Synaptic plasticity, astrocytes and morphological homeostasis

Recent discoveries suggest that astrocytes are an integral part of synaptic connections, as they sense and modulate synaptic activity. Moreover, there is evidence that astrocytes change the number of synaptic connections directly via synaptogenic signals or indirectly, by modifying the morphology of axons and dendrites. Here, we formulate the hypothesis that astrocytes mediate the morphological homeostasis of nerve cells, which is any adaptation of the morphology of a neuron to preserve its ability to respond to and generate synaptic activity during learning and mernory-induced changes. We argue that astrocytes control neuronal morphology locally and across long-ranging assemblies of neurons and that on the other hand, astrocytes, are part of the engram with plasticity-related changes affecting their morphology. (c) 2006 Elsevier Ltd. All rights reserved.