Researchers at Brown University in Rhode Island have shown that anandamide, a cannabinoid-like chemical produced naturally in the body, plays a role in mediating the sensation of pain.
Experimenters electrically stimulated rats in a part of their brain called the periaqueductal grey (PAG) which connects the spinal cord with cerebral hemispheres. The PAG is nearly identical in animals and humans. Stimulating the PAG simulates pain, and the rats' brains produced anandamide in response to the pain sensations.

Scientists also injected a chemical irritant into the rats which creates "lasting agony," and the poor beasts' anandamide levels reached even higher.

Anandamide levels were measured using mass spectrometer technology. Lead rat-torturer/researcher Dr Walker said the findings could be useful for pain treatment where opiates are ineffective.