Le Syndrome de l'X fragile (FXS) est la forme la plus fréquente de retard mental héréditaire. Il est causé par l’inactivation du gène FMR1 codant une RNA Binding Protein (FMRP) impliquée dans le contrôle de la traduction. Afin de mieux comprendre la fonction de FMRP, nous nous somme intéressé à ses interacteurs et mon travail s’est organisé en deux parties: la caractérisation de l'interaction FMRP/ARNm GRK4 et la caractérisation de la fonction neuronale de CYFIP1/2, deux protéines interacteurs de FMRP. Nous avons confirmé l'interaction FMRP/ARNm GRK4 et identifié une portion contenant deux motifs ACUK / WGGA, connu pour être de nouvelles cibles pour FMRP. FMRP se lie à GRK4 via son domaine RGG-box et régule négativement sa traduction. Dans les cellules granulaires du cervelet, GRK4 se lie au récepteur GABABR(GBR), induisant sa désensibilisation. Sachant l’importance de la signalisation GBR du cervelet dans la coordination motrice, un niveau élevé de GRK4 peut contribuer au déficit de l'apprentissage moteur et la coordination des mouvements dans FXS. Nous avons également caractérisé la fonction neuronale de CYFIP1/2 en induisant leur knockdown (KD). Ces protéines appartiennent au complexe WAVE (WRC) qui est impliqué dans la régulation de l’établissement de la polarité axonale et dendritique. Nous avons identifié un mécanisme de co-régulation de la transcription des ARNm codant les membres du WRC lors de l’altération de l'expression de CYFIP1/2. Le KD CYFIP1/2 modifie également neuronale ramification et connectivités. L'interaction de FMRP/CYFIP1/2 permettrait de comprendre les mécanismes impliqués dans le développement des anomalies des épines dendritiques dans FXS. / Fragile X syndrome (FXS) is the most common form of inherited mental retardation. It is caused by the silencing of the FMR1 gene, which encodes for an RNA-binding protein (FMRP) involved in translational control. To better understand the function of FMRP, we are interested in its interactors and so my work was organized into two main parts: the characterization of the interaction between FMRP and GRK4 mRNA and the characterization of the neuronal function of CYFIP1/2, two FMRP interacting proteins. We confirmed in vivo and in vitro the FMRP/ GRK4 mRNA interaction and identified a portion containing two ACUK/WGGA motifs, known to be a novel targets for FMRP. FMRP binds this target via its RGG box domain and negatively modulates the expression of GRK4 at the translational level only in cerebellum. In cerebellar granule cells, GRK4 interacts directly with the GABAB receptor (GBR), promoting its desensitization. Since in cerebellum GBR signaling has a relevant role in motor coordination, an elevated level of GRK4 can contribute to deficits of motor learning and movement coordination in FXS. Next, we characterized the function of CYFIP1/2 in neurons by inducing their knockdown (KD). CYFIP1/2 are components of the canonical WAVE regulatory complex (WRC), important in the spatiotemporal regulation of actin dynamics to get correct axonal and dendrites polarity and branching. We identified a co-regulation of transcription of mRNA coding the WRC members when the expression of CYFIP1/2 is disturbed. KD CYFIP1/2 also alters neuronal branching. The FMRP/CYFIP1/2 interaction would allow us to understand the mechanisms involved in the development of dendritic spines abnormalities in FXS.

Autism is one of the leading causes of human intellectual disability (ID). More than 1% of the human population has autism spectrum disorders (ASDs), and it has been estimated that over 50% of those with ASDs also have ID. Fragile X syndrome (FXS) is the most common inherited form of mental retardation and is the leading known genetic cause of autism, affecting approximately 1 in 4000 males and 1 in 8000 females. Approximately 30% of boys with FXS will be diagnosed with autism in their later lives. The cause of FXS is through an over-expansion of the CGG trinucleotide repeat located at the 5’ untranslated region of the FMR1 gene, leading to hypermethylation of the surrounding sequence and eventually partially or fully silencing of the gene. Therefore, the protein product of the gene, fragile X mental retardation protein (FMRP), is reduced or missing. As a single-gene disorder, FXS offers a scientifically tractable way to examine the underlying mechanism of the disease and also shed some light on understanding ASD and ID. The mouse model of FXS (Fmr1−/y mice) is widely accepted and used as a good model, offering good structural and face validity. Since a primary deficit of FXS is believed to be altered neuronal communication, in this thesis I examined white matter tract and dendritic spine abnormalities in the mouse model of FXS. Loss of FMRP does not alter the gross morphology of the white matter. However, recent brain imaging studies indicated that loss of FMRP could lead to some minute abnormalities in different major white matter tracts in the human brain. The gross white matter morphology and myelination was unaltered in the Fmr1−/y mice, however, a small but significant increase of axon diameter in the corpus callosum (CC) was found compared to wild-type (WT) controls. Our computation model suggested that the increase of axon diameter in the Fmr1−/y mice could lead to an increase of conduction velocity in these animals. One of the key phenotypes reported previously in the loss of FMRP is the increase of “immature” dendritic spines. The increase of long and thin spines was reported in several brain regions including the somatosensory cortex and visual cortex in both FXS patients and the mouse model of FXS. Although recent studies which employed state-of-the-art microscopy techniques suggested that only minute differences were noticed between the WT and Fmr1−/y mice. In agreement with previous findings, I found an increase of dendritic spine density in the visual cortex in the Fmr1−/y mice, and spine morphology was also different between the two genotypes. We found that the spine head diameter is significantly increased in the CA1 area of the apical dendrites of the Fmr1−/y mice compared to WT controls. Dendritic spine length is also significantly increased in the same region of the Fmr1−/y mice. However, apical spine head size does not alter between the two genotypes in the V1 region of the visual cortex, and spine length is significantly decreased in the Fmr1−/y mice compared to WT animals in this region. Lovastatin, a drug known as one of the 3-hydroxy-3-methyl-glutaryl-CoA (HMG-CoA) reductase inhibitors, functions as a modulator of the mitogen-activated protein kinases (MAPK) pathway through inhibiting Ras farnesylation, was used in an attempt to rescue the dendritic spine abnormalities in the Fmr1−/y mice. Mice lacking FMRP are susceptible to audiogenic seizure (AGS). Previous work has shown that 48 hr of lovastatin treatment reduced the incidence of AGS in the Fmr1−/y mice. However, chronic lovastatin treatment failed to rescue the spine density and morphology abnormalities in the Fmr1−/y mice. Mouse models are invaluable tools for modelling human diseases. However inter-strain differences have often confounded results between laboratories. In my final Chapter of this thesis, I compared two commonly used C57BL/6 substrains of mice by recording their electrophysiological responses to visual stimuli in vivo. I found a significant increase of high-frequency gamma power in adult C57BL/6JOla mice, and this phenomenon was reduced during the critical period. My results suggested that the C57BL/6JOla substrain has a significant stronger overall inhibitory network activity in the visual cortex than the C57BL/6J substrain. This is in good agreement with previous findings showing a lack of open-eye potentiation to monocular deprivation in the C57BL/6JOla substrain, and highlights the need for appropriate choice of mouse strain when studying neurodevelopmental models. They also give valuable insights into the genetic mechanisms that permit experience-dependent developmental plasticity. In summary, these findings give us a better understanding of the fine structure abnormalities of the Fmr1−/y mice, which in turn can benefit future discoveries of the underlying mechanisms of neurodevelopmental disorders such as ID and ASDs.

No description available.

Das Fehlen des FMR1-Genprodukts FMRP ist ursächlich für die Entstehung des Phänotyps bei Patienten mit Fragilem-X-Syndrom. Es kommt hierbei auf Grund einer Hypermethylierung der DNA im Bereich der FMR1-Promotorregion zu einer Hemmung der Transkription. Im Rahmen dieser Arbeit wurde untersucht, ob eine Behandlung mit Methotrexat, welches eine Hypomethylierung der DNA verursacht, eine Therapieoption für Patienten mit Fragilem-X-Syndrom darstellt. Es wurden Fibroblasten von Patienten mit Fragilem-X-Syndrom kultiviert und währenddessen mit Methotrexat behandelt. Hierbei trat eine Reaktivierung der FMR1-Transkription auf, FMRP konnte allerdings nicht reproduzierbar detektiert werden. Auch in der Untersuchung des Methylierungsstatus der FMR1-Promotorregion zeigte sich nach Behandlung keine Reduktion der Methylierung. Der fehlende Nachweis von FMRP in den behandelten Patientenzellen macht es unwahrscheinlich, dass MTX im Rahmen dieser Erkrankung klinische Anwendung finden wird.

Submitted by admin tede (tede@pucgoias.edu.br) on 2016-08-18T13:16:28Z No. of bitstreams: 1 Roberto Carlos Gomes da Silva.pdf: 3176847 bytes, checksum: b508a4a3eb30a62abd86ea9330f277e4 (MD5) / Made available in DSpace on 2016-08-18T13:16:28Z (GMT). No. of bitstreams: 1 Roberto Carlos Gomes da Silva.pdf: 3176847 bytes, checksum: b508a4a3eb30a62abd86ea9330f277e4 (MD5) Previous issue date: 2008-04-09 / Since DNA structure was described, several studies have been carried out in genetics that promoted a revolution in the practice of medicine. Human syndromes that were practically undiagnosed became easily diagnosed with molecular tools. However, most of the genetic diseases remain under diagnostic obscurity, increasing health concerns for affected people and public demand for preventive health care such as the case of Fragile-X Syndrome, the most common heritable form of mental retardation in humans. FXS is caused by an expansion of CGG repeat sequence in the promoter region of FMR1 gene, located in Xq27.3. Both men and women are affected by FXS and pre-mutation can expand to a full mutation in the next generation. Under full mutation status ( 200 repeats) the gene is silenced and FMRP protein is not produced causing mental retardation, speech delay, and behavior problems, the most frequent symptoms in FXS. Prevalence of FXS is estimated in 1:4000 and 1:8000 and of carriers in the general population as 1:813 and 1:259 for men and women, respectively. Because of FXS potential to affect subsequent generations it is crucial to properly diagnose the syndrome. Laboratory analysis of DNA from FXS, using PCR or Southern Blotting, allows reaching the diagnosis in 99% of cases carrying mutated genes. However, to date the Brazilian Public Health System does not recognize the molecular methods to reach complete diagnostic in FXS. Early diagnose would allow fore more appropriate and efficient therapy approaches, favoring satisfactory development of all affected people, minimizing their suffering and the burden on their families, increasing, on the other hand, their quality of life which should go beyond survival. / A partir da descrição da estrutura do DNA, várias pesquisas foram desenvolvidas na área da Genética, promovendo uma revolução na prática da medicina. Síndromes, antes difíceis ou até impossíveis de serem detectadas, com tecnologia e ferramentas moleculares, tornaram-se facilmente diagnosticadas. Entretanto, diversas doenças ainda persistem na obscuridade de diagnóstico e geram problemas de saúde pública como é o caso da Síndrome do X-Frágil (SXF), que é a causa mais comum de retardo mental masculino herdado, e que consiste na expansão do número de cópias de uma seqüência de bases CGG do DNA no gene FMR1, localizado no cromossomo Xq27.3. A SXF afeta tanto homens quanto mulheres e a pré-mutação poderá expandir-se à mutação completa nas próximas gerações. Os portadores da pré-mutação continuam produzindo a proteína FMRP e os portadores da mutação completa são afetados pela SXF, pois o gene FMR1 é silenciado, e a proteína não é produzida, causando retardo mental, problemas de linguagem e de comportamento. A prevalência da SXF é estimada em 1:4000 e 1:8000, e para portadores na população em geral é 1:813 e 1:259 para homens e mulheres respectivamente. A importância do reconhecimento clínico e diagnóstico da SXF vem do fato de que as gerações futuras poderão estar comprometidas. O estudo do DNA para X-frágil pela PCR e Southern blotting permite determinar com segurança superior a 99% quem é portador da pré-mutação do gene FMR1 e quem possui a mutação completa. Entretanto, o SUS não reconhece os métodos moleculares, apesar do diagnóstico permitir intervenções terapêuticas, com respostas bastante eficientes, favorecendo o desenvolvimento de modo integral das pessoas afetadas, minimizando seu sofrimento e de seus familiares, uma vez que a qualidade de vida deve ir além da sobrevivência.

L'objectif de ce projet est l’étude de la plasticité des circuits corticaux dans le contexte de l'apprentissage des souris « sauvages » et modèles du syndrome de l’X fragile. Des études sur l'efficacité de la combinaison d'enregistrement des potentiels de champ locaux extracellulaires avec la stimulation laser UV (LSPS) pour cartographier les réseaux ont été réalisées. Nous avons trouvé des enregistrements de champs extracellulaires qui pourraient être utilisés pour détecter les réponses synaptiques évoquées par LSPS. Nos résultats indiquent une méthode alternative pour obtenir des cartes complètes de réseaux intracorticaux excitateurs. Ensuite, nous avons développé un paradigme d'apprentissage associatif sensoriel et étudié ses effets sur les réseaux intracorticaux excitateurs du cortex baril. Ex vivo un affaiblissement des projections excitatrices entre les couches 4 et 2/3 qui dans les colonnes de vibrisses C a été observée. Enfin, nous avons utilisé ces mêmes approches dans une souris modèle du syndrome de l'X fragile (FXS). Pour étudier les liens entre les déficits sensoriels, l'apprentissage associatif et les altérations fonctionnelles des réseaux sensoriels, nous avons utilisé un modèle de souris mutantes dans lequel la pathologie FXS était ciblée sur la couche 4 du cortex somatosensoriel. Il a été constaté que les souris WT présentaient une dépression similaire, alors qu'elle était absente FXS. En conclusion, les études sur les mutants sensoriels de type sauvage ont mis en lumière les conséquences de l'apprentissage sur les réseaux corticaux sensoriels et les liens entre la plasticité des réseaux corticaux sensoriels et les capacités cognitives. / The aim of this project is to study the plasticity of the cortical circuits in the context of the learning of wild type mice and models of Fragile X Syndrome. First, investigations into the efficacy of recording combination of extracellular local field potentials with UV laser stimulation (LSPS) to map networks were performed. We found extracellular field records could be used to detect the synaptic responses evoked by LSPS. Our results indicate an alternative method for obtaining complete maps of excitatory intracortical networks. Next, we developed a sensory associative learning paradigm and studied its effects on excitatory intracortical networks the barrel cortex. Ex vivo a weakening of the excitatory projections between layers 4 and 2/3 which in the columns of vibrissae C was observed and declined function of the speed of the behavioural response. Finally, we used these same approaches in a Fragile X Syndrome (FXS) model mouse. To study the links between sensory deficits, associative learning, and functional alterations of sensory networks, we used a model of mutant mice in which the FXS pathology was targeted to the layer 4 of the somatosensory cortex. Our hypotheses were that behavioural conditioning would change the cortical sensory circuits of the FXS sensory mutant and that the abnormal plasticity of these circuits would in turn affect the performance. It was found the WT mice exhibited a similar depression, whereas it was absent FXS. In conclusion, wild type mouse and FXS sensory mutant studies shed light on the consequences of learning on sensory cortical networks and on the links between plasticity of sensory cortical networks and cognitive abilities.

<p> Fragile X Syndrome (FXS) is the most common inherited disease of mental impairment, typically caused by a mutation in the Fragile X mental retardation 1 (FMRJ) gene. The clinical features are thought to result from abnormal neurobiology due to a lack of the Fragile X mental retardation protein (FMRP). Previously, it was thought that FMRP was confined exclusively to neurons; however, our laboratory recently discovered that astrocytes also express FMRP. Consequently, it is possible that astrocytes also suffer abnormalities as a result of a lack of FMRP. Astrocytes play integral roles in the development and maintenance of communication in the central nervous system. Therefore, it is now important to determine the contribution of astrocytes to the abnormal neuronal phenotype seen in FXS. In these experiments, neurons and astrocytes were independently isolated from wild type (WT) or FMRJ null mice and grown in a coculture. Neurons were evaluated using immunocytochemistry in combination with computer-aided morphometric and synaptic protein analyses. The findings presented here provide convincing evidence that Fragile X astrocytes contribute to the abnormal neurobiology seen in FXS . Fragile X astrocytes alter the dendrite morphology and excitatory synaptic protein expression of WT neurons in culture; and, importantly, when Fragile X neurons are grown with WT astrocytes these changes are prevented. Interestingly, the Fragile X astrocytes appear to act by causing a delay in development; even WT neurons grown in the presence of Fragile X astrocytes, that displayed an abnormal phenotype at 7 days in culture, exhibited nearly normal dendrite morphology and expression of excitatory synapses at 21 days. Furthermore, the results suggest that the dendritic abnormalities induced by the Fragile X astrocytes specifically target neurons with a spiny stellate morphology. This research establishes a role for astrocytes in the development of the abnormal neurobiology seen in FXS, and as such, the results presented here have significant implications for Fragile X research. The novel prospect that astrocytes are key contributing components in the development of FXS provides an exciting new direction for investigations into the mechanisms underlying FXS, with many unexplored avenues for potential treatment strategies. </p> / Thesis / Doctor of Philosophy (PhD)

Le Syndrome de l’X Fragile (SXF) est la forme héréditaire de retard mental la plus fréquente et la cause la mieux caractérisée de troubles du spectre autistique (TSA). Elle est causée par une mutation causant l’inactivation du gène Fmr1 (codant pour la protéine FMRP). La sensibilité accrue aux stimuli sensoriels est une caractéristique importante du SXF et des TSA, mais les mécanismes sous-jacents sont encore mal compris. Nous avons constaté que la suppression du gène Fmr1 entrainait une hyperexcitabilité sensorielle dans le modèle murin du SXF. Les souris Fmr1KO nécessitaient significativement moins d'informations tactiles pour l'exploration haptique, et les représentations évoquées par les informations tactiles provenant des vibrisses dans le cortex somatosensoriel primaire (S1) se propageaient à une vitesse plus élevée chez les souris Fmr1KO par rapport aux souris témoins sauvages.Au niveau cellulaire, il a été montré que les ARNm de plusieurs sous-unités de canaux ioniques (par exemple HCN1, KCNMA1) jouant un rôle clé dans le traitement de l'information dendritique / neuronale étaient des cibles de la protéine FMRP (Liao et al, 2008; Darnell et al, 2011). Sur la base de ces observations, nous avons étudié les canalopathies comme une caractéristique importante du SXF. Nous avons testé de possibles dysfonctionnement des canaux ioniques, et leurs conséquences sur le traitement de l'information dendritique dans les neurones pyramidaux du néocortex de la couche 5 chez les souris Fmr1KO, en utilisant une combinaison d’approches électrophysiologiques et d’imagerie calcique bi-photonique. Nos résultats ont montré que les dendrites des neurones pyramidaux du S1 étaient hyperexcitables, facilitant ainsi le couplage des entrées d’information synaptique à la génération de potentiel d'action en sortie dans les neurones. Cette altération était, au moins en partie, attribuable à un dysfonctionnement des canaux Ih et BKCa et a été partiellement restaurée par l'activation pharmacologique des canaux BKCa. Ces résultats plaident en faveur d'un rôle nouveau et crucial des canalopathies dans l'expression de l'hyperexcitabilité sensorielle dans le SXF. / Fragile X Syndrome (FXS) is the most common form of inherited mental retardation syndrome and most well characterized cause of Autism Spectrum Disorders (ASD), and it is caused by a silencing mutation of the gene Fmr1 (encoding the protein FMRP). Increased sensitivity to sensory stimuli is a prominent feature of FXS and ASD, but its underlying mechanisms are poorly understood. We found that deletion of the Fmr1 gene results in somatosensory hyper-excitability in a mouse model for FXS. Fmr1 knockout (Fmr1KO) mice required significantly less tactile information for haptic exploration, and touch-evoked whisker representations in the primary somatosensory cortex (S1) spread with increased velocity in Fmr1KO mice compared to wild-type control. At the cellular level, it has been shown that the mRNAs of several ion channel subunits (e.g. HCN1, KCNMA1) playing key roles in dendritic/neuronal information processing are regulated by FMRP (Liao et al., 2008; Darnell et al., 2011). Based on these observations, we investigated channelopathies as a prominent feature of FXS. We probed ion channel dysfunction, and its consequence for dendritic information processing in neocortical pyramidal neurons of layer 5 in Fmr1KO mice, using a combination of electrophysiological and 2-photon calcium imaging approaches. Our results showed that dendrites of S1 pyramidal neurons were hyper-excitable, facilitating the coupling of synaptic input to the generation of action potential output in these neurons. This defect was, at least in part, attributable to a dysfunction of Ih channels and BKCa channels and was partially rescued by pharmacological activation of BKCa channels. These findings argue for a novel and critical role for channelopathies in the expression of sensory hyper-excitability in FXS.

<p><a></a><a>The visual system is capable of interpreting immense sensory complexity, allowing us to quickly identify behaviorally relevant stimuli in the environment. It performs this task with a hierarchical organization that works to detect, relay, and integrate visual stimulus features into an interpretable form. To understand the complexities of this system, visual neuroscientists have benefited from the many advantages of using mice as visual models. Despite their poor visual acuity, these animals possess surprisingly complex visual systems, and have been instrumental in understanding how visual features are processed in the primary visual cortex (V1). However, a growing body of literature has shown that primary sensory areas like V1 are capable of more than basic feature detection, but can express neural activity patterns related to learning, memory, categorization, and prediction. </a></p> <p>Visual experience fundamentally changes the encoding and perception of visual stimuli at many scales, and allows us to become familiar with environmental cues. However, the neural processes that govern visual familiarity are poorly understood. By exposing awake mice to repetitively presented visual stimuli over several days, we observed the emergence of low frequency oscillations in the primary visual cortex (V1). The oscillations emerged in population level responses known as visually evoked potentials (VEPs), as well as single-unit responses, and were not observed before the perceptual experience had occurred. They were also not evoked by novel visual stimuli, suggesting that they represent a new form of visual familiarity in the form of low frequency oscillations. The oscillations also required the muscarinic acetylcholine receptors (mAChRs) for their induction and expression, highlighting the importance of the cholinergic system in this learning and memory-based phenomenon. Ongoing visually evoked oscillations were also shown to increase the VEP amplitude of incoming visual stimuli if the stimuli were presented at the high excitability phase of the oscillations, demonstrating how neural activity with unique temporal dynamics can be used to influence visual processing.</p> <p>Given the necessity of perceptual experience for the strong expression of these oscillations and their dependence on the cholinergic system, it was clear we had discovered a phenomenon grounded in visual learning or memory. To further validate this, we characterized this response in a mouse model of Fragile X syndrome (FX), the most common inherited form of autism and a condition with known visual perceptual learning deficits. Using a multifaceted experimental approach, a number of neurophysiological differences were found in the oscillations displayed in FX mice. Extracellular recordings revealed shorter durations and lower power oscillatory activity in FX mice. Furthermore, we found that the frequency of peak oscillatory activity was significantly decreased in FX mice, demonstrating a unique temporal neural impairment not previously reported in FX. In collaboration with Dr. Christopher J. Quinn at Purdue, we performed functional connectivity analysis on the extracellularly recorded spikes from WT and FX mice. This analysis revealed significant impairments in functional connections from multiple layers in FX mice after the perceptual experience; some of which were validated by another graduate student (Qiuyu Wu) using Channelrhodopsin-2 assisted circuit mapping (CRACM). Together, these results shed new light on how visual stimulus familiarity is differentially encoded in FX via persistent oscillations, and allowed us to identify impairments in cross layer connectivity that may underlie these differences. </p> <p>Finally, we asked whether these oscillations are observable in other brain areas or are intrinsic to V1. Furthermore, we sought to determine if the oscillating unit populations in V1 possess uniform firing dynamics, or contribute differentially to the population level response. By performing paired recordings, we did not find prominent oscillatory activity in two visual thalamic nuclei (dLGN and LP) or a nonvisual area (RSC) connected to V1, suggesting the oscillations may not propagate with similar dynamics via cortico-thalamic connections or retrosplenial connections, <a>but may either be uniquely distributed across the visual hierarchy or predominantly</a> restricted to V1. Using K-means clustering on a large population of oscillating units in V1, we found unique temporal profiles of visually evoked responses, demonstrating distinct contributions of different unit sub-populations to the oscillation response dynamics.</p>

<div>The visual system is responsible for processing visual input, inferring its environmental causes, and assessing its behavioral significance that eventually relates to visual perception and guides animal behavior. There is emerging evidence that visual perception does not simply mirror the outside world but is heavily influenced by contextual information. Specifically, context might refer to the sensory, cognitive, and/or behavioral cues that help to assess the behavioral relevance of image features. One of the most famous examples of such behavior is visual or optical illusions. These illusions contain sensory cues that induce a subjective percept that is not aligned with the physical nature of the stimulation, which, in turn, suggests that a visual system is not a passive filter of the outside world but rather an active inference machine.</div><div>Such robust behavior of the visual system is achieved through intricate neural computations spanning several brain regions that allow dynamic visual processing. Despite the numerous attempts to gain insight into those computations, it has been challenging to decipher the circuit-level implementation of contextual processing due to technological limitations. These questions are of great importance not only for basic research purposes but also for gaining deeper insight into neurodevelopmental disorders that are characterized by altered sensory experiences. Recent advances in genetic engineering and neurotechnology made the mouse an attractive model to study the visual system and enabled other researchers and us to gain unprecedented cellular and circuit-level insights into neural mechanisms underlying contextual processing.</div><div>We first investigated how familiarity modifies the neural representation of stimuli in the mouse primary visual cortex (V1). Using silicon probe recordings and pupillometry, we probed neural activity in naive mice and after animals were exposed to the same stimulus over the course of several days. We have discovered that familiar stimuli evoke low-frequency oscillations in V1. Importantly, those oscillations were specific to the spatial frequency content of the familiar stimulus. To further validate our findings, we investigated how this novel form of visual learning is represented in serotonin-transporter (SERT) deficient mice. These transgenic animals have been previously found to have various neurophysiological alterations. We found that SERT-deficient animals showed longer oscillatory spiking activity and impaired cortical tuning after visual learning. Taken together, we discovered a novel phenomenon of familiarity-evoked oscillations in V1 and utilized it to reveal altered perceptual learning in SERT-deficient mice.</div><div>16</div><div>Next, we investigated how spatial context influences sensory processing. Visual illusions provide a great opportunity to investigate spatial contextual modulation in early visual areas. Leveraging behavioral training, high-density silicon probe recordings, and optogenetics, we provided evidence for an interplay of feedforward and feedback pathways during illusory processing in V1. We first designed an operant behavioral task to investigate illusory perception in mice. Kanizsa illusory contours paradigm was then adapted from primate studies to mouse V1 to elucidate neural correlates of illusory responses in V1. These experiments provided behavioral and neurophysiological evidence for illusory perception in mice. Using optogenetics, we then showed that suppression of the lateromedial area inhibits illusory responses in mouse V1. Taken together, we demonstrated illusory responses in mice and their dependence on the top-down feedback from higher-order visual areas.</div><div>Finally, we investigated how temporal context modulates neural responses by combining silicon probe recordings and a novel visual oddball paradigm that utilizes spatial frequency filtered stimuli. Our work extended prior oddball studies by investigating how adaptation and novelty processing depends on the tuning properties of neurons and their laminar position. Furthermore, given that reduced adaptation and sensory hypersensitivity are one of the hallmarks of altered sensory experiences in autism, we investigated the effects of temporal context on visual processing in V1 of a mouse model of fragile X syndrome (FX), a leading monogenetic cause of autism. We first showed that adaptation was modulated by tuning properties of neurons in both genotypes, however, it was more confined to neurons preferring the adapted feature in FX mice. Oddball responses, on the other hand, were modulated by the laminar position of the neurons in WT with the strongest novelty responses in superficial layers, however, they were uniformly distributed across the cortical column in FX animals. Lastly, we observed differential processing of omission responses in FX vs. WT mice. Overall, our findings suggest that reduced adaptation and increased oddball processing might contribute to altered perceptual experiences in FX and autism.</div>