Meth-related Memories Erased in Mice and Rats

Scientists have successfully erased drug-associated memories in mice and rats without affecting any other recollections, according to a study published in the journal Biological Psychiatry. The findings point to a clear method through which memories can be disrupted, even as all others remain carefully intact, according to the researchers.

"Our memories make us who we are, but some of these memories can make life very difficult," said Courtney Miller, an assistant professor at The Scripps Research Institute who led the research. "Not unlike in the movie Eternal Sunshine of the Spotless Mind, we're looking for strategies to selectively eliminate evidence of past experiences related to drug abuse or a traumatic event. Our study shows we can do just that in mice -- wipe out deeply engrained drug-related memories without harming other memories."

The researchers were able to achieve this by going after actin, the protein that makes up the infrastructure of all cells.

To produce a memory, the structure of nerve cells must be altered through changes in the dendritic spines, or the small structure responsible for receiving electrochemical signals from other neurons.

Knowing that actin is responsible for these changes, the scientists inhibited actin polymerization, or the creation of large, chain-like molecules, by blocking the molecular motor myosin II. They did this in the brains of mice and rats during the maintenance phase of meth-related memory formation.

Previous behavioral tests showed the animals consistently lost any memories associated with meth even as others remained unscathed.

During the experiment, the researchers trained mice and rats to associate meth with a series of rich tactile, visual and scent-related cues. They then then injected the animals with the inhibitor days later in the creatures' home environment, after which the mice and rats showed no interest in those cues. All other responses to other memories, such as food rewards, remained the same, however.

Why meth-related memories are so fragile is not clear; however, the scientists believe it could have something to do with the role of dopamine, a neurotransmitter involved in reward and pleasure centers in the brain and known to change dendritic spines. Previous studies reveal dopamine is released during learning and drug withdrawal.

"We are focused on understanding what makes these memories different," Miller said. "The hope is that our strategies may be applicable to other harmful memories, such as those that perpetuate smoking or PTSD."