Getting out of the Shadow: Extracellular Brain Spaces Unveiled

Super-resolution imaging of the extracellular space in living brain tissue. 

Super-resolution imaging of the extracellular space in living brain tissue. Tonnesen J, VVGK Inavalli and Nägerl UV.  Cell. 2018 Feb 22;172(5):1108-1121.e15. doi: 10.1016/j.cell.2018.02.007.

Prof. U. Valentin Nägerl, PhD Institut Interdisciplinaire de Neurosciences (IINS) CNRS UMR 5297 / Université de Bordeaux / Centre Broca Nouvelle-Aquitaine / Bordeaux Neurocampus / Email : *protected email*

The extracellular space (ECS) of the brain provides the physical scene and the signaling platform where neurons and glial cells play in concert. While ECS occupies one fifth of brain volume, its topology is incredibly complex and miniaturized, challenging traditional investigative approaches. The team of Valentin Nägerl of the Interdisciplinary Institute of Neuroscience in Bordeaux has developed a method based on super-resolution microscopy to visualize the ECS in living brain tissue and thus unveil one of the most important puzzles and borders of neuroscience. This study was published February 22, 2018 in the journal Cell




Valentin Nägerl’s team has developed a revolutionary method to visualize living brain tissue in a panoramic but detailed manner. The technique allows for the first time not only to see individual brain cells and their complex networks, but also to reveal the entire surrounding anatomical context. It’s like being able to see leaves, trees and the forest at the same time. Although many different bioimaging techniques already exist, they all have serious limitations: regular optical microscopy usually only visualizes a few individual cells and does not have sufficient spatial resolution to see their structural details, while microscopy electronics can only apply to fixed brain tissue, that is, death. In contrast, the new approach can take extremely accurate images of the complete anatomical architecture of all cells at the same time in living brain tissue. The researchers achieved this feat by adding a fluorescent dye to the brain tissue fluid, making all cells visible as silhouettes (this dye remaining outside the cells).

For this simple concept to work, the researchers had to build an advanced super-resolution optical microscope, so that the images had sufficient contrast and spatial resolution. Because cells look like shadows in a shining sea, the new technique is called super-resolution shadow imaging (SUSHI).

SUSHI not only visualizes the anatomical organization of living brain tissue with spatial resolution at the nanoscale, but at the same time allows us to see the small spaces that separate all brain cells from one another, which are collectively called “space”. extracellular brain “. This space is considered very important for neural communication and cerebral homeostasis, but it has never been imagined directly before because it is so compact and convoluted. The SUSHI technique will allow researchers to map this unexplored space and examine it in animal models of brain diseases, such as stroke, epilepsy and Alzheimer’s disease, where the extracellular space of the brain is likely to be affected.

In addition, the extracellular labeling strategy greatly mitigates the photo-bleaching and photo-toxicity problems associated with traditional imaging approaches. As a direct variant of STED microscopy, the SUSHI method allows the study of the structure and dynamics of ECS and neuropile in a living brain.

Figure : Super-resolution shadow imaging (SUSHI) makes all brain cells visible “all at once”. The image on the left shows an overview of the neurons of the hippocampus, which is the archetypal center of mammalian brain memory. At the top zoom and after the color inversion, the image on the right reveals the entanglement of brain tissue with a spatial resolution at the nanoscale. The green neuron has been labeled with a fluorescent protein and thus stands out from the rest of the inversely labeled tissue.


Prof. U. Valentin Nägerl, PhD Institut Interdisciplinaire de Neurosciences (IINS) CNRS UMR 5297 / Université de Bordeaux