From whole-organ imaging to in-silico blood flow modeling: a new multi-scale network analysis for revisiting tissue functional anatomy

We present a multi-disciplinary image-based blood flow perfusion modeling of a whole organ vascular network for analyzing both its structural and functional properties. We show how the use of Light-Sheet Fluorescence Microscopy (LSFM) permits whole-organ micro- vascular imaging, analysis and modelling. By using adapted image post-treatment workflow, we could segment, vectorize and reconstruct the entire micro-vascular network composed of 1.7 million vessels, from the tissue-scale, inside a * 25 × 5 × 1 = 125mm 3 volume of the mouse fat pad, hundreds of times larger than previous studies, down to the cellular scale at micron resolution, with the entire blood perfusion modeled. Adapted network analysis revealed the structural and functional organization of meso-scale tissue as strongly connected communities of vessels. These communities share a distinct heterogeneous core region and a more homogeneous peripheral region, consistently with known biological functions of fat tissue. Graph clustering analysis also revealed two distinct robust meso-scale typical sizes (from 10 to several hundred times the cellular size), revealing, for the first time, strongly connected functional vascular communities. These community networks support heterogeneous micro-environments. This work provides the proof of concept that in-silico all-tissue perfusion modeling can reveal new structural and functional exchanges between micro-regions in tissues, found from community clusters in the vascular graph

Hypothalamic eIF2α signaling regulates food intake.

The reversible phosphorylation of the α subunit of eukaryotic initiation factor 2 (eIF2α) is a highly conserved signal implicated in the cellular adaptation to numerous stresses such as the one caused by amino acid limitation. In response to dietary amino acid deficiency, the brain-specific activation of the eIF2α kinase GCN2 leads to food intake inhibition. We report here that GCN2 is rapidly activated in the mediobasal hypothalamus (MBH) after consumption of a leucine-deficient diet. Furthermore, knockdown of GCN2 in this particular area shows that MBH GCN2 activity controls the onset of the aversive response. Importantly, pharmacological experiments demonstrate that the sole phosphorylation of eIF2α in the MBH is sufficient to regulate food intake. eIF2α signaling being at the crossroad of stress pathways activated in several pathological states, our study indicates that hypothalamic eIF2α phosphorylation could play a critical role in the onset of anorexia associated with certain diseases.This work was supported by grants from “Fondation pour la Recherche Médicale,” “Société Française de Nutrition,” Ajinomoto Amino Acid Research Program (3ARP), and “Agence Nationale pour la Recherche.”This is the final version of the article. It first appeared from Elsevier via http://dx.doi.org/10.1016/j.celrep.2014.01.00

3D analysis of the whole subcutaneous adipose tissue reveals a complex spatial network of interconnected lobules with heterogeneous browning ability

Adipose tissue, as the main energy storage organ and through its endocrine activity, is interconnected with all physiological functions. It plays a fundamental role in energy homeostasis and in the development of metabolic disorders. Up to now, this tissue has been analysed as a pool of different cell types with very little attention paid to the organization and putative partitioning of cells. Considering the absence of a complete picture of the intimate architecture of this large soft tissue, we developed a method that combines tissue clearing, acquisition of autofluorescence or lectin signals by confocal microscopy, segmentation procedures based on contrast enhancement, and a new semi-automatic image analysis process, allowing accurate and quantitative characterization of the whole 3D fat pad organization. This approach revealed the unexpected anatomic complexity of the murine subcutaneous fat pad. Although the classical picture of adipose tissue corresponds to a superposition of simple and small ellipsoidal lobules of adipose cells separated by mesenchymal spans, our results show that segmented lobules display complex 3D poly-lobular shapes. Despite differences in shape and size, the number of these poly-lobular subunits is similar from one fat pad to another. Finally, investigation of the relationships of these subunits between each other revealed a never-described organization in two clusters with distinct molecular signatures and specific vascular and sympathetic nerve densities correlating with different browning abilities. This innovative procedure reveals that subcutaneous adipose tissue exhibits a subtle functional heterogeneity with partitioned areas, and opens new perspectives towards understanding its functioning and plasticity

Ring-waves generated by water drops impacting on water surfaces at rest

Radar observations of the ocean surface can be affected by impacting raindrops. Ring-wave measurements are presented for drops of 2.2 and 2.8 mm in diameter impacting on fresh and salt water surfaces initially at rest. They are based on the observation of the mirror image of a sharp edge on the perturbed surface. The retrieved wave profiles show a rather stable characteristic wavenumber (0.2 mm1) and very small wave amplitudes: the fraction of the incident kinetic energy converted into ring-waves is of the order of 1%

Angular errors in trihedrals used for radar calibrations

The effects of non-orthogonality of trihedral corner reflectors are significant when the reflector dimensions are large compared to the wavelength. Therefore, a high frequency approach is adopted combining geometrical and physical optics. A simple frequency dependent relationship is proposed for the maximum cross-section loss due to a given angular uncertainty. Polarization purity and phase stability are also addressed

Two-scale models for rough surface scattering: Comparison between the boundary perturbation method and the integral equation method

This paper presents a comparison between two models for rough surface scattering computations: the boundary perturbation method (BPM) and the integral equation method (IEM). They differ in two fundamental aspects: the method used to compute the electric and magnetic fields on the surface and the surface information required for the computation. The two approaches lead analytically to the same solution in the two asymptotic cases of very large and very small vertical displacements, with no intermediate scales. For a composite surface the solution of the BPM is expressed as the sum of two terms, while a series development up to higher orders can be formulated with the IEM. In this paper, the comparison is restricted to composite surfaces and, particularly, to the ocean surface. After presenting a method for the two-scale decomposition of a rough surface, which satisfies the constraints of the electromagnetic model for each scale, we compute the scattering by the ocean surface using both models for various instrumental configurations and surface conditions. We show that considering the accuracy of usual radar measurements and under the assumptions made for the development of the models, both methods give very similar results. Since the BPM is based on a simple physical argument and appears to be more efficient than the two-scale IEM with regard to the computation time, the BPM should be preferred for ocean-like rough surfaces

A brief increase in free fatty acids towards the brain reduces food intake in rats

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Céphalées chez l'enfant: quand et quelle imagerie?

There are various causes of headaches in children. The majority of cases are considered as primary and include migraine and tension headaches. Headaches secondary to an underlying pathology are much less frequent. The aim of imaging will be to depict lesions that can benefit from specific therapy and hence improve life quality and expectancy of the affected child. In case of secondary headaches, imaging will have to precise the diagnosis, which is based mainly upon history of the disease and clinical findings. These findings are important to the radiologist as they will help to choose the more adequate technique between CT scan and MRI. This choice is based upon the presumed diagnoses, degree of emergency and availability of the technique. Knowledge of the differential diagnoses influences the way to perform the examination itself (choice of slice thickness, plane of imaging, MR sequences, need for an MR angiogram or injection of contrast medium.). In our opinion, dedicated MR imaging is the technique of choice to investigate secondary headaches in children given its superior sensitivity in depicting certain tumors (glioma of the pons, posterior fossa tumors.), intracranial hypotension, Chiari I malformation, lesions of the hypothalamo-hypophyseal axis etc...English AbstractJournal ArticleReviewinfo:eu-repo/semantics/publishe