The memory uncovers the secret of its “fuel”
Astrocytes in the brains
Researchers from the Brain Mind Institute at EPFL and the Mount Sinai School of Medicine in New York have highlighted the crucial role played by a by-product of glucose – lactate – in the formation of long-term memory. This could lead to new therapeutic perspectives for some neurological disorders.
The “biological hard disk”, which stores our memories, remains mostly a mystery. An essential stage in the understanding of the mechanisms of our memory has however been reached by a Swiss-American research team. Pierre Magistretti, holder of the Asterion chair and Director of the Brain Mind Institute at EPFL, together with Christina Alberini, of the Mount Sinai School of Medicine in New York, have just published in the Journal Cell the – surprising – results of their joint research.
The latter has enabled the proof of the importance of astrocytes in memorization. These cells, which exist in very large quantities in the brain (they are more numerous than the neurons) and which we know are found at the interface between the blood system and the synapses, turn out to be a supplier of energy for the neurons. They feed them with lactate, a “cousin” of glucose in that it originates from the same precursor – glycogen – of which a stock is present in these star-shaped cells. The researchers have been able to prove that this lactate was an indispensable condition for memorization processes to occur.
Their experiments have been conducted on rats, trained to beware of a dark room where they received an electric shock. Under normal conditions, they learn straight away that there is a problem and therefore subsequently hesitate to leave a lighter area, although in fact they much prefer darkness. “By intervening on their hippocampus, we manage to stop the production or transport of lactate by the astrocytes”, explains Pierre Magistretti. “And we have been able to observe that although these rats retained short-term memory, on the other hand they completely forgot about the danger after 24 hours, and would rush into the dark room.”
Glucose doesn't fit
Even more interesting, in a second phase of the experiment, the supply of exogenous lactate directly to the hippocampus resulted in the restoration of the rat’s memorization capacities. The same procedure performed with glucose, on the other hand, did not produce any result. “This shows the importance of this particular substance, and opens up new fields of investigation in the area of neurological diseases where the memory is affected, such as Alzheimer”, adds Pierre Magistretti. Which does not exclude that it could even be possible to artificially stimulate the memory by acting on the production and transportation of this lactate.
Neuroscientists had already been able to ascertain that memorization depended on “neuroplasticity”, that is, a physical and durable modification of the network of synapses connecting the neurones. But we still don’t know how and why these changes happen. “Our research provides an element of response: it seems that, in a way, this lactate is the fuel behind these modifications. And we suspect that it plays an even more important role” suggests the professor, who has already undertaken new research in this direction.
There will almost certainly be follow-ups to this research, which is already an important step forward. “The interest for the astrocytes and lactate, which have not been the object of significant study, will certainly increase over the next few years”, anticipates Pierre Magistretti.