Ketamine-xylazine anaesthesia blocks consolidation of ocular dominance changes in kitten visual cortex

In the visual cortex of mammals, response properties of single neurons can be changed by restricted visual experience during early postnatal development. Covering one eye for four to eight hours when kittens are at the peak of the sensitive period is sufficient to weaken the influence of the occluded eye on cortical neurons resulting in a noticeable shift of ocular dominance towards the open eye. The underlying changes in synaptic connections do not occur so readily when a kitten is anaesthetized and paralysed. We report here that an ocular dominance shift is prevented in alert kittens that receive repeated brief monocular exposures when these are followed by ketamine-xylazine anaesthesia. This retrograde effect on cortical plasticity suggests that the process by which synaptic activity is converted into structural changes has been disturbed.     

Changes in geniculate cell size following brief monocular blockade of retinal activity in kittens

When a kitten is subjected to monocular lid suture early in life, cells in laminae of the lateral geniculate nucleus (LGN) connected to the sutured eye grow less than normal and cells in those laminae connected to the non-sutured eye grow more than normal. These changes are seen primarily in the binocular segment of the LGN, which corresponds to the central visual field, and are due to competition either between intracortical afferents originating from the different LGN laminae, or directly among cells within the LGN. The afferent deprivation induced by lid suture, however, is not complete, as retinal ganglion cells fire tonically both in darkness and in light. It is generally thought that this tonic retinal activity is necessary to maintain neuronal excitability at normal threshold in the central visual pathway. In the visual cortex of developing kittens, we previously showed a long-lasting change in ocular dominance of binocular cells by a brief blockade of retinal activity in one optic nerve. We report here that a complete blockade of retinal activity in one eye causes major changes in LGN cell size within 1 week. These changes occur throughout the LGN, including the monocular segment where binocular competition does not occur. The results indicate that tonic retinal activity may have an important role in the control of geniculate cell size.     

Ocular dominance shift in kitten visual cortex caused by imbalance in retinal electrical activity

Monocular lid suture during the sensitive period early in the life of a kitten disrupts normal development of inputs from the two eyes to the visual cortex, causing a decrease in the fraction of cortical cells responding to the deprived eye. Such an ocular dominance shift has been assumed to depend on patterned visual experience, because no change in cortical physiology is produced by inequalities between the two eyes in retinal illumination or temporally modulated diffuse light stimulation. A higher-level process, involving gating signals from areas outside striate cortex, has been proposed to ensure that sustained changes in synaptic efficacy occur only in response to behaviourally significant visual inputs. To test whether such a process is necessary for ocular dominance plasticity, we treated 4-week-old kittens with visual deprivation and monocular tetrodotoxin (TTX) injections to create an imbalance in the electrical activities of the two retinas in the absence of patterned vision. After 1 week of treatment we determined the ocular dominance distribution of single units in primary visual cortex. In all kittens studied, a significant ocular dominance shift was found. In addition to this physiological change, there was an anatomical change in the lateral geniculate nucleus, where cells were larger in laminae receiving input from the more active eye. Our results indicate that patterned vision is not necessary for visual cortical plasticity, and that an imbalance in spontaneous retinal activity alone can produce a significant ocular dominance shift.     

Change in pattern of ongoing cortical activity with auditory category learning

Humans are able to classify novel items correctly by category; some other animals have also been shown to do this. During category learning, humans group perceptual stimuli by abstracting qualities from similarity relationships of their physical properties. Forming categories is fundamental to cognition and can be independent of a 'memory store' of information about the items or a prototype. The neurophysiological mechanisms underlying the formation of categories are unknown. Using an animal model of category learning, in which frequency-modulated tones are distinguished into the categories of 'rising' and 'falling' modulation, we demonstrate here that the sorting of stimuli into these categories emerges as a sudden change in an animal's learning strategy. Electro-corticographical recording from the auditory cortex shows that the transition is accompanied by a change in the dynamics of cortical stimulus representation. We suggest that this dynamic change represents a mechanism underlying the recognition of the abstract quality (or qualities) that defines the categories.     

Temporal patterns of human cortical activity reflect tone sequence structure

Despite growing interest in temporal aspects of auditory neural processing, little is known about large-scale timing patterns of brain activity during the perception of auditory sequences. This is partly because it has not been possible to distinguish stimulus-related activity from other, endogenous brain signals recorded by electrical or magnetic sensors. Here we use amplitude modulation of unfamiliar, approximately 1-minute-long tone sequences to label stimulus-related magnetoencephalographic neural activity in human subjects. We show that temporal patterns of activity recorded over particular brain regions track the pitch contour of tone sequences, with the accuracy of tracking increasing as tone sequences become more predictable in structure. In contrast, temporal synchronization between recording locations, particularly between sites over the left posterior hemisphere and the rest of the brain, is greatest when sequences have melody-like statistical properties, which may reflect the perceptual integration of local and global pitch patterns in melody-like sequences. This method is particularly well suited to studying temporal neural correlates of complex auditory sequences (such as speech or music) which engage multiple brain areas as perception unfolds in time.     

Bilateral amblyopia after a short period of reverse occlusion in kittens

The majority of neurones in the visual cortex of both adult cats and kittens can be excited by visual stimulation of either eye. Nevertheless, if one eye is deprived of patterned vision early in life, most cortical cells can only be activated by visual stimuli presented to the nondeprived eye and behaviourally the deprived eye is apparently useless. Although the consequences of monocular deprivation can be severe, they can in many circumstances be rapidly reversed with the early implementation of reverse occlusion which forces the use of the initially deprived eye. However, by itself reverse occlusion does not restore a normal distribution of cortical ocular dominance and only promotes visual recovery in one eye. In an effort to find a procedure that might restore good binocular vision, we have examined the effects on acuity and cortical ocular dominance of a short, but physiologically optimal period of reverse occlusion, followed by a period of binocular vision beginning at 7.5 weeks of age. Surprisingly, despite the early introduction of binocular vision, both eyes attained acuities that were only approximately 1/3 of normal acuity levels. Despite the severe bilateral amblyopia, cortical ocular dominance appeared similar to that of normal cats. This is the first demonstration of severe bilateral amblyopia following consecutive periods of monocular occlusion.     

Increasing dominance of large lianas in Amazonian forests

Ecological orthodoxy suggests that old-growth forests should be close to dynamic equilibrium, but this view has been challenged by recent findings that neotropical forests are accumulating carbon and biomass, possibly in response to the increasing atmospheric concentrations of carbon dioxide. However, it is unclear whether the recent increase in tree biomass has been accompanied by a shift in community composition. Such changes could reduce or enhance the carbon storage potential of old-growth forests in the long term. Here we show that non-fragmented Amazon forests are experiencing a concerted increase in the density, basal area and mean size of woody climbing plants (lianas). Over the last two decades of the twentieth century the dominance of large lianas relative to trees has increased by 1.7-4.6% a year. Lianas enhance tree mortality and suppress tree growth, so their rapid increase implies that the tropical terrestrial carbon sink may shut down sooner than current models suggest. Predictions of future tropical carbon fluxes will need to account for the changing composition and dynamics of supposedly undisturbed forests.     

Archaeal dominance in the mesopelagic zone of the Pacific Ocean

The ocean's interior is Earth's largest biome. Recently, cultivation-independent ribosomal RNA gene surveys have indicated a potential importance for archaea in the subsurface ocean. But quantitative data on the abundance of specific microbial groups in the deep sea are lacking. Here we report a year-long study of the abundance of two specific archaeal groups (pelagic euryarchaeota and pelagic crenarchaeota) in one of the ocean's largest habitats. Monthly sampling was conducted throughout the water column (surface to 4,750 m) at the Hawai'i Ocean Time-series station. Below the euphotic zone (> 150 m), pelagic crenarchaeota comprised a large fraction of total marine picoplankton, equivalent in cell numbers to bacteria at depths greater than 1,000 m. The fraction of crenarchaeota increased with depth, reaching 39% of total DNA-containing picoplankton detected. The average sum of archaea plus bacteria detected by rRNA-targeted fluorescent probes ranged from 63 to 90% of total cell numbers at all depths throughout our survey. The high proportion of cells containing significant amounts of rRNA suggests that most pelagic deep-sea microorganisms are metabolically active. Furthermore, our results suggest that the global oceans harbour approximately 1.3 x 10(28) archaeal cells, and 3.1 x 10(28) bacterial cells. Our data suggest that pelagic crenarchaeota represent one of the ocean's single most abundant cell types.     

试论明中后期山东驿递的破坏与巡抚洪芳洲的整顿举措

驿递作为我国古代交通方式之一,在国家的政治、经济、军事和文化交流等方面发挥着极为重要的作用,但在明朝中后期却遭到严重的破坏。巡抚洪芳洲面对山东如此破坏的驿递,向皇帝上疏,提出整顿措施。     

Disruption of the actin cytoskeleton in yeast capping protein mutants

Capping protein controls the addition of actin subunits to the barbed end of actin filaments and nucleates actin polymerization in vitro. Capping protein has been identified in all eukaryotic cells examined so far; it is a heterodimer with subunits of relative molecular masses 32,000-36,000 (alpha-subunit) and 28,000-32,000 (beta-subunit). In skeletal muscle, capping protein (CapZ) probably binds the barbed ends of actin filaments at the Z line. The in vivo role of this protein in non-muscle cells is not known. We report here the characterization of CAP2, the single gene encoding the beta-subunit of capping protein in Saccharomyces cerevisiae. Yeast cells in which the CAP2 gene was disrupted by an insertion or a deletion had an abnormal actin distribution, including the loss of actin cables. The mutant cells were round and large, with a heterogeneous size distribution, and, although viable, grew more slowly than congenic wild-type cells. Chitin, a cell wall component restricted to the mother-bud junction in wild-type budding yeast, was found on the entire mother cell surface in the mutants. The phenotype of CAP2 disruption resembled that of temperature-sensitive mutations in the yeast actin gene ACT1, indicating that capping protein regulates actin-filament distribution in vivo.     

NMDA receptors in the visual cortex of young kittens are more effective than those of adult cats

Acidic amino acids, such as glutamate and aspartate, are thought to be excitatory transmitters in the cerebral neocortex and hippocampus. Receptors for these amino acids can be classified into at least three types on the basis of their agonists. Quisqualate-preferring receptors and kainate-preferring receptors are implicated in the mediation of synaptic transmission in many regions including the hippocampus and visual cortex, whereas N-methyl-D-aspartate (NMDA)-preferring receptors are thought to be involved in modulating synaptic efficacy, for example in longterm potentiation, a form of synaptic plasticity in the hippocampus. In the visual cortex of the cat and monkey, it is well established that synaptic plasticity, estimated by susceptibility of binocular responsiveness of cortical neurons to monocular visual deprivation, disappears after the 'critical' period of postnatal development. Here we report that during the critical period in young kittens, a selective NMDA-receptor antagonist blocks visual responses of cortical neurons much more effectively than it does in the adult cat. This suggests that NMDA receptors may be involved in establishing synaptic plasticity in the kitten visual cortex.     

全局数据包络分析法在应急决策中的应用

随着灾害的增加,应急决策系统的快速发展,对应急管理的要求是使用小的投入将损失降到最低。全局数据包络分析法能够总揽全局,对异构的部门进行效率评价,用预估挽回损失与付出的总代价的比值来估算预案之间对突发事件处理的相对有效度,可用来分析各部门物资、人员的投入对灾害救援的效果。     

复合污染底泥植物修复过程中多酚氧化酶活性变化

为了确定不同植物对复合污染底泥的修复效果,采用室外盆栽试验,比较了不同植物修复方式、互作条件下多酚氧化酶活性。结果表明:(1)植物-菌根真菌以及植物-菌根真菌-土著细菌联合修复方式,能够提高多酚氧化酶的活性,促进植物生长并吸收底泥中污染物;(2)玉米和黑麦草互作过程中,玉米-菌根真菌联合修复方式修复效果较好。黑麦草和紫花苜蓿互作过程中,黑麦草-菌根真菌修复方式的效果较好;(3)低温对酶活性影响较大。研究结论有助于确定复合污染底泥的最佳修复方式。     

Structure of C3b reveals conformational changes that underlie complement activity

Resistance to infection and clearance of cell debris in mammals depend on the activation of the complement system, which is an important component of innate and adaptive immunity. Central to the complement system is the activated form of C3, called C3b, which attaches covalently to target surfaces to amplify complement response, label cells for phagocytosis and stimulate the adaptive immune response. C3b consists of 1,560 amino-acid residues and has 12 domains. It binds various proteins and receptors to effect its functions. However, it is not known how C3 changes its conformation into C3b and thereby exposes its many binding sites. Here we present the crystal structure at 4-A resolution of the activated complement protein C3b and describe the conformational rearrangements of the 12 domains that take place upon proteolytic activation. In the activated form the thioester is fully exposed for covalent attachment to target surfaces and is more than 85 A away from the buried site in native C3 (ref. 5). Marked domain rearrangements in the alpha-chain present an altered molecular surface, exposing hidden and cryptic sites that are consistent with known putative binding sites of factor B and several complement regulators. The structural data indicate that the large conformational changes in the proteolytic activation and regulation of C3 take place mainly in the first conversion step, from C3 to C3b. These insights are important for the development of strategies to treat immune disorders that involve complement-mediated inflammation.