共查询到20条相似文献,搜索用时 31 毫秒
1.
N. Brose 《Die Naturwissenschaften》1999,86(11):516-524
12 nerve cells with up to 1015 synapses. In principle, synaptogenesis takes place in two consecutive steps that are most likely mediated by cell adhesion
molecules. First, an arriving axonal growth cone identifies its appropriate partner cell, creating an initial contact, and,
second, specific axonal and dendritic protein components are recruited to this initial contact site, forming a functional
synapse. Three cell adhesion systems have recently been shown to be specifically enriched at synaptic contacts: the cadherin/catenin
system, the cadherinlike neuronal receptors, and the β-neurexin/neuroligin system. Components of all three cell adhesion systems
have been localized to synaptic contacts using immunogold electron microscopy but are also present outside of synapses. The
present short review discusses the possible role of these synaptic cell adhesion molecules in synaptogenesis. 相似文献
2.
针对平板式光生物反应器,以补充有碳源的SE(Brostol's solution)培养基作为普通小球藻生长的水环境,研究了载体表面粗糙度、藻细胞接种量、培养液pH值和液体流量对小球藻细胞在固体基质表面吸附特性的影响.结果表明:藻细胞在各载体表面的吸附密度均随时间进行呈现先快速增大再逐渐趋于平缓的变化趋势;在实验条件下,随载体表面粗糙度和藻液中藻细胞接种量增大,载体表面对小球藻细胞的吸附率均增大,吸附密度也增大;当藻液pH值为6左右时,小球藻在载体表面的吸附密度达到最大;液体流量为0.65 mL·min-1时,载体表面对小球藻细胞的吸附能力最强.各参数对藻细胞吸附密度影响的重要程度依次为藻细胞接种量、培养基pH值、液体流量. 相似文献
3.
M. R. Ulm MD K. Chalubinski C. Ulm B. Plöckinger J. Deutinger G. Bernaschek 《黑龙江环境通报》1995,15(4):368-372
Recently, sonography of the fetal face has gained increasing importance in prenatal diagnosis. It is not yet clear whether sonographic depiction of fetal tooth germs would have an influence on the prenatal diagnosis of ectodermal dysplasia syndromes. During routine malformation screening, horizontal sections of fetal jaws were visualized and examined for tooth germs in 124 pregnant women following sonographic ‘facing’. Histological jaw sections of fetuses that had died in utero at various gestational ages were produced in order to examine the degree of correspondence between the sonographic and histological findings. At least four tooth germs were found in the jaws of all fetuses between 19 and 34 gestational weeks (n=104). Although jaw visualization was possible between 14 and 18 gestational weeks (n=20), the exact number and location of the tooth germs could not be determined. Assessment of tooth germs may become increasingly important, as aplasia of the tooth germs is one of the principal signs of various hereditary ectodermal diseases. 相似文献
4.
蛋白质对PVDF超滤膜污染行为的界面微观作用力解析 总被引:4,自引:4,他引:0
采用原子力显微镜,结合自制微颗粒探针,对膜-污染物及污染物-污染物间微观作用力进行了检测分析,考察了不同p H条件下牛血清蛋白(BSA)在不同界面特性PVDF超滤膜上的膜污染行为.结果表明,在膜过滤初期,通量剧烈衰减主要由BSA和膜之间黏附力作用导致,在膜过滤后期,BSA与BSA之间的黏聚作用则是影响后期膜污染行为的主要因素;PA膜-BSA和PP膜-BSA之间的黏附作用力均大于BSA-BSA之间的黏聚作用力,说明在整个膜过滤过程中,BSA与PVDF超滤膜之间的黏附作用对膜污染起主导作用;相同p H条件下,PA膜-BSA之间的微观作用小于PP膜-BSA之间的相互作用力,说明亲水性较强的PA膜具有较强的抗污染性;而PA膜和PP膜过滤后期BSA-BSA之间黏聚力相差不大,也进一步说明膜过滤过程中膜-污染物之间的微观作用力是影响膜污染行为的主要因素. 相似文献
5.
The hydrolase Notum (also known as Wingful) has been implicated in shaping the distribution gradient of the morphogen Wingless in Drosophila by modifying the Wingless-binding heparan sulfate proteoglycan (HSPG) core glypicans Dally and Dally-like. Here we report on the expression of a Notum homolog during the embryonic development of the spider Cupiennius salei. Notum is expressed in two to three stripes in the posterior region of the germband where new segments are formed. At this location no Wingless expression is present, suggesting that Notum may be involved in the regulation of another HSPG-binding morphogen, possibly Hedgehog. In older segments, however, expression of Notum and Wingless roughly coincides. In the appendages, Notum is expressed in ventral mesodermal cells, directly adjacent to the Wingless expressing ectodermal cells. This could indicate a role for the mesoderm in regulating morphogen gradient formation in the ectoderm. 相似文献
6.
聚合氯化铁-腐殖酸(PFC-HA)絮体的不同拓扑空间下分形维数的研究 总被引:1,自引:0,他引:1
通过对PFC混凝去除水中HA过程中所形成的PFC-HA絮体的研究结果表明,原水pH分另4为9.0、7.0和5.0时,最佳投药量下形成的絮体的平均沉降速度之间的比值为1.17:1.00:0.49,而且所有絮体的水平投影方向的平均直径与垂直投影方向的平均直径的比值均接近0.85.结合Logan公式和有效密度-长轴的双对数关系计算出的絮体三维空间的分形维数Df较为可靠,在本试验中3种pH的原水下形成的PFC-HA絮体的Df均小于2.0.絮体沉降速度的变化是质量分形维数Df、有效密度和粒径等因素的变化综合影响结果,因此,絮体的Df、有效密度各自的变化趋势有可能与沉降速度的不一致.原水pH=7.0时絮体的Df稍大于原水pH=9.0时絮体的Df,但比原水pH=5.0时絮体的Df大11.73%.可见,与原水pH=9.0时形成的絮体相比,原水pH=7.0时形成了稍微密实的小絮体,但原水pH=5.0时却形成了较为疏松的、很小的絮体.在本试验的图像分辨率下,PFC-HA絮体在一维拓扑空间下的分形维数D1比较低,一般都低于1.10.基于投影面积-长轴关系计算的二维拓扑空间的分形维数D2变化趋势为样品3稍大于样品2,样品1最小;然而基于投影面积一周长计算的二维拓扑空间的分形维数D2却呈现不同的变化趋势.另外,尽管PFC-HA絮体的Df小于2,但其与基于投影面积-长轴关系计算的二维拓扑空间的分形维数D2不相等,不符合Meakin的结论,这与本试验中CCD相机的分辨率和絮体样本数量有关. 相似文献
7.
Hariyama T 《Die Naturwissenschaften》2000,87(7):327-330
This paper deals with the structure and function of the intracerebral ocelli in the caudal area of the brain of the Japanese
firefly. A pair of epilaterally placed specialized pigmented organs was found at the caudal ends of the brains of the fireflies
Luciola cruciata and L. lateralis. On the basis of light and transmission electron micrographs of both male and female individuals these organs seemed photoreceptive
in nature. Intracellular and extracellular recordings were obtained from the intracerebral ocelli of the fireflies with microelectrodes.
The physiological evidence revealed that the cells found in the brain were, indeed, photoreceptors.
Received: 7 April 2000 / Accepted in revised form: 16 June 2000 相似文献
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铁铝氧化物是土壤的重要组分之一,其对土壤中有机无机组分的迁移具有重要影响.本文以枯草芽孢杆菌和荧光假单胞菌为研究对象,通过批吸附实验和DLVO理论,探究铁铝复合氧化物对细菌的粘附作用及其作用机制.结果表明,铁铝复合氧化物对细菌的粘附随着平衡浓度的增加而增加,吸附过程可用Langmuir方程拟合.铁铝1∶3复合氧化物对枯草芽孢杆菌和荧光假单胞菌的最大吸附量分别为3717.43和2792.29 mg·g~(-1),铁铝3∶1复合氧化物对枯草芽孢杆菌和荧光假单胞菌的最大吸附量分别为3455.58和2760.33 mg·g~(-1).随着pH值的增大,两种铁铝复合氧化物对两种细菌的吸附量均呈下降趋势.铁铝1∶3复合氧化物对两种细菌的吸附量均大于铁铝3∶1复合氧化物.静电吸引力是铁铝复合氧化物与细菌之间相互作用的主要因素之一. 相似文献
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D. Costa A. Borrell E. Margarit A. Carrió A. Soler I. Balmes X. Estivill A. Fortuny 《黑龙江环境通报》1995,15(2):141-148
Fluid from pleural effusion (n=2) and cystic hygroma (n=7) was obtained from eight fetuses, between 13 and 32 weeks of pregnancy at the time when a conventional prenatal diagnosis procedure was carried out. As these fluids contain lymphocytes, they were processed like peripheral blood. A karyotype was obtained in 4 days in both cases of pleural effusion and in four out of seven samples of cystic hygroma. An abnormal karyotype was detected in three of the four samples of cystic hygroma: two trisomies 21 and a monosomy X. Different parameters were evaluated in order to predict the feasibility of obtaining a cytogenetic diagnosis. Our data showed that if the amount of fluid obtained was ⩾4 ml and the initial lymphocyte count (ILC) was >0.2 × 106 cells/ml, a cytogenetic diagnosis was possible from an initial concentration of cultured lymphocytes )ICCL) of >0.06 × 106 cells/ml. 相似文献
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R. Achiron MD O. Pinhas-Hamiel S. Lipitz Z. Heiman B. Reichman S. Mashiach 《黑龙江环境通报》1994,14(7):523-526
Cytomegalovirus is the most common cause of congenital viral infection. In utero infection is usually suspected in patients with growth-retarded fetuses or when maternal illness precipitates serological investigations. A case is presented where routine ultrasound examination at 30 weeks' gestation in an asymptomatic patient demonstrated mild fetal ventriculomegaly. Transvaginal ultrasound enabled the visualization of intraventricular adhesions and small periventricular cysts. The suspected diagnosis of in utero cytomegalovirus infection was confirmed by the presence of IgM antibodies in fetal blood and subsequently by isolation of the virus from the infant's urine. The presence of mild fetal ventriculomegaly should prompt transvaginal brain imaging. 相似文献
14.
Effects of Serotonergic and Opioidergic Drugs on Escape Behaviors and Social Status of Male Crickets
We examined the effects of selective serotonin depletion and opioid ligands on social rank and related escape behavior of
the cricket Gryllus bimaculatus. Establishment of social rank in a pair of males affected their escape reactions. Losers showed a lower and dominants a higher
percentage of jumps in response to tactile cercal stimulation than before a fight. The serotonin-depleting drug α-methyltryptophan
(AMTP) caused an activation of the escape reactivity in socially naive crickets. AMTP-treated animals also showed a lower
ability to become dominants. With an initial 51.6±3.6% of wins in the AMTP group, the percentage decreased to 26±1.6% on day
5 after injection. The opiate receptor antagonist naloxone affected fight and escape similarly as AMTP. In contrast to naloxone,
the opioid agonist [d-Ala2, N-Me-Phe4, Gly5-ol]-enkephalin decreased escape responsiveness to cercal stimulation in naive and subordinate crickets. We suggest that serotonergic
and opioid systems are involved in the dominance induced depression of escape behavior.
Received: 27 July 1998 / Accepted in revised form: 31 March 1999 相似文献
15.
通过中外文数据库对微颗粒在表面粘附的力学模型研究成果进行了检索,分析发现这些模型抽象、不直观,不利于理解和研究粘附的机理,基于此,利用MATLAB软件对这些粘附力学模型进行可视化模拟,通过归纳、分析和总结评价,提出今后的研究方向. 相似文献
16.
为研究室内颗粒物的自然沉降和黏附玻璃表面的规律,将普通硅酸盐玻璃载玻片以与水平面呈不同夹角(0°,45°和90°)放置于实验室中,研究载玻片表面在未处理、经玻璃清洗剂或TiO2处理条件下,不同放置时间(1,3,10和30 d)内其黏附颗粒物的特性.结果表明:经TiO2预处理的载玻片表面黏附的颗粒物质量与放置时间呈正比,与水平面夹角呈反比;而未处理和经玻璃清洗剂处理的载玻片的上述关系不明显.经清洗剂预处理的载玻片表面的颗粒物数浓度、遮光比相对较小,说明可以通过表面预处理防止玻璃表面黏尘.载玻片表面黏附颗粒物的平均粒径不随放置时间、与水平面夹角和预处理试剂种类变化而明显改变,粒径主要集中在15~25 μm. 相似文献
17.
鄱阳湖典型区铜锈环棱螺体内微塑料分布特征 总被引:4,自引:4,他引:0
微塑料能够被水生生物摄入并对其产生毒性效应.以5条汇入鄱阳湖河流的入湖口、鄱阳湖出湖口和南矶山自然保护区为研究区,采集优势底栖动物铜锈环棱螺样品,对其进行组织消解并分离其中的微塑料,利用显微镜和红外光谱鉴定微塑料,分析鄱阳湖典型区铜锈环棱螺体内微塑料分布特征.结果表明,鄱阳湖典型区铜锈环棱螺体内微塑料丰度为(0.52±0.15)~(2.48±0.90) n·g-1,赣江入湖口铜锈环棱螺体内微塑料丰度高于其他入湖口,南矶山湿地自然保护区铜锈环棱螺体内微塑料丰度最小.研究区铜锈环棱螺体内微塑料以粒径小于1 mm的透明纤维为主.铜锈环棱螺肠道微塑料丰度高于肌肉组织.本研究表明人类活动是影响铜锈环棱螺体内微塑料丰度的重要因素,对底栖动物中微塑料的调查有助于人们全面了解微塑料污染的生态风险. 相似文献
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微滤过程中腐殖酸与膜表面黏附特性的试验研究 总被引:4,自引:4,他引:0
为了进一步研究微滤过程中腐殖酸对微滤膜的污染机制,通过运用原子力显微镜(AFM),结合自制的PVDF胶体探针考察了不同的pH、离子强度以及钙离子浓度等水质条件下膜-腐殖酸与腐殖酸-腐殖酸之间微观黏附力的变化趋势以及与膜的通量衰减幅度之间的相关性.结果发现,微观黏附力是膜面污染产生的根本原因.由于pH的电性中和以及离子强度的电性屏蔽作用,膜-腐殖酸以及腐殖酸-腐殖酸之间黏附力随着pH的减小或离子强度的增大都呈增大趋势;而随着钙离子浓度的增大,由于少量钙离子的"架桥"作用以及过量时的电性中和作用,两种黏附力先增大后减小.各条件下,膜-腐殖酸与腐殖酸-腐殖酸之间黏附力都呈相同的变化趋势,且与对应污染膜的通量衰减幅度具有正相关性,为更加深入了解膜污染的形成机制提供了一定的理论支持. 相似文献
20.
M. Salvy Y. Capowiez Y. Le Conte M. Salvy J.-L. Clément 《Die Naturwissenschaften》1999,86(11):540-543
Varroa jacobsoni is an ectoparasite of honey bees which reproduces in capped brood cells. Multi-infestation is frequently observed in worker
brood and can be interpreted as an aggregative phenomenon. The aim of this study was to determine whether the distribution
of V. jacobsoni in worker brood cells relies on a random or an aggregative process. We studied the distribution of Varroa females in capped worker brood at similar age by comparing, by a Monte Carlo test, the observed frequency distribution of
mites per cell to simulated distributions based on a random process. A complementary approach, using the "nearest neighbor
distances" (NND) with Monte Carlo tests, was investigated to study the spatial distribution (a) between mites in different
cells and (b) between infested cells in brood. The observed distributions did not differ significantly from that expected
by a random process, and we conclude that there is no aggregation during invasion of V. jacobsoni in worker brood.
Received: 29 April 1999 / Accepted in revised form: 26 August 1999 相似文献