We would all feel pleasure if we took drugs she says but we would not all keep taking the

“We would all feel pleasure if we took drugs,” she says, “but we would not all keep taking the drug until addiction.” What she wanted to find out was why drug addicts were addicts and what got them hooked in the first place. When she scanned people addicted to drugs, she found that the neuro-receptors in their brains that produced (or responded to) dopamine had been reduced. It was found the heavier the use of the drug (cocaine in this case), the greater the reduction of dopamine receptors.Addicts who then stopped taking cocaine did not recover their dopamine receptors. In other words, the longer drug addiction goes on, the less pleasure a given amount of a drug will provide because the addict’s brain is producing less and less dopamine.The receptors seemed to be selectively destroyed in the orbito-frontal cortex – the outer frontal region of the brain which is responsible for processing memories of learned behavioural patterns: it helps us remember how to achieve specific goals. An animal with an impaired orbito-frontal cortex will still press a lever to obtain a drug even if the drug never appears.

By damaging his or her orbito-frontal cortex, a drug abuser will continue trying to take the drug even if, because of the reduction of dopamine receptors, they are no longer deriving much pleasure from the experience.To make sure that her work was scientifically valid, Dr Volkow carried out brain scans on controls – people who were not drug addicts. She was surprised to find a huge variation in the amount of dopamine receptors, and therefore the amount of dopamine, that a “normal” person would produce. Some of the people with the lowest number of dopamine receptors had as few as drug addicts. “If someone has naturally low levels of dopamine, not dissimilar levels to drug abusers, what does that mean for their likelihood of addiction?” asks Dr Volkow.To find out, she gave a group of people some drugs – a type of amphetamine. Half of them liked it, half didn’t: the people who thought it unpleasant had a lot of dopamine receptors; those who liked it had few. “The people who had the low level of dopamine receptors will be more prone to try drugs to increase their natural dopamine, these are the people who will like drugs,” concludes Dr Volkow, adding: “This means that the effects of a drug are produced by the interaction between the drug and your unique biochemistry so that you personally achieve an optimal level of dopamine stimulation.”This permanent change to the brain which underlies addiction also interests Dr Eric Nestler, from the Department of Psychiatry and Center for Neuroscience at the University of Texas Southwestern Medical Center in Dallas.

He believes he has found one of the changes that take place in the brain at a molecular level in response to drugs.A protein called delta FosB accumulates in a brain region known as the nucleus accumbens when a person takes drugs such as opium, cocaine, amphetamines, nicotine, alcohol and phencyclidine or “angel dust”. It remains in the brain long after drug-taking has ceased, and is likely to cause people to become more sensitive to the effect of drugs, to behave more compulsively, and to take drugs more often.In essence, Dr Nester thinks that delta FosB is a molecular switch that, once triggered, helps to turn a drug user into an abuser. This protein also has an effect on dopamine as it reduces the size of dopamine receptors so that they produce less dopamine.So can this research help prevent drug addiction? Dr Volkow wanted to find out whether altering the amount of dopamine a person produced might help reduce the risk of them becoming a drug addict Her researchers made a group of mice alcoholic. They then inserted a gene into the mice which caused the number of dopamine receptors in their brains to increase by 50 per cent Immediately the mice voluntarily stopped drinking But the effect was only temporary. The added gene produced more dopamine receptors for only about eight days.It is at least a start; a person with naturally low levels of dopamine may eventually be able to take a drug which boosts the number of his or her receptors so that he or she won’t feel the need to take drugs to achieve that feel-good state.

Currently there are a few drugs in clinical trials which may be of some help. Naltrexone is used for alcoholics and heroin addicts, Baclofen may alleviate cocaine abuse and Buproprion is helping smokers quit.But there might never be a magic cure for addiction, according to Dr Charles O’Brian, from Penn State University in Philadelphia, who studies craving in drug abusers. He says these drugs need to be used in conjunction with therapy and support groups such as Alcoholics Anonymous. “The best they can do,” he says, “is buy time to help addicts learn new, more helpful responses to their addiction.”. Genes matter in determining our health, but so does the womb – we neglect its influence at our peril.

Unlike in the adult, where eating less is good for you, undernutrition in the womb can have very negative consequences. Mothers may even have to be warned not to try “fattening up” children that are thin at birth. Many of the most important studies that show this come from Professor David Barker at the University of Southampton. Genes matter in determining our health, but so does the womb – we neglect its influence at our peril. Unlike in the adult, where eating less is good for you, undernutrition in the womb can have very negative consequences.