Patients with alterations in this gene may be particularly susceptible to stress and may respond with drinking

Prof Rainer Spanagel

If true then a simple genetic test could, they say, help doctors to identify recovering alcoholics who are at risk of relapsing.

Prof Rainer Spanagel and colleagues compared normal mice with a strain of mutant mice that lacked the gene responsible for making the CRH1 receptor.

They first offered both groups a free choice between water and alcohol at different concentrations. Both groups opted for a solution of 8% alcohol.

Stress test

The researchers exposed both groups of mice to two types of stress. One involved an attack by an unfamiliar mouse and the other required the mice to swim on three consecutive days.

After each experience, all the mice continued to drink the normal amount of alcohol.

However, three weeks later the mutant mice began drinking approximately three times more alcohol than the normal mice.

The mutant mice continued to drink significantly more alcohol six months later. Three months after the tests, the normal mice were still drinking the original amount.

Further tests found that the brains of the mutant mice had changed - in particular, those regions that "reward" alcohol.

The authors said they were not sure why it took the mutant mice three weeks to react to their stressful experiences by drinking more.

But they added that previous studies have pointed to a wide range of responses to stress that can trigger drinking.

Nevertheless, they are confident the model can be applied to humans.

"Mimicking addictive behaviour in animals is much easier than mimicking depressed or schizophrenic behaviour," said Prof Spanagel.

"There is a pretty good link in comparison with other disorders."

He added: "We think that with our model, we have the neurobiological mechanism underlying a very specific phenotype of alcoholic patient.

"Patients with alterations in this gene may be particularly susceptible to stress and may respond with drinking."

Important findings

Alan Leshner, chief executive of the American Association for the Advancement of Science, described the findings as important.

"We've long known that stress is the biggest cause of relapse for many, but not all addicts, even those who've long been in recovery.

"This important study points both to the underlying mechanisms of this effect and potential targets for prevention and treatment efforts."