Abstract

DO.20.01

Homeostatic mechanisms of Müller glial cells – increasing the signal-to-noise ratio and supporting neuronal survival

Andreas Reichenbach
Paul-Flechsig-Institut für Hirnforschung, Universität Leipzig

Objective: Even before the first vertebrates developed, there occurred a cell fate division among the neural cells. Neurons became further specialized for information processing whereas glial cells underwent a specialization towards homeostatic functions; this division of labor was accompanied by different expression of the common ancestral genes. Most likely, the homeostatic functions of glial cells serve two main purposes, (i) increasing the signal-to-noise ratio and (ii) supporting neuronal survival. In the retina, these glial functions require a collaboration between Müller cells and retinal pigment epithelial (RPE) cells.
Methods: To test this hypothesis, we used current laser microscopy and pharmacological approaches, to find out whether Müller cells may (i) facilitate light transport to the photoreceptors in our inverted retina, and (ii) support neuronal survival by efficient water clearance and volume regulation.
Results: We show that (i) indeed Müller glial cells are light-guiding fibers which bypass the light through the light-scattering elements of the inner retinal layers, and (2) Müller cells are capable of very efficient water transport and fast volume regulation; in elevated glutamate concentrations, neuronal somata and synaptic processes swell whereas the Müller cell processes in the inner retina even become thinner. This reduces the shrinkage of the extracellular space volume.
Conclusions: Our results confirm the hypothesis that Müller glial cells – in collaboration with RPE cells – guarantee for a high signal-to-noise ratio in light stimulation of the photoreceptors, as well as for a compensation of swelling of neuronal elements in response to physiological neurotransmitter release. This means that glial cells perform a homeostatis of the extracellular space and thus allow for a normal functioning and survival of the neurons.

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