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Current Opinion in Neurobiology

Pankaj Dubey, Kent Jorgenson, Subhojit Roy
The actin cytoskeleton in neurons plays critical roles in axonal growth and synaptic organization. Until recently, most studies on axonal actin were limited to terminal growth cones or synapses, whereas the organization of actin along the shaft of the axon was relatively ignored. However, experiments using super-resolution microscopy and live imaging have revealed previously unknown actin structures along the axonal shaft, such as periodic 'actin rings' circumferentially wrapping underneath the plasma membrane and dynamic actin pools deeper within the axon shaft (termed actin 'hotspots' and 'trails')...
July 10, 2018: Current Opinion in Neurobiology
Alessandro Simi, Michèle Studer
The subdivision of the mammalian neocortex into specialized modality-specific areas is responsible for the processing of sensory information followed by an adequate motor response. This process, called arealization, depends on the graded expression of transcription factors in neocortical progenitors and postmitotic neurons prenatally, and on external activity-dependent cues driven by thalamocortical axons during postnatal stages. Thalamic inputs are guided within an intrinsically determined genetic framework to selectively target and innervate layer 4 (L4) cortical neurons in a somatotopic manner...
July 10, 2018: Current Opinion in Neurobiology
Ofer Yizhar, Oded Klavir
Animals constantly evaluate their environment in order to avoid potential threats and obtain reward in the form of food, shelter and social interactions. In order to appropriately respond to sensory cues from the environment, the brain needs to form and store multiple cue-outcome associations. These can then be used to form predictions of the valence of sounds, smells and other sensory inputs arising from the surroundings. However, these associations must be subject to constant update, as the environment can rapidly change...
July 2, 2018: Current Opinion in Neurobiology
Faye McLeod, Patricia C Salinas
Dynamic changes in the structure and function of synapses in response to the environment, termed synaptic plasticity, are the cellular basis of learning and memory. At excitatory synapses, activation of NMDA receptors by glutamate leads to calcium influx triggering intracellular pathways that promote the trafficking of AMPA receptors to the post-synaptic membrane and actin remodeling. New evidence shows that Wnt secreted proteins, known for their role in synapse development, are essential for early stages of long-term potentiation, a form of plasticity that increases synaptic strength...
July 2, 2018: Current Opinion in Neurobiology
Martha W Bagnall, David Schoppik
Most animals orient their bodies with respect to gravity to facilitate locomotion and perception. The neural circuits responsible for these orienting movements have long served as a model to address fundamental questions in systems neuroscience. Though postural control is vital, we know little about development of either balance reflexes or the neural circuitry that produces them. Recent work in a genetically and optically accessible vertebrate, the larval zebrafish, has begun to reveal the mechanisms by which such vestibular behaviors and circuits come to function...
June 25, 2018: Current Opinion in Neurobiology
Márcia M Aranha, Maria Luísa Vasconcelos
Innate responses are often sexually dimorphic. Studies of female specific behaviors have remained niche, but the focus is changing as illustrated by the recent progress in understanding the female courtship responses and egg-laying decisions. In this review, we will cover our current knowledge about female behaviors in these two specific contexts. Recent studies elucidate on how females process the courtship song. They also show that egg-laying decisions are extremely complex, requiring the assessment of food, microbial, predator and social cues...
June 22, 2018: Current Opinion in Neurobiology
Caitlin E Moyer, Yi Zuo
Dendritic spines are the postsynaptic sites of most excitatory synapses in the cerebral cortex. Their morphology and density change throughout life, reflecting the maturation and reorganization of excitatory circuits. The development of in vivo two-photon microscopy has enabled the monitoring of the same dendritic spines over time during different developmental periods. In this review we focus on recent in vivo imaging studies in rodents that have revealed cell type-specific and region-specific structural dynamics of dendritic spines...
June 21, 2018: Current Opinion in Neurobiology
Takuji Iwasato, Reha S Erzurumlu
Molecular identification of neuronal types and genetic and imaging approaches to characterize their properties reveal morphological, physiological and dynamic aspects of sensory circuit development. Here we focus on the mouse tactile sensory circuitry, with particular emphasis on the main trigeminal pathway that connects the whiskers, the major tactile organ in rodents, to the neocortex. At each level of this pathway, neurogenesis, axonal elongation, pathfinding, target recognition and circuit reorganization including dendritic refinement of cortical layer 4 neurons occur contemporaneously and a multitude of molecular signals are used in differing combinations...
June 13, 2018: Current Opinion in Neurobiology
Haiwen Chen, Ai-Hui Tang, Thomas A Blanpied
Synapses differ markedly in their performance, even amongst those on a single neuron. The mechanisms that drive this functional diversification are of great interest because they enable adaptive behaviors and are targets of pathology. Considerable effort has focused on elucidating mechanisms of plasticity that involve changes to presynaptic release probability and the number of postsynaptic receptors. However, recent work is clarifying that nanoscale organization of the proteins within glutamatergic synapses impacts synapse function...
June 11, 2018: Current Opinion in Neurobiology
Annalisa Paolino, Laura R Fenlon, Rodrigo Suárez, Linda J Richards
Long-range projection neurons of the neocortex form the major tracts of the mammalian brain and are crucial for sensory-motor, associative and executive functions. Development of such circuits involves neuronal proliferation, specification and migration, as well as axonal elongation, navigation and targeting, where growing axons encounter multiple guidance cues and integrate these signals to execute guidance decisions. The complexity of axon guidance mechanisms in the formation of long-range neuronal projections has suggested that they might be under control of transcription factors, which are DNA-binding proteins that regulate the expression of downstream genes...
June 9, 2018: Current Opinion in Neurobiology
Kirill E Volynski, Shyam S Krishnakumar
Quantal neurotransmitter release at nerve terminals is tightly regulated by the presynaptic Ca2+ concentration. Here, we summarise current advances in understanding how the interplay between presynaptic Ca2+ dynamics and different Ca2+ release sensors shapes action potential-evoked release on a timescale from hundreds of microseconds to hundreds of milliseconds. In particular, we review recent studies that reveal the synergistic roles of the low Ca2+ affinity/fast release sensors synaptotagmins 1, 2 and 9 and the high affinity/slow release sensor synaptotagmin 7 in the regulation of synchronous and asynchronous release and of short-term synaptic plasticity...
June 7, 2018: Current Opinion in Neurobiology
Adil G Khan, Sonja B Hofer
Vision is an active process. What we perceive strongly depends on our actions, intentions and expectations. During visual processing, these internal signals therefore need to be integrated with the visual information from the retina. The mechanisms of how this is achieved by the visual system are still poorly understood. Advances in recording and manipulating neuronal activity in specific cell types and axonal projections together with tools for circuit tracing are beginning to shed light on the neuronal circuit mechanisms of how internal, contextual signals shape sensory representations...
June 5, 2018: Current Opinion in Neurobiology
David Robbe
A long-standing hypothesis postulates that the striatum is essential for the concurrent selection of adaptive actions and repression of inappropriate alternatives. Here, classical and recent anatomical and physiological studies are reviewed to show that, in mammals, the striatum can detect discrete task-relevant sensory stimuli and continuously track somatosensory information associated with the generation of simple movements and more complex actions. Rather than contributing to the immediate selection of actions, the striatum may monitor the sensorimotor state of animals by integrating somatosensory information and motor-related signals on a moment-by-moment basis...
May 31, 2018: Current Opinion in Neurobiology
Ilsong Choi, Jae-Yun Lee, Seung-Hee Lee
Sensory perception in the real world requires proper integration of different modality inputs. Process of multisensory integration is not uniform. It varies from individual to individual and changes at different behavioral states of the animal. What factors affect multisensory integration? How does the mammalian brain reconstruct a multisensory world at different states? Here, we summarize recent findings on bottom-up and top-down factors that can modulate sensory processing and multisensory integration. We discuss cortical circuits that are responsible for modulation of multisensory processing based on recent rodent studies...
May 17, 2018: Current Opinion in Neurobiology
Amy M LeMessurier, Daniel E Feldman
That experience shapes sensory tuning in primary sensory cortex is well understood. But effective neural population codes depend on more than just sensory tuning. Recent population imaging and recording studies have characterized population codes in sensory cortex, and tracked how they change with sensory manipulations and training on perceptual learning tasks. These studies confirm sensory tuning changes, but also reveal other features of plasticity, including sensory gain modulation, restructuring of firing correlations, and differential routing of information to output pathways...
May 15, 2018: Current Opinion in Neurobiology
Phillip Bokiniec, Niccolò Zampieri, Gary R Lewin, James Fa Poulet
Thermal information about skin surface temperature is a key sense for the perception of object identity and valence. The identification of ion channels involved in the transduction of thermal changes has provided a genetic access point to the thermal system. However, from sensory specific 'labeled-lines' to multimodal interactive pathways, the functional organization and identity of the neural circuits mediating innocuous thermal perception have been debated for over 100 years. Here we highlight points in the system that require further attention and review recent advances using in vivo electrophysiology, cellular resolution calcium imaging, optogenetics and thermal perceptual tasks in behaving mice that have begun to uncover the anatomical principles and neural processing mechanisms underlying innocuous thermal perception...
May 15, 2018: Current Opinion in Neurobiology
Craig Blackstone
Hereditary spastic paraplegias (HSPs) are neurologic disorders characterized by prominent lower-extremity spasticity, resulting from a length-dependent axonopathy of corticospinal upper motor neurons. They are among the most genetically-diverse neurologic disorders, with >80 distinct genetic loci and over 60 identified genes. Studies investigating the molecular pathogenesis underlying HSPs have emphasized the importance of converging cellular pathogenic themes in the most common forms of HSP, providing compelling targets for therapy...
May 10, 2018: Current Opinion in Neurobiology
Tara E Tracy, Li Gan
The accumulation of pathological tau in the brain is associated with neuronal deterioration and cognitive impairments in tauopathies including Alzheimer's disease. Tau, while primarily localized in the axons of healthy neurons, accumulates in the soma and dendrites of neurons under pathogenic conditions. Tau is found in both presynaptic and postsynaptic compartments of neurons in Alzheimer's disease. New research supports that soluble forms of tau trigger pathophysiology in the brain by altering properties of synaptic and neuronal function at the early stages of disease progression, before neurons die...
May 9, 2018: Current Opinion in Neurobiology
Patricia Gaspar, Nicolas Renier
In the rodent somatosensory system, the disproportionally large whisker representation and their specialization into barrel-shaped units in the different sensory relays has offered experimentalists with an ideal tool to identify mechanisms involved in brain map formation. These combine three intertwined constraints: Firstly, fasciculation of the incoming axons; secondly, early neural activity; finally, molecular patterning. Sophisticated genetic manipulations in mice have now allowed dissecting these mechanisms with greater accuracy...
May 9, 2018: Current Opinion in Neurobiology
Frédéric Causeret, Eva Coppola, Alessandra Pierani
The mature cerebral cortex only contains a fraction of the cells that are generated during embryonic development. Indeed some neuronal populations are produced in excess and later subjected to partial elimination whereas others are almost completely removed during the first two postnatal weeks in mice. Although the identity of cells that disappear, the time course and mechanisms of their death are becoming reasonably well established, the meaning of producing supernumerary cells still remains elusive. In this review, we focus on recent data that shed a new light on the mechanisms involved in adjusting cell numbers and discuss the significance of refinement versus complete elimination of cell populations in the developing cortex...
May 5, 2018: Current Opinion in Neurobiology
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