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PubMed2005

Epileptiform activity preferentially arises outside tumor invasion zone in glioma xenotransplants.

Seizures occur commonly with brain tumors. The underlying mechanisms are not understood. We analyzed network and cellular excitability changes in tumor-invaded and sham neocortical tissue in vitro using a rat glioblastoma model. Rat C6 glioma cells were transplanted into rat neocortex, yielding diffusely invading gliomas resembling human glioblastomas. We hypothesized that network excitability would increase in regions neighboring the tumor, and that initiation of epileptic discharges might be correlated to a higher density of intrinsically bursting neurones. Voltage-sensitive dye imaging revealed epileptic activity to be initiated in paratumoral zones (1-2 mm from main tumor mass), in contrast to control tissue, where epileptic foci appeared randomly throughout the neocortex. Neuronal firing patterns revealed significantly more intrinsically bursting neurones within these initiation zones than in regions directly adjacent to the tumor or in control tissue. We conclude that gliomas are associated with a higher density of intrinsically bursting neurones, and that these may preferentially initiate epileptiform events.

Action Potentials↗
PubMed1994

Diffusing capacity dependent on lung volume and age in normal subjects.

In this study we determined reference values of total diffusing capacity of carbon monoxide (DLCO) and DLCO per liter alveolar volume (DLCO/VA) at total lung capacity (TLC) and at lung volumes below TLC in sitting position. In 55 healthy nonsmoking volunteers (20-85 yr old), we determined reference values at TLC level in which age was the only parameter. In a subgroup (n = 16) these references did not change by correction for normal variability in hemoglobin concentration. In all volunteers DLCO decreased and DLCO/VA increased with decreasing VA. The increase in DLCO/VA was linear and less in older subjects. We derived equations to calculate reference values of DLCO/VA for lung volumes at and below TLC with two methods: 1) "random coefficients linear" model, which calculates the reference values directly, and 2) a conversion method, which calculates DLCO/VA for lower VA levels from reference values at TLC. An advantage of the conversion method is the suitability of DLCO/VA reference values at TLC of other populations. A disadvantage is the greater standard deviation of these reference values compared with those obtained by the random coefficients linear method. DLCO can be found by multiplying DLCO/VA with VA.

Adult↗
PubMed1993

Reaction-diffusion control of heart development: evidence for activation and inhibition in precardiac mesoderm.

In axolotl embryos homozygous for the cardiac-lethal (c) gene, the heart never begins to beat. Recently, we demonstrated that the c gene affects the heart mesoderm directly, making the latter incapable of responding to normal inductive stimuli. Based on these results, we proposed that a reaction-diffusion mechanism controls the later stages of vertebrate cardiogenesis. In the present study, we use a series of transplantations to examine the precardiac mesoderm of wild-type and cardiac-lethal mutant axolotl embryos for the activation and inhibition predicted by our model. When one or both heart primordia in c/c embryos were replaced with +/+ tissue at early stages, functional hearts developed, indicating that an activator-like activity is present in wild-type heart mesoderm. At later stages, replacement of the entire heart-field mesoderm also rescued mutant embryos, but replacement of only the heart-forming mesoderm did not, indicating that the mutant heart field has inhibitory properties. These results demonstrate that activator- and inhibitor-like factors are present in pre-cardiac mesoderm and thus provide evidence for reaction-diffusion control of postinductive heart development.

Ambystoma↗
PubMed1999

Protein diffusion in charged polyacrylamide gels. Visualization and analysis.

Protein diffusion in anionic, cross-linked polyacrylamide-based gels supported in fused-silica capillaries was characterized by a direct visualization method. Microphotography was used to obtain transient protein concentration profiles in these gels using cytochrome c as a probe molecule. Gels based on acrylamido-methylpropane sulfonic acid with 2.5-10% N,N'-methylene-bisacrylamide as a cross-linker and with a total polymer concentration of 0.21 g/cm3 yielded diffuse protein concentration profiles which were quantitatively consistent with a Fickian diffusion model. An analytical method was developed to calculate the diffusivity as a function of protein concentration in the gel from the experimental profiles. The diffusivity was found to assume values in the range 2.5-5.5x10(-8) cm2/s and varied somewhat with the protein concentration in the gel. The effects of some of the polymer properties, such as cross-link density, polymer concentration and charge, were also investigated for a limited range of conditions to derive qualitative trends. Results showed that the transport rates increased with a decrease in the cross-link density, were extremely reduced when the polymer concentration was doubled, and were slightly increased when the charge density was decreased by half by polymerizing a 1:1 mixture of acrylamide and acrylamido-methylpropane sulfonic acid monomers.

Acrylic Resins↗
PubMed2003

Solid stress generated by spheroid growth estimated using a linear poroelasticity model.

The unchecked growth of a solid tumor produces solid stress, causing deformation of the surrounding tissue. This stress can result in clinical complications, especially in confined environments such as the brain, and may also be responsible for pathophysiological anomalies such as the collapse of blood and lymphatic vessels. High stress levels may also inhibit further cell division within tumors. Unfortunately, little is known about the dynamics of stress accumulation in tumors or its effects on cell biology. We present a mathematical model for tumor growth in a confined, elastic environment such as living tissue. The model, developed from theories of thermal expansion using the current configuration of the material element, allows the stresses within the growing tumor and the surrounding medium to be calculated. The experimental observation that confining environments limit the growth of tumor spheroids to less than the limit imposed by nutrient diffusion is incorporated into the model using a stress dependent rate for tumor growth. The model is validated against experiments for MU89 tumor spheroid growth in Type VII agarose gel. Using the mathematical model and the experimental evidence we show that the tumor cell size is reduced by solid stress inside the tumor spheroid. This leads to the interesting possibility that cell size could be a direct indicator of solid stress level inside the tumors in clinical setting.

Animals↗
PubMed1996

Transverse relaxation in random bead packs: comparison of experimental data and numerical simulations.

Inverse Laplace transform techniques are commonly used to convert nuclear magnetic resonance (NMR) relaxation data in porous media into lifetime distributions. In this connection, we present a direct comparison of T2 measurements made on monosized packings of sintered glass beads and numerical simulations based on the grain consolidation model. Three systems, with porosities of 0.38, 0.22, and 0.14, were studied, and in each case we found that the position and width of the measured T2 distribution was well represented by the random walk simulations. These systems are generally in the fast diffusion (weak surface relaxation) regime and have relatively narrow T2 distributions. For this reason, we have found that inverse Laplace transform techniques are particularly sensitive to random noise in the measured and simulated decay spectra.

Computer Simulation↗
PubMed2004

Influence of operating parameters on the retention of chromatographic particles by thermal field-flow fractionation.

We have investigated the retention behavior of chromatographic particles in thermal field-flow fractionation (FFF). Retention time is found to increase with increasing temperature drop across the channel thickness, as expected for species exhibiting a thermophoretic mobility. Experiments have been performed with a vertically oriented channel rather than by using the classical horizontal configuration as this leads to much more reproducible retention data. In acetonitrile, silica-based particles are more retained than octadecyl-bonded silica particles, which confirms our previous finding, by means of a different method, that the thermophoretic mobility of the latter is smaller than that of the former. Whatever the type of particles and the nature of the carrier liquid, the relative retention time is observed to decrease with increasing carrier flow rate. This indicates that a hydrodynamic lift force acts on particles to move them away from the accumulation wall, as is usually observed in all FFF experiments with micrometer-sized particles. However, upward and downward flow directions in the vertical channel lead to similar retention data, indicating that inertial lift forces have a minor influence on retention. In addition, the relative retention time steadily decreases with increasing sample concentration, suggesting that the hydrodynamic lift force increases significantly with sample concentration. Accordingly, we speculate that a new transport phenomenon, called shear-induced hydrodynamic diffusion, not previously accounted for in the modeling of retention in FFF, is controlling the migration of the particles in the FFF channel. Implications of the influence of this phenomenon in other FFF experiments are discussed.

Chemical Fractionation↗
PubMed1994

Diffusion and metabolism of prednisolone farnesylate in viable skin of the hairless mouse.

The diffusion and metabolism of prednisolone 21-farnesylate were investigated in viable skin of the hairless mouse in vitro. The prodrug ester was extensively metabolized in viable skin, while it was stable in the donor and receptor solutions. The rate of appearance of the prodrug and its metabolite prednisolone was markedly influenced by the direction of the skin placed between the in vitro diffusion half-cells. The rate of bioconversion of the prodrug was determined as a function of the distance from the surface of the skin. The prodrug was increasingly metabolized with the distance from the surface of the skin, indicating that the responsible enzymes are enriched in the lower layers of the viable skin. A model with linearly increasing enzyme activity in the viable skin accounts for the in vitro profiles of the diffusion/metabolism of the prodrug in the viable skin of hairless mouse.

Animals↗
PubMed2000

Spatiotemporal growth of faceted and curved single crystals

The spatiotemporal growth of single crystals in a crystalline polymer has been investigated theoretically based on a nonconserved time dependent Ginzburg-Landau equation (known as TDGL model A). In the description of the total free energy, a double-well local free energy density signifying metastability of crystal ordering is combined with a nonlocal free energy term representing an interface gradient. The resulting nonlinear reaction diffusion equation after renormalization possesses a solitary wave property. Two-dimensional numerical calculations were performed to elucidate the faceted single crystal growth including square, rectangular, diamond-shaped, and curved single crystals. A three-dimensional simulation was also undertaken for the emergence of diamond-shaped single crystals in polyethylene. Of particular importance is that the model field parameters can be linked directly to the material parameters of polyethylene single crystals. Simulation with various elements of the interface gradient coefficient tensor captures various topologies of polymer single crystals.

Journal Article↗
PubMed2002

Free growth and instability morphologies in directional melting of alloys.

The dynamics of melting morphologies, namely, liquid droplets in the bulk solid and liquid dendrites due to morphological instability of the phase boundary, is observed in situ and in real time during directional melting of transparent succinonitrile-acetone alloys in a cylinder. Specific patterns are associated to grain boundaries. A model based on free growth but with time-dependent superheating is proposed for the lateral growth of the liquid inclusions. Contrary to what is largely believed, it is shown that free melting is not the mere reversal of free crystal growth, basically because solute diffusion is much lower in the solid, which imposes a boundary layer approach.

Journal Article↗
PubMed1991

Transcutaneous chemical collection of caffeine in normal subjects: relationship to area under the plasma concentration-time curve and sweat production.

A novel transcutaneous chemical collection device (TCD) has been developed to study the phenomenon of outward transcutaneous chemical migration. The TCD is a Bandaid-like device containing an immobilized aqueous media and binding reservoir material to prevent back-transfer into the skin. This device, when placed against the skin, allows collection and quantitation of chemicals that diffuse directly through the skin from within the body. The relationship of the amount of drug collected in the TCD to the amount in the body available for collection (as represented by the area under the plasma-concentration time curve, AUC) and the effects of sweating, a potential confounding factor, on collection of drug in a TCD were studied, using caffeine as a model compound. TCD were placed on the skin of normal male volunteers. Twenty-four hours later subjects took caffeine by mouth. Blood samples were collected and TCD were removed at various times after drug intake and analyzed by HPLC for caffeine. Studies of the sweating effect were carried out in a similar manner, except that one arm of each subject was maintained at 40 degrees C to induce local sweating, the other arm acted as a non-sweating control. The amount of caffeine collected was linearly related to the AUC. Sweating seemed to have a large (40%) contribution to transdermal collection in the early period (5.5 h) of the study, but this difference was much less (14%) at longer collection times (10 h).

Adult↗
PubMed1995

Roles of oxidative stress in activation of Kupffer and Ito cells in liver fibrogenesis.

An increasing body of experimental evidence is emerging to incriminate oxidative stress as a pivotal signal for liver fibrogenesis. This paper reviews the results from our studies testing this hypothesis. In the rat model of alcoholic liver disease, the importance of oxidative stress was supported by marked accentuation of liver fibrosis by dietary supplementation of iron, a pro-oxidant, and the significant correlation of the liver malondialdehyde (MDA) and 4-hydroxynonenal (4HNE) levels with the hepatic collagen accumulation. Both MDA and 4HNE adduct epitopes were detected intensely and diffusely in close association with collagen deposition. The direct cause and effect relationship between MDA/4HNE and Ito cell stimulation was indicated by the demonstration of Ito cell collagen gene induction by these aldehydes in culture. In primary cultures of rat Kupffer cells (KC), addition of antioxidants such as alpha-tocopherol acetate and succinate suppressed mRNA expression and the release of interleukin (IL)-6 and tumour necrosis factor alpha (TNF alpha). In rats with biliary fibrosis, an increase in the liver MDA level was accompanied by enhanced mRNA expression of procollagen alpha 1(I) and transforming growth factor beta 1 in Ito cells; and that of TNF alpha and IL-6 in KC. Furthermore, the gel shift assay of KC nuclear extracts showed enhanced NF-kB DNA binding activity. These results support the proposal that enhanced oxidative stress constitutes an important signal for activation of Kupffer and Ito cells in experimental liver fibrogenesis.

Aldehydes↗
PubMed1999

Decompressive craniectomy, reperfusion, or a combination for early treatment of acute "malignant" cerebral hemispheric stroke in rats? Potential mechanisms studied by MRI.

BACKGROUND AND PURPOSE: Both early reperfusion and decompressive craniectomy have proved beneficial in the treatment of large space-occupying "malignant" hemispheric stroke. The aim of this study was to directly compare the benefit of reperfusion with that of craniectomy and to study the effects of combined treatment in a rat model of focal cerebral ischemia. METHODS: Cerebral ischemia was introduced in 28 rats. Four groups were investigated: (1) no treatment, (2) decompressive craniectomy, (3) reperfusion, and (4) reperfusion and craniectomy as treatment at 1 hour after middle cerebral artery occlusion. Perfusion- and diffusion-weighted MRI were performed serially from 0.5 to 6 hours after middle cerebral artery occlusion. RESULTS: The 6-hour DWI-derived hemispheric lesion volumes in the reperfusion group (10.2+/-3.9%), the craniectomy group (23.0+/-6.4%), and the combination group (21.8+/-12.4) were significantly smaller than that in the control group (44.1+/-5.4%) (P<0.05). Reperfusion, craniectomy, and combined treatment led to higher perfusion in the cortex compared with the control group, whereas only reperfused animals achieved significantly higher perfusion in the basal ganglia. In 5 animals, combined reperfusion and decompressive craniectomy resulted in an early contrast media enhancement. CONCLUSIONS: Early reperfusion and craniectomy were shown to be effective in decreasing infarction volume by improving cerebral perfusion. Reperfusion remains the best therapy in malignant hemispheric stroke. Combined treatment yields no additional benefit compared with single treatment, probably because of early blood-brain barrier breakdown.

Acute Disease↗
PubMed1998

In vitro bovine ciliary body/epithelium in a small continuously perfused Ussing type chamber.

Our goal is to assess the viability of an in vitro preparation of bovine ciliary body/epithelium (CBE) in a small volume Ussing-type chamber. A new small volume Ussing-type chamber with continuous perfusion was developed for bovine CBE. The trans-CBE electrical parameters were monitored and the electrical responses of the CBE to ouabain (1 and 0.01 mM) were recorded. The trans-CBE fluxes of [14C]-L-ascorbate and [3H]-L-glucose were also studied. The bovine CBE preparation was stable inside the chamber in terms of its potential difference (PD), short circuit current (SCC) and trans-CBE resistance. They were -0.51+/-0.05 mV (aqueous side negative), -5.43+/-0.04 microAcm-2 and 94+/-2 Q.cm2 (mean s.e.m., n=35), respectively. The preparation hyperpolarised when 0.01 mM ouabain was administered to the aqueous side, depolarised when ouabain was applied to the stromal side. [3H]-L-glucose diffusion was about 74 nEq h(-1)cm(-2) in either direction (n=12). Taking the area magnification factor of the CBE into consideration, the diffusional L-glucose flux across the bovine CBE was comparable to other tight epithelia. A significant net ascorbate flux (0.26+/-0.05 nEq h(-1)cm(-2), n=4, p<0.01) was found in the stroma to aqueous direction. We have developed a viable in vitro bovine CBE preparation which was (1) electrically stable, (2) responsive to ouabain, (3) tight to L-glucose diffusion, and (4) capable of actively secreting ascorbate. A net trans-CBE chloride transport (0.81+/-0.30 microEq h(-1)cm(-2), n=12, p=0.01) from stromal to aqueous side was found in the present in vitro model under short-circuited conditions.

Animals↗
PubMed1975

[Toxicology of epidithio-dioxopiperazines. 1. Studies on toxicity of cyclosarcosylsarcosineepitetrasulfide in guinea pigs and rats].

The present paper deals with the toxic effect of a mycotoxin of the group of epidithio-dioxopiperazines: cyclo-sarcosyl-sarcosin-epitetrasulfide, particularly upon the liver of guinea-pigs and rats. The sporidesmines, related to the compound tested, cause chronic obstructive cholangitis characteristic of a disease in sheep endemic in New Zealand. This type of cholangitis was attempted to be reproduced in order to establish an experimental model of producing biliary cirrhosis in animals. The acute and subacute LD50 in rats and guinea-pigs were determined intraperitoneally and intragastrally. In neither mode of application nor in short-term nor in chronic test could we find any specific, dose dependent changes of bile ducts. Merely, parenteral administration of lethal doses led to unspecific subcapsular liver necroses obviously due to direct diffusion of the toxic agent. The discrepancy between the efficacy of the toxic grass in New Zealand and the substance tested in the study is discussed.

Administration, Oral↗
PubMed1992

Development and characterization of an experimental model of brain abscess in the rat.

Brain abscesses were produced in the rat by direct intracerebral injection of agarose beads laden with Staphylococcus aureus. The method proved to be easy, reproducible, effective and was associated with a low mortality rate. The histopathologic features of the experimental abscess are similar to other animal models and to human abscesses. The encapsulation of the lesion, macrophage/microglial response, astrocytic activation, and changes in the surrounding brain parenchyma were studied by immunohistochemistry. Edema, diffuse microglial activation and diffuse astrocytosis characterized the early reaction of the injected cerebral hemisphere. After day 10, edema subsided, and the microglial and astrocytic responses became restricted to the area around the lesion. Fibronectin deposition in the capsule preceded the appearance of myofibroblasts, which was concurrent with the beginning of collagen deposition on day 9. Hypervascularity of the capsule appeared as early as day 6 and persisted through day 28. This study suggests that brain abscess formation can be separated into three components: an initial period of edema and glial activation; an intermediate phase of neovascularization and fibronectin deposition; and a final phase of collagen deposition and progressive fibrosis. This new model offers an excellent paradigm for the analysis of neural tissue reaction and de novo fibrous tissue deposition.

Animals↗
PubMed1983

Regeneration of spinal neurons in inframammalian vertebrates: morphological and developmental aspects.

This review discusses regeneration of spinal neurons in inframammalian vertebrates. In contrast to the limited regeneration of nerve fibers in mammalian spinal cord, relatively complete regeneration of spinal cord, including the formation of new neurons, occurs in cyclostomes, selachians, teleosts, and urodele amphibians. The various experimental techniques which have been used to accelerate or enhance regeneration of spinal cord, such as implantation of peripheral nerve bridges, application of growth factors or chemical agents, and the application of exogenous electrical fields, are discussed. Processes involved in regeneration of other systems, e.g., the trophic effect of nerve fibers, the effect of certain hormones, and the effects of the blastema, are discussed as they may relate to regeneration in the spinal cord. Recent work on the factors which influence nerve outgrowth is discussed. Factors such as diffusible chemical gradients, contact with other cells, pre-formed channels for nerve growth, and differences in adhesivity of neurites for the substratum may act to control the direction of axon outgrowth in regeneration as well as normal embryonic development. This article next reviews work from our laboratory on regeneration of spinal neurons in the teleost, Sternarchus albifrons. We have used Sternarchus as a model system for the study of regeneration and remyelination since: 1. spinal cord readily regenerates after amputation of the tail, 2. new nerve cell bodies are formed during this regeneration, and 3. Sternarchus contains large neurogenic electric organs which also regenerate after tail amputation. The axons of the electric organ arise from spinal neurons and have a highly specific and complex morphology which is recapitulated after regeneration. Studies on Sternarchus indicate that new nerve cell bodies are produced during regeneration from the enlarged ependymal cells. Initially, many more of the electromotor neurons are produced in regenerated spinal cord than are present normally. Cell death subsequently occurs in some of these asynaptic cells, reducing the number of electrocytes in older regenerated cord to a more normal condition. The spinal electromotor neurons in Sternarchus have also been used to demonstrate that section of the axon in an asynaptic neuron will produce a typical "axon reaction" in the cell body. It is interesting that cell death during regeneration and the retrograde axon reaction both appear to occur without loss of synaptic elements in these normally asynaptic cells. Neurites grow through regenerating Sternarchus spinal cord in small bundles, in close contact with adjacent ependymal cell processes. Longitudinal channels, filled with neurites, are seen extending through many stages of regenerating Sternarchus cord, usually near the periphery of the cord. There are numerous invaginations of the peripheral edge of regenerating cord and its associated external lamina. These infoldings may be involved in the generation of the neurite filled channels.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗
PubMed1996

Structure of the LexA repressor-DNA complex probed by affinity cleavage and affinity photo-cross-linking.

The structure of the complex of full-length Escherichia coli LexA repressor with a consensus operator DNA fragment has been probed by affinity photo-cross-linking and affinity cleavage. These methods allow the determination of approximate intermolecular distances between a given protein residue and a base or sugar moiety within the operator. In a first step unique cysteine residues were introduced in positions 7, 28, 38, or 52 of the protein. In all four cases, the original amino acid was an arginine. The four amino acids in these positions were expected to be situated on the surface of LexA interacting with DNA, as inferred from the structure of the LexA DNA binding domain [Fogh et al. (1994) EMBO J. 13, 3936-3944]. In a second step, these unique cysteine side chains of the purified proteins were chemically modified either with 4-azidophenacyl bromide or with S-(2-pyridylthio)cysteaminyl-EDTA. The first set of derivatives gives rise to UV-induced cross-linking which may be revealed by alkali/heat treatment; the second leads to direct DNA cleavage in the proximity of the derivatized amino acid. To reduce hydroxyl radical diffusion, the EDTA-iron cleavage reactions were done in the presence of high amounts of glycerol. The results indicate that amino acids 7 and 52 are near nucleotide pairs 8-12 of the operator and that amino acids 28 and 36 of LexA are near nucleotide pairs 5-8 of the operator. The results unambiguously define the orientation of the LexA DNA binding domain relative to the operator and provide support for the model of the LexA-operator complex proposed by Knegtel et al. [(1995) Proteins 21, 226-236]. Ethylation interference experiments further suggest that Arg-7 contacts the phosphate group between nucleotides 8 and 9 as predicted by the model.

Affinity Labels↗