A simple novel approach for detecting blood–brain barrier permeability using GPCR internalization
Csaba, Z., T. Vitalis, C. Charriaut-Marlangue, I. Margaill, B. Coqueran, P. L. Leger, I. Parente, A. Jacquens, L. Titomanlio, C. Constans, C. Demene, M. D. Santin, S. Lehericy, N. Perrière, F. Glacial, S. Auvin, M. Tanter, J. F. Ghersi-Egea, H. Adle-Biassette, J. F. Aubry, P. Gressens, and P. Dournaud
Neuropathology and Applied Neurobiology 47, no. 2, 297-315 (2021)
Résumé: © 2020 British Neuropathological Society Aims: Impairment of blood–brain barrier (BBB) is involved in numerous neurological diseases from developmental to aging stages. Reliable imaging of increased BBB permeability is therefore crucial for basic research and preclinical studies. Today, the analysis of extravasation of exogenous dyes is the principal method to study BBB leakage. However, these procedures are challenging to apply in pups and embryos and may appear difficult to interpret. Here we introduce a novel approach based on agonist-induced internalization of a neuronal G protein-coupled receptor widely distributed in the mammalian brain, the somatostatin receptor type 2 (SST2). Methods: The clinically approved SST2 agonist octreotide (1 kDa), when injected intraperitoneally does not cross an intact BBB. At sites of BBB permeability, however, OCT extravasates and induces SST2 internalization from the neuronal membrane into perinuclear compartments. This allows an unambiguous localization of increased BBB permeability by classical immunohistochemical procedures using specific antibodies against the receptor. Results: We first validated our approach in sensory circumventricular organs which display permissive vascular permeability. Through SST2 internalization, we next monitored BBB opening induced by magnetic resonance imaging-guided focused ultrasound in murine cerebral cortex. Finally, we proved that after intraperitoneal agonist injection in pregnant mice, SST2 receptor internalization permits analysis of BBB integrity in embryos during brain development. Conclusions: This approach provides an alternative and simple manner to assess BBB dysfunction and development in different physiological and pathological conditions.
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Quantitative Measurement of the Thermal Contact Resistance between a Glass Microsphere and a Plate
Doumouro, J., E. Perros, A. Dodu, N. Rahbany, D. Leprat, V. Krachmalnicoff, R. Carminati, W. Poirier, and Y. De Wilde
Physical Review Applied 15, no. 1 (2021)
Résumé: © 2021 American Physical Society. Accurate measurements of the thermal resistance between micro-objects made of insulating materials are complex because of their small size, low conductivity, and the presence of various ill-defined gaps. We address this issue using a modified scanning thermal microscope operating in vacuum and in air. The sphere-plate geometry is considered. Under controlled heating power, we measure the temperature on top of a glass microsphere glued to the probe as it approaches a glass plate at room temperature with nanometer accuracy. In vacuum, a jump is observed at contact. From this jump in temperature and the modeling of the thermal resistance of a sphere, the sphere-plate contact resistance RK=(1.4±0.18)×107KW-1 and effective radius r=36±4 nm are obtained. In air, the temperature on top of the sphere shows a decrease starting from a sphere-plate distance of 200μm. A jump is also observed at contact, with a reduced amplitude. The sphere-plate coupling out of contact can be described by the resistance shape factor of a sphere in front of a plate in air, placed in a circuit involving a series and a parallel resistance that are determined by fitting the approach curve. The contact resistance in air RK - =(1.2±0.46)×107KW-1 is then estimated from the temperature jump. The method is quantitative without requiring any tedious multiple-scale numerical simulation, and is versatile to describe the coupling between micro-objects from large distances to contact in various environments.
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Artificial light may change flight patterns of bats near bridges along urban waterways
Barré, K., K. Spoelstra, Y. Bas, S. Challéat, R.-K. Ing, C. Azam, G. Zissis, D. Lapostolle, C. Kerbiriou, and I. Le Viol
Animal Conservation (2020)
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A direct linear inversion for discontinuous elastic parameters recovery from internal displacement information only
Ammari, H., E. Bretin, P. Millien, and L. Seppecher
Numerische Mathematik 147, no. 1, 189-226 (2021)
Résumé: © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature. The aim of this paper is to present and analyze a new direct method for solving the linear elasticity inverse problem. Given measurements of some displacement fields inside a medium, we show that a stable reconstruction of elastic parameters is possible, even for discontinuous parameters and without boundary information. We provide a general approach based on the weak definition of the stiffness-to-force operator which conduces to see the problem as a linear system. We prove that in the case of shear modulus reconstruction, we have an L2 stability with only one measurement under minimal smoothness assumptions. This stability result is obtained through the proof that the linear operator to invert has closed range. We then describe a direct discretization which provides stable reconstructions of both isotropic and anisotropic stiffness tensors.
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