Washington - The brain stores the craving for cocaine in a different place than it registers the high caused by the drug, researchers said on Thursday in a finding that points to a promising new approach for treating addicts.
Scientists at the Albert Einstein College of Medicine in New York used rats to study a vexing problem - how to prevent cocaine addicts who seem to have kicked the habit from relapsing. The findings suggest that a solution may be blocking a brain chemical that largely has been overlooked in addiction research.
"If you listen to patients' stories, one thing that you hear over and over again are the intense cravings that are very, very hard to suppress and that eventually lead to the relapse," said Dr Stanislav Vorel, who led the research.
"So a major question is - what are these cravings, how are they triggered, how can we prevent them and how can patients learn to cope with them?" he added.
The researchers hooked the rats on cocaine by delivering intravenous doses when the rodents pushed a lever in their cages. The researchers then made the rats quit cold turkey by replacing the cocaine with a saline solution. After a week, the animals stopped pressing the lever seeking a cocaine fix.
The researchers then sought to trigger a relapse by electrically stimulating two parts of the brain.
One was the "reward" or "liking" center that registers the high from using the drug - a brain pathway that involves a chemical called dopamine.
The other was in the hippocampus region of the brain, which is associated with memory and involves glutamate, an entirely different brain chemical. This region appears to register the memory of a drug's effects and the craving for it, Vorel said.
Stimulating the hippocampus caused an intense craving for cocaine, the study found. The rats repeatedly pressed the lever that previously had delivered cocaine.
The researchers then demonstrated that a chemical that blocks glutamate prevented the relapse even in rats whose hippocampus region had been electrically stimulated.
The study was published in the journal Science.
In separate research that has not yet been published, Vorel said his laboratory found that electrical stimulation of the almond-shaped brain structure related to memory, the amygdala, also caused relapse.
Glutamate is a neurotransmitter involved in essential brain functions such as learning and memory. Vorel said developing a drug targeting glutamate may be able to help a cocaine addict quit the drug for good.
The development of drugs to treat cocaine addiction has consistently focused on dopamine, which is connected to the brain's "liking" region rather than the "wanting" produced by stimulating the memory area, said Vorel.
But Vorel's new research shows that glutamate could be a better target for anti-craving medication, he added.
Vorel said relapse is the single biggest obstacle to successful cocaine addiction treatment.
"I believe that an addicted brain is different than a normal brain, and it becomes for a very, very long time - if not forever - sensitive to triggers of relapse," Vorel said.
"Patients will do well for long or short periods of time. But even years after their last cocaine use, they're still vulnerable to relapse." - Reuters