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关键词： clathrin   endocytic vesicles   endocytosis   internalization   yeast  

摘要： The process of endocytosis is a complex series of events involving the coordinated activity of many proteins. In animal cells, clathrin plays a vital role in the invagination of the plasma membrane leading to formation of vesicles during endocytosis. The study of endocytosis in yeast cells has been hindered by a debate about the role of clathrin in early internalization steps. This review summarizes the evidence for and against clathrin's involvement in internalization from the yeast plasma membrane.

关键词： 人工神经网络   硬件实现   脉中调制技术   突触权值存储   在片学习  

摘要： 神经网络实现技术是神经网络研究的一个重要方面.用软件编程模拟实现神经网络取得了很好的应用效果,但用硬件直接实现的人工神经网各,才能在真正意义上体现神经网络的并行处理信息的能力,更好地满足实时应用的要求.该文以神经网络的硬件实现为研究内容,提出了一种新型的结合脉冲技术、数字技术和模拟技术的在片(on-chip)学习神经网络的硬件实现方案.提出了采用电流型脉冲宽度调制(PWM)技术的突触和神经元电路的设计,解决了权值长期存储的神经网络实现的难点和问题,设计了实现神经网络学习的算法的学习电路,给出了在片学习神经网络系统的实现方案.

关键词： 图象滤波   模糊神经网络   模糊系统   脉冲噪声   滤波器  

摘要： 针对一般模糊神经网络结构复杂、不利于硬件实现的问题 ,提出了一种基于 Sugeno型模糊神经网络的新型脉冲噪声滤波器 .该滤波器采用神经网络的结构设计 ,有利于噪声模式的检测 ,其内含于神经网络中的模糊推理机制不仅能够有效地滤除脉冲噪声 ,而且又不破坏图象的细节 .该滤波器还采用能够获得全局解的遗传算法来对网络参数进行调整 .初步研究表明 ,该模糊神经滤波器在滤除景物图象中的脉冲噪声方面 。

关键词： 人工神经网络   脉冲流算法   VLSI  

摘要： 人工神经网络以其自组织、自适应、自学习能力以及非线性、非局域性、非定常性和非凸性等优点得到广泛重视。本文分析现有人工神经网络模型及算法 ,总结了现有人工神经网络实现上的弊端 ,然后着重讨论了数据模结合的 VL SI人工神经网络技术和脉冲流技术。在现有的各种脉冲流技术基础上 ,给出一个以模拟方式实现突触乘积和突触输出累加 ,数字方式实现权值储存的脉冲流人工神经网络。

关键词： complex logarithmic mapping   invariant code   neural networks   pattern recognition   pulse coding of shape   shape representation   template matching  

摘要： The paper deals with the invariant recognition of patterns, and aims at developing (i) their pulse-coded representation;and (ii) an algorithm for their recognition. The proposed pattern encoder utilizes the properties of complex logarithmic mapping (CLM) (computed with reference to the center of gravity, CoG, of the shape), which maps rotation and scaling in its domain to shifts in its range. The encoder, then, invokes a pulse-encoding scheme similar to the one proposed by Dodwell [1] in order to handle these: shifts, thereby generating pulse-codes invariant to scaling, rotation, and shift in the input shape. These pulses are then fed to a novel multi-layered neural recognizer which (i) invokes template matching with a distinctly implemented architecture;and (ii) achieves robustness (to noise and pattern deformation) by virtue of its overlapping strategy for code classification. The proposed encoder-recognizer (E-R), which is hardware implementable by a high-speed electronic switching circuit, call add new patterns on-line to the existing ones. The E-R is illustrated with experimental results. While human visual system has been the main motivation to the proposed model, no claim, however, has been made on its direct biological plausibility. (C) 2001 Pattern Recognition Society. Published by Elsevier Science Ltd. All rights reserved.

关键词： endocytosis   GTP gamma S   MDCK cells   Rho   ricin  

摘要： This paper studies the endocytosis of ricin at the apical pole of polarized MDCK II cells after permeabilization of the cells basolaterally with streptolysin O. Ricin endocytosis after the addition of cytosol with an ATP-regenerating system was 2-3-fold higher than after the addition of a transport medium. A similar increase in ricin endocytosis was obtained by reconstitution of dialyzed cytosol with the nonhydrolyzable GTP analog, GTP gammaS, in the presence of an ATP-regenerating system. The nonhydrolyzable GDP analog, GDP betaS, did not increase ricin uptake. In contrast to the data obtained with ricin, GTP IS was found to inhibit apical transferrin uptake in MDCK II cells transfected with the human transferrin receptor, and the data thus imply that GTP gammaS supports clathrin-independent endocytosis. Electron microscopy (EM) demonstrated that free endocytic vesicles were formed from the apical pole of permeabilized MDCK II cells in the presence of GTP IS and that both a ricin-HRP conjugate, HRP, and cationized gold were endocytosed. Ricin endocytosis in the presence of intact cytosol, as well as GTP gammaS-stimulated ricin uptake, was inhibited by Clostridium botulinum C3 transferase, an enzyme found to inactivate Rho proteins. The data demonstrate that apical clathrin-independent endocytosis functions in the presence of GTP gammaS, and suggest that one or more of the small GTP binding proteins of the Rho family is involved in regulation of the epical clathrin-independent endocytosis in MDCK II cells.

关键词： orthoptera   evolution   antennal lobe   receptor neurons   projection neurons  

摘要： The first odor-processing neuropils of insects comprise glomeruli, islets of neuropil, that are supplied by olfactory receptor neurons and give rise to efferent axons to higher brain centers, Glomeruli size and organization varies in a taxon-specific manner across the Insecta, suggesting possible correlates between their organization and chemosensory behaviors in different insect groups. Comparative studies of antennal lobe glomeruli within the Orthoptera have been used to infer how the various taxon-specific arrangements of odorant-processing structures (glomeruli) might have evolved. The cellular arrangements in glomeruli have been surveyed using anterograde filling and Golgi impregnation of antennal receptor neurons projecting to the antennal lobe in Stenopelmatidae, Tettigoniidae, Gryllidae, Tetrigidae and Acrididae. These taxa, which represent the two suborders of Orthoptera, reveal a high correlation between the neural architecture of the glomeruli and structures within the glomeruli, Using a recent molecular phylogeny of the Orthoptera we have mapped the occurrence of glomerular characteristics to infer the evolution of antennal lobe structures in orthopterans. The functional implications of these results are discussed. Copyright (C) 2001 S. Karger AG, Basel.

关键词： 海风藤新木脂素类   血小板活化因子   花生四烯酸   基因表达   拮抗剂   脑缺血  

摘要： 该实验室对海风藤提取物单一成分PAF受体拮抗剂海风藤酮的脑保护机制进行了初步探讨,但此类天然PAF受体拮抗剂的详细药理机制和作用环节以及与银杏类PAF受体拮抗剂二者之间的异同仍不甚明了.该研究正是基于此而设计的.结论:(1)局灶性脑缺血再灌流后,PAF与AA异常代谢密切关联,协同参与了神经细胞损伤发生和发展过程.(2)缺血再灌流脑皮质COX-2基因表达明显增加,PAF是COX-2基因表达的上游信使之一.COX-1可能不参与脑缺血性损害的发生机制.(3)脑缺血再灌流可致PAF受体基因表达异常,推测与缺血再灌流早期内源性PAF的升高及后期缺血周边区胶质细胞的聚集有关.(4)缺血再灌流脑皮质神经元细胞内及膜上PAF受体功能均出现下调,PAF受体基因可能参与了其调控机制.(5)脑缺血再灌流后,两类PAF受体拮抗剂均能:1.显著抑制PAF、TXA<,2>的急剧升高;2.降低COX-2基因的表达;3.减少胶质细胞在缺血区的募集,从而削减再灌流后期PAF受体基因阳性表达细胞数量.(6)海风藤新木脂素类活性成分对脑缺血后TXA<,2>生成及COX-2基因表达有明显抑制作用,提示海风藤新木脂素类活性成分能够治疗缺血脑区AA的代谢紊乱.(7)海风藤新木脂素类活性成分无论是在神经细胞膜上还是胞内PAF受体,对<'3>H-PAF的结合均具有特异性竞争拮抗作用,属竞争性PAF受体拮抗剂;银杏内酯仅能抑制突触膜上<'3>H-PAF的结合,但针对神经细胞胞内PAF受体,并无竞争性.提示两类PAF受体拮抗剂的脑保护分子机理有所不同,前者的作用更可能涉及到缺血神经细胞内的PAF的信号传递及其下游基因的异常表达.

关键词： ORL1 receptor   opioid receptors   knockout mice   autoradiography   transgenic  

摘要： The opioid receptor-like 1 (ORL1) receptor shares a high degree of sequence homology with the classical mu-, delta- and kappa -opioid receptors and a functional mutual opposition between these receptors has been suggested, To further address this possible interaction we have used mu-, delta- and kappa -opioid receptor knockout mice to determine autoradiographically if there are any changes in the number or distribution of the ORL1 receptor, labelled with [H-3]nociceptin, in the brains of mice deficient in each of the opioid receptors. An up-regulation of ORL1 expression was observed across all brain regions in delta -knockouts with cortical regions typically showing a 15-30% increase in binding that was most marked in heterozygous mice. In contrast, ORL1 receptor expression was down-regulated in virtually all brain structures in heterozygous kappa -knockouts although the magnitude of this change was not as great as for the delta -knockouts. No significant alterations in ORL1 receptor expression were observed across brain regions in delta -receptor knockout mice and there were no qualitative differences in ORL1 receptor expression in any groups. These data suggest there are interactions between the ORL1 system and the classical opioid receptors and that the interactions are receptor-specific, The greater differences observed in heterozygous mice suggest that these interactions might be most relevant when there is only partial loss of receptor function. (C) 2001 IBRO. Published by Elsevier Science Ltd. All rights reserved.

关键词： microsporidia   Encephalitozoon spp.   scanning electron microscopy   life cycle  

摘要： This paper presents, for the first time, documentation by detailed scanning electron microscopy of the life cycle of microsporidia of the genus Encephalitozoon. Phase 1 is represented by the extracellular phase with mature spores liberated by the rupture of host cells. To infect new cells the spores have to discharge their polar filament. Spores with everted tubes show that these are helically coiled. When the polar tubules have started to penetrate into a host cell they are incomplete in length. The infection of a host cell can also be initiated by a phagocytic process of the extruded polar filament into an invagination channel of the host cell membrane. After the penetration process, the tube length is completed by polar tube protein which passes through the tube in the shape of swellings. A completely discharged polar tube with its tip is also shown. The end of a polar tube is normally hidden in the cytoplasm of the host cell. After completion of the tube length the transfer of the sporoplasm occurs and phase 2 starts. Phase 2 is the proliferative phase, or merogony, with the intracellular development of the parasite that cannot be documented by scanning electron microscopy. The subsequent intracellular phase 3, or sporogony, starts when the meronts transform into sporonts, documented as chain-like structures which subdivide into sporoblasts. The sporoblasts finally transform directly into spores which can be seen in their host cell, forming bubble-like swellings in the cell surface. (C) 2000 Editions scientifiques et medicales Elsevier SAS.