Aplysia californica
What's the News: Researchers have considerably weakened---and perhaps even erased---long-term memories in Aplysia
, a type of marine slug, and in neurons in a lab dish, by blocking the activity of a particular enzyme. Understanding how to weaken and erase such memories could one day lead to new treatments for people suffering from post-traumatic stress disorder
, who are haunted by memories of traumatic events. How the Heck:
The researchers first gave each slug a painful memory: a shock to its tail. The slug didn't forget the pain, and a week later, they would still retract their tails for a full half minute when someone touched them on the same spot.
Next, the researchers injected the slug with zeta inhibitory peptide, a small protein-like molecule that blocks the activity of kinase M, an enzyme associated with maintaining memories. Twenty-four hours later, when their tails were prodded again, the slug responded as though they'd never been shocked, flinching away from the touch only momentarily before relaxing. "The long-term memory is gone," said neurobiologist David Glanzman, the study's senior author, in a prepared statement.
To examine this memory-weakening effect in isolated neurons, the researchers gave another group of slug the shock, then removed the two-neuron "circuit"---one sensory neuron and one motor neuron---responsible for the tail-retracting reaction to touch. A change in the synapse between these two cells underlies the long-term memory of the tail shock; applying the chemical that inhibits protein kinase M erased that change---which, the researchers suggest, would erase the memory as well.
What's the Context:
This research could eventually help not only to erase traumatic memories in people suffering from PTSD, the researchers suggest, but to treat other conditions in which memory plays a major role, such as substance abuse disorders and Alzheimer's disease.
Other researchers have also been investigating drugs that could erase memories, focusing on a variety of neural mechanisms.
A marine slug may seem like an unusual choice for a study of memory, but Aplysia have been used in a wide range of neuroscience studies, thanks to their large neurons, relatively simple nervous system, and set of behaviors. Many of the same neural processes that underlie memory in these slug underlie memory in mammals, too.
Not So Fast:
It's a long way from helping a slug get over a shock to helping a soldier recover from war-zone trauma and, as Glanzman willingly acknowledged, it will take a lot of research to get from one to the other.
Reference: Diancai Cai, Kaycey Pearce^1, Shanping Chen, and David L. Glanzman. "Protein Kinase M Maintains Long-Term Sensitization and Long-Term Facilitation inAplysia." Journal of Neuroscience, April 27, 2011. DOI:10.1523/JNEUROSCI.4744-10.2011
Image: Wikimedia Commons / Nordelch
