These researchers worked on the mechanism of addiction for the Institute of Neuroscience of the Timone hospital.

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ANNE-CHRISTINE POUJOULAT / AFP

A team of researchers has identified a signal in part of the rats' brains predicting their vulnerability to becoming "addicted" to cocaine, a finding that may help treatments for drug dependence in humans.

"There are people who can consume cocaine every Saturday evening and who will never be addicted, and others who do not resist and fall into addiction", underlines Christelle Baunez, researcher at the Institute of Neurosciences of the Timone hospital (University of Aix-Marseille).

How then to predict the vulnerability to addiction of an individual, and if necessary help him to resist it?

The team led by Christelle Baunez explains it in a study published this Tuesday in the journal

Proceedings

of the American Academy of Sciences (PNAS).

Targeting cocaine research

Her goal was to identify a "predictive marker" to "help the most vulnerable people," she told AFP.

By modeling in animals an experiment centered on a key criterion of dependence, which consists in “consuming something despite the negative consequences of this consumption”.

The experiment therefore consisted in not punishing the taking of cocaine but in punishing its research, in rats already engaged in an "escalation" of consumption of the product.

Once accustomed to the drug-obtaining mechanism of squeezing a lever to release a dose, the rat then had a one in two chance of receiving an electric shock in the paws instead.

The study found that about 15 to 20% of the animals "will still try to play for cocaine, despite the risk they take to have a shock," said the researcher, explaining that "these are they who interest us, because they are really addicted ”.

Abnormal activity

The problem is that nothing in their behavior allows, at the beginning of the first drug taking, to distinguish "before it is too late" the future addicts from the others.

The researchers then found a "magic signature" to identify them, by spotting abnormal electrical activity of neurons in the subthalamic nucleus (NST).

This NST is located in a region of the brain involved, among other things, in cost-benefit decisions.

It is well known in a rare but effective treatment of Parkinson's disease or obsessive-compulsive disorders, thanks to a method of deep brain stimulation using electrodes implanted in this area.

The abnormal activity of neurons in the NST, at a very very low frequency, appears only in "animals which will be future compulsive consumers".

To be sure, the team of researchers from Timone stimulated this area with very low frequencies in rats that were previously sensitive to electric shock (and therefore the least vulnerable to addiction), which made them immediately addicted.

Caution

In a second step, the researchers verified that stimulating this area at another frequency could help the rat to be less dependent.

Because since their first research on the subject in 2005, they know that it works to modify certain behaviors linked to addiction.

The study confirmed that at a very specific, rather low frequency, the stimulation reduced the drug-addicted rat's search for substance.

A mechanism that can be generalized to other substances?

“Partially”, replies Christelle Baunez who reports “rather positive data for the heroine”.

The challenge ahead would be to make these signal detection techniques and correction of abnormal activity in the NST non-invasive.

“The next step for us is to look for an activity that mirrors what we observe deeply” in the NST, according to Christelle Baunez.

A sort of "resonance" of this signal in a more peripheral part of the brain, perhaps detectable with a simple electroencephalogram headset.

This would warn a drug addict patient about his vulnerability to addiction.

As for an intervention on the deep part of the brain to correct an abnormal activity there, without having to penetrate there, it is still in the field of research.

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  • Addiction