A new drug could help weaken disturbing memories and aid in the recovery of Post Traumatic Stress Disorder (PTSD).
The drug histone deacetylase inhibitors (HDACis) has the ability to encourage the brain to replace past traumatic memories with more pleasant ones, a Cell Press news release reported.
"Psychotherapy is often used for treating PTSD, but it doesn't always work, especially when the traumatic events occurred many years earlier," senior study author Li-Huei Tsai of the Massachusetts Institute of Technology, said. "This study provides a mechanism explaining why old memories are difficult to extinguish and shows that HDACis can facilitate psychotherapy to treat anxiety disorders such as PTSD."
Today anxiety disorders are normally treated with exposure-based therapy, which forces the patient to confront fears and stressors head on. When the subjects are exposed to the stimulus it causes them to revisit the traumatic memory, opening a short window where that memory can be modified. Exposure therapies have been known to effectively treat newly-formed memories, but it was unclear if the technique would work for new memories as well.
The researchers exposed mice to a tone, and shocked their feet when it was played. Eventually the mice began to freeze in fear when they heard the tone, even if no shock was administered. The team then played the tone without the electric shock several times to see if the mie could "unlearn" the fear.
"The extinction protocol was successful for mice that were exposed to the tone-shock pairing just one day earlier, but it was not effective for mice that originally formed the traumatic memory one month earlier. The researchers hypothesized that epigenetic modification of genes involved in learning and memory might be responsible for the diminished response of treatment for older memories," the news release reported.
The team wanted to know if the HDACi promoted gene activation in these learning and memory areas, allowing old traumatic memories to be replaced with new non-traumatic ones. Mice that had previously been exposed to the tone and shock and then treated with HDACis learned to stop freezing when the tone was played.
"Collectively, our findings suggest that exposure-based therapy alone does not effectively weaken traumatic memories that were formed a long time ago, but that HDACis can be combined with exposure-based therapy to substantially improve treatment for the most enduring traumatic memories," Tsai said.
