Inhibition of postsynaptic PKC or CaMKII blocks induction but not expression of LTP

Long-term potentiation (LTP) of synaptic transmission is a widely studied cellular example of synaptic plasticity. However, the identity, localization, and interplay among the biochemical signals underlying LTP remain unclear. Intracellular microelectrodes have been used to record synaptic potentials and deliver protein kinase inhibitors to postsynaptic CA1 pyramidal cells. Induction of LTP is blocked by intracellular delivery of H-7, a general protein kinase inhibitor, or PKC(19-31), a selective protein kinase C (PKC) inhibitor, or CaMKII(273-302), a selective inhibitor of the multifunctional Ca2+-calmodulin-dependent protein kinase (CaMKII). After its establishment, LTP appears unresponsive to postsynaptic H-7, although it remains sensitive to externally applied H-7. Thus both postsynaptic PKC and CaMKII are required for the induction of LTP and a presynaptic protein kinase appears to be necessary for the expression of LTP.     

Dentate gyrus NMDA receptors mediate rapid pattern separation in the hippocampal network

Forming distinct representations of multiple contexts, places, and episodes is a crucial function of the hippocampus. The dentate gyrus subregion has been suggested to fulfill this role. We have tested this hypothesis by generating and analyzing a mouse strain that lacks the gene encoding the essential subunit of the N-methyl-d-aspartate (NMDA) receptor NR1, specifically in dentate gyrus granule cells. The mutant mice performed normally in contextual fear conditioning, but were impaired in the ability to distinguish two similar contexts. A significant reduction in the context-specific modulation of firing rate was observed in the CA3 pyramidal cells when the mutant mice were transferred from one context to another. These results provide evidence that NMDA receptors in the granule cells of the dentate gyrus play a crucial role in the process of pattern separation.     

The role of excitatory amino acids and NMDA receptors in traumatic brain injury

Brain injury induced by fluid percussion in rats caused a marked elevation in extracellular glutamate and aspartate adjacent to the trauma site. This increase in excitatory amino acids was related to the severity of the injury and was associated with a reduction in cellular bioenergetic state and intracellular free magnesium. Treatment with the noncompetitive N-methyl-D-aspartate (NMDA) antagonist dextrophan or the competitive antagonist 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid limited the resultant neurological dysfunction; dextrorphan treatment also improved the bioenergetic state after trauma and increased the intracellular free magnesium. Thus, excitatory amino acids contribute to delayed tissue damage after brain trauma; NMDA antagonists may be of benefit in treating acute head injury.     

Tonic activation of NMDA receptors by ambient glutamate enhances excitability of neurons

Voltage clamp recordings and noise analysis from pyramidal cells in hippocampal slices indicate that N-methyl-D-aspartate (NMDA) receptors are tonically active. On the basis of the known concentration of glutamate in the extracellular fluid, this tonic action is likely caused by the ambient glutamate level. NMDA receptors are voltage-sensitive, thus background activation of these receptors imparts a regenerative electrical property to pyramidal cells, which facilitates the coupling between dendritic excitatory synaptic input and somatic action potential discharge in these neurons.     

Driving AMPA receptors into synapses by LTP and CaMKII: requirement for GluR1 and PDZ domain interaction

To elucidate mechanisms that control and execute activity-dependent synaptic plasticity, alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptors (AMPA-Rs) with an electrophysiological tag were expressed in rat hippocampal neurons. Long-term potentiation (LTP) or increased activity of the calcium/calmodulin-dependent protein kinase II (CaMKII) induced delivery of tagged AMPA-Rs into synapses. This effect was not diminished by mutating the CaMKII phosphorylation site on the GluR1 AMPA-R subunit, but was blocked by mutating a predicted PDZ domain interaction site. These results show that LTP and CaMKII activity drive AMPA-Rs to synapses by a mechanism that requires the association between GluR1 and a PDZ domain protein.     

农业科技期刊标注“作者贡献声明”的必要性探讨

对农业科技期刊中作者署名不规范现象进行总结的基础上,分析了造成署名不规范的原因,提出了农业科技期刊刊出“作者贡献声明”的可行性和必要性,认为“作者贡献声明”可以起到规范作者署名,减少文章刊出后引发的纠纷和撤稿的现象。     

Blockade of "NMDA" receptors disrupts experience-dependent plasticity of kitten striate cortex

Intracortical infusion of the "N-methyl-D-aspartate" (NMDA) receptor blocker D,L-2-amino-5-phosphonovaleric acid (APV) renders kitten striate cortex resistant to the effects of monocular deprivation. In addition, 1 week of continuous APV treatment (50 nanomoles per hour) produces a striking loss of orientation selectivity in area 17. These data support the hypothesis that crucial variables for the expression of activity-dependent synaptic modifications are a critical level of postsynaptic activation and calcium entry through ion channels linked to NMDA receptors.     

青稞LTP蛋白基因bltl4．2的克隆及其在低温下的表达

为了解LTP蛋白基因bltl4．2在青稞中的功能,以青稞品种“昆仑12号”为实验材料,克隆得到编码该基因的eDNA序列全长470bp,其中包括249bp的开放阅读框,编码82个氨基酸残基,相对分子质量7709．8,理论p16．52,不稳定系数27．36,是一个稳定的蛋白质。LTP蛋白有2个跨膜区,1-19位置的是从膜内到膜外,57-76位置的是从膜外到膜内,总平均亲水性0．522,是一个高度亲水的小分子蛋白质。序列比对显示编码该蛋白的基因与大麦bltl4．2基因具有较高的同源性（98．9％）。通过RealtimePCR检测得到blH4．2基因在4℃下处理48、24和12h的表达量分别是0h的14．6、13．6和8．3倍,SPSS分析显示bltl4．2基因在不同低温胁迫时间下表达差异显著,说明该基因对青稞的耐寒性起到一定的作用。     

Contributions of bird studies to biology

Birds are widely distributed, highly diversified, and exhibit behavior and social organizations equal in complexity to mammals, yet they are generally more conspicuous and approachable in natural environments. These attributes make birds excellent subjects in many areas of biological research. The topics in which studies on birds have figured prominently include the mechanisms of species formation, the regulation of the distribution and abundance of animals, the effects of the environment on behavior and physiology, the biological and evolutionary significance of variations in social organizations, the encoding of information in animal communication, the sensory basis for migration and navigation, the effects of hormones on nerve cells and behavior, the ontogeny of brain and behavior, and the structure and function of the vertebrate brain. The outstanding record of avian research suggests that birds will continue to provide important models for developing and testing new ideas in various fields of biology.     

关于提升农业高校科技贡献力的思考

为了完成好科教兴农和社会主义新农村建设的伟大工程,需要充分发挥农业高校的科技贡献力,农业高校的人才,技术和资源优势是显而易见的.但是也应该认识到农业高校科研工作存在的种种不足和问题,主要原因是农业经济弱势的长期影响、教师科研积极不高、人才流失严重、科研条件制约、与企业合作不力等,并相应地从抓机遇、抓管理、抓人才、抓团队、抓合作等五个方面提出了对策和建议,以期对农业高校搞好科研事业,提升科技贡献力有所裨益.     

Contributions of 1890 schools to rural development

This article concentrates on 1890 land-grant colleges' and universities' contributions to rural development in 16 southern and border states. The author contends that lifting rural dwellens out of ignorance and poverty has been a major objective of 1890 institutions. During the early years the 1890s sent out change-agents to encourage rural dwellers to improve their standard of living through education and self-help programs. These agents went into rural communities and taught farm families to raise better crops and livestock; improve their homes, schools, and community life; and despite inadequate funding of teaching, research, and extension at these schools, the 1890 schools made significant contributions to rural development. Moreover, the writer contends that the 1890 schools are not outmoded, but essential to rural development and to the education of American citizens during the rest of the 1990s and into the 21st century.     

Contributions of the visual ventral pathway to long-range apparent motion

Objects displaced intermittently across the visual field will nonetheless give an illusion of continuous motion [called apparent motion (AM)] under many common conditions. It is believed that form perception is of minor importance in determining AM, and that AM is mediated by motion-sensitive areas in the "where" pathway of the cortex. However, form and motion typically interact in specific ways when natural objects move through the environment. We used functional magnetic resonance imaging to measure cortical activation to long-range AM, compared to short-range AM and flicker, while we varied stability of structural differences between forms. Long-range AM activated the anterior-temporal lobe in the visual ventral pathway, and the response varied according to the form stability. The results suggest that long-range AM is associated with neural systems for form perception.     

Storage of spatial information by the maintenance mechanism of LTP

Analogous to learning and memory storage, long-term potentiation (LTP) is divided into induction and maintenance phases. Testing the hypothesis that the mechanism of LTP maintenance stores information requires reversing this mechanism in vivo and finding out whether long-term stored information is lost. This was not previously possible. Recently however, persistent phosphorylation by the atypical protein kinase C isoform, protein kinase Mzeta (PKMz), has been found to maintain late LTP in hippocampal slices. Here we show that a cell-permeable PKMz inhibitor, injected in the rat hippocampus, both reverses LTP maintenance in vivo and produces persistent loss of 1-day-old spatial information. Thus, the mechanism maintaining LTP sustains spatial memory.     

Zebrafish Dpr2 inhibits mesoderm induction by promoting degradation of nodal receptors

Nodal proteins, members of the transforming growth factor-beta (TGFbeta) superfamily, have been identified as key endogenous mesoderm inducers in vertebrates. Precise control of Nodal signaling is essential for normal development of embryos. Here, we report that zebrafish dapper2 (dpr2) is expressed in mesoderm precursors during early embryogenesis and is positively regulated by Nodal signals. In vivo functional studies in zebrafish suggest that Dpr2 suppresses mesoderm induction activities of Nodal signaling. Dpr2 is localized in late endosomes, binds to the TGFbeta receptors ALK5 and ALK4, and accelerates lysosomal degradation of these receptors.