Astrocytes potentiate transmitter release at single hippocampal synapses

Astrocytes play active roles in brain physiology. They respond to neurotransmitters and modulate neuronal excitability and synaptic function. However, the influence of astrocytes on synaptic transmission and plasticity at the single synapse level is unknown. Ca(2+) elevation in astrocytes transiently increased the probability of transmitter release at hippocampal area CA3-CA1 synapses, without affecting the amplitude of synaptic events. This form of short-term plasticity was due to the release of glutamate from astrocytes, a process that depended on Ca(2+) and soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) protein and that activated metabotropic glutamate receptors (mGluRs). The transient potentiation of transmitter release became persistent when the astrocytic signal was temporally coincident with postsynaptic depolarization. This persistent plasticity was mGluR-mediated but N-methyl-d-aspartate receptor-independent. These results indicate that astrocytes are actively involved in the transfer and storage of synaptic information.     

Target cell-dependent normalization of transmitter release at neocortical synapses

The efficacy and short-term modification of neocortical synaptic connections vary with the type of target neuron. We investigated presynaptic Ca2+ and release probability at single synaptic contacts between pairs of neurons in layer 2/3 of the rat neocortex. The amplitude of Ca2+ signals in boutons of pyramids contacting bitufted or multipolar interneurons or other pyramids was dependent on the target cell type. Optical quantal analysis at single synaptic contacts suggested that release probabilities are also target cell-specific. Both the Ca2+ signal and the release probability of different boutons of a pyramid contacting the same target cell varied little. We propose that the mechanisms that regulate the functional properties of boutons of a pyramid normalize the presynaptic Ca2+ influx and release probability for all those boutons that innervate the same target cell.     

Activation of central neurons by ventral root afferents

It is a fundamental principle of vertebrate neuronal organization that sensory fibers are restricted to dorsal roots and motor fibers to ventral roots. Recent evidence, however, indicates that there are many sensory fibers in ventral roots. The present report shows that stimulation of these fibers activates neurons in the dorsal horn. This provides evidence at the single-cell level for the importance of ventral root afferents and provides an explanation for the clinical phenomenon of recurrent sensibility.     

Dynamic interaction of stargazin-like TARPs with cycling AMPA receptors at synapses

Activity-dependent plasticity in the brain arises in part from changes in the number of synaptic AMPA receptors. Synaptic trafficking of AMPA receptors is controlled by stargazin and homologous transmembrane AMPA receptor regulatory proteins (TARPs). We found that TARPs were stable at the plasma membrane, whereas AMPA receptors were internalized in a glutamate-regulated manner. Interaction with AMPA receptors involved both extra- and intracellular determinants of TARPs. Upon binding to glutamate, AMPA receptors detached from TARPs. This did not require ion flux or intracellular second messengers. This allosteric mechanism for AMPA receptor dissociation from TARPs may participate in glutamate-mediated internalization of receptors in synaptic plasticity.     

Excitatory and inhibitory motoneurons in the central nervous system of the leech

The locomotion and reflex responses of the leech are brought about by inmuscles that are arranged in a regular, simple pattern in the body wall and that flatten, shorten, lengthen, or bend the animal. In the segmental ganglia, it is possible to recognize by morphological and physiological criteria the individual motoneurons that cause contractions and relaxations of these muscles.     

Presynaptic kainate receptor mediation of frequency facilitation at hippocampal mossy fiber synapses

Inhibition of transmitter release by presynaptic receptors is widespread in the central nervous system and is typically mediated via metabotropic receptors. In contrast, very little is known about facilitatory receptors, and synaptic activation of a facilitatory autoreceptor has not been established. Here we show that activation of presynaptic kainate receptors can facilitate transmitter release from hippocampal mossy fiber synapses. Synaptic activation of these presumed ionotropic kainate receptors is very fast (<10 ms) and lasts for seconds. Thus, these presynaptic kainate receptors contribute to the short-term plasticity characteristics of mossy fiber synapses, which were previously thought to be an intrinsic property of the synapse.     

3种复合型防腐剂对台湾香肠抑菌作用的影响

【目的】研究引起台湾香肠腐败的主要微生物以及有机酸复合物AMC(乳酸、柠檬酸和苹果酸按质量比1∶1∶1混合)、磷酸钠缓冲体系BSP(三聚磷酸钠、焦磷酸钠、六偏磷酸钠按质量比2∶2∶1混合)和抗氧化复合物AO(维生素C、水溶性迷迭香、绿茶提取物按质量比4∶3∶3混合)3种复合型防腐剂对腐败菌的抑制作用。【方法】采用GB/T 4789.17-1994方法对腐败微生物进行检验,经选择培养基培养后,对优势腐败菌进行形态、革兰氏染色、芽孢染色、温度培养、pH培养、接触酶试验鉴定;将3种复配型防腐剂分别喷洒至60 g肠体表面,装袋分别于4,25和37℃条件下放置,以不喷洒任何防腐剂为对照,比较3种复合型防腐剂的抑菌效果。【结果】导致台湾香肠腐败的主要微生物为乳酸杆菌属;3种复合型防腐剂中抑菌效果最好的为有机酸复合物,经AMC处理于4℃放置45 d后,其乳酸菌数为5×107g-1,25℃放置21 d后的乳酸菌数为7.7×106g-1,在37℃高温条件下可以保存5d。【结论】3种防腐剂的抑菌效果表现为有机酸复合物>磷酸钠缓冲体系>抗氧化复合物。     

核芯肥料、包膜厚度对控释肥养分释放性能的影响

【目的】探索核芯肥料、包膜厚度与包膜完整性、控释肥养分释放特性的关系,为控释肥的研制提供理论依据。【方法】采用常温静水培养方法,测定供试控释肥的肥效期,研究核芯肥料(均衡型(F1,15-15-15),高钾型(F2,13-10-21))和包膜厚度(110(C1),130(C2)g/m2)对包膜完整性、控释肥养分释放性能的影响。【结果】采用相同包膜厚度、包膜材料和包膜工艺制造的均衡型控释肥初期溶出率明显低于高钾型控释肥。针对同一核芯、包膜厚度不同的控释肥而言,在包膜厚度为110～130g/m2时,随着包膜厚度的增加,控释肥的初期溶出率降低,肥效期延长。而在同一包膜厚度下,核芯肥料不同时,控释肥的养分释放模式不同,肥效期存在着明显差别。当包膜厚度为110g/m2时,均衡型控释肥(F1C1)和高钾型控释肥(F2C1)的肥效期相等,均为3.5个月;当包膜厚度为130g/m2时,均衡型控释肥(F1C2)的肥效期为9.5个月,高钾型控释肥(F2C2)的肥效期仅为6.5个月,即均衡型控释肥的控释效果明显优于高钾型控释肥。【结论】在一定包膜厚度下,采用表面圆润平整的均衡型核芯肥料有利于制造包膜完整、肥效期长的控释肥。     

超滤分离对虾头自溶产物ACE抑制活性的影响

采用3 000 u、5 000 u、8 000 u的超滤膜对凡纳滨对虾虾头自溶产物进行超滤分级分离,研究各组超滤组分的相对分子质量分布和氨基酸组成的变化,并比较各组超滤组分的血管紧张素转换酶（angiotensin I converting enzyme,ACE）抑制活性。结果表明：利用超滤膜分离虾头自溶液可提高虾头自溶产物的ACE抑制活性,3 000 u超滤组分的ACE抑制活性为0.61 mg/mL,活性居各超滤组分之首;8 000 u超滤膜有效载留了大部分大分子物质,相对分子质量小于3 000 u的多肽随超滤孔径的减小而增多;3 000 u超滤组分中芳香族氨基酸和支链氨基酸均高于其余各超滤组分。     

Single-shot channel activation accounts for duration of inhibitory postsynaptic potentials in a central neuron

In the goldfish Mauthner cell, inhibitory postsynaptic currents evoked by intracellular stimulation of presynaptic neurons decay exponentially, with a mean time constant of 6.65 milliseconds. Analysis of membrane conductance fluctuations induced by iontophoresis of glycine and gamma-aminobutyric acid indicates a mean inhibitory channel lifetime of 7.15 milliseconds. The results thus suggest that the relaxation kinetics of activated inhibitory channels are rate-limiting during decay of the inhibitory postsynaptic current.     

控释配方肥中不同控释养分比例对香蕉产量的影响

【目的】建立香蕉系列控释配方肥的产量效应方程,确定适于香蕉生长发育的控释氮、磷、钾比例,为香蕉产业提供高效、简便的肥料和施肥技术。【方法】采用大田试验及三元二次回归设计,以不施肥和常规施肥(追肥16次)为对照,研究系列控释配方肥(追肥4次)中控释氮、磷、钾比例对香蕉产量的影响,建立适于香蕉生长的最佳控释配方肥方案。【结果】控释氮、钾比例高的控释配方肥较常规施肥增产显著,其中以控释氮比例为46.5%,控释磷比例为3.5%,控释钾比例为18.2%处理的产量最高(30.44 kg/株),增产率达22.65%;系列控释配方肥中,控释氮、钾比例显著影响香蕉产量,而控释磷比例对香蕉产量影响不显著;控释配方肥能够解决香蕉常规施肥后期脱肥问题,且在明显减少施肥次数的条件下能提高香蕉产量。【结论】适于香蕉生长的最佳控释配方肥方案是:控释氮占总氮的33.6%、控释钾占总钾的11.0%,控释磷占总磷的0%,此时香蕉产量为26.6 kg/株。     

苹果酸对高岭石中铝和硅释放的影响

采用间歇法(batch method)模拟研究水洗和酸洗高岭石在苹果酸溶液中的长期溶解效应及其相对溶解能力。结果表明,水洗和酸水高岭石反应液中Al、Si离子浓度均随苹果酸浓度的增加而升高,且酸洗高岭石中Al、Si离子更易释放;当苹果酸浓度为20 mmol·L-1时,反应936 h后,水洗高岭石Al、Si的释放量为0.51 mmol·L-1和0.57 mmol·L-1,分别是酸洗高岭石Al、Si释放量的86.44%和83.82%。高岭石反应前期表现为Si的优先释放,而在反应后期,高浓度苹果酸(≥20 mmol·L-1)反应液中高岭石Al、Si趋于同步释放。高岭石的溶解速率随苹果酸浓度的增加而提高,且酸洗高岭石的溶解速率大于水洗高岭石;在本研究浓度范围内,溶解速率未表现出对苹果酸浓度的饱和性,而显示了随其浓度增加的趋势。苹果酸能显著促进高岭石Al和Si的释放,且酸洗高岭石较水洗高岭石更易溶解。     

化感水稻抑草圈土壤及提取物的化感作用

以化感水稻PI312777和非化感水稻Lemont与稗草在自然条件下土壤共培种植产生的抑草圈现象为研究对象,采用土壤三明治法测定了12 cm有效抑草圈处稗草根际土壤以及经水和70%(体积分数)乙醇提取后的土壤对稗草的抑制作用,以及提取物的生物活性.结果表明:与对照相比,化感水稻PI312777抑制圈土壤显著抑制受体稗草根的生长,而该土壤中水和70%(体积分数)乙醇提取物对莴苣的抑制率分别为42.6%和21.4%.表明水稻有效抑草圈的土壤中含有水溶性和醇溶性化感物质,以水为溶剂提取水稻有效抑草圈土壤物质的效率更高.     

脲醛控释复合肥对茶树叶片叶绿素含量的影响

利用脲醛控释复合肥,在苏州碧螺春茶原产地进行了肥料试验,就其应用效果进行了系统分析。结果表明,脲醛控释复合肥能有效地增加茶树叶片中叶绿素含量,降低叶绿素a/b值。叶绿素含量与茶树生物产量、茶芽的产量和质量以及茶芽萌发早晚呈正相关。与常规复合肥相比,其中施用2号脲醛复合肥,茶树叶片中叶绿素平均含量增加45.3%,茶叶增产17.9%,净增收20.78%。     

不同低温时数对牡丹花芽解除休眠的影响

2002、2003年对牡丹催花品种大胡红、乌龙捧盛、肉芙蓉解除休眠所需的低温时数进行了观测。结果表明,低温的累积对牡丹花芽的发育有质的作用,牡丹不同品种解除休眠的低温时数有明显差异:乌龙捧盛解除休眠的低温时数两年平均为646h,大胡红为547 5h,肉芙蓉为499 5h。     

控释肥料不同用量水平对水稻氮素利用和产量的影响

采用田间试验方法研究了控释肥料不同量水平对水稻的氮素利用和产量的影响。结果表明，在试验设计的氮素用量范围内稻谷产量随控释肥料用量的增加而增加。CRF126、CRF108和CRF90处理的稻谷产量分别比U180处理提高10．4％、7．9％和6．8％。水稻干物积累量呈现出相同的趋势。氮素利用指数表现为CRF108＞CRF90＞U180。植株成熟期的植株吸氮量以CRF126处理为最高，比U180处理增加18．8％，CRF108和CRF90处理的稻株吸氮量达到或接近U180处理。     

不同添加材料对化肥中磷素释放和扩散的影响

采用不同的添加材料与化学磷肥混合,通过室内扩散试验,研究不同添加材料对化学肥料中磷素释放和扩散的影响。结果发现,选用的5种材料(沸石、胡敏酸、聚丙烯酰胺、柠檬酸、羧甲基纤维素)均能不同程度地提高肥料磷在土壤中的有效性。与对照相比,柠檬酸在培养初期(1周)能够促进化学磷肥的溶解和扩散,可使施肥点和外围的速效磷含量升高约2.7倍;胡敏酸、PAM在培养4周后能提高施肥点的速效磷,而且使最外层(7～9cm)的速效磷也有较明显的增加,分别较对照提高75%和68%。