The physiological functions of the NPCs were assessed with recordings of sodium current, sEPSC, and sIPSC. As the NPCs stained positive for Glu1, GABA, and synpasin 1, it is highly likely that the NPCs can signal through synapses with each other. Notably, sEPSC and sIPSC were both present in the NPCs. The amplitude and frequency of both EPSC and IPSC increased with cultured days, indicating the development of mature physiological function. This observation was consistent with previous findings that NPCs generated from iPSCs responded to glutamate or GABA stimulation after two months of neuronal differentiation29 and that sodium channel expression progressively increased in the iPSC-derived neurons, which eventually led to the generation of an action potential30. Overall, our results indicated that morphological maturation precedes functional maturation in these cells.
