Natural chemicals similar to the active ingredient of cannabis wipe out adverse memories in the brain, researchers announced in the Aug. 1 issue of the journal Nature.
Using a model of fear conditioning in mice, German and Italian researchers found that the cannabinoid receptor CB1 is important in erasing fear. In their study, both mutant mice that lacked CB1 and control mice first were exposed to a tone signal and an electric shock. The mice then were exposed repeatedly to the tone only.
When researchers analyzed the behavioral reaction to the potentially fear-inducing signal, they found that all of the mice showed a big fear reaction during the first re-exposure to the tone. When the tone only was repeated over and over again, the control mice quickly recovered from their fear reaction. CB1-deficient mice, however, showed only a small reduction of fear.
Researchers confirmed the impaired ability of CB1-deficient mice to adapt to perceived adverse or dangerous situations in an accompanying pharmacological experiment. They blocked the CB1 receptor using a selective antagonist and found that this affected the fear reaction of the normal mice when the antagonist was applied before memory recall—re-exposure to the tone.
Researchers also found that endocannabinoids, which activate CB1, were enriched in the amygdala—the brain’s fear center—of normal mice immediately after they were re-exposed to the tone.
Researchers hope that these findings will lead to new approaches, such as drugs that boost cannabinoids in the amygdala, for treating people who have posttramatic stress disorders, phobias and panic attacks.
