大全-10-3（10/63杨继第10篇）咖啡因

steinlala

第三题，看了携隐的示例，懂了，但是示例中用的是文字定位法，从语义上去理解，还是不太明白，希望NN指导～～～

文章：
Passage 10 (10/63)
Caffeine, the stimulant in coffee, has been called “the most widely used psychoactive substance on Earth.” Snyder, Daly and Bruns have recently proposed that caffeine affect behavior by countering the activity in the human brain of a naturally occurring chemical called adenosine. Adenosine normally depresses neuron firing in many areas of the brain. It apparently does this by inhibiting the release of neurotransmitters, chemicals that carry nerve impulses from one neuron to the next. Like many other agents that affect neuron firing, adenosine must first bind to specific receptors on neuronal membranes. There are at least two classes of these receptors, which have been designated A1 and A2. Snyder et al (et al: abbr. (Lat) 以及其他人，等人) propose that caffeine, which is structurally similar to adenosine, is able to bind to both types of receptors, which prevents adenosine from attaching there and allows the neurons to fire more readily than they otherwise would.
For many years, caffeine’s effects have been attributed to its inhibition of the production of phosphodiesterase, an enzyme that breaks down the chemical called cyclic AMP. A number of neurotransmitters exert their effects by first increasing cyclic AMP concentrations in target neurons. Therefore, prolonged periods at the elevated concentrations, as might be brought about by a phosphodiesterase inhibitor, could lead to a greater amount of neuron firing and, consequently, to behavioral stimulation. But Snyder et al point out that the caffeine concentrations needed to inhibit the production of phosphodiesterase in the brain are much higher than those that produce stimulation. Moreover, other compounds that block phosphodiesterase’s activity are not stimulants.
To buttress their case that caffeine acts instead by preventing adenosine binding, Snyder et al compared the stimulatory effects of a series of caffeine derivatives with their ability to dislodge adenosine from its receptors in the brains of mice. “In general,” they reported, “the ability of the compounds to compete at the receptors correlates with their ability to stimulate locomotion in the mouse; i.e., the higher their capacity to bind at the receptors, the higher their ability to stimulate locomotion.” Theophylline, a close structural relative of caffeine and the major stimulant in tea, was one of the most effective compounds in both regards.
There were some apparent exceptions to the general correlation observed between adenosine-receptor binding and stimulation. One of these was a compound called 3-isobutyl-1-methylxanthine (IBMX), which bound very well but actually depressed mouse locomotion. Snyder et al suggests that this is not a major stumbling block (stumbling block: n.障碍物, 绊脚石) to their hypothesis. The problem is that the compound has mixed effects in the brain, a not unusual occurrence with psychoactive drugs. Even caffeine, which is generally known only for its stimulatory effects, displays this property, depressing mouse locomotion at very low concentrations and stimulating it at higher ones.

题目：
According so Snyder et al, caffeine differs from adenosine in that caffeine
(A) stimulates behavior in the mouse and in humans, whereas adenosine stimulates behavior in humans only
(B) has mixed effects in the brain, whereas adenosine has only a stimulatory effect
(C) increases cyclic AMP concentrations in target neurons, whereas adenosine decreases such concentrations
(D) permits release of neurotransmitters when it is bound to adenosine receptors, whereas adenosine inhibits such release
(E) inhibits both neuron firing and the production of phosphodiesterase when there is a sufficient concentration in the brain, whereas adenosine inhibits only neuron firing

正确答案：
(D) permits release of neurotransmitters when it is bound to adenosine receptors, whereas adenosine inhibits such release

关于携隐的文字定位法得出答案，基本明白了，但从语义上不明白。

杨继书中的答案：
D、正确。当咖啡因附着在腺苷的受体上时，会促成神经元传导物质的释放，而腺苷抑制此种作用。见原文L19-L25，咖啡因附着腺苷受体上阻止腺苷附着。因此它肯定会促进神经元传导物质的释放。

疑问：
“咖啡因附着腺苷受体上阻止腺苷附着”，这个我承认，但是这就能得到“它肯定会促进神经元传导物质的释放”的结论吗？

不明白～～～～～

zm_patrickS

D选项并没有说会促进，只是说 permits, 允许、许可，在这里可以是‘造成’的意思。杨继用“促成”也没有促进的意思。

steinlala

怎么看得出来“permits release of neurotransmitters ” 呢？

steinlala

第一段前部分说Adenosine 这种东西会 inhibiting the release of neurotransmitters ，后部分说caffeine这种东西可以prevents adenosine from attaching there（these receptors），caffeine抑制adenosine触碰receptors，这就能说明caffeine允许neurotransmitters的释放吗？

还是不懂~~~~

steinlala

这道题的题目问caffeine differs from adenosine，两者之间的区别，但是文中并没有强对比的信息呀，甚至连弱对比我都没有找到，这是属于什么题型呢？ 取非吗？不像。细节题？或者其他什么？？

imbalancey

同问啊 ，怎么也看不出来哪说了permits release of neurotransimtters