Neuromodulators signal through astrocytes to alter neural circuit activity and behavior

Astrocytes associate with synapses throughout the brain and express receptors for neurotransmitters that can elevate intracellular calcium (Ca(2+)) (1-3). Astrocyte Ca(2+) signaling has been proposed to modulate neural circuit activity (4), but pathways regulating these events are poorly defined and in vivo evidence linking changes in astrocyte Ca(2+) to alterations in neurotransmission or behaviors is limited. Here we show Drosophila astrocytes exhibit activity-regulated Ca(2+) signaling events in vivo. Tyramine (Tyr) and octopamine (Oct) released from Tdc2(+) neurons signal directly to astrocytes to stimulate Ca(2+) increases through the octopamine-tyramine receptor (Oct-TyrR) and the TRP channel Waterwitch (Wtrw), and astrocytes in turn modulate downstream dopaminergic (DA) neurons. Tyr or Oct application to live preparations silenced dopaminergic (DA) neurons and this inhibition required astrocytic Oct-TyrR and Wtrw. Increasing astrocyte Ca(2+) signaling was sufficient to silence DA neuron activity, which was mediated by astrocyte endocytic function and adenosine receptors. Selective disruption of Oct-TyrR or Wtrw expression in astrocytes blocked astrocyte Ca(2+) signaling and profoundly altered olfactory-driven chemotaxis behavior and touch-induced startle responses. Our work identifies Oct-TyrR and Wtrw as key components of the astrocyte Ca(2+) signaling machinery, provides direct evidence that Oct- and Tyr-based neuromodulation can be mediated by astrocytes, and demonstrates that astrocytes are essential for multiple sensory-driven behaviors.