Since the greatest effect of nicotine on EPSCs occurred immediately after the application of nicotine, we analyzed responses from each cell during the initial 10 s exposures to sequential additions of 0.1 to 6 μM nicotine (Fig. 4G,H). The apparent desensitization in N398 was maintained during addition of higher doses of nicotine to the same patched cells. The amplitudes increased notably in D398 at higher doses (3 and 6 μM) while the N398 neurons exhibited minimal changes in frequency or amplitude of response. The combined effect of nicotine dose and CHRNA5 genotype on EPSC frequency was significant overall at p = 0.00046 using a Tukey post-hoc test of an ANOVA linear mixed-effects model with repeated measures (n = 115/group, with a minimum of 25 cells in at least 3 different cultures from each of 3 different subjects per group). These results show that N398 neurons have higher initial responsiveness to nicotine but with enhanced desensitization. These data are largely in line with the notion that was reported previously using a heterologous expression system14. Therefore, the enhanced excitatory response and subsequent
