M-109 increases spontaneous GABAergic synaptic activity. Recordings were made from a P26 layer 2/3 pyramidal cell.A, C, The neuron showed no significant spontaneous synaptic activity at either −60 mV (A) or 0 mV (C) holding potential. B, Bath application of M-109 (100 μm) dramatically increased the frequency of spontaneous synaptic currents. D, The synaptic currents induced by 5-HT3 receptor activation reversed around −20 mV, indicating that they were GABAA receptor-mediated.E, F, Recordings from the same cell shown at expanded time scale. Outward currents recorded at −20 or 0 mV were completely abolished by 50 μm picrotoxin (F) or 10–20 μm bicuculline, demonstrating that they were mediated by GABAA receptors.G, Time course of the frequency increase induced by M-109 for the cell shown in A. H, I, Both ICS and picrotoxin suppressed the frequency increase in GABAergic spontaneous activity induced by M-109.