Narrow Pathways Research Articles

Oxygen consumption of calvarial bone cells in vitro

Tissues with tortuous and narrow diffusion pathways and cells that are remote from blood vessels nonetheless can show high metabolic activity of which the underlying bases (transport mechanisms) are not fully understood. In one such bone tissue, the O2 consumption was measured by analyzing the decrease in the partial pressure of oxygen (Po2) in a closed chamber containing calvarial fragments from adult guinea pigs (250-400 g) or from neonatal rats and guinea pigs. The O2 consumption of fragments from adult guinea pigs amounted to 0.05, 0.066, and 0.095 ml/100 g* minute at 24, 27, and 36.5 degrees C, respectively. When the temperature exceeded 43 degrees C, O2 consumption irreversibly stopped. Both antimycin A and rotenone, which block the respiratory chain, reduced O2 consumption to approximately 20% of control values. O2 consumption was significantly higher in neonatal animals (0.369 ml/100 g* minute at 27 degrees C) and could be blocked completely by antimycin A. On the basis of the high consumption of O2 by bone cells, we hypothesize that specialized transport systems, i.e., gap junctions, are required to provide a sufficient supply of nutrients to cells in osseous tissue.

Marine SP Surveys for Dam Seepage Investigations: Evaluation of Array Geometries through Modeling and Field Trials

Marine spontaneous potential (SP) surveys have been used on reservoirs for several decades. Most surveys have used gradient arrays towed at the surface or at some depth in the water column. Water column gradient arrays are efficient, but at the cost of some sensitivity. Other surveys have used a single fixed electrode and a roving electrode dragged across the reservoir bottom. These surveys have typically been labor intensive and logistically limited. Finite difference models and field trials were used to evaluate the sensitivity and field productivity of gradient arrays and roving electrode arrays, in the water column and on the reservoir floor, for detecting narrow seepage pathways in a large reservoir. The pre‐survey finite‐difference models suggested the greatest sensitivity would be achieved with the electrodes at the sediment‐water interface. The gradient array models produced a bipolar anomaly with the spacing between the spikes equal to the electrode spacing. The single roving electrode models produced the sharpest, most easily interpreted anomalies. Single roving electrode and gradient arrays were field tested. Several electrode coupling modes were tested, including electrodes suspended at different heights in the water column, mechanically planted in the sediment, and dragged across the sediment (benthic arrays). The field trials demonstrated that physical coupling between the electrodes and the sediment significantly improved survey results. Benthic gradient arrays were most suitable for reconnaissance surveys. Benthic single roving electrode arrays were most suitable for detailed surveys in areas of suspected seepage features. The field trials were followed by two production surveys using a benthic single roving electrode array. The surveys successfully mapped seepage paths under the clay liner of the reservoir. The detected anomalies were generally less than 3 meters wide, which made high spatial sampling density and accurate position control critically important.

Cell cycle of neural crest cells in the early migratory stage in vivo

Abstract. The fact that directional migration of neural crest cells (NCC) in vivo occurs in narrow pathways at high cell density, together with our preliminary results showing their high proliferative behaviour, supports the view that a ‘population pressure’ could be an important factor in the mechanism of early dispersion of NCC.The purpose of this work was to establish the cranial proliferative pattern of chick embryo NCC during their early migratory stage in vivo. Growth rates and parameters of cell cycle were obtained from cell populations at several cephalic levels by means of autoradiography after labelling with [3H]dT. The labelled cell index of NCC (Forebrain, 0.288; Midbrain, 0.206; and Hindbrain, 0.134) was significantly greater than in other cells populations (e.g. for the neural tube cells: 0.085, 0.030, and 0.031, respectively). The cell generation time was the shortest in NCC (16 h), compared to ectoderm (33 h), mesoderm (58 h) and endoderm (72 h). The duration of the cell cycle phases for NCC were: M, 0.29 h; G1, 11.23 h; S, 3.40 h; and G2, 1.02 h.These quantitative results show that NCC have the greatest proliferative rate in young chick embryos. In relation to cranial regions, the data are consistent with the idea that, in the early migratory phase of this cell population in vivo, migration is in part driven by population pressure.

Excitation wave propagation within narrow pathways: Geometric configurations facilitating unidirectional block and reentry

The propagation of excitation waves in narrow pathways of 2D excitable media through regions of impermeable media and decreased excitability media is investigated as a model of reentrant arrhythmias in the heart. Arrhythmia occurrences are common in the presence of infarct scars where regions of normal tissue are interspersed with inexcitable ones. Propagation through narrow pathways with three idealized geometric configurations are considered: propagation through narrow paths with either parallel borders, tapered borders, or a combination of these. The focus of this study is on the conditions for unidirectional block and reentry appearance. It is shown that in narrow paths with only parallel borders unidirectional block is impossible, regardless of the properties of the border media. In this case only bidirectional propagation or block is possible, depending on the pathway width. Unidirectional block can occur, however, when the narrow path has a tapered shape. Waves propagating from the wide end of the pathway die out at the narrow end, while waves propagating in the opposite direction are able to pass through. An approximate relationship between the geometry of the pathway and wave front curvature is obtained. This provides a simple approach to estimate the critical curvature value in computer simulations of various excitable media or in experiments with real media. A new computer simulation approach is proposed to closely approximate the dependence of stationary speed of propagation on wave front curvature. In computer simulations of a two dimensional grid of 128 × 128 membrane segments, using the modified FitzHugh-Nagumo equations, the arrangement of two or more pathways in parallel permits reentry if at least one pathway has a configuration causing unidirectional block, and the medium at the site of unidirectional block has sufficient time to recover from the previous excitation. The latter is facilitated by anisotropic conduction properties of the media especially in the case with impermeable borders. Thus, there exist specific geometric configurations of two dimensional narrow pathways, which allow reentry even when the media properties are uniform.

Construction of a yeast cell fusion system using a fluid integrated circuit

A novel system for cell fusion between prototroph yeasts was constructed using a fluid integrated circuit (FIC) in which all micromanipulating components were photo-lithographically integrated on a small substrate (5 x 7 cm). Each parent protoplast was gradually introduced from each inlet using micropumps made of piezoelectric transducers on the FIC. Two kinds of protoplasts were sent one by one into narrow pathways (the minimum diameter: 50 μm), dielectrophoretically trapped at the opening made at the center of an insulating barrier placed between parallel electrodes and an exclusive one-to-one hybrid was continuously formed under intensive pulses. Each fusant was sent to an outlet.

Guidance of neurite outgrowth by pathways of substratum-adsorbed laminin.

Neurite outgrowth is guided by narrow pathways of bioactive laminin. These pathways are created by ultraviolet light irradiation of laminin-coated coverslips masked with electron microscope grids. Patterned outgrowth of neurites is independent of gross mechanical guidance and guidance caused by substrate limitation. Cells on unirradiated laminin are less readily displaced by shear forces than cells on irradiated laminin. This study suggests that ultraviolet light alters the adhesive properties of laminin and that differential cell-substratum adhesion may guide extending neurites on the purified naturally occurring substance, laminin.

Neural crest cell migration: requirements for exogenous fibronectin and high cell density.

Cells of the neural crest participate in a major class of cell migratory events during embryonic development. From indirect evidence, it has been suggested that fibronectin (FN) might be involved in these events. We have directly tested the role of FN in neural crest cell adhesion and migration using several in vitro model systems. Avian trunk neural crest cells adhered readily to purified plasma FN substrates and to extracellular matrices containing cellular FN. Their adhesion was inhibited by antibodies to a cell-binding fragment of FN. In contrast, these cells did not adhere to glass, type I collagen, or to bovine serum albumin in the absence of FN. Neural crest cell adhesion to laminin (LN) was significantly less than to FN; however, culturing of crest cells under conditions producing an epithelioid phenotype resulted in cells that could bind equally as well to LN as to FN. The migration of neural crest cells appeared to depend on both the substrate and the extent of cell interactions. Cells migrated substantially more rapidly on FN than on LN or type I collagen substrates; if provided a choice between stripes of FN and glass or LN, cells migrated preferentially on the FN. Migration was inhibited by antibodies against the cell-binding region of FN, and the inhibition could be reversed by a subsequent addition of exogenous FN. However, the migration on FN was random and displayed little persistence of direction unless cells were at high densities that permitted frequent contacts. The in vitro rate of migration of cells on FN-containing matrices was 50 microns/h, similar to their migration rates along the narrow regions of FN-containing extracellular matrix in migratory pathways in vivo. These results indicate that FN is important for neural crest cell adhesion and migration and that the high cell densities of neural crest cells in the transient, narrow migratory pathways found in the embryo are necessary for effective directional migration.

Gulfs of Northern Red Sea: Depositional Settings of Distinct Siliciclastic-Carbonate Interfaces: ABSTRACT

The two narrow gulfs of the northern Red Sea, Gulf of Suez and Gulf of Eilat (Aqaba), have had different tectonic histories, but both display active interfingering of siliciclastic and carbonate facies. In an early stage of rifting, these embryonic seas are flanked by rugged mountains (about 2,000 m, 6,500 ft) and narrow coastal plains built of fans composed of poorly sorted terrigenous debris. An arid setting promotes aperiodic transport of siliciclastic sediments as well as deposition of evaporites (coastal sabkhas) and carbonates (reefs and associated sediments). Gulf margins prograde by a combination of rapid fan deposition during flash floods and subsequent carbonate stabilization of terrigenous fans and cones during intervening periods. High-resolution seismic and s de-scan sonar data suggest that narrow pathways for sediment transport are continually active on these features and probably accommodate much of the sediment transport to deep water during small discharge events. Large flash floods may completely overwash carbonates at the distal ends of fans, requiring renewed reef development. Rapid siliciclastic deposition, coupled with biological and chemical binding of carbonates as well as their tendency toward vertical buildups, results in steep slopes along the gulf margins. The Gulf of Suez is shallow ( 12 km, 7.5 mi) and geometrically complicated strait separates it from the northern Red Sea. In contrast, the Gulf of Eilat is deep ( 50 cm/sec, 20 in./sec)--tend to streamline reefs and sediment bodies, creating spindle-shaped carbonate platforms. The Gulf of Eilat has no mid-gulf platforms, but a complex of reef-dominated carbonates exists on gulf-normal structural blocks at the Strait of Tiran. A cross section reduction of this already narrow strait by lowering of sea level, reef growth, and/or sedimentation could drasticall change the basin-filling process through restricted flow by eliminating reef growth and initiating salt deposition. End_of_Article - Last_Page 541------------

Pathways and mechanisms of avian trunk neural crest cell migration and localization

Crest cells individualized at the dorsal border of the neural tube, while they became surrounded by a fibronectin-rich matrix. Crest cells initiated their migration between the basement membranes of the neural tube and the ectoderm. In the vagal region, crest cells migrated in a fibronectin-rich environment between the ectoderm and the dermomyotome, very rapidly reaching the apex of the pharynx. In the trunk region, crest cells opposite the bulk of the somite accumulated at the junction between the somite, the neural tube, and the ectoderm; they resumed their migration at the onset of the dissociation of the somite into dermomyotome and sclerotome. Migration occurred more ventrally along the neural tube; nevertheless, the formation of the rapidly expanding sclerotome prevented crest cells from reaching the paranotochordal region. Thereafter, crest cells accumulated between the neural tube, the dermomyotome, and the sclerotome, where ultimately they formed the dorsal root ganglia. In contrast, cells opposite the intersomitic space did not encounter these obstacles and utilized a narrow pathway formed between the basement membranes of the two adjacent somites. This pathway allowed crest cells to reach the most ventral regions of the embryo very rapidly; they accumulated along the aorta to form the aortic plexuses, the adrenal medulla, and the sympathetic ganglia. The basic features of the migration pathways are (1) a strict delimitation by the fibronectin-rich basement membranes of the surrounding tissues, (2) a formation of space concomitant with the migration of crest cells, (3) a transient existence: continued migration is correlated with the presence of fibronectin, whereas cessation is correlated with its focal disappearance. The crest cells are characterized by their inability to traverse basement membranes and penetrate within tissues. We propose that the combination of active proliferation, unique motility properties, and the presence of narrow pathways are the major mechanisms ensuring correct directionality. Morphologically defined transient routes of migration along with developmentally regulated changes in the extracellular matrix and in the adhesive properties of crest cells are most probably involved in their stabilization in defined territories and their aggregation into ganglia.

Acholi Folk Tales

TOWARDS SUNSET, as the day's work is over, you can see, moving along narrow pathways, in single file, groups of men and boys, carrying logs or branches of wood, as well as their hoes. You can also hear the flutes of the herdsboys bringing the cattle home. The women and girls have returned home from the gardens much earlier to prepare the evening meal and to do other domestic chores. On arrival, the younger boys take turns to make the outdoor fire Mac wang Oo, whilst the older men have their hot baths. Soon, all those not otherwise engaged, come and sit around the fire, waiting for supper. The stage is set for talking folk tales.

A hypersthene andesite from Drumyat (Ochils)

The structure of the West End of the Ochils, where they terminate in the cliff overlooking Bridge of Allan and the Forth valley, is well exposed in many fine natural sections. Their extreme west end consists of massive beds of volcanic conglomerate, seen well in the narrow pathways behind Airthrey Castle. These are only irregularly bedded, and, while large blocks are few, they are, on the whole, coarse, and contain little fine detritus. The blocks have a rounded and distinctly water-worn appearance, and it is possible, every here and there, to find among them nests and patches of sand and shale, in a few places, amounting to distinct beds of sandstone. The general dip is to the N.W. about 10°. The lavas are strikingly limited in development in the western area, while, as we ascend the slopes of Dumyat, they gradually become more and more important, and, finally, in very great measure replace the fragmental rocks. In the precipitous face of the hill overlooking Menstrie and Logie Church, every bed of lava and ash can be well seen, as they follow one another in regular succession. They form a regularly interbedded series, the lavas thinning out gradually as they pass westwards, while the ash beds close over them—a feature suggesting their origin from a volcanic focus situated to the eastward or southeastward. On the level moor, which forms the back of Dumyat, the sections are not quite so clear, but the structure is not difficult to read. The Sherriffmuir Road,