Reactive astrogliosis, in which astrocytes exhibit altered morphology and an upregulation of glial fibrillary acidic protein (GFAP), characterizes many neurological diseases, including epilepsy. The authors investigated whether it is accompanied by alterations in the organization of astrocytic processes. They filled astrocytes in cortical mouse brain slices with lipophilic coloured dyes that become incorporated into the cellular membrane and reveal the fine structure of the cell. Confirming previous studies, comparisons of adjacent astrocytes labelled with two different dyes showed that the processes of each astrocyte occupy a specific 'domain' that shows little overlap with that of neighbouring astrocytes.
Next the authors examined astrocytes in slices taken from mice in which a ferrous chloride solution had been injected into the cortex as a model of traumatic brain-injury-induced epilepsy. Within 1 week of the injury, the domain organization of astrocytes that were classified as 'reactive' owing to their upregulation of the marker GFAP was disrupted. There was a 15-fold increase in the overlap between the space occupied by the processes of adjacent cells, and this increase persisted for up to 6 months after the injury. The loss of domain organization coincided with structural changes in the excitatory neurons that were contacted by the astrocytes, including loss of dendritic spines.
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