多种化学突触性能比较的数值模拟

目的:运用数值模拟的方法实现不同化学突触模型。方法:通过化学突触将两个Hodgkin-Huxley神经元连接构建简单的化学突触连接模型。运用Simulink软件和DSP Builder软件分别对5种化学突触数学模型建模,得到化学突触的突触电流模拟结果。采用相关系数法量化分析这几种化学突触的模拟结果。结果:不同化学突触的数学模型突触电流波形不同;数学描述和建模过程最简单的是化学突触模型1;化学突触模型1、突触模型2和突触模型3的相关系数较接近且较小,其次是化学突触模型4的相关系数,相关系数最大的是化学突触模型5,该模型实现了高精度神经元动作电位的传递。结论:突触模型5是最接近于生物学实际的化学突触;化学突触的模拟结果为后续运用硬件实现化学突触奠定了基础。     

不同类型突触输入对电突触连接神经元同步化放电的调控

目的同步化放电在神经信息传递和编码过程中极为重要,如何调控神经元之间的同步化放电也一直是脑科学研究的热点之一。本文利用计算机模拟的方法,研究突触输入类型和相对强度的不同对同步化放电活动的调控作用。方法首先基于Izhikevich神经元模型,构造一个三神经元网络,然后添加不同类型的突触输入(电突触、兴奋性化学突触及抑制性化学突触),最后设定其中一个神经元为调控器,分析另外两个神经元的同步化放电活动。结果对于电突触和兴奋性化学突触输入,当两个神经元接收到的输入强度接近时,同步性会增强,反之则会减弱。而对于抑制性化学突触输入,当调控器神经元的放电频率较低时,同步性的变化与电突触和兴奋性化学突触的情况类似;当调控器神经元的频率较高时,同步化活动显著地被压制。结论电突触连接神经元之间的同步化活动会受到外界突触输入类型及相对大小的调控,为进一步探索神经系统中同步化活动的起源和调控提供了参考。     

神经营养因子对颅脑损伤保护作用的研究进展

神经营养因子广泛存在于脑及周围神经系统.无论在体内或体外它们都能促进神经系统的发育,维持神经元的生长、存活与分化;并可影响神经系统的突触可塑性.神经营养因子通过激活其特异性高亲和力酪氨酸激酶受体自身磷酸化而进行信号传递.颅脑损伤可以诱导神经营养因子基因表达,从而对受损的神经元产生保护作用,促使神经元功能恢复.     

卡洛琳斯研究院诺贝尔委员会决定将2000年生理/医学奖授予Arvid Carlsson、 Paul Greengard、 Eric Kandel

在人类大脑中存在着上千亿个神经细胞,它们以极其复杂的神经作用网络相连.来自一个神经细胞的信息通过不同的化学递质向其它细胞传递,信号在一个特殊的边接点中进行传递,即突触.一个神经细胞拥有几个与其它神经细胞相连的突触.     

大鼠神经元突触重塑参与神经免疫调节网络的功能重建

目的 探讨神经免疫调节网络的功能重建模式。 方法 用大鼠全基因芯片检测技术分析下丘脑外侧区神经免疫调节功能相关信号表达;用数据库分析差异基因的功能树。结果 免疫组大鼠基因表达谱有632个差异基因（其中免疫2天组374个,免疫4天组62个,免疫6天组196个）;对差异基因中的398个上调差异基因进行功能树相关分析显示27个基因为参与信号传导功能的已知功能基因,涉及31个细胞功能信号传导路,涵盖了已知的突触重塑不同的信号传导路。结论 突触重塑可能构成神经免疫调节网络功能重建的重要模式。     

神经颗粒素与脑突触可塑性的相关性研究进展

大量研究表明,突触损伤是各种疾病导致学习记忆等智能障碍的重要病理机制之一,而脑内突触蛋白在突触信号传递中发挥重要作用.因此,脑特异性蛋白质在生理及疾病状态下突触传递功能改变中的作用已成为当前的研究热点之一.     

转录因子Npas4影响抑制性突触发育的功能依赖性调节

哺乳动物大脑神经元的活性可以调节兴奋性突触和抑制性突触的发育和成熟。神经元活性的诸多作用都是通过兴奋性突触谷氨酸盐的释放以及突触后神经元钙流入来介导的,中枢神经系统的神经元接收来自谷氨酸能神经元的兴奋性突触的输入信号和来自释放GABA的中间神经元抑制性的输入信号。兴奋性突触和抑制性突触之间适当的平衡对感觉信息的表达、命令信号的执行以及更高级的认知功能起着关键作用。     

突触形成调控蛋白的研究与进展

背景：干细胞在体外也被证实可以分化为神经元细胞,然而干细胞分化成神经细胞后如何形成突触连接而实现信息传递功能,以及突触形成的调控机制是什么,这些尚未可知。 目的：通过对2000年以来影响突触形成调控蛋白的实验研究检索,总结这些蛋白在突触研究中的作用。 方法：以“synapse、synaptogenesis”为检索词,应用计算机检索中国知网和pubmed数据库相关文章,排除重复性研究,保留39篇文章做进一步分析。 结果与结论：突触形成的过程主要包括3个方面的相关内容：①突触结构的形成。②一些突触由无活性到有活性的转换。③非必要突触的消除。而与之相关的蛋白及其功能得以肯定并得到初步研究的主要有血小板反应蛋白、突触分化诱导基因产物、突触细胞黏附分子、主要组织相容性复合物Ⅰ型、肌细胞增强因子2、脆性X智力低下蛋白等。这些蛋白在突触的形成,发育和成熟过程中发挥着重要作用。     

星形胶质细胞和突触传递的相互作用

神经系统中的信息传递主要通过化学性突触进行。化学性突触由突触前膜、突触间隙和突触后膜组成。突触前膜释放兴奋性或抑制性神经递质作用于突触后膜相应的受体，产生兴奋性突触后电位(EPSP)或抑制性突触后电位(IPSP)，实现化学信号到电信号的转变，从而完成信息传递。众所周知，中枢神经系统的基本构件除构成突触的神经元外，还有大量的胶质细胞，如星形胶质细胞、少突胶质细胞、小胶质细胞、室管膜细胞和脉络丛上皮细胞等。传统观念认为，这些胶质细胞对神经元及其附近的毛细血管仅起支持、分隔和辅助代谢的作用。然而，最近十多年的研究表明，星形胶质细胞还可与突触传递相互作用，这些作用必然对中枢神经系统的信息传递等方面产生重要的影响。因此，本文在简介星形胶质细胞和突触位置关系的基础上，对星形胶质细胞和突触传递相互作用的研究进展进行综述。     

神经信息物质

<正> 本世纪初,Cajal提出了神经元之间没有原生质联系的观点,即所谓神经元学说(neuronal doctrine)。尽管当时争议颇大,且遭到了Golgi的强烈反对,但随着神经元科学研究手段的发展,这一学说得到了证实。神经元是一个独立的结构与功能单位,彼此之间不连续。神经元之间的信号传递主要发生在特化了的膜结构——突触部位。突触传递的中心环节是必需有神经递质参与;近年来的研究还表明,神经元也能在非突触部位释放所含的神经活性物质,经细胞外液或/和脑脊液扩散,和远隔部位靶细胞上的受体结合,产生特异的生物学效应。神经元之间这种不依赖突触结构的信息传递,即所谓非突触或旁突触传递(Parasynaptic transmission)。已知的参与非突触调节的神经活性物质不下百种,仅嗅球     

Optically teasing apart neural swelling and depolarization

We measured birefringence, 90 degree scattered light, and voltage sensitive dye changes from lobster walking leg nerves. Systematic application of key chemical agents revealed separate cellular mechanisms underlying fast optical signals. Each agent exhibited mixed effects, some having a greater effect on cellular swelling and refractive index, and some altering membrane potential. Birefringence changes were tightly correlated with voltage sensitive dye signals and were perturbed by those agents that altered membrane potential. Signals from light scattered at 90 degrees corroborated the hypothesis that large angle scattering signals arise from changes in the interstitial spaces and were perturbed by those agents that altered cellular swelling and refractive index. We conclude that multiple cellular mechanisms can be exploited to measure rapid optical signals. Since birefringence produces much larger changes than scattering, the use of polarized light might lead to improvements in imaging neural activity with high temporal resolution, especially since birefringence changes corresponded closely to membrane potential.     

Aging‐dependent expression of synapse‐related proteins in the mouse brain

A synapse is a cell adhesion structure that permits a neuron to pass a chemical or electrical signal to another neuron. They connect neurons and form neural networks that are essential for brain functions, such as learning and memory. At a chemical synapse, the presynapse and the postsynapse are connected by cell adhesion molecules. The presynapse contains synaptic vesicles and their release machinery, whereas the postsynapse contains postsynaptic densities and receptors for the neurotransmitters. Many proteins constituting a synapse have been identified, but their life‐span expression profiles remain elusive. Here, we investigated the expression levels of representative synapse‐related proteins by Western blot using the extranuclear supernatant fraction of the brains of mice at various ages. These proteins were classified into seven groups depending on their expression profiles during the embryonic stage, those from postnatal day 6 (P6) to P30, and those after P90. The expression levels of the majority of the proteins were gradually increased from the embryonic stage and then decreased at P14 or P30. After P90, the expression levels were not markedly changed or, in some proteins, increased. These results indicate that the expression levels of the synapse‐related proteins are regulated orderly in an aging‐dependent manner.     

In situ characterization of a rectifying electrical junction

Electrical synapses play significant roles in neural processing in invertebrate and vertebrate nervous systems. The view of electrical synapses as plain bidirectional intercellular channels represents a partial picture because rectifying electrical synapses expand the complexity in the communication capabilities of neurons. Rectification derives, mostly, from the sensitivity of electrical junctions to the transjunctional potential (V(j)) across the coupled cells. We analyzed the characteristics of this sensitivity and their effect on neuronal signaling, studying rectifying junctions present in the leech nervous system. The NS neurons, a pair of premotor nonspiking neurons present in each midbody ganglion, are electrically coupled to virtually every excitatory motor neuron. Studied at rest, only hyperpolarizing signals can be transmitted from NS to the motoneurons, and only depolarizing signals are conducted in the opposite direction. Our results show that small changes in the NS membrane potential (V(m)) exerted an effective control of the firing frequency of the CV motoneurons (excitor of circular muscles). This effect revealed the existence of a threshold V(j) across which the electrical synapse shifts from a nonconducting to a conducting state. The junction can operate as a relatively symmetrical bidirectional bridge provided that the transmitted signals do not cross this threshold transjunctional potential.     

缝隙连接参与认知功能的机制研究

缝隙连接(gap junction,GJ)是真核细胞之间特化的提供直接物质和信息交流的连接结构,介导相邻细胞之间的电偶联和小分子物质的细胞间转移,这种物质和能量的交流称为缝隙连接介导的细胞间通讯(gap iunctional intercellular communication,GJIC).以往的研究提示,缝隙连接在神经系统的胚胎发育、细胞分化和生长控制等生物过程中起重要作用.     

Innervation and activity dependent dynamics of postsynaptic oxidative metabolism

Despite extensive investigations into the mechanisms of aerobic respiration in mitochondria, the spontaneous metabolic activity of individual cells within a whole animal has not been observed in real time. Consequently, little is known about whether and how the level of mitochondrial energy metabolism is regulated in a cell during development of intact systems. Here we studied the dynamics of postsynaptic oxidative metabolism by monitoring the redox state of mitochondrial flavoproteins, an established indicator of energy metabolism, at the developing Drosophila neuromuscular junction. We detected transient and spatially synchronized flavoprotein autofluorescence signals in postsynaptic muscle cells. These signals were dependent on the energy substrates and coupled to changes in mitochondrial membrane potential and Ca2+ concentration. Notably, the rate of autofluorescence signals increased during synapse formation through contact with the motoneuronal axon. This rate was also influenced by the magnitude of synaptic inputs. Thus, presynaptic cells tightly regulate postsynaptic energy metabolism presumably to maintain an energetic balance during neuromuscular synaptogenesis. Our results suggest that flavoprotein autofluorescence imaging should allow us to begin assessing the progress of synapse formation from a metabolic perspective.     

Alpha-band power in the left frontal cortex discriminates the execution of fixed stimulus during saccadic eye movement

NB-2/contactin-5 plays an important role in synapse formation in the developing auditory system of rodents. In this study, to further elucidate the molecular role of NB-2 in synapse formation, we examined the interaction between NB-2 and amyloid precursor-like protein 1 (APLP1), as well as their possible co-localization at the synapse. Pull-down assays and cell surface binding assays demonstrated that NB-2 interacts with APLP1. Furthermore, the protein expression profile of APLP1 in western blots was similar to that of NB-2, and localization of APLP1 mRNA partially overlapped that of NB-2 mRNA. In cultured hippocampal neurons, immunofluorescence signals for both NB-2 and APLP1 overlapped with synapsin, a presynaptic marker. Biochemical analysis showed that both NB-2 and APLP1 were enriched in the presynaptic fraction. These results indicate that NB-2 forms a cis-complex with APLP1 on the presynaptic membrane.     

Enhancement of short-term synaptic plasticity by prior environmental stress

All chemical synapses can rapidly up- or downregulate the strength of their connections to reshape the postsynaptic signal, thereby stressing the informational importance of specific neural pathways. It is also true that an organism's environment can exert a powerful influence on all aspects of neural circuitry. We investigated the effect of a prior high-temperature stress on the short-term plasticity of a neuromuscular synapse in the hindleg tibial extensor muscle of Locusta migratoria. We found that the prior stress acted to precondition the synapse by increasing the upper temperature limit for synaptic transmission during a subsequent stressful exposure. As well, preexposure to a stressful high-temperature environment increased short-term facilitation of excitatory junction potentials concurrent with a decrease in excitatory junction potential amplitude and a reduction in its temporal parameters. We conclude that a stressful environment can modify synaptic physiological properties resulting in an enhancement of short-term plasticity of the synapse.     

Input-output relations of the feedback synapse between horizontal cells and cones in the tiger salamander retina.

1. The input-output relation of the feedback synapse between horizontal cells (HCs) and cones was studied by simultaneously recording the light responses of the HCs and of cones the outer segments of which were truncated off. 2. The postsynaptic light response of the truncated cone was depolarizing and free of direct influence of photocurrents. These postsynaptic light responses were graded and sustained; their waveform resembled that of the HC light responses. 3. Input-output relation of the HC-cone feedback synapse was obtained by plotting the simultaneous voltage points of the HC and truncated cone light responses. At the resting potential of the cone (-40 mV), the voltage gain of the feedback synapse was about -0.33 when VHC = -20 mV and it was about -0.03 when VHC = -60 mV. 4. At more hyperpolarized cone voltages, the feedback signals in cones became smaller, and they reversed at about -67 mV. The voltage gain of the feedback synapse at VHC = -20 mV was about -0.23, -0.18, -0.07, and +0.2 when Vcone = -44.5, -52.5, -65, and -77.5 mV, respectively. 5. Light hyperpolarized the HC, which resulted in a conductance change (delta Gs) in cones. The cone conductance decreased progressively as the HCs were increasingly hyperpolarized, and delta Gs reached a maximum value of 0.93 nS when the HCs were hyperpolarized from -20 to -52 mV. 6. The peak light responses of intact cones were plotted against the peak HC light responses. This gives the relationship between the pre- and postsynaptic voltages of the cone-HC (forward) and HC-cone (feedback) synapses at any given light intensity. Combining this relationship with the input-output relations obtained at various voltages of the truncated cones allows the input-output relation of the feedback synapse for light-evoked signals to be obtained. 7. The input-output relation of the feedback synapse for light-evoked signals was bell-shaped, because the feedback light responses were controlled by two opposing factors: as the light became brighter, the postsynaptic conductance change increased, but the driving force decreased. 8. For light-evoked signals, the slope gain (slope of the input-output relation) of the HC-cone feedback synapse was negative (varied from -0.33 to 0) when VHC lay between -20 and -52 mV; and it was positive (0 to +0.8) when VHC lay between -52 and -72 mV. 9.(ABSTRACT TRUNCATED AT 400 WORDS)     

Neuroengineering modeling of single neuron and neural interface

The single neuron has attracted widespread attention as an elementary unit for understanding the electrophysiological mechanisms of nervous systems and for exploring the functions of biological neural networks. Over the past decades, much modeling work on neural interface has been presented in support of experimental findings in neural engineering. This article reviews the recent research results on modeling electrical activities of the single neuron, electrical synapse, neuromuscular junction, and neural interfaces at cochlea. Single neuron models vary form to illustrate how neurons fire and what the firing patterns mean. Focusing on these two questions, recent modeling work on single neurons is discussed. The modeling of neural receptors at inner and outer hair cells is examined to explain the transforming procedure from sounds to electrical signals. The low-pass characteristics of electrical synapse and neuromuscular junction are also discussed in an attempt to understand the mechanism of electrical transmission across the interfaces.     

The metabolic cost of neural information

We derive experimentally based estimates of the energy used by neural mechanisms to code known quantities of information. Biophysical measurements from cells in the blowfly retina yield estimates of the ATP required to generate graded (analog) electrical signals that transmit known amounts of information. Energy consumption is several orders of magnitude greater than the thermodynamic minimum. It costs 10(4) ATP molecules to transmit a bit at a chemical synapse, and 10(6)-10(7) ATP for graded signals in an interneuron or a photoreceptor, or for spike coding. Therefore, in noise-limited signaling systems, a weak pathway of low capacity transmits information more economically, which promotes the distribution of information among multiple pathways.