Conformational switch of syntaxin-1 controls synaptic vesicle fusion

During synaptic vesicle fusion, the soluble N-ethylmaleimide-sensitive factor-attachment protein receptor (SNARE) protein syntaxin-1 exhibits two conformations that both bind to Munc18-1: a "closed" conformation outside the SNARE complex and an "open" conformation in the SNARE complex. Although SNARE complexes containing open syntaxin-1 and Munc18-1 are essential for exocytosis, the function of closed syntaxin-1 is unknown. We generated knockin/knockout mice that expressed only open syntaxin-1B. Syntaxin-1B(Open) mice were viable but succumbed to generalized seizures at 2 to 3 months of age. Binding of Munc18-1 to syntaxin-1 was impaired in syntaxin-1B(Open) synapses, and the size of the readily releasable vesicle pool was decreased; however, the rate of synaptic vesicle fusion was dramatically enhanced. Thus, the closed conformation of syntaxin-1 gates the initiation of the synaptic vesicle fusion reaction, which is then mediated by SNARE-complex/Munc18-1 assemblies.     

Stereotyped position of local synaptic targets in neocortex

The microcircuitry of the mammalian neocortex remains largely unknown. Although the neocortex could be composed of scores of precise circuits, an alternative possibility is that local connectivity is probabilistic or even random. To examine the precision and degree of determinism in the neocortical microcircuitry, we used optical probing to reconstruct microcircuits in layer 5 from mouse primary visual cortex. We stimulated "trigger" cells, isolated from a homogenous population of corticotectal pyramidal neurons, while optically detecting "follower" neurons directly driven by the triggers. Followers belonged to a few selective anatomical classes with stereotyped physiological and synaptic responses. Moreover, even the position of the followers appeared determined across animals. Our data reveal precisely organized cortical microcircuits.     

A synaptic vesicle protein with a novel cytoplasmic domain and four transmembrane regions

Complementary DNA and genomic clones were isolated and sequenced corresponding to rat and human synaptophysin (p38), a major integral membrane protein of synaptic vesicles. The deduced amino acid sequences indicate an evolutionarily highly conserved protein that spans the membrane four times. Both amino and carboxyl termini face the cytoplasm, with the latter containing ten copies of a tyrosine-rich pentapeptide repeat. The structure of synaptophysin suggests that the protein may function as a channel in the synaptic vesicle membrane, with the carboxyl terminus serving as a binding site for cellular factors.     

Identification of synaptophysin as a hexameric channel protein of the synaptic vesicle membrane

The quaternary structure and functional properties of synaptophysin, a major integral membrane protein of small presynaptic vesicles, were investigated. Cross-linking and sedimentation studies indicate that synaptophysin is a hexameric homo-oligomer, which in electron micrographs exhibits structural features common to channel-forming proteins. On reconstitution into planar lipid bilayers, purified synaptophysin displays voltage-sensitive channel activity with an average conductance of about 150 picosiemens. Because specific channels and fusion pores have been implicated in vesicular uptake and release of secretory compounds, synaptophysin may have a role in these processes.     

G protein betagamma subunit-mediated presynaptic inhibition: regulation of exocytotic fusion downstream of Ca2+ entry

The nervous system can modulate neurotransmitter release by neurotransmitter activation of heterotrimeric GTP-binding protein (G protein)-coupled receptors. We found that microinjection of G protein betagamma subunits (Gbetagamma) mimics serotonin's inhibitory effect on neurotransmission. Release of free Gbetagamma was critical for this effect because a Gbetagamma scavenger blocked serotonin's effect. Gbetagamma had no effect on fast, action potential-evoked intracellular Ca2+ release that triggered neurotransmission. Inhibition of neurotransmitter release by serotonin was still seen after blockade of all classical Gbetagamma effector pathways. Thus, Gbetagamma blocked neurotransmitter release downstream of Ca2+ entry and may directly target the exocytotic fusion machinery at the presynaptic terminal.     

产程早期干预矫正枕后位对分娩方式的影响

目的 :探讨足月妊娠枕后位产程早期进行预防性干预对分娩方式的影响。方法 :研究组 10 0例 (经 B超或阴检诊断为枕后位的先兆临产至潜伏期的初产妇 ,取胎儿脊柱侧侧俯卧位 ,宫口开大 3cm未破膜者常规消毒下行人工破膜术 ,宫颈水肿者给予 2 %普鲁卡因 4m L +阿托品 0 .5 mg局部封闭 ,如胎方位仍不正 ,徒手旋转胎头至枕前位 ;对照组10 0例 (条件与研究组相同 ) ,不予上述预防性干预。结果 :研究组剖宫产率为 16 % ,对照组为 74% ,差异有显著性 (P<0 .0 1)。结论 :产程早期预防性干预枕后位 ,可缩短产程 ,降低剖宫产率。     

Quantal secretion from adrenal medulla: all-or-none release of storage vesicle content

Neurogenic secretion of catecholamines from the adrenal medulla in rabbits, induced by administration of insulin, caused decreases in both the dopamine-beta-hydroxylase activity and the catecholamine content of the storage vesicle fraction. After sedimentation through a sucrose density gradient, the storage vesicles obtained from insulin-treated animals had the same density and the same ratio of dopamine-beta-hydroxylase to catecholamine as did vesicles from untreated animals. These and other data indicate that neurogenic secretion from the adrenal medulla occurs by an all-or-none release from the storage vesicles.     

Bruchpilot promotes active zone assembly, Ca2+ channel clustering, and vesicle release

The molecular organization of presynaptic active zones during calcium influx-triggered neurotransmitter release is the focus of intense investigation. The Drosophila coiled-coil domain protein Bruchpilot (BRP) was observed in donut-shaped structures centered at active zones of neuromuscular synapses by using subdiffraction resolution STED (stimulated emission depletion) fluorescence microscopy. At brp mutant active zones, electron-dense projections (T-bars) were entirely lost, Ca2+ channels were reduced in density, evoked vesicle release was depressed, and short-term plasticity was altered. BRP-like proteins seem to establish proximity between Ca2+ channels and vesicles to allow efficient transmitter release and patterned synaptic plasticity.     

Vesicular glutamate transporters 1 and 2 target to functionally distinct synaptic release sites

Vesicular glutamate transporters (VGLUTs) 1 and 2 show a mutually exclusive distribution in the adult brain that suggests specialization for synapses with different properties of release. Consistent with this distribution, inactivation of the VGLUT1 gene silenced a subset of excitatory neurons in the adult. However, the same cell populations exhibited VGLUT1-independent transmission early in life. Developing hippocampal neurons transiently coexpressed VGLUT2 and VGLUT1 at distinct synaptic sites with different short-term plasticity. The loss of VGLUT1 also reduced the reserve pool of synaptic vesicles. Thus, VGLUT1 plays an unanticipated role in membrane trafficking at the nerve terminal.     

蔬菜质量分级和销售渠道拓展对 菜农收益的影响研究

农业是我国的基础产业,蔬菜作为农产品的一个必要组成部分,其发展水平对农民生活生产有重要影响。蔬菜品质区别大而且供给链较长,且蔬菜的市场价格时高时低,这种不稳定性使菜农的蔬菜出售价格不高,对菜农有不利影响。因此,在我国现有的市场条件下,寻找一种保障菜农基本利润的措施以提高菜农的收益是很有必要的。通过理论推导,得出了蔬菜质量分级和销售渠道拓展能够有效提高菜农的利润,提出了相应的政策建议。     

产地和部位对卷烟原料化学成分含量的影响

【目的】提供烟草制造可替代的卷烟原料选择方案和生产不同类型的卷烟产品提供备选方案,分析不同产地和不同部位对卷烟原料化学成分含量的影响.【方法】以全国18个省及其内部产地中主要卷烟原料产地的528个C3F等级的烟叶样品的烟叶原料为试验材料,采用箱形图和变异系数相结合的方式分析产地对各种化学成分含量的影响;以全国18个省份的1 449个烟叶样本的C3F、X2F和B2F为试验材料,采用变异系数和t检验相结合的方式分析部位对化学成分含量的影响.【结果】产地因素对卷烟原料化学成分中的钾、氯等2项指标的影响显著,对pH的影响最小.部位因素对卷烟原料中总植物碱、总氮、石油醚提取物和钾等4种化学成分影响较大,其中对总植物碱的影响最大,对pH的影响最小.【结论】产地和部位对卷烟原料的化学成分具有一定影响,烟草企业在卷烟生产和产品研发中,可通过对不同产地和部位的卷烟原料的选择和不同搭配,实现对卷烟原料各种化学成分原料的调整,以达到产品生产和研发的目的.     

FMDV抗原表位与hsp70的融合表达及表达产物对小鼠的免疫应答

将人工合成的O型口蹄疫病毒主要表位基因与结核杆菌热休克蛋白70(HSP70)基因克隆入酵母表达载体pPICZαA中,以电穿孔法转化酵母菌X-33,用Zeocin平板筛选重组子,PCR鉴定后甲醇诱导表达.SDS-PAGE显示,其相对分子质量为89 000,表达量约为190 mg·L-1;免疫印迹分析证实表达产物具有免疫反应性.融合蛋白以皮下接种的方式对8只小鼠进行3次免疫,然后通过ELISA和MTT分别检测抗体水平和淋巴细胞增殖反应.结果表明,融合蛋白既能诱导细胞免疫应答,又能诱导体液免疫应答,其产生的抗体水平接近于常规灭活疫苗.MTT试验结果显示,融合蛋白的A570为0.381±0.072,灭活疫苗的A570为0.340±0.050,表明融合蛋白的细胞免疫应答水平高于后者.提示,hsp70作为分子佐剂在口蹄疫基因工程疫苗研究中具有很好的应用前景.     

交换性阳离子对磷灰石中磷和钙释放的影响

研究了以Ｌｉ~＋、Ｎａ~＋、Ｋ~＋、ＮＨ~＋_４等一价阳离子取代磷灰石表面交换性二价阳离子对磷灰石中磷和钙释放的影响，并就可能涉及的机理进行了探讨．     

安全屏障对储油罐区池火灾多米诺效应概率的影响

随着石油储库朝大型化、集约化方向发展,罐区工艺与设备日趋繁杂,一旦发生火灾事故,极易引发多米诺效应,导致灾难性后果.为了降低石油储库事故对周边人员、环境等造成的影响,基于主动、被动、应急与响应措施3种安全屏障的性能,采用事件树与贝叶斯网络方法针对不同安全屏障建模,进而对事故多米诺效应概率进行定量评估.结果表明:多层安全...     

茶树不同轻修剪模式对假眼小绿叶蝉种群及茶叶产量、品质的影响

研究了夏剪、冬剪两种轻修剪模式对茶假眼小绿叶蝉种群及茶叶产量、品质的影响。结果表明,1~4月,叶蝉数量少,对茶树为害极轻,虫口密度以夏剪稍高于冬剪;在春茶结束后即实施夏剪,6~10月间其虫口密度明显低于冬剪,表明在叶蝉为害高峰期之前,采取轻修剪措施可有效控制虫口密度,减少虫害损失。不同轻修剪模式对茶叶产量影响较明显,夏剪的春、夏茶产量分别比冬剪高21.3%~36.5%、6.61%~26.3%,对茶叶品质也有明显影响。     

偏振波谱光态矢量光照参量对东亚飞蝗偏光响应效应的影响

为明确偏振波谱光态光照参量对蝗虫趋偏响应效应的影响作用,获取蝗虫偏振诱导光场的技术特征,研制蝗虫偏振诱导光源,利用蝗虫偏光响应试验装置测试了蝗虫对紫、蓝部分偏光及线偏光的响应特征,以此优选波谱偏振光态矢量的作用模式,分析偏振波谱光态光照参量对蝗虫偏光响应机制的影响,探讨蝗虫偏光波谱矢量敏感模式变化的原因。结果表明,部分偏光中,紫波谱未引起而蓝波谱导致蝗虫视响应与视趋性敏感矢量发生改变;线偏光中,紫、蓝波谱均影响蝗虫趋偏响应效应的矢量敏感模式,且波谱相同,部分偏光矢量置向模式对蝗虫的操控诱导、视趋强度的调控性优于线偏光,而偏振矢量光态相同,紫波谱的作用效果强于蓝波谱。蝗虫趋偏响应效应与偏振波谱、偏振光态的异质作用效应有关,且线偏紫波谱120°左右置向矢量对蝗虫的诱导效果最强(94.5%),而紫波谱部分偏光左60°及右150°矢量对蝗虫视趋强度的作用效果最强(68.5%);部分偏光矢量置向模式的作用效果与波谱光致性视敏偏振效应有关,且蓝波谱中偏振度越高而光照度越低,矢量模式的操控诱导性越强,紫波谱中偏振度越低而光照度越强,矢量模式对蝗虫趋偏聚集程度的作用效果越强。从而,线偏与部分偏光不同矢量光照交替刺激模式可提高蝗虫趋偏响应敏感性。     

谷子在旱作农业中的地位和作用

本文简要叙述了谷子在旱作农业生产中的重要地位和作用.     

农业干旱程度概率分布的研究

分析了目前各种农业干旱评估指标的不足,建立了能反映干旱给农业造成损失大小的农业干旱评估指标量化模型。利用该农业干旱程度评估模型,通过模拟和非参数检验对农业干旱程度的概率分布进行了研究,并利用河南省濮阳市实际资料,计算了当地农业干旱程度的概率分布。