The Early Cretaceous San Juan Plutonic Suite, Ecuador: A magma chamber in an oceanic plateau ?

Sections through an oceanic plateau are preserved in tectonic slices in the Western Cordillera of Ecuador (South America). The San Juan section is a sequence of mafic-ultramafic cumulates. To establish that these plutonic rocks formed in an oceanic plateau setting, we have developed criteria that discriminate intrusions of oceanic plateaus from those of other tectonic settings. The mineralogy and crystallization sequence of the cumulates are similar to those of intra-plate magmas. Clinopyroxene predominates throughout, and orthopyroxene is only a minor component. Rocks of intermediate composition are absent, and hornblende is restricted to the uppermost massive gabbros within the sequence. The ultramafic cumulates are very depleted in light rare-earth elements (LREE), whereas the gabbros have flat or slightly enriched LREE patterns. The composition of the basaltic liquid in equilibrium with the peridotite, calculated using olivine compositions and REE contents of clinopyroxene, contains between 16% and 8% MgO and has a flat REE pattern. This melt is geochemically similar to other accreted oceanic plateau basalts, isotropic gabbros, and differentiated sills in western Ecuador. The Ecuadorian intrusive and extrusive rocks have a narrow range of epsilonNd(i) (+8 to +5) and have a rather large range of Pb isotopic ratios. Pb isotope systematics of the San Juan plutonic rocks and mineral separates lie along a mixing line between the depleted mantle (DMM) and the enriched-plume end members. This suggests that the Ecuadorian plutonic rocks generated from the mixing of two mantle sources, a depleted mid-oceanic ridge basalt (MORB) source and an enriched one. The latter is characterized by high (Pb-207/Pb-204)(i) ratios and could reflect a contamination by recycled either lower continental crust or oceanic pelagic sediments and (or) altered oceanic crust (enriched mantle type I, EMI). These data suggest that the San Juan sequence represents the plutonic components of an Early Cretaceous oceanic plateau, which accreted in the Late Cretaceous to the Ecuadorian margin.

Intracortical connectivity of layer VI pyramidal cells in the barrel cortex of mice

ABSTRACT : The whisker-to-barrel pathway of rodents is formed by a series of somatotopic projections from the mystacial whisker follicles to the layer IV of the primary somatosensory cortex such that each follicle corresponds to a cluster of cortical neurons called barrel. Barrels are present in layer IV but form part of functional columns that comprise the entire depth of the somatosensory cortex. Interestingly, the cortex of the barrelless mouse strain (BRL) is organized such a manner that thalamocortical afferents do not remodel their projections in layer IV and barrels fail to appear. Nevertheless, functionally, a columnar organization persists, indicating that functional columns are not only provided by thalamocortical projections and layer IV cells. Since in the visual cortex of cats, layer VI cells contribute to the response properties of layer IV neurons, we wonder whether layer VI pyramidal cells could contribute to the columnar organization of the primary somatosensory cortex of mice. To address -this question, we morphologically analyzed the distribution of intracortical axon collaterals of layer VI neurons after in-vivo juxtacellular injections of biocytin in the C2 barrel column. Injected hemispheres were tangentially serial cut and intracortical collaterals of individual layer VI neurons were reconstructed at the light microscopic level. The position of axonal boutons was recorded to evaluate the distribution of presumed synaptic contacts. In normal (NOR) mice, cluster analysis shows that layer VI pyramidal cells can be classified in four statistically different clusters of neurons. Moreover, we assume that two classes are formed by cortico-cortical neurons and two classes are formed by cortico-thalamic neurons. Looking at the direction of the main axon in the white matter, we noticed that its orientation correlates perfectly with the type of neuron: cortico-cortical neurons send main axon medially whereas cortico-thalamic neurons send main axon laterally. Performing the same study in the BRL strain, we showed that the BRL mutation affects layer VI pyramidal cells tangentially and radially: the effects of the mutation are illustrated by a significant decrease of the index of colurnnarization and a significant decrease of percentage of boutons in granular and supragranular layers comparing to NOR neurons. In spite of these differences, the same four classes of layer VI neurons have been found in BRL mice. Using a tangential analysis of the boutons distribution, we showed that putative synapses are distributed mainly in the C2 barrel column. This was observed for each layer, type of neuron, cluster or strain, indicating that layer VI pyramidal cells could participate to the functional columnar organization of the barrel cortex. To determine post-synaptic partners of layer VI neurons in layer IV, we conducted an ultrastructural analysis of layer VI-to-IV contacts. We showed that synapses principally occur on spines and spiny dendritic shafts, supposed to belong to excitatory neurons. We furthermore showed that pre-synaptic elements are significantly different between en passant and terminaux contacts, which support hypothesis that terminaux boutons should show longer duration of facilitation than en passant boutons. RÉSUMÉ : Le «whisker-to-barrel pathway» des rongeurs est caractérisé par une série de projections somatotopiques depuis les follicules des moustaches ('whiskers') jusqu'à la couche IV de l'aire somatosensorielle primaire, de telle façon que chaque follicule corresponde à un groupe de neurones corticaux appelés tonneaux (`barrels'). Les tonneaux sont seulement présents en couche IV mais font partie de colonnes fonctionnelles qui s'étendent sur toute la profondeur du cortex somatosensoriel. Chez les souris mutantes barrelless (BRL), le cortex somatosensoriel est organisé de façon telle que lés afférences thalamocorticales ne remodellent pas leurs projections en couche IV et que les tonneaux n'apparaissent pas. Fonctionnellement, pourtant, une organisation en colonnes persiste, ce qui indique que les colonnes fonctionnelles ne sont pas uniquement produites par les projections thalamocorticales et par les cellules de la couche IV. Puisque les cellules de la couche VI contribuent à influencer les réponses des cellules de la couche IV dans le cortex visuel du chat, nous nous sommes demandé si ces cellules ne pourraient pas aussi contribuer à l'organisation en colonnes du cortex somatosensoriel primaire de la souris. Pour répondre à cette question, nous avons analysé de façon morphologique la distribution intracorticale des collatéraux axonaux de neurones de la couche VI. Suite à des injections juxtacellulaires de biocytine in-vivo dans la colonne C2, les hémisphères cérébraux ont été tangentiellement coupés en série et les collatéraux intracorticaux des neurones de la couche VI ont été reconstruits en microscopie optique. La position des boutons axonaux a aussi été enregistrée pour évaluer la distribution des contacts synpptiques potentiels. Chez les souris NOR, une analyse multivariée montre que les cellules pyramidales de la couche VI sont distribuées en quatre classes. Deux de ces classes sont probablement formées de neurons cortico-corticaux, alors que les deux autres sont probablement formées de neurones corticothalamiques. En observant la direction de l'axone principal dans la matière blanche, nous avons noté que son orientation est parfaitement corrélée avec le type supposé de neurone : les neurones corticocorticaux envoient leurs axones principaux médiallement, alors que les neurons cortico-thalamiques envoient leurs axones principaux latéralement. En menant la même étude chez les souris BRL, nous avons montré que la mutation affecte les cellules pyramidales de la couche VI de façon tangentielle, mais aussi radiaire : les effets de 1a mutation se traduisent par une diminution significative de l'index de « columnarization » et de la connectivité en couches granulaire et supragranulaire. Malgré ces différences, les quatre mêmes classes de neurones ont été retrouvées. En utilisant une analyse tangentielle de la distribution des boutons, nous avons montré que les synapses potentielles sont distribuées principalement dans la colonne C2. Cette observation a été faite dans chaque couche, chaque type de neurones, chaque classe de neurones et chaque souche de souris, indicant que les cellules de la couche VI participent certainement à l'organisation en colonne du cortex somatosensoriel. Pour déterminer les partenaires post-synaptiques des cellules de la couche VI en couche IV, nous avons conduit une analyse ultrastructurelle de ces contacts. Nous avons montré que les synapses interviennent principalement sur les épines et sur les dendrites supposés appartenir à des cellules excitatrices. Nous avons aussi montré que les éléments pré-synaptiques de ces synapses sont significativement differents selon le type de bouton, en passant ou terminal, ce qui supporte l'hypothèse que les boutons terminaux seraient capables d'une plus longue facilitation.

L'Apologie pour Origène de Pamphile et Eusèbe et les développements sur Origène dans le livre VI de l'Histoire ecclésiastique

(Résumé de l'ouvrage) Il dualismo della vita dell'esegeta a 30 anni dalla ricostruzione di Pierre Nautin, tra documentazione e interpretazione.

Intracortical connectivity of layer VI pyramidal neurons in the somatosensory cortex of normal and barrelless mice.

In mice, barrels in layer IV of the somatosensory cortex correspond to the columnar representations of whisker follicles. In barrelless (BRL) mice, barrels are absent, but functionally, a columnar organization persists. Previously we characterized the aberrant geometry of thalamic projection of BRL mice using axonal reconstructions of individual neurons. Here we proceeded with the analysis of the intracortical projections from layer VI pyramidal neurons, to assess their contribution to the columnar organization. From series of tangential sections we reconstructed the axon collaterals of individual layer VI pyramidal neurons in the C2 barrel column that were labelled with biocytin [controls from normal (NOR) strain, 19 cells; BRL strain, nine cells]. Using six morphological parameters in a cluster analysis, we showed that layer VI neurons in NOR mice are distributed into four clusters distinguished by the radial and tangential extent of their intracortical projections. These clusters correlated with the cortical or subcortical projection of the main axon. In BRL mice, neurons were distributed within the same four clusters, but their projections to the granular and supragranular layers were significantly smaller and their tangential projection was less columnar than in NOR mice. However, in both strains the intracortical projections had a preference for the appropriate barrel column (C2), indicating that layer VI pyramidal cells could participate in the functional columnar organization of the barrel cortex. Correlative light and electron microscopy analyses provided morphometric data on the intracortical synaptic boutons and synapses of layer VI pyramidal neurons and revealed that projections to layer IV preferentially target excitatory dendritic spines and shafts.

Récit ethnographique d'une expérience partagée de la fête de San Juan/Inti Raymi à Otavalo (Andes équatoriennes)

Cet article constitue une tentative de récit ethnographique qui compte rendre l'expérience vécue de la fête de San Juan/Inti Raymi dans la région d'Otavalo (Andes équatoriennes) de différents acteurs et de l'anthropologue. L'auteur s'essaie à la description minutieuse afin de montrer, à partir d'une perspective pragmatique, le développement des actions dans l'espace et dans le temps, permettant de mettre en évidence le savoir pratique et la créativité de ses interlocuteurs, ainsi que la dimension d'indétermination des situations. Par ce faire, aucune explication sous-jacente ou cachée est recherchée, le sens se trouvant dans la pratique festive même. L'abondance des détails a également pour objectif de faire vivre aux lecteurs les situations et de leur faire prendre conscience de leur caractère complexe et situé.

Analysis of past and future dam formation and failure in the Santa Cruz River (San Juan province, Argentina)

Around 11.5 * 106 m3 of rock detached from the eastern slope of the Santa Cruz valley (San Juan province, Argentina) in the first fortnight of January 2005. The rockslide?debris avalanche blocked the course, resulting in the development of a lake with maximum length of around 3.5 km. The increase in the inflow rate from 47,000?74,000 m3/d between April and October to 304,000 m3/d between late October and the first fortnight of November, accelerated the growing rate of the lake. On 12 November 2005 the dam failed, releasing 24.6 * 106 m3 of water. The resulting outburst flood caused damages mainly on infrastructure, and affected the facilities of a hydropower dam which was under construction 250 km downstream from the source area. In this work we describe causes and consequences of the natural dam formation and failure, and we dynamically model the 2005 rockslide?debris avalanche with DAN3D. Additionally, as a volume ~ 24 * 106 m3of rocks still remain unstable in the slope, we use the results of the back analysis to forecast the formation of a future natural dam. We analyzed two potential scenarios: a partial slope failure of 6.5 * 106 m3 and a worst case where all the unstable volume remaining in the slope fails. The spreading of those potential events shows that a new blockage of the Santa Cruz River is likely to occur. According to their modeled morphometry and the contributing watershed upstream the blockage area, as the one of 2005, the dams would also be unstable. This study shows the importance of back and forward analysis that can be carried out to obtain critical information for land use planning, hazards mitigation, and emergency management.

Early onset collagen VI myopathies: Genetic and clinical correlations.

OBJECTIVE: Mutations in the genes encoding the extracellular matrix protein collagen VI (ColVI) cause a spectrum of disorders with variable inheritance including Ullrich congenital muscular dystrophy, Bethlem myopathy, and intermediate phenotypes. We extensively characterized, at the clinical, cellular, and molecular levels, 49 patients with onset in the first 2 years of life to investigate genotype-phenotype correlations. METHODS: Patients were classified into 3 groups: early-severe (18%), moderate-progressive (53%), and mild (29%). ColVI secretion was analyzed in patient-derived skin fibroblasts. Chain-specific transcript levels were quantified by quantitative reverse transcriptase polymerase chain reaction (qRT-PCR), and mutation identification was performed by sequencing of complementary DNA. RESULTS: ColVI secretion was altered in all fibroblast cultures studied. We identified 56 mutations, mostly novel and private. Dominant de novo mutations were detected in 61% of the cases. Importantly, mutations causing premature termination codons (PTCs) or in-frame insertions strikingly destabilized the corresponding transcripts. Homozygous PTC-causing mutations in the triple helix domains led to the most severe phenotypes (ambulation never achieved), whereas dominant de novo in-frame exon skipping and glycine missense mutations were identified in patients of the moderate-progressive group (loss of ambulation). INTERPRETATION: This work emphasizes that the diagnosis of early onset ColVI myopathies is arduous and time-consuming, and demonstrates that quantitative RT-PCR is a helpful tool for the identification of some mutation-bearing genes. Moreover, the clinical classification proposed allowed genotype-phenotype relationships to be explored, and may be useful in the design of future clinical trials.

The Vi element. A transposon-like repeated DNA sequence interspersed in the vitellogenin locus of Xenopus laevis.

A repeated DNA element in Xenopus laevis is described that is present in about 7500 copies dispersed throughout the genome. It was first identified in the 5' flanking region of one vitellogenin gene and was therefore named the Vi element. Seven copies are present within the vitellogenin gene region, three of them within introns of the genes A1, A2 and B2, and the other four copies in the gene flanking regions. Four of these copies have been sequenced. The Vi element is bounded by a well-conserved 13 base-pair inverted repeat; in addition, it is flanked by a three base-pair direct repeat that appears to be site-specific. The length of these four copies varies from 112 to 469 base-pairs; however, sequence homology between the different copies is very high. Their structural characteristics suggest that length heterogeneity may have arisen by either unequal recombinations, deletions or tandem duplications. Altogether, the characteristics and properties of the Vi element indicate that it might represent a mobile genetic element. One of the four copies sequenced is inserted close (position -535) to the transcription initiation site of the vitellogenin gene B2 in a region otherwise showing considerable homology with the closely related gene B1. Nevertheless, the presence of the Vi element does not seem to influence significantly the estrogen-controlled expression of gene B2. In addition, three alleles of this gene created by length polymorphism in intron 3 and in the Vi element inserted near the transcription initiation site are described.