In order to test whether the N398 variant alters synapse function, we measured spontaneous postsynaptic currents (sPSCs, Fig. 2L). Both N398 and D398 neurons exhibited robust sPSCs, which is indicative of mature synapse formation and synaptic transmission among these neurons. Interestingly, consistent with the slightly greater spontaneous AP firing frequency in N398 DA neurons, the N398 DA neurons also exhibited greater spontaneous postsynaptic synaptic activity when compared to the D398 neurons (Fig. 2L,M), indicated by the increased frequency and the amplitudes of the sPSCs in N398 neurons when compared to the D398 DA neurons. These results were supported by postsynaptic electrophysiological analysis in response to 3 μM nicotine stimulation (Supplemental Fig. 1). Results illustrate that D398 DA neurons respond variably to nicotine exposure, but more N398 neurons seemed to be potentiated by nicotine. Therefore, neurons in the N398 cultures have a higher excitability due to more synaptic activity.
