Figure 3. Trains of interneuron firing induce GABA_A receptor-mediated currents in an adjacent astrocyte in the SLM.

A, representative dual whole-cell patch clamp recording from SLM (dotted line) interneuron–astrocyte pair using GAD67-GFP knock-in mice. The left panel shows an overlay image of GFP (green) and SR101 (red) fluorescence and an infrared differential interference contrast image at the border of the SR and the SLM. The two patch electrodes in the SLM, emphasized with continuous lines, were placed on a close interneuron–astrocyte pair identified by GFP and SR101 fluorescence, respectively. Scale bar: 20 μm. Trains of interneuron firing initiated by repetitive current injection (right bottom) induced inward currents in the astrocyte, which we labelled as inhibitory synapse-driven astrocytic currents, I_inh-astro (right top); the arrangement is the same in subsequent figures. B, effects of BIC on I_inh-astro. At 20 μm (top panel) or at much lower concentrations (2 μm; bottom panel), BIC completely and reversibly blocked the inward currents. C, I_inh-astro recorded in Hepes-buffered extracellular solution was similar to that in HCO₃⁻-buffered solution (A and B). (D) I_inh-astro recorded in isolated SLM. Dendrites of pyramidal neurons inserting into the SLM were isolated from the cell soma by transversely cutting a slice in the SR (left panel). Astrocytic currents were similarly induced by trains of interneuron firing in this slice (right panel). Scale bar: 100 μm. BIC, bicuculline methiodide; Py., pyramidal neurons; SLM, stratum lacunosum-moleculare; SR, stratum radiatum.