Scientists make pain-control discovery

Breakthrough could lead to drugs to help fight depression and addiction as well as discomfort

New drugs for treating a range of illnesses from depression to chronic pain could result from studies that reveal for the first time the detailed molecular structure of the brain's "pleasure molecules", scientists said.

Researchers have deciphered the atomic three-dimensional structure of the brain's opioid receptors, the protein molecules that are intimately involved in the control of pain and feelings of wellbeing, as well as being the target of the opioid drugs such as morphine, codeine and heroin.

They said that unravelling of the structure of the opioid receptors on such a minutely detailed level will accelerate the development of new drugs that can alleviate anxiety and depression as well as novel treatments for chronic pain and addiction.

"Once we see the structure of the receptor, it becomes easier for us to develop drugs that target the receptor in ways that might be beneficial for medical therapy," said Professor Bryan Roth of the University of North Carolina School of Medicine in Chapel Hill.

There are four types of opioid receptor which work together in ways that are not completely understood. Two of them have been deciphered by two teams of researchers who published their work in the journal Nature.

Professor Roth's group worked on the "kappa" opioid receptor which is known to respond to one of the most powerful natural hallucinogenic drugs, salvinorin A, which is derived from the plant Salvia divinorum, commonly known as "magic mint".

According to the US National Institute on Drug Abuse there has been a surge in the use of salvia among young Americans, with more than one in 20 young adults saying they have experimented with magic mint in the past year.

The second opioid receptor analysed in detail is the "mu" opioid which is involved in the control of pleasure and pain-relief by binding to the body's endorphin neurotransmitters. The same receptor is targeted by synthetic opioid drugs such as morphine, codeine and heroin – as well as opium.

While the kappa opioid receptor appears to elevate a person's mood, the mu receptor can depress mood and produce "dissociative psychedelic experiences", which is how magic mint produces its effect, the scientists said.

Studies on laboratory animals have indicated the drugs that can block the action of the kappa opioid receptors could be used to treat addiction, provide pain-relief and reduce the symptoms of irritable bowel syndrome, he said.

Even the psychedelic effect associated with the activation of the kappa receptor protein could be useful in providing fresh insights into human perception and consciousness, Professor Roth said.

Update: Spelling of opioid corrected.