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The gene that gets people hooked on cocaine has been found - and certain people could be more at risk than others.

Those who have an altered form of a the protein could be at higher risk of addiction, according to scientists.

The gene controls levels of the brain chemical glutamate which has been found to play a key role in drug dependence.

Rats with a mutated form of the protein, called mGluR2, produced more of the neurotransmitter - which eliminated cocaine's 'rewards'.

This is what keeps addicts wanting more opening the door to the gene could be 'packing a double punch.'

(Image: Getty)

The researchers said it could act as a biomarker for screening those at risk of cocaine addiction - and as a therapeutic target for drug development.

Dr Zheng-Xiong Xi, of the US's National Institute on Drug Abuse, said: "Our work suggests that, if you could take a medicine to activate mGluR2 activity, then it would decrease or significantly inhibit both cocaine-taking and cocaine-seeking behaviours."

The study published in Cell Reports found rats that can't control glutamate were more likely to kick the habit once addicted.

This suggests the gene, which protects nerve cells from being destroyed by excess glutamate, is involved in modulating the reward-seeking behaviour associated with drug addiction.

(Image: Moment RF)

The rats were more likely to consume cocaine when it was made freely available but less likely to seek it when they had to make more effort to obtain it.

When cocaine was no longer available, the rats were quicker to cease the behaviours that had previously resulted in the drug's delivery.

Even when cocaine was subsequently re introduced, they showed reduced interest for drug seeking, constituting a lower rate of relapse.

Dr Xi said: "The gene-knockout mice don't enjoy much reward when they take the cocaine. So when the drug is available to them, the animals work to increase their intake to feel rewarded.

"But when the drug is difficult to get, the reward isn't worth it anymore, the animal just wants to quit."

Low or absent mGluR2 expression caused the rodents to experience a lessened neurological reward when taking cocaine.

(Image: E+)

At the cellular level, the research illuminates the role that glutamate - the most abundant neurotransmitter in all vertebrates and a prominent contributor to pathways of learning, memory, and anxiety in humans - plays in cocaine addiction.

This goes beyond previous findings that focused on dopamine response, the 'feelgood' chemical more commonly associated with reward seeking, as the main culprit.

Deleting mGluR2 causes nerve cells to be awash in glutamate before any cocaine is ingested.

Cocaine "works" by binding to receptors in place of neurotransmitters like glutamate and dopamine, forcing them to float around and excite neuron junctions, or synapses.

So the pre-existing flood of glutamate limits its power to deliver a neurological reward.

The researchers also plan on studying the influence of mGluR2 - which has been preliminarily associated with alcohol and nicotine addictions - in relation to opiates such as heroin.

Added Dr Xi: "It seems that mGluR2 may be a common target for treating addictions to many drugs."

The finding adds to evidence glutamate, a neurotransmitter central to learning and memory, is also central to addiction.