Circuit mechanisms of navigation strategy learning in mice.

Navigation tasks involve the gradual selection and deployment of increasingly effective searching procedures to reach targets. The brain mechanisms underlying such complex behavior are poorly understood, but their elucidation might provide insights into the systems linking exploration and decision making in complex learning. Here, we developed a trial-by-trial goal-related search strategy analysis as mice learned to navigate identical water mazes encompassing distinct goal-related rules and monitored the strategy deployment process throughout learning. We found that navigation learning involved the following three distinct phases: an early phase during which maze-specific search strategies are deployed in a minority of trials, a second phase of preferential increasing deployment of one search strategy, and a final phase of increasing commitment to this strategy only. The three maze learning phases were affected differently by inhibition of retrosplenial cortex (RSC), dorsomedial striatum (DMS), or dorsolateral striatum (DLS). Through brain region-specific inactivation experiments and gain-of-function experiments involving activation of learning-related cFos+ ensembles, we unraveled how goal-related strategy selection relates to deployment throughout these sequential processes. We found that RSC is critically important for search strategy selection, DMS mediates strategy deployment, and DLS ensures searching consistency throughout maze learning. Notably, activation of specific learning-related ensembles was sufficient to direct strategy selection (RSC) or strategy deployment (DMS) in a different maze. Our results establish a goal-related search strategy deployment approach to dissect unsupervised navigation learning processes and suggest that effective searching in navigation involves evidence-based goal-related strategy direction by RSC, reinforcement-modulated strategy deployment through DMS, and online guidance through DLS.

Burst-Dependent Bidirectional Plasticity in the Cerebellum Is Driven by Presynaptic NMDA Receptors.

Numerous studies have shown that cerebellar function is related to the plasticity at the synapses between parallel fibers and Purkinje cells. How specific input patterns determine plasticity outcomes, as well as the biophysics underlying plasticity of these synapses, remain unclear. Here, we characterize the patterns of activity that lead to postsynaptically expressed LTP using both in vivo and in vitro experiments. Similar to the requirements of LTD, we find that high-frequency bursts are necessary to trigger LTP and that this burst-dependent plasticity depends on presynaptic NMDA receptors and nitric oxide (NO) signaling. We provide direct evidence for calcium entry through presynaptic NMDA receptors in a subpopulation of parallel fiber varicosities. Finally, we develop and experimentally verify a mechanistic plasticity model based on NO and calcium signaling. The model reproduces plasticity outcomes from data and predicts the effect of arbitrary patterns of synaptic inputs on Purkinje cells, thereby providing a unified description of plasticity.

Data in support of the identification of neuronal and astrocyte proteins interacting with extracellularly applied oligomeric and fibrillar α-synuclein assemblies by mass spectrometry.

α-Synuclein (α-syn) is the principal component of Lewy bodies, the pathophysiological hallmark of individuals affected by Parkinson disease (PD). This neuropathologic form of α-syn contributes to PD progression and propagation of α-syn assemblies between neurons. The data we present here support the proteomic analysis used to identify neuronal proteins that specifically interact with extracellularly applied oligomeric or fibrillar α-syn assemblies (conditions 1 and 2, respectively) (doi: 10.15252/embj.201591397[1]). α-syn assemblies and their cellular partner proteins were pulled down from neuronal cell lysed shortly after exposure to exogenous α-syn assemblies and the associated proteins were identified by mass spectrometry using a shotgun proteomic-based approach. We also performed experiments on pure cultures of astrocytes to identify astrocyte-specific proteins interacting with oligomeric or fibrillar α-syn (conditions 3 and 4, respectively). For each condition, proteins interacting selectively with α-syn assemblies were identified by comparison to proteins pulled-down from untreated cells used as controls. The mass spectrometry data, the database search and the peak lists have been deposited to the ProteomeXchange Consortium database via the PRIDE partner repository with the dataset identifiers PRIDE: PXD002256 to PRIDE: PXD002263 and doi: 10.6019/PXD002256 to 10.6019/PXD002263.

α-synuclein assemblies sequester neuronal α3-Na+/K+-ATPase and impair Na+ gradient.

Extracellular α-synuclein (α-syn) assemblies can be up-taken by neurons; however, their interaction with the plasma membrane and proteins has not been studied specifically. Here we demonstrate that α-syn assemblies form clusters within the plasma membrane of neurons. Using a proteomic-based approach, we identify the α3-subunit of Na+/K+-ATPase (NKA) as a cell surface partner of α-syn assemblies. The interaction strength depended on the state of α-syn, fibrils being the strongest, oligomers weak, and monomers none. Mutations within the neuron-specific α3-subunit are linked to rapid-onset dystonia Parkinsonism (RDP) and alternating hemiplegia of childhood (AHC). We show that freely diffusing α3-NKA are trapped within α-syn clusters resulting in α3-NKA redistribution and formation of larger nanoclusters. This creates regions within the plasma membrane with reduced local densities of α3-NKA, thereby decreasing the efficiency of Na+ extrusion following stimulus. Thus, interactions of α3-NKA with extracellular α-syn assemblies reduce its pumping activity as its mutations in RDP/AHC.

Cerebellum involvement in cortical sensorimotor circuits for the control of voluntary movements.

Sensorimotor integration is crucial to perception and motor control. How and where this process takes place in the brain is still largely unknown. Here we analyze the cerebellar contribution to sensorimotor integration in the whisker system of mice. We identify an area in the cerebellum where cortical sensory and motor inputs converge at the cellular level. Optogenetic stimulation of this area affects thalamic and motor cortex activity, alters parameters of ongoing movements and thereby modifies qualitatively and quantitatively touch events against surrounding objects. These results shed light on the cerebellum as an active component of sensorimotor circuits and show the importance of sensorimotor cortico-cerebellar loops in the fine control of voluntary movements.

Functional role of the cerebellum in gamma-band synchronization of the sensory and motor cortices.

The cerebellum is an essential structure for the control of movement. It sends abundant ascending projections to the cerebral cortex via the thalamus, but its contribution to cortical activity remains largely unknown. Here we studied its influence on cortical neuronal activity in freely moving rats. We demonstrate an excitatory action of the cerebellum on the motor thalamus and the motor cortex. We also show that cerebellar inactivation disrupts the gamma-band coherence of local field potential between the sensory and motor cortices during whisking. In contrast, phase locking of neuronal activities to local gamma oscillations was preserved in the sensory and motor cortices by cerebellar inactivation. These results indicate that the cerebellum contributes to coordinated sensorimotor cortical activities during motor activation and thus participates in the multiregional cortical processing of information.

Environmental enrichment decreases GABAergic inhibition and improves cognitive abilities, synaptic plasticity, and visual functions in a mouse model of Down syndrome.

Down syndrome (DS) is the most common genetic disorder associated with mental retardation. It has been repeatedly shown that Ts65Dn mice, the prime animal model for DS, have severe cognitive and neural plasticity defects due to excessive inhibition. We report that increasing sensory-motor stimulation in adulthood through environmental enrichment (EE) reduces brain inhibition levels and promotes recovery of spatial memory abilities, hippocampal synaptic plasticity, and visual functions in adult Ts65Dn mice.

Activation of Rho GTPases triggers structural remodeling and functional plasticity in the adult rat visual cortex.

A classical example of age-dependent plasticity is ocular dominance (OD) plasticity, triggered by monocular deprivation (MD). Sensitivity of cortical circuits to a brief period of MD is maximal in juvenile animals and downregulated in adult age. It remains unclear whether a reduced potential for morphological remodeling underlies this downregulation of physiological plasticity in adulthood. Here we have tested whether stimulation of structural rearrangements is effective in promoting experience-dependent plasticity in adult age. We have exploited a bacterial protein toxin, cytotoxic necrotizing factor 1 (CNF1), that regulates actin dynamics and structure of neuronal processes via a persistent activation of Rho GTPases. Injection of CNF1 into the adult rat visual cortex triggered a long-lasting activation of the Rho GTPase Rac1, with a consequent increase in spine density and length in pyramidal neurons. Adult rats treated with CNF1, but not controls, showed an OD shift toward the open eye after MD. CNF1-mediated OD plasticity was selectively attributable to the enhancement of open-eye responses, whereas closed-eye inputs were unaffected. This effect correlated with an increased density of geniculocortical terminals in layer IV of monocularly deprived, CNF1-treated rats. Thus, Rho GTPase activation reinstates OD plasticity in the adult cortex via the potentiation of more active inputs from the open eye. These data establish a direct link between structural remodeling and functional plasticity and demonstrate a role for Rho GTPases in brain plasticity in vivo. The plasticizing effects of Rho GTPase activation may be exploited to promote brain repair.

Brain plasticity and disease: a matter of inhibition.

One major goal in Neuroscience is the development of strategies promoting neural plasticity in the adult central nervous system, when functional recovery from brain disease and injury is limited. New evidence has underscored a pivotal role for cortical inhibitory circuitries in regulating plasticity both during development and in adulthood. This paper summarizes recent findings showing that the inhibition-excitation balance controls adult brain plasticity and is at the core of the pathogenesis of neurodevelopmental disorders like autism, Down syndrome, and Rett syndrome.

Food restriction enhances visual cortex plasticity in adulthood.

Neural circuits display a heightened sensitivity to external stimuli during well-established windows in early postnatal life. After the end of these critical periods, brain plasticity dramatically wanes. The visual system is one of the paradigmatic models for studying experience-dependent plasticity. Here we show that food restriction can be used as a strategy to restore plasticity in the adult visual cortex of rats. A short period of food restriction in adulthood is able both to reinstate ocular dominance plasticity and promote recovery from amblyopia. These effects are accompanied by a reduction of intracortical inhibition without modulation of brain-derived neurotrophic factor expression or extracellular matrix structure. Our results suggest that food restriction could be investigated as a potential way of modulating plasticity.

Serotonin triggers a transient epigenetic mechanism that reinstates adult visual cortex plasticity in rats.

Cortical circuitries are highly sensitive to experience during early life but this phase of heightened plasticity decreases with development. We recently demonstrated that fluoxetine reinstates a juvenile-like form of plasticity in the adult visual system. Here we explored cellular and molecular mechanisms that underlie the occurrence of these plastic phenomena. Adult rats were intracortically treated with serotonin (5-HT) whereas long-term fluoxetine-treated rats were infused with the 5-HT(1A) -receptor antagonist WAY-100635, brain-derived neurotrophic factor (BDNF) scavenger trkB-IgG or the mitogen-activated protein kinase inhibitor U0126. Plasticity was assessed as variations of visual cortex responsiveness after unilateral eyelid suture and reverse occlusion by using an electrophysiological approach. Real-time PCR and chromatin immunoprecipitation analysis were then used to explore alterations in gene expression and modifications of chromatin structure associated with the plastic outcome caused by fluoxetine in the visual system. Local infusion of 5-HT into visual cortex restored susceptibility to monocular deprivation in adulthood whereas infusion of WAY-100635, trkB-IgG or U0126 prevented the process of plasticity reactivation in fluoxetine-treated animals. Long-term fluoxetine treatment promoted a transient increase of Bdnf expression in the visual cortex, which was paralleled by an increased histone acetylation status at Bdnf promoter regions and by decreased expression of Hdac5. Accordingly, enhancing histone acetylation levels by systemic treatment with Trichostatin-A reactivated plasticity in the adult while WAY-100635-infusion prevented epigenetic modifications in Bdnf promoter areas. The data suggest a key role for 5-HT(1A) receptor and BDNF-trkB signalling in driving a transitory epigenetic remodelling of chromatin structure that underlies the reactivation of plasticity in the visual system.

GABAergic inhibition in visual cortical plasticity.

Experience is required for the shaping and refinement of developing neural circuits during well defined periods of early postnatal development called critical periods. Many studies in the visual cortex have shown that intracortical GABAergic circuitry plays a crucial role in defining the time course of the critical period for ocular dominance plasticity. With the end of the critical period, neural plasticity wanes and recovery from the effects of visual defects on visual acuity (amblyopia) or binocularity is much reduced or absent. Recent results pointed out that intracortical inhibition is a fundamental limiting factor for adult cortical plasticity and that its reduction by means of different pharmacological and environmental strategies makes it possible to greatly enhance plasticity in the adult visual cortex, promoting ocular dominance plasticity and recovery from amblyopia. Here we focus on the role of intracortical GABAergic circuitry in controlling both developmental and adult cortical plasticity. We shall also discuss the potential clinical application of these findings to neurological disorders in which synaptic plasticity is compromised because of excessive intracortical inhibition.

Reducing intracortical inhibition in the adult visual cortex promotes ocular dominance plasticity.

Experience-dependent plasticity in the cortex is often higher during short critical periods in postnatal development. The mechanisms limiting adult cortical plasticity are still unclear. Maturation of intracortical GABAergic inhibition is suggested to be crucial for the closure of the critical period for ocular dominance (OD) plasticity in the visual cortex. We find that reduction of GABAergic transmission in the adult rat visual cortex partially reactivates OD plasticity in response to monocular deprivation (MD). This is accompanied by an enhancement of activity-dependent potentiation of synaptic efficacy but not of activity-dependent depression. We also found a decrease in the expression of chondroitin sulfate proteoglycans in the visual cortex of MD animals with reduced inhibition, after the reactivation of OD plasticity. Thus, intracortical inhibition is a crucial limiting factor for the induction of experience-dependent plasticity in the adult visual cortex.

Plasticity in the adult brain: lessons from the visual system.

While cortical circuits display maximal sensitivity to sensory experience during critical periods of early postnatal development, far less plasticity is present in the mature brain. Ocular dominance shift of visual cortical neurons in response to eye occlusion and recovery of visual functions from a period of sensory deprivation are two classical models in the study of critical period determinants in the visual cortex. Recent papers employing various pharmacological and environmental strategies have shown that it is possible to reinstate much greater levels of plasticity in the adult visual cortex than previously suspected. These studies point toward intracortical inhibition as a crucial determinant for critical period regulation in the visual system and have a great potential for therapeutic rehabilitation and recovery from injury in the adult brain.

Metoclopramida com estímulo de ganho de peso em lactentes

A proposta desta investigaçäo, foi avaliar a droga metoclopramida como estimulante da produçäo de leite materno. Dez lactentes normais, que foram exlusivamente amamentados ao seio com pouco ganho de peso, foram os pacientes selecionados para o estudo. Suas mäes foram randomizadas para receber placebo (4 casos) ou metoclopramida (6 casos) numa dose de 10 mg, oralmente, 3 vezes por dia, num estudo duplo cego. Näo houve diferença significativa quanto a idade, peso de nascimento e período de tratamento entre os dois grupos; contudo o grupo da metocloparamida ganhou significantemente maior peso do que o grupo placebo (p < 0.01). Estes resultados têm sido confirmados por outros estudos, que mostraram, também um aumento significante dos níveis plasmáticos de prolactina e produçäo de leite, depois do tratamento com metoclopramida. A metoclopramida pode ser usada com sucesso para estimular a produçäo de leite materno em mäes que tiveram diminuiçäo desta secreçäo

Leite materno: componentes e propriedades imunológicas / Maternal milk: components and immunological properties

Os autores fazem uma revisäo bibliográfica sobre o Aleitamento Materno, demonstrando através de sua composiçäo e propriedades imunológicas que este é o alimento mais completo para o lactante