Rock art taphonomy in Lesser Antilles: study of wall weathering and engravings preservation in two preColumbian caves on Marie-Galante Island.

International audienceThe islands of Guadeloupe deliver some caves and rock shelters occupied in precolumbian times, including rare engraved caves whose age of occupation remains unclear and some burial caves used in the Late Ceramic Age. Question arises whether the absence of engravings in these latter sites reflects an archaeological reality or, in contrast, is linked to poor conditions for the preservation of cave art. Here we present a study carried out to determine the conditions of conservation of precolumbian rock art. This study was conducted in two sites of Marie-Galante, the cave Blanchard, without obvious engravings but with a funeral dimension, and the Morne Rita cave, rich in engravings. This work includes a series of hygrothermal measurements, the determination of authigenic minerals, and the study of both cave sediments.Two types of cavities can be opposed in terms of micro-climate pattern and transformation of the walls. Caves acting as trap cold air, like Morne Rita cave, have a high humidity which causes a light corrosion of the rock and mineral crust formation. Engravings modification proceeds mainly by their recovery by mineralization and the petroglyphs are relatively well preserved. In contrast, sites acting as warm air traps, like Blanchard cave, are characterized by an unstable air mass that promotes the entrance of drying air rich in salt-sprays, especially when sites are not far from the coast, which is the most frequent case in the Lesser Antilles. As a result, rock is exposed to salt weathering, and walls retreat caused by this phenomenon has been estimated in the order of a millimeter per century. This rate is sufficient to result in the disappearance of engravings that could exist in such sites. The walls of the Blanchard cave were examined in detail to find any traces of weathered petroglyphs, and we present here a wall morphology that could be explained by this hypothesis.This study highlights the control of site microclimatic pattern on the preservation of petroglyphs and concludes, therefore, on the existence of a bias in the distribution of rock caves in the Lesser Antilles where decorated caves were probably many more that which is currently found. The implications of this result on precolumbian cave occupation models are finally discussed

A calcium-based plasticity model for predicting long-term potentiation and depression in the neocortex

Pyramidal cells (PCs) form the backbone of the layered structure of the neocortex, and plasticity of their synapses is thought to underlie learning in the brain. However, such long-term synaptic changes have been experimentally characterized between only a few types of PCs, posing a significant barrier for studying neocortical learning mechanisms. Here we introduce a model of synaptic plasticity based on data-constrained postsynaptic calcium dynamics, and show in a neocortical microcircuit model that a single parameter set is sufficient to unify the available experimental findings on long-term potentiation (LTP) and long-term depression (LTD) of PC connections. In particular, we find that the diverse plasticity outcomes across the different PC types can be explained by cell-type-specific synaptic physiology, cell morphology and innervation patterns, without requiring type-specific plasticity. Generalizing the model to in vivo extracellular calcium concentrations, we predict qualitatively different plasticity dynamics from those observed in vitro. This work provides a first comprehensive null model for LTP/LTD between neocortical PC types in vivo, and an open framework for further developing models of cortical synaptic plasticity.We thank Michael Hines for helping with synapse model implementation in NEURON; Mariana Vargas-Caballero for sharing NMDAR data; Veronica Egger for sharing in vitro data and for clarifications on the analysis methods; Jesper Sjöström for sharing in vitro data, helpful discussions, and feedback on the manuscript; Ralf Schneggenburger for helpful discussions and clarifications on the NMDAR calcium current model; Fabien Delalondre for helpful discussions; Francesco Casalegno and Taylor Newton for helpful discussion on model fitting; Daniel Keller for helpful discussions on the biophysics of synaptic plasticity; Natali Barros-Zulaica for helpful discussions on MVR modeling and generalization; Srikanth Ramaswamy, Michael Reimann and Max Nolte for feedback on the manuscript; Wulfram Gerstner and Guillaume Bellec for helpful discussions on synaptic plasticity modeling. This study was supported by funding to the Blue Brain Project, a research center of the École polytechnique fédérale de Lausanne, from the Swiss government’s ETH Board of the Swiss Federal Institutes of Technology. E.B.M. received additional support from the CHU Sainte-Justine Research Center (CHUSJRC), the Institute for Data Valorization (IVADO), Fonds de Recherche du Québec–Santé (FRQS), the Canada CIFAR AI Chairs Program, the Quebec Institute for Artificial Intelligence (Mila), and Google. R.B.P. and J.DF. received support from the Spanish “Ministerio de Ciencia e Innovación” (grant PGC2018-094307-B-I00). M.D. and I.S. were supported by a grant from the ETH domain for the Blue Brain Project, the Gatsby Charitable Foundation, and the Drahi Family Foundation

Coupled Cu and Mn charge and orbital orders in YBa₂Cu₃O₇/Nd 0.65 (Ca 1-y Sr y ) 0.35 MnO₃ multilayers

The observation of a charge density wave in the underdoped cuprate high Tc superconductors (Cu-CDW) raised a debate about its relationship with superconductivity. In bulk YBa2Cu3O7−δ the Cu-CDW is incipient and mainly pinned by defects. Nevertheless, a large magnetic field can induce a true long-range Cu- CDW order as it suppresses superconductivity. An enhanced Cu-CDW order was also observed in YBa2Cu3O7/La2/3Ca1/3MnO3 multilayers. Here, we show that the magnitude of the Cu-CDW in YBa2Cu3O7−δ / Nd0.65(Ca1-ySry)0.35MnO3 multilayers can be varied by adjusting the strength of the manganite charge and orbital order via the Sr content (tolerance factor). Furthermore, we resolve the reconstruction of the crystal field levels of the interfacial Cu ions that are also affected by the manganite charge and orbital order. This tuneable interfacial coupling and Cu- CDW in YBa2Cu3O7−δ can be used for studying the relationship between the Cu- CDW and superconductivity and, possibly, for inducing new intertwined quantum states

The proteasome inhibitor MG-132 sensitizes PC-3 prostate cancer cells to ionizing radiation by a DNA-PK-independent mechanism

BACKGROUND: By modulating the expression levels of specific signal transduction molecules, the 26S proteasome plays a central role in determining cell cycle progression or arrest and cell survival or death in response to stress stimuli, including ionizing radiation. Inhibition of proteasome function by specific drugs results in cell cycle arrest, apoptosis and radiosensitization of many cancer cell lines. This study investigates whether there is also a concomitant increase in cellular radiosensitivity if proteasome inhibition occurs only transiently before radiation. Further, since proteasome inhibition has been shown to activate caspase-3, which is involved in apoptosis, and caspase-3 can cleave DNA-PKcs, which is involved in DNA-double strand repair, the hypothesis was tested that caspase-3 activation was essential for both apoptosis and radiosensitization following proteasome inhibition. METHODS: Prostate carcinoma PC-3 cells were treated with the reversible proteasome inhibitor MG-132. Cell cycle distribution, apoptosis, caspase-3 activity, DNA-PKcs protein levels and DNA-PK activity were monitored. Radiosensitivity was assessed using a clonogenic assay. RESULTS: Inhibition of proteasome function caused cell cycle arrest and apoptosis but this did not involve early activation of caspase-3. Short-time inhibition of proteasome function also caused radiosensitization but this did not involve a decrease in DNA-PKcs protein levels or DNA-PK activity. CONCLUSION: We conclude that caspase-dependent cleavage of DNA-PKcs during apoptosis does not contribute to the radiosensitizing effects of MG-132