In the quest to find the biological route of drug addiction, research at Cambridge University, UK, is revealing what makes some people more vulnerable than others. Speaking at Europe's major neuroscience conference in Geneva, Professor Barry Everitt described what they now believe causes the switch from occasional, 'recreational' use to a compulsive habit.
Professor Everitt and researchers in the Cambridge lab have discovered there is a shift in the control of drug seeking behaviour in the brain. Taking drugs - for example, cocaine - generates reinforcing or 'rewarding' effects mediated by the ventral striatum of the brain. In some people, however, drug taking escalates to become a strong habit, difficult to relinquish, and which is eventually controlled by the dorsal striatum, a region of the brain associated with habit learning.
"We also needed to find out why some people are vulnerable to this switch from one brain region to another," said Professor Everitt. "People who are addicted to drugs tend to be impulsive, a characteristic which may have a genetic, as well as an environmental basis."
Brain imaging studies in the Cambridge lab have revealed that impulsive rats have low levels of dopamine D2/3 receptors in the ventral striatum which greatly escalates their cocaine intake when given access to the drug. Dopamine is a neurotransmitter (a chemical messenger) involved with the brain's reward systems and plays a major role in addiction. Drugs such as cocaine bind to dopamine receptors and stimulate the response.