In mammals, newborns needtake in a lot of information, and this, quickly, to survive. A feat that is made possible thanks to synapses dites “silent”. The latter are connections between neurons that cannot yet carry out neurotransmission. If they are abundant at birth, scientists estimate thatthey become rarer with age.
This discovery concerning these silent synapses was made in baby mice several decades ago. Recently, researchers from MIT in the United States have shown that scarcity is much less extreme.
The article reporting this discovery was published on Nature November 30. The lead author is Mark Harnett who is a neuroscientist at MIT.
An unexpected discovery
During their work, the researchers did not want to examine silent synapses in particular. In fact, they were just continuing from previous works re the location of the dendrites (extensions of neurons).
Eventually, the team was able to capture not only images of the dendrites, but also those dendritic filopodia.
“Filopodia allow a memory system to be both flexible and robust. You need flexibility to acquire new information, but you also need stability to retain important information. »
Mark Harnett
What surprised the researchers was the high concentration of dendritic filopodia in the brain of adult mice. It’s a first ! Especially since a large part of the filopodia had only one type of neurotransmitter receptor (NMDA receptor).
In fact, a mature and functional synapse should have two types of neurotransmitter receptors. In the absence of the second (AMPA receptors), these are synapses “silent”. Admittedly, synapses are still immature. However, these connections can be activated according to the scientists.
Possible thanks to a new imaging technique
For imaging, researchers typically fluoresce cells using a variety of methods. The goal is to illuminate the cells they wish to observe.
Unfortunately, fluorescence causes glare, which complicates the observation of dendritic filopodia. Moreover, they are fragile, so they can be destroyed during the preparation of the samples to be observed. That is why this discovery was only possible recently.
In 2021, a new imaging technique has been developed. She is called « epitope-preserving magnified analysis of the proteome » or eMAP. It was the latter that allowed scientists to better observe silent synapses.
Concretely, the eMAP takes advantage of a gel in order toimmobilize the cellular structures as well as delicate proteins (such as filopodia). This is what allowed the team to take very high resolution images of the fluorescent dendrites.
SOURCE : SCIENCEALERT