Abstract
Astrocytes, the dominant glial cell type, modulate synaptic information transmission. Each astrocyte is organized in non-overlapping domains. Here, a formally based model of the possible significance of astrocyte domain organization is proposed. It is hypothesized that each astrocyte contacting n neurons with m synapses via its processes generates dynamic domains of synaptic interactions based on qualitative criteria so that it exerts a structuring of neuronal information processing. The formalism (morpho-grammatics) describes the combinatorics of the various astrocytic receptor types for occupancy with cognate neurotransmitters. Astrocytic processes are able both to contact synapses and retract from them. Rhythmic oscillations of the astrocyte may program the domain organization, where clock genes may play a role in rhythm generation. For the interpretation of a domain organization a player of a string instrument is used as a paradigm. Since astrocytes form networks (syncytia), the interactions between astrocyte domains may be comparable to the improvisations in a jazz ensemble. Given the fact of a high combinational complexity of an astrocyte domain organization, which is formally demonstrable, and an uncomputable complexity of a network of astrocyte domains, the model proposed may not be testable in biological brains, but robotics could be a real alternative.
Highlights
Astrocytes, the dominant glial cell type, have become the focus of much attention in the past two decades
It is hypothesized that each astrocyte contacting n neurons with m synapses via its processes generates dynamic domains of synaptic interactions based on qualitative criteria so that it exerts a structuring of neuronal information processing
Astrocytes are thereby able to respond to neuronal activity in a receptor-dependent fashion, and in return they can modulate synaptic transmission by transmitter release, thereby permitting feedback control of neuronal activity levels [2,3]
Summary
Astrocytes, the dominant glial cell type, have become the focus of much attention in the past two decades. In addition to their roles in many of the supportive functions of the brain, new functions are beginning to emerge. Astrocytes are not themselves electrically excitable, they release transmitters, triggered by increases in cytosolic Ca2+ concentrations that modulate the activity of neighboring cells, including both neurons and other glia. Astrocytes are thereby able to respond to neuronal activity in a receptor-dependent fashion, and in return they can modulate synaptic transmission by transmitter release, thereby permitting feedback control of neuronal activity levels [2,3]. I hypothesize that each astrocyte contacting n neurons with m synapses via its processes generates dynamic domains of synaptic interactions based on qualitative criteria, so that it exerts a structuring of neuronal information processing
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