Developmental biology - Nerve Function|
How to 'transfer' a memory"
Research in marine snails could lead to new treatments restoring memories or altering a traumatic one...
UCLA biologists report they have transferred a memory from one marine snail to another, creating an artificial memory in recipient snails. They did this by injecting RNA from one snail to the other. Such research could lead to new ways to lessen the trauma of painful memories or restore lost memories using RNA.
The marine snail is an excellent model animal for studying brain and memory as scientists know more about its simple form of learning than any other organism. Their cellular and molecular processes seem to be very similar to humans, even though the snail has about 20,000 neurons in its central nervous system and humans are thought to have about 100 billion.
RNA, or ribonucleic acid, has been widely known as a cellular messenger that makes proteins and carries out DNA's instructions to other parts of the cell. It is now understood to have other important functions besides protein coding, including regulation of a variety of cell processes involved in development and disease.
"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."
David Glanzman PhD, Professor, Intergrative Biology and Physiology and Neurobiology, and Brain Research Institute, University of California at Los Angeles, and senior author of the study.
The team's research is published May 14 in eNeuro, the online journal of the Society for Neuroscience.
In the study, mild electric shocks were administered to the tails of a species of marine snail called Aplysia. The snails received five tail shocks, one every 20 minutes, and then five more 24 hours later. The shocks increased a snail's defensive withdrawal reflex, displayed as protection from potential harm.
When researchers later tapped the snails, those given tail shocks contracted defensively (with a memory of the pain ?) in a position lasting an average of 50 seconds. This response is attributed as learning and called sensitization. Snails not previously given shocks contracted for only about one second.
Scientists extracted RNA from the nervous systems of those marine snails that received tail shocks one day after their second series of shocks, and also from marine snails not having received any shocks. Then RNA from the first (sensitized) group was injected into seven marine snails who had not received any shocks, and RNA from this second group was injected into a control group of seven snails who also had not received any shocks.
Remarkably, the seven snails that received RNA from snails given shocks — behaved as if they themselves had received the tail shocks. They displayed defensive contraction of their bodies lasting an average of 40 seconds.
"It's as though we transferred the memory," said Glanzman. As expected, the control group of snails did not display any lengthy nerve contraction.
Image of a human neuron. Credit: Cornell University
Next, researchers added RNA to Petri dishes containing neurons extracted from snails who had or had not received shocks. Some of the Petri dishes contained only sensory neurons, and others contained only motor neurons responsible for neural reflex in snails. Aplysia given electric tail shocks had more excited sensory neurons.
In petri dish experiments:
• RNA from shocked snails increased excitability in sensory neurons but not motor neurons.
• RNA from unshocked snails didn't increase excitability in sensory neurons.
In the field of neuroscience, it has long been believed memories are stored in synapses, with each neuron having thousand of synapses. Glanzman believes memories are stored in the nucleus of neurons as synapses continually change chemically, stating: "If memories were stored at synapses, there is no way our experiment would have worked."
In the future, Glanzman feels it will be possible RNA will be used to awaken and restore memories made dormant in early stage Alzheimer's disease. He and his colleagues published research in the journal eLife in 2014 indicating that lost memories can be restored.
There are many kinds of RNA, and in future research, Glanzman plans to identify those types of RNA useful for memory transfer.
The precise nature of the engram, the physical substrate of memory, remains uncertain. Here, it is reported that RNA extracted from the central nervous system of Aplysia given long-term sensitization training induced sensitization when injected into untrained animals; furthermore, the RNA-induced sensitization, like training-induced sensitization, required DNA methylation. In cellular experiments, treatment with RNA extracted from trained animals was found to increase excitability in sensory neurons, but not in motor neurons, dissociated from naïve animals. Thus, the behavioral, and a subset of the cellular, modifications characteristic of a form of nonassociative long-term memory in Aplysia can be transferred by RNA. These results indicate that RNA is sufficient to generate an engram for long-term sensitization in Aplysia and are consistent with the hypothesis that RNA-induced epigenetic changes underlie memory storage in Aplysia.
Authors: Alexis Bédécarrats, Shanping Chen, Kaycey Pearce, Diancai Cai and David L. Glanzman.
The research was funded by the National Institute of Neurological Disorders and Stroke, the National Institute of Mental Health and the National Science Foundation.
Return to top of page
May 23, 2018 Fetal Timeline Maternal Timeline News News Archive
Aplysia californica emitting ink cloud. Image source: Wikipedia