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In an awake state, neurons in the cerebral cortex fire irregularly and electroencephalogram (EEG) recordings display low-amplitude, high-frequency fluctuations. During sleep, neurons oscillate between 'on' periods, when they fire as in an awake brain, and 'off' periods, when they stop firing altogether and the EEG displays high-amplitude slow waves. However, what happens to neuronal firing after a long period of being awake is not known. Here we show that in freely behaving rats after a long period in an awake state, cortical neurons can go briefly 'offline' as in sleep, accompanied by slow waves in the local EEG. Neurons often go offline in one cortical area but not in another, and during these periods of 'local sleep', the incidence of which increases with the duration of the awake state, rats are active and display an 'awake' EEG. However, they are progressively impaired in a sugar pellet reaching task. Thus, although both the EEG and behaviour indicate wakefulness, local populations of neurons in the cortex may be falling asleep, with negative consequences for performance. 相似文献
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The teratogenic effect of cadmium can be diminished by a number of mechanisms including zinc and pretreatment with cadmium and mercury. In this study, the oral administration of alpha-mercapto-beta-(2-furyl)-acrylic acid (MFA) protects against cadmium-induced malformations and embryonic death. This protection is probably mediated by the chelation of the cadmium ion rather than metallothionein (MT) synthesis. 相似文献
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Sexual mimicry among animals is widespread, but does it impart a fertilization advantage in the widely accepted 'sneak-guard' model of sperm competition? Here we describe field results in which a dramatic facultative switch in sexual phenotype by sneaker-male cuttlefish leads to immediate fertilization success, even in the presence of the consort male. These results are surprising, given the high rate at which females reject copulation attempts by males, the strong mate-guarding behaviour of consort males, and the high level of sperm competition in this complex mating system. 相似文献
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Castro-Tirado AJ de Ugarte Postigo A Gorosabel J Jelínek M Fatkhullin TA Sokolov VV Ferrero P Kann DA Klose S Sluse D Bremer M Winters JM Nuernberger D Pérez-Ramírez D Guerrero MA French J Melady G Hanlon L McBreen B Leventis K Markoff SB Leon S Kraus A Aceituno FJ Cunniffe R Kubánek P Vítek S Schulze S Wilson AC Hudec R Durant M González-Pérez JM Shahbaz T Guziy S Pandey SB Pavlenko L Sonbas E Trushkin SA Bursov NN Nizhelskij NA Sánchez-Fernández C Sabau-Graziati L 《Nature》2008,455(7212):506-509
Magnetars are young neutron stars with very strong magnetic fields of the order of 10(14)-10(15) G. They are detected in our Galaxy either as soft gamma-ray repeaters or anomalous X-ray pulsars. Soft gamma-ray repeaters are a rare type of gamma-ray transient sources that are occasionally detected as bursters in the high-energy sky. No optical counterpart to the gamma-ray flares or the quiescent source has yet been identified. Here we report multi-wavelength observations of a puzzling source, SWIFT J195509+261406. We detected more than 40 flaring episodes in the optical band over a time span of three days, and a faint infrared flare 11 days later, after which the source returned to quiescence. Our radio observations confirm a Galactic nature and establish a lower distance limit of approximately 3.7 kpc. We suggest that SWIFT J195509+261406 could be an isolated magnetar whose bursting activity has been detected at optical wavelengths, and for which the long-term X-ray emission is short-lived. In this case, a new manifestation of magnetar activity has been recorded and we can consider SWIFT J195509+261406 to be a link between the 'persistent' soft gamma-ray repeaters/anomalous X-ray pulsars and dim isolated neutron stars. 相似文献
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Summary Sodium arsenate crosses the placental barrier in pregnant Syrian hamsters following injection in teratogenic or tracer doses on the 8th day of gestation.This work was supported by USPHS grant ES-00697. 相似文献
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Cadmium effects and biochemical status in hamsters following acute exposure in late gestation 总被引:1,自引:0,他引:1
Summary A normally teratogenic dose of cadmium ions administered to hamsters late in gestation does not cross the placental barrier nor does it result in placental pathology. Our finding, which differs from data for other rodents, may be due to differences in the chemical status of cadmium in the placental cytosols.This project has been financed in part with Federal funds from the U. S. Environmental Protection Agency under grant number R 81 1078. The contents do not necessarily reflect the views and policies of the Environmental Protection Agency nor does mention of trade names or commerical products constitute endorsement of recommendation for use. 相似文献
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