Figure 2.

Mechanisms of astrocyte dysfunction that affect neural circuit development. (a) The establishment of appropriate neural circuits requires interplay between both neurons and astrocytes during development. Variations in the precise timing of the neurogenic to gliogenic switch can lead to a dearth (b) or surplus (c) of astrocytes. Too few astrocytes may eliminate essential cues required for axon guidance, neuronal survival, or synapse formation, while precocious astrogenesis may limit the number of neurons available to contribute to specific circuits. Alternately, neurogenesis and astrogenesis may proceed normally with circuit dysfunction arising from primary astrocyte pathology instead. (d) The secretion of toxic factors or the absence of survival and/or synaptogenic signals may contribute to the pathogenesis of aberrant neural circuits.