Xenon gas is commonly used for diagnostic inhalation because of its anesthetic properties but more recently it has been used by the Russians to cheat in the Olympics, and the cycling community has followed suit, because of its EPO - Erythropoietin - hormone producton ability.

It may also be a treatment for post-traumatic stress disorder (PTSD) and other memory-related disorders, according to a new paper in PLOS One.

"In our study, we found that xenon gas has the capability of reducing memories of traumatic events," said Edward G. Meloni, PhD, assistant psychologist at McLean Hospital and an assistant professor of Psychiatry at Harvard Medical School. "It's an exciting breakthrough, as this has the potential to be a new treatment for individuals suffering from PTSD."

Meloni, and colleagues examined whether a low concentration of xenon gas could interfere with a process called re-consolidation – a state in which reactivated memories become susceptible to modification. 

Multiple Xe exposures after fear memory reactivations do not enhance amnestic effects on conditioned freezing. (A) Schematic of the experimental design for multiple Xe-exposure treatment. In addition to administering Xe (25%) or Air for 1 h after Reactivation, animals were exposed a second time to Xe (25%) or Air for 1 h immediately after PR-LTM1 and freezing was again probed 48 h later, (PR-LTM2). (B&C) Percent freezing to context alone and context + tone (respectively) in animals exposed to Xe (25%) or Air for 1 hr immediately after Reactivation and PR-LTM1. (D&E) Normalized freezing data to context and tone. Data are expressed as % differences from the first Reactivation test day in order to compare the effects of multiple Xe exposures. A second Xe exposure did not alter freezing either to context alone or context + tone at PR-LTM2 compared to PR-LTM1. ***P<0.0005; **P<0.005; *P<0.05; Air–1 exposure, n = 11; Air–2 exposures, n = 9; Xe–1 exposure, n = 11; Xe–2 exposures, n = 10. Data are shown as mean ± s.e.m. 

"We know from previous research that each time an emotional memory is recalled, the brain actually restores it as if it were a new memory. With this knowledge, we decided to see whether we could alter the process by introducing xenon gas immediately after a fear memory was reactivated," explained Meloni.

The investigators used an animal model of PTSD called fear-conditioning to train rats to be afraid of environmental cues that were paired with brief footshocks. Reactivating the fearful memory was done by exposing the rats to those same cues and measuring their freezing response as a readout of fear. "We found that a single exposure to the gas, which is known to block NMDA receptors involved in memory formation in the brain, dramatically and persistently reduced fear responses for up to 2 weeks. It was as though the animals no longer remembered to be afraid of those cues", said Dr. Meloni.

Meloni points out that the inherent properties of a gas such as xenon make it especially attractive for targeting dynamic processes such as memory reconsolidation. "Unlike other drugs or medications that may also block NMDA receptors involved in memory, xenon gets in and out of the brain very quickly. This suggests that xenon could be given at the exact time the memory is reactivated, and for a limited amount of time, which may be key features for any potential therapy used in humans."

"The fact that we were able to inhibit remembering of a traumatic memory with xenon is very promising because it is currently used in humans for other purposes, and thus it could be repurposed to treat PTSD," added Kaufman.

For these investigators, several questions remain to be addressed with further testing. "From here we want to explore whether lower xenon doses or shorter exposure times would also block memory reconsolidation and the expression of fear. We'd also like to know if xenon is as effective at reducing traumatic memories from past events, so-called remote memories, versus the newly formed ones we tested in our study".

Meloni and Kaufman indicate that future studies are planned to test if the effects of xenon in rats seen in their study translate to humans. Given that intrusive re-experiencing of traumatic memories – including flashbacks, nightmares, and distress and physiological reactions induced when confronted with trauma reminders – is a hallmark symptom for many who suffer from PTSD, a treatment that alleviates the impact of those painful memories could provide welcome relief.

Citation: Meloni EG, Gillis TE, Manoukian J, Kaufman MJ (2014) Xenon Impairs Reconsolidation of Fear Memories in a Rat Model of Post-Traumatic Stress Disorder (PTSD). PLoS ONE 9(8): e106189. doi:10.1371/journal.pone.0106189. Source: McLean Hospital