Models of distributed associative memory networks in the brain

Summary Although experimental evidence for distributed cell assemblies is growing, theories of cell assemblies are still marginalized in theoretical neuroscience. We argue that this has to do with shortcomings of the currently best understood assembly theories, the ones based on formal associative memory models. These only insufficiently reflect anatomical and physiological properties of nervous tissue, and their functionality is too restricted to provide a framework for cognitive modeling. We describe cell assembly models that integrate more neurobiological constraints and review results from simulations of a simple nonlocal associative network formed by a reciprocal topographic projection. Impacts of nonlocal associative projections in the brain are discussed with respect to the functionality they can explain.     

褪黑素对大鼠空间学习记忆的影响及其机制研究

本研究运用Morris水迷宫和电生理学方法 ,以逃避潜伏期、穿环系数和海马CA1区突触长时程增强(long termpotentiation ,LTP)为指标 ,研究褪黑素对大鼠空间学习记忆能力的影响。实验结果显示 :( 1)在Morris水迷宫 6d训练中 ,对照组大鼠后 4d平均逃避潜伏期为 18 4 4± 2 7s,褪黑素组为 3 0 0 2± 3 6s,两者有显著差异 (P <0 0 1) ;训练 6d后 ,褪黑素组穿环系数为 2 5 68± 2 3 2 % ,明显小于对照组的 4 3 3 3± 2 85 % (P <0 0 1)。( 2 )采用微量注射法给予海马CA1区褪黑素 ,强直后 60min ,fEPSP斜率为基准值的 114 2 8± 1 80 % ,显著低于对照组的 169 71±6 4 8% (P <0 0 1)。( 3 )预先给予东莨菪碱 ,不影响褪黑素对海马CA1区LTP的抑制 ,强直后 60minfEPSP斜率为基准值的 113 70± 5 5 5 %。( 4 )提前给予荷包牡丹碱后给予褪黑素 ,强直后 60minfEPSP斜率为基准值的 162 2 9±10 5 2 % ,明显大于褪黑素组 (P <0 0 1) ,而与对照组无显著差异 (P >0 0 5 )。上述结果表明 ,褪黑素对大鼠的空间学习记忆能力及海马CA1区LTP均有明显的抑制作用 ,两者相关 ;东莨菪碱不能阻断褪黑素对海马CA1区LTP的抑制作用 ,而荷包牡丹碱可以阻断褪黑素对LTP的抑制 ,提示褪黑素的作用可能不是由胆碱能系统所介     

Behavioural and physiological characterization of inbred mouse strains: prospects for elucidating the molecular mechanisms of mammalian learning and memory

With the advent of recombinant DNA methodology, it has become possible to dissect the molecular mechanisms of complex traits, including brain function and behaviour. The increasing amount of available information on the genomes of mammalian organisms, including our own, has facilitated this research. The present review focuses on a somewhat neglected area of genetics, one that involves the study of inbred mouse strains. It is argued that the use of inbred mice is complementary to transgenic approaches in the analysis of molecular mechanisms of complex traits. Whereas transgenic technology allows one to manipulate a single gene and investigate the in vivo effects of highly specific, artificially induced mutations, the study of inbred mouse strains should shed light on the roles of naturally occurring allelic variants in brain function and behaviour. Systematic characterization of the behavioural, electrophysiological, neurochemical, and neuroanatomical properties of a large number of inbred strains is required to elucidate mechanisms of mammalian brain function and behaviour. In essence, a 'mouse phenome' project is needed, entailing the construction of databases to investigate possible causal relationships amongst the phenotypical characteristics. This review focuses on electrophysiological and behavioural characterization of mouse strains. Nevertheless, it is emphasized that the full potential of the analysis of inbred mouse strains may be attained if techniques of numerous disciplines, including gene expression profiling, biochemical analysis, and quantitative trait loci (QTL) mapping, to name but a few, are also included.     

Fungal pathogens of Euphorbia heterophylla and E. hirta in Brazil and their potential as weed biocontrol agents

A two-year survey of the fungi associated with two important congeneric pantropical weeds, Euphorbia heterophylla and E. hirta, was conducted in part of their native range in southern Brazil. Sampling was concentrated mainly in Rio de Janeiro State and ten species were identified as pathogens of these weeds. Two taxa, Botrytis ricini and Uromyces euphorbiae, were common to both weed hosts. Alternaria euphorbiicola, Bipolaris euphorbiae, Melampsora sp., Oidium sp. and Sphaceloma poinsettiae were recorded only from E. heterophylla, whereas Colletotrichum gloeosporioides, Sphaceloma sp. and Sphaerotheca fuliginea were restricted to E. hirta. Botrytis ricini and Colletotrichum gloeosporioides are new records for E. hirta, and Alternaria euphorbiicola and Sphaerotheca fuliginea are new host records for Brazil. Bipolaris euphorbiae, previously identified as Helminthosporium sp., is considered to be the correct name for the causal agent of a major disease of E. heterophyllum in Brazil. The potential of these pathogens as biocontrol agents is discussed and the mycobiota associated with both these weeds worldwide is reviewed.This revised version was published online in October 2005 with corrections to the Cover Date.     

Spatial and temporal variation in disease levels of a floral smut (Anthracoidea heterospora) on Carex nigra

1 Data are presented from a 4-year study on the incidence of infection by the non-systemic smut fungus Anthracoidea heterospora of florets of the sedge Carex nigra .
2 Beetles of the species Phalacrus substriatus may act as vectors, transmitting A. heterospora between different C. nigra tussocks. Path analysis clearly showed that the number of vectors on individual tussocks was an important factor explaining levels of infection of A. heterospora .
3 The year-to-year correlations in incidence of A. heterospora disease for individual C. nigra plants were high, indicating that the same plants consistently experience high levels of disease. There were also high year-to-year correlations in the abundance of P. substriatus beetles on individual plants.
4 A second natural enemy of the sedge, the gall mite Phytoptus caricis , also showed high between-year correlations in levels of infestation. Since P. caricis competes for the same resource as A. heterospora , we predicted that high levels of P. caricis infestation should have a negative effect on disease levels. However, there was in general a positive effect of P. caricis infestation on A. heterospora disease levels.
5 This study shows that for understanding levels of disease of A. heterospora , both within-year effects as well as transient effects must be included. Phenotypic variation among plants in susceptibility to infection by A. heterospora could explain the observed patterns of disease but they could also be the result of host choice by the beetle.     

Relationship between visual learning/memory ability and brain cAMP level in Drosophila

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A Simple Technique for Purifying Fungal Cultures Contaminated with Bacteria and Mites

A simple technique was developed for purifying fungal cultures contaminated with bacteria and mites. It was based on the observation that the growth of bacteria and movement of mites were confined to the upper surface of the agar. A culture contaminated with bacteria and mites was transferred to a piece of clean paper with the upper surface facing down. Small thin pieces (approximately 3 mm × 3 mm × 0.5 mm) of agar were removed from the exposed surface and transferred to a V-8 agar plate. Colonies that developed from these agar pieces were free from bacteria and mites.