of strain variation and growth phase of culture on dry weight and hexosamine content of cell wall layers of a marine pseudomonad.

Two variants of marine pseudomonad B-16 (ATCC 19855) differing in that one, variant 3, formed opaque colonies and the other, variant 7, formed translucent colonies were examined to determine if the variants differed in the amount and hexosamine content of their three outer cell wall layers. In both variants, the three outer layers of the cell wall, the loosely bound outer layer, the outer double-track layer, and the underlying (periplasmic space) layer contributed less to the dry weight of the cells when the cells were harvested in the stationary than in the logarithmic phase of growth. The hexosamine content of the layers of variant 3 increased dramatically as the cells went from the logarithmic to the stationary phase. The hexosamine content of the layers of variant 7 changed little by comparison. Thus cells of the variant which forms opaque colonies enrich the outer layers of their cell wall with hexosamine when grown to stationary phase.

Cell Wall↗
PubMed1982

Responsiveness of longitudinal and circular muscle layers of the portal vein.

This study was performed to compare mechanical activity produced by acetylcholine and histamine in longitudinal and circular muscle layers of the portal vein. Peak tension was measured in longitudinal and circular muscle strips from portal veins of rabbits as they were superfused with acetylcholine and histamine (10(-6) to 10(-4) M). Responses to acetylcholine were three to four times greater in longitudinal muscle than in circular muscle; for example, acetylcholine (10(-5) M) produced contractions of 1.6 +/- 0.2 X 10(3) (mean +/- SE) dynes in longitudinal muscle and 0.4 +/- 0.09 X 10(3) dynes in circular muscle. In the same strips, histamine produced similar responses in the two layers: histamine (10(-5) M) produced contractions of 0.4 +/- 0.1 X 10(3) dynes in longitudinal and 0.4 +/- 0.1 X 10(3) dynes in circular muscle. Histological studies of portal vein muscle strips showed that the longitudinal muscle layer is three to four times thicker than the circular muscle layer. Thus, in response to acetylcholine, tension developed in each muscle layer is proportional to the thickness of that layer. In response to histamine, however, longitudinal muscle develops less tension than is predicted by the thickness of the muscle layer. We conclude that longitudinal and circular muscle layers of the rabbit portal vein differ in their responsiveness to histamine.

Acetylcholine↗