Transition of elastomers from a rubber to glassy state under laser shock conditions.

The mechanical behaviour of polycarbonate and polydimethylsiloxane (Sylgard184) is studied in this work under laser shock conditions that induce high pressure and strain rates. Laser shock, usually used to reinforce metals, is chosen here because of its capacity to produce strain rates in the 106 s1 range and pressures of GPa order. The pressure and strain rates produced are extracted from the backface velocity profiles and reproduced with the FEM simulation on Abaqus for each laser shot. These two parameters lead to a glass transition shift in the polymers that can induce significant behaviour modifications. We show that Sylgard184, an elastomer with a glass transition temperature of 147 K, exhibits glassy behaviour under such laser shock conditions. By contrast, polycarbonate is already a glassy polymer in its normal state with a glass transition temperature of 415 K; no drastic change in behaviour under shock is evidenced. To discuss these findings in relation to the different mobility domains of the polymer chains under extreme conditions, dielectric relaxation spectroscopy (DRS) measurements are performed to characterize the limits of the rubbery and glassy behaviour for both polymers. As a result, the coupling of the two techniques provides a deeper understanding of the contribution of both the strain rate and pressure to the dynamic glass transition in polymers and thus expands the experimental study range of the two polymers to a strain rate that had not previously been reached.

[Severe impaction of the maxillary canines: a risk for the premolars]. / Inclusion profonde des canines maxillaires: un danger pour les prémolaires.

Since scanning has been in use for diagnosing dental embedding, it has been evidenced that the lesions generated by the embedded maxillary cuspid on the adjacent teeth are not rare but are fraught with consequences.

Cell biological changes of outer cortical root cells in early determinate nodulation.

In the symbiosis of leguminous plants and Rhizobium bacteria, nodule primordia develop in the root cortex. This can be either in the inner cortex (indeterminate-type of nodulation) or outer cortex (determinate-type of nodulation), depending upon the host plant. We studied and compared early nodulation stages in common bean (Phaseolus vulgaris) and Lotus japonicus, both known as determinate-type nodulation plants. Special attention was paid to the occurrence of cytoplasmic bridges, the influence of rhizobial Nod factors (lipochitin oligosaccharides [LCOs]) on this phenomenon, and sensitivity of the nodulation process to ethylene. Our results show that i) both plant species form initially broad, matrix-rich infection threads; ii) cytoplasmic bridges occur in L. japonicus but not in bean; iii) formation of these bridges is induced by rhizobial LCOs; iv) formation of primordia starts in L. japonicus in the middle root cortex and in bean in the outer root cortex; and v) in the presence of the ethylene-biosynthesis inhibitor aminoethoxyvinylglycine (AVG), nodulation of L. japonicus is stimulated when the roots are grown in the light, which is consistent with the role of cytoplasmic bridges during nodulation of L. japonicus.

Use of green fluorescent protein color variants expressed on stable broad-host-range vectors to visualize rhizobia interacting with plants.

We developed two sets of broad-host-range vectors that drive expression of the green fluorescent protein (GFP) or color variants thereof (henceforth collectively called autofluorescent proteins [AFPs]) from the lac promoter. These two sets are based on different replicons that are maintained in a stable fashion in Escherichia coli and rhizobia. Using specific filter sets or a dedicated confocal laser scanning microscope setup in which emitted light is split into its color components through a prism, we were able to unambiguously identify bacteria expressing enhanced cyan fluorescent protein (ECFP) or enhanced yellow fluorescent protein (EYFP) in mixtures of the two. Clearly, these vectors will be valuable tools for competition, cohabitation, and rescue studies and will also allow the visualization of interactions between genetically marked bacteria in vivo. Here, we used these vectors to visualize the interaction between rhizobia and plants. Specifically, we found that progeny from different rhizobia can be found in the same nodule or even in the same infection thread. We also visualized movements of bacteroids within plant nodule cells.

A Lotus japonicus nodulation system based on heterologous expression of the fucosyl transferase NodZ and the acetyl transferase NoIL in Rhizobium leguminosarum.

Heterologous expression of NodZ and NolL proteins in Rhizobium leguminosarum bv. viciae led to the production of acetyl fucosylated lipo-chitin oligosaccharides (LCOs), indicating that the NolL protein obtained from Mesorhizobium loti functions as an acetyl transferase. We show that the NolL-dependent acetylation is specific for the fucosyl penta-N-acetylglucosamine species. In addition, the NolL protein caused elevated production of LCOs. Efficient nodulation of Lotus japonicus by the NodZ/NolL-producing strain was demonstrated. Nodulation efficiency was further improved by the addition of the ethylene inhibitor L-alpha-(2-aminoethoxyvinyl) glycine (AVG).

An ecological approach to planning dysfunction: script execution.

Planning, which concerns many activities in everyday life, is a two-stage process. The first one predetermines a course of actions aimed at achieving some specific goals. It is founded on managerial knowledge or overlearned sequences of events and may be tested by script generation. The second stage entails monitoring and guiding the execution of the plan to a successful conclusion. It must take into account environmental contingencies and may be tested by script execution. If the frontal lobes intervene not only in managerial knowledge (Grafman, 1989) but also in binding the plan with contextual environment (Damasio, Tranel and Damasio, 1991; Shallice and Burgess, 1991), script execution would be more sensitive than script generation to planning deficits. To test this hypothesis, script execution and script generation were compared in 11 patients with a dysexecutive syndrome and 10 matched controls, using three scripts of daily life activities: (1) 'shopping for groceries'; (2) 'cooking'; (3) 'answering a letter and finding the way to post the reply'. Two way ANOVAs showed more errors in execution than in generation, more errors in patients than in controls, and a greater difference between execution and generation in patients than in controls. Furthermore, 'context neglect' and 'environmental adherence' were the two types of errors that best differentiated patients from controls. Finally, the total number of errors in execution correlated with the score on behavioral questionnaires answered by occupational therapists. These results confirm our hypothesis and suggest that script execution may be a valid ecological approach to estimate the severity of deficits in daily life activities.

At which steps of spatial working memory processing do striatofrontal circuits intervene in humans?

Striatofrontal circuits have been implicated in spatial working memory in non-human and human primates. To determine at which steps of information processing (stimulus encoding, storage or response programming) they intervene, we compared 32 levodopa-treated patients with idiopathic Parkinson's disease (PD) and 32 matched control subjects in a visuo-spatial pattern span paradigm. Our testing procedure allowed us to evaluate the influence of: (1) the type of encoding (controlled vs free); (2) the nature of interference during a 10 s delay (spatial vs verbal); and (3) response elaboration (reproduction vs error detection). As expected, the performance of control subjects was significantly better in controlled than in free encoding, in verbal than in spatial interference and in detection than in reproduction, clearly demonstrating the sensitivity of the procedure to these factors. Compared to controls, PD patients were impaired in all conditions and the severity of the deficit was significantly correlated with that observed in tests of executive functions. The global pattern of performance, however, was identical to that of controls. These data confirm the involvement of striatofrontal circuits in spatial working memory in humans and suggest that the executive working memory component intervenes at all steps of working memory processing.

Stimulation of tyrosine phosphorylation of distinct proteins in response to antibody-mediated ligation and clustering of alpha 3 and alpha 6 integrins.

The interaction of cells with components of the extracellular matrix through their integrin receptors results in the stimulation of tyrosine phosphorylation of several proteins, suggesting that these receptors play a key role in signal transduction. Here we report that antibody-mediated ligation and clustering of alpha 3 beta 1 and alpha 6 beta 1/alpha 6 beta 4 integrins resulted in the stimulation of tyrosine phosphorylation of proteins that are specific for each heterodimer. Thus, ligation and clustering of the alpha 3 beta 1 integrin on human prostate carcinoma cells (PC-3) and human umbilical vein endothelial cells (HUVEC) with anti-alpha 3 antibodies resulted in the stimulation of tyrosine phosphorylation of a 55 kDa protein. In contrast, ligation and clustering of the alpha 6 beta 1 integrin on these cells with anti-alpha 6 antibody resulted in the dramatic stimulation of tyrosine phosphorylation of a 90 kDa protein in addition to a 52 kDa protein, and ligation and clustering of alpha 5 beta 1 on HUVEC did not result in the apparent stimulation of tyrosine phosphorylation of any proteins. Clustering with anti-beta 1 antibodies triggered the tyrosine phosphorylation of all of these proteins, whereas ligation and clustering of PC-3 cells with an anti-beta 4 antibody resulted in the tyrosine phosphorylation of a distinct 62 kDa protein. Since the PC-3 cells express both alpha 6 beta 1 and alpha 6 beta 4, these data suggest that these two receptors can transduce distinct signals. All of the phosphorylations could be inhibited by treating the cells with Genistein, a tyrosine kinase inhibitor. Antibody-mediated ligation and clustering of integrins on the two types of cells did not result in the stimulation of tyrosine phosphorylation of pp125 focal adhesion kinase, although this was observed upon cell attachment and spreading on fibronectin, laminin and anti-alpha 3 monoclonal antibody. Collectively, these data demonstrate that cross-linking of different integrin heterodimers can stimulate tyrosine kinase activities, leading to the phosphorylation of distinct proteins, which are also different from those observed when cells are allowed to spread on a matrix.

Stimulation of tyrosine phosphorylation and accumulation of GTP-bound p21ras upon antibody-mediated alpha 2 beta 1 integrin activation in T-lymphoblastic cells.

Integrins are a family of heterodimeric integral plasma membrane proteins that behave as receptors for components of the extracellular matrix and also mediate cell to cell adhesion. Occupation of integrins can result in the transduction of intracellular signals, leading to cytoskeletal reorganization, tyrosine phosphorylation, and induction of gene expression. We report here that the ligation of alpha 2 beta 1 integrin by collagen-adhesion stimulatory anti-alpha 2 and anti-beta 1 antibodies resulted in the accumulation of p21ras in the active GTP-bound state in Jurkat T-lymphoblastoid cells. The activation was accompanied by the tyrosine phosphorylation of proteins of 47-52 kDa. This stimulation of tyrosine phosphorylation and p21ras activation was specific for the activating antibodies and occurred within 2 min of the addition of these antibodies. Although treatment of the cells with the protein kinase C activator, phorbol 12-myristate 13-acetate also resulted in an induction of both cell attachment to collagen and of p21ras activation, tyrosine phosphorylation was not observed. These results demonstrate that alpha 2 beta 1 integrin activation can result in the specific stimulation of tyrosine phosphorylation of 47-52-kDa proteins, as well as activation of a signaling pathway involving p21ras.

Genetic differences in heat-induced tolerance to cadmium in cultured mouse embryos are not correlated with changes in a 68-kD heat shock protein.

Heat-induced cross-tolerance to cadmium was investigated in two inbred strains of mice, BALB/c and SWV, using a whole embryo culture system. Embryos were exposed to a pretreatment of 5 min at 43 degrees C and subsequently to an embryotoxic concentration of cadmium, 1.75 microM. The two types of embryos responded differently to the heat pretreatment, as cross-tolerance was induced in SWV but not in BALB/c mice. In SWV embryos, prior exposure to 43 degrees C for 5 min essentially eliminated the negative effects of cadmium on embryonic development and growth. However, in BALB/c embryos, no protection was observed. The variation in development of cross-tolerance in embryos from the two strains of mice was not correlated with differences in the induction of a 68-kD heat-shock protein (hsp68). There was a rapid increase in this protein in both strains after the initial heat exposure but not excess induction in the SWV strain that developed tolerance. The induction of hsp68 is therefore not sufficient to elicit cross-tolerance, and other mechanisms are likely to be important in the protective response of the embryo.

[An outbreak of allergy to horses in children. A review of 56 recent cases]. / Recrudescence de l'allergie au cheval chez l'enfant? A propos de 56 observations récentes.

Over the past 11 years, signs of allergy were observed in 56 children and adolescents in contact with horses. The cases consisted of 35 boys and 21 girls, 35 of them were under 10 years of age. The main clinical signs were ocular symptoms (36), asthma (30) and rhinopharyngitis (24). All the children had very positive cutaneous prick tests and specific IgE (class 3 and 4: 62%) and were polysensitized. In several children, the first manifestation occurred at the time of the first known contact with a horse or pony. No further contact was usually the only therapeutic solution. In disabled children, allergy to horses must be considered when clinical signs of allergy occur during therapeutic riding sessions.

Heat-shock induced tolerance to the embryotoxic effects of hyperthermia and cadmium in mouse embryos in vitro.

Mammalian embryos growing in vitro are harmed by short elevations in the culture temperature. However, a relatively mild hyperthermic exposure can induce thermotolerance, a transient state of resistance to the effects of a subsequent heat exposure. The present study examines the induction of tolerance to heat and cross-tolerance to another teratogen, cadmium, in day 8 CD-1 mouse embryos in vitro. The ability of a mild heat pretreatment (5 min at 43 degrees C) to partially protect embryos against an embryotoxic heat exposure (20 min at 43 degrees C) was demonstrated. The frequency of death was reduced from 43% to 20%, abnormal branchial arches from 44% to 13.2%, and retarded turning from 22% to 5% in pretreated embryos. Other malformations, such as small forebrains and microphthalmia, were not affected, and the rate of exencephaly was significantly increased. The same heat pretreatment (5 min at 43 degrees C) was also found to reduce the damaging effects of a subsequent exposure to 1.75 microM cadmium. In the absence of pretreatment, cadmium caused 55% embryo deaths and 87% malformations, but prior heat exposure caused significant reductions in these frequencies to 29% and 55%. The total morphological score was higher in the pretreated group, as were the measurements of the yolk sac diameter, crown-rump length, and head length. Thus, embryos that have developed resistance to hyperthermia are also partially protected against the harmful effects of a second teratogen, cadmium. The response of the embryo to elevated temperatures may be involved in the development of tolerance to a variety of stresses.

[Does the allergic child become sensitized to small domestic mammals (guinea pig, hamster, rabbit?)]. / L'enfant allergique se sensibilise-t-il aux petits mammifères domestiques (cobaye, hamster, lapin)?

Our own works show among allergic children a frequency of sensitization of 30% to cats and of 17% to dogs. But, the proportion of sensitizations to other small domestic mammals such as guinea pigs, hamsters of rabbits seems to be unknown. Among atopic children with a known contact with those pets we noted: for guinea pig: 29% positive cutaneous or RAST tests 21% clinical signs in presence of animals; for hamster respectively 28% and 6.5%; for rabbit respectively 18% and 12.3%. Guinea pigs seem to be more sensitizing animals, followed by rabbits, then by hamsters. As for cats and dogs, eviction is imperative when a sensitization is demonstrated.

Interaction between the splotch mutation and retinoic acid in mouse neural tube defects in vitro.

The interaction between the splotch gene (Sp) and all-trans retinoic acid (RA) was investigated using cytogenetically marked Sp/+ and +/+ mouse embryos cultured in the presence of RA. Retinoic acid retarded the development of and had a teratogenic effect on mouse embryos in culture. In particular, RA had seemingly opposite effects on the posterior neural tube, inducing abnormally early fusion in some embryos and causing a dose-dependent delay in others. When the effects of RA on identified Sp/+ and +/+ embryos were compared, the only observed difference in their responses was in the degree of the delay in posterior neuropore (PNP) closure. At the end of the culture period, among the untreated control embryos, the Sp heterozygotes showed retardation of PNP closure compared to +/+ embryos. In addition, the RA treatment was found to have induced a greater delay in posterior neural tube closure in Sp/+ than in +/+ embryos. The basis for this difference in response to RA is presumed to be the retardation of PNP closure that is caused by the Sp gene in heterozygous form. The effects of the gene and the teratogen are additive and the gene carriers thus have greater mean PNP lengths at the end of culture. Since the length of the PNP is an indication of an embryo's likelihood of developing spina bifida, this provides an explanation for the observation that Sp/+ embryos are more sensitive to the spina bifida-causing effects of RA than are +/+ embryos.

Histological comparison of the effects of the splotch gene and retinoic acid on the closure of the mouse neural tube.

The splotch gene (Sp) and all-trans retinoic acid (RA) interact to cause spina bifida in mouse embryos. To investigate the mechanisms of action of the two, the spinal regions of Sp homozygotes, RA-treated wild-type, and control wild-type embryos were examined histologically by light microscopy on day 9 of gestation. The mean numbers of cells per section in the neural tube, mesoderm, and notochord were determined, along with the percentages of mitotic and pyknotic nuclei and the numbers of migrating neural crest cells. As well, the effect of Sp and RA on the extracellular matrix was studied histochemically with Alcian blue staining for glycosaminoglycans. The main defect in Sp homozygotes was a marked reduction in the number of migrating neural crest cells and the amount of extracellular matrix around the neural tube. Retinoic acid, on the other hand, caused a number of disruptions in the embryo, including abnormalities in the position of the notochord and the shape of the neural tube. Sp and RA delay neural tube closure and thus cause neural tube defects, through different mechanisms. However, the combined effects of the gene and teratogen on the embryo lead to a greater inhibition of neural tube closure than when either is present separately.

[Can Acarus siro be considered an allergenic mite in children? Evaluation of 248 cases]. / Acarus siro peut-il être considéré comme un acarien allergisant chez l'enfant? Bilan de 248 explorations.

Among 248 allergic children we noted 44 children (21%) with strongly or moderately positive cutaneous tests (In seven out of these tested children respiratory provocation tests are very positive). They are urban children and their houses are not different from other allergic children. They are mostly boys (72%), more than 5 years old (91%), with an asthma (84%), a radiological sinusitis (45%), an hypereosinophilia (88%) and elevated total IgE (90%). 43/44 children also have positive cutaneous tests to Dermatophagoides pteronyssinus mite. Since respiratory sensitivity is exquisite, we undertook a specific hyposensitization for some patients with encouraging results.

[Comparison of specific IgE levels versus various milk proteins in 76 eczematous children]. / Comparaison des dosages des IgE spécifiques vis-à-vis des diverses protéines du lait chez 76 enfants eczémateux.

Among 76 eczematous children, we realized a RAST test for whole milk and milk specific proteins: lactalbumin, lactoglobulin and casein. One of these RAST tests, at least, was positive for 27 children. Whole milk RAST test is the most frequently positive (77%) but some non specific reactions seem to interfere: only three children are clinically milk sensitive. Among specific proteins, lactalbumin is more frequently positive (59%) than lactoglobulin (51%) and casein (18%). Eczematous children with positive milk RAST tests, if compared to other eczematous children, have currently more mite allergies and positive egg RAST tests. They have a tendency (non significative) to be more frequently breast fed. The positivity of milk RAST tests seems to belong to a polysensitization and infrequently concerns a clinical allergy.

[What problems does childhood toxocariasis currently pose? Apropos of 6 clinical cases]. / Quels problèmes posent actuellement les toxocaroses de l'enfant? (a propos de six observations cliniques).

About six observations of toxocariasis (visceral larva migrans syndrome). We relate six observations of toxocariasis among children. In one case, an ocular localization is probable. For other five patients, they are inapparent forms. The allergologist pediatrician may be consulted because of a major hypereosinophilia (greater than 10,000/mm3) and an elevation of total IgE (greater than 2,000 UI/ml). Allergic and current parasitologic assays are negative and diagnostic key is given by toxocara serology. We insist on interest and reliability of passive hemagglutination test with a purified antigen (titer greater than or equal to 1/320). Treatment now is preferably flubendazole (50 mg/kg/day for six days) eventually renewed.