The new findings could one day help to restore lost memories or reduce the trauma of painful memories, according to the researchers.
In their paper, Glanzman and colleagues say their results raise many new questions about the mechanics of memory storage and the nature of the engram. 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.
The marine snails or Aplysia Californica were given minor electric shocks by the scientists only after proper administration of the shocks. Animals have developed a protective reflex, expressed in the contraction of the muscles during 50 seconds in subsequent contacts with the electrodes.
The snails were trained to develop a defensive reaction.
The researchers trained one cohort of the molluscs to exhibit a defensive reflex when their tails were stimulated by mild electric shocks. But the ones injected with RNA from the trained snails? (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). "If circulating neural RNAs can transfer behavioral states and tendencies, orchestrating both the transient feeling and the more permanent memory, it suggests that human memory-just like mood-will only be explained by exploring the interplay between bodies and brains".
As expected, the control group of snails did not display the lengthy contraction. When Glanzman repeated the experiment with RNA from sea snails that had been hooked up to wires but not shocked, the reflex behaviour did not transfer. But scientists have been studying sea snails for a long time, and they know an bad lot about how the organisms learn. Like all mollusks, these snails have groups of neurons called ganglia, rather than brains.
Glanzman said the next step in this research is to transfer RNA in more complex animals, like mice. Also, it's worth noting that the snails were not hurt during this experiment. Adding RNA from a marine snail that was not given the tail shocks did not produce this increased excitability in sensory neurons. Currently, most neuroscientists believe that memories are stored in connections between neurons, known as synapses, not simply within the cells themselves. "Obviously further work needs to be carried out to determine whether these changes are robust and what are the underlying mechanisms", said Prof Seralynne Vann, who studies memory at Cardiff University.