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The formation of various forms of memory involves a series of distinct cellular and molecular mechanisms, many of which are not fully understood. There are highly conserved pathways that are involved in learning, memory, and synaptic plasticity, which is the primary substrate for memory storage. The formation of short-term (across minutes) memory is mediated by local changes in synapses, while long-term (across hours to days) memory storage is associated with activation of transcription and synthesis of proteins that modify synaptic function. Transcription factors, which can either repress or activate transcription, play a vital role in driving protein synthesis underlying synaptic plasticity and memory, whereby protein synthesis provides the necessary building blocks to accommodate structural changes at the synapse that foster memory formation. Recent data implicate several families of transcription factors that appear critically important in the regulation of memory. In this Topic we will focus on the families of transcription factors thus far found to be critically involved in synaptic plasticity and memory formation. These include cAMP response element binding protein (CREB), Rel/nuclear factor B (Rel/NFB), CCAAT enhancer binding protein (C/EBP), and early growth response factor (Egr). In recent years, numerous studies have implicated epigenetic mechanisms, changes in gene activity and expression that occur without alteration in gene sequence, in the memory consolidation process. DNA methylation and chromatin remodeling are critically involved in learning and memory, supporting a role of epigenetic mechanisms. Here we provide more evidence of the importance of DNA methylation, histone posttranslational modifications and the role of histone acetylation and HDAC inhibitors in above mentioned processes.

Learning --- Memory --- Transcription Factors --- synaptic plasticity --- epigenetics

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This eBook is a collection of articles from a Frontiers Research Topic. Frontiers Research Topics are very popular trademarks of the Frontiers Journals Series: they are collections of at least ten articles, all centered on a particular subject. With their unique mix of varied contributions from Original Research to Review Articles, Frontiers Research Topics unify the most influential researchers, the latest key findings and historical advances in a hot research area! Find out more on how to host your own Frontiers Research Topic or contribute to one as an author by contacting the Frontiers Editorial Office: frontiersin.org/about/contact

Science: general issues --- Pharmacology --- Alzheimer’s disease --- preclinical studies --- drug research and development --- neurodegeneration --- synaptic plasticity

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Neuroplasticity refers to the ability of the Central Nervous System (CNS) to alter its structure and function in response to a variety of physiological and pathological processes such as development, cognition, injury or neurological diseases. Since more than four decades, studies on synaptic plasticity in the context of memory and learning attracted a remarkable interest. Soon after first seminal works on synaptic plasticity were published, research in this field was extended by studies on non-synaptic as wells as structural plasticity towards a goal to understand cellular and molecular determinants of cognition. Over the past two decades, yet two additional crucial players in neuroplastic phenomena started to be intensely investigated – glial cells and the extracellular matrix (ECM). Growing awareness that glial cells, especially astrocytes, are important regulators of synaptic functions gave rise to a novel concept of a tri-partite synapse. Also, over the last two decades, a growing body of evidence has accumulated that the extracellular matrix (ECM) in the brain is strongly involved in regulation of neurons, in particular, in synaptic plasticity. Thus, a concept of tetra-partite synapse was put forward by some neuroscientists. The cross-talk between neuron-glia-ECM system involves enzymatic degradation of proteins or peptides and amino acids occurring in each of these brain constituents by means of a variety of proteases. Importantly, it has been realized that proteases such as serine proteases and matrix metalloproteinases, not only accompany “robust” phenomena such as cell division, or development or neurodegnerative conditions but may play a very subtle signaling functions, particularly important in memory acquisition. Indeed, the repertoire of substrates for these enzymes covers a wide variety of proteins known to play important role in the neuroplastic phenomena (e.g. BDNF, TNF-a, ephrin systems, various cell adhesion molecules, etc.). In result, the role of metalloproteinases and such serine proteases as tissue plasminogen activator (tPA), neuropsin or neurotrypsin in synaptic plasticity as well as in learning and memory has been particularly well demonstrated. It needs to be emphasized, however, that in spite of a remarkable progress in this field, several basic questions regarding molecular and cellular mechanisms remain unanswered. Potential involvement of so many important players (various proteases and their substrates in neurons, glia and in ECM) points to an enormous potential for plasticity phenomena but makes also studies into underlying mechanisms particularly difficult. In the proposed Research Topic we provide both review of the current state of the art and present some original reports on specific aspects of the role of proteolysis in neuroplasticity phenomena. The present ebook starts with extensive reviews describing involvement of proteolysis not only in synaptic plasticity but also in regulating endogenous excitability and structural changes at the network, cellular and subcellular levels. Cross-talk between neuroplasticity and proteolysis is also emphasized in the context of development and in relation to various pathologies. Whereas in the first part of the present ebook, the major focus is on metalloproteinases, the successive articles address the role of neuropsin and thrombin. The Research Topic is concluded with a series of articles describing the components of extracellular matrix and adhesion proteins and their elaboration by mechanisms dependent directly or indirectly on proteolysis. We do hope that the present ebook will further stimulate the interest in the fascinating investigations into neuroplasticity-proteolysis cross-talk.

structural plasticity --- nuropathology --- excitability --- Extracellular Matrix --- neurodevelopment --- Cell Adhesion Molecules --- synaptic plasticity

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Once a day, every individual lay down and becomes unconscious. Isn’t sleep a strange thing to do? Despite the risks associated with it, our ancestors used to sleep too, suggesting that it should provide an evolutionary advantage. Thus, it raises a fundamental question: why do we sleep? Among all essential functions of sleep, research has proved its preponderant role in memory formation and consolidation. 
At the cellular level, memory is achieved through processes referred to as synaptic plasticity and translating the remarkable ability of the brain to constantly evolve due to various stimuli. Furthermore, differences in the neuronal firing patterns have been highlighted between wake and sleep: during sleep, neurons are bursting while during wake, neurons show a tonic firing pattern. 

Memory is an abstract concept, it is not a simple task to understand the processes behind it. As experimental evidence provides insights about how plasticity is induced, modeling techniques reproducing experimental data can give insights about memory mechanisms. Literature is broad concerning plasticity modeling. In this work, a concise review of phenomenological models is conducted.

Then, some of them are implemented in a conductance-based model able to switch from waking to sleep, i.e. from tonic to bursting activity. Compared to simplified spiking neuron model, this conductance-based model is a powerful tool to be able to faithfully replicate neuronal behavior in waking and sleeping period. Reproduction of experimental protocols is carried in tonic mode as well as the impact of variability in the firing pattern to mimic more in vivo situations. As the ultimate goal of this thesis is to see the impact of existing models on memory consolidation during sleep, their robustness and behaviour during a bursting period are investigated. It led to unsatisfactory results regarding memory consolidation, highlighting the limitations of those phenomenological models. The behaviour of the models implemented highly depends on the method used to bound the synaptic weight in-between extreme values. Finally, insights about neuromodulation are suggested as improvements.

synaptic plasticity --- computational neurosciences --- memory consolidation --- neuronal modeling --- Ingénierie, informatique & technologie > Multidisciplinaire, généralités & autres

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Autism spectrum disorders (ASDs) are a group of genetically and clinically heterogeneous neurodevelopmental disorders characterized by impaired reciprocal social interactions and communication, and restricted and repetitive patterns of behaviors and interests. Studies in genetics, neurobiology and systems biology are providing insights into the pathogenesis of ASDs. Investigation of neural and synaptic defects in ASDs not only sheds light on the molecular and cellular mechanisms that govern the function of the central nervous system, but may lead to the discovery of potential therapeutic targets for autism and other cognitive disorders. Our Research Topic which constitutes this e-book documents the recent development and ideas in the study of pathogenesis and treatment of ASDs, with an emphasis on syndromic disorders such as fragile X and Rett syndromes. In addition, model systems and methodological approaches with translational relevance to autism are covered herein. We hope that the Research Topic will enhance the global knowledge base in the autism research community and foster new research directions in autism related biology.

MeCP2 --- Treatment --- Fragile X Syndrome --- Pathogenesis --- FMRP --- Autism Spectrum Disorders --- Pharmacology --- Synaptic deficits --- synaptic plasticity --- Rett Syndrome