5-Nitrofurans are synthetic antibacterial agents. In general, nitrofurans have been shown to be toxic and mutagenic to cultured mammalian cells and carcinogenic in rodents. The possibility that human exposure to nitrofurans may be causing genetic damage or cancer has stimulated research directed towards elucidating the metabolism and mechanism of action of these compounds. A comprehensive understanding of the molecular basis of nitrofuran action may also be useful for comprehending the mechanism of action of other aryl and heterocyclic nitro compounds. It is known that enzymatic reduction of nitrofurans to reactive but uncharacterized metabolites that damage DNA constitutes an important "activation" step in both bacteria and hypoxic mammalian cells. However, since the known mammalian enzymes having nitroreductase activity are reported to be strongly inhibited by molecular oxygen, the relation of reductive activation to the DNA-damaging effects of nitrofurans in intact animals or in aerobic cultured cells is unclear. In rodents the liver is a major site of nitrofuran reduction in vivo. Net reduction of 5-nitro-2-furaldehyde semicarbazone (nitrofurazone) by rat liver homogenate was found to be relatively insensitive to oxygen when compared to net nitroreduction by milk xanthine oxidase. Intermediates generated in the aerobic nitroreduction bound tightly and probably covalently to protein. The nitroreductase in the rat liver preparation was identified as xanthine oxidoreductase by its apparent MW, substrate specificity and inhibition by allopurinol. Xanthine oxidoreductase is known to function in vivo as xanthine dehydrogenase (D form) which is converted to xanthine oxidase (0 form) during purification and storage. The 0 form is considered to be the major cytosolic nitroreductase and its activity is strongly inhibited by oxygen in vitro. Net nitroreduction by the D form has not been studied previously. In the rat liver preparation the bulk of the aerobic nitroreductase activity was associated with the D form of xanthine oxidoreductase during chromatography on CM cellulose, heat conversion of D form to 0 form and chemical interconversion of D form to 0 form and back to D form. Thus, net reduction of nitrofurazone by xanthine dehydrogenase is considerably less sensitive to inhibition by oxygen than is net nitroreduction by rat liver or milk xanthine oxidase. The ability of xanthine dehydrogenase to reduce nitrofurazone aerobically to highly reactive species in vitro suggests that this enzyme may play a role in a nitroreductive process which contributes to the mutagenic and carcinogenic action of nitrofurans and other nitroheterocyclic and nitroaromatic compounds in vivo. On the other hand, the nitroreductase activity of xanthine dehydrogenase in non-target tissues may, in some cases, decrease the amount of nitrocompound available in target tissues and hence play a "protective" role. / Thesis / Master of Science (MSc)

Le fascia est un tissu conjonctif mou présent à plusieurs endroits dans le corps. Selon la littérature, le fascia pourrait jouer un rôle biomécanique au sein du système musculo-squelettique. On croit donc que la dégradation ou des lésions des fascias pourraient être la cause de certains troubles musculo-squelettiques. Il importe donc d'étudier la mécanobiologie de ce tissu in vivo, c'est-à-dire son évolution dans le temps en réponse aux stimuli mécaniques auxquels il est soumis. Pour ce faire, il est nécessaire de trouver un modèle biologique compatible à notre étude. Par le présent projet, on désire procéder à l'examen de la queue de rat comme modèle expérimental pour l'étude mécanobiologique du fascia in vivo. La queue de rat sera considérée comme un modèle expérimental valide si : (1) on démontre théoriquement et/ou expérimentalement qu'il contribue à la biomécanique de la queue; (2) il est possible d'influencer son évolution temporelle par l'application de chargements spécifiques; et (3) on peut identifier ou développer une technique d'analyse permettant d'évaluer cette évolution. L'investigation des deux premiers points a nécessité la modélisation mécanique de la queue de rat à l'aide du logiciel Adams/View. Afin de modéliser et paramétrer judicieusement les composantes de la queue de rat, on a donc : étudié exhaustivement l'anatomie de la queue de rat par la revue littéraire, la dissection et différentes techniques d'imagerie; effectué une revue littéraire sur les dernières avancées scientifiques sur le fascia de même que sur les propriétés mécaniques des différentes structures anatomiques (tissus) de la queue; programmé un traitement d'images pour évaluer l'aire transversale et le bras de levier des structures complexes; développé une méthodologie de tests pour la caractérisation des propriétés mécaniques de la peau et du fascia de la queue de rat. Deux points sur trois ont été validés au cours de ce projet. Le modèle de queue de rat a permis de valider qu'il serait possible de modifier les stimuli mécaniques auxquels le fascia est soumis par blocage et/ou déformation d'une articulation par un appareillage de type Ilizarov. De plus, l'élaboration des tests de traction sur le fascia a permis de confirmer la possibilité d'évaluer l'évolution du fascia en fonction des stimuli mécaniques auxquels il est imposé. En conclusion, le modèle ne démontre pas la contribution du fascia à la biomécanique de la queue puisqu'il ne modélisait que son apport en rigidité longitudinale. Par contre, la modélisation a apporté d'autres hypothèses à propos du rôle joué par le fascia. Un nouveau modèle testant son rôle en cisaillement et en rigidité radiale devra être créé. On conserve donc l'hypothèse que la queue de rat constitue un bon modèle pour l'étude mécanobiologique du fascia in vivo.

La neurotensine est un peptide découvert de manière fortuite en 1973 (Carraway et al., 1973). Dans le système nerveux, on la retrouve dans les zones impliquées dans le contrôle de la douleur (Dobner, 2005). Lorsqu'elle est injectée en intrathécal et en supraspinal elle exerce un effet analgésique en douleur aiguë (Clineschmidt et al., 1977; Kalivas et al., 1982; Urban et al., 1993). Plus récemment, son effet analgésique en intrathécal dans un modèle de douleur tonique a été démontré (Roussy et al., 2008). Le mécanisme proposé pour cette analgésie est qu'elle initierait un contrôle inhibiteur descendant qui inhiberait la transmission des stimuli nociceptifs périphériques (Dobner, 2006). Jusqu'à maintenant, son effet n'a pas été étudié en douleur neuropathique. La douleur neuropathique est une douleur chronique initiée ou causée par une lésion primaire du système nerveux. Plus [de] 3.75 million d'Américains en sont atteints (Chong et al., 2003) et malheureusement, il existe un nombre limité de médicaments efficaces pour cette affliction. Il existe plusieurs modèles animaux de douleur neuropathique chez le rat. Le modèle le plus largement reconnu est le modèle de constriction chronique du nerf sciatique (Bennett et al., 1988). À ce jour, 3 récepteurs lui ont été identifiés. NTR1 et NTR2 sont des récepteurs à sept domaines transmembranaires couplés aux protéines G et sont tous deux impliqués dans l'analgésie induite par la NT (Buhler et al., 2005). NTR3 est une protéine totalement différente possédant un seul domaine transmembranaire et dont le rôle n'est pas encore connu (Kitabgi, 2002). Dans cette étude, nous avons utilisé le modèle de constriction chronique du sciatique chez le rat pour démontrer que la neurotensine ainsi que ses analogues peptidiques modifiés, NT69L et PD149163, à différentes doses exercent un effet analgésique en douleur neuropathique.La douleur a été quantifiée par le test de von Frey électronique automatique et le test plantaire. Le PD149163 est un agoniste spécifique du récepteur NTR1 et il a provoqué un effet analgésique marqué. Ces résultats démontrent donc pour la première fois l'implication du récepteur NTR1 dans l'inhibition de la douleur d'origine neuropathique.

No description available.

In the rat, before the establishment of the chorioallantoic placenta, the nutritional requirements of the post-implantation embryo, are met solely by the visceral yolk sac and therefore a study of its structure and functions is essential to a full understanding of early embryonic nutrition. A method has been developed for maintaining the rat visceral yolk sac in organ culture over a prolonged period, having first removed the embryo by microsurgery at 9.5 days or alternatively allowing it to die within its own amnion. The yolk sac continues to grow as a closed vesicle, and can reach a diameter of 2cm. The system has been called the 'giant' yolk sac. The 'giant' yolk sac and in vivo yolk sac have been compared using various criteria. A detailed morphological study was made, including a quantitative analysis of the vacuolar compartment. The endocytic capacity of both systems was studied using three different substrates; those used were 125I-polyvinylpyrrolidone (PVP), a non-degradable macromolecule, taken up in the fluid phase and accumulated within the yolk sac tissue, 125I-bovine serum albumin (BSA) taken up by adsorptive pinocytosis and digested within the lysosomes and 125I-IgG (and colloidal gold-IgG) taken up with great efficiency by specific receptor mediated endocytosis. Also a preliminary study of 14C-amino acid uptake was made. In many instances the 'giant' yolk sac functioned very similarly to the in vivo yolk sac and therefore seems an ideal model for studying transport across an epithelial sheet. It is particularly useful as its continuous epithelium separates the exocoelom from the external culture medium. The fluid maintained within the exocoelom of the 'giant' yolk sac should be an excellent source of processed histiotroph essential for embryonic nutrition during organogenesis. Experiments carried out indicate that some of the trophic factors necessary for growth are present in this fluid.

A handful of rat species are among the most pervasive mammal species across the globe, primarily because of their close relationship with humans. The processes involved in this relationship, commensalism, are described in detail. Two rat species, Rattus rattus and Rattus exulans, are the focus of this thesis and their biology and taxonomy are described and discussed. Their modern distributions are the direct result of some of the earliest and most extensive human migration events in human history. The archaeology of the Pacific and Indian Oceans is described and migration vectors and spheres of interaction are identified. These possible patterns of human migration and exchange networks provide testable hypotheses that can be investigated using the subject rat species as proxies for long distance human movement. Modern and archaeological tooth samples of R. exulans and modern samples of R. rattus are analysed using geometric morphometrics. The results reveal important aspects of human migration and differences between these species' biology. R. exulans was likely to have been transported out of Island Southeast Asia at a very early date. Human colonisation of the Pacific occurred in a series of complex pulses and pauses that are clearly reflected in the R. exulans data. For the first time it is possible to demonstrate, within one dataset, the multiple origins and directions of colonisation across the Pacific. The R. rattus data provides a striking comparison, showing very different results that allude to a different level of modern gene-­‐ flow and therefore a difference in behaviour and biology. The results provide a framework for comparison with future archaeological material. The results presented and hypotheses raised have immediate application to existing archaeological material and areas of interest. Further commensal species should be examined following similar lines of questioning as applied here.

Des métastases cérébrales vont se développer chez 10 à 30% des patients atteints de cancer. La radiothérapie fait partie des possibilités de traitement, et ceci même si les dommages induits au cerveau par des rayonnements ionisants sont potentiellement importants. Nous proposons l’utilisation de l’Imagerie par Résonance Magnétique fonctionnelle (IRMf) sur le rat pour mieux comprendre ces effets. Ce mémoire traite de la mise en place d’un tel protocole d’IRMf. Les principaux points abordés sont la préparation de l’animal, les différentes insultes et stimulations sensorielles possibles ainsi que la méthode d’acquisition. Notre protocole d’insulte hyperoxique permet de déceler des dommages physiques d’origine vasculaire suite à une intense irradiation dans le cerveau du rat. Toutefois, la même procédure associée à une stimulation mécanique de la patte arrière de l’animal n’amène pas de changement observable à l’IRMf sur un sujet sain. Malgré tout, ce type de stimulation induit une réponse respiratoire, même sous anesthésie d’isoflurane. Une telle méthode n’est donc pas adéquate à l’étude d’animaux anesthésiés, surtout ceux dont la réponse cérébrale pourra avoir été réduite par une irradiation. Quelques améliorations et modifications du protocole seraient possiblement à même de permettre une mesure reproductible de la réponse d’IRMf à une stimulation sensorielle. Le présent mémoire décrit les tentatives de mise en place d’une stimulation sensorielle donnant lieu à une activation IRMf reproductible et localisée. De plus, un protocole de traitement d’image adapté au petit animal ainsi qu’une implémentation de la méthode keyhole ont été mis en place. L’insulte hyperoxique et ses effets sur le cerveau de rat ont été explorés plus en détail.

L-glutamate (Glu) is the major excitatory neurotransmitter in the mammalian central nervous system. Monitoring extracellular Glu is critical to understanding Glu regulation to discriminate physiological and pathological roles. To overcome the limitations of previous in vivo extracellular Glu studies, we developed Glu selective microelectrode arrays with better spatial and temporal resolutions than commonly used techniques like microdialysis. We used these microelectrode arrays to characterize basal and potassium-evoked Glu neurotransmission in the normal rat brain. We then investigated disease-related Glu alterations in a rat model of Parkinson's disease and normal Glu regulation in young and aged rhesus monkeys. In the normal anesthetized rat striatum and frontal cortex, basal Glu was regulated by active release and uptake mechanisms, fully TTX-dependent, and measured at ~2 micromolar levels. Potassium-evoked Glu kinetics were fast, concentration-dependent, and rapidly reproducible at 15-20 seconds intervals. In the unilateral 6-hydroxydopamine-lesioned rat, there were significant bilateral increases in potassium-evoked Glu release in the striatum and frontal cortex compared to hemisphere-matched non-lesioned rats. Ipsilateral striatal effects may have been related to DA loss, while contralateral striatal effects and the bilateral frontal corticaleffects may have resulted from parkinsonian neurotransmitter changes or bilateral neuranatomical connectivity, especially in the cortex. There were also alterations in Glu kinetics in the nucleus accumbens in both non-lesioned and lesioned rats. With appropriate technological and methodological modifications, we successfully recorded normal Glu signaling in anesthetized nonhuman primates in the operating room. Fast potassium-evoked Glu signals were recorded in the motor cortex of all monkeys, and Glu ejections showed robust Glu uptake in the motor and frontal cortices of all monkeys. These findings are comparable to initial rat studies. Slow evoked Glu kinetics and high basal Glu levels with oscillatory behavior were recorded in the frontal cortex. The primary age-related differences between monkeys were the nearly ten-fold increases in the volumes of Glu ejected needed in the aged monkey to achieve amplitude-matched signals in the motor and frontal cortices and a decreased uptake rate in the motor cortex. Preliminary work with excised human tissue and future plans for patient-oriented research and clinical applications are discussed.

No description available.

3,4-(±)-Methylenedioxymethamphetamine (MDMA) is a synthetic amphetamine derivative commonly used as a recreational drug. Although the selectivity of MDMA for the serotonergic system in rat and humans is well established, the specific mechanism associated with MDMA-induced neurotoxicity is not fully understood. The long-term neurotoxicity of MDMA appears to be dependent upon systemic metabolism since direct administration of MDMA into the brain fails to reproduce the neurotoxic effects seen following peripheral administration, indicating that the parent compound alone is unlikely to be responsible for the neurotoxicity. MDMA is O-demethylenated to the catechol metabolite N-methyl-α-methyldopamine (N-Me-α-MeDA) and N-demethylated to MDA by cytochrome (s) P450 (CYP450). Thioether (glutathione and N-acetylcysteine) metabolites of N-Me-α-MeDA and α-MeDA are neurotoxic and can be found in rat brain following s.c. injection of MDMA. Because multidose administration of MDMA is typical of drug intake during rave parties, we investigated the effects of multiple doses of MDMA on the concentration of neurotoxic thioether metabolites in rat brain. Administration of MDMA at 12-h intervals for a total of four injections led to a significant accumulation of the N-Me-α-MeDA thioether metabolites in striatal dialysate. In contrast, acute release of 5-HT concentrations was decreased. Since isoenzymes of the CYP2D subfamily (30% metabolism), and the CYP2B or CYP3A1 isoforms, catalyze the low and high KM O-demethylenation reactions, respectively, we subsequently examined the potential role of CYP2D1 in both a genetic and pharmacological model. The data is consistent with the hypothesis that systemic metabolism of MDMA contributes to MDMA-induced serotonergic neurotoxicity via the 20) generation of reactive metabolites. In both the genetic and pharmacological models of CYP2D1 deficiency, attenuation of MDMA-mediated decreases in brain 5-HT concentrations were in the same range (30-40%). Finally, we examined the contribution of various transporters using genetic and pharmacological models to investigate the mechanisms regulating the concentration of thioether metabolites in MDMA neurotoxicity. The data suggest that by regulating various transporters and brain concentrations of the neurotoxic thioether metabolites of MDMA, may subsequently modulate the degree of neurotoxicity. However, further studies are necessary to understand the precise mechanism by which Mrp’s and Oat1 transporters modulate MDMA-neurotoxicity. Taken together, these studies are consistent with the view that neurotoxicity of MDMA requires systemic metabolism to form α-MeDA and N-Me-α- MeDA by CYP2D6. Therefore, It is likely that neurotoxicity is mediated by the formation of systemic neurotoxic metabolites.