Fragment of cognition

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A stunning 3D reconstruction unveils the molecular machinery of a neuronal connection.

Synapse with 60 types of proteins
The 60 proteins of a synaptic bouton

The 60 types of proteins of a synaptic bouton, involved in various cellular processes in neuronal communication, such as the release of neurotransmitters and the recycling of vesicles. Source: Wilhelm et al. (2014), Science, reprinted with permission from AAAS; Burkhard Rammner (3D imagery); Sven Truckenbrodt, University of Göttingen.

A microscopic tour de force

German scientists have reconstructed the architecture of a synaptic bouton, molecule by molecule.

This cellular structure transmits information from one neuron to the next.

Their 3D model reveals for the first time the machinery behind this process, which involves almost 300,000 proteins and 400 vesicles.

This arsenal is found in the trillions of neuronal connections in the human brain.

Silvio Rizzoli’s team at the University of Göttingen used a combination of electron microscopy, super-resolution microscopy and molecular-analysis tools to examine several million synaptic boutons extracted from rat brains.

With these techniques they were able to determine the shape of the boutons and quantify and localise the vesicles, as well as 60 different types of proteins.

The final visualisation corresponds to an “average” synapse.

Princeton University neuroscientist Sebastian Seung, who was not involved in the research, calls it a technical tour de force:

“The model shows as never before the complexity and beauty of the structure of a synapse.”

 

 

Illustration of how a synapse works

How a synapse works

Communication between two neurons is a complex process: the first neuron emits an electrical signal, which is transformed into a chemical signal before being received by the second neuron, which converts it back into an electrical signal.

This electrical-chemical-electrical transformation occurs in the synapse, the place where the two neurons meet, and it is done via molecules stored in tiny spheres called synaptic vesicles.

To emit its signal, the first neuron fuses its membrane with these vesicles, which then release their cargo of thousands of molecules (neurotransmitters) into the space between the neurons. They will be captured by receptors on the second neuron, which will then transform them back into an electrical signal.

Illustration of the exterior and interior of a synaptic bouton

Synaptic bouton (left): This extremity of a neuron, also known as a presynaptic terminal, is essential for transmitting information in the brain. 300,000 proteins (right): Researchers from the Universitiy of Göttingen in Germany have accurately reproduced the interior of the synaptic bouton. Source: Wilhelm et al. (2014), Science, reprinted with permission from AAAS; Burkhard Rammner (3D imagery); Sven Truckenbrodt, University of Göttingen.

– By Benjamin Bollmann

Technologist 02.015

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