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Sci Rep. 2015 Dec 1;5:16471. doi: 10.1038/srep16471.

Ion exchanger in the brain: Quantitative analysis of perineuronally fixed anionic binding sites suggests diffusion barriers with ion sorting properties.

Author information

Paul Flechsig Institute for Brain Research, University of Leipzig, Liebigstrasse 19, D04103 Leipzig, Germany.
Physics Department, University of North Texas, 1155 Union Circle #311427, Denton, Texas 76203, USA.
EMBL Hamburg, Building 25A, DESY, Notkestraße 85, D22603 Hamburg, Germany.
Physik-Department E15, Technische Universität München, James-Franck-Straße, D85748 Garching, Germany.
Max-Planck-Innovation GmbH, Amalienstrasse 33, D80799 Munich, Germany.


Perineuronal nets (PNs) are a specialized form of brain extracellular matrix, consisting of negatively charged glycosaminoglycans, glycoproteins and proteoglycans in the direct microenvironment of neurons. Still, locally immobilized charges in the tissue have not been accessible so far to direct observations and quantifications. Here, we present a new approach to visualize and quantify fixed charge-densities on brain slices using a focused proton-beam microprobe in combination with ionic metallic probes. For the first time, we can provide quantitative data on the distribution and net amount of pericellularly fixed charge-densities, which, determined at 0.4-0.5 M, is much higher than previously assumed. PNs, thus, represent an immobilized ion exchanger with ion sorting properties high enough to partition mobile ions in accord with Donnan-equilibrium. We propose that fixed charge-densities in the brain are involved in regulating ion mobility, the volume fraction of extracellular space and the viscosity of matrix components.

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