Brain chemicals wipe out bad memories, study says International Herald Tribune 1.8.02

London: Feel-good chemicals in the brain, similar to the active ingredient in cannabis, can wipe out bad memories, German scientist said in a finding that could lead to new treatments for anxiety disorders and phobias. Researchers at the Max Planck Institute in Munich have shown that natural chemical in the brain similar to THC, the active ingredient in marijuana that produces the high, dampen nerve cell action and wipe out unpleasant memories. THC, or tetrahydrocannabinol, and similar molecules in the brain known as cannabinoids binds to the brain’s chemical receptors and can create a feeling of euphoria. Cannabis and hashish, witch contain THC, have been used for centuries for medicinal and recreational purpose. Doctor Beat Lutz and his team created transgenic, or genetically modified, mice without a cannabinoid receptor. When they conditioned them to associate a musical tone with electric shock, the mice produced a fear reaction, and conditioned to react even when the tone was not followed by a shock, Lutz said. Normal mice quickly stopped reacting to the tone once it was not associated with a shock, but the genetically modified mice without the cannabinoid receptor took much longer to forget their fear. Lutz and his team, whose research is published in the science journal Nature, also showed that blocking the receptor in normal mice prevented the animals from forgetting the painful memory. When the scientists studied an almond shaped area of the brain called the amygdala, central to storing memory and fear, in transgenic and normal mice, they discovered it was flooded with natural chemicals, or endocannabinoids, when the mice were gradually forgetting the learned response to the shock. Lutz believes that the chemicals help to wipe out the fair or memory of the unpleasant response by binding to the cannabinoid receptors, he said Wednesday. Smoking cannabis would not produce the same effect in humans, Lutz said, because it overflows the brain and is not specific enough to extinguish the unpleasant memory. "The finding that the endocannabinoids contribute to extinction raises the possibility that drugs that target these molecules and their receptors could be useful new treatment for anxiety disorders" Pankaj Sah, of the Australian National University in Canberra, said in a commentary in Nature.