Chemoattraction of a bactivorous ciliate to bacteria surface compounds

The locomotory response to cell surface compounds extracted from two prey species,Vibrio natriegens andVibrio neries, was tested for a bacterivorous ciliate,Pseudochnilembus marinus Thompson 1966. Chemoattraction of the ciliate to the surface compounds stabilized in agarose baits was not equal for the two prey species. Fractionation of the extracts suggested the attractive substance was a high molecular weight compound. The expression of the differential response was dependant on the physiological condition and prior prey species exposure of the ciliate test population. The recognition and response to material normally found on the surface of prey cells supports evidence for the involvement of chemical sensing of gradients of prey particles and dissolved compounds of prey origin in the natural swimming behavior of bacterivorous ciliates. The prey species-specific reactions and influence of ciliate physiological state on chemosensory response suggest ciliate-bacteria interactions may be more complex than preciously assumed.     

Inhibitory Modulation by Sodium Ions of the N-Methyl-D-Aspartate Recognition Site in Brain Synaptic Membranes

Specific binding of radiolabeled L-glutamic acid (Glu) was examined using rat brain synaptic membranes treated with a low concentration of Triton X-100. The binding drastically increased in proportion to increasing concentrations of the detergent used up to 0.1%. Addition of 100 mM sodium acetate significantly potentiated the binding in membranes not treated with Triton X-100, whereas it markedly inhibited the binding in Triton-treated membranes. The binding in Triton-treated membranes was inversely dependent on incubation temperature and reached a plateau within 10 min after the initiation of incubation at 2 degrees C, whereas the time required to attain equilibrium at 30 degrees C was less than 1 min. Sodium acetate invariably inhibited the binding detected at both temperatures independently of the incubation time via decreasing the affinity for the ligand. The binding was significantly displaced by agonists and antagonists for an N-methyl-D-aspartate (NMDA)-sensitive subclass of brain excitatory amino acid receptors, but not by those for the other subclasses. Inclusion of sodium acetate reduced the potencies of NMDA agonists to displace the binding without virtually affecting those of NMDA antagonists. Moreover, sodium ions inhibited the ability of Glu to potentiate the binding of N-[3H] [1-(2-thienyl)cyclohexyl]piperidine to open NMDA channels in Triton-treated membranes. These results suggest that sodium ions may play an additional modulatory role in the termination process of neurotransmission mediated by excitatory amino acids via facilitating a transformation of the NMDA recognition site from a state with high affinity for agonists to a state with low affinity.     

Contrasting Neurochemical Interactions of Tiletamine, a Potent Phencyclidine (PCP) Receptor Ligand, with the N-Methyl-D-Aspartate-Coupled and -Uncoupled PCP Recognition Sites

Neurochemical interactions of tiletamine, a potent phencyclidine (PCP) receptor ligand, with the N-methyl-D-aspartate (NMDA)-coupled and -uncoupled PCP recognition sites were examined. Tiletamine potently displaced the binding of [3H]1-(2-thienyl)cyclohexylpiperidine with an IC50 of 79 nM without affecting sigma-, glycine, glutamate, kainate, quisqualate, or dopamine (DA) receptors. Like other PCP ligands acting via the NMDA-coupled PCP recognition sites, tiletamine decreased basal, harmaline-, and D-serine-mediated increases in cyclic cGMP levels and induced stereotypy and ataxia. Tiletamine was nearly five times more potent than PCP at inhibiting the binding of 3-hydroxy[3H]PCP to its high-affinity NMDA-uncoupled PCP recognition sites. However, following parenteral administration, dizocilpine maleate (MK-801), ketamine, PCP, dexoxadrol, and 1-(2-thienyl)cyclohexylpiperidine HCl, but not tiletamine, increased rat pyriform cortical DA metabolism and/or release, a response modulated by the NMDA-uncoupled PCP recognition sites. Pretreatment with tiletamine did not attenuate the MK-801-induced increases in rat pyriform cortical DA metabolism, a result suggesting that tiletamine is not a partial agonist of the NMDA-uncoupled PCP recognition sites in this region. However, following intracerebroventricular administration (100-500 micrograms/rat), tiletamine increased pyriform cortical DA metabolism with a bell-shaped dose-response curve. These data indicate a differential interaction of tiletamine with the NMDA-coupled and -uncoupled PCP recognition sites. The paradoxical effects of tiletamine suggest that tiletamine might activate receptor(s) or neuronal pathways of unknown pharmacology.     

Lectin Binding to Radopholus citrophilus and R. similis Proteins

Lectin-binding glycoproteins in seven populations of two burrowing nematode sibling species were probed with five different biotinylated lectins on Western blots, and differences were correlated with nematode ability to parasitize citrus and to overcome citrus rootstock resistance. Banding patterns of molecular weight standards were fit best by an exponential decay function, and a predictive equation was used to estimate molecular weights (r² = 0.999). A band (131 kDa) that labeled with the lectin Concanavalin A (Con A) occurred in extracts from cuticles and egg shells of populations of Radopholus citrophilus that parasitize citrus. Wheat germ agglutin labeled a band (58 kDa) in aqueous homogenates of populations that reproduce in roots of citrus rootstock normally resistant to burrowing nematodes. The two sibling species R. citrophilus and R. similis were distinguished by a high molecular weight Con A-labeled band (608 kDa) from cuticle and egg shells. Probing blots with the lectin Limulus polyphemus agglutinin indicated that each population contained a band (12-16 kDa) specifically inhibited by the addition of 25 mM neuraminic acid, suggesting that glycoproteins with sialic acid moieties are present in burrowing nematodes.     

Patterned distribution of membrane-associated Ca2+ during pore formation inMicrasterias

Summary During the stage of pore formation developing cells ofMicrasterias denticulata show a patterned distribution of fluorescent dots on the plasma membrane after treatment with chlorotetracycline. The center-to-center spacing of these dots corresponds with the distances between the individual cell wall pores ofMicrasterias. Therefore it is supposed that the patterned distribution of pores and their formation which is mediated by special pore vesicles are related to local accumulations of membrane-associated Ca²⁺. Membrane-associated Ca²⁺ seems not only to be functional in tip growth but to be a general mediator for recognition and fusion processes between various vesicles and the plasma membrane.     

探索以“霍乱弧菌检测虚拟仿真实验”为载体的混合式实验教学模式

虚拟仿真实验是一种现代信息化和智慧教学的重要方法,对高等医学院校教学质量的发展起到重要的推进作用。我们自主开发建设的“霍乱弧菌检测与防控虚拟仿真实验”,既弥补了因生物安全问题不能开展的实验教学,也解决了微生物学检验实验教学中存在的操作标准化问题。采用“三步进阶”混合教学模式,实现以“学生为中心”的师生互动模式,创建“设计性实验报告”,与育人元素有机结合,培育医学生的职业使命感。细化考核标准,实现过程性评价。探索课前启发铺垫、课中内化升华、课后巩固拓展混合式实验教学模式,有效提高学生的实验技能,实现知行合一、素能共育的教学目标。     

中国主要农产品虚拟要素贸易网络结构特征分析

据虚拟水概念定义虚拟要素,并将其划分为虚拟资源要素和虚拟生态要素两类,选取虚拟资源要素中的耕地要素和虚拟生态要素中的化肥/农药要素为研究对象,定量分析2002—2016年以粮食贸易为载体的虚拟耕地、虚拟化肥/农药要素的贸易量,构建虚拟要素贸易网络,通过复杂网络的研究方法,结果表明:2002—2016年我国主要农产品虚拟耕地、化肥/农药要素的贸易总量呈下降趋势,降幅分别约25.51%、8.01%;虚拟耕地要素网络节点入度较大的为长江中下游、华南、西南地区,出度较大的为黄淮海和东北地区,虚拟化肥/农药要素网络与之相反;地区间节点强度的差异性大,虚拟耕地要素差值最大可达1459.56万hm²,虚拟化肥/农药要素达61.38万t;二者网络节点度和强度的累积分布均符合幂律分布规律,其尾部的"重尾"现象揭示了节点度和强度的高可变性以及网络结构的脆弱性;虚拟耕地要素的输入区网络同配,输出区网络异配,揭示了地区间耕地要素的流动既呈集聚又有分散的态势,虚拟化肥/农药要素网络节点相关性皆为减函数,网络异配,揭示了虚拟化肥/农药要素在八大区域间联通的状况。网络结构特征分析为研究网络抗毁...     

资阳人头骨化石的内部解剖结构

资阳人头骨化石,是新中国成立后首次发现的保存较为完整的人类化石,曾经引起学术界的广泛关注。由于其出土的具体位点和层位不是很清楚,对其年代目前还存有争议。长期以来,对资阳人的研究局限于传统的头骨外部形态的描述和测量。本文利用高分辨率工业CT(Computed tomography)扫描资阳人头骨,并对其内部解剖结构 (包括骨壁结构、额窦、骨内耳迷路、颞骨乳突小房、颅内模) 进行3D虚拟复原和研究,以期获得更多的形态信息。CT断层图显示资阳人头骨的骨壁板障层较厚,远大于外板层和内板层,支持以往研究认为的该头骨属于50岁以上个体的鉴定结果。额窦呈叶形,局限于两侧眼眶的内上方;左、右侧额窦的表面积分别为1780mm²和2910mm²。骨性内耳迷路半规管的大小及其比例,与尼安德特人不同,而位于晚更新世和全新世现代人变异范围之间。颞骨乳突小房为气化型,几乎占据了整个乳突部。根据复原的颅内模,资阳人的颅容量约为1250mL。颅内模的各项测量数值虽然都偏小,但脑的绝大多数形态特征、宽-高指数、顶叶-脑长指数都位于现代人的变异范围之内,而与直立人和更新世古老型...     

基于模式识别的景观格局分析与尺度转换研究框架

景观格局分析和尺度转换是生态学和地理学研究的核心问题之一.尽管多年来投入了大量的精力,然而由于尺度效应的复杂性和尺度转换过程的不确定性,仍然没有找到合适的方法.目前关于尺度转换的研究存在两个误区,其一是过分重视空间尺度的转换,忽略了过程尺度的转换;其二是过分强调了对不同尺度间数量关系的外推与转换,忽略了不同尺度间生态规律的外推与转换.在系统分析了景观格局与尺度转换研究现状、存在问题和难点的基础上,提出了借用模式识别的原理和方法,针对特定的生态过程,开展景观格局分析与尺度转换的思路.认为尺度转换的关键在于通过识别不同尺度上影响生态过程的主导因子,找到各个尺度上“格局（环境因子空间组合）-过程”、尺度间“格局-格局”之间的对应关系,通过建立“环境-格局-过程”模式识别数据库,就能够建立不同尺度之间基于模式识别的尺度转换方法.