Newborns need to quickly memorize a huge amount of new information as they learn to navigate the world.
Silent synapses—immature connections between neurons that do not yet have neurotransmitter activity—are thought to be devices that enable rapid information storage at an early age.
These potential neural connections, first discovered several decades ago in newborn mice, were thought to disappear as the animals aged. A recent study by researchers at the Massachusetts Institute of Technology in the US found that this attenuation may not be as extreme as originally thought.
The team did not plan to specifically consider these potential links. Instead, they continued previous work on the arrangement of neuron extensions called dendrites.
And we got a little more than we expected. He photographed not only the dendrites, but the countless tiny filamentous protrusions that emerge from them, called filamentous pedicels.
“The first thing we saw, and it was very strange and unexpected, was the presence of filopodia everywhere (thin, membranous protrusions that act as antennas for exploring the cell’s environment”), says Mark Harnett, an MIT neuroscientist and senior author. paper.
It is usually hidden in the fluorescent light used to illuminate the cell during imaging, and this new imaging process uses a gel to help hold delicate cell structures and proteins in place, allowing researchers to better study them by manipulating tissues.
Viruses expressing green fluorescent protein were injected into two male and two adult mice to help illuminate the appropriate tissues for imaging. Their primary visual cortex was then excised and cut into 1 mm sections before incubation in eMAP monomer hydrogel solution and fixed between glass slides.
For the first time, the researchers were able to see that there were concentrations of philopedia in the brains of adult mice not seen in adult mice. Moreover, many structures have only one of the two neurotransmitter receptors protruding from the mature synapse. Without the second, they were effectively “silent” connections between neurons.
The researchers then asked if silent adult synapses could be activated.
They showed that this was made possible by the release of the neurotransmitter glutamate at the ends of the filaments, producing a small electrical current after ten milliseconds.
This action “opens” the synapses within minutes, stimulating the accumulation of lost receptors and allowing philopedia to form a connection with neighboring nerve fibers.
These receptors are normally blocked by magnesium ions, but the current releases them, allowing the philopedia to receive a message from another neuron.
The team found that activating silent synapses was much easier than changing the activity of dendritic spines on mature neurons.
Researchers are currently studying whether silent synapses are present in adult brain tissue.
This article was published in the journal Nature.
Source: Science Alert