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1
Real, Esteban. « Models of Visual Processing by the Retina ». Thesis, Harvard University, 2012. http://dissertations.umi.com/gsas.harvard:10210.
Texte intégralRésumé :
The retina contains neural circuits that carry out computations as complex as object motion sensing, pattern recognition, and position anticipation. Models of some of these circuits have been recently discovered. A remarkable outcome of these efforts is that all such models can be constructed out of a limited set of components such as linear filters, instantaneous nonlinearities, and feedback loops. The present study explores the consequences of assuming that these components can be used to construct models for all retinal circuits. I recorded extracellularly from several retinal ganglion cells while stimulating the photoreceptors with a movie rich in temporal and spatial frequencies. Then I wrote a computer program to fit their responses by searching through large spaces of anatomically reasonable models built from a small set of circuit components. The program considers the input and output of the retinal circuit and learns its behavior without over-fitting, as verified by running the final model against previously unseen data. In other words, the program learns how to imitate the behavior of a live neural circuit and predicts its responses to new stimuli. This technique resulted in new models of retinal circuits that outperform all existing ones when run on complex spatially structured stimuli. The fitted models demonstrate, for example, that for most cells the center--surround structure is achieved in two stages, and that for some cells feedback is more accurately described by two feedback loops rather than one. Moreover, the models are able to make predictions about the behavior of cells buried deep within the retina, and such predictions were verified by independent sharp-electrode recordings. I will present these results, together with a brief collection of ideas and methods for furthering these modeling efforts in the future.Physics
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Guerreiro, Pedro Miguel Rito. « Visual programming in a heterogeneous multi-core environment ». Master's thesis, Universidade de Évora, 2009. http://hdl.handle.net/10174/18505.
Texte intégralRésumé :
É do conhecimento geral de que, hoje em dia, a tecnologia evolui rapidamente. São criadas novas arquitecturas para resolver determinadas limitações ou problemas. Por vezes, essa evolução é pacífica e não requer necessidade de adaptação e, por outras, essa evolução pode Implicar mudanças. As linguagens de programação são, desde sempre, o principal elo de comunicação entre o programador e o computador. Novas linguagens continuam a aparecer e outras estão sempre em desenvolvimento para se adaptarem a novos conceitos e paradigmas. Isto requer um esforço extra para o programador, que tem de estar sempre atento a estas mudanças. A Programação Visual pode ser uma solução para este problema. Exprimir funções como módulos que recebem determinado Input e retomam determinado output poderá ajudar os programadores espalhados pelo mundo, através da possibilidade de lhes dar uma margem para se abstraírem de pormenores de baixo nível relacionados com uma arquitectura específica. Esta tese não só mostra como combinar as capacidades do CeII/B.E. (que tem uma arquitectura multiprocessador heterogénea) com o OpenDX (que tem um ambiente de programação visual), como também demonstra que tal pode ser feito sem grande perda de performance. ABSTRACT; lt is known that nowadays technology develops really fast. New architectures are created ln order to provide new solutions for different technology limitations and problems. Sometimes, this evolution is pacific and there is no need to adapt to new technologies, but things also may require a change every once ln a while. Programming languages have always been the communication bridge between the programmer and the computer. New ones keep coming and other ones keep improving ln order to adapt to new concepts and paradigms. This requires an extra-effort for the programmer, who always needs to be aware of these changes. Visual Programming may be a solution to this problem. Expressing functions as module boxes which receive determined Input and return determined output may help programmers across the world by giving them the possibility to abstract from specific low-level hardware issues. This thesis not only shows how the CeII/B.E. (which has a heterogeneous multi-core architecture) capabilities can be combined with OpenDX (which has a visual programming environment), but also demonstrates that lt can be done without losing much performance.
3
Törnquist, Alba Lucia. « Visual outcome, ocular findings, and visual processing skills after allogeneic stem cell transplantation in children / ». Stockholm, 2010. http://diss.kib.ki.se/2010/978-91-7409-809-9/.
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Talebi, Vargha. « Spatiotemporal receptive fields of simple cells in early visual cortex ». Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=119418.
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In order to claim that the behaviours of early visual cortex neurons are fully understood, it must be possible to create models of them that can predict responses to any arbitrary type of stimuli. Thus the underlying theme of this thesis is to explore stimuli and implement system identification approaches appropriate for the estimation of receptive field (RF) models, as well as to quantitatively examine their response properties. Specifically, I aim to address the following questions: 1) what types of stimuli provide the most robust and generalizable RF models? 2) are cortical simple cell RF models classified into distinct categories? and 3) what are the spatiotemporal response properties of the RF models?To answer these questions, I use artificial and natural stimuli in conjunction with regularized regression system identification, to estimate RF models of visual cortical neurons. The use of natural stimuli is more appropriate as they drive more ecologically relevant responses. Regularized regression system identification techniques, which have antecedents in the field of machine learning, have a number of advantages: 1) they are based on regression and therefore appropriate for a wide range of stimuli including natural images; 2) they incorporate regularization to prevent overfitting; and 3) they allow for the estimation of full 3D (i.e., space-space-time) spatiotemporal RFs in a computationally tractable manner. I investigate simple cells of a somewhat higher cortical processing area (cat area 18), thereby providing a more challenging medium for our experiments. Results from Chapter 2 showed that white noise stimuli usually elicited weak responses, yielding poor RF models, while short bar and natural image stimuli drove strong responses yielding RF models with high predictive ability. However, RF models derived from natural images better predicted responses to other types of novel stimuli, when compared to models derived from broadband artificial stimuli (i.e., white noise, short bars). Furthermore, natural image-derived RF models performed well when used to predict responses to sinewave gratings.Chapter 3 revealed that early cortical simple cells could be delineated into three distinct categories, based on spatial RF structure and output nonlinearity. These three classes were: 1) non-oriented cells with expansive nonlinearities; 2) oriented cells with expansive nonlinearities; and 3) oriented cells with compressive nonlinearities. Our sample was split between these three types, suggesting that large numbers of non-oriented cells could be readily found in brain areas beyond the lateral geniculate nucleus and layer 4 striate cortex. Additionally, our results suggested that compressive output nonlinearities were much more common than previously believed. In Chapter 4 I identified a number of spatiotemporal response properties that varied amongst the three types of simple cells. These included optimal spatial frequency, latency, duration, responsivity, and direction selectivity. Of these, optimal spatial frequency was the most interesting as it showed segregation of our sample into distinct clusters, suggesting that optimal spatial frequency may be another dimension along which categorically distinct classes of cortical neurons could be established. Results also revealed that the three cell types effectively covered a large range of temporal latencies and durations. Finally, the two classes of oriented cells differed in their levels of responsivity, suggesting that expansive versus compressive nonlinearities may reflect the degree to which a nonlinear gain control mechanism is engaged. Collectively, the three studies in this thesis demonstrate the powerful potential of natural image stimuli and regularized regression system identification techniques, making them ideal candidates for routine use in visual neuroscience studies. RF models derived from natural images have revealed that physiological response...Afin de prétendre que les comportements des neurones du cortex visuel sont pleinement compris, il doit être possible de créer des modèles de ceux-ci qui peuvent entièrement prédire leurs réponses à tout type arbitraire de stimuli. Le thème sous-jacent de cette thèse est donc d'explorer les stimuli et les approches d'identification de système appropriés pour l'estimation de tels modèles de champ récepteur (CR), ainsi que d'examiner de façon quantitative les propriétés de leur réponse. Plus précisément, je cherche à répondre aux questions suivantes: 1) quels types de stimuli donnent des modèles de CR les plus robustes et généralisables?; 2) est-ce que les modèles de CR des cellules corticales simples sont classés en catégories distinctes?; et 3) quelles sont les propriétés des réponses spatiotemporelles des modèles de CR?Pour répondre à ces questions, j'utilise des stimuli artificiels et naturels en conjonction avec l'identification de système par régression régularisée, pour estimer les modèles de CR des neurones du cortex visuel. L'utilisation de stimuli naturels est plus appropriée, car elle entraîne des réponses plus écologiquement pertinentes. Les techniques d'identification de système par régression régularisée, qui ont des antécédents dans le domaine de l'apprentissage automatique, comportent un certain nombre d'avantages: 1) elles sont basées sur la régression et donc appropriées pour un large éventail de stimuli, y compris les images naturelles; 2) elles incorporent la régularisation afin d'éviter le sur-ajustement; et 3) elles permettent l'estimation de CR spatiotemporels 3D complets (c.-à-d., espace-espace-temps) de manière calculable par ordinateur. J'étudie les cellules simples d'une région corticale de niveau de traitement légèrement plus haut (chat, aire 18), offrant ainsi un milieu plus stimulant pour nos expériences. Les résultats du Chapitre 2 ont démontré que l'utilisation de bruit blanc comme stimuli suscitait généralement de faibles réponses, produisant de pauvres modèles de CR, tandis que l'utilisation de barres courtes et d'images naturelles comme stimuli provoquait de fortes réponses, ce qui donne des modèles de CR ayant une grande capacité prédictive. Toutefois, les modèles de CR dérivés d'images naturelles ont mieux prédit les réponses à d'autres types de nouveaux stimuli, par rapport aux modèles dérivés de stimuli artificiels à large bande (c.-à-d., bruit blanc, barres courtes). De plus, les modèles de CR dérivés d'images naturelles ont bien performé lorsqu'utilisés pour prédire les réponses aux grilles sinusoïdales. Le Chapitre 3 a révélé que les cellules corticales simples pouvaient être délimitées en trois catégories distinctes, basées sur la structure spatiale des CR et sur la non-linéarité de sortie. Ces trois catégories étaient: 1) les cellules non-orientées avec des non-linéarités à expansion; 2) les cellules orientées avec des non-linéarités à expansion; et 3) les cellules orientées avec des non-linéarités à compression. Notre échantillon a été réparti entre ces trois types, ce qui suggère qu'un grand nombre de cellules non-orientées peuvent être facilement trouvées dans les zones du cerveau au-delà du corps genouillé latéral et de la couche 4 du cortex strié. De plus, nos résultats suggèrent que les non-linéarités à compression de sortie sont beaucoup plus fréquentes qu'on ne le croyait auparavant. Dans le Chapitre 4, j'ai identifié un certain nombre de propriétés des réponses spatiotemporelles qui variaient entre les trois types de cellules simples. Il s'agissait notamment de la fréquence spatiale optimale, de la latence, de la durée, de la réactivité et de la sélectivité directionnelle. Parmi celles-ci, la fréquence spatiale optimale était la plus intéressante, car elle a démontré la ségrégation de notre échantillon en grappes distinctes. Ceci suggère que la fréquence spatiale optimale peut être une autre dimension au long de laquelle des classes de neurones corticaux...
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Gillett-Cooper, Anita M. « Development and degeneration in visual pathways ». Thesis, University of Oxford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.670398.
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Hesam, Shariati Nastaran. « A functional model for primary visual cortex ». Thesis, The University of Sydney, 2012. http://hdl.handle.net/2123/8753.
Texte intégralRésumé :
Many neurons in mammalian primary visual cortex have properties such as sharp tuning for contour orientation, strong selectivity for motion direction, and insensitivity to stimulus polarity, that are not shared with their sub-cortical counterparts. Successful models have been developed for a number of these properties but in one case, direction selectivity, there is no consensus about underlying mechanisms. This thesis describes a model that accounts for many of the empirical observations concerning direction selectivity. The model comprises a single column of cat primary visual cortex and a series of processing stages. Each neuron in the first cortical stage receives input from a small number of on-centre and off-centre relay cells in the lateral geniculate nucleus. Consistent with recent physiological evidence, the off-centre inputs to cortex precede the on-centre inputs by a small interval (~4 ms), and it is this difference that confers direction selectivity on model neurons. I show that the resulting model successfully matches the following empirical data: the proportion of cells that are direction selective; tilted spatiotemporal receptive fields; phase advance in the response to a stationary contrast-reversing grating stepped across the receptive field. The model also accounts for several other fundamental properties. Receptive fields have elongated subregions, orientation selectivity is strong, and the distribution of orientation tuning bandwidth across neurons is similar to that seen in the laboratory. Finally, neurons in the first stage have properties corresponding to simple cells, and more complex-like cells emerge in later stages. The results therefore show that a simple feed-forward model can account for a number of the fundamental properties of primary visual cortex.
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Field, Gregory Darin. « The limits to absolute visual sensitivity / ». Thesis, Connect to this title online ; UW restricted, 2004. http://hdl.handle.net/1773/10552.
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Folsom, Tyler C. « Neural networks modeling cortical cells for machine vision / ». Thesis, Connect to this title online ; UW restricted, 1994. http://hdl.handle.net/1773/6135.
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Tarczy-Hornoch, Kristina. « Physiology of synaptic inputs to layer IV of cat visual cortex ». Thesis, University of Oxford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337608.
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10
Rudiger, Philipp John Frederic. « Development and encoding of visual statistics in the primary visual cortex ». Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/25469.
Texte intégralRésumé :
How do circuits in the mammalian cerebral cortex encode properties of the sensory environment in a way that can drive adaptive behavior? This question is fundamental to neuroscience, but it has been very difficult to approach directly. Various computational and theoretical models can explain a wide range of phenomena observed in the primary visual cortex (V1), including the anatomical organization of its circuits, the development of functional properties like orientation tuning, and behavioral effects like surround modulation. However, so far no model has been able to bridge these levels of description to explain how the machinery that develops directly affects behavior. Bridging these levels is important, because phenomena at any one specific level can have many possible explanations, but there are far fewer possibilities to consider once all of the available evidence is taken into account. In this thesis we integrate the information gleaned about cortical development, circuit and cell-type specific interactions, and anatomical, behavioral and electrophysiological measurements, to develop a computational model of V1 that is constrained enough to make predictions across multiple levels of description. Through a series of models incorporating increasing levels of biophysical detail and becoming increasingly better constrained, we are able to make detailed predictions for the types of mechanistic interactions required for robust development of cortical maps that have a realistic anatomical organization, and thereby gain insight into the computations performed by the primary visual cortex. The initial models focus on how existing anatomical and electrophysiological knowledge can be integrated into previously abstract models to give a well-grounded and highly constrained account of the emergence of pattern-specific tuning in the primary visual cortex. More detailed models then address the interactions between specific excitatory and inhibitory cell classes in V1, and what role each cell type may play during development and function. Finally, we demonstrate how these cell classes come together to form a circuit that gives rise not only to robust development but also the development of realistic lateral connectivity patterns. Crucially, these patterns reflect the statistics of the visual environment to which the model was exposed during development. This property allows us to explore how the model is able to capture higher-order information about the environment and use that information to optimize neural coding and aid the processing of complex visual tasks. Using this model we can make a number of very specific predictions about the mechanistic workings of the brain. Specifically, the model predicts a crucial role of parvalbumin-expressing interneurons in robust development and divisive normalization, while it implicates somatostatin immunoreactive neurons in mediating longer range and feature-selective suppression. The model also makes predictions about the role of these cell classes in efficient neural coding and under what conditions the model fails to organize. In particular, we show that a tight coupling of activity between the principal excitatory population and the parvalbumin population is central to robust and stable responses and organization, which may have implications for a variety of diseases where parvalbumin interneuron function is impaired, such as schizophrenia and autism. Further the model explains the switch from facilitatory to suppressive surround modulation effects as a simple by-product of the facilitating response function of long-range excitatory connections targeting a specialized class of inhibitory interneurons. Finally, the model allows us to make predictions about the statistics that are encoded in the extensive network of long-range intra-areal connectivity in V1, suggesting that even V1 can capture high-level statistical dependencies in the visual environment. The final model represents a comprehensive and well constrained model of the primary visual cortex, which for the first time can relate the physiological properties of individual cell classes to their role in development, learning and function. While the model is specifically tuned for V1, all mechanisms introduced are completely general, and can be used as a general cortical model, useful for studying phenomena across the visual cortex and even the cortex as a whole. This work is also highly relevant for clinical neuroscience, as the cell types studied here have been implicated in neurological disorders as wide ranging as autism, schizophrenia and Parkinson’s disease.
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Garcia-Verdugo, Rosa. « Single-cell plasticity in mouse visual cortex following retinal lesions ». Diss., Ludwig-Maximilians-Universität München, 2015. http://nbn-resolving.de/urn:nbn:de:bvb:19-184736.
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Kisby, Brian M. (Brian Matthew). « Lean visual management in an ERP/MES-controlled production cell ». Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/49778.
Texte intégralRésumé :
Thesis (M.B.A.)--Massachusetts Institute of Technology, Sloan School of Management; and, (S.M.)--Massachusetts Institute of Technology, Engineering Systems Division; in conjunction with the Leaders for Manufacturing Program at MIT, 2009.Includes bibliographical references (p. 94).
As a company grows, more and more effort is needed to control and coordinate operations. Typically, this is accomplished through an evolving collection of systems and processes, such as an Enterprise Resource Planning (ERP) system, but such systems also influence how a company does business, reviews performance, and communicates results. Manufacturing Execution Systems (MES) are often used in conjunction with ERP systems to streamline and enable actual manufacturing processes. A third type of system, the visual management system, is used to take production out of the closed, computerized realm and make it open, intuitive, and efficient. Visual Management, as a lean concept, can be a simple and effective means to efficiently regulate inventory levels and production activities. However, when visual management systems are to be embedded within a broader ERP/MES system, certain conditions and support systems are requisite, the absence of which will render the visual management system ineffective, at best, or destructive, at worst. Furthermore, there are fundamental issues around implementing visual management, be it high-tech or low-tech. This thesis will describe a case study of the process to manage the design and implementation of a visual management system, while addressing various stakeholders' needs and refined business objectives. Theories and frameworks of Enterprise Architecting and Change Management are utilized to analyze which functions the visual management system should perform and how to achieve operator buy-in.
by Brian M. Kisby.
S.M.
M.B.A.
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Valavanis, Stavros. « Algorithms for estimating visual motion parameters from ganglion cell responses ». Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/46519.
Texte intégralRésumé :
Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2008.Includes bibliographical references (p. 170-171).
This thesis is intended to present a specific sub-problem of a larger one we call the "Inverse Problem". We wish to estimate the velocity (speed and direction) of an edge of light which is moving on the photoreceptor layer of a rabbit retinal patch. We make these estimates based solely on the electrical responses measured from the retinal ganglion cells (RGCs). To this end, we develop five novel algorithms. The first four of these are least squares based and the fifth one employs a maximum likelihood approach. We present a sensitivity analysis on the four least squares algorithms. We also develop a novel method for reweighing these least squares algorithms so as to minimize a weighted sum of the variances of our estimates. The fifth algorithm is significantly more complex than the first four as it involves creating cell models through "training"; moreover, it uses the entirety of each cell's response whereas the least squares algorithms use only first order statistics of each cell's response. We present and compare the results of the top performing least squares algorithm with the fifth algorithm on data recorded from a retinal patch. Through simulations, we explore the effects of using a small number of closely "clustered" cells on the performance of these two algorithms.
by Stavros Valavanis.
M.Eng.
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Lindqvist, Niclas. « Neurotrophic Factor Receptors in the Normal and Injured Visual System : Focus on Retinal Ganglion Cells ». Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3402.
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Kerr, Simon. « Visual based finger interactions for mobile phones ». Thesis, Rhodes University, 2010. http://hdl.handle.net/10962/d1006621.
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Vision based technology such as motion detection has long been limited to the domain of powerful processor intensive systems such as desktop PCs and specialist hardware solutions. With the advent of much faster mobile phone processors and memory, a plethora of feature rich software and hardware is being deployed onto the mobile platform, most notably onto high powered devices called smart phones. Interaction interfaces such as touchscreens allow for improved usability but obscure the phone’s screen. Since the majority of smart phones are equipped with cameras, it has become feasible to combine their powerful processors, large memory capacity and the camera to support new ways of interacting with the phone which do not obscure the screen. However, it is not clear whether or not these processor intensive visual interactions can in fact be run at an acceptable speed on current mobile handsets or whether they will offer the user a better experience than the current number pad and direction keys present on the majority of mobile phones. A vision based finger interaction technique is proposed which uses the back of device camera to track the user’s finger. This allows the user to interact with the mobile phone with mouse based movements, gestures and steering based interactions. A simple colour thresholding algorithm was implemented in Java, Python and C++. Various benchmarks and tests conducted on a Nokia N95 smart phone revealed that on current hardware and with current programming environments only native C++ yields results plausible for real time interactions (a key requirement for vision based interactions). It is also shown that different lighting levels and background environments affects the accuracy of the system with background and finger contrast playing a large role. Finally a user study was conducted to ascertain the overall user’s satisfaction between keypad interactions and the finger interaction techniques concluding that the new finger interaction technique is well suited to steering based interactions and in time, mouse style movements. Simple navigation is better suited to the directional keypad.
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Gnyawali, Subodh. « Melanopsin cell contributions to visual perception and decision making in humans ». Thesis, Queensland University of Technology, 2022. https://eprints.qut.edu.au/231544/1/Subodh_Gnyawali_Thesis.pdf.
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This thesis investigates the visual processes mediated via the fifth and most sparsely represented photoreceptor class in the human eye; melanopsin ganglion cells. It was determined that melanopsin-directed lighting increases the contrast sensitivity of the canonical cone pathway to enhance the perception of brightness. The melanopsin pathway also transmits visual information independently of rod and cone mediated vision. During decision making, its activation produces a signature biphasic pupil dilation. These outcomes inform the development of new energy-efficient lighting spectrums designed to modulate the effects of light on mood and cognition mediated via the melanopsin pathway.
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Gauthier, Jeffrey Lee. « The population perspective how primate retinal ganglion cells collectively encode visual space / ». Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2008. http://wwwlib.umi.com/cr/ucsd/fullcit?p3311417.
Texte intégralRésumé :
Thesis (Ph. D.)--University of California, San Diego, 2008.Title from first page of PDF file (viewed July 31, 2008). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 48-53).
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Wang, Chun. « Monocular and binocular neural interactions in the visual system of the cat ». Thesis, The University of Sydney, 1993. https://hdl.handle.net/2123/26632.
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In the following text, I am going to introduce briefly the conceptual framework concerning the neuronal interactions taking place in the mammalian (cat) dorsal lateral geniculate nucleus and the visual cortex. At the end, I will list the issues addressed in this thesis.
Interactions between centre and surround
One of the well-known neural interaction phenomena in the early stages of visual information processing is the interaction between the receptive field centre and surround. The receptive fields of most neurones in the retina and the dorsal lateral geniculate nucleus (LGNd) are constructed from, at least, two mutually antagonistic, concentrically organized regions (centre and surround). This arrangement probably underlies the ability of the visual system to extract the luminance difference in a small region of visual space. Although the receptive field properties of the LGNd cells are very similar to those of the retinal ganglion cells, the centre-surround antagonism appears to be much stronger in the receptive fields of the LGNd neurones. It is believed that enhanced centre-surround antagonism observed in the LGNd is a result of a further neural signal processing which improves the contrast sensitivity. Since there are substantial differences between X and Y cells in both the spatial extent of centre and surround and characteristics of their responses to both stationary and moving visual stimuli, they are believed to play different roles in the spatial and temporal domains of analysis of visual information (cf. for reviews Stone et al., 1979; Casagrande & Norton, 1991). X cells appear to be mainly involved in pattern recognition while Y cells appear to serve mainly as motion detectors. X-lagged cells, the predominant subgroup of a newly discovered subclass of cat LGNd cells, are supposed to play an important role complementary to that of X non-lagged cells in providing high spatial resolution in the low temporal frequency domain (Mastronarde, 1987a, b; Humphrey & Weller, 1988). X lagged cells are characterised by their "delayed and long lasting" responses to visual stimuli and to the small size of their receptive field centres which are known to be comparable to those of X non-lagged cells (Mastronarde, 1987a, b, 1992). However, little is known about the properties of their receptive field surround which is supposed to be critical for sharpening up the spatial resolution.
The traditional concept of centre-surround organization of the receptive field of the retinal ganglion cells (Kuffler, 1953) has been substantially modified by the discovery of the "periphery effect" (McIlwain, 1964, 1966) or "shift effect" (Kriiger & Fischer, 1973; Fischer & Kriiger, 1974). The periphery effect indicates that the peripheral area from which centre responses can be influenced is much greater than the conventional surround. The experiments of Enroth-Cugell and Jakiela (1980) have further demonstrated that without changing the total amount of light falling on the receptive field and without evoking a response per se the responses elicited from the receptive field of ganglion cells can be suppressed by the Spatio-temporal changes in the background. Thus, a non—linear mechanism seems to be involved in the interaction between the centre and periphery of the receptive fields of retinal ganglion cells. Although in lower vertebrates (for example, the amphibian Necturus (mudpuppy); Werblin, 1972) there are some indications that the remote effect may be mediated by amacrine cells, neuronal circuitry underlying these effects and their functional significance to a large extent remain unknown.
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Chen, Baiyu. « Suprachiasmatic nucleus projecting retinal ganglion cells in golden hamsters development, morphology and relationship with NOS expressing amacrine cells ». Click to view the E-thesis via HKUTO, 2006. http://sunzi.lib.hku.hk/hkuto/record/B37238218.
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Dallimore, Elizabeth Jane. « Molecular and cellular characteristics of early vs late born retinal ganglion cells ». University of Western Australia. School of Anatomy and Human Biology, 2009. http://theses.library.uwa.edu.au/adt-WU2009.0138.
Texte intégralRésumé :
[Truncated abstract] Developmentally, the rodent retinocollicular projection is often thought of as a homogenous projection of retinal ganglion cell (RGC) axons, however the extensive period of RGC neurogenesis and sequential arrival of their axons into central targets such as the superior colliulus (SC) suggests otherwise. RGC axons are already present in the developing SC at embryonic (E) day 16.5-17. RGCs born on E15 have innervated the SC by birth, whereas axons derived from RGCs that are born last (E19) do not grow into the SC until postnatal (P) days 4-6 (Dallimore et al., 2002). These observations may go someway to explaining why, after SC lesions in rats at P2, there is greater growth distal to the lesion site compared to lesions made at P6 (Tan and Harvey, 1997b). It may be that the post lesion growth is simply de novo growth of axons from late-born RGCs rather than regeneration of pre-existing, injured axons. Early and late cohorts of growing RGC axons presumably encounter different developmental terrains as they grow from retina to central targets, possibly resulting in differences in developmental milestones and growth potentials. There may also be differences in guidance cues, further suggesting that gene expression in early vs late born RGCs may differ. To examine differences between early (E15) and late (E19) born RGCs during development, the time-course and extent of programmed RGC death in normal rat pups, and RGC death following the removal of target-derived trophic factors, was assessed. ... On the other hand, LCM captured GCL analysed for gene expression at P0 and P7 revealed decreases in AKT, Math5, Notch1, c-jun, DCC, Arginase-1 mRNA levels and a considerable decrease in GAP-43 expression. It is not surprising to see differences in gene expression between whole eye and the more specific GCL samples, as the cells in all layers of the retina have very different functions and different developmental profiles. It is important to note decreases in mRNA expression in the GCL for a number of the genes analysed at P0 and P7, reflecting cessation of RGC death and completion of axonal growth into central visual targets. I also examined at the protein level expression of DCC, Arginase1, c-Jun and Bcl-2 at birth (P0) in BrdU labeled RGCs born on E15 or E19. When comparing the percentage of double labelled cells compared to the total number of cells expressing each protein, Bcl-2, c-Jun and Arg1 were expressed more in E15 RGCs (22.90%, 72.71%, and 16.44% respectively in E15 RGCs, compared with 0.52%, 13.17% and 3.59% in E19 RGCs). In contrast, DCC was expressed more at birth in E19 RGCs (18.05% in E19 RGCs compared with 9.23% in E15 RGCs). This shows there is clearly a difference in the expression of proteins in the two cohorts of RGCs, which is consistent with PCR data and with their growth state as their axons encounter the changes in the newborn brain. The overall findings of this research suggest that seemingly homogenous populations of neurons are quite different in their developmental profile and in their response to injury. This work may provide new ways of determining better strategies for CNS repair and the most effective way of targeting cells for regeneration and survival.
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Rubin, Glen R. « Comparisons between behavioral and electrophysiological measures of visual function in rodent models of retinal degeneration ». Thesis, Birmingham, Ala. : University of Alabama at Birmingham, 2009. https://www.mhsl.uab.edu/dt/2009p/rubin.pdf.
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DE, SIMONE CHIARA. « Biotin-anandamide : a new tool to visualize anandamide inside the cells ». Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2010. http://hdl.handle.net/2108/1187.
Texte intégralRésumé :
L’endocannabinoide anandamide è un lipide neuromodulatorio non carico che è inattivato grazie al suo assorbimento cellulare e successivo catabolismo. Mentre la biosintesi e la degradazione dell’anandamide sono state chiarite in dettaglio, il meccanismo attraverso cui essa entra all’interno della cellula rimane ancora non chiaro. Vi è un generale accordo solo sul fatto che il movimento dell’anandamide attraverso la membrana plasmatica è rapido, ha una cinetica di saturazione ed è temperatura dipendente. Mentre molti sono gli studi che descrivono un assorbimento mediato da uno specifico trasportatore di questo endocannabinoide, solo pochi lavori hanno proposto che il trasporto avvenga attraverso semplice diffusione passiva o attraverso endocitosi mediata da caveolae/lipid rafts. L’unica cosa certa però ad oggi è che, la mancanza del clonaggio e dell’espressione di questa ipotetica proteina trasportatrice, ha impedito lo sviluppo di strumenti molecolari che potrebbero dare una definitiva risposta della reale presenza di un trasportatore sulla superficie cellulare. Allo stesso tempo, non sono ancora stati messi a punto analoghi dell’anandamide che ci consentano di visualizzare i suoi movimenti attraverso la membrana plasmatica e di conseguenza il suo destino all’interno della cellula.
Il nostro gruppo ha sintetizzato e caratterizzato un analogo dell’anandamide (b-AEA) che possiede la stessa lipofilia del composto madre. Abbiamo usato metodi biochimici e di microscopia impiegando la b-AEA come strumento per visualizzare l’accumulo, la distribuzione ed i movimenti intracellulari dell’anandamide.
Abbiamo scelto di modificare la testa polare della molecola poiché questo cambiamento strutturale non influenza la cinetica del trasporto. I nostri studi ci hanno consentito di chiarire la presenza di strutture intracellulari dette adiposomi, che possono accumulare anandamide e che potrebbero essere coinvolti nel suo trasporto verso la FAAH. Usando la nostra molecola biotinilata abbiamo inoltre identificato due proteine citosoliche, l’albumina e la Hsp70.2, come potenziali trasportatori che legano l’anandamide e che potrebbero formare un sistema di trasporto in grado di consentire, in modo veloce ed efficiente, il movimento dell’anandamide all’interno della cellula.The endocannabinoid anandamide is an uncharged neuromodulatory lipid that is inactivated through its cellular uptake and subsequent catabolism. While the biosynthesis and degradation of AEA have been clarified in considerable detail, the mechanism of AEA uptake has remained elusive. There is a general consensus only on the fact that AEA movement through the plasma membrane is rapid, saturable, temperature-dependent. While many studies describe a transporter-mediated uptake of AEA via a selective “anandamide membrane transporter”, only a few papers proposed that the transport occurs by simple diffusion or endocytosis via caveolae/lipid rafts. As a matter of fact, the lack of cloning and expression of the purported transporter protein has prevented the development of molecular tools which could give definitive proof of the presence of a true transporter on the cell surface. In the same line, AEA analogs able to visualize AEA movement across the plasma membrane and its subsequent fate within the cell, are still missing. We synthesized and characterized a biotinylated analog of AEA (biotin-AEA) that has the same lipophilicity of the parent compound. We used biochemical assays and fluorescence microscopy employing b-AEA as a tool to visualize accumulation, intracellular distribution and trafficking of AEA inside the cells. We chose to modify the polar head of AEA because this structural change does not influence the kinetics of AEA uptake. Our studies led us to clarify the presence of molecular structures, the adiposomes, as a way to accumulate AEA and that could be involved in its delivery to FAAH. Using our biotinylated probe, we also identified two cytosolic proteins (albumin and Hsp70.2) as potential AEA-binding carriers which might form a delivery system to rapidly and efficiently assist the intracellular trafficking of AEA.
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Tomorsky, Johanna. « Molecular Mechanisms of Laminar Circuit Formation in Visual Cortex ». Thesis, University of Oregon, 2019. http://hdl.handle.net/1794/24539.
Texte intégralRésumé :
The mammalian visual system develops to perform many complex tasks that allow us to perceive the natural world. These tasks rely on a dense network of synaptic connections transporting visual information both to and within visual cortex (V1). The laminar organization and functional properties of visual cortical neurons are largely conserved across mammals, and the mouse has been adopted as a model organism to study the development of this cortical circuit. Neurons in each cortical layer must find the correct synaptic partners for the optimal receipt, transfer, and processing of information. The molecular cues guiding the development of these connections, however, are largely unknown.
In this thesis, I identify and then examine the role of molecular factors important for synapse formation in layer 2/3 (L2/3) of visual cortex. L2/3 neurons are highly interconnected and fire selectively to a refined set of visual stimuli. The developmental refinement of these visual preferences has been shown to occur in the week following eye opening, corresponding with a period of intense synapse formation and dynamic gene expression in mouse V1. In Chapters II–IV, I use the TU-tagging technique to identify molecular factors enriched L2/3 neurons before and after eye opening and identify several candidate genes with potential functions in synapse formation.
In Chapter V, I examine the function of cell adhesion molecules nectin-1 and nectin-3, identified here as enriched in L2/3 visual cortex at eye opening, and previously shown to interact across synaptic junctions. I focus mainly on the effect of nectin-3 (having post-synaptic localization in hippocampus) on post-synaptic dendritic spine densities in developing L2/3 cortical neurons. I show that nectin-3 knockdown further increases spine densities after eye opening, while overexpressing a full length or truncated nectin-3 protein reduces spine densities. I conclude that nectin-3 may have a role in synapse formation following eye opening, and propose a mechanism describing the effects observed. Here, I describe a unique approach for understanding how cell-type specific connections are formed in visual cortex, beginning with the spatiotemporal examination gene expression and followed by the spatiotemporal manipulation of a single gene.
This dissertation includes previously published co-authored material.
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Chen, Baiyu, et 陳白羽. « Suprachiasmatic nucleus projecting retinal ganglion cells in golden hamsters development, morphology and relationship with NOS expressingamacrine cells ». Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B37238218.
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Masri, Rania. « Neurons of the primate retina : A qualitative and quantitative analysis ». Thesis, The University of Sydney, 2019. http://hdl.handle.net/2123/21165.
Texte intégralRésumé :
Parallel processing begins in the retina, where input from photoreceptors is transmitted to 12 types of bipolar cell. Bipolar cells are interneurons that propagate visual signals to over 17 types of ganglion cell, which are output neurons of the retina. In this way various vertical pathways are formed that deliver different sensory signals to the brain. This thesis comprises a detailed map of the cell types that contribute to parallel processing in primate retina. Chapter 1 introduces the structure of the primate retina and describes the morphology of retinal cells and their contribution to visual processing. Chapter 2 provides a survey of ganglion cell types in marmoset retina. Ganglion cells were transfected with a plasmid for the expression of a synaptic marker conjugated to green fluorescent protein. At least 17 morphological types of ganglion cell were identified. The contribution of widefield ganglion cells is greater to peripheral than to foveal vision, whereas the fovea is dominated by midget and parasol cells. Outside the fovea ganglion cell diversity in marmoset retina is likely as great as that reported for non-primates. In Chapter 3 particle-mediated gene transfection was applied to post mortem human retina. Human retinas maintained their morphology and immunohistochemical properties for at least 3 days in culture. This study showed that gene transfection can be used to target cells in the human retina, with the potential to study their connectivity and structural changes in diseases. Chapter 4 provides a quantitative analysis of the major cell populations in the inner nuclear layer (INL) of normal human retina. Immunohistochemical markers were applied to vertical sections to label and quantify horizontal, bipolar, amacrine and Müller cells across the retina. Cone photoreceptors and ganglion cells were also counted. With the exception of the fovea, the proportion of different cell populations in the INL is comparable across all eccentricities and comparable to non-human primates and other mammals. The cone to cone bipolar cell ratio was constant across the retina suggesting that convergence and divergence do not change with eccentricity. The data provided in this thesis will serve as a reference for the interpretation of abnormalities in disease, and the informed targeting of treatments in human retinas.
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Bruce, Freyja Mairi. « Determining the roles of DSCAM and SDK proteins in vertebrate visual system development ». Thesis, University of Aberdeen, 2012. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=185643.
Texte intégralRésumé :
Axons are directed along stereotypic pathways to their targets by cues arrayed in the extracellular environment. Identifying the cellular and molecular nature of these signals is of high interest and the developing optic pathway is a useful model system for achieving this. Although previous studies have identified several molecules essential for optic pathway formation, in vivo only subsets of retinal axons rely on them. I focused on the Dscam (Down’s syndrome cell adhesion molecule) and Sidekick (Sdk) cell adhesion molecules for potentially playing crucial roles in this system. In situ hybridisation in the embryonic mouse visual system showed Dscam and Sdk-1 expression in the RGC layer of the retina, along the optic pathway and in the visual targets. Sdk-2 was detected in the glia of the optic nerve and optic chiasm, marking the pathway that RGC axons follow, but not in RGCs. No DscamL1 was detected in RGCs or the optic pathway at the stages investigated and it was discounted from future analysis. In vitro, DSCAM promoted RGC axon outgrowth, whereas SDK 1 was inhibitory. SDK 2 had no effect on RGC axon outgrowth, suggesting it does not play a direct role in their pathfinding. Repeating this assay using retinal explants from the Dscamdel17 mouse mutant, showed that DSCAM enhanced retinal axon outgrowth, at least in part, through homophilic interactions. Analysis of visual system development in Dscam mutants showed DSCAM involvement in RGC axon fasciculation and in enhancing their growth, particularly within the ipsilateral optic tract. Retinal cell counts revealed that DSCAM played diverse roles in controlling cell number. Pre- and postnatal retinas lacking DSCAM contained more RGCs and mitotic cells. Postnatally, Dscam-/- retinas also show decreased cell death. In many cases, defect severity was dose-dependent, with an intermediate phenotype in the heterozygous mice, implicating DSCAM in the neurological defects of Downs’ Syndrome patients.
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Ghali, Rodney. « Non-neuronal cell response to axonal damage in the visual paths of goldfish ». Thesis, McGill University, 1996. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=24005.
Texte intégralRésumé :
Patterns of proliferation and changes in total cell number in the optic nerve, tract and tectum of goldfish have been examined following optic nerve crush or optic enucleation, using bromodeoxyuridine to label the proliferating cells. In general, an increase in proliferation and total cell number in all parts of the visual system was observed peaking between 7 and 14 days and resolving itself to normal or near normal levels by 32 days postoperative. Enucleation resulted in elevated proliferation values as compared to animals with an optic nerve crush, at least one early timepoint in each part of the visual system, but overall, there is little to suggest that axons are exerting a major effect on the cellular response. Finally, a seasonal effect on the proliferative response of non-neuronal cells and axonal regrowth has been demonstrated. Fish acclimatized under autumn-like conditions showed a faster initiation of the non-neuronal cell response and an enhanced rate of axonal regrowth when compared to fish acclimatized under spring-like conditions. It is believed that photoperiod plays a major role in the seasonal effects observed with temperature playing only a minor one.
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McGuire, Jennifer J. « Visual induction of Fos in amacrine cells regulates ocular growth and refraction in chick ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape7/PQDD_0018/MQ48025.pdf.
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Quast, Kathleen Beth. « Functional Development and Plasticity of Parvalbumin Cells in Visual Cortex : Role of Thalamocortical Input ». Thesis, Harvard University, 2012. http://dissertations.umi.com/gsas.harvard:10709.
Texte intégralRésumé :
Unlike principal excitatory neurons, cortical interneurons comprise a diverse group of distinct subtypes. They can be classified by their morphology, molecular content, developmental origins, electrophysiological properties and specific connectivity patterns. The parvalbumin-positive \((PV^+)\), large basket interneuron has been implicated in two cortical functions: 1) the control and shaping of the excitatory response, and 2) the initiation of critical periods for plasticity. Disruptions in both phenomena have been implicated in the etiology of cognitive developmental disorders. Careful characterization of \(PV^+\) cell function and plasticity in response to their primary afferent, the thalamocortical synapse, is needed to directly relate their vital contribution at a synapse-specific or network level to whole animal behavior. Here, I used electrophysiological, anatomical and molecular genetic techniques in a novel slice preparation to elucidate \(PV^+\) circuit development and plasticity in mouse visual cortex.
I found that GFP-positive \(PV^+\) cells in layer 4 undergo a rapid maturation after eye opening just prior to onset of the critical period. This development occurs across a number of intrinsic physiological properties that shape their precise, fast spiking. I further optimized and characterized a visual thalamocortical slice to examine the primary afferent input onto both pyramidal and \(PV^+\) cells. Thalamic input onto \(PV^+\) cells is larger, faster and again matures ahead of the critical period. Both the intrinsic and synaptic properties of \(PV^+\) cells are then maintained by a secreted homeoprotein, Otx2 (Sugiyama et al, 2008), which is mediated by an extracellular glycosaminoglycan recognition. Since the plasticity of fast-spiking, inhibitory neurons is dramatically distinct from their neighboring pyramidal neurons in vivo (Yazaki-Sugiyama et al. 2009), I directly examined the plasticity of thalamocortical synapses in vitro. After brief monocular deprivation, thalamic input specifically onto \(PV^+\) cells is reduced while remaining unaltered in pyramidal cells. Deprivations prior to critical period onset or in GAD65 knockout mice neither produce a shift of visual responsiveness in vivo (Hensch et al, 1998) nor reduce thalamocortical input onto \(PV^+\) cells. These results directly confirm that \(PV^+\) cells are uniquely sensitive to visual experience, which may drive further rewiring of the surrounding excitatory cortical network.
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Svoboda, Hanno. « The role of protein synthesis in branching and synaptogenesis in the visual system ». Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610032.
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Ireland, Shelley Margaret Lorraine. « The plasticity of the visual system following damage of the brachium of the superior colliculus in neonatal and adult hamsters : ». Thesis, [Hong Kong : University of Hong Kong], 1991. http://sunzi.lib.hku.hk/hkuto/record.jsp?B13204907.
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Munden, Iona M. E. « The areal extent and summative properties of complex cell receptive fields in cat striate cortex ». Thesis, Keele University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305870.
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Grether, Megan E. (Megan Elizabeth). « Molecular genetic analysis of larval visual system development and programmed cell death in Drosophila ». Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/17341.
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Town, Jason Paul. « A Screen for Defects in Axon-Glial Cell Interactions in the Drosophila Visual System ». Thesis, The University of Arizona, 2011. http://hdl.handle.net/10150/144975.
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Antolik, Jan. « Unified developmental model of maps, complex cells and surround modulation in the primary visual cortex ». Thesis, University of Edinburgh, 2011. http://hdl.handle.net/1842/4875.
Texte intégralRésumé :
For human and animal vision, the perception of local visual features can depend on the spatial arrangement of the surrounding visual stimuli. In the earliest stages of visual processing this phenomenon is called surround modulation, where the response of visually selective neurons is influenced by the response of neighboring neurons. Surround modulation has been implicated in numerous important perceptual phenomena, such as contour integration and figure-ground segregation. In cats, one of the major potential neural substrates for surround modulation are lateral connections between cortical neurons in layer 2/3, which typically contains ”complex” cells that appear to combine responses from ”simple” cells in layer 4C. Interestingly, these lateral connections have also been implicated in the development of functional maps in primary visual cortex, such as smooth, well-organized maps for the preference of oriented lines. Together, this evidence suggests a common underlying substrate the lateral interactions in layer 2/3—as the driving force behind development of orientation maps for both simple and complex cells, and at the same time expression of surround modulation in adult animals. However, previously these phenomena have been studied largely in isolation, and we are not aware of a computational model that can account for all of them simultaneously and show how they are related. In this thesis we resolve this problem by building a single, unified computational model that can explain the development of orientation maps, the development of simple and complex cells, and surround modulation. First we build a simple, single-layer model of orientation map development based on ALISSOM, which has more realistic single cell properties (such as contrast gain control and contrast invariant orientation tuning) than its predecessor. Then we extend this model by adding layer 2/3, and show how the model can explain development of orientation maps of both simple and complex cells. As the last step towards a developmental model of surround modulation, we replace Mexican-hat-like lateral connectivity in layer 2/3 of the model with a more realistic configuration based on long-range excitation and short-range inhibitory cells, extending a simpler model by Judith Law. The resulting unified model of V1 explains how orientation maps of simple and complex cells can develop, while individual neurons in the developed model express realistic orientation tuning and various surround modulation properties. In doing so, we not only offer a consistent explanation behind all these phenomena, but also create a very rich model of V1 in which the interactions between various V1 properties can be studied. The model allows us to formulate several novel predictions that relate the variation of single cell properties to their location in the orientation preference maps in V1, and we show how these predictions can be tested experimentally. Overall, this model represents a synthesis of a wide body of experimental evidence, forming a compact hypothesis for much of the development and behavior of neurons in the visual cortex.
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Dunn, Felice Audris. « Gain control of rod and cone vision in the mammalian retina / ». Thesis, Connect to this title online ; UW restricted, 2007. http://hdl.handle.net/1773/10642.
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Ni, Lina. « Maintenance of Visual Sensitivity in the Drosophila Eye : A Dissertation ». eScholarship@UMMS, 2010. https://escholarship.umassmed.edu/gsbs_diss/457.
Texte intégralRésumé :
High visual sensitivity is a common but important characteristic of animal eyes. It is especially critical for night vision. In animal eyes, photoreceptors are the first to receive the incoming rays of light and they convert the light signals to electrical signals before passing the information to interneurons in the eye and finally to the brain.
To function in dim light conditions, photoreceptors have developed high sensitivities to light. It is reported that both mammalian rod photoreceptors and Drosophilaphotoreceptors can detect single photons.
The high sensitivities of photoreceptors largely depend on a high content of rhodopsin, a light-stimulated G protein-coupled receptor (GPCR), in light sensory organelles, outer segments in mammals and rhabdomeres in Drosophila. Two shared characteristics, the tightly packed photoreceptive membrane and the high concentration of rhodopsin in the membrane, work together to enable the photoreceptors to achieve the high content of rhodopsin in photosensory organelles in both mammals and Drosophila. In this thesis, I have used the Drosophilaeye as a model system to study the molecular mechanisms required for the maintenance of these two characteristics.
In the second chapter, I present a new molecular mechanism of preventing Gq-mediated rhabdomeral degeneration. A new gene named tadr (for torn and diminished rhabdomeres), when mutated, leads to visual sensitivity reduction and photoreceptor degeneration. Degeneration in the tadr mutant is characterized by shrunken and disrupted rhabdomeres. The TADR protein interacts in vitro with the major light receptor Rh1 rhodopsin, and genetic reduction of the Rh1 level suppresses the tadr-induced degeneration, suggesting the degeneration is Rh1-dependent. Nonetheless, removal of phospholipase C (PLC), a key enzyme in phototransduction, and that of Arr2 fail to inhibit rhabdomeral degeneration in the tadr mutant background. Biochemical analyses reveal that, in the tadr mutant, the Gq protein of Rh1 is defective in dissociation from the membrane during light stimulation. Importantly, reduction of Gq level by introducing a hypomorphic allele of Gαq gene greatly inhibits the tadr degeneration phenotype. These results may suggest that loss of a potential TADR-Rh1 interaction leads to an abnormality in the Gqsignaling, which in turn triggers rhabdomeral degeneration independent of the PLC phototransduction cascade. We propose that TADR-like proteins may also protect photoreceptors from degeneration in mammals including humans.
In the third chapter, I present a Drosophila CUB- and LDLa-domain transmembrane protein CULD that counteracts the visual arrestin Arr1-mediated endocytosis to retain rhodopsin in rhabdomeral membrane. CULD is mostly localized in rhabdomeres, but is also detected in scarce rhodopsin endocytic vesicles that contain Arr1. An intracellular region of CULD interacts with Arr1 in vitro. In both culdmutant and knockdown flies, a large amount of rhodopsin is mislocalized in the cell body of photoreceptors through lightdependent, Arr1-mediated endocytosis, leading to reduction of photoreceptor sensitivity. Expressing a wild-type CULD protein in photoreceptors, but not a mutant variant lacking the Arr1-interacting site, rescues both the rhodopsin mislocalization and the low sensitivity phenotypes. Once rhodopsin has been internalized in adult mutant flies, it is reversed only by expression of CULD but not by blocking endocytosis, suggesting that CULD promotes recycling of endocytosed rhodopsin to the rhabdomere. Our results demonstrate an important role of CULD in the maintenance of membrane rhodopsin density and photoreceptor sensitivity. We propose that a common cellular function of CUB- and LDLa-domain proteins, in both mammals and invertebrates, is to concentrate receptors including GPCRs in particular regions of cell membrane.
In summary, the work addressed in this thesis has identified new molecular mechavii nisms underlying the maintenance of visual sensitivity in Drosophila, either through preventing Gq-mediated rhabdomeral degeneration or through antagonizing arrestin-mediated rhodopsin endocytosis. This work has advanced our understanding of visual biology and the general regulatory mechanisms of GPCR signaling, and may provide valuable clues to pathologic studies of human retinal degeneration disorders.
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Patel, Dipankumar Dalubhai. « Subjective effects of cell loss and bit error on compressed audio-visual applications over ATM ». Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314077.
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Inagaki, Tsuyoshi. « NMDA Receptor-Dependent Long-Term Modification in Rat Visual Cortical Inhibitory Cells (RIEM Conference Ⅱ, 2003) ». Research Institute of Environmental Medicine, Nagoya University, 2003. http://hdl.handle.net/2237/7616.
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Kolappan, M. « Afferent visual pathway assessment in an exploratory trial of autologous mesenchymal stem cells in multiple sclerosis ». Thesis, University College London (University of London), 2013. http://discovery.ucl.ac.uk/1414442/.
Texte intégralRésumé :
There is a considerable need for treatments in MS for preventing progressive neurological disability. Assessment of the afferent visual pathway shows potential in investigating new therapies in MS. Mesenchymal Stem Cells exhibit properties of potential therapeutic relevance in progressive MS. A phase I/IIA trial of adult autologous mesenchymal stem cells as a potential therapy for Multiple Sclerosis [MSCIMS] was designed as an open label, pre (up to 20 months) vs. post treatment (up to 10 months) (single intravenous administration of autologous bone marrow derived mesenchymal stem cells) comparison study in ten secondary progressive MS patients. Primary end points were adverse events and secondary end points were efficacy measures. All 10 patients had previous history of clinical optic neuritis: this was in order to enable longitudinal structural and functional assessments of the disease-affected afferent visual pathway. Piecewise linear mixed models were used to assess the change in gradients over time at the point of intervention. All 10 patients tolerated the trial assessments and intervention. No significant or serious adverse events were seen. Improvement after treatment was seen in visual acuity and visual evoked response latency, along with an increase in optic nerve cross-sectional area. The results suggest that autologous mesenchymal stem cells are safe and could possibly promote endogenous repair mechanisms such as remyelination, although a definitive conclusion of this cannot be made from this small study. While MSCIMS was a proof of concept study only, based on the encouraging experience derived from it, there would seem to be potential value in future, larger placebo controlled, double-blinded, randomised therapeutic phase IIb/III trials that could (i) more definitively investigate stem cells as a therapy and (ii) use the visual pathway disease model for investigating the efficacy of potential neuroprotective and reparative therapeutic agents.
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Krieger, Brenna M. « Predicting the Electrophysiological Responses of Murine Alpha Retinal Ganglion Cells to Artificial and Natural Visual Stimuli ». Thesis, Harvard University, 2015. http://nrs.harvard.edu/urn-3:HUL.InstRepos:14226061.
Texte intégralRésumé :
The retina sends many parallel channels of visual information to the brain through the axons of >20 retinal ganglion cell (RGC) populations. The purpose of these distinct circuits for vision remains an open question. Recent results suggest that each cell type responds selectively to a specific feature of the visual scene. These conclusions are derived primarily from experiments with artificial visual stimuli. It is unknown whether the insights gathered under such conditions extend to the natural environment in which the retina evolved. One can address this question by building a mathematical model of RGC responses to artificial stimuli and then testing how well that same model performs with natural visual input. For several RGC types this exercise has failed dramatically, indicating an imperfect understanding of their neural code.
Here we focus on the mouse alpha RGCs, which possess large cell bodies, stout axons, and wide receptive fields. Three subtypes had been previously defined based on their responses to light steps: On-Sustained, Off-Sustained, and Off-Transient. We targeted these RGCs for recording using a transgenic mouse line in which GFP is expressed in all alpha subtypes. Quantitative analysis of the recorded light responses revealed four distinct physiological cell types: an On-Transient alpha RGC in addition to the other three type previously identified. Using both artificial stimuli and natural movies, we measured the visual responses of the mouse alpha cells. We then constructed a simple cascade-style model to link the stimulus to the firing rate.
Based on electrophysiological recording and modeling, we found the visual messages the four alpha RGCs send to the brain to be similar in that they are minimally processed versions of the visual scene. Spatial averaging minimally influenced the responses of the alpha RGCs to the natural movies. Additionally, a simple linear- nonlinear model accounted very well for the visual responses of all four alpha RGC subtypes, correctly predicting at least 70% of the variance in firing. The same model worked for both artificial stimuli (e.g. random flicker) and natural stimuli (mouse-cam and simulated-mouse movies). This successful account of alpha cell function will be valuable as a retina model for understanding cortical vision in the behaving mouse.
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van, Wyk Michiel. « Local edge detectors in the rabbit retina / ». [St. Lucia, Qld.], 2006. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe19350.pdf.
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Apulei, Jessica. « Control of the cerebral cortex plasticity through the non-cell autonomous function of OTX2 homeoprotein ». Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS451.
Texte intégralRésumé :
Au cours du développement postnatal, le cortex cérébral présente des périodes temporelles limitées de plasticité élevée, appelées périodes critiques (PC). Ces fenêtres, qui permettent aux circuits neuronaux d'être formés par des stimuli externes, se trouvent dans de nombreuses régions corticales et sont régulées par plusieurs facteurs qui influencent l'équilibre entre excitation et inhibition. La PC la plus étudiée est celle de la dominance oculaire dans le cortex visuel, et le facteur de transcription OTX2 joue un rôle essentiel. OTX2 est transféré à partir de sources extra-corticales vers une classe spécifique d'interneurones, les cellules à parvalbumine (PV), et ce transfert contrôle l'apparition et la fermeture de la CP dans plusieurs régions corticales. Le but de ma thèse était de mettre en évidence les mécanismes qui sous-tendent l'activité non cellulaire autonome d'OTX2 impliquée dans la régulation de la PC. Au cours du développement postnatal, le cortex cérébral présente des périodes temporelles limitées de plasticité élevée, appelées périodes critiques (PC). Ces fenêtres, qui permettent aux circuits neuronaux d'être formés par des stimuli externes, se trouvent dans de nombreuses régions corticales et sont régulées par plusieurs facteurs qui influencent l'équilibre entre excitation et inhibition. La PC la plus étudiée est celle de la dominance oculaire dans le cortex visuel, et le facteur de transcription OTX2 joue un rôle essentiel. OTX2 est transféré à partir de sources extra-corticales vers une classe spécifique d'interneurones, les cellules à parvalbumine (PV), et ce transfert contrôle l'apparition et la fermeture de la CP dans plusieurs régions corticalesDuring postnatal development, the cerebral cortex has limited temporal periods of high plasticity, called critical periods (CPs). These windows, which allow neural circuitry to be shaped by external stimuli, are found in many cortical regions and are regulated by several factors that influence the balance between excitation and inhibition. The most studied CP is that of ocular dominance in the visual cortex, and the OTX2 homeoprotein transcription factor plays an essential role. OTX2 is transferred from extra-cortical sources into a specific class of interneurons, the parvalbumin (PV) cells, and this transfer controls CP onset and closure in several cortical regions. The aim of my thesis was to reveal the mechanisms underlying OTX2 non-cell autonomous activity implicated in CP regulation. Altogether my work extends our current understanding of cortical plasticity and the role of OTX2 during CPs. I have shown that non-cell autonomous OTX2 regulates cortical postnatal plasticity through direct transcriptional mechanisms and epigenetic modifications
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Lönngren, Ulrika. « Experimental Injury to the Visual System : Molecular Studies of the Retina ». Doctoral thesis, Uppsala universitet, Medicinsk utvecklingsbiologi, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-9344.
Texte intégralRésumé :
Retinal ganglion cells play a crucial role in the relay of visual signals from the eye to the brain. This cell type is affected and eventually lost in the eye disease glaucoma, resulting in progressive and irreversible loss of vision. Studies of the molecular mechanisms leading to retinal ganglion cell death are important for the understanding of the disease and for designing future treatments. This thesis addresses and studies these molecular mechanisms, including alterations in gene expression after experimental retinal injuries. The effects of a neuroprotective drug, brimonidine, after transient retinal ischemia were also studied in order to help explain the mechanisms behind the protective properties of this drug. Several methods, including quantitative reverse transcriptase PCR, micro-arrays, western blot and immunohistochemistry, were used. The results showed that transient retinal ischemia triggers cell division in Müller cells and alters the gene expression of growth factors, their receptors, and intermediate filaments in the retina. Several genes related to the apoptosis process were less affected. Pre-treatment with brimonidine increased the levels of certain growth factors (BDNF, NT3, CNTF, FGF9) compared with vehicle. Brimonidine also had marked effects on genes related to progenitor cells, among them the recognized neural stem cell marker nestin. The increase in levels of nestin after ischemia was countered by brimonidine treatment. Moreover, retinal ganglion cell death following either optic nerve transection or optic nerve crush appears to involve the extrinsic apoptotic pathway although the gene expression response appears to differ between these injuries. The results obtained in this work contribute to an increased understanding of retinal injuries and highlight the importance of Müller cells in the endogenous defense against retinal injuries.
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Birgersson, Erik. « Mathematical Modeling of Transport Phenomena in Polymer Electrolyte and Direct Methanol Fuel Cells ». Doctoral thesis, KTH, Mechanics, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3692.
Texte intégralRésumé :
This thesis deals with modeling of two types of fuel cells:the polymer electrolyte fuel cell (PEFC) and the directmethanol fuel cell (DMFC), for which we address four majorissues: a) mass transport limitations; b) water management(PEFC); c) gas management (DMFC); d) thermal management.
Four models have been derived and studied for the PEFC,focusing on the cathode. The first exploits the slenderness ofthe cathode for a two-dimensional geometry, leading to areduced model, where several nondimensional parameters capturethe behavior of the cathode. The model was extended to threedimensions, where four di.erent flow distributors were studiedfor the cathode. A quantitative comparison shows that theinterdigitated channels can sustain the highest currentdensities. These two models, comprising isothermal gasphaseflow, limit the studies to (a). Returning to a two-dimensionalgeometry of the PEFC, the liquid phase was introduced via aseparate flow model approach for the cathode. In addition toconservation of mass, momentum and species, the model wasextended to consider simultaneous charge and heat transfer forthe whole cell. Di.erent thermal, flow fields, and hydrodynamicconditions were studied, addressing (a), (b) and (d). A scaleanalysis allowed for predictions of the cell performance priorto any computations. Good agreement between experiments with asegmented cell and the model was obtained.
A liquid-phase model, comprising conservation of mass,momentum and species, was derived and analyzed for the anode ofthe DMFC. The impact of hydrodynamic, electrochemical andgeometrical features on the fuel cell performance were studied,mainly focusing on (a). The slenderness of the anode allows theuse of a narrow-gap approximation, leading to a reduced model,with benefits such as reduced computational cost andunderstanding of the physical trends prior to any numericalcomputations. Adding the gas-phase via a multiphase mixtureapproach, the gas management (c) could also be studied.Experiments with a cell, equipped with a transparent end plate,allowed for visualization of the flow in the anode, as well asvalidation of the two-phase model. Good agreement betweenexperiments and the model was achieved.
Keywords:Fuel cell; DMFC; PEFC; one-phase; two-phase;model; visual cell; segmented cell; scale analysis; asymptoticanalysis.
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Taylor, Michael Robert. « Genetic and biochemical analysis of zebrafish with visual function defects / ». Thesis, Connect to this title online ; UW restricted, 2002. http://hdl.handle.net/1773/9242.
Texte intégral
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Garcia-Verdugo, Rosa [Verfasser], et Mark [Akademischer Betreuer] Hübener. « Single-cell plasticity in mouse visual cortex following retinal lesions / Rosa Garcia-Verdugo. Betreuer : Mark Hübener ». München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2015. http://d-nb.info/1075456525/34.
Texte intégral
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Cusato, Wendy Modesto da Silva. « A formação do conceito de células visuais no final do século XIX ». Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/47/47135/tde-29052017-153955/.
Texte intégralRésumé :
A presente proposta visa examinar a formação histórica do conceito de célula visual. Pretendemos delimitar o estudo ao caso das células fotorreceptoras (cones e bastonetes). Em meados da década de 1860 a teoria vigente sobre o processo perceptivo era a das energias específicas dos nervos proposta por Johannes Müller (1801-1858) e desenvolvida posteriormente por Hermann Von Helmholtz (1821-1894). Examinaremos em nossa pesquisa a formação do conceito de tipos específicos de células nervosas associadas aos processos perceptivos (o foco do trabalho são as células do sistema visual). Esse debate envolve a formação dos conceitos de córtex visual, sistema visual, informação nervosa e célula nervosa. O período examinado será o entorno das duas últimas décadas do século XIX (décadas de 1880 e 1890), período em que Ferruccio Tartuferi (1852-1925) propõe a constituição híbrida da retina em 1887 e é marcada também pela formulação da teoria neuronal (teoria formulada principalmente pelo espanhol Santiago Ramón y Cajal)The objective of the present study is to examine the historical formation of the visual cell concept, focussing on the the study of photoreceptor cells (cones and rods). In the mid-1860s, the current theory about the perceptual process was that of the specific energies of nerves proposed by Johannes Müller (1801-1858) and later developed by Hermann Von Helmholtz (1821-1894). Our research will examine the formation of the concept of specific types of nerve cells associated with perceptual processes (the focus of the work are the cells of the visual system). This debate involves the formation of the concepts of visual cortex, visual system, nervous information and nerve cell. The period examined will be the last two decades of the nineteenth century (1880s and 1890s), a period in which Ferruccio Tartuferi (1852-1925) proposed the hybrid constitution of the retina in 1887 and also marked by the formulation of neuronal theory mainly by the Spaniard Santiago Ramón y Cajal
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Guo, Peiyi. « A Glia-Mediated Feedback Mechanism for the Termination of Drosophila Visual Response : A Dissertation ». eScholarship@UMMS, 2010. https://escholarship.umassmed.edu/gsbs_diss/499.
Texte intégralRésumé :
High temporal resolution of vision relies on the rapid kinetics of the photoresponse in the light-sensing photoreceptor neurons. It is well known that the rapid recovery of photoreceptor membrane potential at the end of light stimulation depends on timely deactivation of the visual transduction cascade within photoreceptors. Whether any extrinsic factor contributes to the termination speed of the photoresponse is unknown.
In this thesis, using Drosophilaas a model system, I show that a feedback circuit mediated by both neurons and glia in the visual neuropile lamina is required for rapid repolarization of the photoreceptor at the end of the light response.
In the first part of my thesis work, I provide evidence that lamina epithelial glia, the major glia in the visual neuropile, is involved in a retrograde regulation that is critical for rapid repolarization of the photoreceptor at the end of light stimulation. I identified the gene affected in a slrp (slow receptor potential) mutant that is defective in photoreceptor response termination, and found it needs to be expressed in both neurons and epithelial glia to rescue the mutant phenotype. The gene product SLRP, an ADAM (a disintegrin and metalloprotease) protein, is localized in a special structure of epithelial glia, gnarl, and is required for gnarl formation. This glial function of SLRP is independent of the metalloprotease activity.
In the second part of my thesis work, I demonstrate that glutamatergic transmission from lamina intrinsic interneurons, the amacrine cells, to the epithelial glia is required for the rapid repolarization of photoreceptors at the end of the light response. From an RNAi-based screen, I identified a vesicular glutamate transporter (vGluT) in amacrine cells as an indispensable factor for the rapid repolarization of the photoreceptor, suggesting a critical role of glutamatergic transmission from amacrine cells in this retrograde regulation. Further, I found that loss of a glutamate-gated chloride channel GluCl phenocopies vGluT downregulation. Cell specific knockdown indicates that GluCl functions in both neurons and glia. In the lamina, a FLAG-tagged GluCl colocalized with the SLRP protein in the gnarl-like structures, and this localization pattern of GluCl depends on SLRP, suggesting that lamina epithelial glia receive glutamatergic input from amacrine cells through GluCl at the site of gnarl. Since the amacrine cell itself is innervated by photoreceptors, these observations suggest that a photoreceptor — amacrine cell — epithelial glia — photoreceptor feedback loop facilitates rapid repolarization of photoreceptors at the end of the light response.
In summary, my thesis research has revealed a feedback regulation mechanism that helps to achieve rapid kinetics of photoreceptor response. This visual regulation contributes to the temporal resolution of the visual system, and may be important for vision during movement and for motion detection. In addition, this work may also advance our understanding of glial function, and change our concept about the effect of glutamatergic transmission.
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Ford, Matthew Jonathan. « Design and implementation of transgenic tools to visualise cell cycle progression in mammalian development ». Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/23658.
Texte intégralRésumé :
Cell cycle progression is the series of steps a cell has to take in order to duplicate its DNA and produce two daughter cells. Correct spatial and temporal coordination of the cell cycle is key for the normal development of any organ or tissue and is stringently controlled during embryogenesis and homeostasis. Misregulation of cell cycle progression is causal in many developmental disorders and diseases such as microcephaly and cancer. Fucci (Fluorescent Ubiquitination based Cell Cycle Indicator) is a system that allows for the visualisation of cell cycle progression by the use of two differently coloured fluorescent probes whose abundance is regulated reciprocally during the cell cycle. The probes contain the E3 ligase recognition domains of Cdt1 and Geminin fused to the fluorophores mCherry (red fluorescence) and mVenus (yellow fluorescence) respectively. Cells are therefore labelled red during G1, yellow in the G1/S transition and green during late S/G2 and M phases of the cell cycle. In order to study development and tissue homoeostasis a Fucci expressing mouse line was developed however this has several key limitations: First, the two Fucci probes are expressed from separate loci complicating mouse colony maintenance. Second, the constructs were not inducible, making it impossible to follow cell cycle progression in specific cell lineages and third the mice were generated by random transgenesis which is prone to silencing and can exhibit variation in expression between different tissues. Here I have characterised an improved version of the original Fucci system known as Fucci2a designed by Dr Richard Mort (University of Edinburgh) to overcome these limitations. The Fucci2a genetic construct contains both Fucci probes fused with the Thosea asigna virus self-cleaving peptide sequence T2A. This allows expression of both probes as a single bicistronic mRNA with subsequent cleavage by ribosomal ‘skipping’ during translation to yield separate proteins. A Fucci2a mouse (R26Fucc2aR) was generated by homologous recombination into the ROSA26 locus using the strong, ubiquitous CAG promoter to drive expression and incorporating a floxed-Neo stop cassette. This allows tissue specific activation by Cre recombinase when combined with a second Cre expressing mouse line. Building on the bicistronic Fucci2a technology I have gone on to develop and characterise four new tricistronic reporter constructs which allow for the dual visualisation of cell cycle progression with apoptosis, cytokinesis and ciliogenesis. In each case an additional fluorescent probe was added to the original Fucci2a construct separated by the self-cleaving peptide P2A and the construct characterised in 3T3 stable cell lines. The combination of a dual cilia and cell cycle reporter construct proved fruitful and I have gone on to investigate the relationship between cell cycle progression and ciliogenesis in 3T3 cells and have generated and characterised the R26Arl13b-Fucci2aR mouse line. I have also illustrated the utility of the R26Fucci2aR mouse for generating quantitative data in development research in two development situations; melanocyte development and lung branching morphogenesis. Melanocytes are specialised melanin producing cells responsible for the pigmentation of the hair, skin and eyes. Their precursors, melanoblasts, are derived from the neural crest where they migrate and proliferate before becoming localised to hair follicles and their study provides a good model for understanding the development of other neural crest derived lineages such as the peripheral nervous system. Using time-lapse imaging of ex vivo skin cultures in which melanoblasts are labelled with the Fucci probes I have characterised melanoblast migration and proliferation. In addition, I have shown that Kit signalling, which is necessary for melanoblast migration and survival, controls melanoblast proliferation in a density dependent manner and that melanoblast migration is more persistent in S/G2/M phases of the cell cycle. Lung branching morphogenesis requires constant proliferation at the apical tip of a growing epithelial branch. Loss of epithelial symmetry through an unidentified mechanism (requiring BMP, FgF10, Shh and Wnt signalling) within a branch is required to initiate branching either latterly from the side of a elongating branch by domain branching or by bifurcation of the tip. In the final section of this thesis I performed a comparative analysis of the behaviour of the developing lung epithelium using proliferative status (Fucci2a expression) to categorise each cell. Using a combination of live imaging and immunohistochemistry I have identified a transition zone 100-150μm from the tip of the branching lung epithelium where epithelial cells become stationary and drop out of the cell cycle corresponding with the onset of proximal bronchial progenitor marker Sox2. A comparative gene expression analysis of the proliferating and non-proliferating regions using Fucci2a to distinguish them has eluded to several interesting genes which could influence branching morphogenesis during lung development.