Memory block may help recovering drug addicts stay clean

Erasing out memories linked to drug-taking may one day help recovering addicts to stay "clean".

Scientists were able to reduce drug-seeking behaviour in rats by blocking a memory molecule in the brain.

The research could lead to memory-control drugs that could be taken when addicts are most at risk of surrendering to their cravings.

Memories exist in different states depending on whether they are being recalled or not.

During recall, they can be altered or erased through a process called "reconsolidation".

Scientists hope that employing this technique to block recollections of drug-related memories may help stop reforming addicts falling back into drug-taking.

Such relapses are often triggered when addicts summon up drug-associated memories.

In a series of experiments, the Cambridge scientists trained rats to associate the switching on of a light with cocaine.

The addicted rats were then exposed to the light, thereby "reactivating" the memory of cocaine even when the drug was not present.

Subsequently in an effort to receive more cocaine, the rats would perform tasks which resulted in the light being turned on.

Next the animals were given a chemical that blocked receptor molecules in the brain with a key role in memory.

Receptors are like "switches" which trigger biological events when particular chemicals bind onto them.

When rats received the chemical prior to the "reactivation" session their cocaine-seeking behaviour was curbed.

A single treatment reduced or stopped their obsession with turning on the light for up to four weeks.

Blocking the receptors after or without the reactivation session had no effect on drug-seeking behaviour. This showed that drug-associated memories can only be disrupted at the time they are recalled.

The findings were published today in the Journal of Neuroscience.

Professor Barry Everitt, who led the Medical Research Council-funded scientists, said: "The results suggest that efforts should be made to develop drugs that could be given in a controlled clinical or treatment environment in which addicts would have their most potent drug memories reactivated.

"Such treatments would be expected to diminish the effects of those memories in the future and help individuals resist relapse and maintain their abstinence."

Co-author Dr Amy Milton said: "This is a new approach to the treatment of drug addiction that has great potential. Additionally, this might also be used to treat other neuropsychiatric disorders characterised by maladaptive memories, including post-traumatic stress and phobic anxiety disorders."

(Source: Neuroscience: Cancer Research UK: August 2008)