MARIJUANA-LIKE SUBSTANCE IN BRAIN RELIEVES PAIN

Pain triggers the release of a marijuana-like chemical called anandamide
deep in the brain that works as a natural pain reliever, report US
researchers.

The finding ``may have relevance for the treatment of pain, particularly in
instances where opiates are ineffective,'' according to a report published
in the October 12th issue of the Proceedings of the National Academy of
Sciences. For the first time, anandamide levels were measured in rat brains
using a sensitive method for detecting cannabinoids (marijuana-like
compounds), according to J. Michael Walker and colleagues at Brown
University in Providence, Rhode Island.

The researchers used fine wires to stimulate an area of the rat brain
associated with pain perception. According to the results, stimulation of
this area -- called the periaqueductal gray (PAG) -- resulted in greatly
diminished pain sensitivity in the rat. Furthermore, pain perception
returned to normal when the researchers administered a substance that
blocked anandamide.

The fall in pain perception was paralleled by a significant rise in the
levels of anandamide in the PAG, the scientists report.

Anandamide levels in the brain also rose significantly in response to
painful stimuli, the report indicates.

Taken together, these results support the existence of a pain control
system within the PAG ``that is triggered by pain and promotes analgesia
through the release of anandamide,'' Walker and colleagues conclude.

The researchers suggest that drugs that affect the anandamide system might
form the basis of a modern approach to the treatment of pain.

SOURCE - Proceedings of the National Academy of Sciences
1999;96:12198-12203.