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Biomedical subjects

S Guérin

Publications and source records attributed to S Guérin.

At least 19 recordsLinked to original sources
PubMed2005

Field-free two-direction alignment alternation of linear molecules by elliptic laser pulses.

We show that a linear molecule subjected to a short specific elliptically polarized laser field yields post-pulse revivals exhibiting alignment alternatively located along the orthogonal axis and the major axis of the ellipse. The effect is experimentally demonstrated by measuring the optical Kerr effect along two different axes. The conditions ensuring an optimal field-free alternation of high alignments along both directions are derived.

Journal Article↗
PubMed2005

Efficient and long-lived field-free orientation of molecules by a single hybrid short pulse.

We show that a combination of a half-cycle pulse and a short nonresonant laser pulse produces a strongly enhanced postpulse orientation. Robust transients that display both efficient and long-lived orientation are obtained. The mechanism is analyzed in terms of optimal oriented target states in finite Hilbert subspaces and shows that hybrid pulses can prove useful for other control issues.

Journal Article↗
PubMed2005

Involvement of NO in gastric emptying of semi-solid meal in conscious pigs.

The influence of non-selective nitric oxide synthase (NOS) inhibition on gastric emptying of a semi-solid meal was studied in conscious pigs. Antroduodenal motility and fundic compliance were also assessed to evaluate the mechanisms at the origin of potential alteration in gastric emptying pattern. N(G)-nitro-L-arginine methyl ester (L-NAME; 20 mg kg(-1) i.v.) delayed gastric emptying (half-emptying time of 128.98 +/- 16.86 min vs 73.74 +/- 7.73 min after saline, P < 0.05, n = 6) as a result of decreased proximal gastric emptying. No changes were observed for distal gastric emptying as a result of unchanged antral motility. Similarly, no changes were noted on duodenal motor patterns either in the fasted or in the fed state. L-NAME decreased fundic compliance in fasted state (49 +/- 11 mL mmHg(-1) vs 118 +/- 15 mL mmHg(-1) after saline, P < 0.05, n = 6). As this phenomenon is expected to increase emptying rate, the gastroparesis induced by NOS inhibition is thus likely to originate from distal resistive forces. It is concluded that NO positively modulates gastric emptying.

Animals↗
PubMed2005

Reduced mechanosensitivity of duodenal vagal afferent neurons after an acute switch from milk-based to plant-based diets in anaesthetized pigs.

Acute changes in diet composition and/or origin alter gastric emptying and gastrointestinal motility. One of the hypotheses explaining these alterations involves changes in the sensitivity of duodenal vagal sensory neurons. The aim of this study was to evaluate the characteristics of multimodal duodenal vagal sensory neurons in 20 pigs feed either with milk-based or plant-based diets of identical caloric content. Twenty duodenal vagal afferents were recorded in anesthetized animal from the cervical vagus using the single fiber method. 10 pigs were fed with a milk-based diet (MD) for one month while the diet of the 10 other pigs was changed for plant-based diet (PD) the day preceding the recording session. The behavior of the receptors was tested in basal resting conditions and after challenges with duodenal intralipid and close intra-arterial injection of CCK, 5-HT or capsaicin with and without isovolumetric duodenal distensions at 20, 40 and 60 mmHg. All receptors were slowly adapting C type fiber with a receptor field located 6-7 cm distal to the pylorus. The rate of discharge during distension (20, 40 and 60 mmHg) combined with duodenal intralipid was significantly larger for MD compared with PD. Similarly, the rate of discharge observed during distensions performed with CCK and with 5-HT were greater for MD compared with PD while CCK and 5-HT without distension were equally stimulating for MD and PD. No significant difference was found between groups during capsaicin infusion irrespective of the stimulating pressure. In conclusion, a switch to plant-based diet, when compared to a milk-based diet, results in an overall decrease in mechanical sensitivity of duodenal neurons during lipid, 5HT and CCK challenges, but not in basal conditions or after capsaicin. This reduced sensitivity to distension may explain the diet-induced alteration of gastric emptying that is controlled primarily through a vago-vagal reflex.

Action Potentials↗
PubMed2004

Control of localization and suppression of tunneling by adiabatic passage.

We show that a field of frequency omega combined with its second harmonic 2omega driving a double-well potential allows us to localize the wave packet by adiabatic passage, starting from the delocalized ground state. The relative phase of the fields allows us to choose the well of localization. We can suppress (and restore) the tunneling subsequently by switching on (and off) abruptly the fields at well-defined times. The mechanism relies on the fact that the dynamics is driven to an eigenstate of the Floquet Hamiltonian which is a localized state.

Journal Article↗
PubMed2003

Postpulse molecular alignment measured by a weak field polarization technique.

We report a direct nonintrusive observation of alignment and planar delocalization of CO2 after an intense linearly polarized femtosecond laser pulse excitation. The effects are measured by a polarization technique involving a perturbative probe that itself does not induce appreciable alignment. We show that this technique allows one to measure a signal proportional to -1/3, with theta the angle between the molecular axis and the laser polarization. Simulations that support this analysis allow one to characterize the experimentally observed alignment and planar delocalization quantitatively.

Journal Article↗
PubMed2003

Radiation dose as a risk factor for malignant melanoma following childhood cancer.

The aim of this study was to determine therapy-related risk factors for the development of melanoma after childhood cancer. Among 4401 3-year survivors of a childhood cancer in eight French and British centres and 25120 patients younger than 20 years old at first malignant neoplasm (FMN) extracted from the Nordic Cancer Registries, 16 patients developed a melanoma as a second malignant neoplasm (SMN). A cohort study of the French and British cohorts was performed. In a nested case-control study, the 16 patients who developed a melanoma as a SMN (cases) were matched with 3-5 controls in their respective cohort according to gender, age at the first cancer, the calendar year of occurrence of the first cancer and follow-up. Radiotherapy appeared to increase the risk of melanoma for local doses >15 Gy, Odds Ratio (OR)=13 (95% Confidence Interval (CI): 0.94-174). Regarding chemotherapy, we observed an increased OR for both alkylating agents and spindle inhibitors, OR=2.7 (95% CI: 0.5-14). Children treated for a gonadal tumour as a FMN were found to be at a higher risk of melanoma, OR=8.7 (95% CI: 0.9-86). The adjusted OR for the local radiation dose was 1.07 (95% CI: 1.00-1.15). In conclusion, radiotherapy may contribute to an increased risk of melanoma as a SMN, but only at very high doses of low linear energy transfer radiation. Common genetic origins between gonadal tumours and malignant melanomas are likely.

Adolescent↗
PubMed2002

Orientation of polar molecules by laser induced adiabatic passage.

We show that two overlapping linearly polarized laser pulses of frequencies omega and its second harmonic 2omega can strongly orient linear polar molecules, by adiabatic passage along dressed states. The resulting robust orientation can be interpreted as a laser-induced localization in the effective double well potential created by the fields, which induces a preliminary molecular alignment. The direction of the orientation can be selected by the relative phase of the fields.

Journal Article↗
PubMed2002

[Procalcitonin and viral meningitis: reduction of unnecessary antibiotics by measurement during an outbreak].

OBJECTIVE: Viral meningitis are often treated with antibiotics in emergency because routine analysis of CSF is not always efficient for distinguishing between viral and bacterial infection. The aim of the study was to evaluate the usefulness of procalcitonin (PCT) to reduce antibiotic treatments. METHODS AND RESULTS: A blood PCT level < 0.5 ng/mL was prospectively used for the diagnosis of viral origin of meningitis in 58 patients (two months-14 years), in which enterovirus was isolated by culture or PCR during an outbreak (May-June 2000). CSF cells range was 10 to 2800/mL (m: 244), PMN 5 to 2464/mL and CSF proteins range was 0.19 to 0.92 mg/dL (m: 0.37). Seventeen patients received antibiotic therapy in admission. In nine patients, PCT (dosage was routinely measured 3/week) result < 0.5 ng/mL was obtained in 24 h and in 48 h in six: treatment was then stopped and children led hospital. In two patients, PCT was > 1 ng/mL because of bacterial coinfection. CSF and PCT values were similar to those of an already published control group. CONCLUSION: PCT dosage allowed to shorten hospitalization of 4.47 (controls) to 2.06 (patients) days in patients receiving unnecessary antibiotic treatments. During this outbreak, PCT dosage allowed to reduce 40 days of hospitalization.

Adolescent↗
PubMed2001

Role of vagal innervation on intragastric distribution and emptying of liquid and semisolid meals in conscious pigs.

The role of vagal innervation on emptying patterns and intragastric distributions of liquid and semisolid meals is still controversial. We aimed to record these features after dorsal, ventral and truncal vagotomies, using external gamma scintigraphy in conscious pigs in which the dorsal vagus specifically innervates the proximal stomach. Imaging of the stomach was performed for all experimental situations and before surgery using 99mTc-labelled glucose and porridge meals. Emptying of liquids was faster after dorsal vagotomy, whereas it was unchanged after ventral and truncal vagotomies (T1/2 = 57 +/- 8.5, 31 +/- 14.4, 54 +/- 9.1 and 42 +/- 14.9 min for intact, dorsal, ventral and truncal vagotomies, respectively). On the other hand, truncal vagotomy significantly reduced the emptying rate of semisolids whereas dorsal and ventral vagotomies had no significant effect (T1/2 = 96 +/- 7.2, 113 +/- 8.1, 75 +/- 9.9 and 260 +/- 56.6 min for intact, dorsal, ventral and truncal vagotomies). Morphological analysis of the gastric shape confirmed an overdistended proximal stomach after truncal vagotomy only. For semisolids, proximal stomach emptying followed the same emptying pattern as the entire stomach, irrespective of the surgical procedure. We concluded that the proximal stomach is the main control for the emptying of liquids and semisolids. The vagal control of overall gastric emptying for semisolids is probably identical to that modulating the intragastric distribution of the meal.

Animals↗
PubMed2001

Characteristics and use as spin trapping agent of a beta-phosphorylated nitroso compound, DEPNP.

2-(Diethylphosphonate)-nitrosopropane (DEPNP), prepared by oxidation of the corresponding aminophosphonate, was found to essentially exist as monomer in both water and organic solvents. The mechanisms of its degradation under 80 degrees C heating or visible light exposure were studied by EPR spectroscopy: its decomposition gave rise to paramagnetic by-products, which have been identified as DEPNP/.C(CH(3) )(2) [P(O)(OC(2) H(5) )(2) ] and DEPNP/.P(O)(OC(2) H(5) )(2) spin adducts. Despite this drawback, DEPNP was successfully used as spin trapping agents to scavenge various carbon - and phosphorus-centred free radicals both in aqueous and organic media, giving rise to intense EPR spectra characteristic of the species trapped.

Electron Spin Resonance Spectroscopy↗
PubMed2000

[Procalcitonin in pediatric emergencies: comparison with C-reactive protein, interleukin-6 and interferon alpha in the differentiation between bacterial and viral infections].

OBJECTIVE: Procalcitonin concentration increases in bacterial infections but remains low in viral infections and inflammatory diseases. The change is rapid and the molecule is stable making it a potentially useful marker for distinguishing between bacterial and viral infections. PATIENTS AND METHODS: Procalcitonin (PCT) was determined with an immunoluminometric assay on plasma collected at admission in 436 infants and children hospitalized for bacterial or viral infection. It was compared with C reactive protein, interleukin-6 and interferon-alpha measured on the same sample. RESULTS: PCT was 41.3 +/- 77.4 micrograms/l in children with septicemia or bacterial meningitis (n = 53), 0.39 +/- 0.57 microgram/l in children with viral infection (n = 274) and 3.9 +/- 5.9 micrograms/l in children with a localized bacterial infection who had a negative blood culture (n = 109). PCT was > 1 microgram/l in 126 children with a localized or systemic bacterial infection (sensitivity 78%). PCT was < 1 microgram/l in 258 children with a viral infection (specificity 94%). For differenciation between viral and bacterial infections, CRP value > or = 20 mg/l, IL-6 > 100 pg/ml and interferon-alpha > 0 Ul/ml have 85, 48 and 76% sensitivity and 73, 85 and 92% specificity respectively. CONCLUSIONS: In this study, a PCT value of 1 microgram/l or greater had better specificity, sensitivity and predictive value than CRP, IL-6 and interferon-alpha in children for distinguishing between viral and bacterial infections. PCT may be useful in pediatric emergency room for making decision about antibiotic treatments.

Adolescent↗
PubMed2000

RNA and protein expression of the murine autoimmune regulator gene (Aire) in normal, RelB-deficient and in NOD mouse.

Mutations in the putative transcription factor autoimmune regulator (AIRE) gene are responsible for autoimmune polyendocrinopathy-candidiosis-ectodermal dystrophy (APECED; OMIM#240300), a monogenic recessively inherited disease characterized by destructive autoimmune diseases of the endocrine organs, chronic candidiosis of mucous membranes and ectodermal dystrophies. In this study the expression of murine homolog for AIRE protein, Aire, was detected in a fraction of thymic medullary epithelial cells. Subcellularly, in thymus the protein appears as concentrated into nuclear dot-like structures, whereas in transfected cells the protein is also bound along a cytosolic fibrillar network. By RT-PCR Aire mRNA was detected in thymus, lymph node, spleen and testis although the second round PCR amplified Aire specific band from most mouse tissues analyzed. Furthermore, the Aire mRNA was detected in dendritic cell (DC) populations isolated from thymus and spleen, representing both myeloid- and lymphoid-related lineages of DC. We also demonstrate that the Aire protein is absent in the thymus of RelB-deficient mouse and in NOD thymus most of the Aire positive cells showed an abnormal morphology. These results suggest that the Aire protein is associated with the normal development and/or action of a subset of thymic medullary stromal cells involved in tolerance induction.

Alternative Splicing↗
PubMed2000

Three-dimensional architectures grown by simple 'stigmergic' agents.

A simple model of multi-agent three-dimensional construction is presented. The properties of this model are investigated. Based on these properties, a fitness function is defined to characterize the structured patterns that can be generated by the model. The fitness function assigns a value to each pattern. The choice of the fitness function is validated by the fact that human observers tend to view patterns with high (resp. low) fitness as structured (resp. unstructured). A genetic algorithm based on this fitness function is used to explore the space of possible patterns. The genetic algorithm is able to make use of sub-modules of existing patterns and recombine them to produce novel patterns, but strong epistatic interactions among genes make the fitness landscape rugged and prevent more complex patterns from being produced.

Algorithms↗
PubMed2000

Dynamic changes in the gonadotrope cell subpopulations during an estradiol-induced surge in the ewe.

Whether estradiol targets a subpopulation of gonadotrope cells was investigated in this study. Ovariectomized ewes (OVX) or OVX ewes immunized against GnRH and treated with hourly pulses of GnRH analogue (OVX-IMG) were killed at 6, 12, 16, and 24 h after administration of 50 microg of 17beta-estradiol (E(2)). Control ewes received no E(2) treatment. In OVX or OVX-IMG ewes killed 6 h after E(2) injection, a decrease in gonadotropin plasma levels was observed compared with non-E(2)-treated ewes. In contrast, a surge in gonadotropin plasma concentrations occurred in ewes killed 16 h after injection. The percentage of total immunoreactive gonadotrope cells among the pituitary cells was lower in E(2)-treated ewes compared with nontreated animals. The proportion of monohormonal LH cells was constant throughout the experiment, except at the surge peak, where it was enhanced. In the OVX ewes, the proportion of bihormonal LH/FSH cells was lower in the E(2)-treated ewes compared to the nontreated ewes (P: < 0.001), with a more pronounced decrease 16 h after E(2) injection. A slight increase occurred 12 h after E(2) injection compared with 6 h after injection (P: < 0.05). A similar pattern was observed in the OVX-IMG ewes, except at 12 h after E(2) injection, when no increase occurred. In both OVX and OVX-IMG ewes, injection of E(2) decreased FSHbeta mRNA expression but did not alter the relative levels of LHbeta mRNA. These data suggest that the negative feedback of E(2) on LH and FSH secretion mainly targets the bihormonal cells and occurs, at least in part, directly at the pituitary level. During the gonadotropin surge, the sustained FSH release from the bihormonal cells would induce a switch from bihormonal cells to monohormonal LH cells by depleting these cells of FSH.

Animals↗
PubMed1999

Defective thymocyte maturation in p44 MAP kinase (Erk 1) knockout mice.

The p42 and p44 mitogen-activated protein kinases (MAPKs), also called Erk2 and Erk1, respectively, have been implicated in proliferation as well as in differentiation programs. The specific role of the p44 MAPK isoform in the whole animal was evaluated by generation of p44 MAPK-deficient mice by homologous recombination in embryonic stem cells. The p44 MAPK-/- mice were viable, fertile, and of normal size. Thus, p44 MAPK is apparently dispensable and p42 MAPK (Erk2) may compensate for its loss. However, in p44 MAPK-/- mice, thymocyte maturation beyond the CD4+CD8+ stage was reduced by half, with a similar diminution in the thymocyte subpopulation expressing high levels of T cell receptor (CD3high). In p44 MAPK-/- thymocytes, proliferation in response to activation with a monoclonal antibody to the T cell receptor in the presence of phorbol myristate acetate was severely reduced even though activation of p42 MAPK was more sustained in these cells. The p44 MAPK apparently has a specific role in thymocyte development.

Animals↗
PubMed1999

Differential regulation of the gonadotropin storage pattern by gonadotropin-releasing hormone pulse frequency in the ewe.

The differential control of gonadotropin secretion by GnRH pulse frequency may reflect changes in the storage of LH and FSH. To test this hypothesis, ovariectomized ewes passively immunized against GnRH received pulsatile injections of saline (group 1) or GnRH analogue: 1 pulse/6 h for group 2 or 1 pulse/h for group 3, during 48 h. Immunization against GnRH suppressed pulsatility of LH release and reduced mean FSH plasma levels (3.1 +/- 0.2 vs. 2.2 +/- 0.1 ng/ml before and 3 days after immunization, respectively). Pulsatile GnRH analogue replacement restored LH pulses but not FSH plasma levels. Low and high frequencies of GnRH analogue increased the percentage of LH-containing cells in a similar way (group 1 = 6.9 +/- 0.5% vs. group 2 = 10.5 +/- 0.8%, or vs. group 3 = 9.6 +/- 0.4%). In contrast, the rise of the percentage of FSH-containing cells was greater after administration of the analogue at low frequency than at high frequency (group 1 = 3.7 +/- 0.4% vs. group 2 = 8.4 +/- 0.2%, or vs. group 3 = 5.2 +/- 0.8%). Moreover, while GnRH pulse frequency had no differential effect on FSHbeta mRNA levels, LHbeta mRNA levels were higher under high than low frequency. These data showed that the frequency of GnRH pulses can modulate the gonadotropin storage pattern in the ewe. These changes may be a component of the differential regulation of LH and FSH secretion.

Animals↗