Gene clue to heroin addiction

US researchers have discovered a key gene involved in heroin addiction in rats. The team, based at the firm CV Therapeutics in California, has found that medicines designed to block the protein made by the AGS3 gene can stop heroin-addicted rats craving the drug. The scientists say their findings, published online in the Proceedings of the National Academy of Sciences, could lead to new treatments to prevent heroin addiction relapses in people.

Heroin and other drugs 'hijack' the brain's reward circuit, which is normally triggered by food and sex, amongst other things. Previous research has shown that an area of the brain called the nucleus accumbens plays a vital role in this system. Work published in 2004 revealed that cocaine triggers the mass production of the protein made by the AGS3 gene in the nucleus accumbens. This process is involved in the cravings and feelings of pleasure associated with the drug.

In the latest study, the researchers studied the AGS3 gene and protein in nucleus accumbens cells taken from baby rats. By studying these cells in the laboratory, the scientists discovered that the inner core of the nucleus accumbens - rather than its outer region - is most involved in its drug-related activity. They then designed a drug to block the AGS3 protein, to see if they could prevent drug cravings.

The scientists injected the AGS3 blocker into rats trained to give themselves heroin using a lever. After a short period of 'withdrawal', the rats were given a tiny amount of heroin, which would normally lead to cravings for more of the drug. However, the blocker appeared to prevent the desire for more heroin. Team leader Ivan Diamond said: 'The hope is that we can design a drug that will stimulate or inhibit receptors in the brain and manipulate the pathway that causes drug craving'. US neuroscientist David Shurtleff told New Scientist magazine that it will take 'creativity and additional research to translate this into usable therapies', but that it provided hope for preventing compulsive drug seeking behaviour in people.