Learners not lurkers : connecting conceptual and social networks in science education /

La présente recherche a été subventionnée par le ministère de lEnseignement supérieur, de la Recherche et de la Science dans le cadre du Programme daide à la recherche sur lenseignement et lapprentissage (PAREA).Comprend des références bibliographique

Early-onset Amyloid Deposition and Cognitive Deficits in Transgenic Mice Expressing a Double Mutant Form of Amyloid Precursor Protein 695

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Cerebral blood flow regulation in the human and in a bovine model

The role of perivascular nerve fibers, smooth muscle cells and endothelium in the regulation of human and bovine cerebral artery contractility was investigated in vitro and the effect of cold-storage on vessel function was determined. Stimulation of perivascular nerve endings over a range of transmural electric field stimulation produced frequency- and duration-dependent responses in arteries of both species. The pharmacological properties of the cerebral vessels were studied using 17 different vasoactive agents which acted directly on the smooth muscle and/or on the endothelium. Parallel studies on human and bovine vessels indicate that the cow may be a very useful source of tissue for further experimentation. Cold-storage of cerebral arteries did not significantly alter vessel viability or responsiveness to vasoactive compounds, although a reduction in sensitivity to transmural electric field stimulation in human middle and posterior arteries was observed

The effect of age on the accumulation of amyloidogenic peptides in the human brain and cerebrospinal fluid /

Amyloid deposition in cortical plaques and around cerebral vessels is a hallmark of Alzheimer's disease (AD). Amyloid also accumulates, to a lesser degree, in some nondemented elderly individuals, in the cerebral cortex and in the choroid plexus (CP), a tissue in the cerebral ventricles which produces cerebrospinal fluid (CSF). The cortical amyloid is composed mainly of aggregates of a neurotoxic peptide called amyloid-beta (Abeta), of which there are two main variants, Abeta42 and Abeta40, but the composition of CP amyloid has not been determined, nor is it known if there is a relationship between amyloid deposition in these two locations. This thesis characterizes amyloid deposition in the CP and cortex of normal individuals, and investigates the effects of aging and Abeta on the levels of proteins that may modulate Abeta neurotoxicity and amyloid formation in these locations. Immunohistochemistry identified Abeta and its associated proteins, apolipoprotein (apo) E, apoJ and transthyretin in the CP of normal and AD subjects. However, Western blot analysis revealed that apoE, not Abeta, is the major protein component of the CP amyloid. Soluble forms of Abeta and apoE were identified in the CP and CSF. The concentrations of Abeta42, apoE and transthyretin in the CSF remained constant with age, indicating that the reduced levels of these proteins reported in the CSF of AD patients is not age-related. In addition, we found that the levels of Abeta40 declined, suggesting a change in metabolism of the Abeta precursor with age. In the cerebral cortex, the ratio of Abeta42- to Abeta40-positive plaques remained constant with age at 2.6, but was reduced to 1.6 in AD brains. ApoE, apoJ and transthyretin were present in a small minority of plaques in normal and AD brains, indicating that these proteins do not play a central role in modulating Abeta neurotoxicity in plaques. However, apoE was strongly associated with cerebrovascular amyloid in normal individuals, while Abe