bigpig

There were some apparent exceptions to the general
correlation observed between adenosine-receptor binding
and stimulation. One of these was a compound called
3-isobuty1-1-methylxanthine(IBMX), which bound very
(50) well but actually depressed mouse locomotion. Snyder
et al suggest that this is not a major stumbling block 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
(55) known only for its stimulatory effects, displays this
property, depressing mouse locomotion at very low
concentrations and stimulating it at higher ones.
最后一段也很简单，这也是GMAT文章很普遍的一个现象：为了表示其理论的严谨性，通常作者一会一杆子打死所有反驳，他会承认，的确是有例外的，我不是说没有例外，但是这些例外是可以解释的――不用我说，大家也该知道，S解释的内容才是本段的重点。
化一秒钟回顾本段内容：
存在例外比如IBMXS解释说…况且…
从这里再次看到，S反驳永远通过两个方面来进行，逻辑极其严密。

bigpig

To buttress their case that caffeine acts instead by pre-
(35) venting 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
(40) 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 locomo-
tion.” Theophylline, a close structural relative of caffeine
and the major stimulant in tea, was one of the most
(45) effective compounds in both regards.
本段很简单。化1秒钟问自己：本段讲了些什么？
To buttress…所以做实验实验总结in general说…举例来说，小T…
本段出现的新名词是小T。
再次赞叹GMAT逻辑的严密：反驳老理论还不够，必须通过实践来支持其反驳。实验结果证实了S的理论。这还不够，又通过一个类似的小T的例子加强说明。

bigpig

For many years, caffeine’s effects have been attri-
(20) buted to its inhibition of the production of phosphodi-
esterase, an enzyme that breaks down the chemical
called cyclic AMP.A number of neurotransmitters exert
their effects by first increasing cyclic AMP concentra-
tions in target neurons. Therefore, prolonged periods at
(25) the elevated concentrations, as might be brought about
by a phosphodiesterase inhibitor, could lead to a greater
amount of neuron firing and, consequently, to behav-
ioral stimulation. But Snyder et al point out that the
caffeine concentrations needed to inhibit the production
(30) of phosphodiesterase in the brain are much higher than
those that produce stimulation. Moreover, other com-
pounds that block phosphodiesterase’s activity are not
stimulants.
既然出现了老理论，一定会出现对老理论的反驳。所以老理论本身内容不重要，如何反驳才是最重要的。这里的BUT要注意，but后出现了S人物，又出现了point out，大家就知道，这里就是S对于老理论的反驳了。后面又出现了一个Moreover，说明是S人物进一步的阐述――从这里可以看出GMAT阅读文章论述上的严谨：从一个角度反驳不够，还会从另外一个角度增加反驳的力度和严谨性。
本段有几个语言现象是值得注意的：1.therefore和consequently，表示顺接总结上面的意思，就说明还是在说老理论，时间非常紧张的时候就可以略过不读，当然我本人建议能读都要读，帮助理解也帮助理清逻辑关系；2. for many years表示老理论内容；3. but转折后出现了S人物和point out，说明S要开始反驳了，要特别注意反驳的内容。4. Moreover说明是S反驳的另外一个角度。
看完本段，又要化两秒种回顾一下，本段的内容是什么？
很明显，本段说的是老理论，以及对老理论的反驳。用一句话来概括，就是：老理论认为C是提高balabala的浓度来作用的，S反驳说这样的浓度比C能引起刺激的浓度小得多，而且，其他类似的物质也没有这样的作用。（更清晰的，可以这样总结：老理论认为…，而S提出来两点来反驳，第一点是…，第二点是…）
（说到这里，我忍不住要说点题外话：大家可以看到S对老理论的反驳，非常的符合GMAT的逻辑精神。这个片段完全可以出成一个CR题目。所以说，GMAT中各个部分是融会贯通的，而RC某种程度来说就是一个大逻辑。这里留个作业给大家，请大家自己回答：S采取了哪两种方法来weaken老理论？）
本段出现的新名词是PH，AMP