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Brain not as cramped as thought: study- 13-Aug-2015
Geneva: The brain is not as compact as previously thought, say scientists who developed an innovative technique that rapidly freezes the brain, preserving its true structure.
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, eg showing neurons to be much closer than they actually are.
Scientists at the Swiss Federal Institute of Technology Lausanne (EPFL) have now solved the problem by using a technique that rapidly freezes the brain, preserving its true structure.
Typically, the brain is fixed with stabilising 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 per cent.
This in turn, distorts our understanding of the brain's anatomy, eg the actual proximity of neurons, the structures of blood vessels etc.
A study by Graham Knott at EPFL and led by Natalya Korogod has successfully used an innovative method, called "cryofixation", to prevent brain shrinkage during the preparation for electron microscopy.
The method uses jets of liquid nitrogen to "snap-freeze" brain tissue down to minus 90 degrees Celsius, 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.
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, researchers said.
The research was published in the journal eLife.
