A diffusion barrier maintains distribution of membrane proteins in polarized neurons

The asymmetric distribution of proteins to distinct domains in the plasma membrane is crucial to the function of many polarized cells. In epithelia, distinct apical and basolateral surfaces are maintained by tight junctions that prevent diffusion of proteins and lipids between the two domains. Polarized neurons maintain axonal and somatodendritic plasma membrane domains without an obvious physical barrier. Indeed, the artificial lipid Dil encounters no diffusion barrier at the presumptive domain boundary, the axon hillock. By measuring the lateral mobility of membrane proteins using optical tweezers, we show here that some membrane proteins exhibit markedly reduced mobility in the initial segment of the axon. Disruption of F-actin and low levels of dimethyl sulphoxide (DMSO) abolish this diffusion barrier and lead to redistribution of membrane markers that had previously been polarized. Immobilization in the initial segment may reflect, at least in part, differential tethering to cytoskeletal components. Therefore, the ability to maintain a polarized distribution of membrane proteins depends on a specialized domain at the initial segment of the axon, which restricts lateral mobility and serves as a new type of diffusion barrier that acts in the absence of cell-cell contact.     

Relation of neurons in the nonprimary motor cortex to bilateral hand movement

In the primate cerebral cortex there are at least two somatotopically organized, nonprimary motor fields rostral to the primary motor area. To understand the functions of these multiple motor representations we have compared the neuronal activity in each of these fields while monkeys performed a trained motor task, using right, left or both hands. In the nonprimary motor cortex, activity in a number of neurons was related to the movement the animal chose and performed, whereas in the primary motor cortex, changes in the firing of most neurons were simply related to activity in the contralateral muscles. This result indicates that the nonprimary motor cortex is involved in higher-order coding of the laterality of the motor response, implying that it exerts its motor control function at a higher hierarchical level than its counterpart in the primary motor cortex.     

Primary structure and functional expression of a cyclic nucleotide-activated channel from olfactory neurons.

Odorant signal transduction occurs in the specialized cilia of the olfactory sensory neurons. Considerable biochemical evidence now indicates that this process could be mediated by a G protein-coupled cascade using cyclic AMP as an intracellular second messenger. A stimulatory G protein alpha subunit is expressed at high levels in olfactory neurons and is specifically enriched in the cilia, as is a novel form of adenylyl cyclase. This implies that the olfactory transduction cascade might involve unique molecular components. Electrophysiological studies have identified a cyclic nucleotide-activated ion channel in olfactory cilia. These observations provide evidence for a model in which odorants increase intracellular cAMP concentration, which in turn activates this channel and depolarizes the sensory neuron. An analogous cascade regulating a cGMP-gated channel mediates visual transduction in photoreceptor cells. The formal similarities between olfactory and visual transduction suggest that the two systems might use homologous channels. Here we report the molecular cloning, functional expression and characterization of a channel that is likely to mediate olfactory transduction.     

Actin-dependent organelle movement in squid axoplasm.

Studies of organelle movement in axoplasm extruded from the squid giant axon have led to the basic discoveries of microtubule-dependent organelle motility and the characterization of the microtubule-based motor proteins kinesin and cytoplasmic dynein. Rapid organelle movement in higher animal cells, especially in neurons, is considered to be microtubule-based. The role of actin filaments, which are also abundant in axonal cytoplasm, has remained unclear. The inhibition of organelle movement in axoplasm by actin-binding proteins such as DNase I, gelsolin and synapsin I has been attributed to their ability to disorganize the microtubule domains where most of the actin-filaments are located. Here we provide evidence of a new type of organelle movement in squid axoplasm which is independent of both microtubules and microtubule-based motors. This movement is ATP-dependent, unidirectional, actin-dependent, and probably generated by a myosin-like motor. These results demonstrate that an actomyosin-like mechanism can be directly involved in the generation of rapid organelle transport in nerve cells.     

Binding of myosin I to membrane lipids

The single-headed myosins called myosin-I were first isolated from the protozoan Acanthamoeba and subsequently identified in other cells. We previously reported evidence that myosin-I is responsible for the movement of membranes, extracted from Acanthamoeba, along actin filaments in vitro. Here we show for the first time that myosin-I can bind directly to NaOH-extracted membranes isolated from Acanthamoeba and to vesicles of pure lipids with an affinity sufficient for extensive binding in the cell. Membrane-bound myosin-I may provide a mechanism for many cellular movements previously thought to involve filamentous myosin-II.     

曲柄滑块机构运动模糊可靠性分析的简便方法

文章将模糊可靠性问题转化为传统可靠性问题来计算机械零件的模糊可靠性,由于模糊可靠性问题的复杂性,一般不会得到计算模糊可靠性的解析式。因此,可以将传统可靠性展开成级数的形式,从而得到曲柄滑块机构运动模糊可靠性计算的级数表达式,以便进行模糊可靠性计算。结果表明,采取文中方法,可以大大减少可靠性分析计算量。     

Targeting of transmembrane and GPI-anchored forms of N-CAM to opposite domains of a polarized epithelial cell.

The calcium-independent neural cell adhesion molecule N-CAM is expressed transiently during development in many tissues, including epithelia. The three naturally occurring principal isoforms of N-CAM differ in the way in which they associate with the membrane and in their cytoplasmic domains. These isoforms are generated by developmentally regulated alternative splicing of a single gene: the large cytoplasmic domain (ld) form (relative molecular mass 180,000 (Mr 180K] is specific for post-mitotic neurons; the 120K small cytoplasmic domain (ssd) and 140K small surface domain (sd) forms also occur on other cell types. One function of the different isoforms could be to specify cellular localization; for example, glycosyl phosphatidyl inositol (GPI)-membrane anchoring acts as a targeting signal for expression on the apical surface of polarized epithelial cells. Neurons and epithelial cells may use similar mechanisms for polarizing their plasma membrane proteins. We have therefore investigated the targeting of GPI-anchored (ssd N-CAM, 120K) and transmembrane forms of N-CAM (sd N-CAM, 140K; ld N-CAM, 180K) by comparing the expression of each after transfection of the appropriate complementary DNAs into polarized epithelial cells. We find that isoforms with alternative modes of membrane association are targeted to different surfaces of polarized epithelial cells: ssd N-CAM is expressed on the apical surface, whereas sd and ld N-CAM are expressed on the basolateral surface. These results suggest that the different isoforms of N-CAM determine their own diverse cellular destinations. They also support the hypothesis that the GPI anchor acts as an apical targeting signal in epithelia.     

关于日本大正时期新教育运动的研究

日本大正时期的新教育运动对传统的、注入式的教师中心主义教育教授方法进行了批，提出了儿童中心主义的教育主张。通过创办新型实验学校和对公立学校进行改革的教育实，形成了一整套的教育理论、教授方法，积累了丰富的教学经验，这些对我国的教育改革实践具有重要的借鉴意义。     

Time to collision is signalled by neurons in the nucleus rotundus of pigeons.

Throughout the animal kingdom, the sight of a rapidly approaching object usually signals danger and elicits an escape response. Gibson suggested that the symmetrical expansion of an object's image (looming) is the critical variable determining that the object is on a collision course with the observer. Similarly, large expanding flow-fields like those produced by locomotion may precipitate manoeuvres such as turning or landing. From such observations it has been shown that the optic flow parameter, tau, which specifies time to contact with the approaching object best fits the behavioural data. We describe a subpopulation of neurons in the nucleus rotundus of the pigeon brain that respond selectively to objects moving on a collision course towards the bird.     

Physiology. Cold current in thermoreceptive neurons

We sense the temperature of our skin and surroundings using specific thermoreceptors, which are sensitive to cold and warmth, but little is known about how these receptors transduce temperature into electrical activity. We have discovered an inward ionic current that is activated by moderate cooling in a small number of rat sensory neurons. This current has features that are found in intact cold receptors, including sensitization by menthol, adaptation upon sustained cooling, and modulation by calcium, and is likely to be important in cold sensing.     

非线性反应扩散方程新形式分离解

目的 研究非线性反应扩散方程的新形式泛函分离解.方法 利用广义条件对称方法研究了方程与空间变量相关的泛函分离解.结果与结论 导出了方程具有新形式分离解应满足的条件,并且,获得了一些导出方程的对应精确解.     

塞曼效应中偏振态的量子解释

本文从量子力学的相干态出发 ,通过对氢原子 (且不考虑L—S相互作用时 )几率密度的讨论 ,指出了当Δm =0时原子是一个振荡偶极子 ,当Δm =± 1时 ,原子是一个转动偶极子 ,从而对塞曼效应中偏振态的产生做了详细的说明 ,给出了一种清晰的物理图象 ,澄清了以往教材对Δm =0时偏振态说明的糊涂概念     

源运动的视超光速模型

在源的质心固定的视超光速模型的基础上 ,本文进一步推导出质心运动情况下视超光速运动的视速度方程。然后 ,在喷流方向与源的退行方向相反的情况下 ,推导出核与子源速率相等条件下及核固定条件下求子源真实速度的方程。质心运动情况下的视速度方程 ,包含了质心静止条件下的相对论超光速模型和著名的核固定的 BRM的视速度方程以及低速条件下的牛顿理论     

前向多层代数神经网络隐层神经元数目估计方法

结合目前估计前向三层神经网络隐层神经元数目的方法 ,提出一种向量不交关系来确定多层(层数 >3)前向代数神经网络隐层神经元的数目 ,该方法只须估计出第一隐层神经元的数目 ,其余各层神经数目利用不交关系的算法随之确定 ,通过多项式代数函数实例表明 ,该方法有效