Microglial calcium signal acts as a rapid sensor of single neuron damage in vivo

► In vivo microglia rarely show Ca2+ transients at rest but reliably respond with rapid Ca2+ signals to damage of an individual neuron in their vicinity. ► Damage-induced Ca2+ transients (DICTs) have large amplitudes and are strictly localized to microglia dwelling within a 50-μm vicinity of a damaged neuron. ► DICTs require Ca2+ release from intracellular stores likely caused by an activation of metabotropic P2Y receptors.