A memory was transferred from one animal to another, scientists at UCLA have reported in the journal eNeuro. To do so, the researchers used RNA taken from a marine snail and injected it into another. RNA transmits information from the genetic code to the cell, and while a primary function is to create protein from genes, RNA can also send messages. This work shows that it plays a role in the physiology of memory, and could one day help reduce trauma or restore lost information.
"I think in the not-too-distant future, we could potentially use RNA to ameliorate the effects of Alzheimer's disease or post-traumatic stress disorder," explained the senior author of the work, David Glanzman, a UCLA professor of integrative biology and physiology, and neurobiology.
For this work, the researchers used Aplysia, a type of marine snail. The snails received a tail shock every twenty minutes until they’d had five. They got another five a day later. The withdrawal reflex, which is displayed when the snail is threatened, was enhanced by the shocks. When snails are not shocked, a tap results in a defensive reflex that lasts one second. Shocked snails, however, contracted defensively for fifty seconds when the researchers tapped them; that is a kind of learning that is referred to as sensitization.
RNA was then harvested from the various marine snails’ nervous systems. Seven marine snails that had not gotten shocks received RNA from the shocked or sensitized, marine snails. Seven other un-shocked marine snails got RNA from snails that had also not been exposed to the shock treatment.
The scientists found that the marine snails that received RNA from sensitized snails then behaved as if they had also been shocked. When tapped, their defensive reflex lasted around 40 seconds. There was no such display in the snails that received RNA from snails that were not sensitized. "It's as though we transferred the memory," noted Glanzman.
The researchers also looked at cells in a dish to study how such transplants affected neurons in culture. It has been suggested that memories are stored where neurons connect, at the synapses. Glanzman thinks that they’re actually stored in the nucleus of neurons. The team found that the sensitization caused sensory neurons to become more excitable. When RNA was transferred as it was in the snails, neurons that were from animals that were not shocked became excitable after they received RNA from sensitized animals. That transferable excitability seen in the dish lends credence to Glanzman’s hypothesis.
"If memories were stored at synapses, there is no way our experiment would have worked," said Glanzman.
Glanzman added that marine snails are great models for researching memory. The cell biology of this organism has been studied and characterized extensively, and there are very similar processes at work in human and snail neurons; the snail is just a much simpler organism with far fewer neurons.
Glanzman plans to continue his work and is pursuing research to restore memories in Alzheimer’s patients. He also wants to find out more about the RNA that is transferring memories.