Administering synthetic marijuana (cannabinoids) soon after a traumatic event can prevent PTSD-like (post-traumatic stress disorder) symptoms in rats, caused by the trauma and by trauma reminders. This is according to a new study conducted by Nachshon Korem and Irit Akirav of the Department of Psychology at the University of Haifa, which was published in the journal Neuropsychopharmacology. "The importance of this study is that it contributes to the understanding of the brain basis of the positive effect cannabis has on PTSD and thus supports the necessity to perform human trials to examine potential ways to prevent the development of PTSD and anxiety disorders in response to a traumatic event," the researchers noted.

According to the Israel Medical Association approximately nine percent of the population suffers from post-traumatic stress disorder, whereas among at-risk populations such as combat soldiers, prisoners, victims of assault, citizens in lines of confrontation, etc., the percentages are even higher. A common phenomenon among those who suffer from trauma is that exposure to a "trauma reminder" -- an event that is not traumatic in essence but that evokes the memory of the experience of the traumatic event -- can further heighten the negative effects of the trauma. For example, for a person who has developed post-traumatic syndromes as a result of "Color Red" sirens (air raid sirens), a trauma reminder can occur following a loud car alarm.

In previous studies performed by Dr. Irit Akirav, she discovered that the use of cannabinoids within a specific time window after the traumatic event has occurred reduces PTSD symptoms in rats. In this current study, conducted by Dr. Irit Akirav together with the doctoral student Nachshon Korem, the researchers aimed to examine whether the use of cannabinoids may also moderate the effects of trauma in cases of exposure to trauma reminders. The researchers chose rats because of their great physiological similarity to humans in the way they respond to stressful and traumatic events.

During the first half of the experiment, the rats underwent the traumatic event of receiving an electric shock and were exposed to trauma reminders on the third and fifth days of the trial. After the event, and within the time window found in earlier studies, some of the rats were injected with a cannabinoid substance. The rats then went through extinction procedures for trauma (a conditional psychological procedure similar to exposure therapy in humans, the purpose of which is to cope with post-trauma symptoms).

From the findings it became clear that the rats that were injected with the cannabinoid substance showed no PTSD symptoms such as impaired extinction learning, increased startle response, changes in sensitivity to pain and impaired plasticity in the brain's reward center (the nucleus accumbens), compared to those not injected with the drug. The researchers added that the rats that were injected with the drug showed better results compared to rats who received sertraline (an antidepressant of the SSRI group) a substance that is used in the treatment of PTSD with limited success in reducing symptoms. In fact, for some of the symptoms, the rats that were injected with the drug showed similar behavior to rats exposed to trauma but that were not exposed to trauma reminders. In other words -- cannabis made the effects of trauma reminders "disappear."

Once they found the moderating effect of cannabis on behavioral aspects, the study aimed to examine the neurobiological basis for the improvement caused by the drug. It was found that rats who 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 CB1 receptor, a receptor in the brain that cannabinoids are known to bind to, and receptor GR, the receptor associated with exposure to stress. On the other hand, in rats that received cannabinoids, the increase in the expression of these two receptors was prevented in the hippocampus and prefrontal cortex, areas involved in forming and saving traumatic memories.

"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. 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," the researchers concluded.