Xenon gas may someday be used as a treatment for post-traumatic stress disorder after experiments with mice showed brief exposure dulled reactions to painful memories, a finding doctors called a “breakthrough.”
The research comes amid a growing PTSD crisis in America, where about 7.7 million people are diagnosed with the disorder, according to the National Institutes of Health. Many of them are veterans — about one-third of all veterans have PTSD — but the illness affects victims of any trauma, from rape to robbery to car wrecks. But despite its prevalence, a reliable cure has never surfaced.
Now researchers at McLean Hospital in Belmont, Mass., say they have discovered a potential treatment using the same gas administered into organs for body imaging and into lungs for anesthesia and even doping. Xenon gas also has the unique ability to block NMDA receptors — relays in the brain responsible for memory formation. Blocking NMDA “has the capability of reducing memories of traumatic events," said Dr. Edward G. Meloni, a psychologist at McLean Hospital and at Harvard Medical School, in a statement. "It's an exciting breakthrough, as this has the potential to be a new treatment for individuals suffering from PTSD.”
In their experiment, which they reported Wednesday in PLOS ONE, the scientists conditioned mice to associate certain events with small jolts of electricity to their feet. They measured fear simply through observation: The mice froze when they were scared. But when the mice were given a burst of xenon gas, their fear responses were numbed for as many as two weeks. “It was as though the animals no longer remembered to be afraid of those cues,” Meloni said.
It’s still unclear whether xenon can actually work on old memories. (The memory of the foot shocks was fresh for the mice.) They also want to tinker with dosage before trying the treatment on humans.
The xenon treatment works by disrupting a fascinating process our brains use to code memories. When we learn or experience something, our brains prepare the information to be stored for the long-term through a mechanism called consolidation, according to the book Neural Plasticity and Memory: From Genes to Brain Imaging, edited by Federico Bermúdez-Rattoni. It’s like jotting on a note card the location of a library book you want to find later.
Psychologists used to think consolidation only happened during the formation of new memories. But lately, scientists have observed it happening when old memories are recalled and brought to the surface. The brain updates the note card. This re-consolidation is probably a way to enrich the long-term memory with new knowledge.
Meloni and his team knew xenon disrupted consolidation. They wondered whether it would also disrupt re-consolidation — essentially taking a black Sharpie to the note card. "The fact that we were able to inhibit remembering of a traumatic memory with xenon is very promising,” co-author Dr. Marc J. Kaufman said, because xenon has already been tested and regularly used on humans for other purposes.
Source: Meloni EG, Kaufman MJ, et al. PLOS ONE. 2014.