Reverse replay of behavioural sequences in hippocampal place cells during the awake state

The hippocampus has long been known to be involved in spatial navigational learning in rodents, and in memory for events in rodents, primates and humans. A unifying property of both navigation and event memory is a requirement for dealing with temporally sequenced information. Reactivation of temporally sequenced memories for previous behavioural experiences has been reported in sleep in rats. Here we report that sequential replay occurs in the rat hippocampus during awake periods immediately after spatial experience. This replay has a unique form, in which recent episodes of spatial experience are replayed in a temporally reversed order. This replay is suggestive of a role in the evaluation of event sequences in the manner of reinforcement learning models. We propose that such replay might constitute a general mechanism of learning and memory.     

Organization of cell assemblies in the hippocampus

Neurons can produce action potentials with high temporal precision. A fundamental issue is whether, and how, this capability is used in information processing. According to the 'cell assembly' hypothesis, transient synchrony of anatomically distributed groups of neurons underlies processing of both external sensory input and internal cognitive mechanisms. Accordingly, neuron populations should be arranged into groups whose synchrony exceeds that predicted by common modulation by sensory input. Here we find that the spike times of hippocampal pyramidal cells can be predicted more accurately by using the spike times of simultaneously recorded neurons in addition to the animals location in space. This improvement remained when the spatial prediction was refined with a spatially dependent theta phase modulation. The time window in which spike times are best predicted from simultaneous peer activity is 10-30 ms, suggesting that cell assemblies are synchronized at this timescale. Because this temporal window matches the membrane time constant of pyramidal neurons, the period of the hippocampal gamma oscillation and the time window for synaptic plasticity, we propose that cooperative activity at this timescale is optimal for information transmission and storage in cortical circuits.     

Primate eta-globin DNA sequences and man's place among the great apes

Molecular studies indicate that chimpanzee and gorilla are the closest relatives of man (refs 1-7 and refs therein). The small molecular distances found point to late ancestral separations, with the most recent being between chimpanzee and man, as judged by DNA hybridization. Kluge and Schwartz contest these conclusions: morphological characters group a chimpanzee-gorilla clade with the Asian ape orang-utan in Kluge's cladistic study and with an orang-utan-human clade in Schwartz's study. Clearly, extensive sequencing of nuclear DNA is needed to resolve by cladistic analysis the branching order within Hominoidea. Towards this goal, we are sequencing orthologues of the primate psi eta-globin locus. Here, we compare the newly completed sequences of orang-utan and rhesus monkey with human, chimpanzee, gorilla, owl monkey, lemur and goat orthologues. Our findings substantially increase the evidence indicative of a human-chimpanzee-gorilla clade with ancestral separations around 8 to 6 Myr ago. We also verify that neutral hominoid DNA evolved at markedly retarded rates.     

Comparison of population coherence of place cells in hippocampal subfields CA1 and CA3

The hippocampus, a critical brain structure for navigation, context-dependent learning and episodic memory, is composed of anatomically heterogeneous subregions. These regions differ in their anatomical inputs as well as in their internal circuitry. A major feature of the CA3 region is its recurrent collateral circuitry, by which the CA3 pyramidal cells make excitatory synaptic contacts on each other. In contrast, pyramidal cells in the CA1 region are not extensively interconnected. Although these differences have inspired numerous theoretical models of differential processing capacities of these two regions, there have been few reports of robust differences in the firing properties of CA1 and CA3 neurons in behaving animals. The most extensively studied of these properties is the spatially selective firing of hippocampal 'place cells'. Here we report that in a dynamically changing environment, in which familiar landmarks on the behavioural track and along the wall are rotated relative to each other, the population representation of the environment is more coherent between the original and cue-altered environments in CA3 than in CA1. These results demonstrate a functional heterogeneity between the place cells of CA3 and CA1 at the level of neural population representations.     

Double-stranded cleavage by cell extracts near recombinational signal sequences of immunoglobulin genes

The genes encoding the variable regions of murine immunoglobulin light chains are present in the germ line in two separate segments, V and J. During B lymphocyte differentiation these segments are brought together to form a single unit (for review see ref. 1). Although much is known about the structures of V and J segments, both in germ-line configuration and after rearrangement, essentially nothing is known about the biochemical mechanism of V-J recombination. One possible step in proposed mechanisms of immunoglobulin gene rearrangement is endonucleolytic cleavage of the participating DNA segments before joining. In an attempt to detect such an activity, we have developed an assay for the detection of site-specific double- or single-strand endonucleolytic activity in crude soluble extracts. Using this assay we have detected an activity in extracts of nuclei from mouse B-lymphoid lines and from mouse L cells that is capable of introducing duplex breaks near the recombinational signal sequences of immunoglobulin JK segments. We report the activity here because of its intrinsic interest although we lack any direct evidence that it has a role in V-J recombination.     

The future for stem cell research.

Stem cells have offered much hope by promising to greatly extend the numbers and range of patients who could benefit from transplants, and to provide cell replacement therapy to treat debilitating diseases such as diabetes, Parkinson's and Huntington's disease. The issue of stem cell research is politically charged, prompting biologists to begin engaging in ethical debates, and generating in the general public an unusually high level of interest in this aspect of biology. But excitement notwithstanding, there is a long way to go in basic research before new therapies will be established, and now the pressure is on for scientists and clinicians to deliver.     

Presence of integrated hepatitis B virus DNA sequences in cellular DNA of human hepatocellular carcinoma

Hepatitis B virus (HBV) may be one of the agents involved in the aetiology of human primary liver cancer. This hypothesis is supported by (1) the similarity between the geographical distribution of chronic carriers of the viral surface antigen (HBsAg) and that of hepatocellular carcinoma (HCC); (2) the increase in the prevalence of HBV markers in serum of patients with primary liver cancer when compared with the general population; (3) the observation that HBV infection precedes the development of the tumour. Moreover, these epidemiological indications of an association between HBV infecton and hepatocellular carcinoma are supported by the detection of HBV markers such as HBsAg or viral DNA sequences, although in a non-integrated form in tumour tissue. To study the relationship between HBV and primary liver cancer further, we looked for the presence of free or integrated viral DNA in tumour tissue of human hepatocellular carcinomas and in a HBsAg-producing human hepatoma cell line. Using the blot-transfer hybridization technique and cloned HBV DNA as a probe, we have now demonstrated that the viral DNA is integrated in the cellular genome both in tumour tissue and in a hepatoma cell line.     

Progress in the study of molecular organized assemblies by dielectric relaxation spectroscopy

Because dielectric spectroscopy covers a great many problems in physical and chemical systems occurring in an extremely wide frequency range, the study of this method plays an important role in physical chemistry. As an effective tool to detect inner properties of substance systems, the dielectric spectroscopy method is widely used in chemical systems and has been dramatically developed in recent decade. This review paper describes the applications of the dielectric spectroscopy in the chemical field, and main concentrations are focused on the micelle, microemulsion and other so-called molecular organized assemblies. Some dielectric principles and models proposed for these systems are introduced. In addition, recent technical developments in dielectric spectroscopy and developing trend of this method in other chemical systems are reviewed.     

Halogen bonded two-dimensional supramolecular assemblies studied by high resolution scanning tunneling microscopy

We described the formation of self-organized two-dimensional (2D) assemblies of N-(2,3,5,6-tetrafluoro- 4-iodophenyl)hexadecylamine and 1-dodecyl-imidazole at the liquid/HOPG interface. The two-dimen- sional assemblies showed a fishbone-like pattern structure as revealed by high-resolution scanning tunneling microscopy. Although different interactions can drive the formation of 2D assemblies, as far as we know, this is the first report on halogen bond-driven 2D assemblies.     

多业务CDMA系统在非均匀小区条件下的容量分析

在现有研究成果的基础上,对小区裂化过程中多业务条件下的蜂窝系统的容量进行了分析,并结合CDMA系统参数进行了仿真,以检验多业务对系统容量的影响。仿真结果表明：视频和数据业务由于要求更低的误码率,从而使其信干比要求更苛刻,引入视频和数据业务将会对系统容量产生极大的影响。     

卡尔曼滤波器在海马场电位ripple节律分析中的应用

利用自适应自回归(adaptive autoregressive,AAR)模型和卡尔曼滤波器算法,分析小鼠海马CA1区场电位ripple高频振荡的时频特性.研究发现,与传统的基于短时傅立叶变换的实时频谱分析方法相比,利用AAR模型以及卡尔曼滤波器算法的参数化方法在对ripple高频振荡信号进行实时频谱分析时,具有更高的...     

利用定积分定义求数列极限

讨论了应用定积分定义求数列极限的方法 ,并给出了确定被积函数及积分上、下限的具体步骤     

Enhancement of cellular memory by reducing stochastic transitions

On induction of cell differentiation, distinct cell phenotypes are encoded by complex genetic networks. These networks can prevent the reversion of established phenotypes even in the presence of significant fluctuations. Here we explore the key parameters that determine the stability of cellular memory by using the yeast galactose-signalling network as a model system. This network contains multiple nested feedback loops. Of the two positive feedback loops, only the loop mediated by the cytoplasmic signal transducer Gal3p is able to generate two stable expression states with a persistent memory of previous galactose consumption states. The parallel loop mediated by the galactose transporter Gal2p only increases the expression difference between the two states. A negative feedback through the inhibitor Gal80p reduces the strength of the core positive feedback. Despite this, a constitutive increase in the Gal80p concentration tunes the system from having destabilized memory to having persistent memory. A model reveals that fluctuations are trapped more efficiently at higher Gal80p concentrations. Indeed, the rate at which single cells randomly switch back and forth between expression states was reduced. These observations provide a quantitative understanding of the stability and reversibility of cellular differentiation states.     

Kinase-regulated quantal assemblies and kiss-and-run recycling of caveolae

A functional genomics approach has revealed that caveolae/raft-mediated endocytosis is subject to regulation by a large number of kinases. Here we explore the role of some of these kinases in caveolae dynamics. We discover that caveolae operate using principles different from classical membrane trafficking. First, each caveolar coat contains a set number (one 'quantum') of caveolin-1 molecules. Second, caveolae are either stored as in stationary multi-caveolar structures at the plasma membrane, or undergo continuous cycles of fission and fusion with the plasma membrane in a small volume beneath the surface, without disassembling the caveolar coat. Third, a switch mechanism shifts caveolae from this localized cycle to long-range cytoplasmic transport. We have identified six kinases that regulate different steps of the caveolar cycle. Our observations reveal new principles in caveolae trafficking and suggest that the dynamic properties of caveolae and their transport competence are regulated by different kinases operating at several levels.