Addiction to heroin and morphine can be blocked—and pain relief increased—in rats by targeting an immune system receptor with the drug (+)naloxone, according to a study to be published later today.

The discovery could lead to new drugs that combine pain relief with the ability to suppress addiction to opioid drugs, a team of Australian and U.S. researchers concluded in the study, to be published in the Journal of Neuroscience.

“Our studies have shown conclusively that we can block addiction via the immune system of the brain, without targeting the brain’s wiring,” lead author Mark Hutchinson, Ph.D., ARC Research Fellow in the University of Adelaide’s School of Medical Sciences, said in a statement. “Both the central nervous system and the immune system play important roles in creating addiction, but our studies have shown we only need to block the immune response in the brain to prevent cravings for opioid drugs.”

The team has focused its research efforts on an immune receptor called Toll-Like Receptor 4 (TLR4). While opioid drugs such as morphine and heroin may bind to TLR4 in much the same way bacteria normally binds to the immune system, researchers found that TLR4 acts more as an amplifier for addiction.

The drug (+)naloxone stops that amplification by automatically shutting down the addiction. In addition to stopping the craving for opioids, thus cutting out behaviors associated with addiction, the shutdown also changes brain neurochemistry by ending production of dopamine, a chemical linked to providing addicts with a sense of ‘reward’ from the drug.

“We’ve suspected for some years that TLR4 may be the key to blocking opioid addiction, but now we have the proof,” the study’s senior author, Linda Watkins, Ph.D., director of the Interdepartmental Neuroscience Ph.D. Program and a member of the Center for Neuroscience at University of Colorado Boulder, said in the statement. “This work fundamentally changes what we understand about opioids, reward, and addiction.

“This has the potential to lead to major advances in patient and palliative care,” Dr. Watkins added.

The (+)naloxone study follows by a week the publication of a study in Science Translational Medicine, in which researchers from The Scripps Research Institute found that the combination of buprenorphine and naltrexone caused rats to reduce their intake of cocaine with minimal risk of producing dependence on opioid drugs, “and may be useful as a treatment for cocaine addiction.”

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