Abstract
Astrocytes are complex glial cells that play many essential roles in the brain, including the fine-tuning of synaptic activity and blood flow. These roles are linked to fluctuations in intracellular Ca2+ within astrocytes. Recent advances in imaging techniques have identified localized Ca2+ transients within the fine processes of the astrocytic structure, which we term microdomain Ca2+ events. These Ca2+ transients are very diverse and occur under different conditions, including in the presence or absence of surrounding circuit activity. This complexity suggests that different signalling mechanisms mediate microdomain events which may then encode specific astrocyte functions from the modulation of synapses up to brain circuits and behaviour. Several recent studies have shown that a subset of astrocyte microdomain Ca2+ events occur rapidly following local neuronal circuit activity. In this review, we consider the physiological relevance of microdomain astrocyte Ca2+ signalling within brain circuits and outline possible pathways of extracellular Ca2+ influx through ionotropic receptors and other Ca2+ ion channels, which may contribute to astrocyte microdomain events with potentially fast dynamics.
Highlights
Astrocytes are brain glial cells that contact nearby neurons and enwrap blood vessels with their highly branched processes
Signalling within brain circuits and outline possible pathways of extracellular Ca2+ influx through ionotropic receptors and other Ca2+ ion channels, which may contribute to astrocyte microdomain events with potentially fast dynamics
Astrocytes express a plethora of neurotransmitter receptors, ion channels, and metabolite transporters that respond to nearby neuronal activity and integrate astrocytes into neural networks [1]
Summary
Astrocytes are brain glial cells that contact nearby neurons and enwrap blood vessels with their highly branched processes. A subset of astrocyte MCEs near the plasma membrane of astrocyte processes, have a fast signal onset that closely follows neuronal activity (within 100 ms) and are reproducibly evoked within the same regions during repeated whisker stimulation [17] This suggests that astrocytes have the necessary temporal and spatial Ca2+ signalling to play a rapid role in fine-tuning circuits as discussed below. These examples highlight the diversity of astrocyte-neuron interactions at different synapses and via distinct gliotransmitters; a link between localized MCEs and gliotransmission has not been proven The majority of these studies described above demonstrated a requirement of astrocyte Ca2+ signalling for the modulation of synaptic processes by utilizing Ca2+ chelator BAPTA [39,40,45,56,57] or clamping intracellular Ca2+.
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