Neurons involved in drug addiction relapse identified

Environmental cues associated with prior drug use can provoke a relapse. In a new study, scientists have linked the relapse behavior to specific nerve cells in a part of the brain called the nucleus accumbens. The findings may foster further research into what makes long-abstinent drug users prone to relapse and lead the way to new strategies for treating drug addiction.

“The study finds an increase in neuronal activity that persists after the behavioral response of seeking the drug is absent,” says George Koob, PhD, an addiction researcher at the Scripps Research Institute. “This suggests the existence of a neuroadaptation that may make individuals more vulnerable to resuming drug-taking behavior.”

The study appears in the August 13 issue of The Journal of Neuroscience and was supported by the National Institute on Drug Abuse.

In the study, rats learned that when a tone was sounded they could press a lever and self-administer cocaine. No cocaine was given if the animal pressed the lever in the absence of the tone. Microelectrodes recorded the activity of single neurons in the nucleus accumbens, an area of the brain previously shown to be involved in addiction.

After two weeks of self-administering cocaine, the lever and the tone were removed, and the animals were abstinent for nearly a month. When the lever was returned to the cage, but no cocaine was provided and no tone was sounded, the animals ignored the lever. But when the tone was again sounded, the animals began to press the lever at a fairly high rate, even though no cocaine was given. During this relapse into drug-seeking behavior, neurons in an area of the nucleus accumbens known as the shell were activated by the tone.

The animals eventually stopped pressing the lever—even when the tone was sounded—because no cocaine was dispensed. But brain recordings still showed accumbens neuron activity in response to the tone.

“This activity may reflect the processing of memories that persist even after a long abstinence and may partially explain why environmental cues can provoke a relapse,” says primary author Mark West, PhD, a psychologist at Rutgers University.

West’s co-authors include Udi E. Ghitza, Anthony T. Fabbricatore, Volodymyr Prokopenko and Anthony P. Pawlak. West is a member of the Society for Neuroscience, an organization of more than 32,000 basic scientists and clinicians who study the brain and nervous system. The Society publishes The Journal of Neuroscience. West can be reached at (201) 602-3414.