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Glia Stoke Morphine's Fires
By Jeanne Erdmann
ScienceNOW Daily News
SAN DIEGO, CALIFORNIA--Opioid drugs such as morphine are
the most powerful painkillers. Unfortunately, in some patients
their narcotic effects lead to addiction and the need for
ever-escalating doses to quell pain. New research with rats
shows that blocking morphine's action on glia--a type of support
cell in the nervous system--can reduce these downsides while
heightening its potency against pain.
Over the past decade, scientists have discovered that glial
cells heighten nerve pain, such as sciatica, by exciting the
neurons that transmit pain signals. Morphine deadens pain
by acting at nerve synapses, but it also activates glial cells,
possibly worsening the drug's side effects, such as drowsiness,
tolerance, worsening of pain, and addiction.
To tease apart morphine's effects on glia and neurons, neuroscientists
Linda Watkins and Mark Hutchinson of the University of Colorado,
Boulder, took advantage of a drug called AV411 that blocks
morphine's effects on glia but not on neurons. It boosted
the painkiller: Rats injected with AV411 and morphine showed
less response to a painful test than did rats given morphine
alone. Watkins and Hutchinson also found that over time, morphine
better retained its pain-relieving potency in the rats that
also received AV411.
Doctors prescribe morphine for pain relief, but opioids come
with the potential for addiction or abuse. To check for a
link between glia and morphine addiction, the pair tested
whether blocking morphine's effects on glial cells would keep
rats from craving the drug. In this test, the pain-free animals
learned that they would receive a drug in one area and not
in another. Animals that enjoy receiving a drug tend to return
to the drug area over and over. Rats in the AV411-plus-morphine
group wandered around rather than returning to the drug area,
the researchers reported here 5 November at the annual meeting
of the Society for Neuroscience.
By showing that glial cells "play a previously unsuspected
role in pathological pain," says Nora Volkow, director
of the National Institute on Drug Abuse, the research helps
pave the way toward developing new, potent, nonaddictive medications.
November 9, 2007
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