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Biomedical subjects

P Vincent

Publications and source records attributed to P Vincent.

At least 19 recordsLinked to original sources
PubMed2006

A low level of extragalactic background light as revealed by gamma-rays from blazars.

The diffuse extragalactic background light consists of the sum of the starlight emitted by galaxies through the history of the Universe, and it could also have an important contribution from the 'first stars', which may have formed before galaxy formation began. Direct measurements are difficult and not yet conclusive, owing to the large uncertainties caused by the bright foreground emission associated with zodiacal light. An alternative approach is to study the absorption features imprinted on the gamma-ray spectra of distant extragalactic objects by interactions of those photons with the background light photons. Here we report the discovery of gamma-ray emission from the blazars H 2356 - 309 and 1ES 1101 - 232, at redshifts z = 0.165 and z = 0.186, respectively. Their unexpectedly hard spectra provide an upper limit on the background light at optical/near-infrared wavelengths that appears to be very close to the lower limit given by the integrated light of resolved galaxies. The background flux at these wavelengths accordingly seems to be strongly dominated by the direct starlight from galaxies, thus excluding a large contribution from other sources-in particular from the first stars formed. This result also indicates that intergalactic space is more transparent to gamma-rays than previously thought.

Journal Article↗
PubMed2006

Discovery of very-high-energy gamma-rays from the Galactic Centre ridge.

The source of Galactic cosmic rays (with energies up to 10(15) eV) remains unclear, although it is widely believed that they originate in the shock waves of expanding supernova remnants. At present the best way to investigate their acceleration and propagation is by observing the gamma-rays produced when cosmic rays interact with interstellar gas. Here we report observations of an extended region of very-high-energy (> 10(11) eV) gamma-ray emission correlated spatially with a complex of giant molecular clouds in the central 200 parsecs of the Milky Way. The hardness of the gamma-ray spectrum and the conditions in those molecular clouds indicate that the cosmic rays giving rise to the gamma-rays are likely to be protons and nuclei rather than electrons. The energy associated with the cosmic rays could have come from a single supernova explosion around 10(4) years ago.

Journal Article↗
PubMed2006

Rectal prolapse of intussusception--a single institution's experience.

AIM: The objective was to study the clinical presentation and outcome of intussusceptions prolapsing rectally. METHODS: A retrospective analysis was done of 198 children who presented with intussusception at a single institution over a 5-year period. Of this group, the data of children with intussusception prolapsing rectally was studied. RESULTS: The incidence of prolapsing intussusception in this series was 8%. All 16 patients were infants with an average age of 5 months. The most common presenting features were rectal bleeding and abdominal mass. Only 56% of children had abdominal pain. 4/16 children had abdominal distension and 4 had dehydration. The duration of symptoms was less than 48 hours in 14/16 patients. Air enema reduction (AER) was attempted in 14/16 patients and was successful in 8 patients. The success rate of AER was 57%. One patient developed a perforation during AER. Manual reduction was done in six patients who failed AER and in two patients in whom AER was not attempted because of prolonged duration of symptoms (> 48 hrs). There were no recurrences in this series. CONCLUSION: The incidence of intussusceptions prolapsing rectally is high in this series. It can present in the absence of the cardinal symptoms of intussusception. A high index of clinical suspicion is necessary to make the diagnosis. AER is often successful and must be attempted in children who do not have contraindications for this procedure.

Air↗
PubMed2006

Photodynamic action of red light for treatment of erythrasma: preliminary results.

BACKGROUND: Erythrasma is a superficial cutaneous infection caused by Corynebacterium minutissimum and is characterized by fluorescence under Wood's light (UV) because of the presence of porphyrins. These molecules are photosensitizing and we propose to assess efficacy of red light that activates porphyrins (photodynamic reaction) in treatment of this pathology. OBJECTIVES: Assessment of effects of photodynamic action of red light for treatment of erythrasma without exogenous photosensitizing molecules. METHODS: Thirteen patients with erythrasma were treated by one illumination (80 J/cm2) by red light (broad band, peak at 635 nm) without exogenous photosensitizing molecules. Disappearance or reduction of extent of lesions were observed 2 weeks later. If lesions were still present, a second irradiation was conducted with the same method. RESULTS: Preliminary results are presented. As a result of red light irradiation, we noticed a complete recovery for three patients and, in most other cases, reduction of extent of lesions (mean: -29% after one session). The treatment was well tolerated. CONCLUSION: We report first cases of photodynamic treatment of erythrasma. There are other reports of clinical applications of antimicrobial action of photodynamic therapy in dermatology (acne vulgaris, leishmaniasis, warts, etc.). But there are few applications without addition of exogenous photosensitizing agent. The originality and interest of our study is to use spontaneous presence of porphyrins in the lesions. This technique seems to be an interesting alternative, inexpensive and easy, for the treatment of this localized infection. But an optimal method is still to be determined to improve efficacy.

Adult↗
PubMed2005

A new population of very high energy gamma-ray sources in the Milky Way.

Very high energy gamma-rays probe the long-standing mystery of the origin of cosmic rays. Produced in the interactions of accelerated particles in astrophysical objects, they can be used to image cosmic particle accelerators. A first sensitive survey of the inner part of the Milky Way with the High Energy Stereoscopic System (HESS) reveals a population of eight previously unknown firmly detected sources of very high energy gamma-rays. At least two have no known radio or x-ray counterpart and may be representative of a new class of "dark" nucleonic cosmic ray sources.

Journal Article↗
PubMed2004

High-energy particle acceleration in the shell of a supernova remnant.

A significant fraction of the energy density of the interstellar medium is in the form of high-energy charged particles (cosmic rays). The origin of these particles remains uncertain. Although it is generally accepted that the only sources capable of supplying the energy required to accelerate the bulk of Galactic cosmic rays are supernova explosions, and even though the mechanism of particle acceleration in expanding supernova remnant (SNR) shocks is thought to be well understood theoretically, unequivocal evidence for the production of high-energy particles in supernova shells has proven remarkably hard to find. Here we report on observations of the SNR RX J1713.7 - 3946 (G347.3 - 0.5), which was discovered by ROSAT in the X-ray spectrum and later claimed as a source of high-energy gamma-rays of TeV energies (1 TeV = 10(12) eV). We present a TeV gamma-ray image of the SNR: the spatially resolved remnant has a shell morphology similar to that seen in X-rays, which demonstrates that very-high-energy particles are accelerated there. The energy spectrum indicates efficient acceleration of charged particles to energies beyond 100 TeV, consistent with current ideas of particle acceleration in young SNR shocks.

Journal Article↗
PubMed2002

Tuning of nanotube mechanical resonances by electric field pulling.

We show here that field emission (FE) can be used to directly observe the vibration resonances nu(R) of carbon nanotubes (CNTs) and that the tension created by the applied field allows the tuning of these resonances by up to a factor of 10. The resonances are observable by the changes they create in the FE pattern or the emitted FE current. The tuning is shown to be linear in voltage and to follow from the basic physics of stretched strings. The method allows one to study the mechanical properties of individual multiwall carbon nanotubes within an ensemble and follow their evolution as the CNTs are modified. The tuning and detection should be useful for nanometric resonant devices.

Journal Article↗
PubMed2002

Hot nanotubes: stable heating of individual multiwall carbon nanotubes to 2000 k induced by the field-emission current.

Field emission (FE) electron spectroscopy from an individual multiwalled carbon nanotube (MWNT) is used to measure quantitatively stable temperatures at the apex, T(A), of up to 2000 K induced by FE currents approximately 1 microA. The high T(A) is due to Joule heating along the length of the MWNT. These measurements also give directly the resistance of the individual MWNT which is shown to decrease with temperature, and explain the phenomenon of FE-induced light emission which was observed simultaneously. The heating permits thermal desorption of the MWNT and, hence, excellent current stability.

Journal Article↗
PubMed2002

A novel polymer produced by a bacterium isolated from a deep-sea hydrothermal vent polychaete annelid.

AIMS: The objective of the present work was to describe an aerobic, mesophilic and heterotrophic marine bacterium, designated HYD657, able to produce an exopolysaccharide (EPS). It was isolated from a East Pacific Rise deep-sea hydrothermal vent polychaete annelid. METHODS AND RESULTS: This micro-organism, on the basis of the phenotypical features and genotypic investigations, can be clearly assigned to the Alteromonas macleodii species and the name A. macleodii subsp. fijiensis biovar deepsane is proposed. Optimal growth occurs between 30 and 35 degrees C, at pH between 6.5 and 7.5 and at ionic strengths between 20 and 40 g x l(-1) NaCl. The G + C content of DNA was 46.5%. This bacterium excreted, under laboratory conditions, an EPS consisting of glucose, galactose, rhamnose, fucose and mannose as neutral sugars along with glucuronic and galacturonic acids and a diacidic hexose identified as a 3-0-(1 carboxyethyl)-D-glucuronic acid. Its average molecular mass was 1.6 x 10(6) Da. CONCLUSIONS: The bacterium HYD657, for which the name A. macleodii subsp. fijiensis biovar deepsane is proposed, produces an unusual EPS in specific medium. SIGNIFICANCE AND IMPACT OF THE STUDY: Due to its interesting biological activities, applications have been found in cosmetics. Its probable contribution to the filamentous microbial mat in the Alvinella pompejana microenvironment can be also mentioned.

Alteromonas↗
PubMed2002

[Symptomatology and specific characteristics of chronic gastritis caused by Helicobacter pylori infection in children in the Czech population--epidemiologic, clinical, endoscopic and histomorphologic study].

BACKGROUND: H. pylori infection is associated with gastritis and peptic ulcer in children and adults. H. pylori acquisition seems to occur predominantly in childhood. Some data have reported H. pylori non-related chronic gastritis. Little information is available about the relationship between H. pylori, clinicopathologic features and long-term effects of infection in childhood. The purpose of this study was to compare the differences between chronic gastritis due to H. pylori with those of chronic gastritis not associated with H. pylori infection. METHODS AND RESULTS: 92 children (13.8 +/- 3.5 years) were take into they shaded group. 51 children were H. pylori positive, 41 children had no evidence of H. pylori. Epidemiological and clinical data, endoscopic appearance and histologic examination were evaluated. There were no differences in age and gender among the children. There was a significant correlation between H. pylori infection and parental education (p < 0.05) and habitat crowding (the number of rooms). There were no differences in clinical diagnosis and occurrence of any predominant symptom between the two groups. There was an association with a detrimental influence on daily life and activities in H. pylori patients (p < 0.01). Extradigestive symptoms (chronic urticaria, sideropenic anemia) were significantly more common in the H. pylori positive group (p < 0.05). 21 children (41.6%) were H. pylori positive/cagA positive, 15 of them (30.3%) were H. pylori positive/vacA positive. Findings of antral nodularity were more frequent in H. pylori positive children than in H. pylori negative (p < 0.000001). There were no differences in erythematous gastritis, haemorrhage and mucosal ulceration. H. pylori density score did not differ in various part of the gastric mucosa (antrum, corpus). Chronic gastritis was found to be more severe in patients with H. pylori infection compared with H. pylori-negative gastritis. Statistically significant was the increased presence of neutrophils, edema, monocytes, lymphoid follicles, the intensity of inflammation and mucosal oedema in the gastric mucosa in H. pylori positive children. There were no differences in the incidence of foveolar hyperplasia, mucosal atrophy, intestinal metaplasia and erosion. CONCLUSION: H. pylori related chronic gastritis may be considered as a specific form of inflammation and it may be associated with a typical clinical symptomatology in a subgroup of children in Czech population. Precautions in life style may diminish H. pylori-related disease in children.

Adolescent↗
PubMed2001

Cyclic AMP imaging in neurones in brain slice preparations.

The second messenger cascade of cyclic AMP (cAMP) plays an important physiological role in neurones, modulating neuronal excitability and synaptic transmission. The fluorescent probe FlCRhR allows real time ratiometric imaging of cAMP changes inside cells (Nature 349 (1991) 694). Until now, the only way to introduce FlCRhR into cells was microinjection, which restricted the use of FlCRhR to large invertebrate neurones. This report describes the use of the patch-clamp technique to deliver FlCRhR into the cytosol of several types of neurones in brain slice preparations. Direct activation of adenylate cyclase by forskolin produced marked increases in fluorescence ratio, confirming that the probe can report cAMP increases. However, some neurones failed to exhibit a cAMP response and this lack of response was related to the nucleus integrity. Stimulation of membrane receptors positively coupled to adenylate cyclase elicited cAMP increases in various neuronal cell types. This is the first report of a cAMP response to neuromodulators measured by an imaging technique in neurones in brain slices. The method described here could find many applications such as testing the ability of agonists to specifically activate the cAMP cascade in identified neurones, studying the kinetics of the cAMP response and determining the subcellular localisation of cAMP changes.

Animals↗
PubMed2001

Phosphatidylserine delivery to endoplasmic reticulum-derived vesicles of plant cells depends on two biosynthetic pathways.

Vesicles formed from endoplasmic reticulum (ER) by a cell-free system of leek cells (Allium porrum) are enriched in phosphatidylserine (PS), especially species containing very long chain fatty acids (VLCFA, at least 20 carbon atoms). In plant cells, PS is formed either by PS synthase or the serine exchange enzyme, although it is not known which pathway(s) contribute(s) to PS delivery in the ER-derived vesicles (EV), nor to what extent this occurs. Taking advantage of a cell-free system, we have shown that PS enrichment originates mainly from the serine exchange enzyme which is the only pathway that synthesizes the VLCFA-PS species. On the other hand, both enzymes synthesize PS with long chain fatty acids (up to 18 carbon atoms), but these species are given to the EV by PS synthase.

Endoplasmic Reticulum↗
PubMed2001

Phosphatidylserine increase in rat liver endomembranes during the acute phase response.

The acute phase response (APR) is responsible for great changes in protein and lipid metabolism. For example, marked changes are observed in the metabolism of fatty acids, triglycerides, cholesterol and sphingolipids. Those lipids are partly recovered in the lipoproteins and subsequently in the plasma. Beside these lipid families, nothing is known about phospholipids and their synthesis in endomembranes during the APR. Our studies show that phosphatidylserine synthesis is stimulated during the APR and that this lipid is increased in the endoplasmic reticulum (ER) and the ER-derived vesicles.

Acute-Phase Reaction↗
PubMed2001

Familial and community environmental risk factors for Helicobacter pylori infection in children and adolescents.

BACKGROUND: The aim of the study was to identify familial and community environmental risk factors associated with Helicobacter pylori infection in a pediatric population. METHODS: Children requiring diagnostic upper endoscopy were included in the study during a 2-year period. During endoscopy, five gastric biopsies were performed for the histologic or bacteriologic diagnosis, or both, of H. pylori infection. Epidemiologic data collected by a questionnaire were analyzed using the chi-square test or Fisher test and stepwise logistic regression. RESULTS: The authors included 436 patients (242 boys), aged 2 days to 17.9 years (median, 2.7 years). H. pylori prevalence was 7.3%. Univariate analysis found H. pylori was more common in older patients (P < 0.00001), in children who had at least one parent born in a developing country (P < 0.02) or with a low socioeconomic status (P < 0.02), and in those living in crowded conditions (P < 0.02). Children whose mother worked at home were more frequently infected than children whose mother worked outside the home (P < 0.02). Attendance at nursery or school before the age of 6 years was not associated with infection. Logistic regression showed a strong association with H. pylori only for age and number of persons at home. CONCLUSIONS: The source of H. pylori is intrafamilial rather than from a community, such as nursery and school attended at a young age. The number of persons in the home influences the infection status of children but not by the presence of the mother in home. These data suggest that H. pylori infection transmission occurs from siblings or the father rather than from mother.

Adolescent↗