The SPET scans allowed the researchers to check how the system was working by injecting a radiation-emitting chemical which seeks out working NMDA receptors.
AstraZeneca and Naurex say their new compounds deliver the rapid benefits of ketamine without the disturbing side effects because they act differently on the NMDA receptor.
Recently there has been a resurgence of interest in ketamine because of studies showing that at much lower doses than required for anesthesia, it appears to be a rapid and powerful antidepressant agent, presumably because it blocks an important type of receptor in the brain, known as the NMDA receptor.
Pharmaceutical companies have made a habit of targeting the wrong cause (acetylcholinesterase inhibitors which are basically useless since as the disease progresses acetylcholinesterase activity declines by 85 percent), one aspect of the disease (Namenda as an antagonist for NMDA receptors), or insisting on a partially flawed mechanism for the disease (amyloid plaques).