-Caveat Lector-
http://www.eurekalert.org/releases/bu-brm100899.html
EMBARGOED FOR RELEASE: 11 OCTOBER 1999 AT 17:00 ET US
Contact: Kristen Cole [EMAIL PROTECTED]
401-863-7508
Brown University
Brain releases marijuana-like substance in response to pain, study
finds
PROVIDENCE, R.I. - Pain triggers the brain's release of a naturally
produced cannabinoid, a compound similar to the active ingredient in
marijuana, according to a new study by Brown researchers that documented its
release in the brain's pain response system for the first time.
The cannabinoid known as anandamide produced analgesia - the absence
of a normal sense of pain - in response to pain in anesthetized rats. The
findings are published in the Oct. 12 issue of the Proceedings of the
National Academy of Sciences (PNAS).
Although the existence of non-opiate factors in the brain's pain
suppression system were first noted 20 years ago, little was known about
these substances. Brown researchers were able to measure the anandamide
using a new type of mass spectrometry, which is able to detect minute
amounts of a substance.
Knowledge about a pain-modulatory system based on cannabinoids is
valuable for the future treatment of pain, particularly in instances where
opiates are ineffective, according to J. Michael Walker, psychology
professor and lead researcher.
"There are some types of pain that do not respond well to current
treatments," said Walker. "The fact that you have different modulatory
systems that are effective for different types of pain may offer hope."
Drugs that inhibit the reuptake of anandamide by cells, or block its
degradation, may form the basis of a modern pharmacotherapy for pain, he
said.
Researchers measured the levels of anandamide in the region of the
brain recognized for its role in pain modulation - the periaqueductal gray
(PAG). The PAG is part of the brain stem that connects the cerebral
hemispheres with the spinal cord. It is very similar in animals and humans.
Electrical stimulation of the PAG in anesthetized animal models was
accompanied by both pain suppression and a marked increase in the release of
anandamide. Furthermore, injections of formalin, a chemical irritant that
induces prolonged pain, profoundly elevated the anandamide levels in the
same location of the PAG in anesthetized rats. Although animals did not feel
the pain, researchers were able to observe pain modulation because the brain
responds in the same way.
Researchers used atmospheric pressure-chemical ionization mass
spectrometry to measure the molecular weight of anandamide. This multistep
method permitted the detection of the extremely small amounts of the
anandamide. They found the substance in a different location of the PAG than
the location proven to play a part in the release of natural opiates.
"One of the functions of chemical transmission in the brain is to
modify pain sensitivity, and the brain uses the anandamide for this
purpose," said Walker. "The pain itself triggers this reaction."
The correlation between cannabinoids and pain suppression is not a
startling finding in itself; cannabinoids have been used to treat pain for
centuries. In ancient China, hemp extract was used as a surgical anesthetic,
and archaeological finds in Israel have revealed its use against the pain of
childbirth.
Cannabis is still used to treat pain, despite its illegal status in
most parts of the world. A report early this year by the National Academy of
Sciences Institute of Medicine found that significant amounts of research -
including research by Walker and colleagues - point to the potential to use
marijuana derivatives in treating chronic pain.
However, more research needs to be done to determine whether there
are other naturally produced cannabinoids released in the brain in addition
to anandamide, said Walker.
Other researchers involved in the study were Susan M. Huang, Brown
graduate student; Nicole M. Strangman, Brown graduate student; M. Clara
Saûudo-Peûa, assistant research professor of psychology; and the late Brown
University professor and member of the Chinese Academy of Sciences, Kang
Tsou. The work was supported with funding from the U.S. Public Health
Service and National Institutes of Health. In addition, Brown University and
the National Institute on Drug Abuse financed the purchase of the mass
spectrometer used in the experiments.
###
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