Here, Navarrete et al. explored the direct involvement of astrocytes in a specific form of synaptic plasticity in vivo. In anaesthetized rats, tail-pinch-induced cholinergic activity led to calcium elevations in hippocampal astrocytes and long-term potentiation (LTP) of CA3–CA1 synapses. Interestingly, LTP required metabotropic glutamate receptor activation downstream of the astrocyte calcium signal. In rat hippocampal slices, stimulation of Schaffer collaterals in CA1 recapitulated the events observed in vivo and downregulation of the astrocyte calcium signal prevented LTP. Thus, astrocyte-derived glutamate release may be a necessary component of cholinergic signalling-induced plasticity of hippocampal synapses.