SAN DIEGO--Doctors who treat patients with posttraumatic stress disorder (PTSD) have long sought a therapy that would erase bad memories, or at least keep them in check. Preliminary research on rats and humans presented here 24 October at the meeting of the Society for Neuroscience suggests that a drug already in wide use for treating high blood pressure might have just that effect.
The drug, propranolol, blocks certain receptors for the neurotransmitter norepinephrine and has already shown promise in small clinical trials for PTSD, apparently preventing the formation of traumatic memories. In those studies, emergency room patients given propranolol within a few hours after an accident had fewer symptoms of posttraumatic stress months later. That suggested that propranolol could act as a prophylactic.
The new work hints that propranolol might also work on memories that have already formed. Jacek Dębiec, a neurobiologist at New York University, conditioned rats to fear a tone by pairing it with a mild shock. After training, the rats freeze up in anticipation when they hear the tone. The next day, Dębiec refreshed the rats' memory, exposing them again to the tone and shock. He then gave half of the animals an injection of propranolol. Two days later, untreated rats still remembered what the tone meant; upon hearing it, they froze about 70% of the time. But rats given propranolol froze only about half as often, indicating a weaker memory for the fearful association between sound and shock. Even when Dębiec waited 2 months before reactivating the memory and delivering propranolol, the drug had a similar effect, he reported at the meeting and in a paper published in the current issue of Neuroscience.
Reactivating the memory is key to suppressing it successfully, Dębiec says. He says his findings are consistent with the idea that memories are briefly vulnerable when they're recalled--a controversial notion known as "reconsolidation" that has gained new support in recent years. A poster presentation at the meeting by Melinda Miller, also at New York University, suggested that propranolol may also interfere with reconsolidation of fear memories in humans.
Other researchers say the findings are interesting but should be considered very preliminary. Mark Barad, a psychiatrist at the University of California, Los Angeles, is unimpressed by propranolol's memory-weakening effect in Miller's human study. "It's not as positive an effect as we would like," he says. Still, says Samuel McLean of the University of Michigan, Ann Arbor, it should be easy to test whether propranolol helps PTSD patients who take it after an episode of recalling traumatic memories. Dębiec and Miller say such a pilot study is already under way.