Ca(+) activity maps of astrocytes tagged by axoastrocytic AAV transfer

Astrocytes exhibit localized Ca(2+) microdomain (MD) activity thought to be actively involved in information processing in the brain. However, functional organization of Ca(2+) MDs in space and time in relationship to behavior and neuronal activity is poorly understood. Here, we first show that adeno-associated virus (AAV) particles transfer anterogradely from axons to astrocytes. Then, we use this axoastrocytic AAV transfer to express genetically encoded Ca(2+) indicators at high-contrast circuit specifically. In combination with two-photon microscopy and unbiased, event-based analysis, we investigated cortical astrocytes embedded in the vibrissal thalamocortical circuit. We found a wide range of Ca(2+) MD signals, some of which were ultrafast (≤300 ms). Frequency and size of signals were extensively increased by locomotion but only subtly with sensory stimulation. The overlay of these signals resulted in behavior-dependent maps with characteristic Ca(2+) activity hotspots, maybe representing memory engrams. These functional subdomains are stable over days, suggesting subcellular specialization.