Pure phase-locking of beta/gamma oscillation contributes to the N30 frontal component of somatosensory evoked potentials

BACKGROUND: Evoked potentials have been proposed to result from phase-locking of electroencephalographic (EEG) activities within specific frequency bands. However, the respective contribution of phasic activity and phase resetting of ongoing EEG oscillation remains largely debated. We here applied the EEGlab procedure in order to quantify the contribution of electroencephalographic oscillation in the generation of the frontal N30 component of the somatosensory evoked potentials (SEP) triggered by median nerve electrical stimulation at the wrist. Power spectrum and intertrial coherence analysis were performed on EEG recordings in relation to median nerve stimulation. RESULTS: The frontal N30 component was accompanied by a significant phase-locking of beta/gamma oscillation (25-35 Hz) and to a lesser extent of 80 Hz oscillation. After the selection in each subject of the trials for which the power spectrum amplitude remained unchanged, we found pure phase-locking of beta/gamma oscillation (25-35 Hz) peaking about 30 ms after the stimulation. Transition across trials from uniform to normal phase distribution revealed temporal phase reorganization of ongoing 30 Hz EEG oscillations in relation to stimulation. In a proportion of trials, this phase-locking was accompanied by a spectral power increase peaking in the 30 Hz frequency band. This corresponds to the complex situation of 'phase-locking with enhancement' in which the distinction between the contribution of phasic neural event versus EEG phase resetting is hazardous. CONCLUSION: The identification of a pure phase-locking in a large proportion of the SEP trials reinforces the contribution of the oscillatory model for the physiological correlates of the frontal N30. This may imply that ongoing EEG rhythms, such as beta/gamma oscillation, are involved in somatosensory information processing.Comparative StudyJournal ArticleResearch Support, Non-U.S. Gov'tinfo:eu-repo/semantics/publishe

Targeting the Lactate Transporter MCT1 in Endothelial Cells Inhibits Lactate-Induced HIF-1 Activation and Tumor Angiogenesis

Switching to a glycolytic metabolism is a rapid adaptation of tumor cells to hypoxia. Although this metabolic conversion may primarily represent a rescue pathway to meet the bioenergetic and biosynthetic demands of proliferating tumor cells, it also creates a gradient of lactate that mirrors the gradient of oxygen in tumors. More than a metabolic waste, the lactate anion is known to participate to cancer aggressiveness, in part through activation of the hypoxia-inducible factor-1 (HIF-1) pathway in tumor cells. Whether lactate may also directly favor HIF-1 activation in endothelial cells (ECs) thereby offering a new druggable option to block angiogenesis is however an unanswered question. In this study, we therefore focused on the role in ECs of monocarboxylate transporter 1 (MCT1) that we previously identified to be the main facilitator of lactate uptake in cancer cells. We found that blockade of lactate influx into ECs led to inhibition of HIF-1-dependent angiogenesis. Our demonstration is based on the unprecedented characterization of lactate-induced HIF-1 activation in normoxic ECs and the consecutive increase in vascular endothelial growth factor receptor 2 (VEGFR2) and basic fibroblast growth factor (bFGF) expression. Furthermore, using a variety of functional assays including endothelial cell migration and tubulogenesis together with in vivo imaging of tumor angiogenesis through intravital microscopy and immunohistochemistry, we documented that MCT1 blockers could act as bona fide HIF-1 inhibitors leading to anti-angiogenic effects. Together with the previous demonstration of MCT1 being a key regulator of lactate exchange between tumor cells, the current study identifies MCT1 inhibition as a therapeutic modality combining antimetabolic and anti-angiogenic activities

Is the astronomical forcing a reliable and unique pacemaker for climate? A conceptual model study

There is evidence that ice age cycles are paced by astronomical forcing, suggesting some kind of synchronisation phenomenon. Here, we identify the type of such synchronisation and explore systematically its uniqueness and robustness using a simple paleoclimate model akin to the van der Pol relaxation oscillator and dynamical system theory. As the insolation is quite a complex quasiperiodic signal involving different frequencies, the traditional concepts used to define synchronisation to periodic forcing are no longer applicable. Instead, we explore a different concept of generalised synchronisation in terms of (coexisting) synchronised solutions for the forced system, their basins of attraction and instabilities. We propose a clustering technique to compute the number of synchronised solutions, each of which corresponds to a different paleoclimate history. In this way, we uncover multistable synchronisation (reminiscent of phase- or frequency-locking to individual periodic components of astronomical forcing) at low forcing strength, and monostable or unique synchronisation at stronger forcing. In the multistable regime, different initial conditions may lead to different paleoclimate histories. To study their robustness, we analyse Lyapunov exponents that quantify the rate of convergence towards each synchronised solution (local stability), and basins of attraction that indicate critical levels of external perturbations (global stability). We find that even though synchronised solutions are stable on a long term, there exist short episodes of desynchronisation where nearby climate trajectories diverge temporarily (for about 50 kyr). (...)Comment: 22 pages, 18 figure

Analytical theory of a lunar artificial satellite with third body perturbations

We present here the first numerical results of our analytical theory of an artificial satellite of the Moon. The perturbation method used is the Lie Transform for averaging the Hamiltonian of the problem, in canonical variables: short-period terms (linked to l, the mean anomaly) are eliminated first. We achieved a quite complete averaged model with the main four perturbations, which are: the synchronous rotation of the Moon (rate n_m), the oblateness J2 of the Moon, the triaxiality C_22 of the Moon ( C22≈J2/10 ) and the major third body effect of the Earth (ELP2000). The solution is developed in powers of small factors linked to these perturbations up to second-order; the initial perturbations being sorted ( is first-order while the others are second-order). The results are obtained in a closed form, without any series developments in eccentricity nor inclination, so the solution apply for a wide range of values. Numerical integrations are performed in order to validate our analytical theory. The effect of each perturbation is presented progressively and separately as far as possible, in order to achieve a better understanding of the underlying mechanisms. We also highlight the important fact that it is necessary to adapt the initial conditions from averaged to osculating values in order to validate our averaged model dedicated to mission analysis purposes

Théorie analytique fermée d'un satellite artificiel lunaire pour l'analyse de mission

Le but de ce travail est de développer un outil d'aide à l'analyse de mission pour un satellite artificiel autour de la Lune. Nous développons tout d'abord une théorie analytique qui décrit suffisamment bien la dynamique du satellite lunaire : nous considérons les quatre perturbations majeures de natures différentes qui l'influencent, ainsi que leurs différents couplages. Les résultats sont obtenus sous forme fermée, sans aucun développement en série de l'excentricité ni de l'inclinaison de l'orbite du satellite : la solution s'applique donc à une large gamme de valeurs. Nous utilisons la méthode des Transformées de Lie pour moyenniser deux fois l'Hamiltonien du problème, dans des variables canoniques, ce qui permet d'intégrer des orbites avec un temps de calcul réduit d'un facteur environ 200 000. Grâce à cela, nous produisons des cartes inédites d'espaces de phase (a,i) qui permettent de sélectionner les paramètres orbitaux selon les besoins de la mission lunaire. De nombreuses vérifications analytiques par rapport à la littérature ont été réalisées, et se sont avérées concluantes; la qualité des deux moyennisations a également été vérifiée. Le logiciel développé est souple et permet un traitement automatisé; les intégrations sont automatiquement vérifiées. Nous avons aussi apporté quelques améliorations significatives au manipulateur algébrique des FUNDP, comme l'ajout de fractions symboliques. Par ailleurs, nous résolvons le problème zonal complet du satellite artificiel, étudions l'effet de C22 sur l'inclinaison critique ainsi que l'effet de la Terre sur les durées de vie orbitales limitées de certains satellites lunaires. The aim of this work is to develop a tool helpful to mission analysis of a lunar artificial satellite. We first develop an analytical theory which sufficiently well describes the dynamics of the lunar satellite : we consider the four main perturbations of various kind which influence it, together with their several coupling. The results are obtained in closed form, without any series expansion in eccentricity nor inclination of the orbit of the satellite : so the solution applies for a wide range of values. We use the Lie Transform method for averaging twice the Hamiltonian of the problem, in canonical variables, which allows to integrate orbits with a CPU time reduced by a factor of about 200 000. Thanks to that, we produce unpublished (a,i) phase space maps from which the orbital parameters can be selected on the basis of the needs of the lunar mission. Many conclusive analytical checks with the literature have been performed, and both averaging processes have been checked. The software developed is flexible and allows an automated treatment; the integrations are automatically checked. We also improved significantly the algebraic manipulator of the FUNDP, like the inclusion of symbolic fractions. Moreover, we solve the complete zonal problem of the artificial satellite, we study the effect of C22 on the critical inclination, and also the effect of the Earth on the limited orbital lifetimes of some lunar satellites.(DOCSC00)--FUNDP, 200

L'externalisation des missions de La Défense belge

L’objectif de cet article est d’analyser juridiquement le phénomène d’externalisation des missions de Défense, tel qu’il se déploie en Belgique, ainsi que les nombreux écueils qu’il cause en droit. Pour mener à bien cette analyse, nous procéderons en deux temps. Tout d’abord, nous examinerons la manière dont l’externalisation a réussi à s’imposer (chapitre I). Ensuite, nous tenterons de déterminer les conditions juridiques à la mise en œuvre de l’externalisation, sur la base des cadres constitutionnel, législatif et réglementaire applicables à l’organisation de la Défense ainsi que ses finalités (chapitre II)