(A) Experimental setting (scheme and image): Somatic whole-cell voltage-clamp recording from MC filled with Alexa 594 (red, 50 μM) and TPU of DNI-caged glutamate (DNI; blue star) at GC spines in VGAT-Venus rats (GCs green). (B) Example of consecutive uncaging traces showing urIPSC responses (black) and failures (gray); average of all recordings shown below (red). (C) Effect of GABAAR blockade (bicuculline, BCC, 50 µM, blue) on urIPSCs and spontaneous activity. Top: Example experiment, showing averaged traces. Bottom: Cumulative data on urIPSC amplitude (left panel, n = 7 MCs) and on frequency of spontaneous IPSCs (right panel, n = 6 MCs). (D) Analysis of asynchronous events. Top: Example trace from (B) with analysis intervals pre- and post-uncaging (gray areas, black arrows). Counted events marked by blue arrowheads. Bottom: Normalized IPSC event number and area (integrated activity, relative increase vs control ∆) in pre- vs post-uncaging intervals (n = 27 MCs, see Materials and methods). (E) Properties of first detected triggered urIPSCs (see Materials and methods). Left: Amplitudes (n = 32 MCs, Vm = +10 mV). Dark gray: Amplitude distribution of spontaneous IPSCs for comparison (n = 14 MCs, mean amplitudes). Middle: Release probabilities Pr_GABA (n = 44 MCs). Right: Latencies from TPU onset (n = 36 MCs). (F) Stability of urIPSC recordings. Left: Representative experiment showing individual urIPSC amplitude values over consecutive stimulations (1 TPU per min). Insets: Averaged urIPSC responses in the first (black, n = 3 responses) and last ten minutes (gray, n = 3 responses). Right: Comparison of averaged normalized urIPSC amplitudes separated by 10 min interval (n = 7 MCs).