A chemical found in marijuana may help people cope with post-traumatic stress disorder, according to a new Israeli study on rats.

Being reminded of a traumatic event often re-traumatizes people. A loud car alarm, for example, could lead to new PTSD symptoms in someone traumatized by the rocket-warning sirens that wailed across Israel for the past couple months.

In the study, traumatized rats injected with the psychoactive chemical did not experience new PTSD-like symptoms after a “trauma reminder.” The researchers traced the improvement – compared to rats that were not treated or were given an antidepressant – to changes in the brain.

Rats are known to respond to stress and trauma in a similar way to humans. The researchers behind the randomized controlled study, published in the journal Neuropsychopharmacology, say the findings are a step toward PTSD treatments based on cannabinoids, the often-psychoactive ingredients found in marijuana and also produced naturally by the human body.

“The findings of our study suggest that the connectivity within the brain’s fear circuit changes following trauma, and the administration of cannabinoids prevents this change from happening,” said Dr. Irit Akirav, a psychologist at the University of Haifa, who conducted the study in collaboration with doctoral student Nachshon Korem. “This study can lead to future trials in humans regarding possible ways to prevent the development of PTSD and anxiety disorders in response to a traumatic event.”

Some 9 percent of Israelis have PTSD, and the rate is even higher in at-risk groups, like combat soldiers, first responders, prisoners, and victims of assault, according to the Israel Medical Association. PTSD symptoms can be debilitating and include recurring flashbacks, avoidance or numbing of memories of the traumatic event, and a fight-or-flight response.

In previous research, Akirav found that giving rats cannabinoids soon after a traumatic event reduced their PTSD symptoms. The researchers replicated this finding in the study and went on to test the power of cannabinoids to protect against the negative effects of reminders of the trauma.

In the study, rats that had been traumatized with a series of electric shocks were put back in the shock-giving situation to remind them of the experience. The rats that were given the cannabinoid, WIN 55,212-2, two hours later did not show new PTSD-like symptoms, such as avoiding the trauma reminder, startling more easily, becoming more of less sensitive to pain, or having lower activity in the “pleasure center” of their brains, the nucleus accumbens.

The cannabinoid used in the study is man-made and produces effects similar to those of tetrahydrocannabinol, or THC, the main psychoactive ingredient in marijuana.

On the other hand, rats that were given the selective serotonin re-uptake inhibitor sertraline, which is used with limited success to treat PTSD symptoms in people, were only slight less affected by the trauma reminders than untreated rats were.

To understand how the cannabinoid eliminated PTSD-like symptoms, the researchers looked at some of the rats’ brains. The rats that were exposed to trauma and to trauma reminders showed an increase in the expression of two receptors in the brain associated with emotional processing: The cannabinoid receptor type 1 and the glucocorticoid receptor — both of which have been shown to play a role in regulating stress.

In rats that were given the cannabinoid, the expression of the receptors did not take place in the hippocampus or in the prefrontal cortex, areas of the brain involved in forming and saving traumatic memories.

Based on the results and past research, the researchers suggest that trauma changes the “fear circuit” in the brain, contributing to PTSD symptoms. Adding synthetic cannabinoids to the mix appears to help the body’s innate cannabinoids, called endocannabinoids, to prevent the problematic changes.

The study’s findings could lead to trials in humans and one day to cannabinoid-based drugs to help treat PTSD symptoms, the researchers said. Marijuana is sometimes prescribed for PTSD in Israel and parts of the United States.