Electrophysiology of cultured iN cells was performed essentially as described (Maximov and Südhof, 2005; Pang et al., 2011). Stimulus artifacts for evoked synaptic responses were removed for graphic representation. For electrophysiological recordings of transplanted cells, we prepared acute coronal slices (140 μm) of striatum from mice 6 weeks after transplantation using a vibratome (Leica, VT1200 S). GFP-positive hES-iN cells in slices were visualized using an X-cite 120Q fluorescence lamp (Lumen Dynamics) and an Olympus BX51WI microscope equipped with a Rolera-XR camera (Qimaging). Whole-cell patches were established at room temperature using MPC-200 manipulators (Sutter Instrument) and Multiclamp 700B amplifier (Molecular Devices) controlled by Clampex 10 Data Acquisition Software (Molecular Devices). Cells were recorded in current-clamp mode for intrinsic firing properties and switched to voltage-clamp mode (−70 mV) for synaptic measurements. Evoked responses were generated using a concentric bipolar electrode (FHC) connected to Isolated Pulse Stimulator 2100 (A–M systems). Picrotoxin (50 μM, Tocris) was used to block inhibitory synaptic responses. For more details, see Supplementary Methods.
