Neuron Connections Visualized in 3D

A team of researchers in Germany has managed to obtain three-dimensional (3D) images of the vesicles and filaments involved in communication between neurons. The technique is based on an innovative technology in electron microscopy, which cools cells so rapidly that their biologic structures can be frozen while fully active.

The scientists involved in the project were from the Max Planck Institute of Biochemistry (Martinsried, Germany), led by the Spanish physicist Dr. Rubén Fernández-Busnadiego. "We used electron cryotomography, a new technique in microscopy based on ultra-fast freezing of cells, in order to study and obtain three-dimensional images of synapsis, the cellular structure in which the communication between neurons takes place in the brains of mammals, " stated Dr. Fernández-Busnadiego, a physicist at the Max Planck Institute of Biochemistry, and lead author of the study, published in January 2010 issue of the Journal of Cell Biology and a physicist at the Max Planck Institute of Biochemistry.

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. During this study, the researchers focused on the tiny vesicles (measuring around 40 nm in diameter), which transport and release the neurotransmitters from the presynaptic terminals.

"Thanks to the use of certain pharmacological treatments and the advanced 3D imaging analysis method we have developed, it is possible to observe the 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,” explained Dr. Fernández-Busnadiego.

The filaments connect the vesicles and connect them with the active area, the part of the cellular membrane from which the neurotransmitters are released. According to the Spanish physicist, 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.

The technique upon which these discoveries are based, electron cryotomography, makes it possible to obtain 3D images of the inside of cells and to minimize any changes to their structure. This is possible because the cells are not fixed with chemical reagents, but are vitrified--meaning they are frozen so fast that the water inside them does not have time to crystallize, and remains in solid state.

These samples, which are always maintained at liquid nitrogen temperatures (below -140 ºC), can be viewed using specially equipped microscopes. Moreover, this method does not require any kind of additional staining; meaning the density of the biologic structures can be observed directly.

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Max Planck Institute of Biochemistry