A new study by researchers at the New York University School of Medicine and their collaborators across the U.S. suggests that there is a connection between the number of cannabinoid receptors in the brain and the effects of post-traumatic stress disorder (PTSD), according to an NYU press release.

Cannabinoid receptors, or CB1 receptors, are part of a large system of chemicals and signaling pathways from the brain to the body, NYU says. They play a role in the formation of memories, and in transmitting messages about appetite, pain, and mood to the body. Studies have shown that certain chemicals, like cannabis, can combine with naturally produced neurotransmitters to activate CB1 receptors, which in turn can impair memory and reduce anxiety.

The study, which was published online in Molecular Psychiatry and will be presented at the Society of Biological Psychiatry's annual meeting, is the first to use brain imaging to show that PTSD sufferers have lower concentrations of at least one of these neurotransmitters, called anandamide, than healthy people, NYU says. The researchers enrolled 60 participants in their study: some already diagnosed with PTSD, some with some history of trauma but no PTSD diagnosis, and some with no trauma or PTSD diagnosis. They then administered a tracer to illuminate the participants' CB1 receptors when exposed to a PET scan, and found that the PTSD sufferers — particularly women — had more CB1 receptors in the parts of their brains linked to fear and anxiety than the healthy participants, NYU says. They also found a lower level of anandamide in those with PTSD, leading to an increased number of CB1 receptors.

"There's not a single pharmacological treatment out there that has been developed specifically for PTSD," said lead author and NYU researcher Alexander Neumeister in the statement. "That's a problem. There's a consensus among clinicians that existing pharmaceutical treatments such as antidepressant simple do not work." In fact, he added, anecdotal evidence has shown that some PTSD sufferers who use marijuana, a cannabinoid, experience more symptom relief than with antidepressants.

These findings could be used to accurately diagnose PTSD, and could point the way to a viable target for treatment, NYU says. Current diagnostic techniques rely on subjective observation, making it a hard condition to diagnose. Now, Neumeister said, this study offers a possible biological explanation for the condition, which affects about 20 percent of the veterans of the Iraq and Afghanistan wars, and an estimated eight million Americans every year.

Source: A Neumeister, M D Normandin, R H Pietrzak, et al. Elevated brain cannabinoid CB1 receptor availability in post-traumatic stress disorder: a positron emission tomography study. Molecular Psychiatry. 2013 Available at http://www.nature.com/mp/journal/vaop/ncurrent/full/mp201361a.html. Accessed April 14, 2013.