Ca2+ activity maps of astrocytes tagged by axo-astrocytic AAV transfer

Astrocytes exhibit localized Ca2+ microdomain (MD) activity thought to be
actively involved in information processing in the brain. However,
functional organization of Ca2+ 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 axo-astrocytic AAV transfer to
express genetically encoded Ca2+ 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 Ca2+ 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 Ca2+ activity hotspots, maybe
representing memory engrams. These functional subdomains are stable over
days, suggesting subcellular specialization.