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381.
Population biology of infectious diseases: Part I. 总被引:20,自引:0,他引:20
If the host population is taken to be a dynamic variable (rather than constant, as conventionally assumed), a wider understanding of the population biology of infectious diseases emerges. In this first part of a two-part article, mathematical models are developed, shown to fit data from laboratory experiments, and used to explore the evolutionary relations among transmission parameters. In the second part of the article, to be published in next week's issue, the models are extended to include indirectly transmitted infections, and the general implications for infectious diseases are considered. 相似文献
382.
Depressant effect of moonlight on activity of aquatic insects 总被引:6,自引:0,他引:6
N H Anderson 《Nature》1966,209(5020):319-320
383.
Summary Early removal of the optic cup of the chick embryo prevents innervation of the contralateral optic lobe. This reduces the rate of development of citrate synthetase. The posthatch increase of the level of this enzyme related to oxidative metabolism is not impaired by denervation of the chick optic lobe. 相似文献
384.
385.
386.
Oestrogen receptors and antagonism of steroid hormone action 总被引:11,自引:0,他引:11
387.
Selective impairment of learning and blockade of long-term potentiation by an N-methyl-D-aspartate receptor antagonist, AP5 总被引:33,自引:0,他引:33
Recent work has shown that the hippocampus contains a class of receptors for the excitatory amino acid glutamate that are activated by N-methyl-D-aspartate (NMDA) and that exhibit a peculiar dependency on membrane voltage in becoming active only on depolarization. Blockade of these sites with the drug aminophosphonovaleric acid (AP5) does not detectably affect synaptic transmission in the hippocampus, but prevents the induction of hippocampal long-term potentiation (LTP) following brief high-frequency stimulation. We now report that chronic intraventricular infusion of D,L-AP5 causes a selective impairment of place learning, which is highly sensitive to hippocampal damage, without affecting visual discrimination learning, which is not. The L-isomer of AP5 did not produce behavioural effects. AP5 treatment also suppressed LTP in vivo. These results suggest that NMDA receptors are involved in spatial learning, and add support to the hypothesis that LTP is involved in some, but not all, forms of learning. 相似文献
388.
The organizer factors Chordin and Noggin are required for mouse forebrain development 总被引:20,自引:0,他引:20
Bachiller D Klingensmith J Kemp C Belo JA Anderson RM May SR McMahon JA McMahon AP Harland RM Rossant J De Robertis EM 《Nature》2000,403(6770):658-661
In mice, there is evidence suggesting that the development of head and trunk structures is organized by distinctly separated cell populations. The head organizer is located in the anterior visceral endoderm (AVE) and the trunk organizer in the node and anterior primitive streak. In amphibians, Spemann's organizer, which is homologous to the node, partially overlaps with anterior endoderm cells expressing homologues of the AVE markers cerberus, Hex and Hesx1. For mice, this raises the question of whether the AVE and node are independent of each other, as suggested by their anatomical separation, or functionally interdependent as is the case in amphibians. Chordin and Noggin are secreted bone morphogenetic protein (BMP) antagonists expressed in the mouse node, but not in the AVE. Here we show that mice double-homozygous mutants that are for chordin and noggin display severe defects in the development of the prosencephalon. The results show that BMP antagonists in the node and its derivatives are required for head development. 相似文献
389.
Effect of immunization with a vaccinia-HIV env recombinant on HIV infection of chimpanzees 总被引:2,自引:0,他引:2
S L Hu P N Fultz H M McClure J W Eichberg E K Thomas J Zarling M C Singhal S G Kosowski R B Swenson D C Anderson 《Nature》1987,328(6132):721-723
Acquired immunodeficiency syndrome (AIDS) is caused by human immunodeficiency virus (HIV) and is now recognized as a worldwide epidemic for which there is no cure or vaccine. Chimpanzees are the only other animals that can be infected by HIV, and therefore the chimpanzee-HIV model system is useful for testing potential HIV vaccines. However, with one exception, there have been no reports of clinical manifestations of AIDS in chimpanzees. We report here results of an HIV vaccine trial in which nine chimpanzees were first immunized with either a recombinant vaccinia virus expressing the envelope glycoproteins of HIV strain LAV-1 (v-env5) or a control recombinant vaccinia virus and were then challenged with a high or low dose of LAV-1. Although HIV-specific antibody and T-cell responses were elicited by immunization, virus was isolated from lymphocytes of all challenged chimpanzees, indicating that immunization did not prevent infection by HIV. Among the animals that received a higher dose of LAV-1, one of two control chimpanzees, but none of the four v-env5-immunized chimpanzees developed substantial and persistent lymphadenopathy. 相似文献
390.
Woyke T Teeling H Ivanova NN Huntemann M Richter M Gloeckner FO Boffelli D Anderson IJ Barry KW Shapiro HJ Szeto E Kyrpides NC Mussmann M Amann R Bergin C Ruehland C Rubin EM Dubilier N 《Nature》2006,443(7114):950-955
Symbioses between bacteria and eukaryotes are ubiquitous, yet our understanding of the interactions driving these associations is hampered by our inability to cultivate most host-associated microbes. Here we use a metagenomic approach to describe four co-occurring symbionts from the marine oligochaete Olavius algarvensis, a worm lacking a mouth, gut and nephridia. Shotgun sequencing and metabolic pathway reconstruction revealed that the symbionts are sulphur-oxidizing and sulphate-reducing bacteria, all of which are capable of carbon fixation, thus providing the host with multiple sources of nutrition. Molecular evidence for the uptake and recycling of worm waste products by the symbionts suggests how the worm could eliminate its excretory system, an adaptation unique among annelid worms. We propose a model that describes how the versatile metabolism within this symbiotic consortium provides the host with an optimal energy supply as it shuttles between the upper oxic and lower anoxic coastal sediments that it inhabits. 相似文献