Laning and clustering transitions in driven binary active matter systems

It is well known that a binary system of nonactive disks that experience driving in opposite directions exhibits jammed, phase separated, disordered, and laning states. In active matter systems, such as a crowd of pedestrians, driving in opposite directions is common and relevant, especially in conditions which are characterized by high pedestrian density and emergency. In such cases, the transition from laning to disordered states may be associated with the onset of a panic state. We simulate a laning system containing active disks that obey run-and-tumble dynamics, and we measure the drift mobility and structure as a function of run length, disk density, and drift force. The activity of each disk can be quantified based on the correlation timescale of the velocity vector. We find that in some cases, increasing the activity can increase the system mobility by breaking up jammed configurations; however, an activity level that is too high can reduce the mobility by increasing the probability of disk-disk collisions. In the laning state, the increase of activity induces a sharp transition to a disordered strongly fluctuating state with reduced mobility. We identify a novel drive-induced clustered laning state that remains stable even at densities below the activity-induced clustering transition of the undriven system. We map out the dynamic phase diagrams highlighting transitions between the different phases as a function of activity, drive, and density.

Evolution of ELNES spectra as a function of experimental settings for any uniaxial specimen: A fully relativistic study

We perform calculations of the fully relativistic, corrected geometrical weighting of the pi* and sigma* transitions measured from the 1s core loss electron energy loss spectroscopy (EELS) spectrum in any uniaxial specimen. We present a complete calculation of the differential scattering cross-section (DSCS), taking into account the collection angle, the illumination angle and the tilt of the sample over the optical axis. Owing to high electron velocity in an EELS experiment, the relativistic correction has to be considered. We thus, present a relativistic, corrected DSCS by using the theory recently developed by Jouffrey et al. [Ultramicroscopy 102 (2004) 61] and P. Schattschneider et al. [Phys. Rev. B 72 (2005) 045142]. The relativistic correction is first performed in the natural coordinate system of the scattering event. We then point out a straightforward method to introduce this correction in the microscopic coordinate system, where all calculations have to be done to be experimentally useful. Using the fully corrected DSCS, we present an expression predicting the evolution of the R=pi*/(pi*+sigma*) ratio (related to the ratio of sp2 and sp3 bondings) as a function of experimental settings. We show how the R-evolution can be predicted, for any experimental setting, by the knowledge of one unique reference value. We verify on graphite specimens, the validity of the R-calculation by comparing theoretical predictions presented in this work with experimental data published elsewhere [Daniels et al., Ultramicroscopy 96 (2003) 523 and Menon et al., Ultramicroscopy 74 (1998) 83].

Degeneration of dopaminergic neurons triggers an expression of individual enzymes of dopamine synthesis in non-dopaminergic neurons of the arcuate nucleus in adult rats

Non-dopaminergic neurons expressing individual complementary enzymes dopamine (DA) synthesis were shown to produce DA in cooperation [Ugrumov, M., Melnikova, V., Ershov, P., Balan, I., Calas A., 2002. Tyrosine hydroxylase- and/or aromatic L-amino acid decarboxylase-expressing neurons in the rat arcuate nucleus: ontogenesis and functional significance. Psychoneuroendocrinology 27, 533-548; Ugrumov, M.V., Melnikova, V.I., Lavrentyeva, A.V., Kudrin, V.S., Rayevsky, K.S., 2004. Dopamine synthesis by non-dopaminergic neurons expressing individual complementary enzymes of the dopamine synthetic pathway in the arcuate nucleus of fetal rats. Neuroscience 124, 629-635]. This study was aimed at testing our hypothesis that the cooperative synthesis of DA in non-dopaminergic neurons is an adaptive reaction under functional insufficiency of the dopaminergic system. Functional insufficiency of the tuberoinfundibular dopaminergic system was provoked by 6-OHDA-induced degeneration of dopaminergic neurons in the arcuate nucleus in adult rats. Bienzymatic (dopaminergic) neurons and monoenzymatic neurons expressing tyrosine hydroxylase (TH) or aromatic L-amino acid decarboxylase (AADC) were detected with a double-immunofluorescent technique on cryostat sections. The 6-OHDA-induced degeneration of dopaminergic neurons was accompanied by a significant increase of the number of monoenzymatic TH neurons and AADC neurons that appears to support our hypothesis. The reaction of bienzymatic and monoenzymatic neuron populations to the 6-OHDA administration occurred to be region-specific. The former disappeared in the dorsomedial region of the arcuate nucleus while the latter increased in the ventrolateral region. Thus, degeneration of dopaminergic neurons in the arcuate nucleus of adult rats is accompanied by the expression of individual enzymes of DA synthesis in non-dopaminergic neurons that may be an adaptive reaction.

A novel reconstruction algorithm to extend the CT scan field-of-view

For various reasons, a projection dataset acquired on a computed tomography (CT) scanner can be truncated. That is, a portion of the scanned object is positioned outside the scan field-of-view (SFOV) and the line integrals corresponding to those regions are not measured. A projection truncation problem causes imaging artifacts that lead to suboptimal image quality. In this paper, we propose a reconstruction algorithm that enables an adequate estimation of the projection outside the SFOV. We make use of the fact that the total attenuation of each ideal projection in a parallel sampling geometry remains constant over views. We use the magnitudes and slopes of the projection samples at the location of truncation to estimate water cylinders that can best fit to the projection data outside the SFOV. To improve the robustness of the algorithm, continuity constraints are placed on the fitting parameters. Extensive phantom and patient experiments were conducted to test the robustness and accuracy of the proposed algorithm.

Nucleation and growth of single-walled nanotubes: the role of metallic catalysts

We present a review of experimental and theoretical results on the nucleation and growth of single-walled nanotubes, with particular emphasis on the growth of nanotube bundles emerging from catalyst particles obtained from evaporation-based elaboration techniques. General results are first discussed. Experiments strongly suggest a root-growth process in which carbon, dissolved at high temperatures in catalytic particles, segregates at the surface at lower temperatures to form tube embryos and finally nanotubes through a nucleation and growth process. A theoretical analysis of the reasons carbon does not always form graphene sheets to wrap the particles suggests analogies with other surface or interface instabilities, in particular, with those found in epitaxial growth. In the second part, detailed experimental results for nickel-rare earth metal catalysts are presented. By using various electron microscopy techniques, it is shown that carbon and the rare earth metal co-segregate at the surface of the particle and form carbide platelets, providing nucleation sites for nanotubes growing in directions perpendicular to the surface. A simple theoretical model is then presented in which the role of the rare earth metal is just to transfer electrons from metal to carbon. The graphene sheet is shown to become unstable; pentagons and heptagons are favored, which can explain the occurrence of local curvatures and of tube embryos. Finally, a brief discussion of some recent atomistic models is given.

Calculation of the Pitot tube correction factor for Newtonian and non-Newtonian fluids

This paper presents the numerical investigation performed to calculate the correction factor for Pitot tubes. The purely viscous non-Newtonian fluids with the power-law model constitutive equation were considered. It was shown that the power-law index, the Reynolds number, and the distance between the impact and static tubes have a major influence on the Pitot tube correction factor. The problem was solved for a wide range of these parameters. It was shown that employing Bernoulli's equation could lead to large errors, which depend on the magnitude of the kinetic energy and energy friction loss terms. A neural network model was used to correlate the correction factor of a Pitot tube as a function of these three parameters. This correlation is valid for most Newtonian, pseudoplastic, and dilatant fluids at low Reynolds number.

Multicriteria optimization of gluconic acid production using net flow

The biochemical process industry is often confronted with the challenge of making decisions in an atmosphere of multiple and conflicting objectives. Recent innovations in the field of operations research and systems science have yielded rigorous multicriteria optimization techniques that can be successfully applied to the field of biochemical engineering. These techniques incorporate the expert's experience into the optimization routine and provide valuable information about the zone of possible solutions. This paper presents a multicriteria optimization strategy that generates a Pareto domain, given a set of conflicting objective criteria, and determines the optimal operating region for the production of gluconic acid using the net flow method (NFM). The objective criteria include maximizing the productivity and concentration of gluconic acid, while minimizing the residual substrate. Three optimization strategies are considered. The first two strategies identify the optimal operating region for the process inputs. The results yielded an acceptable compromise between productivity, gluconic acid concentration and residual substrate concentration. Fixing the process inputs representing the batch time, initial substrate concentration and initial biomass equal to their optimal values, the remaining simulations were used to study the sensitivity of the optimum operating region to changes in the oxygen mass transfer coefficient, K(L) a, by utilizing a multi-level K(L) a strategy. The results show that controlling K(L) a during the reaction reduced the production of biomass, which in turn resulted in increased productivity and concentration of gluconic acid above that of a fixed K(L) a.

Statistical data validation methods for large cheese plant database

Production data of the cheesemaking process are used to monitor milk fat and protein recoveries in cheese, cheese yield, and composition and eventually to predict these parameters. Due to the large impact of these factors on cheese quality and plant profitability, it is very important to use reliable data for analysis, modeling, and control of the process. This paper tested six methods for detecting erroneous data in industrial cheesemaking databases. The data analyzed came from 4 yr of stirred-curd Cheddar cheese production in an industrial cheesemaking facility, comprising over 10,000 vats. Single vat outliers were detected using a simple statistical criterion of mean +/- 3.6 SD on single variable distributions, Fourier series modeling of seasonal variables (fat, protein, lactose, and total solids in milk, and protein in whey), and the multivariate Mahalanobis outlier analysis. Detection of outlier productions (corresponding to several vats) was done by applying the mean +/- 3.6 SD criterion to variables obtained through calculating the fat mass balance, fat retention coefficient, and yield efficiency. Data treatment enabled the detection of outlier data, but also pinpointed variables with a low reliability (manually registered times). Single variable and multivariable methods proved complementary, and the use of both types of methods is recommended when validating an existing database.

Rapid increase of mitochondrial uncoupling protein and its mRNA in stimulated brown adipose tissue

The increase in mitochondrial uncoupling protein in brown adipose tissue during acute stimulation by exposure of animals to cold was examined. Uncoupling protein level increased during the first hours of tissue stimulation. Use of a cDNA probe shows that synthesis of uncoupling protein mRNA was quickly stimulated. Animals treated with propranolol exhibited neither increase in uncoupling protein mRNA nor increase in the protein itself.

Study of the mode of action of endopolygalacturonase from Fusarium moniliforme

One endopolygalacturonase from Fusarium moniliforme was purified from the culture broth of a transformed strain of Saccharomyces cerevisiae. Its kinetic parameters and mode of action were studied on galacturonic acid oligomers and homogalacturonan. The dimer was not a substrate for the enzyme. The enzyme was shown to follow Michaelis-Menten behaviour towards the other substrates tested. Affinity and maximum rate of hydrolysis increased with increasing chain length, up to the hexamer or heptamer, for which V(max) was in the same range as with homogalacturonan. The enzyme was demonstrated to have a multi-chain attack mode of action and its active site included five subsites ranging from -3 to +2. The final products of hydrolysis of homogalacturonan were the monomer and the dimer of galacturonic acid.

Aspergillus niger I-1472 and Pycnoporus cinnabarinus MUCL39533, selected for the biotransformation of ferulic acid to vanillin, are also able to produce cell wall polysaccharide-degrading enzymes and feruloyl esterases

The filamentous fungal strains Aspergillus niger I-1472 and Pycnoporus cinnabarinus MUCL39533, previously selected for the bioconversion of ferulic acid to vanillic acid and vanillin respectively, were grown on sugar beet pulp. A large spectrum of polysaccharide-degrading enzymes was produced by A. niger and very few levels of feruloyl esterases were found. In contrast, P. cinnabarinus culture filtrate contained low amount of polysaccharide-degrading enzymes and no feruloyl esterases. In order to enhance feruloyl esterases in A. niger cultures, feruloylated oligosaccharide-rich fractions were prepared from sugar beet pulp or cereal bran and used as carbon sources. Number of polysaccharide-degrading enzymes were induced. Feruloyl esterases were much higher in maize bran-based medium than in sugar beet pulp-based medium, demonstrating the ability of carbon sources originating from maize to induce the synthesis of feruloyl esterases. Thus, A. niger I-1472 could be interesting to release ferulic acid from sugar beet pulp or maize bran.

The responses of vasopressin- and tyrosine hydroxylase-expressing neurons of the supraoptic nucleus in rats to chronic osmotic stimulation

The dynamics of intracellular contents of vasopressin and tyrosine hydroxylase in neuron bodies were studied in the supraoptic nucleus and the distant segments of their axons in the posterior lobe of the hypophysis in rats in conditions of salt loading lasting one, two, and three weeks. The number of vasopressin-immununoreactive neurons increased by the end of the second week of osmotic stimulation, due to the onset of vasopressin synthesis in neurons not synthesizing this hormone in normal physiological conditions. The vasopressin concentration decreased in cell bodies and axons during the first two weeks of salt loading, apparently because vasopressin release occurred at a greater level than vasopressin synthesis. During the third week, the intracellular vasopressin content remained essentially constant, demonstrating the establishment of dynamic equilibrium between the synthesis and release of the hormone. The number of tyrosine hydroxylase-immunoreactive neurons and the levels of tyrosine hydroxylase in neuron bodies and axons, at least in the largest swellings (Herring bodies), gradually increased, demonstrating that the rate of tyrosine hydroxylase was greater than its rate of enzymatic degradation. Thus, chronic stimulation of vasopressin neurons was accompanied by a series of adaptive reactions, the most important of which appears to be the expression of vasopressin and tyrosine hydroxylase synthesis by neurons which do not normally synthesize these compounds.

Modeling of pH and acidity for industrial cheese production

A three-layer feedforward neural network was successfully used to model and predict the pH of cheese curd at various stages during the cheese-making process. An extended database, containing more than 1800 vats over 3 yr of production of Cheddar cheese with eight different starters, from a large cheese plant was used for model development and parameter estimation. Neural network models were developed with inputs selected among 33 quantitative and qualitative process variables for final pH of cheese, pH at cutting, and acidity at whey drawing-off and at pressing. In all cases, very high correlation coefficients, ranging from 0.853 to 0.926, were obtained with the validation data. A sensitivity analysis of neural network models allowed the relative importance of each input process variable to be identified. The sensitivity analysis in conjunction with a priori knowledge permitted a significant reduction in the size of the model input vector. A neural network model using only nine input process variables was able to predict the final pH of cheese with the same accuracy as for the complete model with 33 original input variables. This significant decrease in the size of neural networks is important for applications of process control in cheese manufacturing.

Modulation of glutamate neurotoxicity on mesencephalic dopaminergic neurons in primary cultures by the presence of striatal target cells

Glutamate toxicity was compared in substantia nigra (SN)/striatum (STR) and SN/cerebellum (CRB) co-cultures on both the entire neuronal population (neuron specific enolase (NSE) immunopositive cells) and dopaminergic neurons (tyrosine hydroxylase (TH) immunopositive cells). In SN/CRB co-cultures NSE- and TH-positive cells were more sensitive to glutamate-induced toxicity than in SN/STR co-cultures. Moreover, in SN/STR co-cultures as compared to SN/CRB and SN cultures, glutamate toxicity was prevented to a larger extent by TCP, a non-competitive NMDA antagonist. These results suggest that target cells induce a differential expression of the different glutamate receptor subtypes in mesencephalic dopaminergic cells. Alternatively, the presence of target cells may induce the selective development of a subpopulation of dopaminergic neurons expressing predominantly NMDA receptors.

Tyrosine hydroxylase-expressing and/or aromatic L-amino acid decarboxylase-expressing neurons in the mediobasal hypothalamus of perinatal rats: differentiation and sexual dimorphism

In this quantitative and semiquantitative immunocytochemical study, the authors evaluated the differentiation of neurons expressing tyrosine hydroxylase (TH) and/or aromatic L-amino acid decarboxylase (AADC) in the mediobasal hypothalamus (MBH) of male and female rats on embryonic day 18 (E18), E20, and postnatal day 9 (P9). Four neuronal populations were distinguished according to either enzyme expression or neuron location. The earliest and most prominent first population was represented by TH-immunoreactive (IR)/AADC-immunonegative (IN) neurons that were detected initially at E18 and always were located in the ventrolateral region of the MBH. The second population of TH-IN/AADC-IR neurons was observed first at E20 and, after that time, was distributed dorsomedially. The third minor population of TH-IR/AADC-IR neurons initially was detected at E20 and was located dorsomedially. The fourth population was represented by TH-IR/AADC-IN neurons that were distributed in the dorsomedial region at any studied age. The numbers of TH-IR and AADC-IR neurons increased from their initial detection at E18 and E20 until P9. The area of TH-IR and AADC-IR neurons also increased from E18 to E20 and from E20 to P9, respectively. Both TH-IR and AADC-IR neurons showed sex differences in the neuron number, size, and optic density (OD). The numbers of TH-IR neurons in males exceeded those of females at E20 and at P9, although, at P9, sexual dimorphism was a characteristic only of the ventrolateral population. The area and OD of TH-IR neurons from females exceeded those from males in the entire mediobasal hypothalamus (MBH) at E18 and E20 but only in its dorsomedial region at P9. Sexual dimorphism also was an attribute of AADC-IR neurons at E20 and P9. Their number, size, and OD were significantly higher in females than in males. Thus, the MBH of perinatal rats contained two major populations of TH-IR/AADC-IN or TH-IN-AADC-IR neurons and a minor population of TH-IR/AADC-IR neurons. The differentiating neurons expressing either enzyme showed sexual dimorphism.

HREM of CoSi2/SiC heterophase interface: facts and artifacts in the interface distance profile measurements

When studying heterophase interfaces, one of the ultimate goals is to determine the local distortions and to extract a chemical profile. In this respect, HREM is a powerful tool. Nevertheless, the non-linearity of the image formation leads to artifacts both in the images and in the distance profiles extracted from the images. The present SiC/silicide interface study illustrates the misinterpretation, which might arise from measurements made on images recorded under limited experimental conditions.

Neuronal projections to the lateral retrochiasmatic area of sheep with special reference to catecholaminergic afferents: immunohistochemical and retrograde tract-tracing studies

The retrochiasmatic area contains the A15 catecholaminergic group and numerous monoaminergic afferents whose discrete cell origins are unknown in sheep. Using tract-tracing methods with a specific retrograde fluorescent tracer, fluorogold, we examined the cells of origin of afferents to the retrochiasmatic area in sheep. The retrogradely labeled cells were seen by observation of the tracer by direct fluorescence or by immunohistochemistry with specific antibodies raised in rabbits or horses. Among the retrogradely labeled neurons, double immunohistochemistry for tyrosine hydroxylase, dopamine-beta-hydroxylase, and serotonin were used to characterize catecholamine and serotonin FG labeled neurons. The retrochiasmatic area, which included the A15 dopaminergic group and the accessory supraoptic nucleus (SON), received major inputs from the lateral septum (LS), the bed nucleus of the stria terminalis (BNST), the thalamic paraventricular nucleus, hypothalamic paraventricular and supraoptic nuclei, the perimamillary area, the amygdala, the ventral part of the hippocampus and the parabrachial nucleus (PBN). Further, numerous scattered retrogradely labeled neurons were observed in the preoptic area, the ventromedial part of the hypothalamus. the periventricular area, the periaqueductal central gray (CG), the ventrolateral medulla and the dorsal vagal complex. Most of the noradrenergic afferents came from the ventro-lateral medulla (Al group), and only a few from the locus coeruleus complex (A6/A7 groups). A few dopaminergic neurons retrogradely labeled with flurogold were observed in the periventricular area of the hypothalamus. Rare serotoninergic fluorogold labeled neurons belonged to the dorsal raphe nucleus. Most of these afferents came from both sides of the brain, except for hypothalamic supraoptic and paraventricular nuclei. In the light of these anatomical data, we compared our results with data obtained from rats, and we discussed the putative role of these afferents in sheep in the regulation of several specific functions in which the retrochiasmatic area may be involved, such as reproduction.

Comparison of simple neural networks and nonlinear regression models for descriptive modeling of Lactobacillus helveticus growth in pH-controlled batch cultures

A set of 20 Lactobacillus helveticus growth curves was obtained from pH-controlled batch cultures with different pH setpoints, whey permeate and yeast extract concentrations. To find the best descriptive model of the biomass concentration versus time (y = X(t)) growth curve, fitting results of a large number of models were compared with statistical and approximate methods. Models studied included simple neural networks, reparameterized Logistic, Gompertz, Richards, Schnute, Weibull, and Morgan-Mercier-Flodin models, Amrane-Prigent model, and four new models based on autonomous growth functions. Simple neural networks with only four weights were good descriptive models of the growth curves and fitting qualities were similar to those of the best existing four-parameter models, such as the Logistic model. However, meaningful parameters had to be calculated numerically and use of simple neural networks yielded no distinctive advantages over other models. A new five-parameter model, based on an autonomous growth function, yielded the best fitting results, even when the number of model parameters was accounted for in the comparisons. However, the maximum specific growth rate was not always well estimated. Therefore the five-parameter Richards model was chosen as the best descriptive model of the growth curve.

Isolation of homogeneous fractions from wheat water-soluble arabinoxylans. Influence of the structure on their macromolecular characteristics

Water-soluble arabinoxylans from wheat flour were purified and fractionated by graded ethanol precipitation. Six fractions were obtained at 20% (F20), 30% (F30), 40% (F40), 50% (F50), 60% (F60), and 70% (F70) saturation with ethanol. Neutral sugars and (1)H NMR analyses revealed differences in structural characteristics. The Ara/Xyl ratio and the amount of Xylp residues disubstituted increased with ethanol concentration. Ferulic acid content was higher in fractions precipitated at low ethanol percentage. Fractions were refractionated by SEC, leading to 46 subfractions with low polydispersity index. Substitution degree was apparently linearly related to the amount of disubstituted Xylp. Macromolecular characteristics (M(w), [eta], R(G), q, nu) determined by multiangle laser light scattering and viscosimetry were similar among all fractions. A rather flexible conformation was determined for the arabinoxylans, in conflict with the admitted rodlike conformation. The substitution degree had no influence on the conformation or on the rigidity of the polymers. Evidence for the presence of ferulic acid dimers in the water-soluble arabinoxylans is provided, which probably explains the unexpected conformation and macromolecular characteristics.

Structure modelling and site-directed mutagenesis of the rat aromatic L-amino acid pyridoxal 5'-phosphate-dependent decarboxylase: a functional study

The pyridoxal-5'-phosphate-dependent enzymes (B6 enzymes) are grouped into three main families named alpha, beta, and gamma. Proteins in the alpha and gamma families share the same fold and might be distantly related, while those in the beta family exhibit specific structural features. The rat aromatic L-amino acid decarboxylase (AADC; EC(4.1.1.28)) catalyzes the synthesis of two important neurotransmitters: dopamine and serotonin. It binds the cofactor pyridoxal-5'-phosphate and belongs to the alpha family. Despite the low level of sequence identity (approximately 10%) shared by the rat AADC and the sequences of the enzymes belonging to the B6 enzymes family, including the known three-dimensional structures, a multiple sequence alignment was deduced. A model was built using segments belonging to seven of the eleven known structures. By homology, and based on knowledge of the biochemistry of the aspartate aminotransferase, structurally and functionally important residues were identified in the rat AADC. Site-directed mutagenesis of the conserved residues D271, T246, and C311 was carried out in order to confirm our predictions and highlight their functional role. Mutation of D271A and D271N resulted in complete loss of enzyme activity, while the D271E mutant exhibited 2% of the wild-type activity. Substitution of T246A resulted in 5% of the wild-type activity while the C311A mutant conserved 42% of the wild-type activity. A functional model of the AADC is discussed in view of the structural model and the complementary mutagenesis and labelling studies.

Lipid uptake across the wall of an expanded polytetrafluoroethylene vascular graft

Previous studies have shown that vascular grafts were prone to inducing an atherosclerosis-like phenomenon, thus possibly jeopardizing their performance. Furthermore, lipid retention, observed in most synthetic arterial prostheses explanted from humans, appears to have an important role in the progression of this atherosclerotic process, therefore hindering the healing process and neo-intima formation of these synthetic conduits. The current study examined lipid concentration profiles across prosthesis membranes exposed to lipid dispersion under various transmural pressures, flow rates, and durations of exposure. It was demonstrated that the lipids rapidly permeated the prosthesis membrane, as lipid advection increased to a maximum, then steadily decreased until the membrane became completely impermeable to the fluid. The concentration of lipids within the grafts was monitored using FT-IR microspectroscopy, then correlated as a function of time in order to evaluate the mass transfer coefficients and lipid saturation concentration. Lipid sorption, as a function of time, was described by a mechanism taking into account two first-order kinetic models. The lipids were first rapidly adsorbed onto the Teflon(R), potentially influenced by the strong affinity of these lipids for the highly hydrophobic polytetrafluoroethylene polymer. This affinity then enhanced the germination of the lipid deposits that filled in the prosthesis wall. For lipid retention as a function of the transmural pressure and flow rate, no clear tendency was established.

Commercial polyurethanes: the potential influence of auxiliary chemicals on the biodegradation process

This investigation elucidates some aspects of auxiliary chemicals on the biodegradation of two commercial polyurethanes (Pellethane and Corethane). The materials were incubated for 28 days with cholesterol esterase and/or with phosphatidylcholine. Extraction studies were carried out on the two materials, using different solvents, chosen on the basis of solvent polarity. FT-IR spectra for the extracted materials indicated the presence of poly(methylene)n oxide moities, silicone oil, bis-ethylene-stearamide, aromatic moities, and alkyd-urea compounds in Pellethane. Corethane materials were shown to contain some fatty acids, hydrocarbon waxes, ester-based species, and chlorinated compounds. Analysis of incubation solutions by high performance liquid chromatography failed to isolate methylene dianiline (MDA) or any of its derivatives from the various polymer incubation solutions. However, a methanol extract of Corethane samples that were incubated for 28 days in cholesterol esterase did show the presence of MDA. The absence of MDA in the Pellethane methanol extracted samples may reflect the differences in surface additives found for this material versus the Corethane. FT-IR/ATR analysis of polymer surfaces exposed to cholesterol esterase/phospholipids mixture showed that there was an increase in the uptake of phospholipids over samples that were incubated in phospholipid dispersion alone. The results of this study show that some of the auxiliary chemicals found in commercial polyurethanes may hinder the specific release of hydrolytic degradation products and delay polymer degradation. However, it should be recognized that the surface layer containing these compounds is susceptible to change following the interaction between the polyurethane-based devices and elements of the host environment (i.e. lipids, enzymes, etc.). Hence, recognition and identification of these changes will ultimately be important in assessing a commercial polymer's blood compatibility characteristics.

[Response of vasopressin and tyrosine hydroxylase expressing neurons of the rat supraoptic nucleus to chronic osmotic stimulation]

This study has evaluated the dynamic of intracellular vasopressin and tyrosine hydroxylase contents in the neuron cell bodies in the supraoptic nucleus and in the axons of the posterior lobe in rats drinking 2% NaCl for 1, 2, and 3 weeks. The number of vasopressin-immunoreactive neurons increased by the end of the second week of osmotic stimulation that might be explained by the onset of vasopressin synthesis in the neurons which do not synthesize this neurohormone under normal physiological conditions. The concentration of vasopressin fell down continuously during the first two weeks of salt-loading, apparently, due to predominance of the vasopressin release over its synthesis. Over the third week of salt-loading, the intracellular concentration of vasopressin was not changed significantly suggesting the establishment of the dynamic equilibrium between the vasopressin synthesis and release. The number of tyrosine hydroxylase-immunoreactive neurons and the amount of tyrosine hydroxylase in cell bodies and the large axonal swellings, Herring bodies, increased gradually showing that the rate of tyrosine hydroxylase synthesis prevailed over that of its enzymatic degradation. Thus, the chronic stimulation of vasopressin neurons is accompanied by a number of the adaptive reactions; the most important is related to the onset of vasopressin and tyrosine hydroxylase synthesis in the neurons which do not synthetize both of them under normal conditions.

Afferents to the rostral olfactory bulb in sheep with special emphasis on the cholinergic, noradrenergic and serotonergic connections

The olfactory bulb (OB) is involved in the processing of olfactory information particularly through the activation of its afferents. To localize their cell origin in sheep, a specific retrograde fluorescent tracer, Fluoro-Gold, was injected into the olfactory bulb of seven ewes. By using immunocytochemical techniques, retrogradely labeled neurons were colocalized with choline acetyltransferase, tyrosine hydroxylase, dopamine-beta-hydroxylase and serotonin to characterize cholinergic, noradrenergic and serotonergic Fluoro-Gold-labeled neurons. Most afferents originated from the ipsilateral side of the injection site. The OB received major inputs from the anterior olfactory nucleus (AON), the piriform cortex (PC), the olfactory tubercle, the diagonal band of Broca (DBB) and the amygdala. Other retrogradely labeled neurons were observed in the taenia tecta, the septum, the nucleus of the lateral olfactory tract, the preoptic area, the lateral hypothalamic area, the mediobasal hypothalamus, the lateral part of the premammillary nucleus, the paraventricular nucleus of the hypothalamus, the paraventricular thalamic nucleus, the central grey, the substantia nigra (SN), the ventral tegmental area (VTA), the lateral nucleus to the interpeduncular nucleus (IIP), the raphe and the locus coeruleus (LC). Contralateral labeling was also found in the AON, the PC, the SN compacta, the VTA, the IIP and the LC. Cholinergic Fluoro-Gold-labeled neurons belonged to the horizontal and vertical branch of the DBB. Noradrenergic afferents came from the LC and serotoninergic afferents came from the medial raphe nuclei and the 1IP. These data are discussed in relation with olfactory learning in the context of maternal behavior in sheep.

Presence of galanin in dopaminergic neurons of the sheep infundibular nucleus: a double staining immunohistochemical study

The distribution of tyrosine hydroxylase (TH) and of galanin immunoreactive (IR) neurons were examined in the sheep infundibular nucleus. Antisera raised against TH and galanin were used on adjacent sections and for double immunohistochemical staining of the same sections. There was considerable overlap in the distribution of TH and galanin-IR neurons in the medial part of the nucleus. Most of the galanin-IR neurons were also TH-IR, but less than 50% of the TH-IR neurons also expressed galanin immunoreactivity. Neurons immunoreactive to TH alone were observed close to the third ventricle and in the rostral part of the infundibular nucleus. In the median eminence, TH and galanin-IR fibres overlapped mainly in the lateral and dorsal parts of the external layer, but the colocalisation of both antigens could not be assessed on the available material. Thus, in sheep, the population of catecholaminergic neurons of the infundibular nucleus may be subdivided into different subpopulations according to their peptide content, but does not appear segregated as in rat and human.

A continuous and pulsatile flow circulation system for evaluation of cardiovascular devices

The design of a nonpulsatile and pulsatile system using a centrifugal pump is presented. To induce a pulsatile flow with a centrifugal pump, an independent pneumatically driven unit provided flow patterns over a wide range of frequencies and amplitudes. The pulsatile flow was generated by the axial displacement of a cylinder that periodically compressed the flexible conduit that is connected to the pump. The system can accommodate flow rates up to 6,000 ml/min and transmural pressures up to 500 mm Hg and is capable of maintaining the pressure at a constant value. This circuit produced reproducible pressure waves having a frequency up to 4 Hz. The periodicity of the transmural pressure between 80 and 180 mm Hg was similar to the pressure wave propagation observed in peripheral circulation. Capable of adequately reproducing continuous and pulsatile flow, the apparatus is therefore versatile to allow in vitro evaluation of cardiovascular devices.

Lipid uptake in expanded polytetrafluoroethylene vascular grafts

PURPOSE

The mechanisms of vascular prosthesis failure are reported to be associated, in part, with an atherosclerotic degenerative process that is related to an abnormal lipid infiltration. The lipid uptake in expanded polytetrafluoroethylene (ePTFE) vascular grafts was reproduced in vitro, and the effect of time on the permeability of these prostheses was studied.

METHODS

Water permeability tests were carried out under dynamic flow conditions at various hydrostatic pressures. Lipid uptake was simulated by circulating a phosphatidylcholine suspension inside an expanded Teflon prosthesis under pulsatile or continuous transmural pressure ranging between 80 mm Hg and 180 mm Hg, at a flow rate of 500 mL/min and 2000 mL/min, for a duration ranging from 2 hours to 1 month.

RESULTS

Water permeability tests indicated that under hydrostatic pressures of 180 mm Hg and 300 mm Hg, water percolated through the prosthesis wall after an exposure of 720 minutes and 75 minutes, respectively. After exposing the prostheses to the lipid dispersion under the various flow conditions, the fluid convection through the wall occurred. Preferential convection pathways with a constant periodicity were observed across the length of each prosthesis and were, therefore, associated with regularly spaced perforations depicted in the structure of the devices. Phospholipids gradually agglomerated within the prosthesis wall, allowing a restrictive molecular mobility. Infrared spectroscopy results indicated that the lipid uptake depended on the transmural pressure and time of exposure.

CONCLUSION

The occurrence of the membrane permeability may be associated with the dilatation and plastic deformation of the prosthesis. Lipid uptake occurs in ePTFE grafts after an aggressive kinetic process.

Immunolocalization of aromatic L-amino acid decarboxylase, tyrosine hydroxylase, dopamine, and serotonin in the forebrain of Ambystoma mexicanum

To improve basic knowledge about the neurochemical organization of the urodele brain, and to study discrepancies in the localization of monoaminergic markers, we immunohistochemically charted the distribution of four such markers (tyrosine hydroxylase, aromatic L-amino acid decarboxylase, dopamine, and serotonin) in the axolotl (Ambystoma mexicanum) forebrain. Catecholaminergic and serotoninergic systems were found in similar locations to those seen in other Urodela. As seen in other vertebrates, the localization of the different monoaminergic markers reveals some inconsistencies. Cells that are exclusively tyrosine hydroxylase-immunoreactive are observed in the olfactory bulb, anterior olfactory nucleus/nucleus accumbens region, the epichiasmatic portion of the preoptic nucleus, and in the pars intercalaris thalami, whereas cells that are only labelled by aromatic L-amino acid decarboxylase are seen in the anterior olfactory nucleus/nucleus accumbens region, the bed nuclei of the anterior commissure, the posterior portion of the preoptic nucleus, the ventral hypothalamus, and the pars intercalaris thalami. The presence of cells solely serotonin (5-HT)-immunoreactive is suggested for the nucleus infundibularis dorsalis. Conversely, there were no areas that appeared to be exclusively immunoreactive for dopamine. Double-labelling for aromatic L-amino acid decarboxylase/tyrosine hydroxylase and aromatic L-amino acid decarboxylase/serotonin, together with cell counting, confirmed the existence of neurons that express only one monoaminergic marker in amphibian, supporting the hypothesis that these cells are universally present in the central nervous system of vertebrates.