channel-mediated inward/outward currents as well as multiple evoked action potentials with no apparent differences between iNs derived from young and old donors’ fibroblasts (Figure 2H). Quantification of neuronal subtype markers revealed that a consistent majority of the neurons adopted a glutamatergic fate and usually 15%–20% of the cells were gamma aminobutyric acid (GABA)-positive, whereas dopaminergic or serotoninergic markers were only sporadically observed (Figures 2I and S1). Using this iN protocol, functional iNs can be efficiently generated from fibroblasts of all ages with no apparent differences in their basic cellular and functional properties.
