THE brain cells responsible for triggering cravings in recovering drug addicts have been identified.鈥滿ost research on addiction focuses on what happens when people take drugs,鈥� says Danny Winder, a neuroscientist at Vanderbilt University in Nashville, Tennessee. 鈥淭his is among the first to look at what happens during relapse, which is the period that is most difficult to treat.鈥�
To study the conditions that trigger a relapse, Mark West鈥檚 team at Rutgers University in New Jersey trained rats to press a lever to receive cocaine, but only when a specific tone was sounded. The rats came to associate hearing the tone with experiencing the drug, just as a particular place or kind of music might trigger cravings in a recovering addict.
The lever was then taken away. When it was returned after several weeks, the rats ignored it at first. But when the tone was sounded, they started pushing the lever again.
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By using implanted electrodes, West鈥檚 team found that certain brain cells were active only when the tone was sounded (The Journal of Neuroscience, vol 23, p 7239). The cells are in the nucleus accumbens, a crossroads between the dopamine system, which mediates the pleasurable response to things such as drugs or food, and the limbic system, which is involved in motivation and memory. The nucleus accumbens is part of the brain area that has evolved to prime animals for the presence of food or water or a sexual partner. Addictive drugs hijack this normally adaptive system, says Winder, sending users into a pattern of desire when they find themselves in situations familiar from drug-taking sessions.
West hopes that eliminating the neural activity through drugs or behavioural therapy could stop addicts鈥� craving. But his findings show what a tough challenge recovering addicts will face: activity in the rats鈥� nucleus accumbens persisted long after the cocaine had been removed for good and the rats had given up pressing the lever.