Researchers map brain's opioid response in mice

New experiments show how the striatum changes when the highly addictive drug is used.

Brian P. Dunleavy
Researchers in Sweden say they have mapped the region of the brain involved in opioid addiction. Photo by TheDigitalArtist/Pixabay
Researchers in Sweden say they have mapped the region of the brain involved in opioid addiction. Photo by TheDigitalArtist/Pixabay

Dec. 24 (UPI) -- Researchers may be closer to solving some of the mysteries of the brain processes involved in opioid addiction, thanks to a new imaging approach tested in mice.

In experiments performed at the Karolinska Institutet in Stockholm, scientists were able to visualize the organization of different opioid islands in the striatum, the inner part of the brain that regulates rewards, motivation, impulses and motor function. They published the so-called spatio-molecular map Tuesday in the journal Cell Reports.


"Our map forms the basis for a new understanding of the brain's probably most important network for decision-making," lead author Konstantinos Meletis, associate professor of neuroscience at Karolinska Institutet, said in a statement. "It may contribute to an increased understanding of both normal reward processes and the effects of various addictive substances on this network."

According to the U.S. Department of Health and Human Services, more than 10 million Americans misuse opioids, and nearly 50,000 die annually from overdose-related causes. The problem has been referred to as an epidemic.

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In general, the striatum is believed to play a pivotal role in decision-making and the development of various addictions. To learn how, if at all, the region of the brain changes in response to opioids, Meletis and the team created a molecular three-dimensional map of the nerve cells targeted by the highly addictive drugs -- like morphine and heroin -- and showed how they are organized in the striatum.


They did this using single-nucleus RNA sequencing, a method developed to study small differences in individual cells. The resulting "map" of the striatal gene expression, they said, provides the first demonstration of the molecular codes that divide the striatum into three main sub-regions -- a spatial, a patch-matrix and a cell-type specific organization -- after opioids are used.

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The researchers describe their findings as an important step toward understanding how the brain's network governing motivation and drug addiction is organized. This new knowledge, they said, may form the basis for the development of new treatments.

"With this new knowledge we may now begin to analyze the function of different types of nerve cells in different molecularly defined areas," Meletis said. "This is the first step in directly defining the networks' role in controlling decision-making and addiction with the help of optogenetics."

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