Large and long-lasting cytosolic calcium surges in
astrocytes have been described in cultured cells and acute slice preparations.
The mechanisms that give rise to these calcium events have been extensively studied in vitro. However, their existence and functions in the intact brain are unknown. We have topically applied Fluo-4 AM on the cerebral cortex of anesthetized rats, and imaged cytosolic calcium fluctuation in astrocyte populations of superficial cortical layers in vivo, using two-photon laser scanning microscopy. Spontaneous Ca2i events in individual
astrocytes were similar to those observed in vitro.
Coordination of Ca2i events among astrocytes was indicated by the broad cross-correlograms. Increased neuronal discharge was associated with increased astrocytic Ca2i activity in individual cells and a robust coordination of Ca2i signals in neighboring astrocytes. These findings indicate potential neuronglia communication in the intact brain.