Cerebellum shapes hippocampal spatial code

Spatial representation is an active process that requires complex multimodal integration from a large interacting network of cortical and subcortical structures. We sought to determine the role of cerebellar protein kinase C (PKC)-dependent plasticity in spatial navigation by recording the activity of hippocampal place cells in transgenic L7PKCI mice with selective disruption of PKC-dependent plasticity at parallel fiber-Purkinje cell synapses. Place cell properties were exclusively impaired when L7PKCI mice had to rely on self-motion cues. The behavioral consequence of such a deficit is evidenced here by selectively impaired navigation capabilities during a path integration task. Together, these results suggest that cerebellar PKC-dependent mechanisms are involved in processing self-motion signals essential to the shaping of hippocampal spatial representation.     

Temporal and spatial enumeration processes in the primate parietal cortex

Humans and animals can nonverbally enumerate visual items across time in a sequence or rapidly estimate the set size of spatial dot patterns at a single glance. We found that temporal and spatial enumeration processes engaged different populations of neurons in the intraparietal sulcus of behaving monkeys. Once the enumeration process was completed, however, another neuronal population represented the cardinality of a set irrespective of whether it had been cued in a spatial layout or across time. These data suggest distinct neural processing stages for different numerical formats, but also a final convergence of the segregated information to form most abstract quantity representations.     

大气CO2浓度升高对作物根际土壤氮的影响

利用FACE(Free air carbon dioxide enrichment)技术,在两种氮肥施用(低氮LN和常规氮NN)水平下,研究CO2浓度升高对水稻和小麦收获后根际和非根际土壤硝态氮、铵态氮和有机氮的影响.结果表明,相对于对照CO2浓度处理,高CO2浓度处理在显著增加作物生物量的前提下,使水稻季根际土壤硝态氮含量降低,NN水平下降低明显,小麦季变化不大,高CO2浓度处理对作物根际的影响大于非根际.高CO2浓度对土壤铵态氮含量的影响不显著,仅小幅度增加了水稻季和降低了小麦季土壤铵态氮含量,且根际降低幅度大于非根际;增加氮肥施用使土壤铵态氮含量在高CO2浓度处理增加幅度低于对照.高CO2浓度处理并没有显著增加有机氮的含量,在小麦季作物对土壤有机氮的贡献大于水稻季,且增加氮肥施用条件下根际对有机氮的贡献较大.     

The spatial periodicity of grid cells is not sustained during reduced theta oscillations

Grid cells in parahippocampal cortices fire at vertices of a periodic triangular grid that spans the entire recording environment. Such precise neural computations in space have been proposed to emerge from equally precise temporal oscillations within cells or within the local neural circuitry. We found that grid-like firing patterns in the entorhinal cortex vanished when theta oscillations were reduced after intraseptal lidocaine infusions in rats. Other spatially modulated cells in the same cortical region and place cells in the hippocampus retained their spatial firing patterns to a larger extent during these periods without well-organized oscillatory neuronal activity. Precisely timed neural activity within single cells or local networks is thus required for periodic spatial firing but not for single place fields.     

Sequence finishing and mapping of Drosophila melanogaster heterochromatin

Genome sequences for most metazoans and plants are incomplete because of the presence of repeated DNA in the heterochromatin. The heterochromatic regions of Drosophila melanogaster contain 20 million bases (Mb) of sequence amenable to mapping, sequence assembly, and finishing. We describe the generation of 15 Mb of finished or improved heterochromatic sequence with the use of available clone resources and assembly methods. We also constructed a bacterial artificial chromosome-based physical map that spans 13 Mb of the pericentromeric heterochromatin and a cytogenetic map that positions 11 Mb in specific chromosomal locations. We have approached a complete assembly and mapping of the nonsatellite component of Drosophila heterochromatin. The strategy we describe is also applicable to generating substantially more information about heterochromatin in other species, including humans.     

Accelerated evolution of conserved noncoding sequences in humans

Changes in gene regulation likely influenced the profound phenotypic divergence of humans from other mammals, but the extent of adaptive substitution in human regulatory sequences remains unknown. We identified 992 conserved noncoding sequences (CNSs) with a significant excess of human-specific substitutions. These accelerated elements were disproportionately found near genes involved in neuronal cell adhesion. To assess the uniqueness of human noncoding evolution, we examined CNSs accelerated in chimpanzee and mouse. Although we observed a similar enrichment near neuronal adhesion genes in chimpanzee, the accelerated CNSs themselves exhibited almost no overlap with those in human, suggesting independent evolution toward different neuronal phenotypes in each species. CNSs accelerated in mouse showed no bias toward neuronal cell adhesion. Our results indicate that widespread cis-regulatory changes in human evolution may have contributed to uniquely human features of brain development and function.     

不同航行条件下的主机操作

在不同航行条件下,船舶操纵性能有一定程度的变化,在详细分析了各种情况时主机运行工作的变化规律前提下,对正确判断航行情况并恰当地操纵主机,保障航行的安全提出了的建议。     

Sequential interplay of nicotinic and GABAergic signaling guides neuronal development

GABA (gamma-aminobutyric acid), the major inhibitory transmitter in the brain, goes through a transitory phase of excitation during development. The excitatory phase promotes neuronal growth and integration into circuits. We show here that spontaneous nicotinic cholinergic activity is responsible for terminating GABAergic excitation and initiating inhibition. It does so by changing chloride transporter levels, shifting the driving force on GABA-induced currents. The timing of the transition is critical, because the two phases of GABAergic signaling provide contrasting developmental instructions. Synergistic with nicotinic excitation, GABAergic inhibition constrains neuronal morphology and innervation. The results reveal a multitiered activity-dependent strategy controlling neuronal development.     

Structure and function of an essential component of the outer membrane protein assembly machine

Integral beta-barrel proteins are found in the outer membranes of mitochondria, chloroplasts, and Gram-negative bacteria. The machine that assembles these proteins contains an integral membrane protein, called YaeT in Escherichia coli, which has one or more polypeptide transport-associated (POTRA) domains. The crystal structure of a periplasmic fragment of YaeT reveals the POTRA domain fold and suggests a model for how POTRA domains can bind different peptide sequences, as required for a machine that handles numerous beta-barrel protein precursors. Analysis of POTRA domain deletions shows which are essential and provides a view of the spatial organization of this assembly machine.     

Synfire chains and cortical songs: temporal modules of cortical activity

How can neural activity propagate through cortical networks built with weak, stochastic synapses? We find precise repetitions of spontaneous patterns of synaptic inputs in neocortical neurons in vivo and in vitro. These patterns repeat after minutes, maintaining millisecond accuracy. Calcium imaging of slices reveals reactivation of sequences of cells during the occurrence of repeated intracellular synaptic patterns. The spontaneous activity drifts with time, engaging different cells. Sequences of active neurons have distinct spatial structures and are repeated in the same order over tens of seconds, revealing modular temporal dynamics. Higher order sequences are replayed with compressed timing.     

长白山次生杨桦林树种多样性格局多尺度分析

从植物种群角度出发研究物种对局域群落多样性格局的影响,有助于更好地揭示群落水平研究中易于被掩 盖的种间互作等作用机制对群落组建过程的影响。研究了不同空间尺度上树种对局域多样性格局的影响,检验了 促进种、中性种和抑制种在群落多样性格局组建中所起的作用。以长白山5.2 hm2 次生杨桦林监测样地数据为基 础,采用单物种-面积关系模型计算29 个树种的ISAR 和mISAR 曲线,并用完全空间随机化方法检验了单物种-面 积关系偏离中性的显著性。研究结果表明,不同树种在不同空间尺度上对局域多样性格局影响不同;样地中臭松、 簇毛槭、色木槭、山杨、水榆和紫椴为多样性促进种,白桦和春榆为多样性抑制种;水曲柳、蒙古栎、山丁子和暴马丁 香在小尺度上为中性种,其他树种在小尺度上均表现为促进种。多样性促进种、中性种和抑制种对群落多样性格 局组建的影响具有明显的尺度依赖性,多样性促进种在中小尺度(0 ~36 m)上比例最高,在群落多样性构建过程中 起主导作用;而中性种在大尺度上比例最高,决定了群落多样性格局的构建过程。因此,多样性促进种和中性种共 同影响着局域群落多样性格局构建,二者的相对作用大小取决于讨论问题的空间尺度。      

Neural correlates of a magnetic sense

Many animals rely on Earth's magnetic field for spatial orientation and navigation. However, how the brain receives and interprets magnetic field information is unknown. Support for the existence of magnetic receptors in the vertebrate retina, beak, nose, and inner ear has been proposed, and immediate gene expression markers have identified several brain regions activated by magnetic stimulation, but the central neural mechanisms underlying magnetoreception remain unknown. Here we describe neuronal responses in the pigeon's brainstem that show how single cells encode magnetic field direction, intensity, and polarity; qualities that are necessary to derive an internal model representing directional heading and geosurface location. Our findings demonstrate that there is a neural substrate for a vertebrate magnetic sense.     

Single-neuron activity and tissue oxygenation in the cerebral cortex

Blood oxygen level-dependent functional magnetic resonance imaging uses alterations in brain hemodynamics to infer changes in neural activity. Are these hemodynamic changes regulated at a spatial scale capable of resolving functional columns within the cerebral cortex? To address this question, we made simultaneous measurements of tissue oxygenation and single-cell neural activity within the visual cortex. Results showed that increases in neuronal spike rate were accompanied by immediate decreases in tissue oxygenation. We used this decrease in tissue oxygenation to predict the orientation selectivity and ocular dominance of neighboring neurons. Our results establish a coupling between neural activity and oxidative metabolism and suggest that high-resolution functional magnetic resonance imaging may be used to localize neural activity at a columnar level.     

Regulation of microtubule dynamics by reaction cascades around chromosomes

During spindle assembly, chromosomes generate gradients of microtubule stabilization through a reaction-diffusion process, but how this is achieved is not well understood. We measured the spatial distribution of microtubule aster asymmetry around chromosomes by incubating centrosomes and micropatterned chromatin patches in frog egg extracts. We then screened for microtubule stabilization gradient shapes that would generate such spatial distributions with the use of computer simulations. Only a long-range, sharply decaying microtubule stabilization gradient could generate aster asymmetries fitting the experimental data. We propose a reaction-diffusion model that combines the chromosome generated Ran-guanosine triphosphate-Importin reaction network to a secondary phosphorylation network as a potential mechanism for the generation of such gradients.     

The effect of histone gene deletions on chromatin structure in Saccharomyces cerevisiae

As a way of studying nucleosome assembly and maintenance in Saccharomyces cerevisiae, mutants bearing deletions or duplications of the genes encoding histones H2A and H2B were analyzed. Previous genetic analysis had shown that only one of these mutants exhibited dramatic and pleiotropic phenotypes. This mutant was also the only one that contained disrupted chromatin, suggesting that the original phenotypes were attributable to alterations in chromosome structure. The chromatin disruption in the mutant, however, did not extend over the entire genome, but rather was localized to specific regions. Thus, while the arrangement of nucleosomes over the HIS4 and GAL1 genes, the telomeres, and the long terminal repeats (delta sequences) of Ty retrotransposons appeared essentially normal, nucleosomes over the CYH2 and UBI4 genes and the centromere of chromosome III were dramatically disrupted. The observation that the mutant exhibited localized chromatin disruptions implies that the assembly or maintenance of nucleosomes differs over different parts of the yeast genome.     

Conflicting evidence about long-distance animal navigation

Because of conflicting evidence about several fundamental issues, long-distance animal navigation has yet to be satisfactorily explained. Among the unsolved problems are the nature of genetic spatial control of migration and the relationships between celestial and magnetic compass mechanisms and between different map-related cues in orientation and homing, respectively. In addition, navigation is expected to differ between animal groups depending on sensory capabilities and ecological conditions. Evaluations based on modern long-term tracking techniques of the geometry of migration routes and individual migration history, combined with behavioral experiments and exploration of the sensory and genetic mechanisms, will be crucial for understanding the spatial principles that guide animals on their global journeys.     

Increased cortical oxidative metabolism due to sensory stimulation: implications for functional brain imaging

Modern functional brain mapping relies on interactions of neuronal electrical activity with the cortical microcirculation. The existence of a highly localized, stimulus-evoked initial deoxygenation has remained a controversy. Here, the activity-dependent oxygen tension changes in the microcirculation were measured directly, using oxygen-dependent phosphorescence quenching of an exogenous indicator. The first event after sensory stimulation was an increase in oxygen consumption, followed by an increase in blood flow. Because oxygen consumption and neuronal activity are colocalized but the delayed blood flow is not, functional magnetic resonance imaging focused on this initial phase will yield much higher spatial resolution, ultimately enabling the noninvasive visualization of fundamental processing modules in the human brain.     

Selective attention from voluntary control of neurons in prefrontal cortex

Animals can learn to voluntarily control neuronal activity within various brain areas through operant conditioning, but the relevance of that control to cognitive functions is unknown. We found that rhesus monkeys can control the activity of neurons within the frontal eye field (FEF), an oculomotor area of the prefrontal cortex. However, operantly driven FEF activity was primarily associated with selective visual attention, and not oculomotor preparation. Attentional effects were untrained and were observed both behaviorally and neurophysiologically. Furthermore, selective attention correlated with voluntary, but not spontaneous, fluctuations in FEF activity. Our results reveal a specific association of voluntarily driven neuronal activity with "top-down" attention and suggest a basis for the use of neurofeedback training to treat disorders of attention.     

秸秆还田对冬小麦品种百农矮抗58根际土壤微生物及土壤酶活性的影响

在大田条件下,以冬小麦百农矮抗58为试材,研究了秸秆还田对其根际土壤微生物数量及土壤酶活性的影响.结果表明,随着生育进程的推进,根际土壤微生物数量和土壤酶活性呈先升高后降低的趋势,其中以开花期表现较高.根际土壤微生物数量和土壤酶活性不同处理间表现为玉米秸秆还田翻耕＞玉米秸秆还田旋耕＞玉米秸秆清除旋耕.由此可知,应进一步...