STUDY SHOWS HOW MARIJUANA AFFECTS PAIN

WASHINGTON, Oct 11 (Reuters) - Pain triggers the release of the brain's
natural version of marijuana, researchers said on Monday.

Their finding helps explain why marijuana can act to relieve pain and adds
to a whole series of studies that show the chemical, one of a class known as
anandamides, has a range of important roles in the brain.

Michael Walker, a psychology professor at Brown University in Providence,
Rhode Island, and colleagues tested pain and anandamide in rats.

They found the brain produced anandamide when they stimulated an area -- the
periaqueductal gray -- known for its role in modulating pain. It also
released anandamide in response to a painful injection of the chemical formalin.

The secretion of anandamide eased the pain, they reported in the Proceedings
of the National Academy of Sciences.

The researchers anaesthetised their rats, but were able to follow the pain
signals and the passage of anandamide in the brain using a new type of mass
spectrometry, which is able to detect minute amounts of a substance.

Walker said the knowledge might be used to devise new painkillers or
analgesics. Perhaps a drug that made more anandamide available would be
useful, he said.

"There are some types of pain that do not respond well to current
treatments," he said in a statement. "The fact that you have different
modulatory systems that are effective for different types of pain may offer
hope."

Anandamides are neurotransmitters -- message-carrying chemicals -- and are
known to be chemically very similar to cannabinoids in cannabis or marijuana.

Cannabis has been used for centuries to help relieve pain.

Other research has found a range of uses for anandamides.

In May, researchers at the University of California at Irvine found that
people with schizophrenia have twice the normal levels anandamide in their
brains.

Anandamides have also been found to help regulate body movement and
coordination, and may also be important in helping sperm get to and
fertilise an egg.