Bipolar disorder affects millions of people around the globe, and its effects - which range from deep depression to mania -- make it one of the world's most serious mental illnesses.

However, the lack of an animal model for bipolar disorder has been a major obstacle to developing better treatments for the disease.

Now, researchers at the National Institute of Health, writing in Molecular Psychiatry, report promising results from an experiment with mice that had been bred with a specific gene defect associated with bipolar disorder. (Unlike some brain diseases, no single gene has been identified as the cause of bipolar disorder, which scientists believe results from a combination of environmental and genetic factors.)

The genetically engineered mice, missing the GluR6 gene, were tested against control mice. The researchers found that mice missing the gene exhibited several manic symptoms, including increased aggression and hyperactivity. Interestingly, when the mice were chronically treated with lithium - a "mood stabilizer" that is often used to treat bipolar disorder - they reduced their hyperactive, aggressive behavior. Further biomedical tests suggested the GluR6 gene may also play a role in regulating the symptoms of mania.

If further tests on the newfound animal model are successful, the authors wrote, they are hopeful of bringing some of the new treatments into clinical tests.