Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
The status of ethnic minority has been reported to be associated with a tendency toward sedentary behavior. The Guadeloupean population is composed of Afro-Caribbeans and an Asian Indian minority. This study examined the association of ethnicity and physical activity on the island. Energy expenditures (EE), energy intakes (EI), and macronutrient intakes of 122 Guadeloupean workers (60 Indians and 62 controls) were assessed by three consecutive 24-h recalls. Two-way analyses of variance were conducted to test the hypothesis of an effect of ethnicity, taking the potential effect of sex into account, on these variables. Asian Indians reported lower EE (P=0.011), lower EE/EI ratios (P=0.001), and lower physical activity (P=0.003) than their Afro-Carribean counterparts. Their food intakes were not different in terms of EI or macronutrient intake. No sex × ethnicity interactions were significant. The present study reports a tendency toward physical inactivity in Asian Indians of Guadeloupe associated with EI similar to those of controls. Sedentary lifestyles and energetic imbalances are well-documented risk factors for several diseases, including type 2 diabetes and cardiovascular disease, both major public health concerns in Guadeloupe. Strategies to prevent sedentary lifestyles should be considered for Asian Indian Guadeloupeans.
ISSN: 0905-7188

hal-00706161
https://hal.univ-antilles.fr/hal-00706161
DOI : 10.1111/j.1600-0838.2007.00743.x

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
Cytochrome P450 aromatase (P450arom; aromatase) is a microsomal enzyme involved in the production of endogeneous sex steroids by converting testosterone into oestradiol. Aromatase is the product of the cyp19a1 gene and plays a crucial role in the sexual differentiation of the brain and in the regulation of reproductive functions. In the brain of mammals and birds, expression of cyp19a1 has been demonstrated in neuronal populations of the telencephalon and diencephalon. By contrast, a wealth of evidence established that, in teleost fishes, aromatase expression in the brain is restricted to radial glial cells. The present study investigated the precise neuroanatomical distribution of cyp19a1 mRNA during brain development in Xenopus laevis (late embryonic to juvenile stages). For this purpose, we used in situ hybridisation alone or combined with the detection of a proliferative (proliferating cell nuclear antigen), glial (brain lipid binding protein, Vimentin) or neuronal (acetylated tubulin; HuC/D; NeuroβTubulin) markers. We provide evidence that cyp19a1 expression in the brain is initiated from the very early larval stage and remains strongly detected until the juvenile and adult stages. At all stages analysed, we found the highest expression of cyp19a1 in the preoptic area and the hypothalamus compared to the rest of the brain. In these two brain regions, cyp19a1-positive cells were never detected in the ventricular layers. Indeed, no co-labelling could be observed with radial glial (brain lipid binding protein, Vimentin) or dividing progenitors (proliferating cell nuclear antigen) markers. By contrast, cyp19a1-positive cells perfectly matched with the distribution of post-mitotic neurones as shown by the use of specific markers (HuC/D, acetylated tubulin and NeuroβTubulin). These data suggest that, similar to that found in other tetrapods, aromatase in the brain of amphibians is found in post-mitotic neurones and not in radial glia as reported in teleosts.
ISSN: 0953-8194

hal-00994513
https://hal-univ-rennes1.archives-ouvertes.fr/hal-00994513
DOI : 10.1111/jne.12142
PUBMED : 24612124

Éditeur(s) : HAL CCSD Public Library of Science
Résumé : International audience
The capacity of testicular somatic cells to promote and sustain germ cell differentiation is largely regulated by sexual steroids and notably androgens. In fish species the importance of androgens is emphasized by their ability to induce sex reversal of the developing fries and to trigger spermatogenesis. Here we studied the influence of androgens on testicular gene expression in trout testis using microarrays. Following treatment of immature males with physiological doses of testosterone or 11-ketotestosterone, 418 genes that exhibit changes in expression were identified. Interestingly, the activity of testosterone appeared stronger than that of 11-ketotestosterone. Expression profiles of responsive genes throughout testis development and in isolated germ cells confirmed androgens to mainly affect gene expression in somatic cells. Furthermore, specific clusters of genes that exhibit regulation coincidently with changes in the natural circulating levels of androgens during the reproductive cycle were highlighted, reinforcing the physiological significance of these data. Among somatic genes, a phylogenetic footprinting study identified putative androgen response elements within the proximal promoter regions of 42 potential direct androgen target genes. Finally, androgens were also found to alter the germ line towards meiotic expression profiles, supporting the hypothesis of a role for the somatic responsive genes in driving germ cell fate. This study significantly increases our understanding of molecular pathways regulated by androgens in vertebrates. The highly cyclic testicular development in trout together with functions associated with regulated genes reveal potential mechanisms for androgen actions in tubule formation, steroid production, germ cell development and sperm secretion.
ISSN: 1932-6203

inserm-00825763
http://www.hal.inserm.fr/inserm-00825763
http://www.hal.inserm.fr/inserm-00825763/document
http://www.hal.inserm.fr/inserm-00825763/file/Rolland_et_al.pdf
DOI : 10.1371/journal.pone.0053302

Éditeur(s) : Actes de colloques. Ifremer. Brest [ACTES COLLOQ. IFREMER.]. 1985
Résumé : Sexual differentiation of the marine leatherback turtle is sensitive to temperature. Incubation of eggs below 29 degree C results in 100% males, whereas incubationa bove 30 degree C results in 100% potential females at hatching. Therefore, the threshold temperature lies between 29 and 30 degree C as has been found for other marine turtles (Caretta caretta, Chelonia mydas ). Among hatchlings from natural nests in French Guiana, 10% were males, 20% were potential females and 70% had an intermediate phenotype. The sand temperature at 60 cm of depth, near one nest, was recorded and was found to vary between 29 and 30 degree C during the presumed thermosensitive period. These results will be useful to marine turtle hatcheries which seek to manipulate sex ratios among their neonates.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/1983/acte-1241.pdf
http://archimer.ifremer.fr/doc/00000/1241/

Éditeur(s) : HAL CCSD
Résumé : International audience
Spermatogenesis is a highly sophisticated process involved in the transmission of genetic heritage. It includes halving ploidy, repackaging of the chromatin for transport, and the equipment of developing spermatids and eventually spermatozoa with the advanced apparatus (e.g., tightly packed mitochondrial sheat in the mid piece, elongating of the tail, reduction of cytoplasmic volume) to elicit motility once they reach the epididymis. Mammalian spermatogenesis is divided into three phases. In the first the primitive germ cells or spermatogonia undergo a series of mitotic divisions. In the second the spermatocytes undergo two consecutive divisions in meiosis to produce haploid spermatids. In the third the spermatids differentiate into spermatozoa in a process called spermiogenesis. Paracrine, autocrine, juxtacrine, and endocrine pathways all contribute to the regulation of the process. The array of structural elements and chemical factors modulating somatic and germ cell activity is such that the network linking the various cellular activities during spermatogenesis is unimaginably complex. Over the past two decades, advances in genomics have greatly improved our knowledge of spermatogenesis, by identifying numerous genes essential for the development of functional male gametes. Large-scale analyses of testicular function have deepened our insight into normal and pathological spermatogenesis. Progress in genome sequencing and microarray technology have been exploited for genome-wide expression studies, leading to the identification of hundreds of genes differentially expressed within the testis. However, although proteomics has now come of age, the proteomics-based investigation of spermatogenesis remains in its infancy. Here, we review the state-of-the-art of large-scale proteomic analyses of spermatogenesis, from germ cell development during sex determination to spermatogenesis in the adult. Indeed, a few laboratories have undertaken differential protein profiling expression studies and/or systematic analyses of testicular proteomes in entire organs or isolated cells from various species. We consider the pros and cons of proteomics for studying the testicular germ cell gene expression program. Finally, we address the use of protein datasets, through integrative genomics (i.e., combining genomics, transcriptomics, and proteomics), bioinformatics, and modelling.
Systems Biology in Reproductive Medicine

hal-00877749
https://hal.archives-ouvertes.fr/hal-00877749
DOI : 10.3109/19396368.2012.691943
PUBMED : 22788530

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Recent research has linked early life exposure to selective serotonin reuptake inhibitor medications (SSRIs) to modifications of social behaviors in children. Serotonin is a key regulator of neurodevelopment, social behaviors and mental health, and with the growing use of SSRIs to treat maternal affective disorders during the perinatal period, questions have been raised about the benefits and risks of perinatal SSRI exposure on the developing child. This review will highlight how perinatal SSRIs affect maternal care and neurodevelopmental outcomes related to social affiliative behaviors in offspring; such as play behaviors, social interactions, reproductive behaviors, and maternal care of the next generation. We will also review how early life exposure to SSRIs can alter related neurobiology, and the epigenome. Both clinical research and findings from animal models will be discussed. Understanding the impact of perinatal SSRIs on neurobehavioral outcomes will improve the health and well-being of subsequent generations.
ISSN: 0149-7634

hal-01619303
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01619303
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01619303/document
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01619303/file/Perinatal%20selective%20serotonin%20reuptake%20inhibitor%20medication_revised.pdf
DOI : 10.1016/j.neubiorev.2017.04.023

Éditeur(s) : HAL CCSD Society for the Study of Reproduction
Résumé : International audience
Mammalian spermatogenesis is a complex and highly orchestrated combination of processes in which male germline proliferation and differentiation result in the production of mature spermatozoa. If recent genome-wide studies have contributed to the in-depth analysis of the male germline protein-encoding transcriptome, little effort has yet been devoted to the systematic identification of novel unannotated transcribed regions expressed during mammalian spermatogenesis. We report high-resolution expression profiling of male germ cells in rat, using next-generation sequencing technology and highly enriched testicular cell populations. Among 20 424 high-confidence transcripts reconstructed, we defined a stringent set of 1419 long multi-exonic unannotated transcripts expressed in the testis (testis-expressed unannotated transcripts [TUTs]). TUTs were divided into 7 groups with different expression patterns. Most TUTs share many of the characteristics of vertebrate long noncoding RNAs (lncRNAs). We also markedly reinforced the finding that TUTs and known lncRNAs accumulate during the meiotic and postmeiotic stages of spermatogenesis in mammals and that X-linked meiotic TUTs do not escape the silencing effects of meiotic sex chromosome inactivation. Importantly, we discovered that TUTs and known lncRNAs with a peak expression during meiosis define a distinct class of noncoding transcripts that exhibit exons twice as long as those of other transcripts. Our study provides new insights in transcriptional profiling of the male germline and represents a high-quality resource for novel loci expressed during spermatogenesis that significantly contributes to rat genome annotation.
ISSN: 0006-3363

hal-01063924
https://hal.archives-ouvertes.fr/hal-01063924
DOI : 10.1095/biolreprod.114.118166
PUBMED : 24740603

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Perinatal exposure to endocrine-disrupting chemicals may affect thyroid hormones homeostasis and impair brain development. Chlordecone, an organochlorine insecticide widely used in the French West Indies has known estrogenic and progestin properties, but no data is available, human or animal, on its action on thyroid hormone system. Our aim was to evaluate the impact of perinatal exposure to chlordecone on the thyroid hormone system of a sample of infants from the Timoun mother-child cohort in Guadeloupe and their further neurodevelopment. Chlordecone was measured in cord blood and breast milk samples. Thyroid stimulating hormone (TSH), free tri-iodothyronine (FT3), free thyroxine (FT4) were determined in child blood at 3 months (n=111). Toddlers were further assessed at 18 months using an adapted version of the Ages and Stages Questionnaire (ASQ). Cord chlordecone was associated with an increase in TSH in boys, whereas postnatal exposure was associated with a decrease in FT3 overall, and in FT4 among girls. Higher TSH level at 3 months was positively associated with the ASQ score of fine motor development at 18 months among boys, but TSH did not modify the association between prenatal chlordecone exposure and poorer ASQ fine motor score. Perinatal exposure to chlordecone may affect TSH and thyroid hormone levels at 3 months, differently according to the sex of the infant. This disruption however did not appear to intervene in the pathway between prenatal chlordecone exposure and fine motor child development.
ISSN: 0013-9351

hal-01134317
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01134317
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01134317/document
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01134317/file/Perinatal%20exposure%20to%20chlordecone_accepted.pdf
PUBMED : 25747818

Éditeur(s) : HAL CCSD Taylor & Francis (Routledge)
Résumé : International audience
Introduction: The aims of this literature review were to characterize the communications presented during six Association for Research on Intervention in Sport (ARIS) French-speaking congresses from 2000 to 2010 and to compare the research trends between French and English research traditions. The definition of pedagogy is close to the notion of intervention and attempts to study, in an interacting or isolated way, three key components – the educator (professor, coach, teacher's educator), the participants (students, children, adults) and the curriculum/knowledge in specific contexts. The theoretical framework is centred on the social construction of the scientific knowledge. Method: All the communications of the six ARIS congresses (n ¼ 836), reflecting the multiple facets of educational research were analysed. The quantitative treatment of the data, with the assistance of Sphinx software, consisted of univariate (frequencies, percentages) and bi-variate (chi-square statistic) analyses to identify possible significant relations between variables such as the congress, country and sex of author(s), institution, and so on. Findings: The results highlight the commonalties and differences between French and English research about intervention/pedagogy. We notice the continuing expansion of the field of intervention/pedagogy in the Francophone and the Anglophone worlds. But the low participation of the practitioners shows how intricate it is to move educational research closer to everyday practice. The results show that the contexts studied within ARIS are mainly school physical education and teacher's education, then coaching and other contexts. The majority of studies are centred on one component of pedagogy, but rarely on the interactions between the educators and the participants. The Francophone research is essentially descriptive and heuristic, using mostly qualitative methods (interviews and observations). This orientation of Francophone studies towards heuristic research seems to contrast with Anglophone research, even though qualitative research has recently come to dominate. Conclusion: The ARIS researchers have a common object of study (intervention/ pedagogy), share the same ideas and aims, learn how to do it better as they interact regularly and develop a shared repertoire of knowledge, theories and methods. We see here signs of an undeniable wealth of knowledge and the combination of different theories and methods leading to a better understanding of educational phenomena.
ISSN: 1740-8989

hal-01620916
https://hal.univ-antilles.fr/hal-01620916
https://hal.univ-antilles.fr/hal-01620916/document
https://hal.univ-antilles.fr/hal-01620916/file/PESP%20MUSARD%26POGGI%20VA.pdf
DOI : 10.1080/17408989.2013.817008

Éditeur(s) : HAL CCSD Frontiers Media
Résumé : The disease, Heartwater, caused by the Anaplasmataceae E. ruminantium, represents a major problem for tropical livestock and wild ruminants. Up to now, no effective vaccine has been available due to a limited cross protection of vaccinal strains on field strains and a high genetic diversity of Ehrlichia ruminantium within geographical locations. To address this issue, we inferred the genetic diversity and population structure of 194 E. ruminantium isolates circulating worldwide using Multilocus Sequence Typing based on lipA, lipB, secY, sodB, and sucA genes. Phylogenetic trees and networks were generated using BEAST and SplitsTree, respectively, and recombination between the different genetic groups was tested using the PHI test for recombination. Our study reveals the repeated occurrence of recombination between E. ruminantium strains, suggesting that it may occur frequently in the genome and has likely played an important role in the maintenance of genetic diversity and the evolution of E. ruminantium. Despite the unclear phylogeny and phylogeography, E. ruminantium isolates are clustered into two main groups: Group 1 (West Africa) and a Group 2 (worldwide) which is represented by West, East, and Southern Africa, Indian Ocean, and Caribbean strains. Some sequence types are common between West Africa and Caribbean and between Southern Africa and Indian Ocean strains. These common sequence types highlight two main introduction events due to the movement of cattle: from West Africa to Caribbean and from Southern Africa to the Indian Ocean islands. Due to the long branch lengths between Group 1 and Group 2, and the propensity for recombination between these groups, it seems that the West African clusters of Subgroup 2 arrived there more recently than the original divergence of the two groups, possibly with the original waves of domesticated ruminants that spread across the African continent several thousand years ago.
ISSN: 2235-2988

hal-01594501
https://hal.archives-ouvertes.fr/hal-01594501
https://hal.archives-ouvertes.fr/hal-01594501/document
https://hal.archives-ouvertes.fr/hal-01594501/file/paper_MLST_ER_2016_%7B51027B58-C2C7-41C8-9746-BD8A9F387C87%7D.pdf
DOI : 10.3389/fcimb.2016.00111

Éditeur(s) : HAL CCSD
Résumé : International audience
Paracetamol and NSAIDs, in particular acetylsalicylic acid (aspirin) and ibuprofen, are among the most used and environmentally released pharmaceutical drugs. The differences in international trends in the sale and consumption of mild analgesics reflect differences in marketing, governmental policies, habits, accessibility, disease patterns and the age distribution of each population. Biomonitoring indicates ubiquitous and high human exposure to paracetamol and to salicylic acid, which is the main metabolite of acetylsalicylic acid. Furthermore, evidence suggests that analgesics can have endocrine disruptive properties capable of altering animal and human reproductive function from fetal life to adulthood in both sexes. Medical and public awareness about these health concerns should be increased, particularly among pregnant women.
Nature Reviews Endocrinology

hal-01359566
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01359566
DOI : 10.1038/nrendo.2016.55
PUBMED : 27150289

Éditeur(s) : HAL CCSD Taylor & Francis
Résumé : International audience
The pollination of the genus Arum (Araceae) is mainly achieved by deception, the floral odour mimicking the pollinator ovipositing site. In order to discover the sensory organs involved in this attraction, we have studied the antennae of five species of psychodine moth-flies (former Psychoda sensu lato=Psychodini), pollinators of Arum spp. The antennae of the five Psychodini reveal seven types of sensilla: multiporous tribranched sensilla basiconica (sensilla ascoidea), multiporous sensilla basiconica, multiporous sensilla coeloconica, multiporous sensilla auricillica, uniporous sensilla basiconica, aporous sensilla chaetica, aporous Böhm’s sensilla. Each species possesses three, five or six of these sensillum types. All the multiporous sensilla are probably olfactory receptors while the uniporous sensilla basiconica must possess a contact chemoreceptive function. The multiporous tribranched sensilla basiconica (s. ascoidea), present in all the species, are the best candidates for the reception of the odours given off by the ovipositing sites and the inflorescences of Arum. The multiporous sensilla basiconica and the multiporous sensilla coeloconica may be involved respectively as CO2 receptors or thermoreceptors. Psychoda phalaenoides, which is the main pollinator of A. maculatum, is the species which possesses the largest number of antennal sensilla. The sexual dimorphism, studied only in Psycha grisescens, as concerns the number of sensilla and the absence of a sensillum type which differ according to sex, is difficult to interpret.
ISSN: 0037-9271

hal-01096881
https://hal-agroparistech.archives-ouvertes.fr/hal-01096881

Résumé : Deux séries d'expérimentation ont été menées pour tester les performances en nurserie des deux microparticules mises au point dans le groupe IFREMER/FA/SANOFI : l'ACAL et le FRIPPAK FLAKES. Alors qu'en survie et en croissance en taille (longueur totale) aucune différence n'est mise en évidence, l'ACAL permet de produire des prégrossies de poids sec supérieur et nettement plus résistantes aux chocs de salinité que le FRIPPAK.

Droits : 1990 Ifremer
http://archimer.ifremer.fr/doc/00161/27209/25408.pdf
http://archimer.ifremer.fr/doc/00161/27209/

Éditeur(s) : HAL CCSD Lippincott, Williams & Wilkins
Résumé : International audience
BACKGROUND: Addressing vulnerability to heat-related mortality is a necessary step in the development of policies dictated by heat action plans. We aimed to provide a systematic assessment of the epidemiologic evidence regarding vulnerability to heat-related mortality. METHODS: Studies assessing the association between high ambient temperature or heat waves and mortality among different subgroups and published between January 1980 and August 2014 were selected. Estimates of association for all the included subgroups were extracted. We assessed the presence of heterogeneous effects between subgroups conducting Cochran Q tests. We conducted random effect meta-analyses of ratios of relative risks (RRR) for high ambient temperature studies. We performed random effects meta-regression analyses to investigate factors associated with the magnitude of the RRR. RESULTS: Sixty-one studies were included. Using the Cochran Q test, we consistently found evidence of vulnerability for the elderly ages extgreater85 years. We found a pooled RRR of 0.99 (95% confidence interval [CI] = 0.97, 1.01) for male sex, 1.02 (95% CI = 1.01, 1.03) for age extgreater65 years, 1.04 (95% CI = 1.02, 1.07) for age extgreater75 years, 1.03 (95% CI = 1.01, 1.05) for low individual socioeconomic status (SES), and 1.01 (95% CI = 0.99, 1.02) for low ecologic SES. CONCLUSIONS: We found strongest evidence of heat-related vulnerability for the elderly ages extgreater65 and extgreater75 years and low SES groups (at the individual level). Studies are needed to clarify if other subgroups (e.g., children, people living alone) are also vulnerable to heat to inform public health programs
ISSN: 1044-3983

hal-01197347
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01197347
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01197347/document
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01197347/file/Vulnerability%20to%20Heat-related%20Mortality%20A%20Systematic%20Review%2C%20Meta-analysis%2C%20and%20Meta-regression%20Analysis..pdf
DOI : 10.1097/EDE.0000000000000375

Résumé : La tribologie est définie comme la science qui étudie les phénomènes de frottement, d’usure et de lubrification. Elle intervient à chaque fois que deux surfaces sont en mouvement relatif l’une par rapport à l’autre. On la rencontre donc principalement dans les moteurs, les instruments de coupe, les assemblages mécaniques etc. Le frottement et l’usure sont les causes principales des pertes de performances et de durabilité des systèmes. L’usure coute 3 % du PIB en France et on estime que 10 % à 30 % de l’énergie produite dans le monde est consommée par frottement, c’est dire l’importance que porte le monde industriel à cette science.C'est la lubrification qui a pour rôle de minimiser le frottement et de protéger les surfaces de l'usure. Il existe différents régimes de lubrification, cependant les travaux effectués au cours de cette thèse de doctorat s’intéressent exclusivement au régime de lubrification limite. Dans ce régime de lubrification, l’épaisseur du film de lubrifiant est du même ordre de grandeur que la hauteur des aspérités des surfaces en contact et le frottement et l'usure des surfaces peuvent être très sévères. La stratégie mise en place pour lutter contre ces phénomènes consiste à ajouter des additifs à l'huile lubrifiante, qui formeront au cours du frottement un film protecteur (le tribofilm). Il apparait donc primordial de bien caractériser ces tribofilms afin de mieux comprendre les mécanismes de réduction de frottement et de l’usure, qui restent encore à ce jour mal connus.Les nanotechnologies permettent aujourd'hui d'apporter un nouvel éclairage sur cette problématique et nous les avons mises à profit pour étudier le comportement mécanique des tribofilms à l’échelle nanométrique.L’objectif de ce travail est de comprendre les processus de réduction de frottement observés à l’échelle macroscopique lorsque des particules de composés lamellaires sont associées à un liquide de faible viscosité. Les tribofilms étudiés sont formés à partir de trois composés lamellaires différents, le graphite, le thiophosphate de nickel NiPS3 et le bisulfure de molybdène MoS2. Pour ces trois composés, deux types de tribofilms ont été étudiés : ceux formés à partir des particules seules (les tribofilms secs) et ceux formés en présence de liquide (les tribofilms éther).L’analyse des propriétés tribologiques mesurées à macro et nano échelle, nous ont permis de mieux comprendre la contribution des effets individuels et collectifs sur les mécanismes réducteurs de frottement. Ces expériences ont permis de mettre en évidence que la réduction du coefficient de frottement observée à macro-échelle n'est pas due à la nanostructuration des tribofilms ni à une baisse des interactions entre les feuillets mais plutôt à un effet collectif des particules et du liquide.
Tribology is the science of friction phenomena, wear and lubrication. It takes part every time two surfaces are in relative motion. It performs meanly in engine and mechanical systems. Friction and wear are the mean reasons of loose of performance and durability of mechanical systems. Wear costs 3% of the GDP in France and about 10% to 30% of the produced energy in the world is consumed by friction.The aim of lubrication is to reduce friction and protect the surface against wear. There are four different types of lubrication regimes but this study is focused on the boundary regime. In this regime, lubricant thickness is of the same order of the magnitude of the sliding surfaces roughness, leading to a high-level of friction and wear. Additives are added to the lubricating base oil, in order to build a protecting tribofilm. Characterization of the tribofilms appears essential to better understand the friction and wear reduction mechanisms.Nanotechnology allows to bring a new insight on this issue through the study of the mechanical behavior of the tribofilms at nanoscale.The aim of this work is to better understand the process of the friction reduction observed at macroscale when lamellar particles are associated to a low viscosity liquid. The tribofilms are formed from three different lamellar compounds, graphite, nickel thiophosphate NiPS3 and molybdenum disulfide MoS2. Two different kinds of tribofilms are studied: those formed with the solids particles only (dry tribofilms) and those formed in presence of liquid (wet tribofilms).The analyses of the tribological properties measured at nanoscale allow us to better understand the contribution of the individual and collective effects on friction reduction mechanims. We show that the reduction of the friction coefficient observed at macroscale is not related to the surface nanostructuration of the tribofilms neither to the decrease of the interaction energy between the sliding surfaces, but rather to collective effects of the liquid and the particles in the contact.

http://www.theses.fr/2014AGUY0706/document