A highly sensitive in vitro infection assay to explore early stages of mouse mammary tumor virus infection.

Mouse mammary tumor virus (MMTV) infection of adult mice induces a strong response to superantigen (Sag) in their draining lymph nodes, which results from the presentation of Sag by MMTV-infected B cells to Sag-reactive T cells. To date, infection with physiologically relevant doses of MMTV can be detected in vivo only after several days of Sag-mediated T-cell-dependent amplification of infected B cells. Furthermore, no efficient in vitro system of detecting MMTV infection is available. Such a model would allow the dissection of the early phase of infection, the assessment of the contributions of different cell types, and the screening of large panels of molecules for their potential roles in infection and Sag response. For these reasons, we have established an in vitro model for detecting infection which is as sensitive and reproducible as the in vivo model. We found that the viral envelope (Env) protein is crucial for target cell infection but not for presentation of Sag. Furthermore, we show that infection of purified B cells with MMTV induces entry of Sag-responsive T cells into the cell cycle, while other professional antigen-presenting cells, such as dendritic cells, are much less efficient in inducing a response.

Status Epilepticus Severity Score (STESS): a tool to orient early treatment strategy

BACKGROUND : Status epilepticus (SE) treatment ranges from small benzodiazepine doses to coma induction. For some SE subgroups, it is unclear how the risk of an aggressive therapeutic approach balances with outcome improvement. We recently developed a prognostic score (Status Epilepticus Severity Score, STESS), relying on four outcome predictors (age, history of seizures, seizure type and extent of consciousness impairment), determined before treatment institution. Our aim was to assess whether the score might have a role in the treatment strategy choice. METHODS : This cohort study involved adult patients in three centers. For each patient, the STESS was calculated before primary outcome assessment: survival vs. death at discharge. Its ability to predict survival was estimated through the negative predictive value for mortality (NPV). Stratified odds ratios (OR) for mortality were calculated considering coma induction as exposure; strata were defined by the STESS level. RESULTS : In the observed 154 patients, the STESS had an excellent negative predictive value (0.97). A favorable STESS was highly related to survival (P < 0.001), and to return to baseline clinical condition in survivors (P < 0.001). The combined Mantel-Haenszel OR for mortality in patients stratified after coma induction and their STESS was 1.5 (95 % CI: 0.59-3.83). CONCLUSION : The STESS reliably identifies SE patients who will survive. Early aggressive treatment could not be routinely warranted in patients with a favorable STESS, who will almost certainly survive their SE episode. A randomized trial using this score would be needed to confirm this hypothesis.

Early effects of intravitreal triamcinolone on macular edema: mechanistic implication.

PURPOSE: To evaluate the early effects of intravitreal triamcinolone acetonide (TA) on cystoid macular edema associated with retinal vein occlusion and diabetic retinopathy. DESIGN: Prospective, interventional, small case series. PARTICIPANTS: Four patients with cystoid macular edema resulting from retinal vein occlusion or diabetic retinopathy of more than 4 months' duration and evaluated as suitable for treatment with intravitreous injection of TA. METHODS: After ophthalmic examination, including visual acuity assessment, intraocular pressure (IOP) measurement, and optical coherence tomography (OCT) analysis, the patients received a single intravitreal injection of 4 mg TA. After the injection, consecutive visual acuity assessment, IOP measurement, and OCT analysis were performed after 1 hour, 6 hours, 1 week, and 2 weeks. MAIN OUTCOME MEASURE: Optical coherence tomography assessment of macular thickness. RESULTS: Macular thickness and edema initially were reduced as early as 1 hour after TA injection. A further continuous decrease was observed during the 2 weeks after treatment. CONCLUSIONS: This rapid effect of intravitreal TA is interpreted to indicate that nongenomic effects on retinal or retinal pigment epithelial cell membranes, or both, may be responsible for this phenomenon. Identifications of these mechanisms may help design alternative, more specific drugs for the treatment of macular edema.

Early-Stage Primary Bone Lymphoma: A Retrospective, Multicenter Rare Cancer Network (RCN) Study.

PURPOSE: Primary bone lymphoma (PBL) represents less than 1% of all malignant lymphomas. In this study, we assessed the disease profile, outcome, and prognostic factors in patients with Stages I and II PBL.¦PATIENTS AND METHODS: Thirteen Rare Cancer Network (RCN) institutions enrolled 116 consecutive patients with PBL treated between 1987 and 2008 in this study. Eighty-seven patients underwent chemoradiotherapy (CXRT) without (78) or with (9) surgery, 15 radiotherapy (RT) without (13) or with (2) surgery, and 14 chemotherapy (CXT) without (9) or with (5) surgery. Median RT dose was 40 Gy (range, 4-60). The median number of CXT cycles was six (range, 2-8). Median follow-up was 41 months (range, 6-242).¦RESULTS: The overall response rate at the end of treatment was 91% (complete response [CR] 74%, partial response [PR] 17%). Local recurrence or progression was observed in 12 (10%) patients and systemic recurrence in 17 (15%). The 5-year overall survival (OS), lymphoma-specific survival (LSS), and local control (LC) were 76%, 78%, and 92%, respectively. In univariate analyses (log-rank test), favorable prognostic factors for OS and LSS were International Prognostic Index (IPI) score ≤1 (p = 0.009), high-grade histology (p = 0.04), CXRT (p = 0.05), CXT (p = 0.0004), CR (p < 0.0001), and RT dose >40 Gy (p = 0.005). For LC, only CR and Stage I were favorable factors. In multivariate analysis, IPI score, RT dose, CR, and CXT were independently influencing the outcome (OS and LSS). CR was the only predicting factor for LC.¦CONCLUSION: This large multicenter retrospective study confirms the good prognosis of early-stage PBL treated with combined CXRT. An adequate dose of RT and complete CXT regime were associated with better outcome.

T cell receptor delta gene rearrangement and T early alpha (TEA) expression in immature alpha beta lineage thymocytes: implications for alpha beta/gamma delta lineage commitment.

Mature T cells comprise two mutually exclusive lineages expressing heterodimeric alpha beta or gamma delta antigen receptors. During development, beta, gamma, and delta genes rearrange before alpha, and mature gamma delta cells arise in the thymus prior to alpha beta cells. The mechanism underlying commitment of immature T cells to the alpha beta or gamma delta lineage is controversial. Since the delta locus is located within the alpha locus, rearrangement of alpha genes leads to deletion of delta. We have examined the rearrangement status of the delta locus immediately prior to alpha rearrangement. We find that many thymic precursors of alpha beta cells undergo VDJ delta rearrangements. Furthermore, the same cells frequently coexpress sterile T early alpha (TEA) transcripts originating 3' of C delta and 5' of the most upstream J alpha, thus implying that individual alpha beta lineage cells undergo sequential VDJ delta and VJ alpha rearrangements. Finally, VDJ delta rearrangements in immature alpha beta cells appear to be random, supporting models in which alpha beta lineage commitment is determined independently of the rearrangement status at the TCR delta locus.

Early intensification and autologous stem cell transplantation in patients with systemic AL amyloidosis: a single-centre experience.

Primary systemic amyloidosis (AL amyloidosis) continues to have a very poor prognosis. Most therapeutic strategies remain unsatisfactory. Conventional chemotherapy is known to offer at best only moderate efficacy. Several studies have yielded higher complete response rates after high-dose chemotherapy and autologous stem cell transplantation (ASCT) in addition to improving outcomes in a subgroup of patients. However, the superiority of an intensive approach in AL amyloidosis has not been confirmed in a randomised trial. The precise role of ASCT remains unclear. We report our experience in 16 patients diagnosed with AL amyloidosis and treated in a multidisciplinary approach with high-dose melphalan and ASCT. Median age was 59 (39-71) years. The kidneys were predominantly affected in 75% of cases; two or more organs were affected in 38%. Median time from diagnosis to transplantation was 2 (1-4) months. Three patients (19%) developed acute renal failure and required transient dialysis. Transplant-related mortality was 6% after 100 days. Haematological complete response (CR) was obtained in nine (56%) and organ response in six (38%) patients. Nine out of 12 patients (75%) with kidney involvement exhibited a sustained clinical benefit at 12 months. Half of all the patients (n = 8) were alive after a median follow-up of 33 months, including two in continuous CR. This suggests that high-dose chemotherapy and ASCT are still valid treatment options in AL amyloidosis and that a significant number of patients with renal involvement might benefit from this approach.

Early pregnancy sex steroids and maternal risk of epithelial ovarian cancer.

Well-established associations between reproductive characteristics and epithelial ovarian cancer (EOC) support an involvement of sex steroid hormones in the etiology of EOC. Limited previous studies have evaluated circulating androgens and the risk of EOC, and estrogens and progesterone have been investigated in only one of the previous studies. Furthermore, there is little data on potential heterogeneity in the association between circulating hormones and EOC by histological subgroup. Therefore, we conducted a nested case-control study within the Finnish Maternity Cohort and the Northern Sweden Maternity Cohort to investigate the associations between circulating pre-diagnostic sex steroid concentrations and the histological subtypes of EOC. We identified 1052 EOC cases among cohort members diagnosed after recruitment (1975-2008) and before March 2011. Up to three controls were individually matched to each case (n=2694). Testosterone, androstenedione, 17-hydroxyprogesterone (17-OHP), progesterone, estradiol (E2), and sex hormone-binding globulin levels were measured in serum samples collected during the last pregnancy before EOC diagnosis. We used conditional logistic regression to estimate odds ratios (ORs) and 95% CIs. Associations between hormones and EOC differed with respect to tumor histology and invasiveness. Sex steroid concentrations were not associated with invasive serous tumors; however, doubling of testosterone and 17-OHP concentration was associated with approximately 40% increased risk of borderline serous tumors. A doubling of androgen concentrations was associated with a 50% increased risk of mucinous tumors. The risk of endometrioid tumors increased with higher E2 concentrations (OR: 1.89 (1.20-2.98)). This large prospective study in pregnant women supports a role of sex steroid hormones in the etiology of EOC arising in the ovaries.

Early stage primary bone lymphoma : a retrospective, multicenter rare cancer network (RCN) study

IntroductionLe lymphome primaire de l'os (LPO) représente moins de 1% de tous les lymphomes malins. Dans cette étude, nous avons évalué le profil de la maladie, les résultats thérapeutiques, et les facteurs pronostiques d'une série consécutive de patients atteints de LPO de stade I et II. Matériel et méthodeDans treize institutions du Réseau des Cancers Rares (Rare Cancer Network), 116 patients ont été traités pour un LPO entre 1987 et 2008, et sont l'objet de cette étude rétrospective. Quatre-vingt-sept patients ont subi une chimioradiothérapie (CXRT) sans (78), ou avec (9) une chirurgie, 15 ont bénéficié de radiothérapie (RT) sans (13), ou avec (2) chirurgie, 14 d'une chimiothérapie (CXT) sans (9), ou avec (5) chirurgie. La dose médiane de RT était de 40 Gy (4-60). Le nombre médian de cycles de CXT était de 6 (2-8). Le suivi médian était de 41 mois (6-242). RésultatsLe taux de réponse global à la fin du traitement était de 91% (74% de réponses complètes et 17% de réponses partielles). Une récidive locale ou une progression ont été observées chez 12 (10%) patients et une récidive systémique chez 17 (15%) patients. La survie globale, la survie spécifique, et le contrôle local à 5 ans ont été de 76%, 78% et 92%, respectivement. En analyse univariée (log-rank test), les facteurs pronostiques favorables pour la survie globale et la survie spécifique étaient: un indice pronostique international (IPI) inférieur ou égale à 1 (P = 0.009), un grade histologique élevé (P = 0.04), une CXRT (P = 0.05), une CXT (P = 0.0004), une réponse complète (P <0.0001), et une dose de supérieure à 40 Gy (p = 0.005). Concernant le contrôle local, seules la rémission complète et stade I ont été des facteurs favorables. En analyse multivariée, le score IPI, la dose de RT, la rémission complète, et la CXT ont influencé le résultat de façon indépendante en ce qui concerne la survie globale et la survie spécifique. La rémission complète a été le seul facteur prédictif pour le contrôle local. ConclusionCette étude multicentrique rétrospective confirme le bon pronostic du LPO de stade précoce traité par une combinaison de chimio-radiothérapie. Une dose de suffisant de radiothérapie et un nombre adéquat de cycles de chimiothérapie ont été suivis des résultats les plus favorables.

Lake dwellers occupation gap in Lake Geneva (France-Switzerland) possibly explained by an earthquake-mass movement-tsunami event during Early Bronze Age

High-resolution seismic and sediment core data from the 'Grand Lac' basin of Lake Geneva reveal traces of repeated slope instabilities with one main slide-evolved mass-flow (minimum volume 0.13 km3) that originated from the northern lateral slope of the lake near the city of Lausanne. Radiocarbon dating of organic remains sampled from the top of the main deposit gives an age interval of 1865-1608 BC. This date coincides with the age interval for a mass movement event described in the 'Petit Lac' basin of Lake Geneva (1872-1622 BC). Because multiple mass movements took place at the same time in different parts of the lake, we consider the most likely trigger mechanism to be a strong earthquake (Mw 6) that occurred in the period between 1872 and 1608 BC. Based on numerical simulations, we show the major deposit near Lausanne would have generated a tsunami with local wave heights of up to 6 m. The combined effects of the earthquake and the following tsunami provide a possible explanation for a gap in lake dwellers occupation along the shores of Lake Geneva revealed by dendrochronological dating of two palafitte archaeological sites.

Effects of an early intervention on maternal post-traumatic stress symptoms and the quality of mother-infant interaction: The case of preterm birth

Preterm birth may represent a traumatic situation for both parents and a stressful situation for the infant, potentially leading to difficulties in mother-infant relationships. This study aimed to investigate the impact of an early intervention on maternal posttraumatic stress symptoms, and on the quality of mother-infant interactions, in a sample of very preterm infants and their mothers. Half of the very preterm infants involved in the study (n=26) were randomly assigned to a 3-step early intervention program (at 33 and 42 weeks after conception and at 4 months' corrected age). Both groups of preterm infants (with and without intervention) were compared to a group of full-term infants. The impact of the intervention on maternal posttraumatic stress symptoms was assessed 42 weeks after conception and when the infants were 4 and 12 months of age. The impact of the intervention on the quality of mother-infant interactions was assessed when the infants were 4 months old. Results showed a lowering of mothers' posttraumatic stress symptoms between 42 weeks and 12 months in the group of preterm infants who received the intervention. Moreover, an enhancement in maternal sensitivity and infant cooperation during interactions was found at 4 months in the group with intervention. In the case of a preterm birth, an early intervention aimed at enhancing the quality of the mother-infant relationship can help to alleviate maternal post-traumatic stress symptoms and may have a positive impact on the quality of mother-infant interactions.

Transgenic reexpression of GLUT1 or GLUT2 in pancreatic beta cells rescues GLUT2-null mice from early death and restores normal glucose-stimulated insulin secretion.

GLUT2-null mice are hyperglycemic, hypoinsulinemic, hyperglucagonemic, and glycosuric and die within the first 3 weeks of life. Their endocrine pancreas shows a loss of first phase glucose-stimulated insulin secretion (GSIS) and inverse alpha to beta cell ratio. Here we show that reexpression by transgenesis of either GLUT1 or GLUT2 in the pancreatic beta cells of these mice allowed mouse survival and breeding. The rescued mice had normal-fed glycemia but fasted hypoglycemia, glycosuria, and an elevated glucagon to insulin ratio. Glucose tolerance was, however, normal. In vivo, insulin secretion assessed following hyperglycemic clamps was normal. In vitro, islet perifusion studies revealed that first phase of insulin secretion was restored as well by GLUT1 or GLUT2, and this was accompanied by normalization of the glucose utilization rate. The ratio of pancreatic insulin to glucagon and volume densities of alpha to beta cells were, however, not corrected. These data demonstrate that 1) reexpression of GLUT1 or GLUT2 in beta cells is sufficient to rescue GLUT2-null mice from lethality, 2) GLUT1 as well as GLUT2 can restore normal GSIS, 3) restoration of GSIS does not correct the abnormal composition of the endocrine pancreas. Thus, normal GSIS does not depend on transporter affinity but on the rate of uptake at stimulatory glucose concentrations.

Low latitude Paleocene to early Eocene radiolarian systematics, biochronology and paleoenvironmental analysis

Highly diverse radiolarian faunas of latest Maastrichtian to early Eocene age have been recovered from the low latitude realm in order to contribute to the clarification of radiolarian taxonomy, construct a zonation based on a discrete sequence of co-existence intervals of species ranging from the late Paleocene to early Eocene and to describe a rich low latitude latest Cretaceous to late Paleocene fauna. 225 samples of late Paleocene to early Eocene age have been collected from ODP Leg 171 B-Hole 1051 A (Blake Nose), DSDP Leg 43-Site 384 (Northwest Atlantic) and DSDP Leg 10-Sites 86, 94, 95, 96. Sequences consist of mainly pelagic oozes and chalks, with some clay and ash layers. A new imaging technique is devised to perform (in particular on topotypic material) both transmitted light microscopy and SEM imaging on individual radiolarian specimens. SEM precedes transmitted light imaging. Radiolarians are adhered to a cover slip (using nail varnish) which is secured to a stub using conductive levers. Specimens are then photographed in low vacuum (40-50Pa; 0.5mbar), which enables charge neutralization by ionized molecules of the chamber atmosphere. Thus gold coating is avoided and subsequently this allows transmitted light imaging to follow. The conductive levers are unscrewed and the cover slip is simply overturned and mounted with Canada balsam. In an attempt towards a post-Haeckelian classification, the initial spicule (Entactinaria), micro- or macrosphere (Spumellaria) and initial spicule and cephalis (Nassellaria) have been studied by slicing Entactinaria and Spumellaria, and by tilting Nassellaria in the SEM chamber. A new genus of the family Coccodiscidae is erected and Spongatractus HAECKEL is re-located to the subfamily Axopruinae. The biochronology has been carried out using the Unitary Association Method (Guex 1977, 1991). A database recording the occurrences of 112 species has been used to establish a succession of 22 Unitary Associations. Each association is correlated to chronostratigraphy via calcareous microfossils that were previously studied by other authors. The 22 UAs have been united into seven Unitary Associations Zones (UAZones) (JP10- JE4). The established zones permit to distinguish supplementary subdivisions within the existing zonation. The low-latitude Paleocene radiolarian zonation established by Sanfilippo and Nigrini (1998a) is incomplete due to the lack of radiolarian-bearing early Paleocene sediments. In order to contribute to the study of sparsely known low latitude early Paleocene faunas, 80 samples were taken from the highly siliceous Guayaquil Formation (Ecuador). The sequence consists of black cherts, shales, siliceous limestones and volcanic ash layers. The carbonate content increases up section. Age control is supplied by sporadic occurrences of silicified planktonic foraminifera casts. One Cretaceous zone and seven Paleocene zones have been identified. The existing zonation for the South Pacific can be applied to the early-early late Paleocene sequence, although certain marker species have significantly shorter ranges (notably Buryella foremanae and B. granulata). Despite missing marker species in the late Paleocene, faunal distribution correlates reasonably to the Low-Latitude zonation. An assemblage highly abundant in Lithomelissa, Lophophaena and Cycladophora in the upper RP6 zone (correlated by the presence of Pterocodon poculum, Circodiscus circularis, Pterocodon? sp. aff. P. tenellus and Stylotrochus nitidus) shows a close affinity to contemporaneous faunas reported from Site 1121, Campbell Plateau. Coupled with a high diatom abundance (notably Aulacodiscus spp. and Arachnoidiscus spp.), these faunas are interpreted as reflecting a period of enhanced biosiliceous productivity during the late Paleocene. The youngest sample is void of radiolarians, diatoms and sponge spicules yet contains many pyritized infaunal benthic foraminifera which are akin to the midway-type fauna. The presence of this fauna suggests deposition in a neritic environment. This is in contrast to the inferred bathyal slope depositional environment of the older Paleocene sediments and suggests a shoaling of the depositional environment which may be related to a coeval major accretionary event. RESUME DE LA THESE Des faunes de radiolaires de basses latitudes très diversifiées d'âge Maastrichtien terminal à Eocène inférieur, ont été étudiées afin de contribuer à la clarification de leur taxonomie, de construire une biozonation basée sur une séquence discrète d'intervalles de coexistence des espèces d'age Paléocène supérieur à Eocène inférieur et de décrire une riche faune de basse latitude allant du Crétacé terminal au Paléocène supérieur. L'étude de cette faune contribue particulièrement à la connaissance des insaisissables radiolaires de basses latitudes du Paléocène inférieur. 225 échantillons d'âge Paléocène supérieur à Eocène inférieur provenant des ODP Leg 171B-Site 1051A (Blake Nose), Leg DSDP 43-Site 384 (Atlantique Nord -Ouest) et des DSDP Leg 10 -Sites 86, 94, 95, 96, ont été étudiés. Ces séquences sont constituées principalement de « ooze » et de « chalks »pélagiques ainsi que de quelques niveaux de cendres et d'argiles. Une nouvelle technique d'imagerie a été conçue afin de pouvoir prendre conjointement des images en lumière transmise et au Microscope Electronique à Balayage (MEB) de spécimens individuels. Ceci à été particulièrement appliqué à l'étude des topotypes. L'imagerie MEB précède l'imagerie en lumière transmise. Les radiolaires sont collés sur une lame pour micropaléontologie (au moyen de vernis à ongles) qui est ensuite fixée à un porte-objet à l'aide de bras métalliques conducteurs. Les spécimens sont ensuite photographiés en vide partiel (40-50Pa; 0.5mbar), ce qui permet la neutralisation des charges électrostatiques dues à la présence de molécules ionisées dans l'atmosphère de la chambre d'observation. Ainsi la métallisation de l'échantillon avec de l'or n'est plus nécessaire et ceci permet l'observation ultérieure en lumière transmise. Les bras conducteurs sont ensuite dévissés et la lame est simplement retournée et immergée dans du baume du Canada. Dans une approche de classification post Haeckelienne, le spicule initial (Entactinaires), la micro- ou macro -sphère (Spumellaires) et le spicule initial et cephalis (Nassellaires) ont été étudiés. Ceci a nécessité le sectionnement d'Entactinaires et de Spumellaires, et de pivoter les Nassellaires dans la chambre d'observation du MEB. Un nouveau genre de la Famille des Coccodiscidae a été érigé et Spongatractus HAECKEL à été réassigné à la sous-famille des Axopruninae. L'analyse biostratigraphique à été effectuée à l'aide de la méthode des Associations Unitaires {Guex 1977, 1991). Une base de données enregistrant les présences de 112 espèces à été utilisée poux établir une succession de 22 Associations Unitaires. Chaque association est corrélée à la chronostratigraphie au moyen de microfossiles calcaires précédemment étudiés par d'autres auteurs. Les 22 UAs ont été combinées en sept Zones d'Associations Unitaires (UAZones) (JP10- JE4). Ces Zones permettent d'insérer des subdivisions supplémentaires dans la zonation actuelle. La zonation de basses latitudes du Paléocène établie par Sanfilippo et Nigrini (1998a) est incomplète due au manque de sédiments du Paléocène inférieur contenant des radiolaires. Afin de contribuer à l'étude des faunes peu connues des basses latitudes du Paléocène inférieur, 80 échantillons ont été prélevés d'une section siliceuse de la Formation de Guayaquil (Equateur). La séquence est composée de cherts noirs, de shales, de calcaires siliceux et de couches de cendres volcaniques. La fraction carbonatée augmente vers le haut de la section. Des contraintes chronologiques sont fournies par la présence sporadique de moules de foraminifères planctoniques. Une zone d'intervalles du Crétacé et sept du Paléocène ont été mises en évidence. Bien que certaines espèces marqueur ont des distributions remarquablement plus courtes (notamment Buryella foremanae et B. granulata), la zonation existante pour le Pacifique Sud est applicable à la séquence d'age Paléocène inférieure à Paléocène supérieur basal étudiée. Malgré l'absence d'espèces marqueur du Paléocène supérieur, la succession faunistique se corrèle raisonnablement avec la zonation pour les basses latitudes. Un assemblage contenant d'abondants représentant du genre Lithomelissa, Lophophaena et Cycladophora dans la zone RP6 (correlée par la présence de Pterocodon poculum, Circodiscus circularis, Pterocodon? sp. aff. P. tenellus et Stylotrochus nitidus) montre une grande similitude avec certaines faunes issues des hauts latitudes et d'age semblable décrites par Hollis (2002, Site 1121, Campbell Plateau). Ceci, en plus d'une abondance importante en diatomés (notamment Aulacodiscus spp. et Arachnoidiscus spp.) nous mènent à interpréter cette faune comme témoin d'un épisode de productivité biosiliceuse accrue dans le Paléocène supérieur. L'échantillon le plus jeune, dépourvu de radiolaires, de diatomés et de spicules d'éponge contient de nombreux foraminifères benthiques infaunaux pyritisés. Les espèces identifiées sont caractéristiques d'une faune de type midway. La présence de ces foraminifères suggère un environnement de type néritique. Ceci est en contraste avec l'environnement de pente bathyale caractérisent les sédiments sous-jacent. Cette séquence de diminution de la tranche d'eau peut être associée à un événement d'accrétion majeure. RESUME DE LA THESE (POUR LE GRAND PUBLIC) Les radiolaires constituent le groupe de plancton marin le plus divers et le plus largement répandu de l'enregistrement fossile. Un taux d'évolution rapide et une variation géographique considérable des populations font des radiolaires un outil de recherche sans égal pour la biostratigraphie et la paléocéanographie. Néanmoins, avant de pouvoir les utiliser comme outils de travail, il est essentiel d'établir une solide base taxonomique. L'étude des Radiolaires peut impliquer plusieurs techniques d'extraction, d'observation et d'imagerie qui sont dépendantes du degré d'altération diagénétique des spécimens. Le squelette initial, qu'il s'agisse d'un spicule initial (Entactinaria), d'une micro- ou macro -sphère (Spumellaria) ou d'un spicule initial et d'un cephalis (Nassellaria), est l'élément le plus constant au cours de l'évolution et devrait représenter le fondement de la systématique. Des échantillons provenant de carottes de basses latitudes du Deep Sea Drilling Project et de l' Ocean Drilling ont été étudiés. De nouvelles techniques d'imagerie et de sectionnement ont été développées sur des topotypes de radiolaires préservés en opale, dans le but d'étudier les caractéristiques de leur squelette initial qui n'étaient pas visibles dans leur illustration originale. Ceci aide entre autre à comparer des spécimens recristallisés en quartz, provenant de terrains accrétés, avec les holotypes en opale de la littérature. La distribution des espèces étudiés a fourni des données biostratigraphiques qui ont été compilées à l'aide de la méthode des Associations Unitaires (Guez 1977, 1991). Il s'agit d'un modèle mathématique déterministe conçu pour exploiter la totalité de l'assemblage plutôt que de se confiner à l'utilisation de taxons marqueurs individuels. Une séquence de 22 Associations Unitaires a été établie pour la période allant du Paléocène supérieur à l'Éocène inférieur. Chaque Association Unitaire a été corrélée à l'échelle de temps absolue à l'aide de microfossiles calcaires. Les 22 UAs ont été combinées en sept Zones d'Associations Unitaires (JP10- JE4). Ces Zones permettent d'insérer des subdivisions supplémentaires dans la zonation actuelle. Les radiolaires du Paléocène inférieur à moyen des basses latitudes sont rares. Les meilleures sections connues se trouvent dans les hautes latitudes (Nouvelle Zélande). Quelques assemblages épars ont été mentionnés par le passé en Californie, en Équateur et en Russie. Une séquence siliceuse de 190 mètres dans la Formation de Guayaquil (Équateur), s'étendant du Maastrichtien supérieur au Paléocène supérieur, a fourni des faunes relativement bien préservées. L'étude de ces faunes a permis de mettre en évidence la première séquence complète de radiolaires de basses latitudes dans le Paléocène inférieure. Huit zones allant du Crétacé terminal au Paléocène supérieur ont pu être appliqués et la présence de foraminifères planctoniques a fournie plusieurs points d'attache chronologiques. Dans le Paléocène supérieur, un riche assemblage contenant d'abondants diatomés et radiolaires ayant des similitudes faunistiques marquantes avec des assemblages de hautes latitudes de Nouvelle Zélande, témoigne d'un épisode de productivité biosiliceuse accrue pendant cette période. Étant donné que la pointe du continent sud-américain et l'Antarctique étaient plus proches au cours du Paléocène, ce phénomène peut être expliqué par le transport, le long de la côte ouest de l'Amérique du Sud, d'eaux riches en nutriments en provenance de l'Océan Antarctique. Suite à cet épisode, l'enregistrement en radiolaires est interrompu. Ceci peut être associé à des événements tectoniques régionaux qui ont eu pour effet de diminuer la tranche d'eau relative, rendant l'environnement plus favorable aux foraminifères benthiques qui sont abondamment présents dans l'échantillon le plus jeune de la séquence.

Summary of Early Triassic carbon isotope records

Much attention has been given to the negative d13C anomaly nearly coincident with the Permian-Triassic boundary. New data indicate a stepwise decline in d13C initiating before the Latest Permian extinction event followed by highly variable d13C values during the remaining Early Triassic. d13C values appear much less erratic as global metazoan diversity increased in the Middle Triassic. Given the previously unappreciated magnitude of isotopic change and the number of large d13C excursions that occurred during the Early Triassic, catastrophic mechanisms like methane release/bolide impact become less attractive to explain the Early Triassic carbon isotopic record as a whole.