Slow oscillations in neural networks with facilitating synapses

The synchronous oscillatory activity characterizing many neurons in a network is often considered to be a mechanism for representing, binding, conveying, and organizing information. A number of models have been proposed to explain high-frequency oscillations, but the mechanisms that underlie slow oscillations are still unclear. Here, we show by means of analytical solutions and simulations that facilitating excitatory (E _f) synapses onto interneurons in a neural network play a fundamental role, not only in shaping the frequency of slow oscillations, but also in determining the form of the up and down states observed in electrophysiological measurements. Short time constants and strong E _f synapse-connectivity were found to induce rapid alternations between up and down states, whereas long time constants and weak E _f synapse connectivity prolonged the time between up states and increased the up state duration. These results suggest a novel role for facilitating excitatory synapses onto interneurons in controlling the form and frequency of slow oscillations in neuronal circuits.     

Stochastic P systems and the simulation of biochemical processes with dynamic compartments

We introduce a sequential rewriting strategy for P systems based on Gillespie's stochastic simulation algorithm, and show that the resulting formalism of stochastic P systems makes it possible to simulate biochemical processes in dynamically changing, nested compartments. Stochastic P systems have been implemented using the spatially explicit programming language MGS. Implementation examples include models of the Lotka-Volterra auto-catalytic system, and the life cycle of the Semliki Forest virus.     

Dynamic compression can inhibit chondrogenesis of mesenchymal stem cells

The objective of this study was to investigate the influence of dynamic compressive loading on chondrogenesis of mesenchymal stem cells (MSCs) in the presence of TGF-β3. Isolated porcine MSCs were suspended in 2% agarose and subjected to intermittent dynamic compression (10% strain) for a period of 42 days in a dynamic compression bioreactor. After 42 days in culture, the free-swelling specimens exhibited more intense alcian blue staining for proteoglycans, while immunohistochemical analysis revealed increased collagen type II immunoreactivity. Glycosaminoglycan (GAG) content increased with time for both free-swelling and dynamically loaded constructs, and by day 42 it was significantly higher in both the core (2.5 ± 0.21%w/w vs. 0.94 ± 0.03%w/w) and annulus (1.09 ± 0.09%w/w vs. 0.59 ± 0.08%w/w) of free-swelling constructs compared to dynamically loaded constructs. This result suggests that further optimization is required in controlling the biomechanical and/or the biochemical environment if such stimuli are to have beneficial effects in generating functional cartilaginous tissue.     

干旱区受水资源胁迫的下游绿洲动态变化趋势分析——以黑河流域额济纳绿洲为例

干旱内陆流域下游绿洲的形成与演变对流域地表径流变化响应强烈 .采用绿洲生态斑块动态模拟、植被与水盐状态相关分析、生态需水量估算等方法 ,分别对黑河流域下游额济纳绿洲在不同分水方案与水资源利用情景下的变化趋势进行了研究 .结果表明 ,维持现状绿洲面积不再萎缩 ,在考虑水资源利用合理化的前提下 ,其最低净需水量为 5 .7× 10 8m3 ,如果考虑下游地区人畜生活用水及工业用水 ,同时考虑水量在输送过程中的散失损耗 ,为在近期 (2 0 15年以前 )维持现状绿洲面积 ,狼心山断面入境流量需达到6 .0× 10 8m3 ;而要使绿洲面积恢复到 2 0世纪 80年代初的水平 ,狼心山断面过水量应不低于 8.9× 10 8m3 ,正义峡断面下泄水量要求达到 10 .9× 10 8～ 13.1× 10 8m3 .     

Viscoelastic properties of plasticized methylcellulose and chemically crosslinked methylcellulose

Films of methylcellulose (MC), poly(ethylene glycol)400 (PEG400) plasticized MC, and MC gels (MC crosslinked with glutaraldehyde (GA)) were prepared by casting from aqueous solutions. The swelling test has shown that the MC gels were insoluble in water and that their crosslinking density increased with increasing GA and HCl concentrations. The effect of the addition of PEG400 or GA to MC was investigated through dynamic mechanical analysis (DMA). The DMA analysis of PEG400/MC blends has shown that PEG400 was compatible with MC and was an effective plasticizer since the curves of tan δ against temperature exhibited single peaks (corresponding to a single glass transition temperature), which were displaced to lower values with increasing PEG400 content. The thermogravimetric analysis (TGA) indicated that the thermal stability of MC was not affected by the chemical crosslinking. The tensile strength was slightly increased through crosslinking while the elongation was slightly decreased. The presence of moisture in MC hydrogels decreased the tensile strength and enhanced the elongation while the addition of PEG400 decreased the tensile strength but sharply increased the elongation.     

基于分段线性模板先验的正电子成像重建

正电子发射成像的噪声性能较其它的一些成像方法要差得多,为了提高重建结果的分辨率和噪声特性,一般采用Bayesian重建。Bayesian方法需要选择恰当的先验,这种先验既要能够抑止重建结果的噪声,又要能够保留图像密度的突变信息。分段线性模板图像模型利用从其它模态的形态学成像得到的组织结构信息,构造适合要求的先验分布函数,由于采用的先验函数是非凸的并包含超验参数,一般的优化方法难以处理,采用动态后验模拟的方法可以很好地解决这些问题。     

Dynamic combinatorial libraries of artificial repeat proteins

Repeat proteins are found in almost all cellular systems, where they are involved in diverse molecular recognition processes. Recent studies have suggested that de novo designed repeat proteins may serve as universal binders, and might potentially be used as practical alternative to antibodies. We describe here a novel chemical methodology for producing small libraries of repeat proteins, and screening in parallel the ligand binding of library members. The first stage of this research involved the total synthesis of a consensus-based three-repeat tetratricopeptide (TPR) protein (～14 kDa), via sequential attachment of the respective peptides. Despite the effectiveness of the synthesis and ligation steps, this method was found to be too demanding for the production of proteins containing variable number of repeats. Additionally, the analysis of binding of the individual proteins was time consuming. Therefore, we designed and prepared novel dynamic combinatorial libraries (DCLs), and show that their equilibration can facilitate the formation of TPR proteins containing up to eight repeating units. Interestingly, equilibration of the library building blocks in the presence of the biologically relevant ligands, Hsp90 and Hsp70, induced their oligomerization into forming more of the proteins with large recognition surfaces. We suggest that this work presents a novel simple and rapid tool for the simultaneous screening of protein mixtures with variable binding surfaces, and for identifying new binders for ligands of interest.     

Identification and synthesis of an efficient multivalent E. coli heat labile toxin inhibitor __ A dynamic combinatorial chemistry approach

A polymer based dynamic combinatorial library (DCL) was generated through condensation between aldehyde functionalized linear poly(glycidol) (APG) and galactose containing acylhydrazide derivatives. Pentameric E. coli heat labile enterotoxin B subunit (LTB) was subsequently applied to the DCL as external stimulus, resulting in amplification of a specific acylhydrazone side chain that was further used for the synthesis of a multivalent LTB inhibitor. In the in vitro biological evaluation, this inhibitor exhibited strong inhibition properties as well as low cytotoxicity.