"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" summarises Rubén Fernández-Busnadiego, lead author of the study.
During synapsis, a presynaptic cell releases neurotransmitters to another post-synaptic one, generating an electric impulse in it, thereby allowing nervous information to be transmitted. During this study, the researchers focused on the tiny vesicles that measure around 40 nanometres in diameter, which transport and release the neurotransmitters from the presynaptic terminals.
"Thanks to the use of certain pharmacological treatments and the 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," explains Fernández-Busnadiego.
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. According to the scientists, 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 called electron cryotomography makes it possible to obtain three-dimensional images of the inside of cells and to minimise any changes to their structure. This is possible because the cells are not fixed with chemical reagents, but are vitrified – in other words they are frozen so fast that the water inside them does not have time to crystallise, and remains in solid state. These samples, which are always maintained at liquid nitrogen temperatures, that is below -140 degree Celsius, can be viewed using specially-equipped microscopes.
MEDICA.de; Source: FECYT - Spanish Foundation for Science and Technology