La facticité de la représentation

Ce texte est un accompagnement théorique de l'exposition Piscines, présentée au mois de juin 2008 à la Galerie des Arts Visuels de l'Université Laval. J'y traite de mon travail de création en explicitant les points théoriques et formels essentiels : la représentation et ses mécanismes, le factice et l'apport des traces du travail, le jeu et sa relation à l'art et au rite, et enfin, l'hétérotopie et son rapport à la problématique du fragment et de la totalité

Limited TTP supply affects telomere length regulation in a telomerase-independent fashion

An adequate supply of nucleotides is essential for DNA replication and DNA repair. Moreover, inhibition of TTP synthesis can cause cell death by a poorly characterized mechanism called thymine-less death. In the yeast Saccharomyces cerevisiae, the genes encoding thymidylate synthetase (CDC21) and thymidylate kinase (CDC8) are both essential for de novo TTP synthesis. The effects of temperature-sensitive mutations in these genes have been characterized and, curiously, the phenotypes displayed by cells harboring them include shortened telomeric repeat tracts. This finding raised the possibility that the enzyme telomerase is very sensitive to TTP-pools. We tested this possibility in vivo by assessing telomerase-dependent extension in situations of lowered TTP supply. The results show that the above-mentioned short telomere phenotype is not a consequence of an inability of telomerase to elongate telomeres when TTP synthesis is impaired. Moreover, this telomere shortening was abolished in cells harboring a mutation in DNA polymerase α. Previously, this same mutation was shown to affect the coordination between conventional replication and telomerase-mediated extension. These results thus re-emphasize the importance of the interplay between conventional replication and telomerase-mediated addition of telomeric repeats in telomere replication

Effect of Resistance Training on Hematological Blood Markers in Older Men and Women: A Pilot Study

The aim of this study was to examine the effects of resistance training on hematological blood markers in older individuals. Twenty-nine men and women participated to this study. Subjects were randomized in 2 groups: (1) control (n = 13) and (2) resistance training (n = 16). At baseline and after the intervention, subjects were submitted to a blood sample to determine their hematological profile (red blood cells, hemoglobin, hematocrit, platelets, leukocytes, neutrophils, lymphocytes, monocytes, mean corpuscular volume, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, red cell distribution width). At baseline, no difference was observed between groups. Moreover, we found no significant difference after the intervention on any of these markers. A 6-month resistance program in healthy older individuals seems to have no beneficial nor deleterious effects on hematological blood parameters. However, resistance training was well tolerated and should be recommended for other health purposes. Further studies are needed to confirm these results in a large population

Combined effects of red pepper and caffeine consumption on 24 h energy balance in subjects given free access to foods

The effects of red pepper and caffeine ingestion on energy and macronutrient balances were examined in eight Caucasian male subjects. All subjects participated in two randomly assigned conditions: control and experimental (red pepper and caffeine). After ingesting a standardized breakfast, subjects ate three meals ad libitum (lunch, dinner and breakfast) and snacks which were served approximately 2 h after the lunch and dinner over a 24 h period. Two appetizers (2×322 kJ with or without 3 g red pepper) were given before lunch and dinner, and a drink (decaffeinated coffee with or without 200 mg caffeine) was served at all meals and snacks except for the after-dinner snack. It is also important to note that on the experimental day, 8.6 and 7.2 g red pepper were also added to lunch and dinner respectively. Red pepper and caffeine consumption significantly reduced the cumulative ad libitum energy intake and increased energy expenditure. The mean difference in energy balance between both conditions was 4000 kJ/d. Moreover, the power spectral analysis of heart rate suggested that this effect of red pepper was associated with an increase in sympathetic:parasympathetic nervous system activity ratio. These results indicate that the consumption of red pepper and caffeine can induce a considerable change in energy balance when individuals are given free access to foods

Does cortisol moderate the environmental association between peer victimization and depression symptoms? a genetically informed twin study

Many youths who are victimized by peers suffer from depression symptoms. However, not all bullying victims become depressed and individuals’ biological sensitivity may play an important moderating role in this regard. In line with this notion, peer victimization has been associated with increased depressive symptoms in youth with higher basal cortisol secretion. It is unclear, however, whether this moderating effect of cortisol really concerns the environmental effect of peer victimization on depression. Indeed, genetic factors can also influence individuals’ environmental experiences, including peer victimization, and part of these genetic factors may be those associated with depression. Using a genetically informed design based on 159 monozygotic and 120 dizygotic twin pairs (52% girls) assessed at age 14 years, this study examined whether cortisol secretion moderates the environmental or the genetic association between peer victimization and depression symptoms. Salivary cortisol at awakening was obtained with buccal swabs during four school week days. Peer victimization and depression were assessed via self-reports. Cholesky modeling revealed that peer victimization was associated with depression symptoms via both genetic and environmental pathways. Moreover, the environmental association between peer victimization and depression symptoms steadily increased with increasing levels of morning cortisol. The genetic association between peer victimization and depression symptoms also varied, albeit less, as a function of individuals’ cortisol secretion. These findings support the hypothesis that peer victimization increases internalizing psychopathology mainly in youth with heightened biological reactivity to environmental conditions

Environmental influence of problematic social relationships on adolescents' daily cortisol secretion : a monozygotic twin-difference study

BACKGROUND: This study investigated the potential environmental effects of peer victimization and the quality of relationships with parents and friends on diurnal cortisol secretion in mid-adolescence. METHOD: This study used the monozygotic (MZ) twin-difference design to control for genetic effects and thus estimate the unique environmental influences on diurnal cortisol. Participants were 136 MZ twin pairs (74 female pairs) for whom cortisol was assessed four times per day over four collection days grouped in a 2-week period in grade 8 (mean age = 14.07 years). Participants also provided self-reports of peer victimization from grade 4 to grade 8 and of the relationship quality with the mother, father and best friend in grade 8. RESULTS: The expected pattern of diurnal cortisol secretion was observed, with high levels at awakening followed by an increase 30 min later and a progressive decrease subsequently. Controlling for a host of confounders, only within-twin pair differences in peer victimization and a problematic relationship with the mother were significantly linked to twin differences in diurnal cortisol secretion. Specifically, whereas a more problematic mother-child relationship was associated with morning cortisol secretion, peer victimization was linked to cortisol secretion later in the day (diurnal slope). CONCLUSIONS: Controlling for genetic influences and other confounders, stressful relationships with peers and the mother exert unique and time-specific environmental influences on the pattern of diurnal cortisol secretion in mid-adolescence

Effects of red pepper on appetite and energy intake

Two studies were conducted to investigate the effects of red pepper (capsaicin) on feeding behaviour and energy intake. In the first study, the effects of dietary red pepper added to high-fat (HF) and high-carbohydrate (HC) meals on subsequent energy and macronutrient intakes were examined in thirteen Japanese female subjects. After the ingestion of a standardized dinner on the previous evening, the subjects ate an experimental breakfast (1883 kJ) of one of the following four types: (1) HF; (2) HF and red pepper (10 g); (3) HC; (4) HC and red pepper. Ad libitum energy and macronutrient intakes were measured at lunch-time. The HC breakfast significantly reduced the desire to eat and hunger after breakfast. The addition of red pepper to the HC breakfast also significantly decreased the desire to eat and hunger before lunch. Differences in diet composition at breakfast time did not affect energy and macronutrient intakes at lunch-time. However, the addition of red pepper to the breakfast significantly decreased protein and fat intakes at lunch-time. In Study 2, the effects of a red-pepper appetizer on subsequent energy and macronutrient intakes were examined in ten Caucasian male subjects. After ingesting a standardized breakfast, the subjects took an experimental appetizer (644 kJ) at lunch-time of one of the following two types: (1) mixed diet and appetizer; (2) mixed diet and red-pepper (6 g) appetizer. The addition of red pepper to the appetizer significantly reduced the cumulative ad libitum energy and carbohydrate intakes during the rest of the lunch and in the snack served several hours later. Moreover, the power spectral analysis of heart rate revealed that this effect of red pepper was associated with an increase in the ratio sympathetic: parasympathetic nervous system activity. These results indicate that the ingestion of red pepper decreases appetite and subsequent protein and fat intakes in Japanese females and energy intake in Caucasian males. Moreover, this effect might be related to an increase in sympathetic nervous system activity in Caucasian males

Evidence of a unique and common genetic etiology between the CAR and the remaining part of the diurnal cycle : a study of 14 year-old twins

Introduction By and large, studies have reported moderate contributions of genetic factors to cortisol secreted in the early morning and even smaller estimates later in the day. In contrast, the cortisol awakening response (CAR) has shown much stronger heritability estimates, which prompted the hypothesis that the etiology of cortisol secretion may vary according to the time of day. A direct test of this possibility has, however, not yet been performed. Objective To describe the specific and common etiology of the CAR, awakening level and cortisol change from morning to evening in an age-homogenous sample of twin adolescents. Methods A total of 592 participants of the Québec Newborn Twin Study, a population-based 1995–1998 cohort of families with twins in Canada, have collected saliva at awakening, 30 min later, at the end of afternoon and in the evening over four collection days. Results Multivariate Cholesky models showed both specific and common sources of variance between the CAR, awakening and cortisol diurnal change. The CAR had the strongest heritability estimates, which, for the most part, did not overlap with the other indicators. Conversely, similar magnitudes of genetic and environmental contributions were detected at awakening and for diurnal change, which partially overlapped. Conclusion Our study unraveled differences between the latent etiologies of the CAR and the rest of the diurnal cycle, which may contribute to identify regulatory genes and environments and detangle how these indicators each relate to physical and mental health

The Quebec newborn twin study at 21

This paper is a revised and updated edition of a previous description of the Quebec Newborn Twin Study (QNTS), an ongoing prospective longitudinal follow-up of a birth cohort of twins born between 1995 and 1998 in the greater Montreal area, Québec, Canada. The goal of QNTS is to document individual differences in the cognitive, behavioral, and social-emotional aspects of developmental health across childhood, their early genetic and environmental determinants, as well as their putative role in later social-emotional adjustment, school, health, and occupational outcomes. A total of 662 families of twins were initially assessed when the twins were aged 6 months. These twins and their family were then followed regularly. QNTS now has 16 waves of data collected or planned, including 5 in preschool. Over the last 24 years, a broad range of physiological, cognitive, behavioral, school, and health phenotypes were documented longitudinally through multi-informant and multimethod measurements. QNTS also entails extended and detailed multilevel assessments of proximal (e.g., parenting behaviors, peer relationships) and distal (e.g., family income) features of the child’s environment. QNTS children and a subset of their parents have been genotyped, allowing for the computation of a variety of polygenic scores. This detailed longitudinal information makes QNTS uniquely suited for the study of the role of the early years and gene–environment transactions in development

Association between Abdominal Fat (DXA) and Its Subcomponents (CT Scan) before and after Weight Loss in Obese Postmenopausal Women: A MONET Study

Introduction. Subcutaneous fat (ScF) and visceral fat (VF) measurements using CT scan are expensive and may imply significant radiation doses. Cross-sectional studies using CT scan showed that ScF and VF are significantly correlated with abdominal fat measured by DXA (AF-DXA). The association has not been studied after a weight loss. Objective. To determine (1) the associations between AF-DXA and ScF and VF before and after weight loss and (2) the associations between their changes. Methods. 137 overweight/obese postmenopausal women were divided in two groups (1-caloric restriction or 2-caloric restriction + resistance training). AF was assessed using DXA and CT scan. Results. Correlations between AF-DXA and ScF (before: r = 0.87, after; r = 0.87; P < .01) and, AF-DXA and VF (before: r = 0.61, after; r = 0.69; P < .01) are not different before and after the weight loss. Correlations between delta AF-DXA and delta ScF (r = 0.72; P < .01) or delta VF (r = 0.51; P < .01) were found. Conclusion. The use of AF-DXA as a surrogate for VF after weight loss is questionable, but may be interesting for ScF