Abstract
In brain grey matter, excitatory synaptic transmission activates glutamate uptake into astrocytes, inducing sodium signals which propagate into neighboring astrocytes through gap junctions. These sodium signals have been suggested to serve an important role in neuro-metabolic coupling. So far, it is unknown if astrocytes in white matter—that is in brain regions devoid of synapses—are also able to undergo such intra- and intercellular sodium signalling. In the present study, we have addressed this question by performing quantitative sodium imaging in acute tissue slices of mouse corpus callosum. Focal application of glutamate induced sodium transients in SR101-positive astrocytes. These were largely unaltered in the presence of ionotropic glutamate receptors blockers, but strongly dampened upon pharmacological inhibition of glutamate uptake. Sodium signals induced in individual astrocytes readily spread into neighboring SR101-positive cells with peak amplitudes decaying monoexponentially with distance from the stimulated cell. In addition, spread of sodium was largely unaltered during pharmacological inhibition of purinergic and glutamate receptors, indicating gap junction-mediated, passive diffusion of sodium between astrocytes. Using cell-type-specific, transgenic reporter mice, we found that sodium signals also propagated, albeit less effectively, from astrocytes to neighboring oligodendrocytes and NG2 cells. Again, panglial spread was unaltered with purinergic and glutamate receptors blocked. Taken together, our results demonstrate that activation of sodium-dependent glutamate transporters induces sodium signals in white matter astrocytes, which spread within the astrocyte syncytium. In addition, we found a panglial passage of sodium signals from astrocytes to NG2 cells and oligodendrocytes, indicating functional coupling between these macroglial cells in white matter.
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Abbreviations
- AMPA:
-
α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid
- AP5:
-
D-(-)-2-Amino-5-phosphonopentanoic acid
- ATP:
-
Adenosine triphosphate
- CA1:
-
Cornu ammonis 1
- Cx:
-
Connexin
- DAPI:
-
4′,6-diamidino-2-phenylindole
- EYFP:
-
Enhanced yellow fluorescent protein
- GABA:
-
Gamma-aminobutyric acid
- GFP:
-
Green fluorescent protein
- GLAST:
-
Glutamate aspartate transporter
- GLT1:
-
Glutamate transporter 1
- hGFAP:
-
Human glial fibrillary acidic protein
- Iba1:
-
Ionized calcium-binding adapter molecule 1
- mGluR:
-
Metabotropic glutamate receptor
- MPEP:
-
2-Methyl-6-(phenylethynyl)pyridine hydro-chloride
- MRS2179:
-
2′-deoxy-N6-methyladenosine 3′,5′-bisphosphate tetrasodium salt
- NBQX:
-
2,3-Dihydroxy-6-nitro-7-sulfamoyl-benzo(F) quinoxaline
- NCX:
-
Sodium/calcium exchanger
- NG2:
-
Neural/glial antigen 2
- NMDA:
-
(R)-2-(Methylamino)succinic acid
- PBS:
-
Phosphate buffered saline
- PLP:
-
Proteolipid protein
- PPADS:
-
Pyridoxalphosphate-6-azophenyl-2′,4′-disulfonic acid tetrasodium salt
- ROI:
-
Region of interest
- SBFI(-AM):
-
Sodium-binding benzofuran isophthalate(-acetoxymethyl ester)
- SEM:
-
Standard error of the mean
- SR101:
-
Sulforhodamine 101
- TFB-TBOA:
-
(3 S)-3-[[3-[[4-(Trifluoromethyl)benzoyl]amino]phenyl]methoxy]-L-aspartic acid
- TTX:
-
Tetrodotoxin
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Acknowledgements
This work was supported by the Deutsche Forschungsgemeinschaft (SPP1757 “Glial Heterogeneity”, Ro2327/8 − 1). We thank Simone Durry for excellent technical assistance. The authors thank Dr. Gerald Seifert and Prof. Christian Steinhäuser, University of Bonn, Germany, as well as Prof. Nikolaj Klöcker, Heinrich Heine University Duesseldorf, Germany, for providing transgenic reporter animals (hGFAP-GFP, PLP-GFP, NG2-EYFP).
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This study was carried out in strict accordance with the institutional guidelines of the Heinrich Heine University Düsseldorf, as well as the European Community Council Directive (86/609/EEC). All experiments were communicated to and approved by the Animal Welfare Office at the Animal Care and Use Facility of the Heinrich Heine University Düsseldorf (institutional act number: O52/05), following the recommendation of the European Commission (published in: Euthanasia of experimental animals, Luxembourg: Office for Official Publications of the European Communities, 1997; ISBN 92–827–9694-9).
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Moshrefi-Ravasdjani, B., Hammel, E.L., Kafitz, K.W. et al. Astrocyte Sodium Signalling and Panglial Spread of Sodium Signals in Brain White Matter. Neurochem Res 42, 2505–2518 (2017). https://doi.org/10.1007/s11064-017-2197-9
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DOI: https://doi.org/10.1007/s11064-017-2197-9