Fractalkine-induced activation of the phosphatidylinositol-3 kinase pathway attentuates microglial activation in vivo and in vitro

Several neurodegenerative disorders are associated with evidence of inflammation, one feature of which is increased activation of microglia, the most likely cellular source of inflammatory cytokines like interleukin-1β. It is now recognized that interaction of microglia with other cells contributes to maintenance of microglia in a quiescent state and the complementary distribution of the chemokine, fractalkine (CX₃CL1) on neurons and its receptor (CX₃CR1) on microglia, suggests that this interaction may play a role in modulating microglial activation. Here we demonstrate that both soluble and membrane-bound fractalkine attenuate lipopolysaccharide-induced microglial activation in vitro. We also show that fractalkine expression is reduced in the brain of aged rats and this is accompanied by an age-related increase in microglial activation. Treatment of aged rats with fractalkine attenuates the age-related increase in microglial activation and the evidence indicates that fractalkine-induced activation of the phosphatidylinositol-3 kinase pathway is required to maintain microglia in a quiescent state both in vivo and in vitro .     

乌岩岭国家级自然保护区种子植物区系的特征分析

乌岩岭国家级自然保护区地处亚热带,气候温暖湿润。该地区植物种类丰富,共有野生种子植物134科、578属、1197种;根据地史资料和自然条件,通过对种子植物种类的组成和分布区类型的分析,认为该区系起源古老,区系成分复杂;珍稀特有植物多,如南方红豆杉、钟萼木、香果树、福建柏、榧树、闽楠、花榈木等大量古老树种,并且绝大多数具有重要的经济价值和科研价值;区内578属可分为14个类型,热带和温带分布的属分别占48．6％和49．2％（不包括世界分布类型）,具较明显的南北过渡的现象,与世界各地有广泛的联系。这些区系特征与本区古老的地质和优越的水热条件密切相关。     

广东东部不同生活型植物热带植物区系属性的比较研究

通过对粤东种子植物生活型的调查和统计分析,将粤东2226种种子植物划分为6类生活型。各种木本生活型共有1198种,占53.8%;各种草本类型共有1028种植物,占46.2%。从各生活型的种的区系成分分析来看,该地各生活型热带性成分比例强弱的顺序是：乔木种〉木质藤本种〉灌木种〉陆生草本〉草质藤本〉水生草本。     

Research progress on the effects of soil erosion on vegetation

The relationship between vegetation and soil erosion deserves attention due to its scientific importance and practical applications. A great deal of information is available about the mechanisms and benefits of vegetation in the control of soil erosion, but the effects of soil erosion on vegetation development and succession is poorly documented. Research shows that soil erosion is the most important driving force for the degradation of upland and mountain ecosystems. Soil erosion interferes with the process of plant community development and vegetation succession, commencing with seed formation and impacting throughout the whole growth phase and affecting seed availability, dispersal, germination and establishment, plant community structure and spatial distribution. There have been almost no studies on the effects of soil erosion on seed development and availability, of surface flows on seed movement and redistribution, and their influences on soil seed bank and on vegetation establishment and distribution. However, these effects may be the main cause of low vegetation cover in regions of high soil erosion activity and these issues need to be investigated. Moreover, soil erosion is not only a negative influence on vegetation succession and restoration, but also a driving force of plant adaptation and evolution. Consequently, we need to study the effects of soil erosion on ecological processes and on development and regulation of vegetation succession from the points of view of pedology and vegetation, plant and seed ecology, and to establish an integrated theory and technology for deriving practical solutions to soil erosion problems.     

神经生长因子与神经系统老化

老化通常指生物体生长发育成熟以后,随年龄增加生理机能逐渐减退,内环境稳定性下降,组织器官逐渐发生退行性改变,最终走向衰老、死亡的过程。神经系统老化是神经元退行性病变形成的基础和条件。由于神经生长因子（nerve growth factor,NGF）与中枢神经系统胆碱能神经元的存活和可塑性调节密切相关,所以NGF在神经系统老化和神经退行性变疾病如老年性痴呆（Alzheimer’s disease,AD）的发生发展过程中发挥重要作用。本文综述了NGF在脑老化中的变化及其与AD发病机制的关系。     

Symmetric faces are a sign of successful cognitive aging

It has been proposed that a common cause underlies individual differences in bodily and cognitive decline in old age. No good marker for this common cause has been identified to date. Here, fluctuating asymmetry (FA), an indicator of developmental stability that relates to intelligence differences in young adults, was measured from facial photographs of 216 surviving members of the Lothian Birth Cohort 1921 at age 83 and related to their intelligence at ages 11, 79 and 83 years. FA at age 83 was unrelated to intelligence at ages 11 and 79 and to cognitive change between 11 and 79 years. It was, however, associated with intelligence and information processing efficiency at age 83 and with cognitive change between 79 and 83 years. Significant results were limited to men, a result predicted by sex differences in life history tradeoffs and life expectancy. Results were stronger when directional asymmetries were corrected in facial FA measures. Thus, FA is a candidate marker for the common cause of differential senescence.     

Epizoochorous seed dispersal in relation to seed availability – an experiment with a red fox dummy

Questions: Is the red fox a potential vector for epizoochorous seed dispersal? Can seed attachment and retention be predicted from plant and seed traits? Location: Grasslands in southern Norway. Methods: Epizoochorous seed attachment on the red fox was studied by walking a dummy fox through the vegetation and comparing seeds found on the dummy with the estimated seed availability in the vegetation. Seed retention, i.e. the ability of different seeds to stay on the fox, was estimated in a separate experiment. Seed attachment and retention were related to plant and seed traits using statistical models that account for heteroscedasticity and zero‐inflated data. Results: The majority of seeds attached to the fox originated from a few species, but also species without specific seed traits that are supposed to enhance epizoochory attached at least some seeds to the fox. The probability of seed attachment was positively related to plant height, bristle and hooked seed appendages, and negatively related to winged appendages, seed mass, and seed sphericity. Seed retention was positively related to the seed traits bristles, hooks and pappus. For several species, the results indicate a high potential for dispersal over long distances. Conclusions: In modern agricultural landscapes, large herbivores are often restricted in their mobility or are found at low densities, and other animal vectors may therefore be important for seed dispersal. In our study, a range of plant species were able to disperse by attaching seeds to, and having their seeds retained in, the fox fur some distance. We suggest that the red fox may be an important vector for epizoochorous seed dispersal in the agricultural landscape.     

Habitat degradation,topography and rainfall variability interact to determine seed distribution and recruitment in a sand dune grassland

Question: Understanding the mechanisms underlying how habitat degradation, topography and rainfall variability interactively affect seed distribution and seedling recruitment is crucial for explaining plant community patterns and dynamics. Interactions between these major factors were studied together in a semiarid sand dune grassland. Location: Eastern Inner Mongolia, China. Methods: The study system used four sites of fixed, semifixed, semishifting and shifting sand dune grasslands, representing a gradient of habitat degradation. We investigated the density of germinable seeds deposited in the top 5 cm of soil and in situ seedling emergence (number of seedlings emerging early in the growing season) and establishment (number of plants recruited at the end of the growing season) at three topographic positions (dune top, windward and leeward sides) within each site over 2 years that differed in rainfall. Habitat characteristics (i.e. vegetation cover, plant species composition and diversity, soil moisture and nutrient availability and soil erodibility) of the four sites were also measured. Results: Habitat degradation (i.e. decreased vegetation cover and enhanced wind erosion rate) significantly reduced the size of the germinable soil seed bank. On average, germinable seed number from the high‐vegetation cover fixed dune was 36‐fold larger than the low‐vegetation cover shifting dune, and eight‐ and two‐fold larger, respectively, than the semishifting and semifixed dunes with intermediate vegetation cover. We observed within‐habitat variability in seed distribution, but among‐topographic position variation differed among habitats. Seedling recruitment showed large between‐year, and among‐ and within‐habitat variability, but these variations varied significantly depending on the response variables evaluated (i.e. initial seedling density, final plant density, emergence rate and recruitment rate). Path analysis revealed complex density‐dependent positive and negative, direct and indirect effects of germinable seed density and initial seedling density on recruitment, but the relative importance of these density‐dependent effects varied depending on habitat type and rainfall availability. Conclusion: Our results suggest that habitat degradation, microtopography and rainfall availability interact in shaping sand dune seed bank and plant community recruitment patterns and dynamics. Their effects were mainly mediated through changes in both the biotic and abiotic environment during the process of habitat deterioration.     

Causes of plant community divergence in the early stages of volcanic succession

Question: How do temporal changes in plant communities occur after volcanic eruptions? What characteristics determine successional divergence or convergence? Location: The summit area of Mount Usu, northern Japan, completely destroyed by 1‐3 m of thick ash and pumice during the 1977‐1978 eruptions. Habitats were classified into three types: gullies where the pre‐eruption topsoil was exposed due to the erosion of tephra (EG), gullies covered with tephra (CG), and outside of gullies covered with thick tephra (OG). Methods: Plant community structure was monitored for 15 years from 1983 to 1997 in 14 2 m × 5 m permanent plots. The data were summarized by species diversity, life form, and the detrended correspondence analysis. Results: The common species were perennial herbaceous plants, but habitat preferences differed between species. Seed bank species, including a nitrogen fixer Trifolium repens, were dominant in EG, and excluded the establishment of the later colonists. Pioneer trees slowly increased in cover. The detrended correspondence analysis indicated that species composition in the earlier stages did not differ greatly between plots. Thereafter, three patterns of temporal community changes were observed: seed bank species persisted in EG, and in OG and CG forest development proceeded or community structure did not change greatly. Conclusion: Pre‐eruption topsoil contributed to revegetation by the supply of seed bank and nutrients in the earliest stages, but resulted in the delay of forest development due to the persistence of seed bank species. Plant community divergence was driven by the persistence of earlier colonists.     

Post‐fire tree establishment patterns at the alpine treeline ecotone: Mount Rainier National Park,Washington, USA

Questions: Does tree establishment: (1) occur at a treeline depressed by fire, (2) cause the forest line to ascend upslope, and/or (3) alter landscape heterogeneity? (4) What abiotic and biotic local site conditions are most important in structuring establishment patterns? (5) Does the abiotic setting become more important with increasing upslope distance from the forest line? Location: Western slopes of Mount Rainier, USA. Methods: We performed classification analysis of 1970 satellite imagery and 2003 aerial photography to delineate establishment. Local site conditions were calculated from a LIDAR‐based DEM, ancillary climate data, and 1970 tree locations in a GIS. We used logistic regression on a spatially weighted landscape matrix to rank variables. Results: Considerable establishment after 1970 caused forest line elevation to increase over 150 m in specific locations. Landscape heterogeneity increased with distance from the 1970 forest line. At a broad spatial context, we found establishment was most common near existing trees (0‐50 m) and at low elevations (1250‐1350 m). Slope aspect (W, NW, N, NE, and E), slope angle (40‐60°), and other abiotic factors emerged as important predictors of establishment with increasing upslope distance from the forest line to restricted spatial extents. Conclusions: Favorable climatic conditions likely triggered widespread tree establishment. Readily available seed probably enhanced establishment rates near sexually mature trees, particularly in the less stressful environment at low elevations. The mass effect of nearly ubiquitous establishment in these areas may have obscured the importance of the abiotic setting to restricted spatial extents. Topographic variability apparently produced favorable sites that facilitated opportunistic establishment with increasing upslope distance from the forest line, thereby enabling additional trees to invade the alpine tundra.