To determine the physiological properties of our in vitro-derived interneurons, we performed patch clamp electrophysiology between D65 and D75 (Figure S2). Most patched cells exhibited electrophysiological properties of immature neurons, with relatively depolarized membrane potentials and high membrane resistance. As a result of the relatively high membrane resistances of these cells, it was difficult to obtain stable recordings. However, by holding cells at −65 mV, we elicited action potentials with current injection (Figure S2D). Spontaneous inhibitory post-synaptic currents in voltage clamp mode were abolished with application of picrotoxin, suggesting that these events were mediated by GABAergic cells (Figure S2E). These data suggest that the in vitro-derived inhibitory interneurons are indeed GABAergic.
