RC - DEC 19

Caffeine, the stimulant in coffee, has been called
"the most widely used psychoactive substance on Earth ."
Synder, Daly and Bruns have recently proposed that
caffeine affects behavior by countering the activity in
(5) 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.
(10) 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 propose that caffeine, which is struc-
(15) turally 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 attri-
(20) buted 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
(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 behavioral
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 compounds
that block phosphodiesterase's activity are not
stimulants.
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 locomotion."
Theophylline, a close structural relative of caffeine
and the major stimulant in tea, was one of the most
(45) 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-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.

1. The primary purpose of the passage is to

(A) discuss a plan for investigation of a phenomenon that is not yet
fully understood
(B) present two explanations of a phenomenon and reconcile the
differences between them
(C) summarize two theories and suggest a third theory that overcomes
the problems encountered in the first two
(D) describe an alternative hypothesis and provide evidence and
arguments that support it
(E) challenge the validity of a theory by exposing the inconsistencies
and contradictions in it

2. 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

3. In response to experimental results concerning IBMX, Snyder et al
contended that it is not uncommon for
psychoactive drugs to have

(A) mixed effects in the brain
(B) inhibitory effects on enzymes in the brain
(C) close structural relationships with caffeine
(D) depressive effects on mouse locomotion
(E) the ability to dislodge caffeine from receptors in the brain

4. According to Snyder et al, all of the following compounds can bind
to specific receptors in the brain EXCEPT

(A) IBMX
(B) caffeine
(C) adenosine
(D) theophylline
(E) phosphodiesterase

5. Snyder et al suggest that caffeine's ability to bind to A1 and A2
receptors can be at least partially attributed to
which of the following?

(A) The chemical relationship between caffeine and phosphodiesterase
(B) The structural relationship between caffeine and adenosine
(C) The structural similarity between caffeine and neurotransmitters
(D) The ability of caffeine to stimulate behavior
(E) The natural occurrence of caffeine and adenosine in the brain

6. The author quotes Snyder et al in lines 38-43 most probably in order to

(A) reveal some of the assumptions underlying their theory
(B) summarize a major finding of their experiments
(C) point out that their experiments were limited to the mouse
(D) indicate that their experiments resulted only in general correlations
(E) refute the objections made by supporters of the older theory


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Archaeology as a profession faces two major problems.
First, it is the poorest of the poor. Only paltry
sums are available for excavating and even less is available
for publishing the results and preserving the sites
(5) once excavated. Yet archaeologists deal with priceless
objects every day. Second, there is the problem of illegal
excavation, resulting in museum-quality pieces being
sold to the highest bidder.
I would like to make an outrageous suggestion that
(10) would at one stroke provide funds for archaeology and
reduce the amount of illegal digging. I would propose
that scientific archeological expeditions and governmental
authorities sell excavated artifacts on the open
market. Such sales would provide substantial funds for
(15) the excavation and preservation of archaeological sites
and the publication of results. At the same time, they
would break the illegal excavator's grip on the market,
thereby decreasing the inducement to engage in illegal
activities.
(20) You might object that professionals excavate to
acquire knowledge, not money. Moreover, ancient artifacts
are part of our global cultural heritage, which
should be available for all to appreciate, not sold to the
highest bidder. I agree. Sell nothing that has unique
(25) artistic merit or scientific value. But, you might reply,
everything that comes our of the ground has scientific
value. Here we part company. Theoretically, you may be
correct in claiming that every artifact has potential scientific
value. Practically, you are wrong.
(30) I refer to the thousands of pottery vessels and ancient
lamps that are essentially duplicates of one another. In
one small excavation in Cyprus, archaeologists recently
uncovered 2,000 virtually indistinguishable small jugs in
a single courtyard, Even precious royal seal impressions
(35) known as/melekh handles have been found in abundance---
more than 4,000 examples so far.
The basements of museums are simply not large
enough to store the artifacts that are likely to be discovered
in the future. There is not enough money even to
(40) catalogue the finds; as a result, they cannot be found
again and become as inaccessible as if they had never
been discovered. Indeed, with the help of a computer,
sold artifacts could be more accessible than are the
pieces stored in bulging museum basements. Prior to
(45) sale, each could be photographed and the list of the
purchasers could be maintained on the computer A
purchaser could even be required to agree to return the
piece if it should become needed for scientific purposes.
It would be unrealistic to suggest that illegal digging
(50) would stop if artifacts were sold on the open market.
But the demand for the clandestine product would be
substantially reduced. Who would want an unmarked
pot when another was available whose provenance was
known, and that was dated stratigraphically by the
professional archaeologist who excavated it?

7. The primary purpose of the passage is to propose

(A) an alternative to museum display of artifacts
(B) a way to curb illegal digging while benefiting the archaeological profession
(C) a way to distinguish artifacts with scientific value from those
that have no such value
(D) the governmental regulation of archaeological sites
(E) a new system for cataloguing duplicate artifacts

8. The author implies that all of the following statements about
duplicate artifacts are true EXCEPT:

(A) A market for such artifacts already exists.
(B) Such artifacts seldom have scientific value.
(C) There is likely to be a continuing supply of such artifacts.
(D) Museums are well supplied with examples of such artifacts.
(E) Such artifacts frequently exceed in quality those already
catalogued in museum collections.

9. Which of the following is mentioned in the passage as a
disadvantage of storing artifacts in museum basements?

(A) Museum officials rarely allow scholars access to such artifacts.
(B) Space that could be better used for display is taken up for storage.
(C) Artifacts discovered in one excavation often become separated from
each other.
(D) Such artifacts are often damaged by variations in temperature and humidity.
(E) Such artifacts' often remain uncatalogued and thus cannot be
located once they are put in storage.

10. The author mentions the excavation in Cyprus (lines 31-34) to
emphasize which of the following points?

(A) Ancient lamps and pottery vessels are less valuable, although more
rare, than royal seal impressions.
(B) Artifacts that are very similar to each other present cataloguing
difficulties to archaeologists.
(C) Artifacts that are not uniquely valuable, and therefore could be
sold, are available in large quantities.
(D) Cyprus is the most important location for unearthing large
quantities of salable artifacts.
(E) Illegal sales of duplicate artifacts are wide-spread, particularly
on the island of Cyprus.

11. The author's argument concerning the effect of the official sale
of duplicate artifacts on illegal excavation is
based on which of the following assumptions?

(A) Prospective purchasers would prefer to buy authenticated artifacts.
(B) The price of illegally excavated artifacts would rise.
(C) Computers could be used to trace sold artifacts.
(D) Illegal excavators would be forced to sell only duplicate artifacts.
(E) Money gained from selling authenticated artifacts could be used to
investigate and prosecute illegal excavators.

12. The author anticipates which of the following initial objections
to the adoption of his proposal?

(A) Museum officials will become unwilling to store artifacts.
(B) An oversupply of salable artifacts will result and the demand for
them will fall.
(C) Artifacts that would have been displayed in public places will be
sold to private collectors.
(D) Illegal excavators will have an even larger supply of artifacts for resale.
(E) Counterfeiting of artifacts will become more commonplace