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271.
Animals learn that a tone can predict the occurrence of an electric shock through classical conditioning. Mice or rats trained in this manner display fear responses, such as freezing behaviour, when they hear the conditioned tone. Studies using amygdalectomized rats have shown that the amygdala is required for both the acquisition and expression of learned fear responses. Freezing to a conditioned tone is enhanced following damage to the dorsal part of the medial prefrontal cortex, indicating that this area may be involved in fear reduction. Here we show that prefrontal neurons reduce their spontaneous activity in the presence of a conditioned aversive tone as a function of the degree of fear. The depression in prefrontal spontaneous activity is related to amygdala activity but not to the freezing response itself. These data indicate that, in the presence of threatening stimuli, the amygdala controls both fear expression and prefrontal neuronal activity. They suggest that abnormal amygdala-induced modulation of prefrontal neuronal activity may be involved in the pathophysiology of certain forms of anxiety disorder. 相似文献
272.
Easton DF Pooley KA Dunning AM Pharoah PD Thompson D Ballinger DG Struewing JP Morrison J Field H Luben R Wareham N Ahmed S Healey CS Bowman R;SEARCH collaborators Meyer KB Haiman CA Kolonel LK Henderson BE Le Marchand L Brennan P Sangrajrang S Gaborieau V Odefrey F Shen CY Wu PE Wang HC Eccles D Evans DG Peto J Fletcher O Johnson N Seal S Stratton MR Rahman N Chenevix-Trench G Bojesen SE Nordestgaard BG Axelsson CK Garcia-Closas M Brinton L Chanock S Lissowska J Peplonska B Nevanlinna H 《Nature》2007,447(7148):1087-1093
Breast cancer exhibits familial aggregation, consistent with variation in genetic susceptibility to the disease. Known susceptibility genes account for less than 25% of the familial risk of breast cancer, and the residual genetic variance is likely to be due to variants conferring more moderate risks. To identify further susceptibility alleles, we conducted a two-stage genome-wide association study in 4,398 breast cancer cases and 4,316 controls, followed by a third stage in which 30 single nucleotide polymorphisms (SNPs) were tested for confirmation in 21,860 cases and 22,578 controls from 22 studies. We used 227,876 SNPs that were estimated to correlate with 77% of known common SNPs in Europeans at r2 > 0.5. SNPs in five novel independent loci exhibited strong and consistent evidence of association with breast cancer (P < 10(-7)). Four of these contain plausible causative genes (FGFR2, TNRC9, MAP3K1 and LSP1). At the second stage, 1,792 SNPs were significant at the P < 0.05 level compared with an estimated 1,343 that would be expected by chance, indicating that many additional common susceptibility alleles may be identifiable by this approach. 相似文献
273.
曹庆杰 《科技导报(北京)》2007,25(23):33-37
SD振子及SD吸引子的动力学行为决定于一个光滑参数α的连续变化。当α>0时,系统表现为光滑特征;当α=0时,系统表现为不连续特性。这是一个具有强非线性特征的振动系统,它提供了一个从光滑动力学行为向不连续动力学行为光滑转迁的典型示范,这种直接的转迁并不需要连续系统的过渡。当系统为光滑动力学性态时,表现出与Duffing系统类似的双井等标准动力学行为;当系统表现为不连续性态时,除表现为标准的双井动力学行为外,也表现出如类鞍点和类同宿轨道等非标准动力学行为,展示了这个系统的转迁过程和特性及其相应的吸引子的复杂动力学行为。 相似文献