The anesthetic and sometimes-recreational drug ketamine -- also called "Special K" -- has shown potential in the treatment of depression, and researchers at the Riken Center for Life Science Technologies in Japan recently used rhesus monkeys to study how the drug works.

Previous studies of ketamine have shown the drug can produce a fast-acting antidepressant effect in severely depressed patients who did not respond to typical depression medications, such as serotonin reuptake inhibitors (SRIs) or monoamine oxidase inhibitors. Riken's international team of researchers, led by Hajime Yamanaka and Hirotaka Onoe, used 3-D imaging technology to look at the function of ketamine in the monkeys.

The researchers analyzed brain images produced by positron emission tomography (PET) scans and found ketamine sparks the activity of serotonin -- "the feel-good" hormone -- in two key areas of the brain that are related to motivation and known to play a role in depression. Ketamine does this by enhancing the ability of serotonin molecules to bind with receptors in these regions of the brain.

The researchers also found that treatment with a second drug -- NBQX, which is believed to block the anti-depressive effect of ketamine in rodents -- cancels out some of the binding capabilities of ketamine.

The results suggest that ketamine's anti-depressive actions are mediated by the improved binding and expression of certain receptors in areas of the brain that relate to motivation. The researchers' findings also indicate the potential for imaging studies in diagnosing major depression and in developing new treatments.