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In order to investigate further the relationship between maternal diabetes and fetal malformation, rat embryos were grown in vitro in the presence of beta-hydroxybutyrate, one of the ketone bodies produced by diabetics. At 10 mM, beta-hydroxybutyrate produced minor abnormalities and at 20 mM it produced major abnormalities in rat embryos. 相似文献
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Long-distance intraretinal connections in birds 总被引:1,自引:0,他引:1
Electrophysiological experiments have shown in both birds and mammals that remote parts of the retina, several millimetres apart, interact at the retinal level. The anatomical basis of this is poorly understood, although in mammals some cells in the ganglion cell layer have axons that terminate in the inner plexiform layer several millimetres from the cell body. In birds, the longest previously reported intraretinal connections were from amacrine cells, extending only a few hundred microns. But we here describe very long connections that span almost the entire extent of the retina in chicks and chick embryos. The parent cell bodies are in the inner nuclear layer of the ventral half of the retina, and they project in topographical order onto the dorsal half. They do not project to the brain. They may be involved in selective switching of attention between the upper and lower parts of the visual field, at an unprecedentedly early stage of visual processing. 相似文献
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More evidence of an advanced hominid at Swartkrans 总被引:1,自引:0,他引:1
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The subglacial Lake Vostok may be a unique reservoir of genetic material and it may contain organisms with distinct adaptations, but it has yet to be explored directly. The lake and the overlying ice sheet are closely linked, as the ice-sheet thickness drives the lake circulation, while melting and freezing at the ice-sheet base will control the flux of water, biota and sediment through the lake. Here we present a reconstruction of the ice flow trajectories for the Vostok core site, using ice-penetrating radar data and Global Positioning System (GPS) measurements of surface ice velocity. We find that the ice sheet has a significant along-lake flow component, persistent since the Last Glacial Maximum. The rates at which ice is frozen (accreted) to the base of the ice sheet are greatest at the shorelines, and the accreted ice layer is subsequently transported out of the lake. Using these new flow field and velocity measurements, we estimate the time for ice to traverse Lake Vostok to be 16,000-20,000 years. We infer that most Vostok ice analysed to date was accreted to the ice sheet close to the western shoreline, and is therefore not representative of open lake conditions. From the amount of accreted lake water we estimate to be exported along the southern shoreline, the lake water residence time is about 13,300 years. 相似文献