Multiphoton fluorescent images with a spatially varying background signal: a ML deconvolution method.

By means of multiphoton laser scanning microscopy, neuroscientists can look inside the brain deeper than has ever been possible before. Multiphoton fluorescent images, as all optical images, suffer from degradation caused by a variety of sources (e.g. light dispersion and absorption in the tissue, laser fluctuations, spurious photodetection and staining deficiency). From a modelling perspective, such degradations can be considered the sum of stochastic noise and a background signal. Among the methods proposed in the literature to perform image deconvolution in either confocal or multiphoton fluorescent microscopy, Vicidomini et al. (2009) were the first to incorporate models for noise (a Poisson process) and background signal (spatially constant) in the context of regularized inverse problems. Unfortunately, the so-called split-gradient deconvolution method (SGM) they used did not consider possible spatial variations in the background signal. In this paper, we extend the SGM by adding a maximum-likelihood estimation step for the determination of a spatially varying background signal. We demonstrate that the assumption of a constant background is not always valid in multiphoton laser microscopy and by using synthetic and actual multiphoton fluorescent images, we evaluate the face of validity of the proposed method, and compare its accuracy with the previously introduced SGM algorithm.

Spatiotemporal dynamics in a ring of N mutually coupled self-sustained systems.

In this paper, we consider the spatiotemporal dynamics in a ring of N mutually coupled self-sustained oscillators in the regular state. When there are no parameter mismatches, the good coupling parameters leading to full, partial, and no synchronization are derived using the properties of the variational equations of stability. The effects of the spatial dimension of the ring on the stability boundaries of the synchronized states are performed. Numerical simulations validate and complement the results of analytical investigations. The influences of coupling parameter mismatch on the forecasted stability boundaries are also highlighted.

Synchronization of two coupled self-excited systems with multi-limit cycles.

We analyze the stability and optimization of the synchronization process between two coupled self-excited systems modeled by the multi-limit cycles van der Pol oscillators through the case of an enzymatic substrate reaction with ferroelectric behavior in brain waves model. The one-way and two-way couplings synchronization are considered. The stability boundaries and expressions of the synchronization time are obtained using the properties of the Hill equation. Numerical simulations validate and complement the results of analytical investigations.

Synchronized states in a ring of mutually coupled self-sustained electrical oscillators.

We investigate in this paper different states of synchronization in a ring of mutually coupled self-sustained electrical oscillators. The good coupling parameters leading to complete and partial synchronization or disordered states are calculated using the properties of the variational equations of stability. A stability map showing domains of synchronization to an external excitation locally injected in the ring is also obtained. In both cases, the numerical simulation validates and complements the results of the analytical investigation.

Fibrinolytic activity in experimental vascular grafts.

The effects of grafting segments of femoral vein in the dog have been studied. The venous segments, either reversed or left in situ, were interposed in the course of the femoral artery; these 'arterialized grafts' were compared with a segment of vein grafted into the venous stream, with normal femoral artery and vein. Histological changes and alterations in fibrinolytic activity were studied after 15, 30 and 90 days. The two types of arterialized venous graft showed similar aspects: normal endothelium (scanning electron microscopy and F VIII immunofluorescence), marked thickening of the smooth muscle cell layer, disappearance of intimal fibrinolytic activity (Todd's technique, quantified by morphometric analysis), associated with a marked increase of antiplasmin activity (Noordhoek Hegt's technique), increase in the activity of vascular plasminogen activator (measured with chromogenic substrates). The venous grafts in the venous stream showed no changes compared to the normal femoral vein. The proliferation of smooth muscle cells following exposure of a segment of vein to arterial conditions appears to be associated with increased synthesis of both an inhibitor of fibrinolysis (antiplasmin), and of vascular plasminogen activator. The contribution of these two factors to the development of the morphological changes in the vessel requires further study.

[Morphologic study of different types of venous grafts. Correlation trial with parietal fibrinolytic activity]. / Etude morphologique de différents types de greffons veineux. Essai de corrélation avec l'activité fibrinolytique pariétale.

In this experimental work, morphological aspects of different vein grafts were studied using both light microscopy, transmission electron microscopy and scanning electron microscopy. The correlation was made with their fibrinolytic activity ; 21 dogs were operated on under general anaesthesia ; "venous grafts" (perfusion of the vascular segments with venous blood) were performed by excision of the femoral vein with reanastomosis at the same site (protocol P1). "Arterialised grafts" (perfusion of a segment of vein with arterial blood at arterial pressure) were performed according to two protocols : P2 in which a segment of femoral artery was replaced with a segment of reversed femoral vein ; P3 in which a segment of femoral artery was by passed with the femoral vein left in situ after destroying the valves using a Fogarty balloon without damage of the intima. The factors affected by surgery are, therefore, disconnection of the vasa vasorum by excision of the vessel in protocols P1 and P2 and increased oxygenation and luminal pressure in protocols P2 and P3. In all the cases, endothelial cells retained the morphological characteristics of venous endothelium. However, the vein grafts in the arterial circulation were thickened and the fibrinolytic activity was changed. Pathogenic mechanisms of these changes are discussed.