Brain postnatal development is characterized by critical periods of experience-dependent remodeling. Termination of this period of intense plasticity is associated with settling of neuronal circuits, allowing for efficient information processing. Failure to end critical periods thus results in neurodevelopmental disorders. Yet, the cellular processes defining the timing of this developmental period remain unclear. Here we show in the visual cortex that astrocytes control the closure of the critical period. We uncover a novel underlying pathway involving regulation of the extracellular matrix that allows interneurons maturation via an unconventional astroglial connexin signaling. We find that timing of the critical period closure is controlled by a marked developmental upregulation of the astroglial protein connexin 30 that inhibits expression of the matrix degrading enzyme MMP9 through the RhoA-GTPase signaling pathway. Our results thus demonstrate that astrocytes not only influence activity and plasticity of single synapses, but are also key elements in the experience-dependent wiring of brain developing circuits.
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