Using an innovative method, EPFL scientists show that the brain is not as compact as we have thought all along.
To study the fine structure of the brain, including its connections between neurons, the synapses, scientists must use electron microscopes. However, the tissue must first be fixed to prepare it for this high magnification imaging method.
This process causes the brain to shrink; as a result, microscope images can be distorted, e.g. showing neurons to be much closer than they actually are. EPFL scientists have now solved the problem by using a technique that rapidly freezes the brain, preserving its true structure. The work is published in eLife.
The shrinking brain
Recent years have seen an upsurge of brain imaging, with renewed interest in techniques like electron microscopy, which allows us to observe and study the architecture of the brain in unprecedented detail. But at the same time, they have also revived old problems associated with how this delicate tissue is prepared before images can be collected.
Typically, the brain is fixed with stabilizing agents, such as aldehydes, and then encased, or embedded, in a resin. However, it has been known since the mid-sixties that this preparation process causes the brain to shrink by at least 30 percent. This in turn, distorts our understanding of the brain's anatomy, e.g. the actual proximity of neurons, the structures of blood vessels etc.
The freezing brain
A study by Graham Knott at EPFL, led by Natalya Korogod and working with Carl Petersen, has successfully used an innovative method, called "cryofixation", to prevent brain shrinkage during the preparation for electron microscopy. The method, whose roots go back to 1965, uses jets of liquid nitrogen to "snap-freeze" brain tissue down to -90oC, within milliseconds. The brain tissue here was mouse cerebral cortex.
The rapid freezing method is able to prevent the water in the tissue from forming crystals, as it would do in a regular freezer, by also applying very high pressures. Water crystals can severely damage the tissue by rupturing its cells. But in this high-pressure freezing method, the water turns into a kind of glass, preserving the original structures and architecture of the tissue.
The next step is to embed the frozen tissue in resin. This requires removing the glass-water and replacing it first with acetone, which is still a liquid at the low temperatures of cryofixation, and then, over a period of days, with resin; allowing it to slowly and gently push out the glassified water from the brain.
The real brain
After the brain was cryofixed and embedded, it was observed and photographed in using 3D electron microscopy. The researchers then compared the cryofixed brain images to those taken from a brain fixed with an "only chemical" method.
The analysis showed that the chemically fixed brain was much smaller in volume, showing a significant loss of extracellular space - the space around neurons. In addition, supporting brain cells called "astrocytes", seemed to be less connected with neurons and even blood vessels in the brain. And finally, the connections between neurons, the synapses, seemed significantly weaker in the chemically-fixed brain compared to the cryofixed one.
The researchers then compared their measurements of the brain to those calculated in functional studies - studies that measure the time it takes for a molecule to travel across that brain region. To the researchers' surprise, the data matched, adding even more evidence that cryofixation preserves the real anatomy of the brain.
"All this shows us that high-pressure cryofixation is a very attractive method for brain imaging," says Graham Knott. "At the same time, it challenges previous imaging efforts, which we might have to re-examine in light of new evidence." His team is now aiming to use cryofixation on other parts of the brain and even other types of tissue.
This work was funded by the Swiss National Science Foundation.
Korogod N, Petersen C, Knott G. Ultrastructural analysis of adult mouse neocortex comparing aldehyde perfusion with cryo fixation. eLife 11 August 2015. DOI: http://dx.
Nik Papageorgiou | EurekAlert!
Unique brain 'fingerprint' can predict drug effectiveness
11.07.2018 | McGill University
Direct conversion of non-neuronal cells into nerve cells
03.07.2018 | Universitätsmedizin der Johannes Gutenberg-Universität Mainz
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
17.07.2018 | Information Technology
17.07.2018 | Materials Sciences
17.07.2018 | Power and Electrical Engineering