Harvard Mental Health Letter

In Brief: Researchers provide insight into the chemistry of fear

In Brief

Researchers provide insight into the chemistry of fear

In experiments involving mice, researchers at MIT's Picower Institute for Learning and Memory and Howard Hughes Medical Institute report that they have identified a chemical pathway that may underlie the persistence of debilitating fear following a traumatic event.

The researchers used genetically engineered mice in which production of a chemical known as Cdk5, produced in the hippocampus, a part of the brain involved in storing memories, can be controlled through the addition of doxycycline (a common antibiotic) in the diet. The mice were placed in a new environment and exposed to mild foot shocks — in other words, subjected to classic Pavlovian fear conditioning — which resulted in a normal "freezing in place" response.

Later, when the mice were repeatedly re-exposed to the location where the foot shocks occurred, the mice with greater-than-normal Cdk5 levels continued to freeze in fear longer than the mice in which production of this chemical was inhibited, indicating that Cdk5 may provide a molecular mechanism underlying the retention or erasure of fear.

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