Transverse Magnetic Anisotropy in Mn12-acetate: Direct Determination by Inelastic Neutron Scattering

A high resolution inelastic neutron scattering (INS) study of fully deuterated Mn$_{12}$-acetate provides the most accurate spin Hamiltonian parameters for this prototype single molecule magnet so far. The Mn$_{12}$-clusters deviate from axial symmetry, a non-zero rhombic term in the model Hamiltonian leading to excellent agreement with observed positions and intensities of the INS peaks. The following parameter set provides the best agreement with the experimental data: $D=-0.0570(1)$ meV, $B_{4}^0=-2.78(7)\cdot 10^{-6}$ meV, $B_{4}^4=-3.2(6)\cdot 10^{-6}$ meV and $\mid$\textit{E}$\mid =6.8(15)\cdot 10^{-4}$ meV. Crystal dislocations are not the likely cause of the symmetry lowering. Rather, this study lends strong support to a recently proposed model, which is based on the presence of several molecular isomers with distinct spin Hamiltonian parameters.Comment: 4 pages, 4 figure

Pressure Dependence of the Magnetic Anisotropy in the "Single-Molecule Magnet" [Mn4O3Br(OAc)3(dbm)3]

The anisotropy splitting in the ground state of the single-molecule magnet [Mn4O3Br(OAc)3(dbm)3] is studied by inelastic neutron scattering as a function of hydrostatic pressure. This allows a tuning of the anisotropy and thus the energy barrier for slow magnetisation relaxation at low temperatures. The value of the negative axial anisotropy parameter $D_{\rm cluster}$ changes from -0.0627(1) meV at ambient to -0.0603(3) meV at 12 kbar pressure, and in the same pressure range the height of the energy barrier between up and down spins is reduced from 1.260(5) meV to 1.213(9) meV. Since the $\rm Mn-Br$ bond is significantly softer and thus more compressible than the $\rm Mn-O$ bonds, pressure induces a tilt of the single ion Mn$^{3+}$ anisotropy axes, resulting in the net reduction of the axial cluster anisotropy.Comment: 4 pages, 3 figure

Narcolepsy-Cataplexy Today

peer reviewedDiagnostic criteria and pathophysiology of narcolepsy- cataplexy have evolved considerably over the last 10 years. The main cause, already mentioned in a previous paper, in the Revue Médicale de Liège, in 2002, is based, in human beings, on a destruction of specific cells located in the lateral and posterior part of the hypothalamus (the perifornical nuclei, containing some 70,000 neurons), producing peptides which stimulate the central nervous system; they are called hypocretins or orexins. The role of autoimmunity in their disappearance becomes more evident. The treatment is simplified but remains symptomatic. It is mainly based on Sodium Oxybate or Gamma-Hydroxybutyrate, syrup, prescribed for the night. The authors report on their own experience in this regard and on future therapeutics more targeted towards the cause of the disease

Nestin-positive mesenchymal stem cells favour the astroglial lineage in neural progenitors and stem cells by releasing active BMP4

BACKGROUND: Spontaneous repair is limited after CNS injury or degeneration because neurogenesis and axonal regrowth rarely occur in the adult brain. As a result, cell transplantation has raised much interest as potential treatment for patients with CNS lesions. Several types of cells have been considered as candidates for such cell transplantation and replacement therapies. Foetal brain tissue has already been shown to have significant effects in patients with Parkinson's disease. Clinical use of the foetal brain tissue is, however, limited by ethical and technical problems as it requires high numbers of grafted foetal cells and immunosuppression. Alternatively, several reports suggested that mesenchymal stem cells, isolated from adult bone marrow, are multipotent cells and could be used in autograft approach for replacement therapies. RESULTS: In this study, we addressed the question of the possible influence of mesenchymal stem cells on neural stem cell fate. We have previously reported that adult rat mesenchymal stem cells are able to express nestin in defined culture conditions (in the absence of serum and after 25 cell population doublings) and we report here that nestin-positive (but not nestin-negative) mesenchymal stem cells are able to favour the astroglial lineage in neural progenitors and stem cells cultivated from embryonic striatum. The increase of the number of GFAP-positive cells is associated with a significant decrease of the number of Tuj1- and O4-positive cells. Using quantitative RT-PCR, we demonstrate that mesenchymal stem cells express LIF, CNTF, BMP2 and BMP4 mRNAs, four cytokines known to play a role in astroglial fate decision. In this model, BMP4 is responsible for the astroglial stimulation and oligodendroglial inhibition, as 1) this cytokine is present in a biologically-active form only in nestin-positive mesenchymal stem cells conditioned medium and 2) anti-BMP4 antibodies inhibit the nestin-positive mesenchymal stem cells conditioned medium inducing effect on astrogliogenesis. CONCLUSIONS: When thinking carefully about mesenchymal stem cells as candidates for cellular therapy in neurological diseases, their effects on resident neural cell fate have to be considered

Dynamic Phase Transitions in Cell Spreading

We monitored isotropic spreading of mouse embryonic fibroblasts on fibronectin-coated substrates. Cell adhesion area versus time was measured via total internal reflection fluorescence microscopy. Spreading proceeds in well-defined phases. We found a power-law area growth with distinct exponents a_i in three sequential phases, which we denote basal (a_1=0.4+-0.2), continous (a_2=1.6+-0.9) and contractile (a_3=0.3+-0.2) spreading. High resolution differential interference contrast microscopy was used to characterize local membrane dynamics at the spreading front. Fourier power spectra of membrane velocity reveal the sudden development of periodic membrane retractions at the transition from continous to contractile spreading. We propose that the classification of cell spreading into phases with distinct functional characteristics and protein activity patterns serves as a paradigm for a general program of a phase classification of cellular phenotype. Biological variability is drastically reduced when only the corresponding phases are used for comparison across species/different cell lines.Comment: 4 pages, 5 figure

Periodic Lamellipodial Contractions Correlate with Rearward Actin Waves

AbstractCellular lamellipodia bind to the matrix and probe its rigidity through forces generated by rearward F-actin transport. Cells respond to matrix rigidity by moving toward more rigid matrices using an unknown mechanism. In spreading and migrating cells we find local periodic contractions of lamellipodia that depend on matrix rigidity, fibronectin binding and myosin light chain kinase (MLCK). These contractions leave periodic rows of matrix bound β3-integrin and paxillin while generating waves of rearward moving actin bound α-actinin and MLCK. The period between contractions corresponds to the time for F-actin to move across the lamellipodia. Shortening lamellipodial width by activating cofilin decreased this period proportionally. Increasing lamellipodial width by Rac signaling activation increased this period. We propose that an actin bound, contraction-activated signaling complex is transported locally from the tip to the base of the lamellipodium, activating the next contraction/extension cycle

Butterfly Hysteresis and Slow Relaxation of the Magnetization in (Et4N)3Fe2F9: Manifestations of a Single-Molecule Magnet

(Et4N)3Fe2F9 exhibits a butterfly--shaped hysteresis below 5 K when the magnetic field is parallel to the threefold axis, in accordance with a very slow magnetization relaxation in the timescale of minutes. This is attributed to an energy barrier Delta=2.40 K resulting from the S=5 dimer ground state of [Fe2F9]^{3-} and a negative axial anisotropy. The relaxation partly occurs via thermally assisted quantum tunneling. These features of a single-molecule magnet are observable at temperatures comparable to the barrier height, due to an extremely inefficient energy exchange between the spin system and the phonons. The butterfly shape of the hysteresis arises from a phonon avalanche effect.Comment: 18 pages, 5 eps figures, latex (elsart

Caseous calcification of the mitral annulus: an uncommon cause of acute mitral regurgitation.

peer reviewe

Energy and Protein Intake After Return Home in Colorectal Surgery Patients With an Enhanced Recovery Program: A Prospective Observational Study.

[en] BACKGROUND: In patients scheduled for colorectal surgery with an enhanced recovery program (ERP), feeding after returning home has been insufficiently investigated. The aim of this study was to measure energy and protein intake during the first month at home. METHODS: Seventy adult patients scheduled for colorectal surgery with ERP were included. Calorie and protein intakes were calculated, and body weight was measured preoperatively and 3, 7, 15, and 30 days after discharge home. Data are mean ± SD or median (interquartile range). RESULTS: Patient characteristics were age 60.0 ± 15.0 years, BMI = 25.9 ± 5.5 kg/m2 , and colon/rectum of 56/14. The duration of hospitalization was 3 (2-5) days. Calorie and protein intakes (21.9 [17.7-28.6] kilocalorie per kilogram of ideal body weight [kcal/kg IBW] and 0.81 [0.61-1.14] g/kg IBW) were significantly reduced (P < .01) by 15% on day 3, compared with preoperative values, and then increased gradually to reach preoperative values after 1 month. Almost 50% of the patients failed to reach the calorie intake target of 25 kcal/kg IBW, and almost no patient reached the protein intake target of 1.5 g/kg IBW 30 days after discharge home. Weight loss after 30 days at home remained at -1.8 ± 2.7 kg. CONCLUSIONS: Colorectal surgery, even in an ERP, is associated with energy and protein intake below the targets recommended for the rehabilitation phase and results in weight loss. Whether nutrition counseling and prolonged administration of protein-enriched oral supplements could accelerate weight gain needs to be explored

First report in the Liege province (Belgium) of a concomitant aortic and mitral valve surgery via a minimally invasive right latero-thoracic approach.

editorial reviewedCompared to median sternotomy, the potential benefits of minimally invasive single aortic or mitral valve surgery include reduction of blood loss, lower morbidity, and shorter intensive care unit and hospital length of stay. However, there are few reports regarding concomitant aortic and mitral valves minimally invasive surgery via mini-thoracotomy. To the authors knowledge, this is the first report in the Liege area, of a successful minimally invasive right latero-thoracic approach for aortic and mitral valve surgery in a 78-year old woman who presented severe and symptomatic aortic stenosis and mitral insufficiency. In addition to the description of the surgical approach, the authors will summarize the current literature on this approach, as well as the clinical evolution of the patient.La chirurgie valvulaire isolée, aortique ou mitrale par voie mini-invasive offre de nombreux avantages par rapport à la sternotomie médiane en termes de réduction des pertes sanguines, de diminution de la morbidité et de réduction des durées de séjour aux soins intensifs et hospitalier global. Toutefois, il existe très peu de données dans la littérature sur la chirurgie combinée mitrale et aortique par mini-thoracotomie. à notre connaissance, nous présentons le premier cas de double chirurgie mitrale et aortique réalisée avec succès par abord latéral thoracique droit dans la région liégeoise chez une patiente de 78 ans qui présentait une sténose aortique et une insuffisance mitrale sévères et symptomatiques. En plus d’une description de notre technique chirurgicale, nous résumerons les grandes séries cliniques publiées dans la littérature sur le sujet, ainsi que l’évolution clinique de notre patiente