Electron Cryotomography to Study and Obtain the 3D Images of Synapsis

Electron cryotomography is an emerging technique that allows the structures of unique biological objects such as individual macromolecules, viruses, and even small whole cells to be reconstructed in their near-native states in three dimensions (3-D) to an approximate 5-nm resolution.  With the advanced technique of electron microscopy, researchers at the Max Planck Institute of Biochemistry, Germany has succeeded in obtaining the 3D images of the vesicles and filaments involved in the communication between neurons.  They preferred the Electron Cryotomography  because, this technique cools the cells quickly therefore their biological structures can be frozen while fully active.

Typically during synapsis, a presynaptic cell (emitter) releases neurotransmitters to another post-synaptic one (recipient), generating an electric impulse in it, thereby allowing nervous information to be transmitted.  The present study,  led by the Spanish physicist Rubén Fernández-Busnadiego, focused on the tiny vesicles (measuring around 40 nanometres in diameter), which transport and release the neurotransmitters from the presynaptic terminals.  Through this finding, it is now possible  to manage huge range of filamentous structures that are within the presynaptic terminal and interact directly with the synaptic vesicles, as well as to learn about their crucial role in responding to the electrical activity of the brain.  Therefore, the filaments connect the vesicles and also connect them with the active area, the part of the cellular membrane from which the neurotransmitters are released. The team described  that , these filamentous structures act as barriers that block the free movement of the vesicles, keeping them in their place until the electric impulse arrives, as well as determining the ease with which they will fuse with the membrane.

There are several advantages for electron cryotomography.  Here the cells are not fixed with chemical reagents, but are vitrified, that is they are frozen so fast that the water inside them does not have time to crystallize, and remains in solid state. Consequently makes it possible to obtain three-dimensional images of the inside of cells and to minimize any changes to their structure.  In this technique the samples maintained at liquid nitrogen temperatures(below -140 ºC) are used and can be viewed specially-equipped microscopes. In addition, this method does not require any kind of additional staining, meaning the density of the biological structures can be observed directly.