Thesis (M.S.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 60-64). Also available on the World Wide Web.

Thesis (M. Sc.)--University of Canterbury, 2006. / Typescript (photocopy). Includes bibliographical references (p. 169-200). Also available via the World Wide Web.

The frontostriatal dopamine system modulates brain function and is affected by both genetic and environmental factors. Dysfunction of this system is associated with many pathological states, including schizophrenia. The enzyme catechol-O- methyltransferase (COMT) metabolises dopamine and its gene contains a polymorphism (Val¹⁵⁸Met) that affects enzyme activity. Delta-9- tetrahydrocannabinol (THC), the main psychoactive component of cannabis, has been suggested to interact with this polymorphism to increase the risk for psychosis and cognitive impairments. Dopaminergic mechanisms are a plausible candidate for mediating this interaction. I used microdialysis coupled with high performance liquid chromatography (HPLC) to examine the effects of THC on extracellular dopamine and its metabolites in the nucleus accumbens, dorsal striatum and medial prefrontal cortex (mPFC) in freely moving mice. Following acute COMT inhibition with tolcapone, THC increased extracellular dopamine levels in the nucleus accumbens in tolcapone-, but not in vehicle-, treated mice. The introduction of the low activity Met allele into the COMT gene produced a highly specific, novel mouse model of the Val158Met polymorphism. In contrast to the effects of acute COMT inhibition, the Met allele protected against THC-induced changes in accumbal dopamine. No interactive neurochemical effects were observed in the dorsal striatum (pharmacological and genetic study) or in a preliminary study of the mPFC (genetic study only). On a progressive ratio task measuring motivational salience, the direction of the interactive effect between COMT genotype and THC differed between 2 independent cohorts and provided tentative leads that stress/arousal-dependent effects on COMT may have a confounding effect. My data provide evidence that COMT activity modulates the effect of THC on accumbal dopamine function, and suggest the mechanism through which this interaction is mediated differs between acute and lifelong reduction in COMT activity. Through the interactive effect on the dopaminergic system, the data provide a potential mechanism for the reported interaction between COMT and cannabis/THC in determining psychosis risk and cognitive impairments.

Utilizing longitudinal panel data from Youth In Transition Project, the Person-Environment fit (P-E Fit) theory and its specific application to the area of delinquency and aggression was investigated longitudinally. Analysis of Covariance Structure Technique (LISREL) was used to address the issues of multi-dimensionality, stability, measurement of total P-E fit and to test the proposed delinquency model. The relationships between P-E fit, psychological strain, and delinquency were tested both cross-sectionally and longitudinally . The student sub-group (those respondents who stayed in school after high school) and the working sub-group (those who went to work after high school) were tested separately. P-E fit had significant negative effect on both psychological strain and delinquency in most of the cross-sectional models. Similar results were obtained in three of the longitudinal models also . The evidence from longitudinal models tended to support the idea that the causal flow of the relationship between P-E fit, psychological strain and delinquency to be from P-E fit to both psychological strain and delinquency. The longitudinal and cross sectional relationship between P-E fit, psychological strain, and delinquency were more pronounced among the working sub-group than the student sub-group of the sample population. P-E fit tended to be quite stable during the high school years and subject to noticeable change when the transition was made to work or college environments.

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In recent years, screening approaches known as two-step methods have been proposed to detect gene-environment interactions for genome-wide association studies (GWAS). Genetic and environmental factors are believed to affect disease outcome as well as various quantitative traits such as height and blood pressure. The performance of the two-step methods has not been demonstrated in the quantitative trait setting. This thesis examines the method proposed by Wang and Abbott (2008) for generating genotyped markers in linkage disequilibrium (LD) and takes this approach in simulating data pertaining to a quantitative trait. The simulation results demonstrate that the two-step methods maintain type I error and have power to detect the quantitative trait locus. In this setting, the EG method (Murcray et al., 2009) is influenced by the strength and structure of the gene-environment dependency, the sample type, and the disease model. As such, the power of the EG method can fluctuate depending on the type of data while the DG method (Kooperberg and LeBlanc, 2008) remains fairly robust across a wide range of scenarios. The performance of the combined two-step approaches (EDGE (Gauderman et al., 2013) and H2 (Murcray et al., 2011) methods) tends to favour the more powerful underlying method. The power of the EDGE method can be improved if DG and EG demonstrates similar power while the H2 method can be made more powerful by choosing the appropriate parameters. / Thesis / Master of Science (MSc)

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No description available.

Due to increased environmental stewardship and fertilizer prices, there is increased interest in using legume mixes in perennial croplands. The objective of this study was to compare quantitative genetic parameters and quantitative trait loci (QTLs) associated with intermediate wheatgrass (Thinopyrum intermedium) when grown in 1) a non-competitive spaced environment, 2) a polyculture with alfalfa (Medicago sativa), and 3) a monoculture with crested wheatgrass (Agropyron desertorum). Traits evaluated include plant growth characteristics (Zadok’s maturity, height, and tiller count), biomass, and forage nutritive value (CP, NDF, ADF, ADL, IVTD, NDFD, NFC, ME, RFQ). A linkage map comprised of 3568 single nucleotide polymorphisms in 21 linkage groups corresponding to 21 homologous chromosome pairs of both parents was used to identify QTLs and QTL x environment interactions (QxE) based on trait averages for each genotype in each environment. Significant genotype x environment interactions were detected for biomass, NDF etc. A total of 26 QTLs were identified, including 6 MASS, 2 TILE, 2 TICR, 1 ZAMA, 1 CP, 3 NDF, 2 ADF, 3 IVTD, and 5 NDFD. A subset of 7 QTLs showed significant QxE interaction. These results indicate that breeders need to evaluate plants in polyculture or swards if these are the intended crop management systems.

Les apports de l’aquaculture représentent aujourd’hui la moitié des produits aquatiques destinés à la consommation humaine. La composition de l’aliment artificiel utilisé en élevage piscicole a fortement évolué ces 30 dernières années. Les produits d’origine végétale terrestre y ont progressivement remplacé les farines et les huiles de poisson lorsque les stocks de pêche minotière utilisés pour leur production se sont rapprochés de leur limite d’exploitation. Toutefois, l’usage exclusif de ces farines et huiles végétales conduit encore à la dégradation de la croissance et de la santé des salmonidés et des poissons marins. Dans le même temps, l’amélioration génétique en pisciculture a permis, depuis 1980, des gains importants sur les caractères de croissance, de santé et de qualité et dispose aujourd’hui de méthodes pour étudier les conséquences de cette profonde transition alimentaire sur les populations actuelles et futures issues des programmes de sélection. En privilégiant la comparaison entre un aliment composé de produits d’origine marine (M) et un aliment entièrement constitué de produits d’origine végétale terrestre (PB), nous avons étudié les voies d’amélioration génétique chez deux espèces majeures du secteur français : le bar européen (Dicentrarchus labrax) et la truite arc-en-ciel (Oncorhynchus mykiss). Dans ce contexte, l’objectif était en particulier d’estimer les héritabilités des caractères d’intérêt et l’importance des interactions génotype-aliment, qui sont à l’origine de reclassement des génotypes en fonction l’aliment utilisé.Les essais réalisés ont confirmés l’effet de la substitution totale sur la croissance et la composition lipidique chez les deux espèces et sur la survie chez le bar. Les héritabilités estimées des poissons nourris avec l’aliment PB pour le poids, la croissance et les paramètres de transformation technologique (rendement carcasse, viscères, tête, filet) sont hautes chez la truite (respectivement 0,69 ; 0,65 ; 0,21-0,58) et modérées chez le bar (respectivement 0,18 et 0,11). Pour ces caractères, les interactions génotype-aliment sont modérées et les corrélations génétiques estimées entre les aliments M et PB sont élevées chez la truite (respectivement 0,90 ; 0,92 ; 0,65-0,96) et chez le bar (respectivement 0,96 ; 0,64). Les gains génétique attendus sont plus élevés avec l’aliment PB qu’avec l’aliment M chez la truite tandis qu’ils sont plus faible chez le bar. La mesure de la réponse à la sélection pour une aptitude à grandir et à survivre en utilisant l’aliment PB a confirmé des gains élevés pour le poids (+35%), la survie (+15,1%) et la biomasse produite (+54,4%) sans impact sur les paramètres de transformation technologique (carcasse, viscères, tête, filet). Les essais réalisés ont confirmé que cette meilleure aptitude était liée à des modifications de l’activité du métabolisme lipidique mais n’ont pas permis de conclure à des liens avec l’ingéré et efficacité alimentaire.Les plus fortes mortalités et le plus faible poids des lots PB durant les jours qui suivent les premières prises alimentaires ainsi que les reclassements familiaux plus importants en début de cycle de vie indiquent que les stades précoces ont une place prépondérante dans l’utilisation de l’aliment d’origine végétale aux niveaux phénotypique et génétique et devront être approfondis.A la vue des résultats obtenus, il semble donc possible d’exploiter la grande plasticité de certaines espèces de poissons pour concevoir des programmes de sélection prenant en compte l’évolution des environnements de production. La limitation mondiale des ressources alimentaire confronte les élevages à des modifications rapides de l’aliment et l’amélioration génétique des cheptels peut aider à faciliter ces transitions alimentaires. / Nowadays, aquaculture contributes to half of the aquatic products intended for human consumption. The composition of aquafeeds strongly evolved in the past 30 years. Terrestrial plant-based products gradually replace fish meal and fish oil, as fish stocks used for their production reach their exploitation limit. However, the use of diets containing vegetable oils and meals only still lead to growth and health degradation in salmonids and marine fish.Besides, breeding programmes in fish farming allowed strong genetic progress, since 1980, on growth, health and quality traits. An important issue for fish breeders is now to understand the consequences of this deep dietary change on the current and future selected populations and to adapt breeding programs accordingly.Focusing on the comparison between two experimental diets, a diet containing marine products (M) and a diet containing only plant-based products, (PB), we investigated the possible impact of the dietary changes on the organization and the objectives of breeding programs in two major species of the French sector: the European sea bass (Dicentrarchus labrax) and the rainbow trout (Oncorhynchus mykiss). A key objective was to estimate the heritabilities of the main traits of economic interest and the importance of genotype by diet interactions, which may cause genotypes rerankings according to diet used. We also sought the potential origin of the variability for ability to use the PB diet and proposed scenarii for evolution of breeding programs.The trials confirmed that substitution of marine ingredients by vegetal ones decreased growth and lipid composition in both species, as well as survival in sea bass and, to a lesser extent in rainbow trout. The estimates of heritabilities for weight, growth and processing traits (carcass viscera, head and filet yields only measured on trout) when fish were fed with the PB diet were high in rainbow trout (respectively 0.69; 0.65; 0.21-0.58) and weak in sea bass (respectively 0.18 and 0.11). In trout and sea bass, these estimates were respectively higher and lower than those obtained when fish were fed the M diet. For these traits, genotype by diet interactions were moderate and the genetic correlations between the M and PB diets were variable in trout (respectively 0.67-0.90; 0.92; 0.65-0.96) and sea bass (respectively 0.51-0.96; 0.64) but could involve important family rerankings according to the period of survey. According to heritability estimates, expected genetic gains would be higher in trout for fish fed the PB diet than for fish fed the M diet when they would be weaker in sea bass. In trout, the measurement of the response to one generation of selection for the ability to grow and survive when fed the PB diet confirmed the results, and provided high genetic gains for body weight (+35%), survival rate (+15,1%) and produced biomass (+ 54,4%) without any impact on the processing traits (carcass, viscera, head, filet). We showed that this ability was associated to modifications in the lipid metabolism activities but could not establish links with feed intake or feed efficiency from our trials. Higher mortality rate and lower body weight in the PB batches during the first days following distribution of PB diet as well as stronger family rerankings in early steps of the survey indicate than the early stages play a key role in the use of plant-based diet at both phenotypic and genetic levels. Further insights dedicated to these particular stages are strongly needed.Based on present results, it seems possible to exploit the great plasticity of some fish species to conceive breeding programs taking into account a changing dietary environment. Facing the world limitation in food resources, genetic improvement of fish livestock can be a useful lever to facilitate dietary transitions.