RNAs are effectively the messenger that carry out the instructions coded into our DNA.
This groundbreaking experiment began with training a group of sea snails belonging to the Aplysia californica species, colloquially known as the California sea hare. The snails acted the same way as if they had been administered shocks. By repeatedly shocking the snail's tail, the animal learns to stay in that defensive position when touched on the siphon, even weeks after the shocks end. Sticking electrodes in the snail's tail and shocking it makes this defensive response last longer, tens of seconds, and sometimes up to nearly a minute. At first, the snails would only curl for a few seconds.
Scientists extracted RNA from the nervous systems of the snails that received the shocks and injected it into a small number of marine snails that had not been sensitised in this way. The snails had been "sensitised" to the shock. (For a control, the team also took RNA from non-shocked snails and injected into naive snails.) When tapped on the siphon 24 hours later, snails that got RNA from shocked snails withdrew their siphon and gill for significantly longer (almost 40 seconds) than did snails that got RNA from non-shocked animals (less than 10 seconds).
But there are many different types of RNA, and Glanzman's team plans to do more research to figure out determine which types most directly impact memory. Tomas Ryan, who studies memory at Trinity College Dublin in Ireland, opined that, as impressive as their study may be, the UCLA team didn't actually transfer a memory, but rather a basic behavioral response that triggered the defense mechanism in the untrained snails. Some dishes had RNA from marine snails that had been given electric tail shocks, and some dishes contained RNA from snails that had not been given shocks. The experiments should also be replicated in organisms other than snails, he says. Adding RNA from a marine snail that was not given the tail shocks did not produce this increased excitability in sensory neurons. According to the researchers, the results show that memories are stored in the nuclei of neurons, where specific genes are activated and synthesizes corresponding ribonucleic acid.
"If memories were stored at synapses, there is no way our experiment would have worked", said Glanzman, who added that the marine snail is an excellent model for studying the brain and memory.
But in a new study, researchers claim to have made headway in understanding the simplest kind of memory a mollusc might form, and, with a swift injection, managed to transfer such a memory from one sea snail to another.
Yes, sea snails may have 20,000 neurons - a paltry sum compared to humans' 100 billion. Seralynne Vann from Cardiff University in the United Kingdom made an interesting point about the chances of applying a similar technique in the study of human memory.