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Endogenous opioids and placebo analgesia

Richard Norman rsnorman at mediaone.net
Thu Jan 27 13:04:08 EST 2000

Where the treatments double blind?  That is, did the experimenter
know which group the subjects were in ?  That might influence the

My first guess is that this is a problem in methodology that the
psychologists are probably more experienced at dealing with.
Physiologists assume that things have simple physical causes
and therefore experiments should work the way the experimental
design indicates.  Unfortunately when you get people involved
as subjects (instead of, say, cells that can't think on their own),
things go terribly wrong.

So are you sure the instructions to the subjects and the details of
how they were approached and questioned carefully controlled?
Are the results really statistically significant?

But your thesis committee probably already went into those questions.

Steve Palmer <spalmer at mdanderson.org> wrote in message
news:86pnq9$pjg$1 at oac2.hsc.uth.tmc.edu...
>     My name is Stephen Palmer, and I am a postdoc at the Dept. of Pain
> Research at the M.D. Anderson Cancer Center, having recently defended my
> dissertation at SUNY Stony Brook.
>     I am writing the group because my dissertation produced results I
> explain, and I am wondering if any of you have any suggestions about what
> may have occurred .  My dissertation addressed the subject of placebo
> analgesia and endogenous opioids.  Previous research has found that
> can alleviate various kinds of pain, but that naloxone (an opioid
> antagonist) can reverse or weaken placebo analgesia.
>     My study was intended to be a replication and extension of the
> research.  I used a 2x2 design in which all subjects received an
> infusion, but half were told that they would receive a potent pain
> while the other half were told that they would only get saline.  In
> actuality, some subjects received saline while others got naloxone.  Cold
> pressor tests (a pain tolerance task) were given before and after the
> infusion.
>     What I expected what that subjects who were told to expect a pain
> reliever but who got saline instead would show a reduction in pain (i.e.
> placebo analgesia).  Subjects who got the pain reliever message plus
> naloxone, on the other hand, would show no change in pain, or at least a
> smaller reduction than the pain reliever/saline group.  The groups who
> told they were getting only saline (and really got either saline or
> naloxone) would show no change.
>     This didn't happen.  Instead, only the pain reliever/naloxone group
> showed pain relief!  The other three groups showed either no change or
> increased pain.  This finding is unlike anything in the prior literature,
> and I have no explanation for it.
>     My question to you is, is there any literature out there which can
> explain these findings?  Are there any other studies, perhaps unpublished
> ones, which have found the same results?  I would appreciate any input you
> could give.

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