Cannabinoids (marijuana) administration after experiencing a traumatic event blocks the development of post-traumatic stress disorder (PTSD)-like symptoms in rats, according to a new study conducted at the University of Haifa and published in the journal Neuropsychopharmacology.

"We found that there is a 'window of opportunity' during which administering synthetic marijuana helps deal with symptoms simulating PTSD in rats," said Dr. Irit Akirav of the University of Haifa's Department of Psychology, who led the study.

In the study, which Dr. Akirav conducted with research student Eti Ganon-Elazar, the researchers set out to examine how administering cannabinoids (synthetic marijuana) affects the development of PTSD-like symptoms in rats, whose physiological reactions to traumatic and stressful events is similar to human reactions.

In the first part of the study, the researchers exposed a group of rats to extreme stress, and observed that the rats did indeed display symptoms resembling PTSD in humans, such as an enhanced startle reflex, impaired extinction learning, and disruption of the negative feedback cycle of the stress-influenced HPA axis.

The rats were then divided into four groups. One was given no marijuana at all; the second was given a marijuana injection two hours after being exposed to a traumatic event; the third group after 24 hours and the fourth group after 48 hours.

A week later, the researchers examined the rats and found that the group that had not been administered marijuana and the group that got the injection 48 hours after experiencing trauma continued to display PTSD symptoms as well as a high level of anxiety.

By contrast, the PTSD symptoms disappeared in the rats that were given marijuana 2 or 24 hours after experiencing trauma, even though these rats had also developed a high level of anxiety.

"This indicates that the marijuana did not erase the experience of the trauma, but that it specifically prevented the development of post-trauma symptoms in the rat model," said Dr. Akirav, who added that the results suggest there is a particular window of time during which administering marijuana is effective. Because the human life span is significantly longer than that of rats, Dr. Akirav explained, one could assume that this window of time would be longer for humans.

The second stage of the study sought to understand the brain mechanism that is put into operation during the administering of marijuana. To do this, they repeated stage one of the experiment, but after the trauma they injected the synthetic marijuana directly into the amygdala area of the brain, the area known to be responsible for response to trauma. The researchers found that the marijuana blocked development of PTSD symptoms in these cases as well. From this the researchers were able to conclude that the effect of the marijuana is mediated by a CB1 receptor in the amygdala.