Results using excitatory iN cell cultures and nicotine exposure confirm the prediction that N398 cells exhibit a more robust network activity response to nicotine specifically in excitatory neurons. This enhanced activity was confirmed by assessing the frequencies of PSCs in response to increasing nicotine exposure (Fig. 4). Results show an increased frequency of PSCs in N398 iN cells at the lowest dose tested (0.1 μM), followed by results at higher doses that were consistent with desensitization of the receptor, as was observed in a Xenopus injection model14. Desensitization was only found in that model with α2β4-containing nAChRs14 and, while other subunit mRNAs were present in our cultures, α2 and β4 mRNAs are prominent. Levels of the α5 subunit mRNA were somewhat lower in N398 mDA neurons (Fig. 1Q), which was confirmed and extended by the RNAseq study (Supplemental Table 3), so it remains possible that reduced neuronal expression of α5 may contribute to the observed nicotine sensitivity. This would agree with results from Chrna5 knockout mouse models as well, where reduced α5 subunit caused substantial behavioral effects910. Observations of the
