New York, Feb 9 (IANS): Administering a single dose of ketamine -- a drug commonly used as general anaesthetic or a rapid-acting antidepressant -- one week before a stressful event can act as a buffer against a heightened fear response and might prevent post-traumatic stress disorder (PTSD), researchers have found.

PTSD is an anxiety disorder that occurs in about one-quarter of individuals who experience psychological trauma.

The symptoms include re-living the trauma -- experiencing repeated flashbacks, hyperarousal, and hyperreactivity -- as well as mood changes, psychological numbing, and chronic physical symptoms such as headache.

The likelihood that PTSD symptoms will develop depends on the nature and intensity of the trauma and an individual's response.

"If our results in mice translate to humans, giving a single dose of ketamine in a vaccine-like fashion could have great benefit for people who are highly likely to experience significant stressors, such as members of the military or aid workers going into conflict zones," said lead author Christine A. Denny, Assistant Professor at Columbia University Medical Center (CUMC) in New York, US.

However, "ketamine is a powerful drug, and we wouldn't advocate widespread use for preventing or reducing PTSD symptoms," Denny added.

For the study, published in the journal Neuropsychopharmacology, the team conducted experiments in mice who were given a small dose of ketamine via a drip or a placebo either one month, one week, or one hour before they were subjected to a series of small shocks.

The mice -- conditioned to associate the test environment with the shocks -- were later returned to the same environment and assessed for their freezing behaviour -- a measure of their conditioned fear response.

Only the mice given ketamine one week before the stressor exhibited reduced freezing when they were returned to the test environment, suggesting that timings of administering dose may be important.