Histologie massive basée sur la microscopie à tomographie par cohérence optique

L’histologie consiste en l’étude des tissus vivants à l’échelle microscopique. Cette discipline a permis de grandes avancées, tant en biologie qu’en médecine, allant de la découverte de la cellule, jusqu’à devenir l’outil de prédilection pour le diagnostic de nombreuses maladies. L’avènement de l’histologie s’est fait en parallèle avec le développement du microscope, nécessaire pour visualiser les tissus sous grossissement. La microscopie est par nature limitée à imager une très petite région d’intérêt et ne donne donc qu’un petit aperçu de l’échantillon en entier. Récemment, des microscopes tomographiques sériels combinant la microscopie au sectionnement du tissu ont permis d’imager automatiquement de larges échantillons de tissu à l’échelle du micron. Des algorithmes spécifiquement développés pour ces appareils permettent de reconstruire dans une grande matrice tridimensionnelle l’échantillon imagé. Dans le cadre de cette thèse, un tel système a été construit avec la tomographie par cohérence optique comme modalité d’imagerie. Cette technique d’imagerie, qui est basée sur la réflectance intrinsèque des tissus, permet une acquisition de données volumétriques à haut débit en plus d’offrir une haute résolution spatiale et une bonne pénétration dans les tissus. Le système développé a permis d’imager de façon fiable et répétable un organe de souris en l’espace de quelques heures avec un voxel d’une taille de (4,88 x 4,88 x 6,5) μm. L’objectif général de ce projet était d’utiliser le système développé pour faire des études de groupe sur la souris, pour répondre à des questions spécifiques. D’abord, une validation du système d’imagerie était de mise pour vérifier que la plateforme d’imagerie donne une représentation fidèle du tissu in vivo. En imageant une population de cerveaux de souris in vivo en imagerie par résonance magnétique, puis avec la plateforme d’imagerie, les déformations entre les modalités d’imageries furent quantifiées. L’utilisation d’outils d’analyses morphométriques développés pour l’imagerie par résonance magnétique a démontré que le sectionnement et la fixation ne déforment pas de façon significative le tissu et que les algorithmes permettant la reconstruction en un volume tridimensionnel donnent une représentation fidèle du cerveau in vivo. Cette démonstration ouvre la voie à des études de groupes s’intéressant à des altérations microscopiques dans un organe entier. Considérant la répétabilité et la fiabilité prouvée de la plateforme d’imagerie, l’effet du vieillissement normal sur le coeur de la souris a été examiné. En comparant les coeurs de souris jeunes à ceux de souris âgées, il a été mis en évidence que des changements dans l’architecture du myocarde s’opèrent en vieillissant. Chez les souris âgées la paroi du ventricule gauche s’épaissit résultant en une diminution du taux de changement d’orientation des fibres musculaires dans cette même paroi. En imageant préalablement la fonction cardiaque de ces mêmes coeurs in vivo, il fut démontré que ces changements microscopiques s’accompagnent de changements fonctionnels.----------ABSTRACT Histology consists in the study of biological tissue at the microscopic scale. This discipline has led to great advances in biology, such as permitting the discovery of the cell and in medicine, where it is to this day the gold standard to detect many diseases. The advent of histology has been brought to in parallel with the development of microscopy, necessary to visualize tissues under magnification. Microscopy is limited to imaging small field of views, thus giving only a small representation of the entire sample. Recently, serial scanning microscopes, combining light microscopy and tissue sectioning have allowed to automatically image large tissue samples, expanding the imaged region to the order of the centimeter while keeping micrometer scale resolution. Post processing algorithms, specifically developed for serial scanning microscopes, are used to reconstruct in large 3D datasets the imaged sample. In this thesis, a serial scanning optical coherence tomography microscope was developed. This imaging modality, based on the intrinsic reflectance of tissue, allows high-speed acquisition of volumetric datasets at micrometer scale spatial resolution and penetrates deep in biological tissue. The developed platform allowed reliable and repeatable imaging of whole mouse organs within a time lapse of a few hours with a voxel size of (4,88 x 4,88 x 6,5) μm. The general objective of this project was to use this developed imaging platform to perform group studies on mice, to answer specific questions on tissue morphology. First, a system validation was required to verify that the imaging platform gives reliable representation of in vivo tissue. By imaging a group of in vivo mice brains with magnetic resonance imaging before serial sectioning, inter-modality deformations were quantified. The use of morphometric analysis tools developed for magnetic resonance imaging demonstrated that tissue sectioning and fixation does not significantly deform tissue and that reconstruction algorithms to obtain a large 3D dataset give a reliable representation of the in vivo brain. This proof of concept investigation opens the way to further group studies looking at microscopic alterations in an entire small animal organ. Considering the previously demonstrated repeatability and reliability of the imaging platform, the effect of normal aging on the mouse heart was examined. By comparing hearts of young and old mice, it was shown that architectural changes in the myocardium occur with aging. In old mice, there was a thickening of the left ventricle wall, which showed a decrease of muscle fiber orientation change. Prior imaging of the cardiac function in vivo revealed that these microscopic changes in morphology were accompanied by changes in the heart function

Modulation de l'activité de structures cérébrales sous-corticales par optogénétique

L’optogénétique est une technique prometteuse pour la modulation de l’activité neuronale. Par l’insertion d’une opsine microbienne dans la membrane plasmique de neurones et par son activation photonique, il devient possible de réguler l’activité neuronale avec une grande résolution temporelle et spatiale. Beaucoup de travaux ont été faits pour caractériser et synthétiser de nouvelles opsines. Ainsi, plusieurs variétés d’opsines sont désormais disponibles, chacune présentant des cinétiques et sensibilités à des longueurs d’onde différentes. En effet, il existe des constructions optogénétiques permettant de moduler à la hausse ou à la baisse l’activité neuronale, telles la channelrhodopsine-2 (ChR2) ou la halorhodopsine (NpHR), respectivement. Les promesses de cette technologie incluent le potentiel de stimuler une région restreinte du cerveau, et ce, de façon réversible. Toutefois, peu d’applications en ce sens ont été réalisées, cette technique étant limitée par l’absorption et la diffusion de la lumière dans les tissus. Ce mémoire présente la conception d’une fibre optique illuminant à un angle de 90° à sa sortie, capable de guider la lumière à des structures bien précises dans le système nerveux central. Nous avons conduit des tests in vivo dans le système visuel de souris transgéniques exprimant la ChR2 dans l’ensemble du système nerveux central. Dans le système visuel, les signaux rétiniens sont conduits au corps genouillé latéral (CGL) avant d’être relayés au cortex visuel primaire (V1). Pour valider la capacité de mon montage optogénétique à stimuler spécifiquement une sous-population de neurones, nous avons tiré profit de l’organisation rétinotopique existant dans le système visuel. En stimulant optogénétiquement le CGL et en tournant la fibre optique sur elle-même à l’aide d’un moteur, il devient possible de stimuler séquentiellement différentes portions de cette structure thalamique et conséquemment, différentes représentations du champ visuel. L’activation des projections thalamiques sera enregistrée au niveau de l’aire V1 à l’aide de l’imagerie optique intrinsèque, une technique qui permet d’imager les variations de la concentration d’oxygène et du volume sanguin dans le tissu neuronal, sur une grande surface corticale. Comme l’organisation rétinotopique est maintenue au niveau de l’aire V1, l’espace activé au niveau du cortex révèlera l’étendue spatiale de notre stimulation optogénétique du CGL. Les expériences in vivo démontrèrent qu’en déplaçant la fibre optique dans le CGL, il nous était possible de stimuler différents sous- ensembles de neurones dans cette structure thalamique. En conclusion, cette étude montre notre capacité à développer un système à base de fibre optique capable de stimuler optogénétiquement une population de neurone avec une grande précision spatiale.Optogentics is a promising technic for neuronal activity modulation. By inserting a microbial opsin in the plasma membrane and by its photonic activation, it is possible to regulate neuronal activity with high temporal and spatial resolution. A lot of work has been done to characterize and synthetize new opsins. Thus, a wide variety of opsins are now available, presenting different kinetics and sensibility to specific wavelengths. Indeed, different opsins can either increase or decrease neuronal activity such as channelrhodopsin-2 (ChR2) or halorhodopsin (NpHR), respectively. This technology has the potential to stimulate a specific region within the brain in a highly reversible manner. However, little work was accomplished in this way, because to limitations due to absorption and scattering of light in biological tissue. This master’s thesis presents the conception of a side-firing optical fiber, capable of guiding light to specific structures within the brain. We conducted in vivo experiments in the visual system of transgenic mice expressing ChR2 in the entire central nervous system. In the visual system, retinal inputs are relayed to the lateral geniculate nucleus (LGN) before reaching the primary visual cortex (V1). To validate the capacity of the designed optogenetic assembly to stimulate specific sub-populations of neurons, we took advantage of the retinotopic organization existing in the visual system. By optogenetically stimulating the LGN and rotating the optical fiber around its axis with a motor, it is possible to sequentially stimulate different portions of this thalamic structure and consequently, different portions of the visual field. Activation of thalamic projections will be recorded in area V1 using intrinsic optical imaging, a technic allowing to image variations of blood oxygenation and blood volume in neuronal tissue over large cortical areas. Activation at the level of the cortex will reveal the spatial extent of the optogenetic stimulation in the LGN as retinotopic organization is maintained in V1 cortical area. In vivo experiments showed that displacing the optical fiber in the LGN allowed stimulation of different neuronal populations within this thalamic structure. In conclusion, this study demonstrates our capacity to develop a fiber-based system capable of optogenetically stimulating neuronal tissue with high spatial precision

Prospective Physicians’ Intention to Adopt Artificial Intelligence: A Configurational Perspective

Artificial intelligence (AI) drives transformation across medical specialities, requiring current and future generations of physicians to navigate ever-changing digital environments. In this context, prospective physicians will play a key role in adopting and applying AI-based health technologies, underlining the importance of understanding their knowledge, attitudes, and intentions toward AI. To dissociate corresponding profiles, we adopted a configurational perspective and conducted a two-stage survey study of 184 (t_0) and 138 (t_1) medical students at a Canadian medical school. Our principal findings corroborate the existence of distinct clusters in respondents’ AI profiles. We refer to these profiles as the AI unfamiliar, the AI educated, and the AI positive, showing that each profile is associated with different intentions towards future AI use. These exploratory insights on the variety of AI profiles in prospective physicians underline the need for targeted and adaptive measures of education and outreach

Repetitive and Retinotopically Restricted Activation of the Dorsal Lateral Geniculate Nucleus with Optogenetics

Optogenetics allows the control of cellular activity using focused delivery of light pulses. In neuroscience, optogenetic protocols have been shown to efficiently inhibit or stimulate neuronal activity with a high temporal resolution. Among the technical challenges associated with the use of optogenetics, one is the ability to target a spatially specific population of neurons in a given brain structure. To address this issue, we developed a side-illuminating optical fiber capable of delivering light to specific sites in a target nucleus with added flexibility through rotation and translation of the fiber and by varying the output light power. The designed optical fiber was tested in vivo in visual structures of ChR2-expressing transgenic mice. To assess the spatial extent of neuronal activity modulation, we took advantage of the hallmark of the visual system: its retinotopic organization. Indeed, the relative position of ganglion cells in the retina is transposed in the cellular topography of both the dorsal lateral geniculate nucleus (LGN) in the thalamus and the primary visual cortex (V1). The optical fiber was inserted in the LGN and by rotating it with a motor, it was possible to sequentially activate different neuronal populations within this structure. The activation of V1 neurons by LGN projections was recorded using intrinsic optical imaging. Increasing light intensity (from 1.4 to 8.9 mW/mm(2)) led to increasing activation surfaces in V1. Optogenetic stimulation of the LGN at different translational and rotational positions was associated with different activation maps in V1. The position and/or orientation of the fiber inevitably varied across experiments, thus limiting the capacity to pool data. With the optogenetic design presented here, we demonstrate for the first time a transitory and spatially-concise activation of a deep neuronal structure. The optogenetic design presented here thus opens a promising avenue for studying the function of deep brain structures

The use of restraint and seclusion in residential treatment care for youth : a systematic review of related factors and interventions

Children placed in residential treatment centers (RTCs) typically present challenging behavior including aggression. In this context, restraint and seclusion (R&S) are seen as “last resort” strategies for educators to manage youth aggression. The use of R&S is controversial, as they can lead to psychological and physical consequences for both the client and the care provider and have yet to be empirically validated as therapeutic. The objectives of this systematic review are to identify the factors related to R&S use in RTCs for youth and to review the interventions aiming to reduce the use of R&S. The identification of these factors is the first step to gaining a better understanding of the decision-making process leading to the use of R&S and ultimately to reducing the use of these strategies to a minimum. Thus, the present systematic review was conducted by searching PubMed, CINAHL, ERIC, and PsycNET for articles published between 2002 and 2017. Key words used were synonyms of R&S, youth, and RTCs. Thirty-one studies met the inclusion criteria: must report on factors affecting the use of R&S in RTCs, must be conducted in RTCs for youth under the age of 21, and must report on original and empirical data. Factors related to the characteristics of the client, the care provider, and the environment, as well as to the implementation of programs for the reduction of R&S, were found to influence the use of R&S in RTCs. A conceptual model is presented. The implementation of programs to reduce R&S use is discussed

Evidence of Late Ediacaran Hyperextension of the Laurentian Iapetan Margin in the Birchy Complex, Baie Verte Peninsula, Northwest Newfoundland: Implications for the Opening of Iapetus, Formation of PeriLaurentian Microcontinents and Taconic – Grampian Orogenesis

The Birchy Complex of the Baie Verte Peninsula, northwestern Newfoundland, comprises an assemblage of mafic schist, ultramafic rocks, and metasedimentary rocks that are structurally sandwiched between overlying ca. 490 Ma ophiolite massifs of the Baie Verte oceanic tract and underlying metasedimentary rocks of the Fleur de Lys Supergroup of the Appalachian Humber margin. Birchy Complex gabbro yielded a Late Ediacaran U–Pb zircon ID–TIMS age of 558.3 ± 0.7 Ma, whereas gabbro and an intermediate tuffaceous schist yielded LA–ICPMS concordia zircon ages of 564 ± 7.5 Ma and 556 ± 4 Ma, respectively. These ages overlap the last phase of rift-related magmatism observed along the Humber margin of the northern Appalachians (565–550 Ma). The associated ultramafic rocks were exhumed by the Late Ediacaran and shed detritus into the interleaved sedimentary rocks. Psammite in the overlying Flat Point Formation yielded a detrital zircon population typical of the Laurentian Humber margin in the northern Appalachians. Age relationships and characteristics of the Birchy Complex and adjacent Rattling Brook Group suggest that the ultramafic rocks represent slices of continental lithospheric mantle exhumed onto the seafloor shortly before or coeval with magmatic accretion of mid-ocean ridge basalt-like mafic rocks. Hence, they represent the remnants of an ocean – continent transition zone formed during hyperextension of the Humber margin prior to establishment of a mid-ocean ridge farther outboard in the Iapetus Ocean. We propose that microcontinents such as Dashwoods and the Rattling Brook Group formed as a hanging wall block and an extensional crustal allochthon, respectively, analogous to the isolation of the Briançonnais block during the opening of the Alpine Ligurian–Piemonte and Valais oceanic seaways.Le complexe de Birchy de la péninsule de Baie Verte, dans le nord-ouest de Terre-Neuve, est constitué d’un assemblage de schistes mafiques, de roches ultramafiques et de métasédiments qui sont coincés entre des massifs ophiolitiques d’ascendance océanique de la Baie Verte au-dessus, et des métasédiments du Supergroupe de Fleur de Lys de la marge de Humber des Appalaches en-dessous. Le complexe de gabbro de Birchy a donné une datation U-Pb sur zircon ID-TIMS correspondant à la fin de l’Édiacarien, soit 558,3 ± 0,7 Ma, alors qu’un gabbro et un schiste tufacé intermédiaire montrent une datation LA-ICP-MS Concordia sur zircon de 564 ± 7,5 Ma et 556 ± 4 Ma, respectivement. Ces datations chevauchent la dernière phase de magmatisme de rift observée le long de la marge Humber des Appalaches du Nord (565-550 Ma). Les roches ultramafiques associées ont été exhumées vers la fin de l’Édiacarien et leurs débris ont été imbriqués dans des roches sédimentaires. Les psammites de la Formation de Flat Point susjacente ont donné une population de zircons détritiques typique de la marge laurentienne de Humber des Appalaches du Nord. Les relations chronologiques et les caractéristiques du complexe de Birchy et du groupe de Rattling Brook adjacent, permettent de penser que ces roches ultramafiques pourraient être des écailles de manteau lithosphérique continental qui auraient été exhumées sur le plancher océanique peu avant ou en même temps que l’accrétion magmatique de roches mafiques basaltiques de type dorsale médio-océanique. Par conséquent, elles seraient des vestiges d’une zone de transition océan-continent formée au cours de l’hyper-extension de la marge de Humber avant l’apparition d’une dorsale médio-océanique plus loin au large dans l’océan Iapétus. Nous proposons que des microcontinents comme de Dashwoods et du groupe de Rattling Brook ont constitués respectivement un bloc de toit et un allochtone crustal d’extension, de la même manière que le bloc Briançonnais a été isolé lors de l’ouverture des bras océaniques alpins de Ligurie-Piémont et de Valais.Fil: Van Staal, Cees R.. Geological Survey of Canada; CanadáFil: Chew, Dave M.. Trinity College Dublin; IrlandaFil: Zagorevski, Alexandre. Geological Survey of Canada; CanadáFil: Mcnicoll, Vicki. Geological Survey of Canada; CanadáFil: Hibbard, James. North Carolina State University; Estados UnidosFil: Skulski, Tom. Geological Survey of Canada; CanadáFil: Castonguay, Sébastien. Geological Survey of Canada; CanadáFil: Escayola, Monica Patricia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos; ArgentinaFil: Sylvester, Paul J.. Memorial University Of Newfoundland; Canad

Validating intravascular imaging with serial optical coherence tomography and confocal fluorescence microscopy

Atherosclerotic cardiovascular diseases are characterized by the formation of a plaque in the arterial wall. Intravascular ultrasound (IVUS) provides high-resolution images allowing delineation of atherosclerotic plaques. When combined with near infrared fluorescence (NIRF), the plaque can also be studied at a molecular level with a large variety of biomarkers. In this work, we present a system enabling automated volumetric histology imaging of excised aortas that can spatially correlate results with combined IVUS/NIRF imaging of lipid-rich atheroma in cholesterol-fed rabbits. Pullbacks in the rabbit aortas were performed with a dual modality IVUS/NIRF catheter developed by our group. Ex vivo three-dimensional (3D) histology was performed combining optical coherence tomography (OCT) and confocal fluorescence microscopy, providing high-resolution anatomical and molecular information, respectively, to validate in vivo findings. The microscope was combined with a serial slicer allowing for the imaging of the whole vessel automatically. Colocalization of in vivo and ex vivo results is demonstrated. Slices can then be recovered to be tested in conventional histology

Motivational profiles for physical activity among adults with type 2 diabetes and their relationships with physical activity behavior

Using self-determination theory, the aim of this study was to examine motivational profiles toward physical activity among adults with type 2 diabetes and how these profiles predict physical activity. In total, 381 adults with type 2 diabetes (188 or 49.3% women, M age = 61.39, SD = 7.29) completed a questionnaire assessing their physical activity motivation and behavior. First, results of a multiple regression analysis showed that intrinsic and identified motives were positively associated with leisure-time physical activity over the past three months while results of a multivariate analysis of covariance revealed that higher levels of intrinsic and identified motives were associated with observing physical activity recommendations for type 2 diabetes (i.e. practicing 150 min of moderate to vigorous physical activity per week). Then, results of a cluster analysis distinguished four distinct motivational profiles: self-determined, controlled, moderate, and non-self-determined. Participants reporting the highest physical activity participation level and observing physical activity recommendations were more likely to present a self-determined profile. The present study highlights the benefits of using both a variable-centered and a motivational profile approach. They also highlight the importance of examining the type of motivation associated with physical activity practice among adults with type 2 diabetes since autonomous forms of motivation positively influence both the frequency of leisure-time physical activity and the observance of physical activity recommendations for type 2 diabetes