Next, we investigated whether functional synapses had developed in the iPSC-derived neurons by recording the synaptic events between neurons. Spontaneous excitatory postsynaptic currents (sEPSC) were recorded at all differentiation stages (Fig. 6A). The sEPSCs amplitude (Fig. 6B, D4 4.4 ± 1.6 pA, n = 21; D7 6 ± 1.5 pA, n = 28; D24 8.8 ± 1.2 pA, n = 25; D38 12.4 ± 1.6 pA, n = 25) and sEPSC frequency progressively increased (Fig. 6C, D4 0.017 ± 0.007 Hz, n = 21; D7 0.06 ± 0.031 Hz, n = 28; D24 0.086 ± 0.017 Hz, n = 25; D38 0.196 ± 0.044 Hz, n = 25) after differentiation was induced. The area of sEPSC did not increase significantly but showed an increasing trend (Fig. 6D, D4 8.64 ± 3.1 pA*ms, n = 21; D7 21.78 ± 3.91 pA*ms, n = 28; D24 39.99 ± 10.53 pA*ms, n = 25; D38 52.77 ± 25.81 pA*ms, n = 25). The glutamate receptor antagonist KyA (3 mM) blocked the sEPSC (data not shown). Spontaneous inhibitory postsynaptic current (sIPSC) could be recorded
