Dual function of thalamic low-vigilance state oscillations: Rhythm-regulation and plasticity

During inattentive wakefulness and non-rapid eye movement (NREM) sleep, the neocortex and thalamus cooperatively engage in rhythmic activities that are exquisitely reflected in the electroencephalogram as distinctive rhythms spanning a range of frequencies from <1 Hz slow waves to 13 Hz alpha waves. In the thalamus, these diverse activities emerge through the interaction of cell-intrinsic mechanisms and local and long-range synaptic inputs. One crucial feature, however, unifies thalamic oscillations of different frequencies: repetitive burst firing driven by voltage-dependent Ca(2+) spikes. Recent evidence reveals that thalamic Ca(2+) spikes are inextricably linked to global somatodendritic Ca(2+) transients and are essential for several forms of thalamic plasticity. Thus, we propose herein that alongside their rhythm-regulation function, thalamic oscillations of low-vigilance states have a plasticity function that, through modifications of synaptic strength and cellular excitability in local neuronal assemblies, can shape ongoing oscillations during inattention and NREM sleep and may potentially reconfigure thalamic networks for faithful information processing during attentive wakefulness

Decoherence-free molecular spin qubits with chemically designed frequencies

Resumen del trabajo presentado a la XII Reunión del grupo de física de la materia condensada de la RSEF (GEFES), celebrada en Salamanca del 1 al 3 de febrero de 2023.We report a sizeable quantum tunnelling splitting for the mononuclear Ni(II) molecular complexes [Ni(Me6tren)Cl](ClO4) (1) and [Ni(2-Imdipa)(NCS)](NCS) (2). With their S = 1 ground state and strong anisotropy, these molecules provide a realization of the simplest non-Kramers system (integer spin). The “clock transition” between levels associated with superpositions of mS = ±1 spin states, with its characteristic non-linear magnetic field dependence, has been directly monitored by heat capacity experiments. The comparison of complex 1 with a Co derivative (S = 3/2), for which tunnelling is forbidden, shows that the clock transition leads to an effective suppression of intermolecular spin–spin interactions. We also show that the splitting admits a chemical tuning via the modification of the ligand shell that determines the magnetic anisotropy. In particular, the weaker magnetic anisotropy of complex 2 makes its qubit frequency compatible with superconducting microwave circuits, and has allowed its direct detection by on-chip broadband transmission experiments.Peer reviewe

Generation of the Brucella melitensis ORFeome version 1.1.

The bacteria of the Brucella genus are responsible for a worldwide zoonosis called brucellosis. They belong to the alpha-proteobacteria group, as many other bacteria that live in close association with a eukaryotic host. Importantly, the Brucellae are mainly intracellular pathogens, and the molecular mechanisms of their virulence are still poorly understood. Using the complete genome sequence of Brucella melitensis, we generated a database of protein-coding open reading frames (ORFs) and constructed an ORFeome library of 3091 Gateway Entry clones, each containing a defined ORF. This first version of the Brucella ORFeome (v1.1) provides the coding sequences in a user-friendly format amenable to high-throughput functional genomic and proteomic experiments, as the ORFs are conveniently transferable from the Entry clones to various Expression vectors by recombinational cloning. The cloning of the Brucella ORFeome v1.1 should help to provide a better understanding of the molecular mechanisms of virulence, including the identification of bacterial protein-protein interactions, but also interactions between bacterial effectors and their host's targets

Rythmes du sommeil et plasticité intrathalamique (caractérisation d'une dépression à long terme des synapses GABAergiques du thalamus au cours des oscillations delta du sommeil profond)

Au sein du thalamus, les neurones GABAergiques du Noyau Réticulé Thalamique (NRT) participent au traitement de l information lors de l éveil et jouent un rôle essentiel dans la genèse des rythmes du sommeil. Au cours des oscillations delta du sommeil à ondes lentes leur activité et celle des neurones thalamocorticaux (TC) sont caractérisées par des décharges répétées et synchrones de bouffées de potentiels d action, sous-tendues par l activation massive du canal calcique de type T. Il est vraisemblable que le rôle de ces activités ne se limite pas à une déconnexion sensorielle du cortex. Mes travaux de doctorat ont porté sur leur possible implication dans une plasticité des synapses NRT -> TC. Cette étude a été menée sur des préparations in vitro de thalamus de rats âgés de 12 à 16 jours. En mimant les activités ayant lieu au cours des oscillations delta, j ai mis en évidence une dépression à long terme (LTD) des courants GABAergiques enregistrés dans les neurones TC suite à la stimulation des fibres du NRT. L induction de cette plasticité nécessite l activation concomitante des récepteurs métabotropiques GABAB post-synaptiques et des canaux calciques de type T. Cette démonstration a été rendue possible par l utilisation du premier bloquant spécifique des canaux calciques de type T, le TTA-P2, dont nous avons préalablement réalisé la caractérisation fonctionnelle. Cette LTD, un modèle rare de plasticité homosynaptique des synapses inhibitrices, et un des premiers exemples de l implication des canaux T dans la régulation des activités synaptiques, pourrait constituer un mécanisme de remodelage synaptique prenant place lors du sommeilPARIS-BIUP (751062107) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Constraining Earthquake Source Processes Through Physics-Based Modeling

Determining principles and conditions governing motion along faults is crucial for assessing how earthquake ruptures start and how large they may ultimately become. This thesis aims to shed light on the physics governing earthquake source processes by (i) developing physics-based numerical models that combine geological observations and laboratory insight with theoretical developments, and (ii) using these models to examine how different physical mechanisms and conditions are reflected in a range of geophysical observations taken together, from heat-flow constraints and seismologically determined properties of earthquakes to geodetic inferences and earthquake frequency-magnitude statistics. We examine the behavior and observable characteristics of numerically simulated sequences of earthquakes and aseismic slip in fault models designed to reproduce well-known features of mature faults that produce large destructive earthquakes. In part, the models are consistent with the inferred low-stress, low-heat operation of mature faults, which host large earthquakes at much lower levels of stress than their expected static strength. We explore two potential explanations for such behavior, one that faults are indeed quasi-statically strong but experience dramatic weakening during earthquakes, or that faults are persistently weak, e.g., due to fluid overpressure. We find that the two classes of fault models can, in principle, be distinguished based on the amount of seismic energy radiated from earthquake ruptures. Dynamic ruptures in the form of self-healing pulses, which occur on quasi-statically strong but dynamically weak faults, result in much larger radiated energy than inferred teleseismically for megathrust events, whereas crack-like ruptures on persistently weak faults are consistent with the seismological observations. The larger radiated energy of self-healing pulses is similar to limited regional inferences for crustal strike-slip faults. Our results suggest that re-evaluating estimates of radiated energy and static stress drop would provide substantial insight into the driving physics of large earthquakes and the absolute stress conditions on faults, with potential differences between tectonic settings. The results also have significant implications for seismic hazard, since our modeling shows that fault models that experience efficient dynamic weakening during ruptures tend to predominantly produce large earthquakes, at the expense of smaller earthquakes. Such behavior is consistent with some mature fault segments, such as several segments of the San Andreas Fault in California that have hosted large earthquakes but are currently nearly seismically quiescent. These considerations can provide physical basis for improving earthquake early warning systems. If mature faults in California are indeed governed by enhanced dynamic weakening, then our results suggest that the likelihood of an earthquake on these faults becoming substantially larger is much higher than typical expectations based on Gutenberg-Richter statistics. By considering average fault stress before simulated earthquake ruptures, we find that critical stress conditions for earthquake occurrence depend on the size and style of motion (e.g. the degree of slip acceleration at the rupture front) during individual ruptures. In particular, the stress conditions required to propagate large earthquake ruptures can be considerably lower than those required for rupture nucleation, and standard notions of quasi-static fault strength based on laboratory studies. Our results demonstrate that the critical stress for earthquake occurrence is not governed by a simple condition such as a certain level of Coloumb stress, as commonly used in studies of stress interactions among faults and earthquake aftershocks patterns. More robust criteria for critical stress conditions would depend on the strength evolution during dynamic rupture and can be explored in numerical simulations. Finally, evaluating the predictive power of numerical earthquake models for future hazards is a topic of great importance for physics-based seismic hazard assessment. Towards that end, we investigate the sensitivity of outcomes from numerical simulations of sequences of earthquakes and aseismic slip, including the long-term interaction of fault segments, to choices in numerical discretization and treatment of inertial, wave-mediated effects. In particular, we find that the rate of earthquake ruptures that manage to jump between two fault segments, a parameter routinely used in seismic hazard studies, is highly sensitive to numerical and physical modeling choices. These results suggest the need for developing different parameterization of seismic hazard than currently used, a task for which numerical modeling is well-suited.</p

Dynamics of Intrinsic Dendritic Calcium Signaling during Tonic Firing of Thalamic Reticular Neurons

International audienceThe GABAergic neurons of the nucleus reticularis thalami that control the communication between thalamus and cortex are interconnected not only through axo-dendritic synapses but also through gap junctions and dendro-dendritic synapses. It is still unknown whether these dendritic communication processes may be triggered both by the tonic and the T-type Ca 2+ channel-dependent high frequency burst firing of action potentials displayed by nucleus reticularis neurons during wakefulness and sleep, respectively. Indeed, while it is known that activation of T-type Ca 2+ channels actively propagates throughout the dendritic tree, it is still unclear whether tonic action potential firing can also invade the dendritic arborization. Here, using two-photon microscopy, we demonstrated that dendritic Ca 2+ responses following somatically evoked action potentials that mimic wake-related tonic firing are detected throughout the dendritic arborization. Calcium influx temporally summates to produce dendritic Ca 2+ accumulations that are linearly related to the duration of the action potential trains. Increasing the firing frequency facilitates Ca 2+ influx in the proximal but not in the distal dendritic compartments suggesting that the dendritic arborization acts as a low-pass filter in respect to the back-propagating action potentials. In the more distal compartment of the dendritic tree, T-type Ca 2+ channels play a crucial role in the action potential triggered Ca 2+ influx suggesting that this Ca 2+ influx may be controlled by slight changes in the local dendritic membrane potential that determine the T-type channels' availability. We conclude that by mediating Ca 2+ dynamic in the whole dendritic arborization, both tonic and burst firing of the nucleus reticularis thalami neurons might control their dendro-dendritic and electrical communications

Un nouvel éclairage sur l’excitabilité thalamocorticale dans l’épilepsie-absence

International audienc

Appendix

This document contains all the supplementary informations

Data from: How ecology and landscape dynamics shape phylogenetic trees

Whether biotic or abiotic factors are the dominant drivers of clade diversification is a long-standing question in evolutionary biology. The ubiquitous patterns of phylogenetic imbalance and branching slowdown have been taken as supporting the role of ecological niche filling and spatial heterogeneity in ecological features, and thus of biotic processes, in diversification. However, a proper theoretical assessment of the relative roles of biotic and abiotic factors in macroevolution requires models that integrate both types of factors, and such models have been lacking. In this study, we use an individual-based model to investigate the temporal patterns of diversification driven by ecological speciation in a stochastically fluctuating geographic landscape. The model generates phylogenies whose shape evolves as the clade ages. Stabilization of tree shape often occurs after ecological saturation, revealing species turnover caused by competition and demographic stochasticity. In the initial phase of diversification (allopatric radiation into an empty landscape), trees tend to be unbalanced and branching slows down. As diversification proceeds further due to landscape dynamics, balance and branching tempo may increase and become positive. Three main conclusions follow. First, the phylogenies of ecologically saturated clades do not always exhibit branching slowdown. Branching slowdown requires that competition be wide or heterogeneous across the landscape, or that the characteristics of landscape dynamics vary geographically. Conversely, branching acceleration is predicted under narrow competition or frequent local catastrophes. Second, ecological heterogeneity does not necessarily cause phylogenies to be unbalanced—short time in geographical isolation or frequent local catastrophes may lead to balanced trees despite spatial heterogeneity. Conversely, unbalanced trees can emerge without spatial heterogeneity, notably if competition is wide. Third, short isolation time causes a radically different and quite robust pattern of phylogenies that are balanced and yet exhibit branching slowdown. In conclusion, biotic factors have a strong and diverse influence on the shape of phylogenies of ecologically saturating clades and create the evolutionary template in which branching slowdown and tree imbalance may occur. However, the contingency of landscape dynamics and resource distribution can cause wide variation in branching tempo and tree balance. Finally, considerable variation in tree shape among simulation replicates calls for caution when interpreting variation in the shape of real phylogenies