Abstract Astrocytes play active roles at synapses and can monitor, respond, and adapt to local synaptic activity. To investigate this relationship, more tools that can selectively activate native G protein signaling pathways in astrocytes with both spatial and temporal precision are needed. Here, we tested AAV8-GFAP-Optoα1AR-eYFP (Optoα1AR), a viral vector to enable activation of G q signaling in astrocytes via light-sensitive α1-adrenergic receptors. To determine if stimulating astrocytic Optoα1AR modulates hippocampal synaptic transmission, recordings were made in CA1 pyramidal cells with surrounding astrocytes expressing Optoα1AR, channelrhodopsin (ChR2), or GFP. Both high-frequency (20 Hz, 45-ms light pulses, 5 mW, 5 min) and low-frequency (0.5 Hz, 1-s pulses at increasing 1, 5, and 10 mW intensities, 90 s per intensity) blue light stimulation were tested. 20 Hz Optoα1AR stimulation increased both inhibitory and excitatory postsynaptic current (IPSC and EPSC) frequency, and the mIPSC effect was largely reversible within 20 min. By contrast, low-frequency stimulation of Optoα1AR did not modulate either IPSCs or EPSCs, whereas the same stimulation of astrocytic ChR2 was effective. These data demonstrate that Optoα1AR activation in astrocytes changes synaptic excitation and inhibition in a stimulation-sensitive manner, demonstrating the efficacy and utility of GFAP-Optoα1AR as a tool in studying astrocyte-neuron interactions.