Abstract
The brain is a dynamic structure with the extracellular space (ECS) taking up almost a quarter of its volume1,2. Signalling molecules, neurotransmitters and nutrients transit via the ECS, which constitutes a key microenvironment for cellular communication3 and the clearance of toxic metabolites. The spatial organization of the ECS varies during sleep4, development5 and aging6 and is probably altered in neuropsychiatric and degenerative diseases7, as inferred from electron microscopy8,9 and macroscopic biophysical investigations2,10. Here we show an approach to directly observe the local ECS structures and rheology in brain tissue using super-resolution imaging. We inject single-walled carbon nanotubes into rat cerebroventricles and follow the near-infrared emission of individual nanotubes as they diffuse inside the ECS for tens of minutes in acute slices. Because of the interplay between the nanotube geometry and the ECS local environment, we can extract information about the dimensions and local viscosity of the ECS. We find a striking diversity of ECS dimensions down to 40 nm, and as well as of local viscosity values. Moreover, by chemically altering the extracellular matrix of the brains of live animals before nanotube injection, we reveal that the rheological properties of the ECS are affected, but these alterations are local and inhomogeneous at the nanoscale.
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Acknowledgements
We thank E. Bézard, M. Blanchard-Desce, B. Bontempi and P. Bon for helpful discussions. We thank the Bordeaux Imaging Center (service unit of the CNRS-INSERM and Univ. Bordeaux). We thank J.P. Salvetat for experimental help with AFM imaging and J. Ferreira for support with histological experiments. This work was supported by CNRS, the Agence Nationale de la Recherche (ANR-14-OHRI-0001-01), IdEx Bordeaux (ANR-10-IDEX-03-02), Labex Brain (ANR-10-LABX-43), Conseil Régional d'Aquitaine (2011-1603009) and the France-BioImaging national infrastructure (ANR-10-INBS-04-01). A.G.G. acknowledges financial support from the Fondation pour la Recherche Médicale and the Fonds Recherche du Québec–Nature et Technologies. J.A.V. acknowledges funding from Marie Curie Individual Fellowship 326442.
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A.G.G., J.A.V., Z.G. and J.P.D. performed the experiments. A.G.G., N.D., B.L. and L.C. performed the analysis. B.L., L.G. and L.C. co-supervised the study. L.G. and L.C. designed the study. All authors discussed the results and co-wrote the manuscript.
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Godin, A., Varela, J., Gao, Z. et al. Single-nanotube tracking reveals the nanoscale organization of the extracellular space in the live brain. Nature Nanotech 12, 238–243 (2017). https://doi.org/10.1038/nnano.2016.248
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DOI: https://doi.org/10.1038/nnano.2016.248
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