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971.
Learning about motivationally important stimuli involves plasticity in the amygdala, a temporal lobe structure. Amygdala‐dependent learning involves a growing number of plasticity‐related signaling pathways also implicated in brain development, suggesting that learning‐related signaling in juveniles may simultaneously influence development. Here, we review the pleiotropic functions in nervous system development and amygdala‐dependent learning of a signaling pathway that includes brain‐derived neurotrophic factor (BDNF), extracellular signaling‐related kinases (ERKs) and cyclic AMP‐response element binding protein (CREB). Using these canonical, plasticity‐related genes as an example, we discuss the intersection of learning‐related and developmental plasticity in the immature amygdala, when aversive and appetitive learning may influence the developmental trajectory of amygdala function. We propose that learning‐dependent activation of BDNF, ERK and CREB signaling in the immature amygdala exaggerates and accelerates neural development, promoting amygdala excitability and environmental sensitivity later in life. 相似文献
972.
Asymmetric interspecific aggression in New Guinean songbirds that replace one another along an elevational gradient
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A common pattern in tropical avifaunas is for closely related species to inhabit largely parapatric elevational distributions such that they replace one another along the elevational gradient. A long‐standing hypothesis for this pattern is that parapatry is maintained by interspecific interference competition mediated by interspecific aggression. However, empirical tests of this hypothesis remain scarce. We used reciprocal playback experiments to measure interspecific aggression in five species‐pairs of New Guinean passerine elevational replacements. We found evidence of interspecific aggression in three species‐pairs. In these three cases, interspecific aggression was asymmetric, with the lower elevation species more aggressive towards the upper elevation species than vice versa. Two patterns suggest that this interspecific aggression is a learned response to the presence of a heterospecific competitor rather than misdirected intraspecific aggression or an evolved response to a competitor. First, when present, interspecific aggression was always strongest at the upper elevation range margin of the lower elevation species (i.e. in the elevational zone in which the two species were found in close proximity and thus interacted with each other), and diminished over very short distances away from this zone. Secondly, the two species‐pairs that did not exhibit interspecific aggression had narrow ‘no man's land’ gaps between their elevational distributions such that heterospecifics did not encounter one another, possibly explaining the lack of interspecific aggression in these examples. Our results support the hypothesis that interspecific aggression is one factor influencing elevational limits in species‐pairs of New Guinean elevational replacements. 相似文献
973.
974.
Hydrophobic tail length plays a pivotal role in amyloid beta (25–35) fibril–surfactant interactions
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Sudipta Bag Susmitnarayan Chaudhury Dibyendu Pramanik Sunando DasGupta Swagata Dasgupta 《Proteins》2016,84(9):1213-1223
The amyloid β‐peptide fragment comprising residues 25–35 (Aβ25‐35) is known to be the most toxic fragment of the full length Aβ peptide which undergoes fibrillation very rapidly. In the present work, we have investigated the effects of the micellar environment (cationic, anionic, and nonionic) on preformed Aβ25‐35 fibrils. The amyloid fibrils have been prepared and characterized by several biophysical and microscopic techniques. Effects of cationic dodecyl trimethyl ammonium bromide (DTAB), cetyl trimethylammonium bromide (CTAB), anionic sodium dodecyl sulfate (SDS), and nonionic polyoxyethyleneoctyl phenyl ether (Triton X‐100 or TX) on fibrils have been studied by Thioflavin T fluorescence, UV–vis spectroscopy based turbidity assay and microscopic analyses. Interestingly, DTAB and SDS micelles were observed to disintegrate prepared fibrils to some extent irrespective of their charges. CTAB micelles were found to break down the fibrillar assembly to a greater extent. On the other hand, the nonionic surfactant TX was found to trigger the fibrillation process. The presence of a longer hydrophobic tail in case of CTAB is assumed to be a reason for its higher fibril disaggregating efficacy, the premise of their formation being largely attributed to hydrophobic interactions. Proteins 2016; 84:1213–1223. © 2016 Wiley Periodicals, Inc. 相似文献
975.
Mary Ellen Druyan Dean Bass Richard Puchyr Karen Urek David Quig Emmett Harmon William Marquardt 《Biological trace element research》1998,62(3):183-197
Expected values, reference ranges, or reference limits are necessary to enable clinicians to apply analytical chemical data
in the delivery of health care. Determination of references ranges is not straightforward in terms of either selecting a reference
population or performing statistical analysis. In light of logistical, scientific, and economic obstacles, it is understandable
that clinical laboratories often combine approaches in developing health associated reference values. A laboratory may choose
to:
Effects of external contamination and anecdotal information from clinicians may be considered.
The clinical utility of hair analysis is well accepted for some elements. For others, it remains in the realm of clinical
investigation. This article elucidates an approach for establishment of reference ranges for elements in human scalp hair.
Observed levels of analytes from hair specimens from both our laboratory’s total patient population and from a physician-defined
healthy American population have been evaluated. Examination of levels of elements often associated with toxicity serves to
exemplify the process of determining reference ranges in hair. In addition the approach serves as a model for setting reference
ranges for analytes in a variety of matrices. 相似文献
1. | Validate either reference ranges of other laboratories or published data from clinical research or both, through comparison of patients test data. |
2. | Base the laboratory’s reference values on statistical analysis of results from specimens assayed by the clinical reference laboratory itself. |
3. | Adopt standards or recommendations of regulatory agencies and governmental bodies. |
4. | Initiate population studies to validate transferred reference ranges or to determine them anew. |
976.
一个有相互干扰的食植系统的研究 总被引:1,自引:0,他引:1
本文运用常微分方程定性理论讨论了一个放牧有相互干扰的食植系统,获得了该系统极限环存在唯一性及全局渐近稳定性的充分条件. 相似文献
977.
Non-conventional media, containing organic solvents as supplement, were exploited to obtain the non-lethal product release of plant cell secondary metabolites, using suspension cultures ofMorinda citrifolia as model system. The results of our preliminary studies about solvent biocompatibility show that the discrimination between biocompatible and toxic solvents can be achieved by means of two parameters: log P and critical solvent concentration. The last one seems to be a better indicator of solvent toxicity for living cells.Abbreviations log P
logarithm of P
- P
solvent partition coefficient in a standard system n-octanol/water 相似文献
978.
The relationship between shoot growth and foliar nitrogen (N) in E. globulus seedlings was studied in the glasshouse to determine standard values for N deficiency and toxicity diagnosis. Seedlings were grown for 9 weeks in yellow sand, at 10 rates of N, applied as ammonium sulphate, calcium nitrate or ammonium nitrate. Shoot dry weight (DW) increased linearly with N rate for all forms of N in the deficiency range. Seedlings continued to respond to higher rates of ammonium and ammonium nitrate than to nitrate. Maximum shoot DW for nitrate fed plants and ammonium nitrate fed plants were 51% and 84% respectively of ammonium fed plants. Total N concentration in the youngest fully expanded leaf (YFEL) ranged from 1.0% to 3.3% in deficient and adequate plants. The critical N concentration for deficiency diagnosis (corresponding to 90% maximum yield) in the YFEL, determined from these growth response curves averaged over all N forms, was 2.6% N. For ammonium nitrate fed plants, total N concentration in the YFEL for the severely deficient, deficient, adequate, and toxic ranges were <1.4%, 1.4–2.5%, 2.6–3.5%, > 4.3%. High total N concentrations were associated with growth depression and toxicity symptoms, which differed with N form. For nitrate fed plants, a total N concentration above 3.3% in the YFEL was associated with severe growth depression, and leaf tip necrosis. The adequate concentration range for ammonium nitrate was similar to values found on a field trial with 7 month old E. globulus trees grown on an exforest site. 相似文献
979.
Solution culture was used to characterise deficiencies or toxicities of several essential elements in Ipomoea batatas cv. Wanmun, and to define the critical concentrations of these elements in young mature leaves during vegetative growth. Tentative critical concentrations for deficiency, expressed on the basis of dry weight of leaf blade, were: nitrogen 3.8%, phosphorus 0.17%, potassium 2.4%, magnesium 0.12%, manganese 20g/g and zinc 10g/g. For manganese and zinc toxicities it was possible only to designate the range within which the critical concentration occurred. Visible symptoms are briefly described. 相似文献
980.
Concurrent, distribution-wide abundance declines of some Pacific salmon species, including Chinook salmon (Oncorhynchus tshawytscha), highlights the need to understand how vulnerability at different life stages to climate stressors affects population dynamics and fisheries sustainability. Yukon River Chinook salmon stocks are among the largest subarctic populations, near the northernmost extent of the species range. Existing research suggests that Yukon River Chinook salmon population dynamics are largely driven by factors occurring between the adult spawner life stage and their offspring's first summer at sea (second year post-hatching). However, specific mechanisms sustaining chronic poor productivity are unknown, and there is a tremendous sense of urgency to understand causes, as declines of these stocks have taken a serious toll on commercial, recreational, and indigenous subsistence fisheries. Therefore, we leveraged multiple existing datasets spanning parent and juvenile stages of life history in freshwater and marine habitats. We analyzed environmental data in association with the production of offspring that survive to the marine juvenile stage (juveniles per spawner). These analyses suggest more than 45% of the variability in the production of juvenile Chinook salmon is associated with river temperatures or water discharge levels during the parent spawning migration. Over the past two decades, parents that experienced warmer water temperatures and lower discharge in the mainstem Yukon River produced fewer juveniles per spawning adult. We propose the adult spawner life stage as a critical period regulating population dynamics. We also propose a conceptual model that can explain associations between population dynamics and climate stressors using independent data focused on marine nutrition and freshwater heat stress. It is sobering to consider that some of the northernmost Pacific salmon habitats may already be unfavorable to these cold-water species. Our findings have immediate implications, given the common assumption that northern ranges of Pacific salmon offer refugia from climate stressors. 相似文献