this will hurt – and now we know why
TRANSCRIPT
This week–
YOU might not believe it, but telling a
lie can cause physical pain. What’s
more there is a name for it, the
nocebo effect.
It can take hold when patients
are given an inert pill and told it will
intensify unpleasant symptoms. Now
its biochemical pathway has been
traced – a breakthrough that could
lead to drugs that reduce pain.
In 1997, Fabrizio Benedetti of the
University of Turin, Italy, and his
colleagues found that patients
recovering from painful surgery
were not susceptible to the nocebo
effect when given injections of
proglumide, which blocks the
action of cholecystokinin (CCK), a
neurotransmitter associated with
anxiety. The team have now carried
out an experiment that shows the
neurotransmitter can turn anxiety
into pain (Journal of Neuroscience,
vol 26, p 12014).
Forty-nine volunteers raised one
forearm vertically until it drained of
blood, then a tourniquet was applied
to prevent its return. With the arm
resting on the bed, they repeatedly
squeezed a hand exerciser. This
would normally induce pain in the
forearm that becomes unbearable
after about 15 minutes.
The volunteers rated their
subjective pain every minute, and
each had blood samples taken just
before the test, and at 5 and 10
minutes after it started. The samples
were tested for the stress hormones
adrenocorticotropic hormone and
cortisol, which serve as an objective
proxy for the level of anxiety felt.
While volunteers given a nocebo
alone reported higher pain than the
control group which had received no
nocebo, subjects given nocebo plus
proglumide reported pain only
equivalent to the control group.
However, their blood chemistry
showed much higher anxiety levels -
the same as those who received just
nocebo. Benedetti says that
proglumide must stop CKK’s normal
function of turning chemical signals
of anxiety into exaggerated pain.
At present, proglumide is the only
CCK blocker licensed for human use,
and it is not particularly effective,
says Benedetti. The Italian team
is now working with drug companies
to produce CCK blockers that can
be incorporated into narcotics,
which will help alleviate both
physiological and psychological pain
simultaneously. Michael Brooks ●
This will hurt – and now we know why
12 | NewScientist | 25 November 2006 www.newscientist.com
–It’s the nocebo effect–
SAND
RA B
AKER
/ALA
MY
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