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本文报道海拔3417m和4280m地区世居藏族和移居汉族青少年运动状态下心肺功能的对比研究。结果显示:3417m和4280m世居藏族的最大氧耗量、无氧阈值及最大心输出量都明显大于汉族,血氧饱和度(Sao2)随运动负荷的增加而降低。海拔3417m藏、汉族的△Sao2分别为7.46%和10.03%,4280m处为8.57%和13.75%,最大心率随海拔升高而下降。研究提示,藏族青少年有较高的最大有氧能力,反映了他们对低氧环境的适应优势。 相似文献
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DON AT AGOSTI 《Systematic Entomology》1994,19(2):93-117
Abstract. The holarctic ant tribe Formicini is revised, the new genus Bajcaridris described, and possible phylogenetic relationships are discussed. The subgenus Iberoformica is synonymized with Formica. A synopsis, diagnosis and keys to the genera are provided. 相似文献
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Most neurons have elaborate dendritic trees that receive tens of thousands of synaptic inputs. Because postsynaptic responses to individual synaptic events are usually small and transient, the integration of many synaptic responses is needed to depolarize most neurons to action potential threshold. Over the past decade, advances in electrical and optical recording techniques have led to new insights into how synaptic responses propagate and interact within dendritic trees. In addition to their passive electrical and morphological properties, dendrites express active conductances that shape individual synaptic responses and influence synaptic integration locally within dendrites. Dendritic voltage-gated Na(+) and Ca(2+) channels support action potential backpropagation into the dendritic tree and local initiation of dendritic spikes, whereas K(+) conductances act to dampen dendritic excitability. While all dendrites investigated to date express active conductances, different neuronal types show specific patterns of dendritic channel expression leading to cell-specific differences in the way synaptic responses are integrated within dendritic trees. This review explores the way active and passive dendritic properties shape synaptic responses in the dendrites of central neurons, and emphasizes their role in synaptic integration. 相似文献
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Background
Many musculoskeltal injuries in the workplace have been attributed to the repetitive loading of muscle and soft tissues. It is not disputed that muscular fatigue is a risk factor for musculoskeltal injury, however the disparity between gender with respect to muscular fatigability and rate of recovery is not well understood. Current health and safety guidelines do not account for sex differences in fatiguability and may be predisposing one gender to greater risk. The purpose of this study was to quantify the sex differences in fatigue development and recovery rate of lower and upper body musculature after repeated bouts of sustained isometric contractions.Methods
Twenty-seven healthy males (n = 12) and females (n = 15) underwent bilateral localized fatigue of either the knee extensors (male: n = 8; female: n = 8), elbow flexors (male: n = 8; female: n = 10), or both muscle groups. The fatigue protocol consisted of ten 30-second sub-maximal isometric contractions. The changes in maximum voluntary contraction (MVC), electrically evoked twitches, and motor unit activation (MUA) were assessed along with the ability to control the sustained contractions (SLP) during the fatigue protocol using a mixed four-factor repeated measures ANOVA (gender × side × muscle × time) design with significance set at p < 0.05.Results
There was a significant loss of MVC, MUA, and evoked twitch amplitude from pre- to post-fatigue in both the arms and legs. Males had greater relative loss of isometric force, a higher rate of fatigue development, and were less capable of maintaining the fatiguing contractions in the legs when compared to the females.Conclusion
The nature of the induced fatigue was a combination of central and peripheral fatigue that did not fully recover over a 45-minute period. The results appear to reflect sex differences that are peripheral, and partially support the muscle mass hypothesis for explaining differences in muscular fatigue.7.
Zhang C Norris-Caneda KH Rottmann WH Gulledge JE Chang S Kwan BY Thomas AM Mandel LC Kothera RT Victor AD Pearson L Hinchee MA 《Plant physiology》2012,159(4):1319-1334
Pollen elimination provides an effective containment method to reduce direct gene flow from transgenic trees to their wild relatives. Until now, only limited success has been achieved in controlling pollen production in trees. A pine (Pinus radiata) male cone-specific promoter, PrMC2, was used to drive modified barnase coding sequences (barnaseH102E, barnaseK27A, and barnaseE73G) in order to determine their effectiveness in pollen ablation. The expression cassette PrMC2-barnaseH102E was found to efficiently ablate pollen in tobacco (Nicotiana tabacum), pine, and Eucalyptus (spp.). Large-scale and multiple-year field tests demonstrated that complete prevention of pollen production was achieved in greater than 95% of independently transformed lines of pine and Eucalyptus (spp.) that contained the PrMC2-barnaseH102E expression cassette. A complete pollen control phenotype was achieved in transgenic lines and expressed stably over multiple years, multiple test locations, and when the PrMC2-barnaseH102E cassette was flanked by different genes. The PrMC2-barnaseH102E transgenic pine and Eucalyptus (spp.) trees grew similarly to control trees in all observed attributes except the pollenless phenotype. The ability to achieve the complete control of pollen production in field-grown trees is likely the result of a unique combination of three factors: the male cone/anther specificity of the PrMC2 promoter, the reduced RNase activity of barnaseH102E, and unique features associated with a polyploid tapetum. The field performance of the PrMC2-barnaseH102E in representative angiosperm and gymnosperm trees indicates that this gene can be used to mitigate pollen-mediated gene flow associated with large-scale deployment of transgenic trees. 相似文献
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A series of acyclic, truncated microcystin analogues, comprised of the dienic beta-amino acid (Adda) and up to four additional amino acids characteristic of the parent toxin, was synthesized and screened for activity as inhibitors of PP1 and PP2A. Despite a recent report to the contrary for a microcystin-derived tetrapeptide degradation product, none approaches the potency of microcystin itself. 相似文献
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Controls on Soil Carbon Dioxide and Methane Fluxes in a Variety of Taiga Forest Stands in Interior Alaska 总被引:21,自引:0,他引:21
CO2 and CH4 fluxes were monitored over 4 years in a range of taiga forests along the Tanana River in interior Alaska. Floodplain alder
and white spruce sites and upland birch/aspen and white spruce sites were examined. Each site had control, fertilized, and
sawdust amended plots; flux measurements began during the second treatment year. CO2 emissions decreased with successional age across the sites (alder, birch/aspen, and white spruce, in order of succession)
regardless of landscape position. Although CO2 fluxes showed an exponential relationship with soil temperature, the response of CO2 production to moisture fit an asymptotic model. Of the manipulations, only N fertilization had an effect on CO2 flux, decreasing flux in the floodplain sites but increasing it in the birch/aspen site. Landscape position was the best
predictor of CH4 flux. The two upland sites consumed CH4 at similar rates (approximately 0.5 mg C m−2 d−1), whereas the floodplain sites had lower consumption rates (0–0.3 mg C m−2 d−1). N fertilization and sawdust both inhibited CH4 consumption in the upland birch/aspen and floodplain spruce sites but not in the upland spruce site. The biological processes
driving CO2 fluxes were sensitive to temperature, moisture, and vegetation, whereas CH4 fluxes were sensitive primarily to landscape position and biogeochemical disturbances. Hence, climate change effects on C-gas
flux in taiga forest soils will depend on the relationship between soil temperature and moisture and the concomitant changes
in soil nutrient pools and cycles.
Received 10 March 1998; accepted 29 December 1999. 相似文献
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Relationships in the Drosophila obscura species group, inferred from mitochondrial cytochrome oxidase II sequences 总被引:2,自引:0,他引:2
We compare the sequences for the mitochondrial cytochrome oxidase II gene
of 13 species of the Drosophila obscura group. The survey includes six
members of the D. affinis subgroup, four of the D. pseudoobscura subgroup,
and three of the D. obscura subgroup. In all species, the gene is 688
nucleotides in length, encoding a protein of 229 amino acids plus the first
position T of the stop codon. The sequences show the typical
high-transition bias for closely related species, but that bias is
essentially eliminated for species pairs of > 5% sequence divergence.
The phylogenetic relationships in the species group are inferred using both
neighbor-joining and maximum parsimony. The two procedures give comparable
results, showing that the D. affinis and D. pseudoobscura subgroups are
monophyletic groupings that appear to have closer affinities to one another
than either has to the D. obscura subgroup. We use transversion distances
to estimate times of divergence, on the basis of three different estimates
of the time of separation of the D. obscura species group from the D.
melanogaster group. If that event occurred 35 Mya, then we can estimate the
origin of the nearctic forms at approximately 22 Mya and the separation of
the D. affinis and D. pseudoobscura subgroups at approximately 17 Mya.
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