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

Morawski M, Reinert T, Meyer-Klaucke W, Wagner FE, Tröger W, Reinert A, Jäger C, Brückner G, Arendt T - Sci Rep (2015)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Paul Flechsig Institute for Brain Research, University of Leipzig, Liebigstrasse 19, D04103 Leipzig, Germany.

ABSTRACT
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.

No MeSH data available.


Elemental profiles of Fe and P across the somata of two neurons one with PN (upper cell) and one without PN (lower cell) extracted from PIXE element imaging data (tissue loaded with 1.68 mM FeCl3).The PN (previously identified within the Ni-map, not shown) localized on the outer surface of the soma shows a local increase in iron concentration several fold above the surrounding extracellular matrix and neuropil. Scale bar: 10 μm.
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f3: Elemental profiles of Fe and P across the somata of two neurons one with PN (upper cell) and one without PN (lower cell) extracted from PIXE element imaging data (tissue loaded with 1.68 mM FeCl3).The PN (previously identified within the Ni-map, not shown) localized on the outer surface of the soma shows a local increase in iron concentration several fold above the surrounding extracellular matrix and neuropil. Scale bar: 10 μm.

Mentions: Anionic “binding sites” fixed to PNs were mapped and analyzed using quantitative elemental imaging of the iron distribution after adding Fe3+-ions as cationic probes. As a visual control but not for the analysis, Fe3+-ions bound to PNs were histochemically stained by the Prussian blue reaction, resulting in a delicate intense blue staining of PNs against a light blue background (Fig. 2A). The corresponding iron distribution in the element image clearly delineates PNs and matches exactly the pattern of the Prussian blue stained iron bound to PNs (Fig. 2B). With the superimposed phosphorus distribution that shows cellular somata, neurons ensheathed by PNs can be distinguished from neurons devoid of PNs. For the analysis of negative charge densities, Prussian blue staining was omitted. Taking a traverse across the two types of neurons their different ability to bind iron in the perineuronal space is demonstrated (Fig. 3).


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

Morawski M, Reinert T, Meyer-Klaucke W, Wagner FE, Tröger W, Reinert A, Jäger C, Brückner G, Arendt T - Sci Rep (2015)

Elemental profiles of Fe and P across the somata of two neurons one with PN (upper cell) and one without PN (lower cell) extracted from PIXE element imaging data (tissue loaded with 1.68 mM FeCl3).The PN (previously identified within the Ni-map, not shown) localized on the outer surface of the soma shows a local increase in iron concentration several fold above the surrounding extracellular matrix and neuropil. Scale bar: 10 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4664884&req=5

f3: Elemental profiles of Fe and P across the somata of two neurons one with PN (upper cell) and one without PN (lower cell) extracted from PIXE element imaging data (tissue loaded with 1.68 mM FeCl3).The PN (previously identified within the Ni-map, not shown) localized on the outer surface of the soma shows a local increase in iron concentration several fold above the surrounding extracellular matrix and neuropil. Scale bar: 10 μm.
Mentions: Anionic “binding sites” fixed to PNs were mapped and analyzed using quantitative elemental imaging of the iron distribution after adding Fe3+-ions as cationic probes. As a visual control but not for the analysis, Fe3+-ions bound to PNs were histochemically stained by the Prussian blue reaction, resulting in a delicate intense blue staining of PNs against a light blue background (Fig. 2A). The corresponding iron distribution in the element image clearly delineates PNs and matches exactly the pattern of the Prussian blue stained iron bound to PNs (Fig. 2B). With the superimposed phosphorus distribution that shows cellular somata, neurons ensheathed by PNs can be distinguished from neurons devoid of PNs. For the analysis of negative charge densities, Prussian blue staining was omitted. Taking a traverse across the two types of neurons their different ability to bind iron in the perineuronal space is demonstrated (Fig. 3).

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Paul Flechsig Institute for Brain Research, University of Leipzig, Liebigstrasse 19, D04103 Leipzig, Germany.

ABSTRACT
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.

No MeSH data available.