Neuronal generation of the leech swimming movement

The swimming movement of the leech is produced by an ensemble of bilaterally symmetric, rhythmically active pairs of motor neurons present in each segmental ganglion of the ventral nerve cord. These motor neurons innervate the longitudinal muscles in dorsal or ventral sectors of the segmental body wall. Their duty cycles are phase-locked in a manner such that the dorsal and ventral body wall sectors of any given segment undergo an antiphasic contractile rhythm and that the contractile rhythms of different segments form a rostrocaudal phase progression. This activity rhythm is imposed on the motor neurons by a central swim oscillator, of which four bilaterally symmetric pairs of interneurons present in each segmental ganglion appear to constitute the major component. These interneurons are linked intra- and intersegmentally via inhibitory connections to form a segmentally iterated and inter-segmentally concatenated cyclic neuronal network. The network appears to owe its oscillatory activity pattern to the mechanism of recurrent cyclic inhibition.     

From swimming to walking with a salamander robot driven by a spinal cord model

The transition from aquatic to terrestrial locomotion was a key development in vertebrate evolution. We present a spinal cord model and its implementation in an amphibious salamander robot that demonstrates how a primitive neural circuit for swimming can be extended by phylogenetically more recent limb oscillatory centers to explain the ability of salamanders to switch between swimming and walking. The model suggests neural mechanisms for modulation of velocity, direction, and type of gait that are relevant for all tetrapods. It predicts that limb oscillatory centers have lower intrinsic frequencies than body oscillatory centers, and we present biological data supporting this.     

S-nitrosylation of matrix metalloproteinases: signaling pathway to neuronal cell death

Matrix metalloproteinases (MMPs) are implicated in the pathogenesis of neurodegenerative diseases and stroke. However, the mechanism of MMP activation remains unclear. We report that MMP activation involves S-nitrosylation. During cerebral ischemia in vivo, MMP-9 colocalized with neuronal nitric oxide synthase. S-Nitrosylation activated MMP-9 in vitro and induced neuronal apoptosis. Mass spectrometry identified the active derivative of MMP-9, both in vitro and in vivo, as a stable sulfinic or sulfonic acid, whose formation was triggered by S-nitrosylation. These findings suggest a potential extracellular proteolysis pathway to neuronal cell death in which S-nitrosylation activates MMPs, and further oxidation results in a stable posttranslational modification with pathological activity.     

Peptide processing and targeting in the neuronal secretory pathway

The abdominal ganglion of the marine mollusk Aplysia contains a pair of identified neuronal clusters, the bag cells, which control egg laying by means of a number of unique regulatory mechanisms. Each neuron in the bag cell clusters synthesizes several peptides derived from a single prohormone and packages them into separate vesicles. These vesicles are then differentially localized in specific neuronal processes, thus segregating peptides destined for autocrine and hormonal release sites. Therefore in this system, protein trafficking through the secretory pathway organizes multiple peptide neurochemical messengers to efficiently regulate simple behaviors.     

Effect of interruption of the visual pathway on the response to geniculate stimulation

Optic nerve section or destruction of the lateral geniculate nucleus increased the amplitude and elevated the recovery cycle of the cortical response to lateral geniculate radiation stimulation in cats. The lesions may have acted by eliminating tonic inhibitory or occlusive volleys originating in the retina, or both.     

Setting the standards: quality control in the secretory pathway

A variety of quality control mechanisms operate in the endoplasmic reticulum and in downstream compartments of the secretory pathway to ensure the fidelity and regulation of protein expression during cell life and differentiation. As a rule, only proteins that pass a stringent selection process are transported to their target organelles and compartments. If proper maturation fails, the aberrant products are degraded. Quality control improves folding efficiency by retaining proteins in the special folding environment of the endoplasmic reticulum, and it prevents harmful effects that could be caused by the deployment of incompletely folded or assembled proteins.     

三疣梭子蟹C-型凝集素CTL5基因的克隆及在病原刺激下的免疫应答

为明确三疣梭子蟹Portunus trituberculatus C-型凝集素CTL5的结构和功能,采用cDNA末端快速扩增(Rapid amplification of cDNA end,RACE)技术克隆获得三疣梭子蟹C-型凝集素CTL5基因(PtCTL5)的cDNA全长。结果表明:PtCTL5基因全长为1026 bp,包含732 bp的开放阅读框,编码了243个氨基酸组成的蛋白,相对分子质量为26 000,为半乳糖结合型凝集素;Blast分析显示,PtCTL5氨基酸序列与克氏原螯虾Procambarus clarkia CTL的一致性最高,为41.84%;系统进化树分析显示,PtCTL5与已发表的三疣梭子蟹的另4种C-型凝集素亲缘关系较远;胚胎及幼体不同发育时期的定量分析表明,PtCTL5在溞状幼体Ⅲ期表达量最高,在胚胎发育的心跳期表达量最低;组织表达分析显示,PtCTL5在血细胞中的表达量最高,肝胰腺中次之;人工注射副溶血弧菌Vibrio parahemolyticus后,PtCTL5在血细胞和肝胰腺中的表达量均于72 h时达到峰值;而注射对虾白斑综合征病毒(WSSV)感染后,PtCTL5在血细胞和肝胰腺中的表达量分别于72、12 h达到峰值且显著高于对照组(P<0.05)。研究表明,C-型凝集素在三疣梭子蟹先天免疫中具有一定的功能,本研究结果可为进一步解析三疣梭子蟹免疫应答机制提供参考。     

从学习到创新农业科技期刊发展之路径

分析了《上海农业学报》的现状及存在问题,提出了今后农业科技期刊进一步发展的路径和方向。     

Excitation and inhibition of neuronal firing in visual cortex by reticular stimulation

The frequency of action potentials of about one-third of the neurons sampled in the striate cortex of awake rabbits was clearly modified by mild stimulation of the reticular core of the brain stem. Reticular stimulation often brought about enhancement of firing in units activated by light, while it usually had the contrary effect upon light-inhibited units.     

From individual dispersal to species ranges: perspectives for a changing world

Dispersal is often risky to the individual, yet the long-term survival of populations depends on having a sufficient number of individuals that move, find each other, and locate suitable breeding habitats. This tension has consequences that rarely meet our conservation or management goals. This is particularly true in changing environments, which makes the study of dispersal urgently topical in a world plagued with habitat loss, climate change, and species introductions. Despite the difficulty of tracking mobile individuals over potentially vast ranges, recent research has revealed a multitude of ways in which dispersal evolution can either constrain, or accelerate, species' responses to environmental changes.     

From Web Resources to Agricultural Ontology: a Method for Semi-Automatic Construction

In recent years,with the rapid development of information science,ontology becomes a popular research topic in the fields of knowledge engineering and information management.The reason for ontology bei...     

A neuron-silicon junction: a Retzius cell of the leech on an insulated-gate field-effect transistor

An identified neuron of the leech, a Retzius cell, has been attached to the open gate of a p-channel field-effect transistor. Action potentials, spontaneous or stimulated, modulate directly the source-drain current in silicon. The electronic signals match the shape of the action potential. The average voltage on the gate was up to 25 percent of the intracellular voltage change. Occasionally weak signals that resemble the first derivative of the action potential were observed. The junctions can be described by a model that includes capacitive coupling of the plasma membrane and the gate oxide and that accounts for variable resistance of the seal.     

Caudate unit responses to nigral stimuli: evidence for a possible nigro-neostriatal pathway

Electrical stimulation of the Substantia nigra evokes depressant and facilitatory responses from individually recorded caudate nucleus neurons. These effects resemble those elicited from caudate cells by microiontophoretic ejections of dopamine. Since histochemical evidence suggests that dopamine-containing fibers link the substantia nigra with the caudate, this pathway may mediate the changes in caudate spike rates produced by nigral stimuli.     

Conversion of ectoderm to mesoderm by cytoplasmic extrusion in leech embryos

The role of cytoplasmic domains in the determination of the fates of ectodermal and mesodermal cells has been investigated in leech embryos. When yolk-deficient cytoplasm (teloplasm) was extruded from the animal pole of the zygote, the ectodermal precursor blastomere was converted to a mesodermal fate. This change of fate can be prevented by replacement of the extruded animal teloplasm with teloplasm from the vegetal pole. The fate of the mesodermal precursor blastomere was unaffected by teloplasm extrusion or rearrangement. These results demonstrate that ectodermal and mesodermal determination offate involves a binary decision dependent on the position of teloplasm along the animal-vegetal axis.     

Dehalogenation: a novel pathway for the anaerobic biodegradation of haloaromatic compounds

Microorganisms of lake sediment and sewage sludge anaerobically metabolized halobenzoates by a novel pathway. The primary degradative event was loss of the aryl halide without the alteration of the aromatic ring. Dehalogenation required strict anaerobic conditions and depended on the halogen and position, but not the number of halogen substituents. A stable methanogenic bacterial consortium was enriched from sludge and found capable of dehalogenating and often mineralizing a variety of halobenzoates to CH(4) and CO(2). The results suggest that reductive dehalogenation of aromatics could be important in removal of some chlorinated xenobiotics from the environment.     

Pertussis toxin-sensitive pathway in the stimulation of c-myc expression and DNA synthesis by bombesin

The bombesin-like peptides are potent mitogens for Swiss 3T3 fibroblasts, human bronchial epithelial cells, and cells isolated from small cell carcinoma of the lung. The mechanism of signal transduction in the proliferative response to bombesin was investigated by studying the effect of Bordetella pertussis toxin on bombesin-stimulated mitogenesis. At nanomolar concentrations, bombesin increased levels of c-myc messenger RNA and stimulated DNA synthesis in Swiss 3T3 cells. Treatment of the cells with pertussis toxin (5 nanograms per milliliter) completely blocked bombesin-enhanced c-myc expression and eliminated bombesin-stimulated DNA synthesis. This treatment had essentially no effect on the mitogenic responses to either platelet-derived growth factor or phorbol 12,13-dibutyrate. These results suggest that the mitogenic actions of bombesin-like growth factors are mediated through a pertussis toxin-sensitive guanine nucleotide-binding protein. Furthermore they indicate that bombesin-like growth factors act through pathways that are different from those activated by platelet-derived growth factor.     

融资制度的运行机制:从政府主导管制到政府约束管制

经过多年市场化导向的改革,中国在许多领域成功地摆脱了计划经济机制,市场机制在资源配置过程中正在发挥基础作用,但在一些关键领域,仍然由国家运用计划行政手段进行资源配置和调控.     

Buying local organic food: a pathway to transformative learning

Food is a powerful symbol in the struggle to transition to a more sustainable pathway since the food choices citizens make have deep environmental and social impacts within their communities and around the world. Using transformative learning theory, this research explored the learning that took place among individual adults who consumed goods directly from local organic producers, and how this behavior affected their worldview. Learning was classified as instrumental, communicative, or transformative. Ultimately, we considered if the learning created lasting change, directed toward a more sustainable society, among learners. Three different models of producer/consumer interfaces located in Atlantic Canada were considered: a market-garden operation, an education and outreach center, and a community shared agriculture project. It was found that all participants experienced some form of learning, either instrumental or communicative, through their participation in organic agriculture. Closing the gap between producer and consumer through direct contact with the farmer at a market, visiting the farm, or participating in food production oneself is both a desirable step in reaching a more sustainable lifestyle and a powerful learning tool in linking the consumer to a host of other environmental and social issues.     

Intestinal M cells: a pathway for entry of reovirus into the host

Thirty minutes after inoculation of reovirus type 1 into the intestinal lumen of the mouse, viruses were found adhering to the surface of intestinal M cells but not other epithelial cells. Within 1 hour, viruses were seen in the M cell cytoplasm and were associated with mononuclear cells in the intercellular space adjacent to the M cell. These findings suggest that M cells are the site where reovirus penetrates the intestinal epithelium.