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'Memory transplant' achieved in snails

15 May 2018

The research provides new clues in the search for the physical basis of memory.

The scientists gave mild electric shocks to the tails of a species of marine snail called Aplysia californica.

The shocked snails had been "sensitised" to the stimulus. Animals have developed a protective reflex, expressed in the contraction of the muscles during 50 seconds in subsequent contacts with the electrodes. Those that had not been given the shocks contracted for only about one second. (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).

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.

DNA methylation appeared to be essential for the transfer of the memory among snails. Unsurprisingly, this control group showed no signs of sensitization.

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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.

In a statement for The Guardian, Glanzman commented on the nature of the experiment, noting that the type of memories that were transplanted from one snail to another was crucial to the success of the procedure. Interestingly, the researchers discovered, adding RNA from the snails that had been given shocks also produced increased excitability in sensory neurons in a Petri dish; it did not do so in motor neurons. He found that introducing the RNA directly to the neurons "increased (their) excitability".

"If memories were stored at synapses, there is no way our experiment would have worked", he said, the BBC reported. (Each neuron has several thousand synapses.) Glanzman holds a different view, believing that memories are stored in the nucleus of neurons.

Professor Glanzman stressed the marine snails were not hurt by the experiment, but they were alarmed.

Researchers find out about the cell science of this straightforward type of learning in this creature than some other type of learning in some other living being, Glanzman said. These are commonly used as animal models for neuroscience because the cellular and molecular processes at work are relatively similar to humans, but they have a far more manageable number of neurons - about 20,000, compared to our 100 billion. In the 1940s, Canadian psychologist Donald Hebb proposed memories are made in the connections between neurons, called synapses, and stored as those connections grow stronger and more abundant.

'Memory transplant' achieved in snails