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 anandami
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Contact: Kristen Cole
Kristen_Cole@brown.edu
401-863-7508
Brown University
11-Oct-1999