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Chronobiological mechanisms regulating time-of-day mediated behaviors, such as sleep and circadian rhythms, are thought to interact with and/or share cellular and molecular signaling cascades that shape synaptic plasticity and neural excitability. These same factors are also known to underlie events that govern higher-order cognitive processing, including learning and memory formation, and often through phylogenetically conserved pathways. This suggests that factors which contribute to adaptive responses to changing environmental stimuli are likely derived from basic evolutionarily ancient processes, and underscores the importance of using both invertebrate and vertebrate models to study the interaction of chronobiology and cognitive processing. This issue highlights current views along with original research on sleep and circadian features of plasticity and memory in multiple species, models, and systems.

Learning --- Sleep --- Memory --- plasticity --- synapse --- circadian rhythms

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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

neurotransmitters --- membrane fusion --- synapse --- receptor --- calcium

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Chronobiological mechanisms regulating time-of-day mediated behaviors, such as sleep and circadian rhythms, are thought to interact with and/or share cellular and molecular signaling cascades that shape synaptic plasticity and neural excitability. These same factors are also known to underlie events that govern higher-order cognitive processing, including learning and memory formation, and often through phylogenetically conserved pathways. This suggests that factors which contribute to adaptive responses to changing environmental stimuli are likely derived from basic evolutionarily ancient processes, and underscores the importance of using both invertebrate and vertebrate models to study the interaction of chronobiology and cognitive processing. This issue highlights current views along with original research on sleep and circadian features of plasticity and memory in multiple species, models, and systems.

Learning --- Sleep --- Memory --- plasticity --- synapse --- circadian rhythms --- Learning --- Sleep --- Memory --- plasticity --- synapse --- circadian rhythms

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The immunological synapse (IS) is a specialised cell-cell adhesion that mediates antigen acquisition and regulates the activation of lymphocytes. Initial studies of the IS showed a structure composed of stable supra-molecular activation clusters (SMAC) organised during the interaction of helper T lymphocytes with B lymphocytes, working as antigen presenting cells. A central SMAC of coalesced T cell receptors (TCRs) and a peripheral SMAC for cell-cell adhesion were observed. IS with similar structure was later described during antigen acquisition by B cells and during the interaction of NK cells with target and healthy cells. More recent research developed with microscopy systems that improve the spatial and temporal resolution has showed the complex molecular dynamics at the IS that governs lymphocyte activation. Currently, the IS is seen as a three-dimensional structure where signalling networks for lymphocyte activation and endosomal and cytoskeleton machinery are polarised. A view has emerged in which dynamic microclusters of signalling complexes are composed of molecular components attached to the plasma membrane and other components conveyed on sub-synaptic vesicles transported to the membrane by cytoskeletal fibers and motor proteins. Much information is nonetheless missing about how the dynamics of the endosomal compartment, the cytoskeleton, and signalling complexes are reciprocally regulated to achieve the function of lymphocytes. Experimental evidence also suggests that the environment surrounding lymphocytes exposed to different antigenic challenge regulates IS assembly and functional output, making an even more complex scenario still far from being completely understood. Also, although some signalling molecular components for lymphocyte activation have been identified and thoroughly studied, the function of other molecules has not been yet uncovered or deeply characterised. This research topic aims to provide the reader with the latest information about the molecular dynamics governing lymphocyte activation. These molecular dynamics dictate cell decisions. Thus, we expect that understanding them will provide new avenues for cell manipulation in therapies to treat different immune-related pathologies.

cytoskeleton dynamics --- intracellular signalling --- Immunological Synapse --- endosomal dynamics --- cytoskeleton dynamics --- intracellular signalling --- Immunological Synapse --- endosomal dynamics

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Synaptic transmission is the basis of neuronal communication and is thus the most important element in brain functions, ranging from sensory input to information processing. Changes in synaptic transmission can result in the formation or dissolution of memories, and can equally lead to neurological and psychiatric disorders. The proteins composing the synapse, and their respective functions, are getting increasingly known. One aspect that has become evident in the last years is that most synaptic functions are performed not by single proteins, but by highly organized multi-protein machineries, which interact dynamically to provide responses optimally suited to the needs of the neuronal network. To decipher synaptic and neuronal function, it is essential to understand the organisational, morphological and functional aspects of the molecular nanomachines that operate at the synapse. We discuss these aspects in 11 different chapters, focusing on the structure and function of the active zone, on the functional anatomy of the synaptic vesicle, and on some of the best known soluble protein complexes from the synapse, including those involved in endocytosis and vesicle recycling.

synaptic protein --- active Zone --- nanomachine --- synapse --- synaptic vesicle --- synaptic protein --- active Zone --- nanomachine --- synapse --- synaptic vesicle