In another test the animals were made to swim in a container from which they could notescape. Bacteria-fed mice attempted to swim for longer than the others before they gave upand had to be rescued. Such persistence is usually interpreted by students of rodentbehaviour as evidence of a more positive mood.
在另一组测试中,研究人员让这些动物在一个无法逃脱的容器内游泳。在这些小鼠放弃游泳并不得不被救出之前,李糖乳杆菌喂养的小鼠试图游泳的时间比其它小鼠更长。这种持久性经常被研究啮齿类动物行为的学生解释为更积极情绪的证据。
Direct measurements of the animals brains supported the behavioural results. Levels ofcorticosterone, a stress hormone, were markedly lower in the bacteria-fed mice than theywere in the control group when both groups were exposed to stressful situations. Thenumber of receptors for gamma-aminobutyric acid, a natural chemical messenger that helpsdampen the activity of certain nerve cells, varied in statistically significant ways between thebrains of the two groups, with more in some parts of the treated animals brains and fewer inothers. Most intriguing of all, when Dr Bravo cut the animals vagus nerveswhich transmitsignals between the gut and the brainthe differences between the groups vanished.
对这些动物大脑的多次直接测量结果支持了行为学方面的效果。当两组小鼠进行应激实验时,喂食李糖乳杆菌的小鼠体内的应激激素皮质甾酮含量比那些对照组的小鼠体内要明显低地多。-氨基丁酸是有助于抑制特定神经细胞活动的自然化学信使。两组小鼠的大脑中-氨基丁酸感受器的数目以统计学上显著的方式改变。-氨基丁酸感受器在处理过的小鼠大脑的一些部分出现较多些,而在没有处理过的小鼠大脑内则少些。最引人注目的是,当布拉沃博士切断这些动物的迷走神经---传输肠道和大脑之间的信号---两组小鼠间的差异突然消失了。
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