Cravings—we all have them. These intense desires can be triggered by a place, a smell, even a picture. For recovering drug addicts, such memory associations can increase vulnerability to relapse. Now researchers at the Florida campus of the Scripps Research Institute have found a chemical that prevents rats from recalling their drug-associated memories. The study, published online in Biological Psychiatry last fall, is also the first of its kind to disrupt memories without requiring active recollection.
Over the course of six days the rats in this study alternated between one of two chambers. On days one, three and five, the animals were injected with methamphetamine hydrochloride—the street drug known as meth—and placed in one room. On the even-numbered days they received a saline placebo and entered a different chamber.
After two more days, half the rodents were given a choice between the rooms. As expected, they showed a clear preference for the place they visited after receiving meth. The other half of the animals were injected with a solution containing Latrunculin A (LatA). This chemical interferes with actin, a protein known to be involved in memory formation. These animals showed no preference between rooms, even up to a day later: their choices seemed not to be driven by a memory of meth.
Previous research has suggested that drugs of abuse alter the way actin functions, causing it to constantly refresh memories associated with these drugs rather than tucking them away into typical memory storage, which is more inert. As a result of their active status, drug memories might remain susceptible to disruption long after their initial formation.
The idea that drug memories might differ in this way is relatively new, so the researchers double-checked this understanding by testing whether LatA could affect food associations. The rats underwent a similar regimen to create a mental link between food and environment. LatA injections had no effect on the animals' reactions to the different chambers, meaning it left the food associations intact.
“The claim that you have an active [actin process] that can maintain the memory days later is really remarkable,” says Gary Lynch, a professor of psychiatry and human behavior at the University of California, Irvine. The next step is to find out what other types of memories—if any—share this property, so that we know exactly what kinds of recall this treatment can target, he says.
Courtney Miller, a co-author of the study and a neurobiologist at Scripps, points out that the technique's limited usefulness helps to alleviate ethical concerns about memory alteration. “You actually couldn't take our discovery and erase a run-of-the-mill memory in the brain, because it simply doesn't work. You can only actually get rid of these drug-associated memories.” Miller emphasizes that the idea behind this research is to give those affected by drug addiction “a fighting chance to stay clean.”