Figure 2. Outward IPSCs are monosynaptic, and predominantly GABA_A receptor mediated.

A, superimposed records of membrane current showing response to a −5 mV step, followed by outward synaptic currents evoked by single-shock electrical stimulation (for 0.1 ms) of the cerebral peduncle at the currents indicated. oIPSC amplitude is graded proportional to stimulus strength. B, oIPSCs evoked by 7 stimuli (0.1 ms, 50 μA) at 100 Hz show no fatigue or failure. C, oIPSC can be completely abolished by the GABA_A receptor antagonist bicuculline (20 μM). D, in some cells, a bicuculline-resistant, strychnine-sensitive portion of the oIPSC was observed. Means of 5 successive events at a holding potential of −70 mV in all records. dl-AP5 (100 μM) and CNQX (20 μM) were present in all cases.