Gating of retinal transmission by afferent eye position and movement signals

Vision in most vertebrates is an active process that requires the brain to combine retinal signals with information about eye movement. Eye movement information may feed forward from the motor control areas of the brain or feed back from the extrinsic eye muscles. Feedback signals elicited by passive eye movement selectively gate retinal outflow at the first relay, the dorsal lateral geniculate nucleus. The gating predominantly facilitates retinogeniculate transmission immediately after eye movement and inhibits transmission when a new steady-state eye position is achieved. These two gating effects are distributed in a complementary fashion across the dorsal lateral geniculate nucleus such that the spatiotemporal activity profile could contribute to object detection and localization.     

Corollary discharge provides accurate eye position information to the oculomotor system

The saccadic system accurately compensates for perturbations of eye position produced by microstimulation of the superior colliculus. This requires that information about the stimulation-induced change in eye position be provided by an extraretinal source--either proprioceptive endings in extraocular muscles or a centrally generated corollary discharge. It is shown that compensation remains intact after elimination of extraocular muscle proprioception, demonstrating that corollary discharge provides accurate eye position information.     

Secretion of activin by interstitial cells in the testis

Activin, a dimer formed by the beta subunits of inhibin, has an effect that is opposite to that of inhibin in a number of biological systems. Which cell types secrete activin in vivo is not known. TM3 cells, a Leydig-derived cell line, contained messenger RNAs that hybridized with human beta A and beta B complementary DNA probes and were similar in size to the porcine messenger RNA for the beta subunits of inhibin. No hybridization to the inhibin alpha subunit was detectable in the TM3 cells. Conditioned medium from TM3 cells and from primary cultures of rat and porcine interstitial cells stimulated the release of follicle-stimulating hormone in a pituitary cell culture assay. It is likely that, in the testis, the Leydig cells secrete activin and the Sertoli cells produce inhibin, or a combination of both.     

Transduction of receptor signals by beta-arrestins

The transmission of extracellular signals to the interior of the cell is a function of plasma membrane receptors, of which the seven transmembrane receptor family is by far the largest and most versatile. Classically, these receptors stimulate heterotrimeric G proteins, which control rates of generation of diffusible second messengers and entry of ions at the plasma membrane. Recent evidence, however, indicates another previously unappreciated strategy used by the receptors to regulate intracellular signaling pathways. They direct the recruitment, activation, and scaffolding of cytoplasmic signaling complexes via two multifunctional adaptor and transducer molecules, beta-arrestins 1 and 2. This mechanism regulates aspects of cell motility, chemotaxis, apoptosis, and likely other cellular functions through a rapidly expanding list of signaling pathways.     

Initiation of proximal-distal patterning in the vertebrate limb by signals and growth

Two broad classes of models have been proposed to explain the patterning of the proximal-distal axis of the vertebrate limb (from the shoulder to the digit tips). Differentiating between them, we demonstrate that early limb mesenchyme in the chick is initially maintained in a state capable of generating all limb segments through exposure to a combination of proximal and distal signals. As the limb bud grows, the proximal limb is established through continued exposure to flank-derived signal(s), whereas the developmental program determining the medial and distal segments is initiated in domains that grow beyond proximal influence. In addition, the system we have developed, combining in vitro and in vivo culture, opens the door to a new level of analysis of patterning mechanisms in the limb.     

水土保持模型的数据生成

遥感技术和地理信息系统的应用为收集和处理水土保持措施的评估数据提供了有效途径。本文联系实际论述了农业非点源侵蚀模型数据自动生成的方法，其统计数据来源有三种：(1)地形图等高线资料；(2)土壤调查绘制的土壤绘图单元；(3)陆地通讯卫星地形图影像分类描绘的陆地覆盖情况。     

Reversal of experimental parkinsonism by lesions of the subthalamic nucleus

Although it is known that Parkinson's disease results from a loss of dopaminergic neurons in the substantia nigra, the resulting alterations in activity in the basal ganglia responsible for parkinsonian motor deficits are still poorly characterized. Recently, increased activity in the subthalamic nucleus has been implicated in the motor abnormalities. To test this hypothesis, the effects of lesions of the subthalamic nucleus were evaluated in monkeys rendered parkinsonian by treatment with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). The lesions reduced all of the major motor disturbances in the contralateral limbs, including akinesia, rigidity, and tremor. This result supports the postulated role of excessive activity in the subthalamic nucleus in Parkinson's disease.     

Storage of methane and freon by interstitial van der Waals confinement

A known host-guest assembly, organized only by means of relatively weak dispersive forces, exhibits hitherto unappreciated thermal stability. The hexagonal close-packed arrangement of calix[4]arene contains lattice voids that can occlude small, highly volatile molecules. This host-guest system can be exploited to retain a range of freons, as well as methane, not only well above their normal boiling points, but also at relatively high temperatures and low pressures. The usually overlooked van der Waals interactions in organic crystals can indeed be used in a highly stable supramolecular system for gas storage.     

扭转振动测试方法及参数识别的研究

本文系统地研究了轴类扭转振动的测试方法及参数识别方法,通过检验和实际应用,表明此方法是可行的,且精度达到工程要求。     

Gatekeepers of the nucleus

Nuclear pore complexes (NPCs) form the site for entry and exit from the nucleus. A convergence of studies have defined the physical framework for the nuclear transport mechanism. This includes definition of the soluble transport machinery required for protein and RNA movement, x-ray structure analysis of transport factors, definitive compositional analysis of yeast NPCs, and documentation of the relative steady state arrangement of NPC components within the portal. With this information, researchers are now in the exciting position to examine the dynamic interplay between shuttling transport factors and the static pore complex.     

利用免疫组化方法确定堆型艾美耳球虫的感染途径及部位

为了能够确定堆型艾美耳球虫(E.acervulina)在感染宿主时的途径及其进攻部位,将兔抗E.acervu-lina 3-1E基因多克隆抗体作为一抗,利用免疫组织化学方法,对鸡E.acervulina的子孢子及裂殖子进行染色。结果表明,虫体从小肠绒毛上皮细胞中感染,经绒毛内毛细血管进入肠腺,并由肠腺基底部向肠腺开口处移行,进入肠绒毛基底部的上皮细胞,逐渐扩散,最后布满整个肠绒毛。     

Perception of environmental signals by a marine diatom

Diatoms are a key component of marine ecosystems and are extremely important for the biogeochemical cycling of silica and as contributors to global fixed carbon. However, the answers to fundamental questions such as what diatoms can sense in their environment, how they respond to external signals, and what factors control their life strategies are largely unknown. We generated transgenic diatom cells containing the calcium-sensitive photoprotein aequorin to determine whether changes in calcium homeostasis are used to respond to relevant environmental stimuli. Our results reveal sensing systems for detecting and responding to fluid motion (shear stress), osmotic stress, and iron, a key nutrient that controls diatom abundance in the ocean.     

The endocrine regulation of aging by insulin-like signals

Reduced signaling of insulin-like peptides increases the life-span of nematodes, flies, and rodents. In the nematode and the fly, secondary hormones downstream of insulin-like signaling appear to regulate aging. In mammals, the order in which the hormones act is unresolved because insulin, insulin-like growth factor-1, growth hormone, and thyroid hormones are interdependent. In all species examined to date, endocrine manipulations can slow aging without concurrent costs in reproduction, but with inevitable increases in stress resistance. Despite the similarities among mammals and invertebrates in insulin-like peptides and their signal cascade, more research is needed to determine whether these signals control aging in the same way in all the species by the same mechanism.     

第一代知识管理和第二代知识管理的比较研究

本文对第一代知识管理和第二代知识管理的概况做了介绍，并从不同的角度对两者进行了比较，指出其中的联系和区别，最后说明了比较研究的意义。     

某越野车传动系统扭振分析与减振研究

针对某四驱越野车在全油门加速工况下的轰鸣声和敲齿声问题,确定该现象是由于发动机的扭转激励引起了传动系统的扭转共振导致。采用多体动力学理论,建立了传动系统的刚柔耦合扭振分析模型,通过仿真结果与实验数据进行对比,验证了模型的准确性。利用此模型进行传动系统的扭振特性分析,发现通过调整离合器减振器的刚度和迟滞阻尼可以有效地控制传动系统的扭振特性,实验结果表明优化后的离合器减振器减振降噪效果明显,车内噪声水平降低10dB左右。     

Regulation of phagosome maturation by signals from toll-like receptors

In higher metazoans, phagocytosis is essential in host defense against microbial pathogens and in clearance of apoptotic cells. Both microbial and apoptotic cells are delivered on a common route from phagosomes to lysosomes for degradation. Here, we found that activation of the Toll-like receptor (TLR) signaling pathway by bacteria, but not apoptotic cells, regulated phagocytosis at multiple steps including internalization and phagosome maturation. Phagocytosis of bacteria was impaired in the absence of TLR signaling. Two modes of phagosome maturation were observed, constitutive and inducible; their differential engagement depended on the ability of the cargo to trigger TLR signaling.     

Induction of pancreatic differentiation by signals from blood vessels

Blood vessels supply developing organs with metabolic sustenance. Here, we demonstrate a role for blood vessels as a source of developmental signals during pancreatic organogenesis. In vitro experiments with embryonic mouse tissues demonstrate that blood vessel endothelium induces insulin expression in isolated endoderm. Removal of the dorsal aorta in Xenopus laevis embryos results in the failure of insulin expression in vivo. Furthermore, using transgenic mice, we show that ectopic vascularization in the posterior foregut leads to ectopic insulin expression and islet hyperplasia. These results indicate that vessels not only provide metabolic sustenance, but also provide inductive signals for organ development.     

Presence of lateral eye lens crystallins in the median eye of the american chameleon

With the use of immunofluorescence techniques, gamma globulin antibody specific for the crystallins of Anolis carolinensis lateral eye lens was applied to sections through the median (parapineal) eye of Anolis carolinensis. Only the median eye lens exhibited fluorescence specific for the crystallins; other structures were negative. These results indicate that the lens of the reptilean median eye shares tissue-specific antigenic determinants with the lens of the lateral eye. This suggests a possible evolutionary relation between the two structures, based on biochemical, as well as previously reported anatomical, criteria.     

Impulsive choice induced in rats by lesions of the nucleus accumbens core

Impulsive choice is exemplified by choosing a small or poor reward that is available immediately, in preference to a larger but delayed reward. Impulsive choice contributes to drug addiction, attention-deficit/hyperactivity disorder, mania, and personality disorders, but its neuroanatomical basis is unclear. Here, we show that selective lesions of the nucleus accumbens core induce persistent impulsive choice in rats. In contrast, damage to two of its afferents, the anterior cingulate cortex and medial prefrontal cortex, had no effect on this capacity. Thus, dysfunction of the nucleus accumbens core may be a key element in the neuropathology of impulsivity.