L'inhibition de réponse joue un rôle majeur dans le contrôle cognitif. Mais les relations entre activité cérébrale et comportement sont particulièrement difficiles à appréhender puisque la fonction est précisément destinée à prévenir tout comportement observable… Dans une première partie, nous proposons une revue de questions mettant en évidence la nécessité d'utiliser des méthodes psychophysiques adaptées. Nous proposons également une analyse systémique des travaux utilisant l'électroencéphalographie, méthode largement privilégiée pour sonder la dynamique des mécanismes inhibiteurs. Dans une seconde partie, nous mettons en œuvre ces propositions dans le cadre d'une étude combinée EEG/IRMf. Grâce à des méthodes avancées de traitement du signal EEG, nous suggérons la mise en jeu de mécanismes automatiques, non sélectifs, d'inhibition de réponse dès lors que le contexte événementiel est incertain. Il reposerait sur la pré-activation d'une circuiterie auto-inhibitrice dans le complexe moteur supplémentaire, implémenté par un large réseau médial frontopariétal. Dans les troisième et quatrième parties, nous montrons le rôle majeur de cette fonction dans d'autres processus cognitifs et illustrons les conséquences cliniques de son dysfonctionnement. Nous montrons en particulier que l'impulsivité n'est pas la seule expression des troubles du contrôle inhibiteur. La difficulté à initier une action constituerait, dans la maladie de Parkinson, une conséquence directe de ce dysfonctionnement. L'implication d'une dérégulation du système noradrénergique et de l'activité du noyau sous-thalamique dans l'occurrence du trouble est suggérée, et les perspectives thérapeutiques discutées / Response inhibition plays a major role in cognitive control. Understanding these mechanisms is essential because their dysfunctions may cause symptoms in many psychiatric and neurological diseases. The relationship between brain activity and behavior are particularly difficult to understand because the function of interest is specifically intended to prevent any observable behavior… In the first part, we propose a review of issues highlighting the need for a new theoretical model and adapted psychophysical methods. We also provide systematic analysis of studies using electroencephalography, widely preferred method for probing the dynamics of inhibitory mechanisms. Convergently, the review calls for revisiting both acquisition methods and processing methods of EEG signal used in conventional studies. In the second part, we implement these proposals by combining advanced treatment methods of EEG signal (blind source separation, analysis test by test, spectral analysis in the sources, location) and comparing these results with the fMRI data. We reveal the involvement of automatic and nonselective inhibitory mechanisms, when the context is uncertain. A large medial frontoparietal network would ensure the implementation. The involvement of an automatic behavior (when the environment becomes predictable) would require a top-down control that deactivates in advance the excitability of the self-inhibitory circuitry of the SMC. In the third and fourth sections, we show the key role of this function in other cognitive processes and illustrate the clinical consequences of its dysfunction. We show in particular that the difficulty in initiating an action (akinesia) would, in Parkinson’s disease, a direct consequence of this dysfunction. The involvement of the noradrenergic system and the activity of the subthalamic nucleus in the occurrence of the disorder are suggested, and therapeutic perspectives discussed

Yaku'amide A shows a unique inhibitory profile against a series of 39 human cancer cell lines (JFCR39). In our efforts to synthesize yaku'amide A, we have optimized our regioselective base-free aminohydroxylation method with a series of nitrogen sources, developed a chiral reagent-mediated aminohydroxylation strategy and chemoselective deprotections of the resulting aminohydroxylation product, and explored a stereospecific E2 dehydration and O-N acyl transfer sequence. In addition, we have prepared the right-hand tetrapeptide and the NTA subunit. For our bulky α,β-dehydroamino acids project, we have developed strategies to incorporate α,β-dehydroamino acids such as ΔVal and ΔEnv into small synthetic peptides via Solid Phase Peptide Synthesis (SPPS). We have also prepared two analogues of a monomeric helical peptide with 13 residues.

The extensive and sometimes incorrect and noncompliant use of various types of antimicrobial agents has accelerated the development of antimicrobial resistance (AMR). In fact, AMR has become one of the greatest global threat to human health in this era. The broad-spectrum antibiotics aminoglycosides (AGs) display excellent potency against most Gram-negative bacteria, mycobacteria, and some Gram-positive bacteria, such as Staphylococcus aureus. The AG antibiotics amikacin, gentamicin, kanamycin, and tobramycin are still commonly prescribed in the U.S.A. for the treatment of serious infections. Unfortunately, bacteria evolve to acquire resistance to AGs via four different mechanisms: i) changing in membrane permeability to resist drugs from entering, ii) upregulating efflux pumps for active removal of intracellular AGs, iii) modifying the antimicrobial target(s) to prevent drugs binding to their targets, and iv) acquiring resistance enzymes to chemically inactivate the compounds. Amongst all, the acquisition of resistance enzymes, AG-modifying enzymes (AMEs), is the most common resistance mechanism identified. Depending on the chemistry each enzyme catalyzes, AMEs can be further divided into AG N-acetyltransferases (AACs), AG O-phosphotransferases (APHs), and AG O-nucleotidyltransferases. To overcome AME-related resistance, we need to better understand these resistance enzymes and further seek ways to either escape or inhibit their actions. In this dissertation, I summarized my efforts to characterize the AAC(6') domain and its mutant enzymes from a bifunctional AME, AAC(6')-Ie/APH(2")-Ia as well as another common AME, APH(3')-IIa. I also explained my attempt to inhibit the action of various AAC enzymes using metal salts. In an effort to explore the current resistance epidemic, I evaluated the resistance against carbapenem and AG antibiotics and the correlation between the resistance profiles and the AME genes in a collection of 122 Pseudomonas aeruginosa clinical isolates obtained from the University of Kentucky Hospital System. Besides tackling the resistance mechanisms in bacteria, I have also attempted to explore a new antifungal option by repurposing an existing antipsychotic drug, bromperidol, and a panel of its derivatives into a combination therapy with the azole antifungals against a variety of pathogenic yeasts and filamentous fungi.

Thesis (M.Sc. (Biochemistry)) -- University of Limpopo, 2013 / Diabetes mellitus is one of the fast growing chronic metabolic disorders throughout the world. It has become a life threatening disease and health burden. So far it can only be managed with commercial therapeutic agents, proper diet and exercise. People particularly from developing countries use medicinal plants to treat this condition. According to WHO, about 80% of the population in developing countries are dependable on medicinal plants. This prompted many researchers to explore the effectiveness and safety of these plants. In the current study ten medicinal plants were randomly chosen, screened for antidiabetic activity by testing their ability to inhibit α-amylase and α-glucosidase enzymes. The plants were tested using in vitro assays. The finely powdered leaves of each plant were extracted with hexane, chloroform, acetone and ethyl acetate. Phytoconstituents of each plant extracts were analyzed using both qualitative and quantitative methods. All plant extracts tested positive for phenols, flavonoids and all negative for starch. Their compounds were better separated in the TEA mobile system on the TLC plates. All plant extracts had more of total phenolics ranging between 0.1-400 GAE/mg than total flavonoids and condensed tannins. Antioxidant activity of the plant extracts was tested quantitatively at various concentrations using DPPH. Most plant extracts were able to scavenge the radicals produced by DPPH at highest concentration of 2.5 mg/mℓ. Not all plant extracts with the highest number of total phenolics had the highest antioxidant activity. For antidiabetic in vitro assays, plant extracts inhibited various percentages of both α-amylase and α-glucosidase activity at concentrations ranging between 0.019- 2.5 mg/mℓ. The best overall activity against both enzymes was observed in acetone and ethyl acetate plant extracts. Cassia abbreviata and Helinus integrifolius were even more active than acarbose which was used as positive control. These plant extracts inhibited both the enzymes in a dose dependent and non-competitive manner. Seeing that both extracts of C. abbreviata and H. integrifolius were consistent when inhibiting both enzymes, they were further evaluated for their effect on glucose uptake by the C2C12 muscle and H-II-4-E liver cells. All the plant extracts tested were able to increase glucose uptake in the muscle cells. However optimal increase was seen in the liver cells when treated with 250 µg/mℓ of acetone and ethyl acetate extracts of C. abbreviata. The cytotoxicity effects of both acetone and ethyl acetate of C. abbreviata and H. integrifolius was tested using the xCelligence system on RAW 264.7 cells. Different cell indexes were obtained after treating the cells with different concentrations (0.05,0.1 and 0.25 mg/mℓ) of each plant extracts respectively. The system was run for three days but the toxic effects of plant extracts were analyzed for the first ten hours. The results obtained shows that cell index decreased as the concentration of the plant extracts was increased. All the plant extracts were less toxic as compared to positive control, Actinomycin D. The leaves of H. integrifolius were further exhaustively extracted with hexane, dichloromethane, acetone, ethyl acetate and methanol respectively. Since the DCM extracts yielded the highest mass in quantity, it was further used for isolation of active compounds. Column chromatography and bioassay guided fraction led to isolation of a mixture of triterpenes identified as α and β-amyrin. The structure was elucidated using nuclear magnetic resonance technique. The inhibitory capability of the isolated compound against α-amylase enzyme was less than the crude extract which inhibited more than 50% of the activity at a concentration of 1 mg/mℓ.Based on the enzymes assays and cell culture work it can be concluded that C. abbreviata and H. integrifolius species are the best inhibitors of carbohydrate digesting enzymes, and therefore be used to manage postprandial hyperglycemia in the people with type 2 diabetes. However more work still need to be conducted for further isolation of more active compounds.

ABSTRACT The morphological premalignant changes in prostate epithelium such as high grade prostatic intraepithelial neoplasia (HGPIN) precede invasive prostate cancer (PC) by several decades. The overall aim of this project was to identify patterns of gene expression in HGPIN and early PC which increase our understanding of the early biology of PC and identify genes and pathways that correlate with an aggressive phenotype. A comprehensive tissue cohort of premalignant prostate lesions was collected in a tissue microarray (TMA) platform that was utilised for high-throughput validation of target genes. Using this unique resource, the expression of the tumour suppressor gene PTEN was assessed using immunohistochemistry in an initial candidate gene approach based on mouse models implicating PTEN in carcinogenesis. No significant difference in expression of PTEN was detected in premalignant and benign epithelium. A transcript profiling approach was undertaken by integrating laser capture microdissection, linear RNA amplification and oligonucleotide microarrays to perform a screen of matched patient samples of normal, HGPIN and PC cells. The expression patterns of two genes encoding secreted proteins, neuropeptide Y (NPY) and macrophage inhibitory cytokine (MIC-1) were validated using immunohistochemistry on TMAs representing the progression model of early PC. Increased expression of these proteins in PC was confirmed to occur early in the disease process and altered expression of NPY and MIC-1 was associated with worse clinical outcome. Further analysis of global gene expression patterns using a structured network knowledge base identified a notable aberration in the expression of extracellular matrix and extracellular matrix associated proteins in HGPIN and provided novel evidence for the role of this class of molecules in the development of PC. In summary, contrary to current dogma based on work in animal models, altered PTEN expression is unlikely to represent an important event in the development of malignancy in the human prostate. In contrast, the expression patterns and prognostic value of NPY and MIC-1 in HGPIN support their further evaluation as biomarkers for the development and progression of PC. The aberrant expression of genes and networks of genes detected in HGPIN will assist in further identification of biological pathways which may be targeted in therapeutic strategies against the development and progression of PC.

<i>Staphylococcus aureus</i> is a ubiquitous organism causing world-wide morbidity and mortality. This species readily develops resistance to antimicrobial agents. Current dosing strategies are based, in part, on minimum inhibitory concentrations (MICs). This susceptibility test fails to detect the presence of first-step resistant mutants often present in large heterogeneous populations of infecting bacteria. Dosing strategies based on MIC results may, in fact, allow for the selective proliferation of resistant subpopulations. The mutant-prevention concentration (MPC) is the drug concentration at which all first-step resistant mutants will be eradicated along with the susceptible cells. Determination of the mutant-selection window (MSW) is possible using MIC and MPC data. When considered together with achievable drug concentrations in human bodily sites, the MSW helps determine which antimicrobials are likely to select for resistance. MIC and MPC testing on clinical isolates of methicillin-susceptible (MSSA) and -resistant (MRSA) S. aureus was performed. Characterization via the polymerase chain reaction, sequencing, and electron microscopy (EM) was done on selected organisms recovered from MPC studies (MPC-recovered). MIC and MPC testing was performed on organisms isolated sequentially from patients with recurring S. aureus infections. Pulsed field gel electrophoresis was performed on these sequential isolates. Based on the MIC and the MPC values, the most potent agents for systemic MSSA and MRSA infections are gemifloxacin and vancomycin, respectively. Re-testing MPC-recovered populations by the MIC showed increased MIC results compared to the parent populations. Macrolide-resistance genes were discovered in S. aureus MPC-recovered populations; in contrast, parental isolates lacked these resistance determinants. EM revealed an increase in cell wall thickness of a vancomycin MPC-recovered population compared to its parental population. Moxifloxacin and vancomycin had the lowest and narrowest MSWs for systemic MSSA and MRSA infections, respectively, compared to the other agents tested. Sequential isolates showed no change in MIC and MPC values. The data presented provides evidence for the application of the MPC test to S. aureus organisms. The MPC data is significant when determining appropriate dosing strategies aimed at preventing resistance.

Tradicionalmente, el concepto de función ejecutiva se ha utilizado para hacer referencia a un comportamiento adaptativo (Mesulam, 2002), que integra y combina habilidades cognitivas que están dirigidas a meta (Welsh, Friedman, y Spieker, 2005). Durante los últimos años se ha asistido a un creciente interés en el estudio de la función ejecutiva en la infancia y niñez (Garon, Bryson, y Smith, 2008). Sin embargo, su exploración ha estado limitada por las dificultades para diseñar tareas adaptadas al nivel de desarrollo de los niños. En general, estas tareas se fundamentan principalmente en el seguimiento de reglas verbales abstractas y analizan el control ejecutivo de los niños en base a sus errores directos. Por el contrario, nuestras tareas permiten la construcción de unas reglas de actuación específicas a partir de las dinámicas que se establecen en el proceso de resolución entre la información perceptiva y la información de la acción, siendo un aspecto fundamental el feedback directo que el sujeto recibe de sus acciones. Asimismo, nuestro diseño metodológico trata de minimizar el papel del lenguaje en la construcción y consecución de la meta. El objetivo general de nuestro estudio fue analizar el desarrollo de la función ejecutiva en niños pequeños en base a las dinámicas entre percepción-acción que se establecen en la resolución de una tarea y que ponen de manifiesto la capacidad del niño para manipular ambas fuentes de información. La muestra estuvo integrada por 150 sujetos de 2.5, 3.5 y 4.5 años de edad, a los que se les administraron tres tareas de distinta dificultad, consistente en la inserción de piezas en unos ejes. Los resultados de este estudio ponen de manifiesto que no sólo la edad guarda una estrecha relación con la habilidad para discernir el criterio adecuado y en concreto, los procesos de cambio y control inhibitorio, sino que la complejidad de la tarea desempeña un papel fundamental. Evidentemente, se producen importantes mejoras con la edad en esas capacidades, pero es realmente la comprensión de la naturaleza de la tarea la que parece desempeñar un papel muy importante en la "voluntad" del niño para querer seguir buscando cómo llegar a la resolución del conflicto. / Traditionally, the concept of executive function has been used to refer to appropriate behaviours (Mesulam, 2002), that integrate and combine cognitive abilities oriented to a goal (Welsh, Friedman, & Spieker, 2005). In last years, a growing interest in the study of executive function in infancy and childhood has developed (Garon, Bryson, & Smith, 2008). However, its study has been limited due to difficulties in designing tasks that are adapted to the subjects' developmental level. In general, these tasks are mainly based in following abstract, verbal rules and analyze executive control based on direct errors. In contrast to this sort of tasks, our tasks allowed the subjects to build their own rules from the dynamics established between perceptual and action information in the resolution process, so that the direct feedback that children received from their action is crucial. Moreover, our procedure tries to minimize the role of language during goal construction and attainment. The general aim of this study was analysing the development of executive function in young children through the dynamics between perception and action established in the resolution of a task. These will show children's ability to work with both information sources. 150 children (2.5, 3.5, and 4.5 years of age) participated in this study. They were asked to complete three different tasks with an increasing difficulty based on inserting wooden pieces in their axes. Results showed that not only age is related to the ability to discriminate the right criterion to solve the task, but also the processes of change, inhibitory control and task complexity are key questions. Obviously, there's an improvement with age in these abilities, but what seems to be the most relevant aspect in this sort of tasks is that children were able to understand the nature of the task and this contribute to their "willing" to keep looking for a solution to the problem.

<i>Staphylococcus aureus</i> is a ubiquitous organism causing world-wide morbidity and mortality. This species readily develops resistance to antimicrobial agents. Current dosing strategies are based, in part, on minimum inhibitory concentrations (MICs). This susceptibility test fails to detect the presence of first-step resistant mutants often present in large heterogeneous populations of infecting bacteria. Dosing strategies based on MIC results may, in fact, allow for the selective proliferation of resistant subpopulations. The mutant-prevention concentration (MPC) is the drug concentration at which all first-step resistant mutants will be eradicated along with the susceptible cells. Determination of the mutant-selection window (MSW) is possible using MIC and MPC data. When considered together with achievable drug concentrations in human bodily sites, the MSW helps determine which antimicrobials are likely to select for resistance. MIC and MPC testing on clinical isolates of methicillin-susceptible (MSSA) and -resistant (MRSA) S. aureus was performed. Characterization via the polymerase chain reaction, sequencing, and electron microscopy (EM) was done on selected organisms recovered from MPC studies (MPC-recovered). MIC and MPC testing was performed on organisms isolated sequentially from patients with recurring S. aureus infections. Pulsed field gel electrophoresis was performed on these sequential isolates. Based on the MIC and the MPC values, the most potent agents for systemic MSSA and MRSA infections are gemifloxacin and vancomycin, respectively. Re-testing MPC-recovered populations by the MIC showed increased MIC results compared to the parent populations. Macrolide-resistance genes were discovered in S. aureus MPC-recovered populations; in contrast, parental isolates lacked these resistance determinants. EM revealed an increase in cell wall thickness of a vancomycin MPC-recovered population compared to its parental population. Moxifloxacin and vancomycin had the lowest and narrowest MSWs for systemic MSSA and MRSA infections, respectively, compared to the other agents tested. Sequential isolates showed no change in MIC and MPC values. The data presented provides evidence for the application of the MPC test to S. aureus organisms. The MPC data is significant when determining appropriate dosing strategies aimed at preventing resistance.

Aquaculture is the fastest growing food industry in the world and it accounts for roughly half of the world's fish supply. The majority of global aquaculture production occurs in freshwater systems that are increasingly subject to multiple uses by different stakeholders. Given the overall scarcity of freshwater on a global scale, freshwater aquaculture will face increasing environmental constraints that will demand an ever better understanding of its potential impacts on the aquatic environment and human health. This thesis consists of a series of studies that, collectively, contribute to further our understanding on the effects of freshwater aquaculture effluents on aquatic ecosystems, on the effects and environmental safety of antibiotics used in freshwater aquaculture on aquatic bacterial communities and on the link between antibiotic pollution and antibiotic resistance. Chapter 2 reviews the effects of freshwater aquaculture effluents on stream ecosystems using land-based salmonid farms as a case study. In this chapter I discuss relevant considerations related to the temporal and spatial scales of effluent discharge and ecological effects that highlight the need to characterize the patterns of stressor discharge when assessing environmental impacts and designing ecological effects studies. I also discuss the potential role of multiple stressors - with an emphasis on veterinary medicines - in disrupting ecosystem structure and function. Overall, the critical analysis presented in this chapter indicates that further research on the effects of veterinary medicines using relevant exposure scenarios would significantly contribute to our understanding of their impact in relation to other effluent stressors. Chapter 3 is a general methods chapter that describes the stream microcosm system used to assess the effects of erythromycin thiocyanate (ERT) and florfenicol (FFC) on bacterial communities of stream biofilms. This chapter presents the results of preliminary experiments whose results provided relevant information on the overall operation of the microcosms and on the variability of major physical and biological variables. This information guided the experimental designs used to assess the effects of FFC and ERT on the bacterial community structure of stream biofilms. Chapter 4 presents the results of the experiment conducted to assess the effects of FFC on the bacterial community structure of developing biofilms. The objective was to assess changes in bacterial community structure along a gradient of FFC concentrations that could provide insight into the type and magnitude of effects that could be expected from episodic exposure of stream biofilms to FFC in headwater streams. At 10 and 20 days of biofilm development, bacterial community structure differentiated in a pattern consistent with the FFC concentration gradient and there was a positive relationship between bacterial richness and bacterial diversity with FFC concentration. At 15 days of biofilm development there was also a positive relationship between FFC concentration and the surface coverage of bacteria and extracellular polymeric substances. These trends declined as the biofilm developed a more complex architecture, in terms of thickness and in the surface coverage of algae. The results are consistent with an initial stimulatory effect of FFC on biofilm formation that triggered changes in bacterial community structure that were gradually compressed as the development of a complex biofilm architecture increased the relative importance of autogenic ecological processes. The results suggest that the co-occurrence of FFC with bacterial pathogens in effluents and wastewaters may favour their persistence in the environment by enhancing biofilm formation. Chapter 5 presents the results of the experiment conducted to assess the effects of ERT on the bacterial community structure of developing biofilms. Currently, Aquamycin® 100 - a Type A medicated article (i.e., Premix) containing 100 g ERT lb-1 and used to produce a Type C medicated feed - is a candidate drug for approval by the US FDA to control mortality associated with bacterial kidney disease in freshwater salmonids. The objective of this experiment was to assess the effects of ERT on the bacterial community structure of stream biofilms using an exposure period consistent with the 28-day treatment regime suggested for Aquamycin® 100. The results provide no evidence to suggest that a 30-day exposure to ERT concentrations in the range of 10 μg L-1 (i.e., 7.3 ± 3.9 μg L-1) would lead to changes in the bacterial community structure or overall bacterial abundance of stream biofilms, while they suggest that these effects may occur at concentrations in the range of 100 μg L-1 (i.e., 87.2 ± 31.1 μg L-1). Chapter 6 attempts to determine whether environmental concentrations of antibiotics and concentrations representing action limits used in environmental risk assessment may exert a selective pressure on clinically relevant bacteria in the environment. In this chapter I use bacterial inhibition as an assessment endpoint to link antibiotic selective pressures to the prevalence of resistance in bacterial populations. Species sensitivity distributions were derived for three antibiotics by fitting log-logistic models to endpoints calculated from minimum inhibitory concentration (MIC) distributions based on worldwide data collated by the European Committee on Antimicrobial Susceptibility Testing (EUCAST). Bacteria represented in these distributions were placed in a broader context by performing a brief phylogenetic analysis. The potentially affected fraction of bacterial genera at measured environmental concentrations of antibiotics and environmental risk assessment action limits was used as a proxy for antibiotic selective pressure. Measured environmental concentrations and environmental risk assessment action limits were also directly compared to wild-type cut-off values. Results suggest that measured environmental concentrations of antibiotics and concentrations representing environmental risk assessment action limits are high enough to exert a selective pressure on clinically relevant bacteria that may lead to an increase in the prevalence of resistance. Chapter 7 presents the results of an exploratory analysis conducted to assess the abundance of class 1 integrons in stream biofilms exposed to FFC and ERT. There was no pattern in the abundance of intI1 genes consistent with the treatment of FFC and ERT, suggesting either the absence of gene cassettes involved in dealing with selective pressures caused by these antibiotics or that the concentrations tested were below those required to give them a selective advantage. Chapter 8 is a brief general discussion that brings together the findings of the thesis and makes suggestions for future research. Key areas identified for future research include assessing in further detail the stimulatory effect of FFC on biofilm formation in complex bacterial communities, the interactive effects of multiple aquaculture effluent stressors on aquatic bacterial communities and their potential effects on the development of antibiotic resistance, the fate of FFC and ERT in stream ecosystems, and further developing the analysis based on MIC distributions presented in chapter 6 to assess the potential effects of antibiotic pollution on the selection of multi-drug resistance in the environment.

No description available.