Scientists at the Austrian Institute of Science and Technology have discovered that electrochemical signals in the memory centers of the brain can be transmitted between neurons in the opposite direction, from dendrite to axon. Previously, it was believed that the transmission of impulses occurs exclusively unilaterally. A previously unknown phenomenon in the human nervous system is reported in an article published in the journal Nature Communications.
Neuroscientists studied the interaction between the bryophyte (mossy) fibers of the hippocampus from the brain and pyramidal neurons using the example of the rat brain, which serves as a model organism. Synaptic contacts are formed between the axons of the bryophytes and the dendrites of the pyramidal cells, through which post-tetanic potentiation is carried out – the most powerful form of synaptic plasticity that forms memory and learning. Post-tetanic potentiation increases the excitability of pyramidal neurons (postsynaptic cells) after a short stimulation of bryophytes (presynaptic cells).
For a long time it was believed that post-tetanic potentiation proceeds unilaterally: from the axon of bryophytes to the dendrites of pyramidal neurons, that is, exclusively presynaptic neurons are responsible for synaptic plasticity.
The results of the new study showed that, as expected, excitement was transmitted from nerve cells of bryophytes to pyramidal neurons, but the transmission of a reverse signal was recorded: when the activity of the postsynaptic neuron increased, synaptic plasticity decreased.
The reverse signal transmission is possibly mediated by glutamate, which is released by dendrites and binds to receptors in the presynaptic membrane. This mechanism, scientists believe, may play an important role in optimizing the storage of information in the human brain. However, researchers have yet to understand why glutamate released by signaling cells does not have the same effect as postsynaptic cell glutamate.