Heterogeneity of Astrocytes in Grey and White Matter
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ORIGINAL PAPER
Heterogeneity of Astrocytes in Grey and White Matter Susanne Köhler1 · Ulrike Winkler1 · Johannes Hirrlinger1,2 Received: 15 July 2019 / Revised: 21 November 2019 / Accepted: 28 November 2019 © Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract Astrocytes are a diverse and heterogeneous type of glial cells. The major task of grey and white matter areas in the brain are computation of information at neuronal synapses and propagation of action potentials along axons, respectively, resulting in diverse demands for astrocytes. Adapting their function to the requirements in the local environment, astrocytes differ in morphology, gene expression, metabolism, and many other properties. Here we review the differential properties of proto‑ plasmic astrocytes of grey matter and fibrous astrocytes located in white matter in respect to glutamate and energy metabo‑ lism, to their function at the blood–brain interface and to coupling via gap junctions. Finally, we discuss how this astrocytic heterogeneity might contribute to the different susceptibility of grey and white matter to ischemic insults. Keywords Astrocytes · Heterogeneity · Grey matter · White matter · Oligodendrocytes
Introduction In the middle of the nineteenth century Rudolph Virchow was the first who described a peculiar type of cells in the brain which we today know as astrocytes. However, he did not know about their enormous tasks and complex func‑ tions and how they contribute to brain function. With the histological studies from Santiago Ramón y Cajal, Camillo Golgi and William Lloyd Andriezen it became clear that there is heterogeneity among astrocytes and they have been categorized into protoplasmic and fibrous astrocytes (Fig. 1), regarding to their different morphologies and ana‑ tomical locations [1]. Protoplasmic astrocytes are the more prevalent type of astrocytes and are distributed mainly in the grey matter (GM) of the brain. Their rather large round somata extend thick and short processes, which branch out into myriads of fine processes. In contrast, the cell bodies of Special Issue: In Honor of Professor Juan Bolanos. * Johannes Hirrlinger [email protected]‑leipzig.de; [email protected] 1
Carl‑Ludwig‑Institute for Physiology, Faculty of Medicine, University of Leipzig, Liebigstr. 27, 04103 Leipzig, Germany
Department of Neurogenetics, Max-Planck-Institute for Experimental Medicine, Hermann‑Rein‑Str. 3, 37075 Göttingen, Germany
2
fibrous astrocytes within the white matter (WM) are often more elongated, and give rise to long, thin, but less branched processes [2]. These morphological differences correlate to the properties and functions of the different brain areas. In GM, the major task for the brain is to compute information at neuronal synapses. Consistently, fine processes of a single astrocyte can contact up to 200.000 synapses in mice, and up to 2 million in humans [3, 4] and contribute to neuro‑ transmitter, ion and energy homeostasis. In contrast, in WM electrical informa
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