Scientists Say They've Transplanted a Memory From One Snail to Another

The California sea hare Aplysia californica. Credit Wikimedia Commons

The California sea hare Aplysia californica. Credit Wikimedia Commons

The "memory transplant" was achieved through ribonucleic acid (RNA) injections and provides new tantalizing clues regarding the memory trace - also known as an engram, the presumed physical substrate of memory. 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. When Glanzman and his colleagues blocked DNA methylation in snails getting RNA from shocked ones, the injected snails withdrew their siphons for only a few seconds when tapped on the siphon. The snails received five tail shocks, one every 20 minutes, and then five more 24 hours later.

When touched lightly on the siphon, the neurons fire, retract the tissue, and contract the gill within the body cavity for a few seconds to protect it against attack.

For the next part of the experiment, the researchers extracted RNA from the sensitized snails (the ones given shocks) and injected it into seven snails that had not received any shocks.

The UCLA team suggests their research might one day allow us to, as the study states, "modify, enhance, or depress memories". Like all mollusks, these snails have groups of neurons called ganglia, rather than brains.

They then added RNA from trained and untrained snails to these dishes to observe the effect on the neurons. 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.

When a marine snail is given electric tail shocks, its sensory neurons become more excitable.

Glanzman also tested the theory on cultured sensory neurons he extracted from the untrained snails that controlled the defensive reflex. The team found that the snail synapses built to "store" a memory weren't necessarily the synapses that were removed from the neural circuits in the memory-erasing experiments.

(Each neuron has several thousand synapses.) Glanzman holds a different view, believing that memories are stored in the nucleus of neurons.

"These are marine snails and when they are alarmed they release a lovely purple ink to hide themselves from predators".

Scientists know more about the cell biology of this simple form of learning in this animal than any other form of learning in any other organism, Glanzman said. "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. 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.

Co-authors are Alexis Bédécarrats, a UCLA postdoctoral scholar who worked in Glanzman's laboratory; and Shanping Chen, Kaycey Pearce and Diancai Cai, research associates in Glanzman's laboratory.

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