http://www.nih.gov/news/pr/jul2007/nimh-24.htm

Faster-Acting Antidepressants Closer to Becoming a Reality
Experimental medication ketamine relieves depression in just hours; points to targets for new medications
A new study has revealed more about how the medication ketamine, when used experimentally for depression, relieves symptoms of the disorder in hours instead of the weeks or months it takes for current antidepressants to work. While ketamine itself probably won’t come into use as an antidepressant because of its side effects, the new finding moves scientists considerably closer to understanding how to develop faster-acting antidepressant medications — among the priorities of the National Institute of Mental Health (NIMH), part of the National Institutes of Health.
Ketamine blocks a receptor called NMDA on brain cells, an earlier NIMH study in humans had shown, but the new study in mice shows that this is an intermediate step. It turns out that blocking NMDA increases the activity of another receptor, AMPA, and that this boost in AMPA is crucial for ketamine’s rapid antidepressant actions. The study was reported online in Biological Psychiatry on July 23, by NIMH researchers Husseini K. Manji, MD, Guang Chen, MD, PhD, Carlos Zarate, MD, and colleagues.
“Our research is showing us how to develop medications that get at the biological roots of depression. This new finding is a major step toward learning how to improve treatment for the millions of Americans with this debilitating disorder; toward eliminating the weeks of suffering and uncertainty they have to endure while they wait for their medications to work,” said NIH Director Elias Zerhouni, M.D.
Almost 15 million American adults have a depressive disorder. During the long wait to begin feeling the effects of conventional medications, patients may worsen, raising the risk of suicide for some. Depressive disorders also affect children and adolescents...