995 resultados para INDUCED RELAXATION


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Large amplitude oscillatory shear (LAOS) coupled with Fourier transform rheology (FTR) was used for the first time to characterize the large deformation behavior of selected bituminous binders at 20 C. Two polymer modified bitumens (PMB) containing recycled EVA and HDPE and two unmodified bitumens were tested with LAOS-FTR. The LAOS-FTR response of all binders was compared at same frequency, at same Deborah number (by tuning the frequency to the relaxation time of each binder) and at same phase shift angle d (by tuning the frequency to the one corresponding to d = 50 in the SAOS response of each sample). In all the approaches, LAOS-FTR results allowed to differentiate between all the nonlinear mechanical characteristics of the tested binders. All binders show LAOS-FTR patterns reminiscent from colloidal dispersions and emulsions. EVA PMB was less prone to strain-induced microstructural changes when compared to HDPE PMB which showed larger values of nonlinear FTR parameters for the range of shear strains tested in LAOS.

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Stress exposure triggers cognitive and behavioral impairments that influence decision-making processes. Decisions under a context of uncertainty require complex reward-prediction processes that are known to be mediated by the mesocorticolimbic dopamine (DA) system in brain areas sensitive to the deleterious effects of chronic stress, in particular the orbitofrontal cortex (OFC). Using a decision-making task, we show that chronic stress biases risk-based decision-making to safer behaviors. This decision-making pattern is associated with an increased activation of the lateral part of the OFC and with morphological changes in pyramidal neurons specifically recruited by this task. Additionally, stress exposure induces a hypodopaminergic status accompanied by increased mRNA levels of the dopamine receptor type 2 (Drd2) in the OFC; importantly, treatment with a D2/D3 agonist quinpirole reverts the shift to safer behaviors induced by stress on risky decision-making. These results suggest that the brain mechanisms related to risk-based decision-making are altered after chronic stress, but can be modulated by manipulation of dopaminergic transmission.

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Dissertação de mestrado em Ordenamento e Valorização de Recursos Geológicos

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Dissertação de mestrado em Genética Molecular

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The present work aims to contribute for the elucidation of the role of oxidative stress in the toxicity associated with the exposure of Pichia kudriavzevii to multi-metals (Cd, Pb and Zn). Cells of the non-conventional yeast P. kudriavzevii exposed for 6 h to the action of multi-metals accumulated intracellular reactive oxygen species (ROS), evaluated through the oxidation of the probe 2,7-dichlorodihydrofluorescein diacetate. A progressive loss of membrane integrity (monitored using propidium iodide) was observed in multi-metal-treated cells. The triggering of intracellular ROS accumulation preceded the loss of membrane integrity. These results suggest that the disruption of membrane integrity can be attributed to the oxidative stress. The exposure of yeast cells to single metal showed that, under the concentrations tested, Pb was the metal responsible for the induction of the oxidative stress. Yeast cells coexposed to an antioxidant (ascorbic acid) and multi-metals did not accumulate intracellular ROS, but loss proliferation capacity. Together, the data obtained indicated that intracellular ROS accumulation contributed to metal toxicity, namely for the disruption of membrane integrity of the yeast P. kudriavzevii. It was proposed that Pb toxicity (the metal responsible for the toxic symptoms under the conditions tested) result from the combination of an ionic mechanism and the intracellular ROS accumulation.

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Transparency document related to this article can be found online at http://dx.doi.org/10.1016/j.bbrc.2015.10.014

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OBJECTIVE: Doppler tissue imaging (DTI) enables the study of the velocity of contraction and relaxation of myocardial segments. We established standards for the peak velocity of the different myocardial segments of the left ventricle in systole and diastole, and correlated them with the electrocardiogram. METHODS: We studied 35 healthy individuals (27 were male) with ages ranging from 12 to 59 years (32.9 ± 10.6). Systolic and diastolic peak velocities were assessed by Doppler tissue imaging in 12 segments of the left ventricle, establishing their mean values and the temporal correlation with the cardiac cycle. RESULTS: The means (and standard deviation) of the peak velocities in the basal, medial, and apical regions (of the septal, anterior, lateral, and posterior left ventricle walls) were respectively, in cm/s, 7.35(1.64), 5.26(1.88), and 3.33(1.58) in systole and 10.56(2.34), 7.92(2.37), and 3.98(1.64) in diastole. The mean time in which systolic peak velocity was recorded was 131.59ms (±19.12ms), and diastolic was 459.18ms (±18.13ms) based on the peak of the R wave of the electrocardiogram. CONCLUSION: In healthy individuals, maximum left ventricle segment velocities decreased from the bases to the ventricular apex, with certain proportionality between contraction and relaxation (P<0.05). The use of Doppler tissue imaging may be very helpful in detecting early alterations in ventricular contraction and relaxation.

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Tese de Doutoramento em Ciência e Engenharia de Polímeros e Compósitos.

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OBJECTIVE: We determined the effects of losartan and PD 123319 (antagonists of the AT1 and AT2 angiotensin receptors, respectively), and [Sar¹, Ala8] ANG II (a relatively peptide antagonist of angiotensin receptors) injected into the paraventricular nucleus (PVN) on water and 3% NaCl intake, and the diuretic, natriuretic, and pressor effects induced by administration of angiotensin II (ANG II) into the medial septal area (MSA) of conscious rats. METHODS: Holtzman rats were used . Animals were anesthetized with tribromoethanol (20 mg) per 100 grams of body weight, ip. A stainless steel guide cannula was implanted into the MSA and PVN. All drugs were injected in 0.5-mul volumes for 10-15 seconds. Seven days after brain surgery, water and 3% NaCl intake, urine and sodium excretion, and arterial blood pressure were measured. RESULTS: Losartan (40 nmol) and [Sar¹, Ala8] ANG II (40 nmol) completely eliminated whereas PD 123319 (40 nmol) partially blocked the increase in water and sodium intake and the increase in arterial blood pressure induced by ANG II (10 nmol) injected into the MSA. The PVN administration of PD 123319 and [Sar¹, Ala8] ANG II blocked whereas losartan attenuated the diuresis and natriuresis induced by MSA administration of ANG II. CONCLUSION: MSA involvement with PVN on water and sodium homeostasis and arterial pressure modulation utilizing ANGII receptors is suggested.

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OBJECTIVE: To determine whether arginine vasopressin releases endothelium-derived nitric oxide (EDNO) from the epicardial coronary artery. METHODS: We studied segments of canine left circumflex coronary arteries suspended in organ chambers to measure isometric force. The coronary artery segments were contracted with prostaglandin F2alpha (2 x 10-6M) and exposed to a unique, strong arginine vasopressin concentration (10-6M) or titrated concentrations (10-9 a 10-5 M). RESULTS: The unique dose of arginine vasopressin concentration (10-6M) induced transient, but significant (p<0.05), relaxation in arterial segments with endothelium, and an increase, not significant, in tension in arteries without endothelium. Endothelium-dependent relaxation to arginine vasopressin was inhibited by Ng-monomethyl-L-arginine (L-NMMA, 10-5M) or N G-nitro-L-arginine (L-NOARG) (10-4M), 2 inhibitors of nitric oxide synthesis from L-arginine. Exogenous L-arginine (10-4M), but not D-arginine (10-4M), reversed the inhibitory effect of L-NMMA on vasopressin-mediated vasorelaxation. Endothelium dependent relaxation to vasopressin was also reversibly inhibited by the vasopressin V1-receptor blocker d(CH2)5Try(Me) arginine vasopressin (10-6M) (n=6, P<0.05). CONCLUSION: Vasopressin acts through V1 endothelial receptors to stimulate nitric oxide release from L-arginine.

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El objetivo principal de este proyecto es estudiar los mecanismos neurobiológicos involucrados en el proceso de sensibilización emocional inducido por la abstinencia a drogas de abuso o por la exposición a un estímulo estresante de caracteristicas incontrolables. El modelo animal de sensibilización a utilizar en este proyecto es la facilitación en la formación de memoria de miedo producida por dichos tratamientos. Nuestra hipótesis sugiere que este proceso es el resultado de un mecanismo desinhibitorio de las interneuronas GABAérgicas del complejo basolateral de la amigdala. Por lo tanto se proponen los siguientes experimentos: 1) El estudio del curso temporal del efecto facilitador sobre la formación de una nueva memoria de miedo luego de la abstinencia a drogas o la exposición a un estímulo estresante (inmovilización). 2) La evaluación de la liberación"in vivo" de dopamina del complejo basolateral de la amigdala durante la adquisición y la expresión de la memoria de miedo en animales previamente expuestos a la abstinencia o al estres. 3) El estudio de la infusión local de antagonistas de receptores dopaminérgicos en el complejo basolateral de la amígdala (BLA) o en el nucleo central de la amígdala (CeA) antes del estrés sobre la adquisición y la expresión de una memoria de miedo. 4) La determinación de la actividad de ERK 1/2 y CREB en el complejo basolateral de la amigdala o en el nucleo central de la amígdala durante la adquisición y la expresión de una memoria de miedo en animales abstinentes o estresados. 5)El estudio de la infusión local de inhibidores de la MEK 1/2 en el complejo basolateral de la amigdala o en el nucleo central de la amígdala antes del estrés sobre la adquisición y la expresión de una memoria de miedo. La facilitación para generar memorias de miedo podría ser un componente crítico del síndrome de abstinencia al etanol responsable de las altas tasas de recurrencia asociadas con el alcoholismo. Por lo tanto se investigará el efecto de la evocación de la memoria de miedo sobre la autoadministración de etanol utilizando un paradigma de libre elección entre agua y soluciones de concentración creciente de etanol en animales en abstinencia al etanol. Con el objeto de investigar si las propiedades reforzantes del etanol están involucradas en el potencial aumento de la ingesta de etanol inducido por la evocación de una memoria de miedo, se evaluará el efecto reforzante de etanol utilizando el paradigma de preferencia por un contexto asociado al etanol.

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Magdeburg, Univ., Fak. für Naturwiss., Diss., 2011