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Biomedical subjects

L Petit

Publications and source records attributed to L Petit.

At least 19 recordsLinked to original sources
PubMed2006

The calcium sensing receptor is directly involved in both osteoclast differentiation and apoptosis.

Intracellular transduction pathways that are dependent on activation of the CaR by Ca(o)2+ have been studied extensively in parathyroid and other cell types, and include cytosolic calcium, phospholipases C, A2, and D, protein kinase C isoforms and the cAMP/protein kinase A system. In this study, using bone marrow cells isolated from CaR-/- mice as well as DN-CaR-transfected RAW 264.7 cells, we provide evidence that expression of the CaR plays an important role in osteoclast differentiation. We also establish that activation of the CaR and resultant stimulation of PLC are involved in high Ca(o)2+-induced apoptosis of mature rabbit osteoclasts. Similar to RANKL, Ca(o)2+ (20 mM) appeared to trigger rapid and significant nuclear translocation of NF-kappaB in a CaR- and PLC-dependent manner. In summary, our data suggest that stimulation of the CaR may play a pivotal role in the control of both osteoclast differentiation and apoptosis in the systems studied here through a signaling pathway involving activation of the CaR, phospholipase C, and NF-kappaB.

Animals↗
PubMed2006

Ground state valency and spin configuration of the Ni ions in nickelates.

The ab initio self-interaction-corrected local-spin-density approximation is used to study the electronic structure of both stoichiometric and nonstoichiometric nickelates. From total energy considerations it emerges that, in their ground state, both LiNiO2 and NaNiO2 are insulators, with the Ni ion in the Ni3+ low-spin state (t(2g)(6)e(g)(1)) configuration. It is established that a substitution of a number of Li/Na atoms by divalent impurities drives an equivalent number of Ni ions in the NiO2 layers from the Jahn-Teller (JT)-active trivalent low-spin state to the JT-inactive divalent state. We describe how the observed considerable differences between LiNiO2 and NaNiO2 can be explained through the creation of Ni2+ impurities in LiNiO2. The indications are that the random distribution of the Ni2+ impurities might be responsible for the destruction of the long-range orbital ordering in LiNiO2.

Journal Article↗
PubMed2006

[Controlled hypernatremia].

Hypernatremia exerts its main effect on the brain through the osmotic gradient it creates on either side of the blood brain barrier, which is impermeable to sodium. This generates a transfer of water from the intracellular to the vascular sector leading to temporary cell shrinkage. Osmoregulation permits cerebral cells to accumulate osmoactive molecules in order to restore their initial volume. It has been demonstrated in animals with brain injury that intracellular dehydration occurs essentially in the nonlesioned hemisphere. In most experimental studies, the reduction in cerebral volume obtained by hypertonic saline (HS) perfusion is accompanied by an intracranial pressure decrease, even under hemorrhagic shock conditions. Initially, clinical studies successfully used HS, as an alternative to mannitol, in the treatment of acute and refractory intracranial hypertension. Then continuous infusion of HS, with the objective of inducing hypernatremia, had produced encouraging effects on intracranial pressure control. However, these results were limited to non-randomized studies, without control groups and mainly in pediatric patients. Nevertheless, the use of HS on intracranial hypertension, refractory to conventional treatments, could be reasonable under strict monitoring of natremia as well as its adverse effects.

Animals↗
PubMed2006

Nonlinear optical properties of glasses in the system Ge/Ga-Sb-S/Se.

We report n2 measurements of selected chalcogenide glasses using a modified Z-scan technique. Measurements were made with picosecond pulses emitted by a 10 Hz Q-switched, mode-locked Nd:YAG laser at 1064 nm under conditions suitable to characterize ultrafast nonlinearities. The nonlinear index increases significantly up to 246 times the n2 for fused silica with an increase of SbS3 units and also very slightly with the replacement of Ge by Ga or S by Se. We have attributed the variation of n2 to the total number of electronic lone pairs and to the position of the absorption band gap, which are induced by the presence of GaS4 units or Se-Se bonds in the glass structure.

Journal Article↗
PubMed2006

Wave reflection and transmission reduction using a piezoelectric semipassive nonlinear technique.

This study addresses the problem of noise reduction using piezoelements. The nonlinear technique, synchronized switch damping (SSD), is implemented. The device is a pulse-tube termination equipped with piezoelements, which allows performant damping of the vibration resulting from an incident acoustic wave. Due to this damping, both reflected and transmitted wave are reduced. In the semipassive damping approach proposed in this paper, energy degradation is strongly enhanced when the piezoelements are continuously switched from open to short circuit synchronously to the strain. This technique has been developed following two strategies. The first is SSD on a short circuit in which the piezoelement is always in open circuit, except for a very brief period at each strain extremum where it is short-circuited. The second approach is SSD on an inductor. The process is very similar, except that instead of forcing the voltage to zero, the voltage is exactly reversed using a controlled oscillating discharge of the piezoelement capacitor on an inductor during switch drive. Due to this switching mechanism, a phase shift appears between the strain and the resulting voltage, thus creating energy dissipation. Following SSD on an piezoelement, attenuations of 15 dB in reflection and 7 dB in transmission were obtained.

Journal Article↗
PubMed2004

Effect of haemodialysis on acoustic shear wave propagation in the skin.

BACKGROUND: Diverse skin alterations may develop in patients under chronic haemodialysis. Among them, signs of premature photo-ageing have been described. AIM: To assess alterations in the physical properties of skin consistent with ageing effects and with cutaneous fluid exchanges during haemodialysis sessions. METHODS: In the first part of the study, 45 haemodialysed patients were compared to 45 age-, sex- and body-mass-index-matched healthy subjects. In the second part of the study, skin of 30 haemodialysed patients was assessed immediately before and after a haemodialysis session. The speed of ultrasound shear wave propagation was measured in each subject. Series of 16 multidirectional resonance running time measurements (RRTM) were performed on the forehead and/or the volar forearm. They were averaged for each subject. The corresponding intra-individual coefficients of variation were calculated as an estimate of the skin mechanical anisotropy. RESULTS: In both haemodialysed patients and their matched controls, RRTM values were significantly higher on the forearms than on the forehead. By contrast, no significant difference was found in RRTM values that could be ascribed to chronic haemodialysis. However, RRTM values were significantly increased as an immediate and probably transient effect of haemodialysis sessions. In healthy subjects, ageing was associated with increased RRTM values. CONCLUSION: Chronic haemodialysis does not appear to influence significantly the functional expression of the dermal ageing process. Subtle fluid movements occurring in the skin during haemodialysis sessions can be assessed by measuring non-invasively the speed of ultrasound shear wave propagation in the skin.

Adult↗
PubMed2003

First-principles calculations of PuO(2+/-x).

The electronic structure of PuO(2+/-x) was studied using first-principles quantum mechanics, realized with the self-interaction corrected local spin density method. In the stoichiometric PuO2 compound, Pu occurs in the Pu(IV) oxidation state, corresponding to a localized f4 shell. If oxygen is introduced onto the octahedral interstitial site, the nearby Pu atoms turn into Pu(V) (f3) by transferring electrons to the oxygen. Oxygen vacancies cause Pu(III) (f5) to form by taking up electrons released by oxygen. At T = 0, the PuO2 compound is stable with respect to free oxygen, but the delicate energy balance suggests the possible deterioration of the material during long-term storage.

Journal Article↗
PubMed2003

Regional variability in mottled subclinical melanoderma in the elderly.

The density in melanin chromatophores becomes heterogeneous in the epidermis during the early events of photoaging. Little is known about the regional variability in the resulting mottled skin appearance on the sun-exposed parts of the body in the elderly. The relationship between these features and the dermal atrophy related to aging is also an area ripe for study. The aim of the present study was to objectively assess and compare such aspects of photoaging in older subjects. A computer-assisted video camera equipped with an internal ultraviolet-emitting unit (Visioscan) was used in combination with image analysis to quantify the infraclinical mottling of the skin on the forehead, neck and dorsal forearm. A Densi Score device served to assess the dermal atrophy by rating the skin folding capacity. A mottled subclinical melanoderma was disclosed on the three evaluation sites in all subjects irrespective of their phototypes. Three main patterns were identified corresponding to regular perifollicular dots, streaky macules along shallow wrinkles and unevenly shaped macules in the interfollicular area. The extent in melanoderma was larger on the forehead than on the neck and forearm. The age after 60 years did not influence the severity of mottled melanoderma, but clearly altered the skin folding capacity. The greatest inter-individual differences in mottled melanoderma were found in phototype II subjects. In conclusion, infraclinical mottled melanoderma is present in all individuals after 60 years of age. This type of epidermal photoaging does not appear to be influenced in older ages. By contrast, skin laxity due to dermal aging continues to progress beyond the age of 60 years.

Aged↗
PubMed2003

Analytic quantification of solar lentigines lightening by a 2% hydroquinone-cyclodextrin formulation.

BACKGROUND: The innate melanin pigmentation of skin is modulated during lifetime by a series of factors, including ageing and chronic ultraviolet light exposure. Actinic lentigines may be of particular concern from a cosmetic point of view. Conventional hypopigmenting agents are usually deceptive. Using cyclodextrins to form inclusion compounds with these agents might represent a more active drug delivery system. OBJECTIVE: To assess sensitive and objective methods predicting the effects of a 2% hydroquinone-cyclodextrin formulation on solar lentigines. STUDY DESIGN: Thirty Asian adults applied a 2% hydroquinone-cyclodextrin formulation once daily on solar lentigines of a forearm for 2 months. The other untreated forearm served as a control. Monthly assessments were performed using skin colorimetry and fluorescence video recording combined with image analysis. Corneomelametry following photodensitometry of cyanoacrylate skin surface strippings was performed after melanin staining of the samples. RESULTS: The control untreated solar lentigines showed no significant variations in the biometrological parameters. By contrast, the test formulation induced lightening of the solar lentigines. Corneomelametry disclosed improvement after 1 months' treatment, whereas the other assessments only reached significance after 2 months. CONCLUSIONS: A 2% hydroquinone-cyclodextrin formulation proved to be effective in lightening actinic lentigines. Corneomelametry predicted the effects discernible at a later stage by in vivo colour assessments of the melanin content.

Administration, Topical↗
PubMed2002

5f electron localization-delocalization transition from UPd3 to UPt3.

The electronic structures of URh (3), UPd (3), UPt (3), and UAu (3) are calculated with the self-interaction corrected local-spin-density approximation. We find that only in URh (3) the f electrons are fully delocalized. UPt (3) has one f electron localized at each U site, while a localized f(2) configuration of the U ion is found for UPd (3). It is predicted that, upon application of a pressure of 25 GPa, UPd (3) will acquire the f(1) configuration and possibly exhibit heavy-fermion behavior. We find that UAu (3) is characterized by the same mixed localized-delocalized f-electron manifold as UPd (3).

Journal Article↗
PubMed2002

Assessment of topical hypopigmenting agents on solar lentigines of Asian women.

BACKGROUND: So-called darkened age spots encompass distinct pathological processes. The efficacy of topical depigmenting agents is difficult to objectivate. OBJECTIVE: To assess the hypopigmenting effect of three cosmetic formulations using objective biometrological methods. METHODS: 50 women of South-East Asian ancestry were enrolled in this pilot study. They had solar lentigines according to dermoscopic criteria. The lesions were treated by topical hypopigmenting formulations. Products were applied twice daily for 2 or 3 months. Assessments at 1-month intervals were made using narrow-band reflectance spectrophotometry, image analysis of video-recorded ultraviolet light reflection and photodensitometry- and image-analysis-assisted corneomelametry. RESULTS: A 20% azelaic acid formulation and another one containing 5% ascorbyl glucosamine, 1% kojic acid and alpha-hydroxyacid esters appeared inefficacious on solar lentigines. A stabilized soy extract showed a better although modest lightening effect when assessed by corneomelametry. The subclinical or faint mottled skin revealed by ultraviolet light examination better responded (p < 0.05) to treatments. CONCLUSION: Focal epidermal hyperpigmentation is better controlled by topical whitening agents when the increase in melanin content reflects a modest functional hyperactivity of melanocytes.

Administration, Topical↗
PubMed2002

[Tanning benches to accusation benches].

Sunbeds used in sun parlours do not garantee a controlled innocuity. By contrast, health hazards are obvious in many instances. Forceful tanning is a transitory aspect behind which the spectrum of many skin changes includes accelerated photoageing, irreversible pigmentary and keratotic changes, and cutaneous malignancies including malignant melanoma. In the absence of protection, the eye is also affected. Even if tanning salon exposure increases the risk for skin cancer by a small amount, it represents a significant potential public health hazard given the number of people attending salons. Digital dermoscopy and ultraviolet light videoscopy are new methods allowing to predict the cutaneous ransom to be paid by the sunbed worshippers.

Humans↗
PubMed2002

[Pharma clinics. How I treat ... recurrent herpes labialis].

Recurrent herpes labialis is a frequent disorder. It occurs following the reactivation of the Herpesvirus (HSV1 and more rarely HSV2) inside the Gasser ganglion. Treatment and prevention of recurrent labial herpes are targeted by specific antiviral agents. Spectacular benefits obtained in the immunocompromised patients are less convincing in otherwise healthy subjects. Other prospective ways of therapy are under consideration, including lipopeptides and physical means aiming at modifying the cutaneous pH.

Acyclovir↗
PubMed2001

Clostridium perfringens epsilon toxin induces a rapid change of cell membrane permeability to ions and forms channels in artificial lipid bilayers.

Epsilon toxin is a potent toxin produced by Clostridium perfringens types B and D, which are responsible for a rapidly fatal enterotoxemia in animals. One of the main properties of epsilon toxin is the production of edema. We have previously found that epsilon toxin causes a rapid swelling of Madin-Darby canine kidney cells and that the toxin does not enter the cytosol and remains associated with the cell membrane by forming a large complex (Petit, L., Gibert, M., Gillet, D., Laurent-Winter, C., Boquet, P., and Popoff, M. R. (1997) J. Bacteriol. 179, 6480-6487). Here, we report that epsilon toxin induced in Madin-Darby canine kidney cells a rapid decrease of intracellular K(+), and an increase of Cl(-) and Na(+), whereas the increase of Ca(2+) occurred later. The entry of propidium iodide that was correlated with the loss of cell viability monitored by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) test indicates that epsilon toxin formed large pores. In artificial lipid bilayers, epsilon toxin caused current steps with a single-channel conductance of 60 pS in 100 mm KCl, which represented general diffusion pores. The channels were slightly selective for anions, but cations could also penetrate. Epsilon toxin formed wide and water-filled channels permeable to hydrophilic solutes up to a molecular mass of at least 1 kDa, which probably represents the basic mechanism of toxin action on target cells.

Animals↗
PubMed2001

So near yet so far: neglect in far or near space depends on tool use.

The study of unilateral spatial neglect has shown that space can be dissociated on a peripersonal versus extrapersonal basis. We report a novel type of dissociation based on tool use in a patient suffering from left neglect. Line bisection was carried out in near and far space, using a stick and a laser pointer. A rightward bias was always found for the former, but not for the latter. Neglect thus appears to be contingent not only on distance, but also on the motor action required by the task.

Aged↗
PubMed2001

A parametric fMRI study of overt and covert shifts of visuospatial attention.

It has recently been demonstrated that a cortical network of visuospatial and oculomotor control areas is active for covert shifts of spatial attention (shifts of attention without eye movements) as well as for overt shifts of spatial attention (shifts of attention with saccadic eye movements). Studies examining activity in this visuospatial network during attentional shifts at a single rate have given conflicting reports about how the activity differs for overt and covert shifts. To better understand how the network subserves attentional shifts, we performed a parametric study in which subjects made either overt attentional shifts or covert attentional shifts at three different rates (0.2, 1.0, and 2.0 Hz). At every shift rate, both overt and covert shifts of visuospatial attention induced activations in the precentral sulcus, intraparietal sulcus, and lateral occipital cortex that were of greater amplitude for overt than during covert shifting. As the rate of attentional shifts increased, responses in the visuospatial network increased in both overt and covert conditions but this parametric increase was greater during overt shifts. These results confirm that overt and covert attentional shifts are subserved by the same network of areas. Overt shifts of attention elicit more neural activity than do covert shifts, reflecting additional activity associated with saccade execution. An additional finding concerns the anatomical organization of the visuospatial network. Two distinct activation foci were observed within the precentral sulcus for both overt and covert attentional shifts, corresponding to specific anatomical landmarks. We therefore reappraise the correspondence of these two precentral areas with the frontal eye fields.

Adult↗