To further characterize iPS-derived neurons, we examined whether functional GABAA, AMPA, and NMDA ionotropic receptors were expressed. Functional GABAA receptors were observed using voltage-clamp mode where a 50µM GABA puff produced an inward current response (Figure 2C). In total, 20 of 20 cells tested responded to GABA. Functional AMPA receptors were observed in current-clamp mode where 50µM glutamate puffs produced a depolarization of the membrane in the presence of 1mM Mg2+. In total, 9 of 9 cells tested responded to glutamate administration under these conditions. This response to glutamate was blocked by the administration of the AMPA antagonist DNQX (Figure 2D). To identify NMDA glutamate receptor responses, a Mg2+ free recording solution containing DNQX to block AMPA receptor activity was used. The puffing pipette contained 50µM glutamate plus 10µM glycine and produced a depolarization of the membrane. This response was blocked when the NMDA antagonist CPP (6µM) was administered in the bath solution (Figure 2E). In total, 27 of 29 cells examined demonstrated functional NMDA responses.
