Researchers discover biological precursor to compulsive drug use

A Cambridge University researcher has announced the discovery of a biological trigger in the brains of some drug users that he believes causes them to switch from occasional use to compulsion and addiction.

Barry Everitt, a professor of behavioral neuroscience at Cambridge's Department of Experimental Psychology, said that the switch from recreational to compulsive use occurs when control over one's desire for a drug transfers from the ventral stratum of the brain (which has been linked with pleasure and rewards) to the dorsal stratum (which is associated with the development of habits).

Everitt announced his findings July 14 during a presentation he gave at the 6th annual FENS Forum for Neuroscience in Geneva, Switzerland.

According to a June 18, 2008 article on the ScienceDaily website, Everitt and his research team had previously separated rats into groups based on behavior patterns, then gave the rodents access to cocaine. The rats that had previously been identified as "highly impulsive" exhibited a compulsion to ingest the cocaine in increasingly larger amounts, while rats from the "novelty seeker" group did not demonstrate the development of addictive symptoms when exposed to the cocaine.

"This study is important because it shows that impulsivity is a vulnerability characteristic that predicts a switch to compulsive drug use when individuals are exposed to and take cocaine," Everett said in the ScienceDaily article. "Therefore, drug addiction is characterized by a shift from impulsive to compulsive behavior."

Earlier research conducted by Jeff Dar (a member of the Everitt group) found low levels of the D2/3 dopamine receptor in the ventral striata of the brains of highly impulsive rats. The findings that were presented during the FENS conference identified the ventral striatum's inability to retain control over drug use as a key factor in the development of compulsive ingestion of a substance.

"Impulsivity clearly interacts with chronic drug taking to precipitate the compulsive drug seeking state of addiction," Everitt was quoted as saying in a July 14 article on the WebMD website. "We are beginning to unravel the neural basis of this interaction."

On his faculty profile page on the Cambridge website, Everitt described the focus of his research as the "neural and psychological mechanisms underlying learning, memory motivation and reward," primarily in the area of drug addiction.

"Taking drugs might begin as a voluntary, or goal-directed, action but may transform in time to become a compulsive habit that is extremely difficult to relinquish," he wrote. "This transition from initial drug use to addiction may occur through the progressive engagement of different learning systems in the brain and we have growing evidence that this is so."

ScienceDaily said Everitt's research "represents a major advance by showing that these neural and behavioural changes are forerunners of the eventual transition to drug addiction."