Stimulus trains of 10 Hz revealed fast synaptic depression, showing that iN cell synapses exhibit short-term plasticity (Fig. 4H). No inhibitory synaptic events were observed when Ngn2-induced human iN cells were co-cultured with glia cells, but strong inhibitory synaptic inputs onto the iN cells were detected when we co-cultured iN cells with mouse cortical neurons (Figs. S4C–S4E). This experiment demonstrated that iN cells integrate into a synaptic network with the mouse cortical neurons, and that they are fully capable of forming inhibitory postsynaptic specializations. Quantifications showed that the vast majority of all iN cells, when co-cultured with mouse glia cells or cortical neurons, contained voltage-gated Na+- and K+-currents, exhibited spontaneous synaptic activity, and displayed evoked EPSCs (Fig. 4I).
