By studying cocaine-addicted rats, researchers at the Albert Einstein College of Medicine in New York and the National Institutes of Health in Baltimore have discovered which region of the brain is involved in cocaine craving. The same region may also be responsible for relapses, the major hurdle in treating drug addiction in people. The results are reported in today's issue of Science.
Whereas previous studies focused on the area of the brain that controls "rewarding" responses by releasing the neurotransmitter dopamine, the region identified by Eliot Gardner, Stanislav Vorel and their colleagues¿an area of the hippocampus called ventral subiculum¿is known to be involved in feelings of "wanting," and therefore directly controls drug-seeking behavior. Neurons there use a different neurotransmitter called glutamate.
During the study, rats were able to self-administer a cocaine-containing solution by pressing a lever connected to a catheter and a pump during 3-hour sessions. In this way, the animals quickly became addicted and would rush to press the lever in every session. When saline was later substituted for cocaine, the rats progressively weaned themselves from the drug and became much less likely to press the lever. But when researchers stimulated the rodents' ventral subiculums with a tiny electrode, the same rats started to press the lever obsessively, showing once again drug-seeking behavior.
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Even more interesting, researchers could prevent these relapses by treating rats with a molecule that blocks glutamate signals, suggesting that this chemical might be investigated as a new treatment to prevent relapse in former cocaine-addicts. "Since wanting a drug is more directly connected to relapse [than liking it], glutamate could prove a promising target for new drug developments designed to treat cocaine addiction," Vorel says. Considering all the social and economic aspects of drug abuse, pharmacological intervention alone may not solve the burden. But it could help cocaine abusers¿which number 1.8 million in the U.S. alone¿kick the habit for good.
