Coming out of the shadows: shedding light on brain extracellular space
The University of Bordeaux team lead by Professor Valentin Nägerl at the Bordeaux Institute for Interdisciplinary Neuroscience (IINS) has developed a method based on super-resolution microscopy to visualize extracellular space in live brain tissue. This new method has shared light on one of the greatest mysteries and frontiers in neuroscience. The study was published on February 22, 2018 in the journal Cell.
Brain Extracellular Space (ECS) provides the physical setting and signaling platform where neurons and glial cells work together. While extracellular space occupies one fifth of brain volume, its topology is incredibly complex and miniaturized, defying conventional investigation approaches.
The research team, lead by Professor Valentin Nägerl at the Institute for Interdisciplinary Neuroscience (IINS)/Bordeaux Neurocampus Center, has developed a revolutionary method for obtaining a panoramic and detailed visualization of live brain tissue. The technique makes it possible, for the first time, not only to view individual cells and their complex networks, but also unmask the entire surrounding anatomical context. This is comparable to being able to see the leaves, trees and forest all at the same time.
Although numerous different bio-imaging techniques are already in existence, they all have serious limitations: conventional optical microscopy generally only views a few individual cells and does not offer sufficient spatial resolution to view their structural details, whereas electron microscopy can only be applied to fixed, i.e. dead, brain tissue.
On the other hand, the novel approach is capable of taking extremely accurate images of the complete anatomical architecture of all the cells simultaneously in live brain tissue. The researchers succeeded in this endeavor by adding a fluorescent dye into brain tissue fluid, making all cells visible as shadows (with the dye remaining outside the cells). This extracellular labeling strategy lessens the photobleaching and phototoxicity problems associated with conventional imaging approaches considerably.
Mapping unchartered space
To make this simple concept actually work, the researchers had to build an advanced super-resolution optical microscope, so that the images would have sufficient contrast and spatial resolution. As the cells resemble shadows in a glistening sea, the new technique is referred to as super-resolution shadow imaging (SUSHI).
SUSHI not only visualizes the anatomical organization of live brain tissue with spatial resolution on a nanometric scale, it also makes it possible to simultaneously view the tiny spaces separating brain cells from one another, which are collectively referred to as brain extracellular space.
This space is considered to play a very important role in neural communication and brain homeostasis, but it had never been previously visualized, as it is highly compact and intricate. The SUSHI technique will enable researchers to map this unchartered space and examine it in animal models of brain diseases, such as strokes, epilepsy and Alzheimer's disease, where the brain extracellular space is liable to be affected.
Super-Resolution Imaging of the Extracellular Space in Living Brain Tissue. an Tønnesen, V.V.G. Krishna Inavalli, U. Valentin Nägerl.
PR. VALENTIN NAGERL
Bordeaux Institute for Interdisciplinary Neuroscience