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Biomedical subjects

J Meunier

Publications and source records attributed to J Meunier.

At least 19 recordsLinked to original sources
PubMed2006

The anti-amnesic and neuroprotective effects of donepezil against amyloid beta25-35 peptide-induced toxicity in mice involve an interaction with the sigma1 receptor.

BACKGROUND AND PURPOSE: The acetylcholinesterase inhibitor, donepezil, is also a high affinity sigma(1) receptor agonist. We examined the involvement of sigma(1) receptors in its anti-amnesic and neuroprotective properties against amyloid beta(25-35) peptide-induced toxicity in mice. EXPERIMENTAL APPROACH: Mice were given an intracerebroventricular (i.c.v.) injection of Abeta(25-35) peptide (9 nmol) 7-9 days before being tested for spontaneous alternation and passive avoidance. Hippocampal lipid peroxidation was measured 7 days after Abeta(25-35) injection to evaluate oxidative stress. Donepezil, the sigma(1) agonist PRE-084 or the cholinesterase (ChE) inhibitors tacrine, rivastigmine and galantamine were administered either 20 min before behavioural sessions to check their anti-amnesic effects, or 20 min before Abeta(25-35) injection, or 24 h after Abeta(25-35) injection and then once daily before behavioural sessions, to check their pre- and post-i.c.v. neuroprotective activity, respectively. KEY RESULTS: All the drugs tested were anti-amnesic, but only the effects of PRE-084 and donepezil were prevented by the sigma(1) antagonist BD1047. Only PRE-084 and donepezil showed neuroprotection when administered pre i.c.v.; they blocked lipid peroxidation and learning deficits, effects inhibited by BD1047. Post i.c.v., PRE-084 and donepezil showed complete neuroprotection whereas the other ChE inhibitors showed partial effects. BD1047 blocked these effects of PRE-084, attenuated those of donepezil, but did not affect the partial effects of the other ChE inhibitors. CONCLUSIONS AND IMPLICATIONS: The potent anti-amnesic and neuroprotective effects of donepezil against Abeta(25-35)-induced toxicity involve both its cholinergic and sigma(1) agonistic properties. This dual action may explain its sustained activity compared to other ChE inhibitors.

Amnesia↗
PubMed2004

Adsorption of oppositely charged polyelectrolyte/surfactant complexes at the air/water interface: formation of interfacial gels.

The adsorption and complexation of polystyrene sulfonate (a highly charged anionic polyelectrolyte) and dodecyltrimethylammonium bromide (a cationic surfactant) at the air-water interface can lead to interfacial gels that strongly influence foam-film drainage and stability. The formation and characteristics of these gels have been studied by combining surface tension, ellipsometry, and foam-film drainage experiments. Simultaneously, the solution electromotive force is measured and used to track the polymer-surfactant interactions in the bulk solution. We find that surface gelation occurs above the critical aggregation concentration in solution but before bulk precipitation of the polymer-surfactant complexes. Furthermore, we reveal that strong readsorption of polymer-surfactant complexes occurs during the resolubilization of the precipitated complexes at high surfactant concentrations (i.e., >>critical micelle concentration). Seemingly overlooked in the past, this readsorption significantly influences the surface rheological properties and foam-film drainage of these systems.

Adsorption↗
PubMed2004

Phase separation in molecular layers of macromolecules at the champagne-air interface.

Bubble and foam stability, which are essential for the hallmark of champagne, rely on the concentration of amphiphilic macromolecules originating from the grape, which form molecular layers at the interface between champagne and gas. Ellipsometry and Brewster angle microscopy experiments were conducted at the air-champagne interface to analyse the lateral organization of the layers of macromolecules. Several kinds of phase separations - leading in some cases to two-dimensional foams - were identified. At the beginning of layer formation, condensed domains develop at the expense of dilute domains. Thereafter, phase separations occur within the condensed domains. These findings may allow advances in the implementation of methods predicting bubble and foam stability of champagnes.

Adsorption↗
PubMed2001

Crossover from first-order to critical wetting: short-range tricritical wetting.

We study wetting in liquid mixtures of methanol and the n-alkanes. Mixing alkanes of different chain lengths, we can examine the crossover between critical (continuous) and first-order (discontinuous) wetting transitions. Measurements of the film thickness and surface specific heat exponent indicate that for carbon number n between 11 (undecane) and 9 (nonane), there is a crossover from first-order to critical wetting with a tricritical wetting point between an effective alkane carbon number of 9.6 and 10. The observed variation of the specific heat exponent in the tricritical region agrees fairly well with the predictions of a simple mean-field model with only short-range interactions.

Journal Article↗
PubMed2001

Aging dynamics in a colloidal glass.

The aging dynamics of colloidal suspensions of Laponite, a synthetic clay, is investigated using dynamic light scattering (DLS) and viscometry after a quench into the glassy phase. DLS allows to follow the diffusion of Laponite particles and reveals that there are two modes of relaxation. The fast mode corresponds to a rapid diffusion of particles within "cages" formed by the neighboring particles. The slow mode corresponds to escape from the cages: its average relaxation time increases exponentially fast with the age of the glass. In addition, the slow mode has a broad distribution of relaxation times, its distribution becoming larger as the system ages. Measuring the concomitant increase of viscosity as the system ages, we can relate the slowing down of the particle dynamics to the viscosity.

Journal Article↗
PubMed2001

Wetting of biological lipids on aqueous substrates.

We study the dynamics and final wetting state of skin lipids on water and brine by fluorescence microscopy and ellipsometry. When a lipid droplet is brought into contact with the water surface, a lipid wetting film spreads out rapidly by a Marangoni effect. Subsequently, this film undergoes a dewetting instability. However, the final equilibrium is not partial wetting. The film breaks up into droplets with a mesoscopic (approximately 50 A) film in between. These observations result from a subtle interplay between short- and long-range forces: surfactants naturally present in the lipids favor wetting, while the van der Waals forces oppose it. In addition, this reveals the likely organization of the hydrolipid film that covers and protects the skin.

Lipids↗
PubMed2001

Inhibition of the finite-time singularity during droplet fission of a polymeric fluid.

When a drop of fluid detaches from a capillary, singular behavior ensues. We show that the addition of very small amounts of polymer inhibits this singularity in an abrupt way and gives rise, after a period of self-similar dynamics as for simple liquids, to long-lived cylindrical necks or filaments which thin exponentially in time. This abrupt change occurs when the elongation rate epsilon* becomes comparable to the inverse of the polymer relaxation time leading to a large elongational viscosity eta(E) of the dilute polymer solution.

Journal Article↗
PubMed2001

Shear-induced first-order sponge-to-lamellar transition in a lyotropic surfactant system.

We report a shear-induced sponge (L3) to lamellar (L(alpha)) transition in a surfactant system. Under a constant shear rate, after a delay time t(n) we observe random nucleation and subsequent growth of the L(alpha) phase, demonstrating that the shear-induced transition is first order. A simple argument for the energy of a two-dimensional nucleus accounts for the observed delay and its shear-rate dependence.

Journal Article↗
PubMed2001

Mini mutagenicity test: a miniaturized version of the Ames test used in a prescreening assay for point mutagenesis assessment.

The bacterial reverse mutagenicity test on Salmonella typhimurium, known as the Ames test, is widely used by regulatory agencies, academic institutions and chemical companies to assess the mutagenic potential of raw compounds. Several attempts have been made to miniaturise the Ames test in order to fit the industrial constraint of screening more products at the low quantities available. The major limitation of these miniaturised versions of the Ames test lies in the impossibility to work with all the six strains used in the regular Ames test, especially with those showing a low spontaneous revertant frequency. We describe here a mini version of the regulatory Ames test protocol that allows a significant reduction of the quantity of test substance needed (300 mg) but remains applicable to all Salmonella strains used in the regulatory protocol. In a preliminary study, 10 in-house chemical compounds have been evaluated in the Mini Mutagenicity Test (MMT) together with some positive control substances. A first set of historical data obtained in 1999 as well as the predictivity and the sensitivity of the MMT are presented and compared to those of the regular Ames test.

Mutagenicity Tests↗
PubMed2001

Chlorhexidine versus povidone iodine in preventing colonization of continuous epidural catheters in children: a randomized, controlled trial.

BACKGROUND: Chlorhexidine is better than povidone iodine for skin preparation before intravascular device insertion or blood culture collection, but it is not known whether chlorhexidine is superior in reducing colonization of continuous epidural catheters. METHODS: Children requiring an epidural catheter for postoperative analgesia longer than 24 h were randomly assigned to receive skin preparation with an alcoholic solution of 0.5% chlorhexidine or an aqueous solution of 10% povidone iodine before catheter insertion. Using surgical aseptic techniques, catheters were inserted into either the lumbar or the thoracic epidural space based on the preferences of the anesthesia team, on clinical indication, or both. Immediately before epidural catheter removal, their insertion site and hub were qualitatively cultures. After their removal, the catheter tips were quantitatively cultured. Catheters were classified as colonized when their tips yielded 1,000 or more colony-forming units/ml in cultures. RESULTS: Of 100 randomly assigned patients, 96 were evaluable. The clinical characteristics of the patients and the risk factors for infection were similar in the two groups. Catheters were kept in place for a median (range) duration of 50 (range, 21-100) h. Catheters inserted after skin preparation with chlorhexidine were one sixth as likely and less quickly to be colonized as catheters inserted after skin preparation with povidone iodine (1 of 52 catheters [0.9 per 100 catheter days] vs. 5 of 44 catheters [5.6 per 100 catheter days]; relative risk, 0.2 [95% confidence interval, 0.1-1.0]; P = 0.02). Coagulase-negative staphylococci were the only colonizing microorganisms recovered, and the skin surrounding the catheter insertion site was the origin of all the colonizing microorganisms. CONCLUSIONS: Compared with aqueous povidone iodine, the use of alcoholic chlorhexidine for cutaneous antisepsis before epidural catheter insertion reduces the risk of catheter colonization in children.

Adolescent↗
PubMed2001

Three-dimensional multimodal brain warping using the demons algorithm and adaptive intensity corrections.

This paper presents an original method for three-dimensional elastic registration of multimodal images. We propose to make use of a scheme that iterates between correcting for intensity differences between images and performing standard monomodal registration. The core of our contribution resides in providing a method that finds the transformation that maps the intensities of one image to those of another. It makes the assumption that there are at most two functional dependencies between the intensities of structures present in the images to register, and relies on robust estimation techniques to evaluate these functions. We provide results showing successful registration between several imaging modalities involving segmentations, T1 magnetic resonance (MR), T2 MR, proton density (PD) MR and computed tomography (CT). We also argue that our intensity modeling may be more appropriate than mutual information (MI) in the context of evaluating high-dimensional deformations, as it puts more constraints on the parameters to be estimated and, thus, permits a better search of the parameter space.

Algorithms↗
PubMed2000

Autoradiographic localization of [3H]nociceptin binding sites in the rat brain.

The binding sites of nociceptin (also named orphanin FQ), the endogenous ligand of ORL1 (opiate receptor like 1), were localized in rat brain, using an autoradiographic procedure. High levels of binding were observed in the cingulate, retrosplenial, perirhinal, insular and occipital cortex, anterior and posteromedial cortical amygdaloid nuclei, basolateral amygdaloid nucleus, amygdaloid complex, posterior hippocampus, dorsal endopiriform, central medial thalamic, paraventricular, rhomboid thalamic, suprachiasmatic, ventromedial hypothalamic nuclei, mammillary complex, superficial gray layer of the superior colliculus, locus coeruleus, dorsal raphe nucleus. More moderate labelling was observed in the prefrontal, fronto-parietal, temporal, piriform cortex, dentate gyrus, anterior olfactory nucleus, olfactory tubercle, shell of nucleus accumbens, claustrum, lateral septum, laterodorsal thalamic, medial habenular, subthalamic, reuniens thalamic nuclei, subiculum, periaqueductal grey matter and pons. A lower binding site density was observed in the anterior and medial hippocampus, olfactory bulb, caudate putamen, the core of the nucleus accumbens, medial septum, ventrolateral, ventroposterolateral and mediodorsal thalamic nuclei, lateral and medial geniculate nuclei, hypothalamic area, substantia nigra, ventral tegmentum area and interpedoncular nucleus. A moderate and similar labelling was found in the dorsal and ventral horn of the spinal cord. No labelling was apparent in the corpus callosum. Thus, it appears that the ORL1 receptor is particularly abundant in the cerebral cortex, limbic system of the rat brain and some areas involved in pain perception.

Animals↗
PubMed2000

First-order and critical wetting of alkanes on water

Ellipsometry measurements of the wetting behavior of different alkanes on water show a sequence of two wetting transitions: a first-order (discontinuous) transition followed by a critical (continuous) one. We report temperature-induced wetting transitions for different alkanes and a novel pressure-induced wetting transition for an alkane mixture. The experiments enable us to determine the global wetting phase diagram as a function of chain length and temperature which we subsequently calculate theoretically. The two transition lines are found to be approximately parallel, in accordance with basic theoretical arguments.

Journal Article↗
PubMed2000

Dynamics of wetting layer formation

We study the formation and growth of wetting layers in the binary liquid mixture cyclohexane-methanol. By progressively deuterating the methanol we can tune the equilibrium wetting layer thickness. Hysteresis of the transition is observed for large thicknesses and is absent for thinner ones. This can be understood by calculating the activation energy for wetting layer nucleation as a function of the film thickness. We also show that the late-stage growth of the wetting layer after the nucleation process follows a power law in time, in agreement with a diffusion-limited growth mechanism proposed theoretically.

Journal Article↗