Non-retinotopic arrangement of fibres in cat optic nerve

Fibres in the mammalian optic nerve are generally thought to be organised retinotopically. Recording electrophysiologically from the cat optic nerve, we found little evidence to support this notion, which led us to investigate the problem by anatomical methods. We made a localised injection of horseradish peroxidase into the lateral geniculate body of the cat, labelling a small clump of retinal ganglion cells and their axons in the optic nerve. These fibres, emanating from neighbouring cells in the retina, became widely scattered through the optic nerve, indicating that retinotopic order is essentially lacking.     

用汇率目标区方法评价1995-2004年人民币汇率

均衡汇率是指一个国家对内、对外同时实现均衡的汇率。研究均衡汇率对国家制定对外经济政策,维持经济稳定具有十分重要的意义。用K rugm an汇率目标区理论建立了人民币均衡汇率汇率目标区模型。选取不同基础经济变量组合建立汇率目标区模型对人民币汇率进行评价。计算结果说明1995—2004年人民币对美元实际汇率对均衡汇率的失调度均小于4%。并用该模型对2005年末人民币均衡汇率进行预测。结果表明目前人民币汇率处于合理水平。     

WNT11 acts as a directional cue to organize the elongation of early muscle fibres

The early vertebrate skeletal muscle is a well-organized tissue in which the primitive muscle fibres, the myocytes, are all parallel and aligned along the antero-posterior axis of the embryo. How myofibres acquire their orientation during development is unknown. Here we show that during early chick myogenesis WNT11 has an essential role in the oriented elongation of the myocytes. We find that the neural tube, known to drive WNT11 expression in the medial border of somites, is necessary and sufficient to orient myocyte elongation. We then show that the specific inhibition of WNT11 function in somites leads to the disorganization of myocytes. We establish that WNT11 mediates this effect through the evolutionary conserved planar cell polarity (PCP) pathway, downstream of the WNT/beta-catenin-dependent pathway, required to initiate the myogenic program of myocytes and WNT11 expression. Finally, we demonstrate that a localized ectopic source of WNT11 can markedly change the orientation of myocytes, indicating that WNT11 acts as a directional cue in this process. All together, these data show that the sequential action of the WNT/PCP and the WNT/beta-catenin pathways is necessary for the formation of fully functional embryonic muscle fibres. This study also provides evidence that WNTs can act as instructive cues to regulate the PCP pathway in vertebrates.     

Alterations in the surface properties of cells responsive to nerve growth factor.

An initial effect of nerve growth factor on a responsive nerve cell line is to increase intracellular cyclic AMP, which in turn leads to a mobilisation of calcium ions. These events are correlated with structural changes in the plasma membrane, increased cell-substratum adhesion, and neurite outgrowth.     

应用于卷烟纸阴燃仪的测量距离标定装置设计

为了检验卷烟纸阴燃速率测试仪(简称阴燃仪)的测量精度,通过对阴燃仪的工作原理的研究,在CSR-Ⅱ型阴燃仪的基础上,设计了一种测量距离标定装置。并对CSR-Ⅱ型阴燃仪进行了标定实验,采用平均值滤波法对实验结果进行了数据处理,由实验结果可以看出,该标定装置能够很好地满足阴燃仪的标定需求。     

Granitic magmatism related to early Paleozoic continental collision in North Qinling

Zircon U-Pb dating of early Paleozoic granitoids in North Qinling yields three age peaks of ~500, -452 and -420 Ma. They can be temporally correlated with high-pressure to ultrahigh-pressure metamorphism at ca. 500 Ma, retrograde granulite-facies meta- morphisms at ca. 450 Ma and amphibolite-facies metamorphism at ca. 420 Ma, respectively. The first episode of granitic magma- tism is considered to have resulted from continental collision, whereas the second and third episodes of magmatism are attributed to crustal uplifting. Combined with the regional geological setting and new results from high-pressure and ultrahigh-pressure metamorphic rocks, the ca. 500 Ma magmatism is interpreted as the result of partial melting of sedimentary rocks in accretionary wedge between the south Qinling microcontinent and the north Qinling belt including the southern margin of the North China Craton. The ca. 450 Ma intensive magmatism is ascribed to dehydration melting of deeply subducted continental crust at thick- ened conditions in response to slab breakoff, and the final magmatism in ca. 420 Ma is interpreted as the product of partial melt- ing during the tectonic transition from contraction to extension.     

Adaptation in the chemotactic guidance of nerve growth cones

Pathfinding by growing axons in the developing nervous system may be guided by gradients of extracellular guidance factors. Analogous to the process of chemotaxis in microorganisms, we found that axonal growth cones of cultured Xenopus spinal neurons exhibit adaptation during chemotactic migration, undergoing consecutive phases of desensitization and resensitization in the presence of increasing basal concentrations of the guidance factor netrin-1 or brain-derived neurotrophic factor. The desensitization is specific to the guidance factor and is accompanied by a reduction of Ca2+ signalling, whereas resensitization requires activation of mitogen-associated protein kinase and local protein synthesis. Such adaptive behaviour allows the growth cone to re-adjust its sensitivity over a wide range of concentrations of the guidance factor, an essential feature for long-range chemotaxis.     

Retinofugal fibres change conduction velocity and diameter between the optic nerve and tract in ferrets

In earlier studies of central nervous fibre tracts, it was tacitly assumed that individual axons are relatively uniform along their length. In the retinofugal pathway in particular, axon diameter, myelin thickness and correlated conduction properties have been treated as constant throughout the optic nerve, chiasm and tract. We report here that the conduction velocities of fibres contributing to the early components of the compound action potential are significantly greater in the optic tract than in the optic nerve of ferrets, and also that the diameters of the largest retinofugal fibres increase from nerve to tract. This observation raises significant questions about the developmental mechanisms in the central nervous system that relate the axons, their diameters, and the glia with which they are myelinated. In addition, it indicates that studies that have relied on the constancy of conduction velocity along the retinofugal course may require reappraisal.     

向量法研究三角形中相关点之间的距离公式

应用两个向量法相关公式探讨了三角形重心、垂心、外心以及内心之间的距离公式。     

Order in the initial retinotectal map in Xenopus: a new technique for labelling growing nerve fibres

Retinal nerve fibres form an orderly map of visual space in several centres in the vertebrate brain. Such topographic maps are a common feature of central nervous system organization, yet the way in which they develop is poorly understood. Early nerve projections in the fetal and neonatal mammalian brain have been found in several cases to be less restricted than those in the adult, suggesting that nerve fibres may initially form a diffuse set of connections in their target structure from which the adult map is sculpted by the elimination of terminals. Indeed, previous electrophysiological data indicate that the retinotectal map in Xenopus laevis might be initially disorganized. We report here, however, that the retinotectal projection is ordered from the beginning of tectal innervation (stage 39/40). We demonstrate this first autoradiographically by tracing groups of growing ganglion cell axons which we labelled by incubating sectors of eye rudiments, before axonal outgrowth, in 3H-proline and replacing them orthotopically. Separate labelling of dorsal and ventral parts of the initial projection showed that retinal fibres are organized topographically, as in the adult, in the tectal rudiment and throughout much of the pathway. Second, we show that visual responses are ordered in the tectum from the first stage that they can be mapped (stage 40). We conclude that the topographic ordering of retinotectal connections develops as a result of directed axonal outgrowth.