Forget everything you know about memories (!) because a new study has turned our knowledge regarding memory formation on its head by showing the ability to transfer memories from animal-to-animal!
Current dogma states that learning-induced modifications of synaptic connections underlie the storage of our long-term memory (LTM); however, recent studies have suggested that neuron cell bodies store LTM in some unidentified manner (See Chen et al., 2014, Johansson et al., 2014, and Ryan et al., 2015). This led researchers from the group of David L. Glanzman (University of California, Los Angeles, USA) to study the formation of LTM in the Aplysia californica sea snail (or Californian sea hare) and they now propose that, incredibly, RNA-induced DNA methylation can encode LTM.
Researchers employ Aplysia californica as a model animal to study the cellular basis of learning and memory because of the simplicity and large size of the neural circuitry. Bédécarrats and colleagues employed the Aplysia gill and siphon withdrawal reflex (shocking stuff indeed!) to study how long-term sensitization training led to the formation of non-associative LTM by assessing the significance of RNA extracted from the Aplysia central nervous system (CNS).
Here are the memorable results from this unforgettable new sea snail study into long-term memory:
- RNA extracted from the CNS of animals that undergo long-term sensitization training induces a reflex enhancement when injected into untrained animals
- Application of a DNA methyltransferase inhibitor (RG-108) demonstrated that both RNA-induced and training-induced sensitization requires DNA methylation
- These data support a model by which RNA-induced DNA methylation encodes LTM
- Sensory neuron hyperexcitability underlies sensitization in sea snails, and the authors discovered that treatment with RNA from trained animals selectively increases excitability in ex vivo cultures of sensory neurons, but not in motor neurons, from untrained animals
The talented team hopes to continue their research in sea snails and discover which specific RNA species mediate non-associative LTM transfer (non-coding and long non-coding RNAs are top of the list!) and the transport mechanisms employed to transfer RNA to Aplysia neurons (exosomes or extra-cellular vesicles?). Furthermore, assays of the genomic targets of the RNA-induced DNA methylation may also help to further our understanding of this incredible process.
Senior author David L. Glanzman shares, “It’s as though we transferred the memory. If memories were stored at synapses, there is no way our experiment would have worked. I think in the not-too-distant future, we could potentially use RNA to ameliorate the effects of Alzheimer’s disease or post-traumatic stress disorder.”
Will this new research move us closer to transplanting our memories? To find out, see all the unforgettable details at eNeuro, May 2018.