'Memory transplant' achieved in snails


Much more research awaits, but for now, these results suggest that at least some kinds of memory could be modified using RNA, and it brings researcher closer to an overall understanding of the physical traces of memory in the nervous system. It is now understood to have other important functions besides protein coding, including regulation of a variety of cellular processes involved in development and disease.

Researchers in the USA achieved the feat by first teaching a group of Aplysia snails - using a series of mild electric shocks - to associate potential danger with a harmless tap on the outside of their shells. As for the snails, the team trained then beforehand to develop a defensive reaction to this procedure. At first, the snails would only retreat for a few seconds, but through repeated shocks, the scientists trained them to curl up for a longer period of time, about 50 seconds.

"So, these snails are alarmed and release ink, but they aren't physically damaged by the shocks", he explained. (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).

Rather than transferring what we think of as a memory, the team transferred something called an RNA or ribonucleic acid. The snails in the control group did not display this behavior, indicating that the injection was responsible.

The shocked snails had been "sensitised" to the stimulus. Some of the dishes contained sensory neurons, and others contained motor neurons, which in the snail are responsible for the reflex.

Glanzman said the next step in this research is to transfer RNA in more complex animals, like mice. A group of untrained snails received RNA from the trained group and the second group received RNA from an untrained group. However, they conclude that their findings offer "dramatic support" for the idea that memory does not have to be stored in synapses.

Professor Glanzman said in future it might be possible to awaken and restore memories that have gone dormant in the early stages of Alzheimer's disease, or ameliorate the effects of post-traumatic stress disorder.

A sea snail has about 20,000 neurons in its central nervous system and a human is thought to have 100 billion, according to the scientists.

"If memories were stored at synapses, there is no way our experiment would have worked", Glanzman told the BBC. The memory is not stored in the RNA itself, he speculates-instead, noncoding RNA produces epigenetic changes in the nucleus of neurons, thereby storing the memory.

Glanzman and his colleagues published research in 2014 suggesting that lost memories could potentially be restored based on this concept.