Bifurcation study of a neural field competition model with an application to perceptual switching in motion integration.

Perceptual multistability is a phenomenon in which alternate interpretations of a fixed stimulus are perceived intermittently. Although correlates between activity in specific cortical areas and perception have been found, the complex patterns of activity and the underlying mechanisms that gate multistable perception are little understood. Here, we present a neural field competition model in which competing states are represented in a continuous feature space. Bifurcation analysis is used to describe the different types of complex spatio-temporal dynamics produced by the model in terms of several parameters and for different inputs. The dynamics of the model was then compared to human perception investigated psychophysically during long presentations of an ambiguous, multistable motion pattern known as the barberpole illusion. In order to do this, the model is operated in a parameter range where known physiological response properties are reproduced whilst also working close to bifurcation. The model accounts for characteristic behaviour from the psychophysical experiments in terms of the type of switching observed and changes in the rate of switching with respect to contrast. In this way, the modelling study sheds light on the underlying mechanisms that drive perceptual switching in different contrast regimes. The general approach presented is applicable to a broad range of perceptual competition problems in which spatial interactions play a role

Identification of a delta5-like fatty acyl desaturase from the cephalopod Octopus vulgaris (Cuvier 1797) involved in the biosynthesis of essential fatty acids

Long-chain polyunsaturated fatty acids (LC-PUFA) have been identified as essential compounds for common octopus (Octopus vulgaris), but precise dietary requirements have not been determined due in part to the inherent difficulties of performing feeding trials on paralarvae. Our objective is to establish the essential fatty acid (EFA) requirements for paralarval stages of the common octopus through characterisation of the enzymes of endogenous LC-PUFA biosynthetic pathways. In this study we isolated a cDNA with high homology to fatty acyl desaturases (Fad). Functional characterisation in recombinant yeast showed the octopus Fad exhibited ∆5 desaturation activity towards saturated and polyunsaturated fatty acyl substrates. Thus, it efficiently converted the yeast’s endogenous 16:0 and 18:0 to 16:1n-11 and 18:1n-13, respectively, and desaturated exogenously added PUFA substrates, 20:4n-3 and 20:3n-6, to 20:5n-3 (EPA) and 20:4n-6 (ARA), respectively. Although the ∆5 Fad enables common octopus to produce EPA and ARA, the low availability of its adequate substrates 20:4n-3 and 20:3n-6, either in the diet or by limited endogenous synthesis from C18 PUFA, might indicate that EPA and ARA are indeed EFA for this species. Interestingly, the octopus ∆5 Fad can also participate in the biosynthesis of non-methylene interrupted FA, PUFA that are generally uncommon in vertebrates but that have been found previously in marine invertebrates including molluscs, and now also confirmed to be present in specific tissues of common octopus

On a coupled PDE model for image restoration

In this paper, we consider a new coupled PDE model for image restoration. Both the image and the edge variables are incorporated by coupling them into two different PDEs. It is shown that the initial-boundary value problem has global in time dissipative solutions (in a sense going back to P.-L. Lions), and several properties of these solutions are established. This is a rough draft, and the final version of the paper will contain a modelling part and numerical experiments

Molecular Phylogeny Restores the Supra-Generic Subdivision of Homoscleromorph Sponges (Porifera, Homoscleromorpha)

Homoscleromorpha is the fourth major sponge lineage, recently recognized to be distinct from the Demospongiae. It contains <100 described species of exclusively marine sponges that have been traditionally subdivided into 7 genera based on morphological characters. Because some of the morphological features of the homoscleromorphs are shared with eumetazoans and are absent in other sponges, the phylogenetic position of the group has been investigated in several recent studies. However, the phylogenetic relationships within the group remain unexplored by modern methods.Here we describe the first molecular phylogeny of Homoscleromorpha based on nuclear (18S and 28S rDNA) and complete mitochondrial DNA sequence data that focuses on inter-generic relationships. Our results revealed two robust clades within this group, one containing the spiculate species (genera Plakina, Plakortis, Plakinastrella and Corticium) and the other containing aspiculate species (genera Oscarella and Pseudocorticium), thus rejecting a close relationship between Pseudocorticium and Corticium. Among the spiculate species, we found affinities between the Plakortis and Plakinastrella genera, and between the Plakina and Corticium. The validity of these clades is furthermore supported by specific morphological characters, notably the type of spicules. Furthermore, the monophyly of the Corticium genus is supported while the monophyly of Plakina is not.As the result of our study we propose to restore the pre-1995 subdivision of Homoscleromorpha into two families: Plakinidae Schulze, 1880 for spiculate species and Oscarellidae Lendenfeld, 1887 for aspiculate species that had been rejected after the description of the genus Pseudocorticium. We also note that the two families of homoscleromorphs exhibit evolutionary stable, but have drastically distinct mitochondrial genome organizations that differ in gene content and gene order

Specialized box C/D snoRNPs act as antisense guides to target RNA base acetylation

Box C/D snoRNAs are known to guide site-specific ribose methylation of ribosomal RNA. Here, we demonstrate a novel and unexpected role for box C/D snoRNAs in guiding 18S rRNA acetylation in yeast. Our results demonstrate, for the first time, that the acetylation of two cytosine residues in 18S rRNA catalyzed by Kre33 is guided by two orphan box C/D snoRNAs–snR4 and snR45 –not known to be involved in methylation in yeast. We identified Kre33 binding sites on these snoRNAs as well as on the 18S rRNA, and demonstrate that both snR4 and snR45 establish extended bipartite complementarity around the cytosines targeted for acetylation, similar to pseudouridylation pocket formation by the H/ACA snoRNPs. We show that base pairing between these snoRNAs and 18S rRNA requires the putative helicase activity of Kre33, which is also needed to aid early pre-rRNA processing. Compared to yeast, the number of orphan box C/D snoRNAs in higher eukaryotes is much larger and we hypothesize that several of these may be involved in base-modifications

Marine pharmacology : potentialities in the treatment of infectious diseases, osteoporosis and Alzheimer's disease.

Several molecules isolated from various marine organisms (microorganisms, algae, fungi, invertebrates, and vertebrates) are currently under study at an advanced stage of clinical trials, either directly or in the form of analogues deduced from structure--activity relationships. Some of them have already been marketed as drugs. The goal of this article is not to present a complete panorama of marine pharmacology but to show that new models and new mechanisms of action of marine substances bring new solutions for tackling some of the major public health problems of the 21st century. These include: malaria, which assails mainly the southern hemisphere; tuberculosis, an infectious disease once believed to be eliminated but alarmingly increasing, especially among HIV-positive populations; and osteoporosis and Alzheimer's disease, the extension of which are correlated with ageing populations, especially in the developed countries

Labiatamides A, B, and other eunicellan diterpenoids from the Senegalese gorgonian Eunicella labiata

Five new diterpenoids of the eunicellan class, labiatamides A-B (1,2) and labiatins A-C (3-5) have been isolated from the organic extract of the Senegalese gorgonian Eunicella labiata. A unique feature of labiatamides A and B (1,2) is the N-methyl acetamide group, an uncommon functionality in soft coral metabolites. Labiatin A (3), possesses an unprecedented ether linkage between C-2 and C-6. The structure elucidations of the new secondary metabolites were provided by comprehensive spectroscopic analyses. Labiatin B exhibited cytotoxic activity against human colon cancer cells (HCT-116) with ED50 = 0.85 μg/ml

First testing of a volcano Doppler radar (Voldorad) at Mount Etna, Italy

International audienceA medium-power (1 kW) Doppler radar of limited weight (110 kg) and working in the UHF band has been developed for active remote sensing of volcanic eruptions. Named Voldorad, this radar is designed to monitor eruptive activities of variable magnitude at medium distance range (-0.5-5 km), in any weather condition, and fills the gap between low-and high-power radar or sodar systems previously tested on volcanoes. Voldorad was operated for the first time during an eruption of Mr. Etna on October 11-12, 19911. Doppler spectra recorded at 1 km distance from the vent reveal powerful echoes during the eruption paroxysm (lava fountains), which gradually decreased along with declining activity. An average vertical velocity of 110-117 m s 4 is inferred for the eruptive jets. by Hort and Sey•ied [1998] and Sey•ied and Hort [1999] is more promising. The first tests were conducted 200-300 m away from the vent, but the operating range could be increased by using a parabolic mirror antenna with a small aperture [Seyfried and Hort, 1999]. Based on the [JHF wind profiler technique [e.g. Ecklund et al., 1990], we have developed and tested a medium-power pulsed Doppler radar specifically devoted to volcanic sounding [Dubosclard et al., 1999]. Named Voldorad, this radar can operate at medium distance (-0.5 to 5 km) from a volcanic vent and is compact enough to be easily set up on a volcano. In the following, we describe this new insreinvent and report preliminary data recorded during an eruptive sequence of Mount Etna (Sicily) in October 1998