Opera Medica et Physiologica

Robert Zorec

Pathobiology of Neurodegeneration: The Role for Astroglia

The cellular basis for neurological diseases: the central role for neuroglia.

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Abstract

The common denominator of neurodegenerative diseases, which mainly affect humans, is the progressive death of neural cells resulting in neurological and cognitive deficits. Astroglial cells are central elements of the homoeostasis, defence and regeneration of the central nervous system, and their malfunction or reactivity contribute to the pathophysiology of neurodegenerative diseases. Pathological remodelling of astroglia in neurodegenerative context is multifaceted. Both astroglial atrophy with a loss of function and astroglial reactivity have been identified in virtually all forms of neurodegenerative disorders. Astroglia may represent a novel target for therapeutic strategies aimed at preventing and possibly curing neurodegenerative diseases.

Excitation-Energy Coupling and Vesicle-Based Signaling in Astrocytes

Introduction

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Abstract

Most of the human brain mass is occupied by the neocortex, which consists of neurons and non-neurons. The latter cells include astrocytes, a heterogeneous glial cell type. While astrocytes have been considered as neuronsubservient entities for almost a century, it is now becoming evident that they are essential in providing homeostatic support to neural networks and that they also actively participate in information processing in the brain. Astrocytes get excited when neurotransmitters bind to their membrane receptors and feed-back by releasing their own signals. This involves vesicles, which store chemicals termed gliotransmitters or more generally gliosignaling molecules. In the former case chemical messengers get released from astrocytic sites proximal to the synapse, which defines communication to occur in the micro-space of contact between the synapse and the astrocyte. In contrast gliosignaling molecules may also be released into the extracellular space. This mode of release resembles the endocrine system. Hence astrocytes are considered to be part of the gliocrine system in the brain, where the glymphatic system mediates the convection of released molecules. This complex system not only plays a role in cell-to-cell communication but also synchronizes the provision of energy for neural networks. Astrocytes contain glycogen, a form of energy store. Excitation of astrocytes by volume transmitters, such as noradrenaline , released by locus coeruleus neurons, activates adrenergic receptors and stimulates glycogenolysis, providing lactate. This chapter briefly reviews how noradrenaline and astrocytes operate to synchronize excitation and energy provision. Moreover, Ca2+ -dependent fusion of the vesicle membrane with the plasma membrane in astrocytes is discussed.

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