Microfluidics based phantoms of superficial vascular network

Several new bio-photonic techniques aim to measure flow in the human vasculature non-destructively. Some of these tools, such as laser speckle imaging or Doppler optical coherence tomography, are now reaching the clinical stage. Therefore appropriate calibration and validation techniques dedicated to these particular measurements are therefore of paramount importance. In this paper we introduce a fast prototyping technique based on laser micromachining for the fabrication of dynamic flow phantoms. Micro-channels smaller than 20 µm in width can be formed in a variety of materials such as epoxies, plastics, and household tape. Vasculature geometries can be easily and quickly modified to accommodate a particular experimental scenario

Ankyrin G restricts ion channel diffusion at the axonal initial segment before the establishment of the diffusion barrier

Ion channel immobilization by ankyrin G is regulated by casein kinase 2 in immature hippocampal neurons

In vivo assembly of the axon initial segment in motor neurons

International audienceThe axon initial segment (AIS) is responsible for both the modulation of action potentials and the maintenance of neuronal polarity. Yet, the molecular mechanisms controlling its assembly are incompletely understood. Our study in single electroporated motor neurons in mouse embryos revealed that AnkyrinG (AnkG), the AIS master organizer, is undetectable in bipolar migrating motor neurons, but is already expressed at the beginning of axonogenesis at E9.5 and initially distributed homogeneously along the entire growing axon. Then, from E11.5, a stage when AnkG is already apposed to the membrane, as observed by electron microscopy, the protein progressively becomes restricted to the proximal axon. Analysis on the global motor neurons population indicated that Neurofascin follows an identical spatio-temporal distribution, whereas sodium channels and beta 4-spectrin only appear along AnkG(+) segments at E11.5. Early patch-clamp recordings of individual motor neurons indicated that at E12.5 these nascent AISs are already able to generate spikes. Using knock-out mice, we demonstrated that neither beta 4-spectrin nor Neurofascin control the distal-to-proximal restriction of AnkG

Developmental Expression of Kv Potassium Channels at the Axon Initial Segment of Cultured Hippocampal Neurons

Axonal outgrowth and the formation of the axon initial segment (AIS) are early events in the acquisition of neuronal polarity. The AIS is characterized by a high concentration of voltage-dependent sodium and potassium channels. However, the specific ion channel subunits present and their precise localization in this axonal subdomain vary both during development and among the types of neurons, probably determining their firing characteristics in response to stimulation. Here, we characterize the developmental expression of different subfamilies of voltage-gated potassium channels in the AISs of cultured mouse hippocampal neurons, including subunits Kv1.2, Kv2.2 and Kv7.2. In contrast to the early appearance of voltage-gated sodium channels and the Kv7.2 subunit at the AIS, Kv1.2 and Kv2.2 subunits were tethered at the AIS only after 10 days in vitro. Interestingly, we observed different patterns of Kv1.2 and Kv2.2 subunit expression, with each confined to distinct neuronal populations. The accumulation of Kv1.2 and Kv2.2 subunits at the AIS was dependent on ankyrin G tethering, it was not affected by disruption of the actin cytoskeleton and it was resistant to detergent extraction, as described previously for other AIS proteins. This distribution of potassium channels in the AIS further emphasizes the heterogeneity of this structure in different neuronal populations, as proposed previously, and suggests corresponding differences in action potential regulation

Fast spectrally encoded Mueller optical scanning microscopy

Mueller microscopes enable imaging of the optical anisotropic properties of biological or non-biological samples, in phase and amplitude, at sub-micrometre scale. However, the development of Mueller microscopes poses an instrumental challenge: the production of polarimetric parameters must be sufficiently quick to ensure fast imaging, so that the evolution of these parameters can be visualised in real-time, allowing the operator to adjust the microscope while constantly monitoring them. In this report, a full Mueller scanning microscope based on spectral encoding of polarization is presented. The spectrum, collected every 10 μs for each position of the optical beam on the specimen, incorporates all the information needed to produce the full Mueller matrix, which allows simultaneous display of all the polarimetric parameters, at the unequalled rate of 1.5 Hz (for an image of 256 × 256 pixels). The design of the optical blocks allows for the real-time display of linear birefringent images which serve as guidance for the operator. In addition, the instrument has the capability to easily switch its functionality from a Mueller to a Second Harmonic Generation (SHG) microscope, providing a pixel-to-pixel matching of the images produced by the two modalities. The device performance is illustrated by imaging various unstained biological specimens

Etude de phénomènes non linéaires du second ordre dans les milieux diffusants en phase liquide. Définition et étude d'une configuration adaptée.

The experimental determination of the first-order optical rank-3 hyperpolarizability tensor is paramount for the development of new molecules endowed with non-linear optical properties. Hyper-Rayleigh scattering (HRS) is a non-linear light scattering technique where the molecules are within an isotropic solution. Because of orientational and statistical fluctuations, only six observables, i.e. six rotational invariants, are measured by HRS. So as to experimentally determine these six observables, we developed and implemented a dual-rotating-retarders polarimeter operating with a tunable pulse laser source and designed for hyper-Rayleigh scattering measurements. The experimental setup was first optimized by reducing the condition number of the polarization processing matrix, thus reducing the statistical errors. Then we calibrated the setup by using a reference sample devoted to wavelength conversion, so as to reduce the systematic errors. Finally, we performed HRS measurements on two well-known molecules, DR1 and Crystal Violet.     La détermination expérimentale des composantes du tenseur d'hyper-polarisabilité est essentielle au développement de nouvelles molécules possédant des propriétés d'optique non-linéaire. La diffusion harmonique de la lumière (DHL) correspond à un phénomène de diffusion non linéaire de la lumière pour laquelle les molécules considérées sont dans une solution isotrope. Du fait des fluctuations d'orientations et de positions des molécules, seules six observables, où invariants orientationnels, sont mesurables par DHL. Afin de déterminer expérimentalement ces six observables, nous avons mis au point un polarimètre à lame de phase tournantes fonctionnant avec une source laser impulsionnelle accordable en longueur d'onde et dédié au mesures de diffusion harmonique de la lumière. Nous avons dans un premier temps optimisé l'architecture du montage polarimétrique en nous appuyant sur la réduction du nombre de conditionnement de la matrice d'appareil, réduisant par la même les erreurs statistiques. Puis nous avons étalonné le montage au moyen d'un échantillon référence dédié à la conversion de longueur d'onde, afin de réduire les erreurs systématiques. Enfin, nous avons réalisé des mesures de diffusion harmonique de la lumière sur deux molécules connues, le DR1 et le Cristal Violet

Étude des phénomènes non linéaires du second ordre dans les milieux diffusants en phase liquide (définition et étude d'une configuration adaptée)

La détermination expérimentale des composantes du tenseur d hyper-polarisabilité b est essentielle au développement de nouvelles molécules possédant des propriétés d optique non-linéaire. La diffusion harmonique de la lumière (DHL) correspond à un phénomène de diffusion non linéaire de la lumière pour laquelle les molécules considérées sont dans une solution isotrope. Du fait des fluctuations d orientations et de positions des molécules, seules six observables, ou invariants orientationnels, sont mesurables par DHL. Afin de déterminer expérimentalement ces six observables, nous avons mis au point un polarimètre à lame de phase tournantes fonctionnant avec une source laser impulsionnelle accordable en longueur d onde et dédié aux mesures de diffusion harmonique de la lumière. Nous avons dans un premier temps optimisé l architecture du montage polarimétrique en nous appuyant sur la réduction du nombre de conditionnement de la matrice d appareil, réduisant par la même les erreurs statistiques. Puis nous avons étalonné le montage au moyen d un échantillon référence dédié à la conversion de longueur d onde, afin de réduire les erreurs systématiques. Enfin, nous avons réalisé des mesures de diffusion harmonique de la lumière sur deux molécules connues, le DR1 et le Cristal Violet.The experimental determination of the first-order optical rank-3 hyperpolarizability tensor b is paramount for the development of new molecules endowed with non-linear optical properties. Hyper-Rayleigh scattering (HRS) is a non-linear light scattering technique where the molecules are within an isotropic solution. Because of orientational and statistical fluctuations, only six observables, i.e. six rotational invariants, are measured by HRS. So as to experimentally determine these six observables, we developed and implemented a dual-rotating-retarders polarimeter operating with a tunable pulse laser source and designed for hyper-Rayleigh scattering measurements. The experimental setup was first optimized by reducing the condition number of the polarization processing matrix, thus reducing the statistical errors. Then we calibrated the setup by using a reference sample devoted to wavelength conversion, sp as to reduce the systematic errors. Finally, we performed HRS measurements on two well-known molecules, DR1 and Crystal Violet.BREST-BU Droit-Sciences-Sports (290192103) / SudocSudocFranceF