A soldier cuts open an opium poppy capsule at a poppy field, during eradication supervised by the Mexican Army on the outskirts of Morelia, Mexico, Thursday, March 4, 2010. (Carlos Jasso)

An international team of scientists has discovered a means of curbing addictions to morphine and heroin in mice and rats while alleviating chronic pain.

By targeting a certain type of pain-receptor cell that amplifies drug cravings the team is confident it has found a mechanism in the human immune system that will eventually lead to more effective therapies for treating addictions to opiates.

“We are identifying a whole new player in this game of drug addiction and chronic pain, which changes how you approach it,” says Linda Watkins, a neuroscience professor at the University of Colorado, Boulder, and the team’s lead researcher. “Are we walking down a path where you can increase the usefulness of opiates without making a whole bunch of drug addicts? We think so.”

In conjunction with Mark Hutchinson, ARC Research Fellow at the University of Adelaide, in Australia, Watkins published an article about the findings in the Aug. 15 edition of The Journal of Neuroscience.

The research, funded largely by grants from the National Institutes of Health, could apply to more substances than just opiates, Watkins says. The trans-Atlantic team is wading into research about cocaine, alcohol and methamphetamine addiction. “We think this is going to be very broad,” she says. 

The team’s findings are based on studies of how certain glial cells,
which generally support neuron activity, activate in the brain and
spinal cord when patients suffer chronic pain. Researchers discovered that morphine, among other opiates, bind to an immune receptor called Toll-Like receptor 4 (TLR4), which has dual functions of broadcasting intense pain and making drugs feel more rewarding. Tests show that a drug called (+)-naloxone can modify TLR4 so that it reduces the drug reward while maintaining pain relief.

“They’re like volume controls,” Watkins says. “They can dial up the pain or the drugs. That juxtaposition makes them very special.”

Tests on rats and mice have been successful. Watkins says clinical trials on humans could begin in 18 months. If they’re successful, Watkins says a modified version of (+)-naloxone — a “super morphine,” in pill form — could present a safer medication for people suffering chronic pain.

“The problem with opiates now is that physicians are scared of making patients addicts, and patients are scared of becoming addicts,” Watkins says.

Watkins knows that curing drug cravings is more than just a physical challenge, given that addiction to opiates can change a person’s brain chemistry. Researchers at the National Institute on Drug Abuse are currently investigating how such treatment would affect a person’s brain, she says.

Follow Gregory Thomas on Twitter: @gregrthomas

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