Centripetal integration of past events by hippocampal astrocytes and its regulation by the locus coeruleus

An essential feature of neurons is their ability to centrally integrate information from their dendrites. The activity of astrocytes, in contrast, has been described as mostly uncoordinated across cellular compartments without clear central integration. Here, we describe conditional centripetal integration as a principle of how astrocytes integrate calcium signals from their distal processes to induce somatic activation. We found in mouse hippocampus that global astrocytic activity, as recorded with population calcium imaging, is well explained as a leaky integration of past neuronal and behavioral events on a timescale of seconds. Salient past events, indicated by pupil dilations, facilitated propagation of calcium signals from distal processes to the soma on this slow timescale. Centripetal propagation was reproduced by optogenetic activation of the locus coeruleus, a key regulator of arousal, and reduced by pharmacological inhibition of α1-adrenergic receptors. Together, our results establish astrocytes as computational units of the brain that slowly and conditionally integrate calcium signals to activate their somata upon behaviorally relevant events.